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Animal models of preeclampsia: investigating pathophysiology and therapeutic targets

Published:March 12, 2021DOI:https://doi.org/10.1016/j.ajog.2020.10.025
      Animal models have been critical in investigating the pathogenesis, mediators, and even therapeutic options for a number of diseases, including preeclampsia. Preeclampsia is the leading cause of maternal and fetal morbidity and mortality worldwide. The placenta is thought to play a central role in the pathogenesis of this disease because it releases antiangiogenic and proinflammatory factors into the maternal circulation, resulting in the maternal syndrome. Despite the deleterious effects preeclampsia has been shown to have on the mother and baby during pregnancy and postpartum, there is still no effective treatment for this disease. Although clinical studies in patients are crucial to identify the involvement of pathogenic factors in preeclampsia, there are obvious limitations that prevent detailed investigation of the quantitative importance of time-dependent mechanisms involved in this syndrome. Animal models allow investigators to perform proof-of-concept studies and examine whether certain factors found in women with preeclampsia mediate hypertension and other manifestations of this disease. In this brief review, we summarize some of the more widely studied models used to investigate pathophysiological mechanisms that are thought to be involved in preeclampsia. These include models of placental ischemia, angiogenic imbalance, and maternal immune activation. Infusion of preeclampsia-related factors into animals has been widely studied to understand the specific mediators of this disease. These models have been included, in addition to a number of genetic models involved in overexpression of the renin-angiotensin system, complement activation, and trophoblast differentiation. Together, these models cover multiple mechanisms of preeclampsia from trophoblast dysfunction and impaired placental vascularization to the excess circulating placental factors and clinical manifestation of this disease. Most animal studies have been performed in rats and mice; however, we have also incorporated nonhuman primate models in this review. Preclinical animal models not only have been instrumental in understanding the pathophysiology of preeclampsia but also continue to be important tools in the search for novel therapeutic options for the treatment of this disease.

      Key words

      Introduction

      Despite its position as the leading cause of maternal death and a major contributor to maternal and perinatal morbidity, there is no effective drug treatment to delay the progression of preeclampsia (PE), and current management therapies have significant limitations.
      • Rana S.
      • Lemoine E.
      • Granger J.P.
      • Karumanchi S.A.
      Preeclampsia: pathophysiology, challenges, and perspectives.
      At present, the only effective treatment for PE is early delivery (removal of the placenta). Thus, the discovery of novel approaches for the treatment of PE is a major unmet need in the field. The identification of therapeutic targets for the treatment of PE can only result from the interplay between basic research involving animal models and clinical research in humans. The study of PE in humans is of critical importance to identify potential biomarkers and pathogenic factors that associate with the progression of PE.
      • McCarthy F.P.
      • Ryan R.M.
      • Chappell L.C.
      Prospective biomarkers in preterm preeclampsia: a review.
      • Phipps E.A.
      • Thadhani R.
      • Benzing T.
      • Karumanchi S.A.
      Pre-eclampsia: pathogenesis, novel diagnostics and therapies.
      • Lekva T.
      • Sugulle M.
      • Moe K.
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      • Dechend R.
      • Staff A.C.
      Multiplex analysis of circulating maternal cardiovascular biomarkers comparing preeclampsia subtypes.
      However, the data obtained from human studies are often correlative and unable to establish cause-and-effect relationships. Moreover, clinical studies in humans have obvious limitations that prevent detailed investigation of the quantitative importance of time-dependent mechanisms involved in this syndrome. In contrast, experimental studies in animal models, despite their limitations, allow investigators to perform proof-of-concept studies. In addition, studies in animal models allow investigators to examine whether certain factors found in women with PE can indeed lead to hypertension and other manifestations of this disease. In this brief review, we attempt to summarize some of the more widely studied and/or recently developed animal models used to investigate pathophysiological mechanisms that are thought to be involved in PE. These mechanisms and resulting models include placental ischemia (reduced uterine perfusion pressure models), impaired angiogenesis (soluble fms-like tyrosine kinase-1 [sFlt-1] chronic excess model), models used to study maternal immune activation in PE, and genetic mouse models that examine specific pathogenic pathways.

      Animal Models of Preeclampsia

      Because the spontaneous development of PE is essentially limited to the human species, the study of PE in patients is of critical importance to identify biomarkers and potential pathogenic factors that correlate with the progression of the syndrome. However, experimental studies in pregnant women have obvious limitations that prevent a complete investigation of many of the mechanisms involved. In contrast, studies in animal models, despite their limitations, allow investigators to isolate and study the many pathways involved in PE. Preclinical studies in rodent animal models have been critical in understanding the pathogenesis of this disease. In investigating therapeutic options, targets identified in small animal models must be tested in nonhuman primates for efficacy and safety before transitioning to human trials. Limited studies have been performed in nonhuman primates to study PE, most likely owing to expense and other limitations in resources. Nevertheless, these studies have contributed to a better understanding of this disease and have been included in this review.

      Models used to study the relationship between placental ischemia and maternal syndrome

      Experimental induction of chronic uteroplacental ischemia (UPI) seems to be a promising animal model to study potential mechanisms of PE. Uterine artery resistance is markedly increased in PE as a result of impaired spiral artery remodeling and placental ischemia.
      • McLeod L.
      How useful is uterine artery Doppler ultrasonography in predicting pre-eclampsia and intrauterine growth restriction?.
      Indeed, the most accurate predictive measurement of early-onset PE is the measurement of angiogenic balance and uterine artery Doppler assessment.
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      • Koch M.A.
      • Freire S.
      • et al.
      Serum inhibin A and angiogenic factor levels in pregnancies with previous preeclampsia and/or chronic hypertension: are they useful markers for prediction of subsequent preeclampsia?.
      Reductions in uteroplacental blood flow in a variety of species lead to a maternal cardiovascular phenotype that closely resembles PE in women.
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      • Yeung K.R.
      • Lim S.M.
      • et al.
      Placental growth factor reduces blood pressure in a uteroplacental ischemia model of preeclampsia in nonhuman primates.
      • Intapad S.
      • Warrington J.P.
      • Spradley F.T.
      • et al.
      Reduced uterine perfusion pressure induces hypertension in the pregnant mouse.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      • Alexander B.T.
      • Rinewalt A.N.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Endothelin type A receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure.
      • Granger J.P.
      • LaMarca B.B.D.
      • Cockrell K.
      • et al.
      Reduced uterine perfusion pressure (RUPP) model for studying cardiovascular-renal dysfunction in response to placental ischemia.
      • Gatford K.L.
      • Andraweera P.H.
      • Roberts C.T.
      • Care A.S.
      Animal models of preeclampsia: causes, consequences, and interventions.
      • Sunderland N.
      • Hennessy A.
      • Makris A.
      Animal models of pre-eclampsia.
      The chronic reduced uteroplacental perfusion pressure (RUPP) rat model was developed and characterized by our laboratory to examine potential pathophysiological mechanisms that mediate cardiovascular and endothelial dysfunction in response to placental ischemia.
      • Granger J.P.
      • LaMarca B.B.D.
      • Cockrell K.
      • et al.
      Reduced uterine perfusion pressure (RUPP) model for studying cardiovascular-renal dysfunction in response to placental ischemia.
      The RUPP surgical procedure is typically performed in timed-pregnant Sprague-Dawley rats (gestation day 14),
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      but the procedure has also been successfully performed in other rat strains, including Wistar rats.
      • Spradley F.T.
      • Ge Y.
      • Haynes B.P.
      • Granger J.P.
      • Anderson C.D.
      Adrenergic receptor blockade attenuates placental ischemia-induced hypertension.
      Uterine perfusion pressure in the gravid rat is reduced by slipping a silver constriction clip around the aorta below the renal arteries, right above the iliac bifurcation where the uterine arteries lie.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      ,
      • Li J.
      • LaMarca B.
      • Reckelhoff J.F.
      A model of preeclampsia in rats: the reduced uterine perfusion pressure (RUPP) model.
      We have found this procedure to reduce uterine perfusion pressure by approximately 40%.
      • Sholook M.M.
      • Gilbert J.S.
      • Sedeek M.H.
      • Huang M.
      • Hester R.L.
      • Granger J.P.
      Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats.
      Because compensation of blood flow to the placenta occurs in pregnant rats through an adaptive increase in ovarian blood flow, branches of both the right and left ovarian arteries that supply the uterus are also clipped.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      The timing of the vessel constriction is an important consideration. During a series of pilot studies to determine the appropriate clip size and the ideal gestational time for reducing uterine perfusion pressure, it was found that placement of the clips before day 14 of gestation in the rat resulted in a significant increase in fetal death. However, placement of clips at gestational day 14 to reduce placental perfusion produces a consistent blood pressure effect and minimizes total fetal reabsorption.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      ,
      • Alexander B.T.
      Placental insufficiency leads to development of hypertension in growth-restricted offspring.
      In response to RUPP, both uterine and placental blood flow are decreased by approximately 40%.
      • Sholook M.M.
      • Gilbert J.S.
      • Sedeek M.H.
      • Huang M.
      • Hester R.L.
      • Granger J.P.
      Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats.
      Arterial pressure increases by approximately 20 to 25 mm Hg by day 19 of pregnancy. In contrast, RUPP in virgin rats results in no significant effect on arterial pressure relative to control virgin rats.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      The hypertension in RUPP rats is associated with increases in total peripheral resistance and decreased cardiac output, which are systemic hemodynamic characteristics consistent with PE in women.
      • Sholook M.M.
      • Gilbert J.S.
      • Sedeek M.H.
      • Huang M.
      • Hester R.L.
      • Granger J.P.
      Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats.
      Glomerular filtration rate and to a lesser extent renal blood flow decrease in the RUPP model relative to normal pregnancy at day 19.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      Although quite variable, an increase in urinary protein excretion has also been observed in the RUPP model compared with normal pregnancy.
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      The reason for the variability is unknown but may be caused by the short time frame of exposure to placental ischemia.
      Angiogenic imbalance, endothelial dysfunction, reduced production of nitric oxide (NO) in vascular tissue, and increases in vascular endothelin (ET)-1 and reactive oxygen species (ROS) production are all characteristics of PE also present in the RUPP rat.
      • Rana S.
      • Lemoine E.
      • Granger J.P.
      • Karumanchi S.A.
      Preeclampsia: pathophysiology, challenges, and perspectives.
      ,
      • LaMarca B.D.
      • Gilbert J.
      • Granger J.P.
      Recent progress toward the understanding of the pathophysiology of hypertension during preeclampsia.
      • Gilbert J.S.
      • Ryan M.J.
      • LaMarca B.B.
      • Sedeek M.
      • Murphy S.R.
      • Granger J.P.
      Pathophysiology of hypertension during preeclampsia: linking placental ischemia with endothelial dysfunction.
      • Khalil R.A.
      • Granger J.P.
      Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models.
      • Sedeek M.
      • Gilbert J.S.
      • Lamarca B.B.
      • et al.
      Role of reactive oxygen specied in hypertension produced by reduced uterine perfusion pressure in pregnant rats.
      • Gilbert J.S.
      • Babcock S.A.
      • Granger J.P.
      Hypertension produced by reduced uterine perfusion in pregnant rats is associated with increased soluble fms-like tyrosine kinase-1 expression.
      • Gilbert J.S.
      • Gilbert S.A.B.
      • Arany M.
      • Granger J.P.
      Hypertension produced by placental ischemia in pregnant rats is associated with increased soluble endoglin expression.
      Placental ischemia in rats also increases placental expression of hypoxia-inducible factor-1α and immunoreactive sFlt-1 in the placenta and plasma.
      • Gilbert J.S.
      • Babcock S.A.
      • Granger J.P.
      Hypertension produced by reduced uterine perfusion in pregnant rats is associated with increased soluble fms-like tyrosine kinase-1 expression.
      Soluble endoglin (sEng) levels are also elevated in the RUPP model.
      • Gilbert J.S.
      • Gilbert S.A.B.
      • Arany M.
      • Granger J.P.
      Hypertension produced by placental ischemia in pregnant rats is associated with increased soluble endoglin expression.
      Moreover, RUPP is associated with decreases in plasma concentrations of vascular endothelial growth factor (VEGF) and placental-derived growth factor (PlGF).
      • Gilbert J.S.
      • Babcock S.A.
      • Granger J.P.
      Hypertension produced by reduced uterine perfusion in pregnant rats is associated with increased soluble fms-like tyrosine kinase-1 expression.
      Fetal growth restriction (FGR), another feature of human PE, is also evident as pup weights are decreased in RUPP rats relative to controls.
      • LaMarca B.D.
      • Gilbert J.
      • Granger J.P.
      Recent progress toward the understanding of the pathophysiology of hypertension during preeclampsia.
      Alexander et al
      • Alexander B.T.
      • Dasinger J.H.
      • Intapad S.
      Fetal programming and cardiovascular pathology.
      have performed a series of studies using the FGR rat offspring from the RUPP model to examine the mechanisms underlying the relationship between birthweight and cardiovascular diseases later in life. Thus, offspring from RUPP rats are also an important model to examine mechanisms of fetal programming of cardiovascular disease.
      The RUPP model has been proven to be a useful tool to examine the mechanisms whereby ischemia initiates a cascade of events resulting in placental inflammation and subsequent systemic inflammation and hypertension in the mother.
      • LaMarca B.
      • Wallace K.
      • Granger J.
      Role of angiotensin II type I receptor agonistic autoantibodies (AT1-AA) in preeclampsia.
      • LaMarca B.D.
      • Ryan M.J.
      • Gilbert J.S.
      • Murphy S.R.
      • Granger J.P.
      Inflammatory cytokines in the pathophysiology of hypertension during preeclampsia.
      • Cornelius D.C.
      • Cottrell J.
      • Amaral L.M.
      • LaMarca B.
      Inflammatory mediators: a causal link to hypertension during preeclampsia.
      • LaMarca B.
      • Cornelius D.C.
      • Harmon A.C.
      • et al.
      Identifying immune mechanisms mediating the hypertension during preeclampsia.
      RUPP rats have increased placental expression and circulating levels of prohypertensive cytokines (tumor necrosis factor [TNF]-α, interleukin [IL]-6, IL-17, etc) and immune cell counts (T and B lymphocytes) and increases in the production of the agonistic autoantibody to the angiotensin II type 1 receptor autoantibody (AT1-AA) and imbalance in T helper (Th) and regulatory T cells (Tregs).
      • LaMarca B.
      • Wallace K.
      • Granger J.
      Role of angiotensin II type I receptor agonistic autoantibodies (AT1-AA) in preeclampsia.
      • LaMarca B.D.
      • Ryan M.J.
      • Gilbert J.S.
      • Murphy S.R.
      • Granger J.P.
      Inflammatory cytokines in the pathophysiology of hypertension during preeclampsia.
      • Cornelius D.C.
      • Cottrell J.
      • Amaral L.M.
      • LaMarca B.
      Inflammatory mediators: a causal link to hypertension during preeclampsia.
      • LaMarca B.
      • Cornelius D.C.
      • Harmon A.C.
      • et al.
      Identifying immune mechanisms mediating the hypertension during preeclampsia.
      Activation of the complement system also occurs in RUPP rats, as detected in the circulation by decreased complement component 3 and increased complement activation product C3a.
      • Lillegard K.E.
      • Johnson A.C.
      • Lojovich S.J.
      • et al.
      Complement activation is critical for placental ischemia-induced hypertension in the rat.
      Cerebrovascular disturbances are now part of the diagnostic criteria for PE when accompanied by new-onset hypertension after 20 weeks’ gestation.
      • Rana S.
      • Lemoine E.
      • Granger J.P.
      • Karumanchi S.A.
      Preeclampsia: pathophysiology, challenges, and perspectives.
      Blood-brain barrier (BBB) disruption, cerebral edema, and impaired cerebral blood flow (CBF) regulation are common cerebrovascular findings in women with PE.
      • Battarbee A.N.
      • Sinkey R.G.
      • Harper L.M.
      • Oparil S.
      • Tita A.T.N.
      Chronic hypertension in pregnancy.
      • Kelly D.M.
      • Rothwell P.M.
      Blood pressure and the brain: the neurology of hypertension.
      • Miller E.C.
      Preeclampsia and cerebrovascular disease.
      • Hammer E.S.
      • Cipolla M.J.
      Cerebrovascular dysfunction in preeclamptic pregnancies.
      However, the mechanisms contributing to these cerebrovascular abnormalities during pregnancy are not completely understood. In the past few years, the RUPP model of placental ischemia has been used to determine whether placental ischemia causes similar characteristics as the clinical syndrome and to begin to dissect the mechanisms that contribute to RUPP-induced cerebrovascular abnormalities. Placental ischemia in the RUPP model leads to increased BBB permeability and cerebral edema.
      • Warrington J.P.
      • Fan F.
      • Murphy S.R.
      • et al.
      Placental ischemia in pregnant rats impairs cerebral blood flow autoregulation and increases blood-brain barrier permeability.
      ,
      • Warrington J.P.
      • Fan F.
      • Duncan J.
      • et al.
      The angiotensin II type I receptor contributes to impaired cerebral blood flow autoregulation caused by placental ischemia in pregnant rats.
      In these studies, impaired CBF and vascular myogenic reactivity were particularly evident at higher perfusion pressures.
      • Warrington J.P.
      • Fan F.
      • Murphy S.R.
      • et al.
      Placental ischemia in pregnant rats impairs cerebral blood flow autoregulation and increases blood-brain barrier permeability.
      ,
      • Ryan M.J.
      • Gilbert E.L.
      • Glover P.H.
      • et al.
      Placental ischemia impairs middle cerebral artery myogenic responses in the pregnant rat.
      The RUPP model also has a shorter latency to the onset of drug-induced seizures and is associated with increased concentrations of proinflammatory cytokines in the cerebrospinal fluid.
      • Warrington J.P.
      Placental ischemia increases seizure susceptibility and cerebrospinal fluid cytokines.
      These findings were consistent with a study using the RUPP rat coupled with high cholesterol in which the threshold for seizures was reduced compared with normal pregnant rats.
      • Warrington J.P.
      Placental ischemia increases seizure susceptibility and cerebrospinal fluid cytokines.
      Importantly, magnesium sulfate has the capability of reducing placental ischemia–induced increases in proinflammatory cytokines in the cerebrospinal fluid.
      • Zhang L.W.
      • Warrington J.P.
      Magnesium sulfate prevents placental ischemia-induced increases in brain water content and cerebrospinal fluid cytokines in pregnant rats.
      Although these studies demonstrated that the RUPP model can be used to study mechanisms of cerebrovascular abnormalities, it is still not known what factors are responsible for BBB disruption, cerebral edema, and impaired CBF after placental ischemia.
      PE is associated with peripartum and postpartum myocardial fibrosis and heart failure.
      • Naseem H.
      • Dreixler J.
      • Mueller A.
      • et al.
      Antepartum aspirin administration reduces activin A and cardiac global longitudinal strain in preeclamptic women.
      • Hall M.E.
      • George E.M.
      • Granger J.P.
      The heart during pregnancy.
      • Shahul S.
      • Rhee J.
      • Hacker M.R.
      • et al.
      Subclinical left ventricular dysfunction in preeclamptic women with preserved left ventricular ejection fraction: a 2D speckle-tracking imaging study.
      Despite the high incidence of serious morbidity and mortality owing to postpartum heart failure after a preeclamptic pregnancy, there is a substantial gap in our knowledge regarding the cardiac dysfunction during PE and how to prevent or reverse it. Recent studies from our laboratory indicate that the RUPP model has many features of cardiac dysfunction seen in women with PE. Importantly, the RUPP model of PE also demonstrates reduced myocardial function (ejection fraction [EF] and global longitudinal strain) seen in women with PE. Furthermore, biomarkers consistent with cardiac fibrosis including cardiac troponin, increased collagen messenger RNA (mRNA) expression, and markers of pathologic hypertrophy including increased brain natriuretic peptide, myosin heavy chain α/β, and atrial natriuretic peptide levels are present in RUPP rats.
      • Bakrania B.A.
      • Hall M.E.
      • Shahul S.
      • Granger J.P.
      The reduced uterine perfusion pressure (RUPP) rat model of preeclampsia exhibits impaired systolic function and global longitudinal strain during pregnancy.
      • Paauw N.D.
      • Joles J.A.
      • Spradley F.T.
      • et al.
      Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats.
      • Gutkowska J.
      • Granger J.P.
      • LaMarca B.B.
      • Danalache B.A.
      • Wang D.
      • Jankowski M.
      Changes in cardiac structure in hypertension produced by placental ischemia in pregnant rats: effect of tumor necrosis factor blockade.
      In addition, we have data indicating that reduced EF and fractional shortening persist up to 8 weeks after delivery in the RUPP model despite blood pressure returning to normal by this time.
      • Paauw N.D.
      • Joles J.A.
      • Spradley F.T.
      • et al.
      Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats.
      Thus, the RUPP model may also be a useful tool to provide a better understanding of the mechanisms underlying cardiac dysfunction that occurs during PE and after delivery.
      Thus, RUPP-induced hypertension in pregnant rats is associated with endothelial dysfunction, angiogenic imbalance, immune activation, and cardiac and cerebrovascular dysfunction, all of which are seen in women with PE (Table 1). A major strength of the RUPP model is that investigators have been able to assess the functional and quantitative role for each of the systems in mediating the hypertension in the RUPP model by using pharmacologic agents to disrupt their actions. The RUPP model has also been used by numerous laboratories as a valuable tool to investigate potential therapeutic targets for the treatment of preeclampsia. Importantly, the RUPP model involves mechanical constriction of vessels that feed the uteroplacental unit as a means to reduce blood flow to the placenta. As a result, the RUPP rat displays a similar phenotype to PE, where placental ischemia is also thought to play a central role. However, a limitation of this model is that it is not useful for studying the mechanisms involved in the abnormal spiral artery remodeling proposed to underlie placental ischemia in women with PE.
      Table 1Features of reduced uterine perfusion pressure model compared with PE
      FeaturesPERUPP rat
      Mean arterial pressure
      Total peripheral resistance
      Circulating sFlt-1
      Circulating sEng
      Circulating free PlGF
      Circulating free VEGF
      Oxidative stress
      AT1-AA
      Prohypertensive cytokines
      T and B lymphocytes
      ET-1
      NO
      Renal plasma flow
      GFR
      GLS
      Ejection fraction
      Cardiac output
      Cerebral blood flow regulation
      Cerebral edema
      BBB permeability
      FGR
      AT1-AA, angiotensin II type I receptor autoantibody; BBB, blood-brain barrier; ET-1, endothelin-1; GFR, glomerular filtration rate; GLS, global longitudinal strain; FGR, fetal growth restriction; NO, nitric oxide; PE, preeclampsia; PlGF, placental-derived growth factor; ROS, reactive oxygen species; RUPP, reduced uterine perfusion pressure; sEng, soluble endoglin; TNF-α, tumor necrosis factor-α; UPI, uteroplacental ischemia; VEGF, vascular endothelial growth factor; ↑, increased; ↓, decreased.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      Although numerous laboratories have used the rat RUPP model, the placental ischemic model of PE has also been applied in mice and in nonhuman primate models. The RUPP technique has been applied in mice, which is especially beneficial in using genetic engineered mice to enhance our understanding of the pathogenesis of placental ischemia–induced hypertension.
      • Intapad S.
      • Warrington J.P.
      • Spradley F.T.
      • et al.
      Reduced uterine perfusion pressure induces hypertension in the pregnant mouse.
      ,
      • Sekimoto A.
      • Tanaka K.
      • Hashizume Y.
      • et al.
      Tadalafil alleviates preeclampsia and fetal growth restriction in RUPP model of preeclampsia in mice.
      Makris et al
      • Makris A.
      • Thornton C.
      • Thompson J.
      • et al.
      Uteroplacental ischemia results in proteinuric hypertension and elevated sFLT-1.
      also characterized a UPI model in radiotelemetered pregnant baboons by selective ligation of 1 uterine artery resulting in a 40% decrease in uteroplacental blood flow. Hypertension, proteinuria, and increased production of antiangiogenic markers were reported in the pregnant baboons compared with control animals that underwent a sham procedure.
      • Makris A.
      • Thornton C.
      • Thompson J.
      • et al.
      Uteroplacental ischemia results in proteinuric hypertension and elevated sFLT-1.
      Makris et al
      • Makris A.
      • Thornton C.
      • Thompson J.
      • et al.
      Uteroplacental ischemia results in proteinuric hypertension and elevated sFLT-1.
      also recently reported that RNA interference modulation of placental sFlt-1 significantly attenuated the blood pressure response to placental ischemia.

      Models used to study the role of angiogenic imbalance

      Angiogenic imbalance is thought to play a central role in the development of PE. Proangiogenic factors, VEGF and PlGF, are produced during pregnancy and are critical in maintaining endothelial integrity. These angiogenic factors bind to VEGF receptors (VEGFR), including VEGFR-1 or Flt-1.
      • Powe C.E.
      • Levine R.J.
      • Karumanchi S.A.
      Preeclampsia, a disease of the maternal endothelium: the role of antiangiogenic factors and implications for later cardiovascular disease.
      ,
      • Failla C.M.
      • De Luca N.
      • Zaccaria M.L.
      • et al.
      Mice over-expressing placenta growth factor in the skin exhibit increased vascularization and vessel permeability independently of VEGF-A.
      sFlt-1 is an alternately spliced variant of the full-length receptor in which the transmembrane and cytosolic domains have been removed, leaving only the extracellular recognition domain.
      • Heydarian M.
      • McCaffrey T.
      • Florea L.
      • et al.
      Novel splice variants of sFlt1 are upregulated in preeclampsia.
      This recognition domain acts as a VEGF antagonist by binding free VEGF and making it unavailable for proper signaling. Increased circulating levels of sFlt-1 and reduced PlGF levels have been documented in women during PE and before the onset of clinical symptoms.
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      Excess sFlt-1 and sEng, which are also significantly increased in PE,
      • Venkatesha S.
      • Toporsian M.
      • Lam C.
      • et al.
      Soluble endoglin contributes to the pathogenesis of preeclampsia.
      cause depletion in the bioavailability of VEGF and PlGF at the detriment of the endothelium and blood pressure regulation.
      Although there is a strong association between angiogenic imbalance and severity of PE, the relative importance of angiogenic factors in PE remains an open area of investigation. A number of experimental models have been used to uncover the mechanisms that link angiogenic imbalance and PE. Overexpression and infusion of sFlt-1 have both been shown to induce a PE-like phenotype.
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      ,
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      ,
      • Lu F.
      • Longo M.
      • Tamayo E.
      • et al.
      The effect of over-expression of sFlt-1 on blood pressure and the occurrence of other manifestations of preeclampsia in unrestrained conscious pregnant mice.
      Maynard et al
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      showed that infusion of an adenovirus (Ad) expressing sFlt-1 in Sprague-Dawley rats at day 8 or 9 of pregnancy causes the development of hypertension, proteinuria, and glomerular endotheliosis by day 16 or 17 of pregnancy (Figure 1). Similarly, infusion of sFlt-1 into pregnant rats induces PE-like symptoms, including hypertension, reduced fetal weight, and increases in vascular ROS.
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      Interestingly, excess sFlt-1 itself is not thought to cause hypertension in PE, but rather the deficiency of free proangiogenic factors such as VEGF and PlGF. In 1 study, mice infused with Ad-sFlt-1 developed hypertension, proteinuria, endotheliosis, and vascular damage. However, when Ad-VEGF was administered in conjunction, these features were alleviated.
      • Szalai G.
      • Romero R.
      • Chaiworapongsa T.
      • et al.
      Full-length human placental SFlt-1-e15a isoform induces distinct maternal phenotypes of preeclampsia in mice.
      These data indicate that free excess sFlt-1 and depletions of free VEGF and PlGF play a major role in PE. Importantly, studies have also investigated full-length human sFlt-1-e15a isoform, which is most abundant in placentas of women with PE. Studies by Szalai et al
      • Szalai G.
      • Xu Y.
      • Romero R.
      • et al.
      In vivo experiments reveal the good, the bad and the ugly faces of sFlt-1 in pregnancy.
      ,
      • Szalai G.
      • Romero R.
      • Chaiworapongsa T.
      • et al.
      Full-length human placental SFlt-1-e15a isoform induces distinct maternal phenotypes of preeclampsia in mice.
      show that infusion of full-length human sFlt-1 in mice also results in hypertension, proteinuria, glomerular injury, and vascular damage.
      Figure thumbnail gr1
      Figure 1MAP and proteinuria of rats after the administration of an Ad-sFlt-1 during pregnancy
      A, MAP and B, proteinuria are shown for rats after the administration of an Ad-sFlt-1 during pregnancy.
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      Sprague-Dawley rats were injected at gestational day 8 or 9 of pregnancy, and data were collected at gestational day 16 or 17. Data are presented as mean+SEM. The asterisk symbol indicates P<.05.
      Ad-sFlt-1, adenovirus expressing soluble fms-like tyrosine kinase-1; MAP, mean arterial pressure; SEM, standard error of the mean; sFlt-1, soluble fms-like tyrosine kinase-1.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      As reported in the RUPP and UPI models, placental ischemia induces significant increases in circulating sFlt-1, and the administration of PlGF in these models has been shown to improve the PE-like phenotype. In the RUPP rat, the administration of 180 μg/kg/d recombinant human (rh) PlGF for 5 days reduced blood pressure and fetal reabsorption in the RUPP rat, in addition to significant increases in placental and fetal weight.
      • Spradley F.T.
      • Tan A.Y.
      • Joo W.S.
      • et al.
      Placental growth factor administration abolishes placental ischemia-induced hypertension.
      Subsequently, another study showed that the administration of 100 μg/kg/d rhPlGF in the UPI nonhuman primate model results in significant improvements in hypertension and proteinuria.
      • Makris A.
      • Yeung K.R.
      • Lim S.M.
      • et al.
      Placental growth factor reduces blood pressure in a uteroplacental ischemia model of preeclampsia in nonhuman primates.
      Most recently, Logue et al
      • Logue O.C.
      • Mahdi F.
      • Chapman H.
      • George E.M.
      • Bidwell 3rd, G.L.
      A maternally sequestered, biopolymer-stabilized vascular endothelial growth factor (VEGF) chimera for treatment of preeclampsia.
      found that the administration of an elastin-like polypeptide linked VEGF construct in the RUPP rat significantly reduces blood pressure. These and other data have led to the hypothesis that the ratio between sFlt-1 and PlGF/VEGF is critical to maintain a healthy endothelium and normal vascular activity. Furthermore, these studies suggest that improving the angiogenic balance in PE could be a therapeutic avenue for treatment. Current therapeutic efforts have also focused on reducing circulating sFlt-1 via apheresis and in doing so improving the angiogenic balance, with promising results.
      • Thadhani R.
      • Hagmann H.
      • Schaarschmidt W.
      • et al.
      Removal of soluble fms-like tyrosine kinase-1 by dextran sulfate apheresis in preeclampsia.
      These clinical data highlight the importance of angiogenic factors in the development of PE.
      • Thadhani R.
      • Hagmann H.
      • Schaarschmidt W.
      • et al.
      Removal of soluble fms-like tyrosine kinase-1 by dextran sulfate apheresis in preeclampsia.
      ,
      • Thadhani R.
      • Kisner T.
      • Hagmann H.
      • et al.
      Pilot study of extracorporeal removal of soluble fms-like tyrosine kinase 1 in preeclampsia.
      Animal models of angiogenic imbalance have also been useful to study the closely associated pregnancy disorder, that is, hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome. Although HELLP syndrome only occurs in 0.2% to 0.8% of pregnancies, it is diagnosed alongside PE in 70% to 80% of cases.
      • Abildgaard U.
      • Heimdal K.
      Pathogenesis of the syndrome of hemolysis, elevated liver enzymes, and low platelet count (HELLP): a review.
      Therefore, it is not surprising that factors induced in animal models of PE also produce a HELLP-like phenotype. Infusion of sFlt-1 and sEng at gestational day 12 results in increased mean arterial pressure, elevated liver enzymes, and reduced platelets and proinflammatory factors such as TNF-α, IL-17, IL-6, CD4+ T cells, and CD8+ T cells.
      • Bean C.
      • Spencer S.K.
      • Bowles T.
      • et al.
      Inhibition of T-cell activation attenuates hypertension, TNFα, IL-17, and blood-brain barrier permeability in pregnant rats with angiogenic imbalance.
      ,
      • Wallace K.
      • Morris R.
      • Kyle P.B.
      • et al.
      Hypertension, inflammation and T lymphocytes are increased in a rat model of HELLP syndrome.
      Interestingly, this model is one of the few that have been studied after delivery to show BBB permeability, persistent hypertension, and indicators of anxiety.
      • Wallace K.
      • Bean C.
      • Bowles T.
      • et al.
      Hypertension, anxiety, and blood-brain barrier permeability are increased in postpartum severe preeclampsia/hemolysis, elevated liver enzymes, and low platelet count syndrome rats.
      The profound effect on immune factors in this model and others of angiogenic imbalance highlight the interactions between these 2 pathways.

      Models used to examine role of agnostic angiotensin II type 1 receptor autoantibodies

      The renin-angiotensin system (RAS) plays an important role in normal pregnancy and in PE. Normal pregnancy is associated with the activation of RAS components with diminished vascular responsiveness to angiotensin II. In contrast, women with PE have reduced angiotensinogen, plasma renin (REN) activity, and angiotensin II but typically exhibit increased vascular responsiveness to angiotensin II.
      • Spaan J.J.
      • Brown M.A.
      Renin-angiotensin system in pre-eclampsia: everything old is new again.
      Herse et al previously reported that the sera from women with PE contain an immunoglobulin G (type 3) autoantibody that reacts with the AT1 receptor. A number of studies have now indicated that women with PE produce this novel agonistic autoantibody to the AT1-AA during pregnancy and up to 8 years after delivery.
      • Rieber-Mohn A.B.
      • Sugulle M.
      • Wallukat G.
      • et al.
      Auto-antibodies against the angiotensin II type I receptor in women with uteroplacental acute atherosis and preeclampsia at delivery and several years postpartum.
      ,
      • Herse F.
      • Staff A.C.
      • Hering L.
      • Müller D.N.
      • Luft F.C.
      • Dechend R.
      AT1-receptor autoantibodies and uteroplacental RAS in pregnancy and pre-eclampsia.
      One animal model used to examine the role of AT1AA is the AT1-AA chronic excess model where purified AT1-AA is infused into normal pregnant rats. A number of investigators have shown that AT1-AA signaling, via the AT1 receptor, results in a variety of physiological effects, including TNF-α and ROS generation, both of which have been implicated in PE.
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      Zhou et al
      • Zhou C.C.
      • Zhang Y.
      • Irani R.A.
      • et al.
      Angiotensin receptor agonistic autoantibodies induce pre-eclampsia in pregnant mice.
      demonstrated that the immunoglobulin isolated from women with PE increases systolic pressure in pregnant mice. Similar studies from LaMarca et al
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      have reported that infusion of purified rat AT1-AA, isolated from the serum collected from a pregnant transgenic rat overproducing components of the RAS, into pregnant rats from day 12 to day 19 of gestation, increased serum AT1-AA and blood pressure. Although these data suggest AT1-AA causes hypertension by direct activation of AT1 receptor, additional pathways involving ET and antiangiogenic factors may also be involved during pregnancy. More recently, Cunningham et al
      • Cunningham Jr., M.W.
      • Vaka V.R.
      • McMaster K.
      • et al.
      Renal natural killer cell activation and mitochondrial oxidative stress; new mechanisms in AT1-AA mediated hypertensive pregnancy.
      showed that renal natural killer cells are activated in renal tissue from AT1-AA–infused rats and that mitochondrial dysfunction is also present in this model. The blood pressure response in AT1-AA–infused animals has been blocked by AT1 receptor antagonists or coinjection of an AT1 receptor antagonist or the 7 amino acid peptide (n7AAc) that selectively blocks the actions of the AT1-AA.
      • Cunningham Jr., M.W.
      • Castillo J.
      • Ibrahim T.
      • et al.
      AT1-AA (angiotensin II type 1 receptor agonistic autoantibody) blockade prevents preeclamptic symptoms in placental ischemic rats.
      The administration of n7AAc in the RUPP rat has also been shown to reduce blood pressure (Figure 2).
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      Another approach to block the effects of endogenous AT1-AA in the RUPP rat is B-cell depletion, which results in a blunted blood pressure response to placental ischemia.
      • LaMarca B.
      • Wallace K.
      • Herse F.
      • et al.
      Hypertension in response to placental ischemia during pregnancy: role of B lymphocytes.
      Figure thumbnail gr2
      Figure 2MAP of normal pregnant rats, the RUPP rat model, and inhibition of the AT1-AA in the RUPP rat (with “n7AAc”)
      These data suggest that AT1-AA plays a role in placental ischemia–induced hypertension. Data are presented as mean+SEM and were retrieved from Cunningham et al.
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      The asterisk symbol indicates P<.05.
      AT1-AA, angiotensin II type 1 receptor autoantibody; MAP, mean arterial pressure; RUPP, reduced uterine perfusion pressure; SEM, standard error of the mean.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      AT1-AA infusion in rats is also associated with angiogenic imbalance and elevated tissue levels of prepro-ET-1.
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      Interestingly, blood pressure response in AT1-AA-infused animals can be blocked by ET type A (ETA) receptor antagonist.
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      These data suggest that AT1-AA–induced hypertension during pregnancy is in part caused by the activation of the ET system.
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      sFlt-1 and sEng are significantly elevated in this model.
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      sFlt-1 levels measured in media from placental explants from AT1-AA–infused rats are also significantly increased.
      • Parrish M.R.
      • Murphy S.R.
      • Rutland S.
      • et al.
      The effect of immune factors, tumor necrosis factor-alpha, and agonistic autoantibodies to the angiotensin II type I receptor on soluble fms-like tyrosine-1 and soluble endoglin production in response to hypertension during pregnancy.
      Interestingly, sEng was not increased in media from placental explant, suggesting another source for its production.
      • Parrish M.R.
      • Murphy S.R.
      • Rutland S.
      • et al.
      The effect of immune factors, tumor necrosis factor-alpha, and agonistic autoantibodies to the angiotensin II type I receptor on soluble fms-like tyrosine-1 and soluble endoglin production in response to hypertension during pregnancy.
      These studies demonstrate an important interaction between inflammatory and angiogenic markers found to be produced excessively in response to placental ischemia.

      Immune activation and cytokines

      One of the earliest and most persistent theories about the origins of PE is that PE is a disorder of immunity and inflammation. This maternal immune tolerance involves crucial interactions between Tregs and uterine natural killer cells that recognize and accept the fetal antigens and facilitate placental growth. Complete failure of this crucial step leads to spontaneous miscarriage, whereas partial failure leads to poor placentation and dysfunctional placental perfusion and chronic immune activation. Increase in proinflammatory cytokines and decreases in uterine natural killer cells and Tregs are observed in women with PE.
      • Cornelius D.C.
      • Cottrell J.
      • Amaral L.M.
      • LaMarca B.
      Inflammatory mediators: a causal link to hypertension during preeclampsia.
      ,
      • Prins J.R.
      • Boelens H.M.
      • Heimweg J.
      • et al.
      Preeclampsia is associated with lower percentages of regulatory T cells in maternal blood.
      In a mouse model, acute Treg depletion from gestational day 3.5 results in fetal loss, increases in proinflammatory markers, and uterine artery resistance. Interestingly, Treg depletion alone does not increase blood pressure. However, in the presence of L-NG-nitroarginine methyl ester (L-NAME), which blocks NO production for proper endothelial function, blood pressure increases by approximately 25% in Treg-depleted mice, but only 15% in normal pregnant mice.
      • Care A.S.
      • Bourque S.L.
      • Morton J.S.
      • Hjartarson E.P.
      • Robertson S.A.
      • Davidge S.T.
      Reduction in regulatory T cells in early pregnancy causes uterine artery dysfunction in mice.
      Treg populations have also been shown to be important in late gestation. Partial or total Treg depletion from gestational day 14.5 in a murine model of susceptibility to preterm birth resulted in greater fetal loss and reduced survival of pups up to 3 weeks of age.
      • Gomez-Lopez N.
      • Arenas-Hernandez M.
      • Romero R.
      • et al.
      Regulatory T cells play a role in a subset of idiopathic preterm labor/birth and adverse neonatal outcomes.
      The RUPP rat is another model that is induced late in pregnancy that also exhibits a reduction in Tregs
      • Wallace K.
      • Richards S.
      • Dhillon P.
      • et al.
      CD4+ T-helper cells stimulated in response to placental ischemia mediate hypertension during pregnancy.
      and increases in Th-17 cells. Cornelius et al
      • Wallace K.
      • Richards S.
      • Dhillon P.
      • et al.
      CD4+ T-helper cells stimulated in response to placental ischemia mediate hypertension during pregnancy.
      ,
      • Cornelius D.C.
      • Amaral L.M.
      • Wallace K.
      • et al.
      Reduced uterine perfusion pressure T-helper 17 cells cause pathophysiology associated with preeclampsia during pregnancy.
      showed that Th-17 cells isolated from the spleen of RUPP rats, cultured, and injected interperitoneally into normal pregnant rats induced a PE-like phenotype. Meanwhile, the administration of Tregs to the RUPP rat reduces hypertension and proinflammatory factors.
      • Cornelius D.C.
      • Amaral L.M.
      • Harmon A.
      • et al.
      An increased population of regulatory T cells improves the pathophysiology of placental ischemia in a rat model of preeclampsia.
      ,
      • Ibrahim T.
      • Przybyl L.
      • Harmon A.C.
      • et al.
      Proliferation of endogenous regulatory T cells improve the pathophysiology associated with placental ischaemia of pregnancy.
      These data suggest that the increased proinflammatory immune cells populations play a deleterious role in PE. These factors all act to cause pathologic activation of the maternal endothelium and directly affect multiple organ systems.
      Proinflammatory cytokines are produced in abundance in PE coupled with deficiencies of antiinflammatory factors, such as IL-10. IL-10 plays an important role in normal pregnancy in regulating the polarization of T cells to a Th-2 phenotype over the proinflammatory Th-1 phenotype.
      • Saito S.
      • Sakai M.
      Th1/Th2 balance in preeclampsia.
      Women with PE have a 2-fold elevation in placental and plasma TNF-α protein levels. It is becoming increasingly evident that proinflammatory cytokines such as IL-6 and TNF-α interact with important blood pressure regulatory systems such as the RAS system, sympathetic nervous system, and endothelial factors.
      • Cornelius D.C.
      • Cottrell J.
      • Amaral L.M.
      • LaMarca B.
      Inflammatory mediators: a causal link to hypertension during preeclampsia.
      TNF-α infusion (50 ng/d) in normal pregnant rats from gestational day 14 to 19 results in elevated blood pressure and increased expression of renal, placental, and aortic prepro-ET-1.
      • Alexander B.T.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Tumor necrosis factor-alpha-induced hypertension in pregnant rats results in decreased renal neuronal nitric oxide synthase expression.
      Moreover, the increase in mean arterial pressure in response to TNF-α is completely abolished in pregnant rats treated with an ETA receptor antagonist.
      • LaMarca B.B.D.
      • Cockrell K.
      • Sullivan E.
      • Bennett W.
      • Granger J.P.
      Role of endothelin in mediating tumor necrosis factor-induced hypertension in pregnant rats.
      Sera from pregnant rats exposed to chronic RUPP increase ET-1 production by cultured endothelial cells, and these levels of ET-1 production are mimicked when cells are exposed to TNF-α.
      • Bakrania B.A.
      • Spradley F.T.
      • Satchell S.C.
      • et al.
      Heme oxygenase-1 is a potent inhibitor of placental ischemia-mediated endothelin-1 production in cultured human glomerular endothelial cells.
      Further studies in this model suggest that TNF-α–induced hypertension could also be caused by decreases in renal NO synthase expression
      • Alexander B.T.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Tumor necrosis factor-alpha-induced hypertension in pregnant rats results in decreased renal neuronal nitric oxide synthase expression.
      and increases in AT1-AA production.
      • LaMarca B.
      • Wallukat G.
      • Llinas M.
      • Herse F.
      • Dechend R.
      • Granger J.P.
      Autoantibodies to the angiotensin type I receptor in response to placental ischemia and tumor necrosis factor alpha in pregnant rats.
      Most recently, TNF-α infusion in pregnant rats has been shown to exhibit impaired cerebrovascular regulation owing to reduced β-epithelial Na+ channel expression.
      • Duncan J.W.
      • Younes S.T.
      • Hildebrandt E.
      • Ryan M.J.
      • Granger J.P.
      • Drummond H.A.
      Tumor necrosis factor-α impairs cerebral blood flow in pregnant rats: role of vascular β-epithelial Na+ channel.
      Systemic activation of the immune cells during pregnancy has been studied as a model of PE. Faas et al
      • Faas M.M.
      • Schuiling G.A.
      • Baller J.F.
      • Visscher C.A.
      • Bakker W.W.
      A new animal model for human preeclampsia: ultra-low-dose endotoxin infusion in pregnant rats.
      showed that injection of low-dose endotoxin to induce an proinflammatory state at gestational day 14 results in hypertension and proteinuria. These animals were also found to have platelet coagulopathy and glomerular injury. An alternative approach to induce systemic inflammation is through the administration of lipopolysaccharide (LPS). A low dose of LPS is adequate to induce FGR, placental nitrosative stress, reduced spiral artery area, hypertension, and proteinuria.
      • Cotechini T.
      • Komisarenko M.
      • Sperou A.
      • Macdonald-Goodfellow S.
      • Adams M.A.
      • Graham C.H.
      Inflammation in rat pregnancy inhibits spiral artery remodeling leading to fetal growth restriction and features of preeclampsia.
      Although these models are not induced through specific PE-related factors, they have been useful in understanding how widespread activation of leukocytes in this disease contributes to its pathogenesis.
      A novel model of PE was recently published where mice were treated with placenta-derived extracellular vesicles (pcEVs) at gestational days 17–18 from women with PE, which resulted in hypertension, proteinuria, and kidney injury. This was associated with increased vascular wall tension and reduced CBF. Interestingly, in virgin mice, hypertension developed within 30 minutes of pcEV infusion.
      • Han C.
      • Wang C.
      • Chen Y.
      • et al.
      Placenta-derived extracellular vesicles induce preeclampsia in mouse models.
      pcEV shedding from the placenta is considered normal throughout pregnancy. However, excess levels are seen owing to the dysfunction placenta in PE.
      • Germain S.J.
      • Sacks G.P.
      • Sooranna S.R.
      • Sargent I.L.
      • Redman C.W.
      Systemic inflammatory priming in normal pregnancy and preeclampsia: the role of circulating syncytiotrophoblast microparticles.

      Models used to study role of endothelin and nitric oxide in preeclampsia

      Endothelial dysfunction is another known stimulus for ET-1 synthesis. Plasma concentration of ET-1 has been measured in a number of studies involving normal pregnant and women with PE. Most investigators have found higher ET-1 plasma concentrations of approximately 2- to 3-fold in women with PE.
      • George E.M.
      • Granger J.P.
      Linking placental ischemia and hypertension in preeclampsia: role of endothelin 1.
      ,
      • Mastrogiannis D.S.
      • O’Brien W.F.
      • Krammer J.
      • Benoit R.
      Potential role of endothelin-1 in normal and hypertensive pregnancies.
      Previous studies have reported that 2- to 3-fold elevation in plasma levels of ET-1 in animals is adequate to impart significant long-term effects on systemic hemodynamics and arterial pressure regulation. Thus, long-term elevations in plasma levels of ET-1 comparable with those measured in women with PE could play a role in mediating the reductions in renal function and elevations in arterial pressure observed in women with PE.
      There are robust increases in ET-1 coupled with marked deficiencies in vasodilatory mediators, including NO, in PE.
      • Perper J.A.
      • Patterson G.T.
      • Backner J.S.
      Face imaging reconstructive morphography. A new method for physiognomic reconstruction.
      ,
      • Sladek S.M.
      • Magness R.R.
      • Conrad K.P.
      Nitric oxide and pregnancy.
      Substantial production of ROS during PE leads to the oxidation of NO and soluble guanylate cyclase (sGC), a critical molecule involved in NO-mediated vasodilation. NO production is reduced in women with PE and in the RUPP and sFlt-1 excess models.
      • Khalil R.A.
      • Granger J.P.
      Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models.
      An important model used to examine the role of NO deficiency in PE is the L-NAME model. In normal pregnant rats, L-NAME administration to block NO production from gestational day 1 to 19 leads to hypertension, proteinuria, elevated sFlt-1, and reduced fetal and placental weight.
      • Ramesar S.V.
      • Mackraj I.
      • Gathiram P.
      • Moodley J.
      Sildenafil citrate decreases sFlt-1 and sEng in pregnant L-NAME treated Sprague-Dawley rats.

      Genetic models used to study preeclampsia mechanisms

      BPH/5

      Perhaps the best characterized genetically linked model for the study of PE is the BPH/5 mouse. The BPH/5 is a strain derivation of the BPH/2 “borderline hypertensive” mouse and exhibits mildly elevated blood pressure throughout the adult life span of the animal. However, Davisson et al
      • Davisson R.L.
      • Hoffmann D.S.
      • Butz G.M.
      • et al.
      Discovery of a spontaneous genetic mouse model of preeclampsia.
      demonstrated that the BPH/5 strain also demonstrates late gestational acute elevations in blood pressure (up to approximately 25 mm Hg), which resolve immediately after parturition, mimicking the effects on blood pressure seen in the patient with typical PE. This was accompanied by proteinuria, glomerulosclerosis, intrauterine growth restriction, maternal endothelial dysfunction, and increased fetal mortality.
      • Davisson R.L.
      • Hoffmann D.S.
      • Butz G.M.
      • et al.
      Discovery of a spontaneous genetic mouse model of preeclampsia.
      Work from the Davisson and Sones laboratories in subsequent years has uncovered a number of additional characteristics similar to human PE, such as altered extravillous trophoblast invasion and placental abnormalities that coincide with increased uterine artery vascular resistance. Importantly, these effects are seen before the onset of hypertension, as is postulated in the human disorder.
      • Dokras A.
      • Hoffmann D.S.
      • Eastvold J.S.
      • et al.
      Severe feto-placental abnormalities precede the onset of hypertension and proteinuria in a mouse model of preeclampsia.
      However, it should be noted that although total circulating angiogenic potential is decreased in the BPH/5, this seems to be associated with decreased VEGF and PlGF rather than increased sFlt-1, an interesting difference from the human syndrome. Recent studies from Sones et al
      • Sones J.L.
      • Merriam A.A.
      • Seffens A.
      • et al.
      Angiogenic factor imbalance precedes complement deposition in placentae of the BPH/5 model of preeclampsia.
      show that angiogenic imbalance precedes complement activation, which has been implicated in the pathogenesis of PE.

      Angiotensinogen/renin overexpression

      Although its role in long-term maintenance of blood pressure is well established, the exact pathophysiological role of the RAS in the development of PE is less clear. To investigate the role of the RAS in pregnancy-induced hypertension, several groups have used transgenic mouse and rodent strains in which females overexpressing human angiotensinogen (AGN) are crossed with males overexpressing human renin (REN).
      • Bohlender J.
      • Ganten D.
      • Luft F.C.
      Rats transgenic for human renin and human angiotensinogen as a model for gestational hypertension.
      • Hering L.
      • Herse F.
      • Geusens N.
      • et al.
      Effects of circulating and local uteroplacental angiotensin II in rat pregnancy.
      • Takimoto E.
      • Ishida J.
      • Sugiyama F.
      • Horiguchi H.
      • Murakami K.
      • Fukamizu A.
      Hypertension induced in pregnant mice by placental renin and maternal angiotensinogen.
      This model has been shown to exhibit late gestational hypertension and proteinuria. Recent studies have also showed the development of postpartum cardiac dysfunction in this model.
      • Kräker K.
      • O’Driscoll J.M.
      • Schütte T.
      • et al.
      Statins reverse postpartum cardiovascular dysfunction in a rat model of preeclampsia.
      Importantly, when the gender of the transgenic animals is swapped (ie, male AGN and female REN), no phenotypic effect is noted, likely owing to species specificity of REN activity and lack of secretion of AGN from the placenta itself. A similar model has been reported in mice overexpressing both REN and AGN, which are chronically hypertensive, as a model of superimposed PE, which also develops very late gestational hypertension and FGR.
      • Denney J.M.
      • Bird C.
      • Gendron-Fitzpatrick A.
      • Sampene E.
      • Bird I.M.
      • Shah D.M.
      Renin-angiotensin system transgenic mouse model recapitulates pathophysiology similar to human preeclampsia with renal injury that may be mediated through VEGF.

      STOX1 overexpression

      Another new potential model that has recently been reported is transgenic overexpression of the transcription factor storkhead box 1 (STOX1) in a murine model. A significant, although often contradictory, body evidence has previously implicated STOX1 dysregulation in the etiology of PE.
      • Haram K.
      • Mortensen J.H.
      • Nagy B.
      Genetic aspects of preeclampsia and the HELLP syndrome.
      ,
      • George E.M.
      • Bidwell G.L.
      STOX1: a new player in preeclampsia?.
      Interestingly, Doridot et al
      • Doridot L.
      • Delpoux A.
      • Lucas B.
      • Vaiman D.
      Preeclampsia-like syndrome in STOX1 overexpressing mice: defects in immune regulation?.
      ,
      • Doridot L.
      • Passet B.
      • Méhats C.
      • et al.
      STOX1 overexpression in mice induces severe preeclampsia-like symptoms prevented by aspirin at low doses.
      showed that STOX1 overexpression leads to increases in systolic blood pressure from very early gestation, proteinuria, renal capillary swelling, fibrin deposition, and elevated levels of sFlt-1 and sEng. The early onset of hypertension suggests abnormal placentation may not be the cause of elevated blood pressure in this model. Nevertheless, the STOX1 overexpression model has been used to study many organ systems related to PE. Recently, studies have shown that STOX1 overexpression in mice results in increased renal artery resistance, cardiac hypertrophy, FGR, and a trend toward increased umbilical resistance.
      • Collinot H.
      • Marchiol C.
      • Lagoutte I.
      • et al.
      Preeclampsia induced by STOX1 overexpression in mice induces intrauterine growth restriction, abnormal ultrasonography and BOLD MRI signatures.
      ,
      • Ducat A.
      • Doridot L.
      • Calicchio R.
      • et al.
      Endothelial cell dysfunction and cardiac hypertrophy in the STOX1 model of preeclampsia.
      In a 2019 study, Miralles et al
      • Miralles F.
      • Collinot H.
      • Boumerdassi Y.
      • et al.
      Long-term cardiovascular disorders in the STOX1 mouse model of preeclampsia.
      showed that STOX1 overexpression in mice with a PE-like phenotype during pregnancy exhibited left ventricular hypertrophy, cardiac fibrosis, and markers of inflammation and cellular stress up to 8 months after delivery.

      Ankyrin repeat and SOCS box containing 4 deletion

      Another model that may be useful in studying vascularization of the placenta in the early stages of PE is the ubiquitin ligase ankyrin repeat and SOCS box containing 4 (ASB4), which promotes the differentiation of vascular lineages in trophoblasts. Townley-Tilson et al
      • Townley-Tilson W.H.D.
      • Wu Y.
      • Ferguson 3rd, J.E.
      • Patterson C.
      The ubiquitin ligase ASB4 promotes trophoblast differentiation through the degradation of ID2.
      showed that in placentas of ASB4−/− mice, trophoblast-to-endothelial cell differentiation is impaired resulting in fewer mature endothelial cells and reduced placental vascularization. Consequently, these mice produced smaller litter sizes and developed hypertension and proteinuria later in gestation.
      • Townley-Tilson W.H.D.
      • Wu Y.
      • Ferguson 3rd, J.E.
      • Patterson C.
      The ubiquitin ligase ASB4 promotes trophoblast differentiation through the degradation of ID2.
      ,
      • Li F.
      • Fushima T.
      • Oyanagi G.
      • et al.
      Nicotinamide benefits both mothers and pups in two contrasting mouse models of preeclampsia.

      ELABELA deficiency

      ELABELA, an endogenous ligand of the apelin receptor, has recently garnered much attention as a biomarker and therapeutic target of PE. Serum levels of ELABELA have been examined during early- and late-onset PE in a number of studies with varying results.
      • Panaitescu B.
      • Romero R.
      • Gomez-Lopez N.
      • et al.
      ELABELA plasma concentrations are increased in women with late-onset preeclampsia.
      ,
      • Huang R.
      • Zhu J.
      • Zhang L.
      • et al.
      Is ELABELA a reliable biomarker for hypertensive disorders of pregnancy?.
      Although some of these studies indicate that ELABELA may be increased in some cohorts, it is generally accepted that ELABELA plays a role in proper extravillous trophoblast migration and is deficient at least in the placentas of women with PE.
      • Georgiadou D.
      • Boussata S.
      • Ranzijn W.H.M.
      • et al.
      Peptide hormone ELABELA enhances extravillous trophoblast differentiation, but placenta is not the major source of circulating ELABELA in pregnancy.
      ,
      • Wang L.
      • Zhang Y.
      • Qu H.
      • et al.
      Reduced ELABELA expression attenuates trophoblast invasion through the PI3K/AKT/mTOR pathway in early onset preeclampsia.
      Animal studies found that ELABELA knockout in mice results in hypertension, proteinuria, impaired placental vascularization, and FGR.
      • Ho L.
      • van Dijk M.
      • Chye S.T.J.
      • et al.
      ELABELA deficiency promotes preeclampsia and cardiovascular malformations in mice.
      Interestingly, the investigators did not see the same results in apelin knockout mice. Furthermore, exogenous ELABELA attenuated these outcomes.
      • Ho L.
      • van Dijk M.
      • Chye S.T.J.
      • et al.
      ELABELA deficiency promotes preeclampsia and cardiovascular malformations in mice.

      Complement component 1q deficiency

      Complement activation has been shown to play a role in not only the clinical manifestation of PE but also spiral artery remodeling. Women with both early and late PE have decreased serum levels of complement component 1q (C1q) compared with those with uncomplicated pregnancies.
      • Jia K.
      • Ma L.
      • Wu S.
      • Yang W.
      Serum levels of complement factors C1q, Bb, and H in normal pregnancy and severe pre-eclampsia.
      In a mouse model of C1q deficiency (C1q−/−), animals develop hypertension, proteinuria, endotheliosis, decreased circulating VEGF, and elevated sFlt-1.
      • Singh J.
      • Ahmed A.
      • Girardi G.
      Role of complement component C1q in the onset of preeclampsia in mice.
      These characteristics are accompanied by increased fetal death.
      • Singh J.
      • Ahmed A.
      • Girardi G.
      Role of complement component C1q in the onset of preeclampsia in mice.

      Dahl salt-sensitive rat

      Clinically, PE can be classed as “superimposed” when a patient is hypertensive before pregnancy. Similarly, the Dahl salt-sensitive (S) rat is hypertensive and develops a PE-like phenotype during pregnancy, including further elevations in blood pressure, proteinuria, glomerulomegaly, increased uterine artery resistance, FGR, and elevated circulating levels of TNF-α and sFlt-1.
      • Gillis E.E.
      • Williams J.M.
      • Garrett M.R.
      • Mooney J.N.
      • Sasser J.M.
      The Dahl salt-sensitive rat is a spontaneous model of superimposed preeclampsia.
      Further studies show postpartum renal injury in these animals despite no long-term blood pressure differences.
      • Turbeville H.R.
      • Taylor E.B.
      • Garrett M.R.
      • Didion S.P.
      • Ryan M.J.
      • Sasser J.M.
      Superimposed preeclampsia exacerbates postpartum renal injury despite lack of long-term blood pressure difference in the Dahl salt-sensitive rat.
      Interestingly, not all strains of hypertensive rats develop a PE-like phenotype during pregnancy. In contrast to the Dahl S rat, blood pressure in the spontaneously hypertensive rat decreases toward late pregnancy. Using this model, Gillis et al
      • Gillis E.E.
      • Mooney J.N.
      • Garrett M.R.
      • Granger J.P.
      • Sasser J.M.
      Sildenafil treatment ameliorates the maternal syndrome of preeclampsia and rescues fetal growth in the Dahl salt-sensitive rat.
      also demonstrated that sildenafil treatment ameliorates the maternal syndrome of PE and rescues fetal growth in the Dahl S rat.

      African green monkey

      The African green monkey (Chlorocebus aethiops sabaeus) has been shown to develop hypertension during adulthood.
      • Rhoads M.K.
      • Goleva S.B.
      • Beierwaltes W.H.
      • Osborn J.L.
      Renal vascular and glomerular pathologies associated with spontaneous hypertension in the nonhuman primate Chlorocebus aethiops sabaeus.
      More recently, Weaver et al
      • Weaver C.
      • Grobe J.
      • Santillan M.
      • Osborn J.
      Fetal growth restriction is associated with spontaneous gestational hypertension in African green monkeys.
      showed that in nonhypertensive adults, some animals develop hypertension and FGR during pregnancy similar to PE.
      Many pathways in this disease have been targeted to produce animal models of PE (Table 2). A summary of the characteristics of each of the models discussed in this review is presented in Table 3.
      Table 2Summary of pathways involved in PE that are studied using animal models
      PathwayAnimal modelReferences
      Placental ischemiaReduced uterine perfusion pressureIntapad et al
      • Intapad S.
      • Warrington J.P.
      • Spradley F.T.
      • et al.
      Reduced uterine perfusion pressure induces hypertension in the pregnant mouse.
      ; Alexander et al
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      Uteroplacental ischemiaMakris et al
      • Makris A.
      • Thornton C.
      • Thompson J.
      • et al.
      Uteroplacental ischemia results in proteinuric hypertension and elevated sFLT-1.
      Angiogenic imbalanceAdenovirus expressing sFlt-1 excessMaynard et al
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      ; Bergmann et al
      • Bergmann A.
      • Ahmad S.
      • Cudmore M.
      • et al.
      Reduction of circulating soluble Flt-1 alleviates preeclampsia-like symptoms in a mouse model.
      sFlt-1 infusionMurphy et al
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      ; Szalai et al
      • Szalai G.
      • Romero R.
      • Chaiworapongsa T.
      • et al.
      Full-length human placental SFlt-1-e15a isoform induces distinct maternal phenotypes of preeclampsia in mice.
      Immune activationRegulatory T-cell depletionCare et al
      • Care A.S.
      • Bourque S.L.
      • Morton J.S.
      • Hjartarson E.P.
      • Robertson S.A.
      • Davidge S.T.
      Reduction in regulatory T cells in early pregnancy causes uterine artery dysfunction in mice.
      TNF-α infusionAlexander et al
      • Alexander B.T.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Tumor necrosis factor-alpha-induced hypertension in pregnant rats results in decreased renal neuronal nitric oxide synthase expression.
      Low-dose endotoxin infusionFaas et al
      • Faas M.M.
      • Schuiling G.A.
      • Baller J.F.
      • Visscher C.A.
      • Bakker W.W.
      A new animal model for human preeclampsia: ultra-low-dose endotoxin infusion in pregnant rats.
      Low-dose lipopolysaccharide infusionCotechini et al
      • Cotechini T.
      • Komisarenko M.
      • Sperou A.
      • Macdonald-Goodfellow S.
      • Adams M.A.
      • Graham C.H.
      Inflammation in rat pregnancy inhibits spiral artery remodeling leading to fetal growth restriction and features of preeclampsia.
      Placenta-derived extracellular vesicle infusionHan et al
      • Han C.
      • Wang C.
      • Chen Y.
      • et al.
      Placenta-derived extracellular vesicles induce preeclampsia in mouse models.
      Renin-angiotensin system activationAgnostic angiotensin II type 1 receptor autoantibody infusionLaMarca et al
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      ; Zhou et al
      • Zhou C.C.
      • Zhang Y.
      • Irani R.A.
      • et al.
      Angiotensin receptor agonistic autoantibodies induce pre-eclampsia in pregnant mice.
      Angiotensinogen/renin overexpressionTakimoto et al
      • Takimoto E.
      • Ishida J.
      • Sugiyama F.
      • Horiguchi H.
      • Murakami K.
      • Fukamizu A.
      Hypertension induced in pregnant mice by placental renin and maternal angiotensinogen.
      ; Denney et al
      • Denney J.M.
      • Bird C.
      • Gendron-Fitzpatrick A.
      • Sampene E.
      • Bird I.M.
      • Shah D.M.
      Renin-angiotensin system transgenic mouse model recapitulates pathophysiology similar to human preeclampsia with renal injury that may be mediated through VEGF.
      Endothelial dysfunctionL-NAME infusionRamesar et al
      • Ramesar S.V.
      • Mackraj I.
      • Gathiram P.
      • Moodley J.
      Sildenafil citrate decreases sFlt-1 and sEng in pregnant L-NAME treated Sprague-Dawley rats.
      Abnormal placentationSTOX1 overexpressionDoridot et al
      • Doridot L.
      • Delpoux A.
      • Lucas B.
      • Vaiman D.
      Preeclampsia-like syndrome in STOX1 overexpressing mice: defects in immune regulation?.
      ; Doridot et al
      • Doridot L.
      • Passet B.
      • Méhats C.
      • et al.
      STOX1 overexpression in mice induces severe preeclampsia-like symptoms prevented by aspirin at low doses.
      ASB4 deletionTownley-Tilson et al
      • Townley-Tilson W.H.D.
      • Wu Y.
      • Ferguson 3rd, J.E.
      • Patterson C.
      The ubiquitin ligase ASB4 promotes trophoblast differentiation through the degradation of ID2.
      ELABELA deficiencyHo et al
      • Ho L.
      • van Dijk M.
      • Chye S.T.J.
      • et al.
      ELABELA deficiency promotes preeclampsia and cardiovascular malformations in mice.
      Complement system activationC1q−/− deficiencySingh et al
      • Singh J.
      • Ahmed A.
      • Girardi G.
      Role of complement component C1q in the onset of preeclampsia in mice.
      Superimposed or spontaneous models of PEBPH/5 modelDavisson et al
      • Davisson R.L.
      • Hoffmann D.S.
      • Butz G.M.
      • et al.
      Discovery of a spontaneous genetic mouse model of preeclampsia.
      Dahl salt-sensitive ratGillis et al
      • Gillis E.E.
      • Williams J.M.
      • Garrett M.R.
      • Mooney J.N.
      • Sasser J.M.
      The Dahl salt-sensitive rat is a spontaneous model of superimposed preeclampsia.
      African green monkeyWeaver et al
      • Weaver C.
      • Grobe J.
      • Santillan M.
      • Osborn J.
      Fetal growth restriction is associated with spontaneous gestational hypertension in African green monkeys.
      ASB4, ankyrin repeat and SOCS box containing 4; C1q, component 1q; L-NAME, L-NG-nitroarginine methyl ester; PE, preeclampsia; sFlt-1, soluble fms-like tyrosine kinase-1; STOX1, storkhead box 1; TNF-α, tumor necrosis factor-α.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      Table 3Summary of features in animal models of PE during pregnancy
      ModelAnimalFeaturesReferences
      RUPPRat↑MAP, ↑proteinuria, ↑sFlt-1, ↑sEng, ↓PlGF, ↓VEGF, ↑ROS, ↑AT1-AA, ↑TNF-α, ↑Tregs, ↑NK cells, ↑ET-1, ↓NO, ↓RPF, ↓GFR, ↑cardiac dysfunction, ↑cardiac hypertrophy, ↓CBF, ↑cerebral edema, ↑ BBB permeability, ↓placental weight, ↑FGRRana et al
      • Rana S.
      • Lemoine E.
      • Granger J.P.
      • Karumanchi S.A.
      Preeclampsia: pathophysiology, challenges, and perspectives.
      ; Alexander et al;
      • Alexander B.T.
      • Kassab S.E.
      • Miller M.T.
      • et al.
      Reduced uterine perfusion pressure during pregnancy in the rat is associated with increases in arterial pressure and changes in renal nitric oxide.
      ; Alexander et al
      • Alexander B.T.
      Placental insufficiency leads to development of hypertension in growth-restricted offspring.
      ; LaMarca et al
      • LaMarca B.D.
      • Gilbert J.
      • Granger J.P.
      Recent progress toward the understanding of the pathophysiology of hypertension during preeclampsia.
      ; Gilbert et al
      • Gilbert J.S.
      • Ryan M.J.
      • LaMarca B.B.
      • Sedeek M.
      • Murphy S.R.
      • Granger J.P.
      Pathophysiology of hypertension during preeclampsia: linking placental ischemia with endothelial dysfunction.
      ; Khalil et al
      • Khalil R.A.
      • Granger J.P.
      Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models.
      ; Sedeek et al
      • Sedeek M.
      • Gilbert J.S.
      • Lamarca B.B.
      • et al.
      Role of reactive oxygen specied in hypertension produced by reduced uterine perfusion pressure in pregnant rats.
      ; Gilbert et al
      • Gilbert J.S.
      • Babcock S.A.
      • Granger J.P.
      Hypertension produced by reduced uterine perfusion in pregnant rats is associated with increased soluble fms-like tyrosine kinase-1 expression.
      ; Gilbert et al
      • Gilbert J.S.
      • Gilbert S.A.B.
      • Arany M.
      • Granger J.P.
      Hypertension produced by placental ischemia in pregnant rats is associated with increased soluble endoglin expression.
      ; LaMarca et al
      • LaMarca B.
      • Wallace K.
      • Granger J.
      Role of angiotensin II type I receptor agonistic autoantibodies (AT1-AA) in preeclampsia.
      ; LaMarca et al
      • LaMarca B.D.
      • Ryan M.J.
      • Gilbert J.S.
      • Murphy S.R.
      • Granger J.P.
      Inflammatory cytokines in the pathophysiology of hypertension during preeclampsia.
      ; Cornelius et al
      • Cornelius D.C.
      • Cottrell J.
      • Amaral L.M.
      • LaMarca B.
      Inflammatory mediators: a causal link to hypertension during preeclampsia.
      ; LaMarca et al
      • LaMarca B.
      • Cornelius D.C.
      • Harmon A.C.
      • et al.
      Identifying immune mechanisms mediating the hypertension during preeclampsia.
      ; Lillegard et al
      • Lillegard K.E.
      • Johnson A.C.
      • Lojovich S.J.
      • et al.
      Complement activation is critical for placental ischemia-induced hypertension in the rat.
      ;Warrington et al
      • Warrington J.P.
      • Fan F.
      • Murphy S.R.
      • et al.
      Placental ischemia in pregnant rats impairs cerebral blood flow autoregulation and increases blood-brain barrier permeability.
      ; Warrington et al
      • Warrington J.P.
      • Fan F.
      • Duncan J.
      • et al.
      The angiotensin II type I receptor contributes to impaired cerebral blood flow autoregulation caused by placental ischemia in pregnant rats.
      ; Bakrania et al
      • Bakrania B.A.
      • Hall M.E.
      • Shahul S.
      • Granger J.P.
      The reduced uterine perfusion pressure (RUPP) rat model of preeclampsia exhibits impaired systolic function and global longitudinal strain during pregnancy.
      ; Gutkowska et al
      • Gutkowska J.
      • Granger J.P.
      • LaMarca B.B.
      • Danalache B.A.
      • Wang D.
      • Jankowski M.
      Changes in cardiac structure in hypertension produced by placental ischemia in pregnant rats: effect of tumor necrosis factor blockade.
      Uteroplacental ischemiaNonhuman primate↑MAP, ↑proteinuria, ↑sFlt-1,Makris et al
      • Makris A.
      • Thornton C.
      • Thompson J.
      • et al.
      Uteroplacental ischemia results in proteinuric hypertension and elevated sFLT-1.
      ; Turanov et al
      • Turanov A.A.
      • Lo A.
      • Hassler M.R.
      • et al.
      RNAi modulation of placental sFLT1 for the treatment of preeclampsia.
      Ad-sFlt-1 infusionRat↑MAP, ↑proteinuria, ↑glomerular endotheliosisMaynard et al
      • Maynard S.E.
      • Min J.Y.
      • Merchan J.
      • et al.
      Excess placental soluble fms-like tyrosine kinase 1 (sFlt-1) may contribute to endothelial dysfunction, hypertension, and proteinuria in preeclampsia.
      sFlt-1 infusionRat↑MAP, ↑proteinuria, ↑prepro-ET-1, ↑ROS, ↓placental weight, ↑FGRMurphy et al
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      Regulatory T-cell depletionMouse↔MAP, ↑proinflammatory markers, ↑UARI, ↑fetal lossCare et al
      • Care A.S.
      • Bourque S.L.
      • Morton J.S.
      • Hjartarson E.P.
      • Robertson S.A.
      • Davidge S.T.
      Reduction in regulatory T cells in early pregnancy causes uterine artery dysfunction in mice.
      AT-AA infusionRat↑MAP, ↑NK cells, ↑sFlt-1, ↑sEng, ↑prepro-ET-1, ↑AT1-AALaMarca et al
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      , Cunningham et al
      • Cunningham Jr., M.W.
      • Vaka V.R.
      • McMaster K.
      • et al.
      Renal natural killer cell activation and mitochondrial oxidative stress; new mechanisms in AT1-AA mediated hypertensive pregnancy.
      ; LaMarca et al
      • LaMarca B.
      • Parrish M.R.
      • Wallace K.
      Agonistic autoantibodies to the angiotensin II type I receptor cause pathophysiologic characteristics of preeclampsia.
      TNF-α infusionRat↑MAP, ↑prepro-ET-1, ↓NOS, ↑AT1-AA, ↓CBFAlexander et al
      • Alexander B.T.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Tumor necrosis factor-alpha-induced hypertension in pregnant rats results in decreased renal neuronal nitric oxide synthase expression.
      ; LaMarca et al
      • LaMarca B.
      • Wallukat G.
      • Llinas M.
      • Herse F.
      • Dechend R.
      • Granger J.P.
      Autoantibodies to the angiotensin type I receptor in response to placental ischemia and tumor necrosis factor alpha in pregnant rats.
      ; Duncan et al
      • Duncan J.W.
      • Younes S.T.
      • Hildebrandt E.
      • Ryan M.J.
      • Granger J.P.
      • Drummond H.A.
      Tumor necrosis factor-α impairs cerebral blood flow in pregnant rats: role of vascular β-epithelial Na+ channel.
      L-NAME infusionRat↑MAP, ↑proteinuria, ↑sFlt-1, ↓placental weight, ↑FGRRamesar et al
      • Ramesar S.V.
      • Mackraj I.
      • Gathiram P.
      • Moodley J.
      Sildenafil citrate decreases sFlt-1 and sEng in pregnant L-NAME treated Sprague-Dawley rats.
      pcEV infusionMouse↑MAP, ↑proteinuria, ↑kidney injury, ↓CBFHan et al
      • Han C.
      • Wang C.
      • Chen Y.
      • et al.
      Placenta-derived extracellular vesicles induce preeclampsia in mouse models.
      BPH/5Mouse↑MAP, ↑proteinuria, ↑endothelial dysfunction, ↑glomerulosclerosis, ↑fetal mortality, ↑UARI, ↔sFlt-1, ↓VEGF, ↓PlGF, ↓impaired cytotrophoblast invasion, ↓ placental weight, ↑FGRDavisson et al
      • Davisson R.L.
      • Hoffmann D.S.
      • Butz G.M.
      • et al.
      Discovery of a spontaneous genetic mouse model of preeclampsia.
      ; Dokras et al
      • Dokras A.
      • Hoffmann D.S.
      • Eastvold J.S.
      • et al.
      Severe feto-placental abnormalities precede the onset of hypertension and proteinuria in a mouse model of preeclampsia.
      ; Sones et al
      • Sones J.L.
      • Merriam A.A.
      • Seffens A.
      • et al.
      Angiogenic factor imbalance precedes complement deposition in placentae of the BPH/5 model of preeclampsia.
      hAGTxhRen overexpressionRat↑MAP, ↑proteinuria, ↑cardiac hypertrophyBohlender et al
      • Bohlender J.
      • Ganten D.
      • Luft F.C.
      Rats transgenic for human renin and human angiotensinogen as a model for gestational hypertension.
      ; Hering et al
      • Hering L.
      • Herse F.
      • Geusens N.
      • et al.
      Effects of circulating and local uteroplacental angiotensin II in rat pregnancy.
      STOX1 overexpressionMouse↑systolic pressure, ↑proteinuria, ↑renal capillary swelling, ↑sFlt-1, ↑sEng, ↑cardiac hypertrophy, ↑FGR, ↑renal artery resistanceDoridot et al
      • Doridot L.
      • Delpoux A.
      • Lucas B.
      • Vaiman D.
      Preeclampsia-like syndrome in STOX1 overexpressing mice: defects in immune regulation?.
      ; Doridot et al
      • Doridot L.
      • Passet B.
      • Méhats C.
      • et al.
      STOX1 overexpression in mice induces severe preeclampsia-like symptoms prevented by aspirin at low doses.
      ; Collinot et al
      • Collinot H.
      • Marchiol C.
      • Lagoutte I.
      • et al.
      Preeclampsia induced by STOX1 overexpression in mice induces intrauterine growth restriction, abnormal ultrasonography and BOLD MRI signatures.
      ; Ducat et al
      • Ducat A.
      • Doridot L.
      • Calicchio R.
      • et al.
      Endothelial cell dysfunction and cardiac hypertrophy in the STOX1 model of preeclampsia.
      Complement C1q deficiencyMouse↑MAP, ↑proteinuria, ↑endotheliosis, ↑sFlt-1, ↓VEGF, ↑fetal deathSingh et al
      • Singh J.
      • Ahmed A.
      • Girardi G.
      Role of complement component C1q in the onset of preeclampsia in mice.
      ASB4 deletionMouse↓placental vascularization, ↑MAP, ↑proteinuria, ↓litter sizeTownley-Tilson et al
      • Townley-Tilson W.H.D.
      • Wu Y.
      • Ferguson 3rd, J.E.
      • Patterson C.
      The ubiquitin ligase ASB4 promotes trophoblast differentiation through the degradation of ID2.
      ; Li et al
      • Li F.
      • Fushima T.
      • Oyanagi G.
      • et al.
      Nicotinamide benefits both mothers and pups in two contrasting mouse models of preeclampsia.
      ELABELA deficiencyMouse↓placental vascularization, ↑MAP, ↑proteinuria, ↑FGRHo et al
      • Ho L.
      • van Dijk M.
      • Chye S.T.J.
      • et al.
      ELABELA deficiency promotes preeclampsia and cardiovascular malformations in mice.
      Dahl salt-sensitive ratRat↑MAP, ↑proteinuria, ↑sFlt-1, glomerulomegaly, ↑UARI, ↑FGRGillis et al
      • Gillis E.E.
      • Williams J.M.
      • Garrett M.R.
      • Mooney J.N.
      • Sasser J.M.
      The Dahl salt-sensitive rat is a spontaneous model of superimposed preeclampsia.
      ; Gillis et al
      • Gillis E.E.
      • Mooney J.N.
      • Garrett M.R.
      • Granger J.P.
      • Sasser J.M.
      Sildenafil treatment ameliorates the maternal syndrome of preeclampsia and rescues fetal growth in the Dahl salt-sensitive rat.
      African green monkeyNonhuman primate↑MAP, ↑FGRRhoads et al
      • Rhoads M.K.
      • Goleva S.B.
      • Beierwaltes W.H.
      • Osborn J.L.
      Renal vascular and glomerular pathologies associated with spontaneous hypertension in the nonhuman primate Chlorocebus aethiops sabaeus.
      ; Weaver et al
      • Weaver C.
      • Grobe J.
      • Santillan M.
      • Osborn J.
      Fetal growth restriction is associated with spontaneous gestational hypertension in African green monkeys.
      ASB4, ankyrin repeat and SOCS box containing 4; Ad-sFlt-1, adenovirus expressing soluble fms-like tyrosine kinase-1; AT1-AA, angiotensin II type 1 receptor autoantibody; BBB, blood-brain barrier; C1q, component 1q; CBF, cerebral blood flow; ET-1, endothelin-1; GFR, glomerular filtration rate; hAGT, human angiotensinogen; hREN, human renin; FGR, fetal growth restriction; L-NAME, L-NG-nitroarginine methyl ester; NK, natural killer; NO, nitric oxide; PE, preeclampsia; PlGF, placental growth factor; ROS, reactive oxygen species; RPF, renal plasma flow; RUPP, reduced uterine perfusion pressure; sEng, soluble endoglin; Tregs, regulatory T cells; TNF-α, tumor necrosis factor-α; VEGF, vascular endothelial growth factor; ↑, increased; ↓, decreased; ↔, unchanged.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.

      Use of animal models to study long-term consequences of preeclampsia

      Because more recent studies have revealed the profound impact of PE later in life for both the mother and baby, long-term consequences have become an important consideration in developing animal models. Although studies in this area are limited, some models have been shown to have persistent features beyond pregnancy. In some cases, such as in the RUPP, postpartum cardiac and renal dysfunctions are present despite return to normal blood pressure in these animals.
      • Paauw N.D.
      • Joles J.A.
      • Spradley F.T.
      • et al.
      Exposure to placental ischemia impairs postpartum maternal renal and cardiac function in rats.
      These data suggest that placental ischemia and the factors involved cause irreversible damage and therefore do substantiate further studies in this area. Long-term studies in which animals undergo multiple pregnancies may also be interesting because cardiovascular risk in women later in life increases with each pregnancy complicated by PE.

      Investigating Therapeutic Options for Preeclampsia Using Animal Models

      Currently, treatment for PE is limited to managing symptoms and in severe cases premature delivery of the fetus, which poses a significant risk to both the mother and baby. Because initial studies in women with PE are obviously impossible, animal models represent a critical tool in this area of study. Although many studies have been performed in animal models, unfortunately limited therapies have reached clinical trials. Nevertheless, investigations in rodent and nonhuman primates continue in the search for a treatment for PE.
      Angiogenic imbalance is an early predictor and central player in the development of PE; therefore, sFlt-1, PlGF, and VEGF remain key therapeutic targets. The administration of PlGF in RUPP rats and UPI nonhuman primates have shown reductions in sFlt-1, blood pressure, and proteinuria.
      • Makris A.
      • Yeung K.R.
      • Lim S.M.
      • et al.
      Placental growth factor reduces blood pressure in a uteroplacental ischemia model of preeclampsia in nonhuman primates.
      ,
      • Spradley F.T.
      • Tan A.Y.
      • Joo W.S.
      • et al.
      Placental growth factor administration abolishes placental ischemia-induced hypertension.
      Another approach that has been studied in nonhuman primates is the administration of short interfering RNAs (siRNAs) that silence the 3 sFlt-1 mRNA isoforms that are responsible for sFlt-1 overexpression in the placenta. In pregnant baboons, UPI was induced and the human siRNA mixture (siRNAsFlt-1-2283/2519) was administered at gestational day 133.
      • Turanov A.A.
      • Lo A.
      • Hassler M.R.
      • et al.
      RNAi modulation of placental sFLT1 for the treatment of preeclampsia.
      Data were collected at intervals of 4 to 6 weeks and showed significant decreases in circulating sFlt-1 levels and reductions in systolic blood pressure and proteinuria (Figure 3). Thadhani et al
      • Thadhani R.
      • Hagmann H.
      • Schaarschmidt W.
      • et al.
      Removal of soluble fms-like tyrosine kinase-1 by dextran sulfate apheresis in preeclampsia.
      ,
      • Thadhani R.
      • Kisner T.
      • Hagmann H.
      • et al.
      Pilot study of extracorporeal removal of soluble fms-like tyrosine kinase 1 in preeclampsia.
      are currently investigating the clearance of sFlt-1 (via apheresis) to improve angiogenic balance in women with PE. These studies show a transient decrease in mean arterial pressure after apheresis and prolonged gestation by up to 15 days.
      Figure thumbnail gr4
      Figure 3Circulating levels of sFlt-1, systolic blood pressure, and proteinuria in the UPI nonhuman primate model of PE
      Circulating levels of A, sFlt-1, B, systolic blood pressure, and C, proteinuria in the UPI nonhuman primate model of PE, after a single dose of human siRNA that silences 3 sFlt-1 isoforms (hsiRNAsFlt-1-2283/2519). These 3 isoforms are responsible for the placental overexpression of sFlt-1 but do not reduce full-length Flt-1 mRNA.
      • Turanov A.A.
      • Lo A.
      • Hassler M.R.
      • et al.
      RNAi modulation of placental sFLT1 for the treatment of preeclampsia.
      Data are presented as mean+SEM. The asterisk symbol indicates P<.001.
      hsiRNA, human short interfering RNA; mRNA, messenger RNA; PE, preeclampsia; SEM, standard error of the mean; sFlt-1, soluble fms-like tyrosine kinase-1; siRNA, short interfering RNA; UPI, uteroplacental ischemia.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      In women, PE is associated with increases in the vascular expression of ET-1 and endothelial activation
      • Khalil R.A.
      • Granger J.P.
      Vascular mechanisms of increased arterial pressure in preeclampsia: lessons from animal models.
      In addition, a number of experimental models of PE are also associated with elevated tissue levels of prepro-ET-1 mRNA. These models have been used to determine whether blockade of the ET system could improve hypertension. Interestingly, in the RUPP model, sFlt-1 infusion, TNF-α infusion, and AT1-AA infusion, the administration of the ETA receptor antagonist reduces the mean arterial pressure
      • Alexander B.T.
      • Rinewalt A.N.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Endothelin type A receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure.
      ,
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      ,
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      ,
      • LaMarca B.B.D.
      • Cockrell K.
      • Sullivan E.
      • Bennett W.
      • Granger J.P.
      Role of endothelin in mediating tumor necrosis factor-induced hypertension in pregnant rats.
      (Figure 4). Results from these studies suggest that ET-1 may be a final common pathway whereby placental factors act on the maternal vasculature to cause vasoconstriction and hypertension. Another avenue to improve endothelial function is by stimulation of the NO-sGC-cyclic guanosine monophosphate (cGMP) pathway. Compounds that promote NO production or blockade of cGMP degradation to increase activity of this pathway are 2 methods that have been tested in animal models
      • Ramesar S.V.
      • Mackraj I.
      • Gathiram P.
      • Moodley J.
      Sildenafil citrate decreases sFlt-1 and sEng in pregnant L-NAME treated Sprague-Dawley rats.
      ,
      • Gillis E.E.
      • Mooney J.N.
      • Garrett M.R.
      • Granger J.P.
      • Sasser J.M.
      Sildenafil treatment ameliorates the maternal syndrome of preeclampsia and rescues fetal growth in the Dahl salt-sensitive rat.
      ,
      • Alexander B.T.
      • Llinas M.T.
      • Kruckeberg W.C.
      • Granger J.P.
      L-arginine attenuates hypertension in pregnant rats with reduced uterine perfusion pressure.
      • Murphy S.R.
      • LaMarca B.
      • Cockrell K.
      • Arany M.
      • Granger J.P.
      L-arginine supplementation abolishes the blood pressure and endothelin response to chronic increases in plasma sFlt-1 in pregnant rats.
      • Oludare G.O.
      • Jinadu H.D.
      • Aro O.O.
      L-arginine attenuates blood pressure and reverses the suppression of angiogenic risk factors in a rat model of preeclampsia.
      • George E.M.
      • Palei A.C.
      • Dent E.A.
      • Granger J.P.
      Sildenafil attenuates placental ischemia-induced hypertension.
      • Terstappen F.
      • Spradley F.T.
      • Bakrania B.A.
      • et al.
      Prenatal sildenafil therapy improves cardiovascular function in fetal growth restricted offspring of Dahl salt-sensitive rats.
      and reached clinical trials.
      • Neri I.
      • Monari F.
      • Sgarbi L.
      • Berardi A.
      • Masellis G.
      • Facchinetti F.
      L-arginine supplementation in women with chronic hypertension: impact on blood pressure and maternal and neonatal complications.
      • Grunewald C.
      • Kublickas M.
      • Carlström K.
      • Lunell N.O.
      • Nisell H.
      Effects of nitroglycerin on the uterine and umbilical circulation in severe preeclampsia.
      • Luzi G.
      • Caserta G.
      • Iammarino G.
      • Clerici G.
      • Di Renzo G.C.
      Nitric oxide donors in pregnancy: fetomaternal hemodynamic effects induced in mild pre-eclampsia and threatened preterm labor.
      • Martínez-Abundis E.
      • González-Ortiz M.
      • Hernández-Salazar F.
      • Huerta-J-Lucas M.T.
      Sublingual isosorbide dinitrate in the acute control of hypertension in patients with severe preeclampsia.
      • Johal T.
      • Lees C.C.
      • Everett T.R.
      • Wilkinson I.B.
      The nitric oxide pathway and possible therapeutic options in pre-eclampsia.
      • Sharp A.
      • Cornforth C.
      • Jackson R.
      • et al.
      Maternal sildenafil for severe fetal growth restriction (STRIDER): a multicentre, randomised, placebo-controlled, double-blind trial.
      • Groom K.M.
      • McCowan L.M.
      • Mackay L.K.
      • et al.
      STRIDER NZAus: a multicentre randomised controlled trial of sildenafil therapy in early-onset fetal growth restriction.
      In animal models, the administration of a phosphodiesterase type 5 inhibitor (sildenafil) can result in reduced blood pressure, increased fetal weight, decreased uterine artery resistance, and improved angiogenic balance.
      • Ramesar S.V.
      • Mackraj I.
      • Gathiram P.
      • Moodley J.
      Sildenafil citrate decreases sFlt-1 and sEng in pregnant L-NAME treated Sprague-Dawley rats.
      ,
      • Gillis E.E.
      • Mooney J.N.
      • Garrett M.R.
      • Granger J.P.
      • Sasser J.M.
      Sildenafil treatment ameliorates the maternal syndrome of preeclampsia and rescues fetal growth in the Dahl salt-sensitive rat.
      ,
      • George E.M.
      • Palei A.C.
      • Dent E.A.
      • Granger J.P.
      Sildenafil attenuates placental ischemia-induced hypertension.
      However, clinical studies showed little to no improvement in women with PE.
      • Sharp A.
      • Cornforth C.
      • Jackson R.
      • et al.
      Maternal sildenafil for severe fetal growth restriction (STRIDER): a multicentre, randomised, placebo-controlled, double-blind trial.
      ,
      • Groom K.M.
      • McCowan L.M.
      • Mackay L.K.
      • et al.
      STRIDER NZAus: a multicentre randomised controlled trial of sildenafil therapy in early-onset fetal growth restriction.
      Figure thumbnail gr3
      Figure 4MAP in animal models of PE, with and without the administration of an ETA receptor antagonist
      Data are shown for studies in the RUPP,
      • Alexander B.T.
      • Rinewalt A.N.
      • Cockrell K.L.
      • Massey M.B.
      • Bennett W.A.
      • Granger J.P.
      Endothelin type A receptor blockade attenuates the hypertension in response to chronic reductions in uterine perfusion pressure.
      sFlt-1 infusion,
      • Murphy S.R.
      • LaMarca B.B.
      • Cockrell K.
      • Granger J.P.
      Role of endothelin in mediating soluble fms-like tyrosine kinase 1-induced hypertension in pregnant rats.
      AT1-AA infusion,
      • LaMarca B.
      • Parrish M.
      • Ray L.F.
      • et al.
      Hypertension in response to autoantibodies to the angiotensin II type I receptor (AT1-AA) in pregnant rats: role of endothelin-1.
      and TNF-α infusion
      • LaMarca B.B.D.
      • Cockrell K.
      • Sullivan E.
      • Bennett W.
      • Granger J.P.
      Role of endothelin in mediating tumor necrosis factor-induced hypertension in pregnant rats.
      models, suggesting that endothelial activation may be a common final pathway in the PE-related hypertension. Data are presented as mean+SEM. The asterisk symbol indicates P<.05.
      AT1-AA, angiotensin II type 1 receptor autoantibody; ETA, endothelin type A; MAP, mean arterial pressure; PE, preeclampsia; RUPP, reduced uterine perfusion pressure; SEM, standard error of the mean; sFlt-1, soluble fms-like tyrosine kinase-1; TNF-α, tumor necrosis factor-α.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.
      In addition to these studies to directly block culprit pathways in PE, a number of vitamins and drug have been tested in animal models, including vitamin D, vitamin B, and statins. In the RUPP model, vitamin D administration reduced blood pressure, ET-1, sFlt-1, and AT1-AA but did not improve fetal outcomes.
      • Faulkner J.L.
      • Cornelius D.C.
      • Amaral L.M.
      • et al.
      Vitamin D supplementation improves pathophysiology in a rat model of preeclampsia.
      • Darby M.M.
      • Wallace K.
      • Cornelius D.
      • et al.
      Vitamin D supplementation suppresses hypoxia-stimulated placental cytokine secretion, hypertension and CD4+ T cell stimulation in response to placental ischemia.
      • Tian X.
      • Ma S.
      • Wang Y.
      • et al.
      Effects of placental ischemia are attenuated by 1,25-dihydroxyvitamin D treatment and associated with reduced apoptosis and increased autophagy.
      In the L-NAME model, vitamin D reduced sFlt-1 and TNF-α.
      • Song J.
      • Li Y.
      • An R.
      Vitamin D restores angiogenic balance and decreases tumor necrosis factor-α in a rat model of pre-eclampsia.
      The administration of the cholesterol-lowering drug, pravastatin, has been shown to improve placental blood flow and weight and long-term cardiovascular outcomes in the C1q−/− mouse.
      • Garrett N.
      • Pombo J.
      • Umpierrez M.
      • Clark J.E.
      • Simmons M.
      • Girardi G.
      Pravastatin therapy during preeclampsia prevents long-term adverse health effects in mice.
      In the RUPP rat, pravastatin treatment results in reduced blood pressure, improved angiogenic balance, and reduced ROS.
      • Bauer A.J.
      • Banek C.T.
      • Needham K.
      • et al.
      Pravastatin attenuates hypertension, oxidative stress, and angiogenic imbalance in rat model of placental ischemia-induced hypertension.
      Although clinical studies have not shown comparable results, no adverse effects have been reported in women.
      • Palacios C.
      • Trak-Fellermeier M.A.
      • Martinez R.X.
      • et al.
      Regimens of vitamin D supplementation for women during pregnancy.
      • Ahmed A.
      • Williams D.J.
      • Cheed V.
      • et al.
      Pravastatin for early-onset pre-eclampsia: a randomised, blinded, placebo-controlled trial.
      • Costantine M.M.
      • Cleary K.
      • Hebert M.F.
      • et al.
      Safety and pharmacokinetics of pravastatin used for the prevention of preeclampsia in high-risk pregnant women: a pilot randomized controlled trial.
      These avenues continue to be researched.

      Conclusions

      PE is a complex, multiorgan disease associated with pregnancy. The discovery of pathophysiological processes involved in PE has resulted from the interplay between basic research involving animal models and clinical research in humans. A number of animal models have been developed to address the many pathways involved in PE (Figure 5). A major consideration for any model of PE is that the animal is manipulated, whether it be surgically, pharmacologically, or genetically, to express these features. Moreover, some of the animal models discussed earlier focus on a single characteristic or mediator in the development of PE. Although these preclinical models have been crucial in understanding the pathophysiological importance of individual factors, it is important to remember that PE is a multiorgan, multifaceted disease that first develops as a result of impaired spiral artery remodeling and placental development. Some of the models discussed earlier such as the ASB4 deletion model and the Dahl S rat could be useful in studying these very early stages of PE. Regardless of the mechanism, each of these animal models has been critical in understanding the following 2 phases of PE: (1) impaired extravillous trophoblast migration and invasion of the endometrium causing placenta ischemia and (2) the release of factors from the ischemic placenta into the maternal circulation leading to endothelial dysfunction and the clinical syndrome. Preclinical studies in animal models have been instrumental not only in understanding the pathophysiology of PE but also in the search for novel therapeutic options for the treatment of this disease.
      Figure thumbnail gr5
      Figure 5Pathways in the pathogenesis of PE that have been shown and studied in animal models
      AT1-AA, angiotensin II type 1 receptor autoantibody; ET, endothelin; FGR, fetal growth restriction; IL, interleukin; NF-κB; nuclear factor kappa-light-chain-enhancer of activated B cells; NO, nitric oxide; PlGF, placental-derived growth factor; PE, preeclampsia; ROS, reactive oxygen species; sEng, soluble endoglin; sFlt-1, soluble fms-like tyrosine kinase-1; Th, T helper cell; TNF-α, tumor necrosis factor-α; Tregs, regulatory T cells; VEGF, vascular endothelial growth factor.
      Bakrania. Animal models of preeclampsia. Am J Obstet Gynecol 2022.

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