15: Progesterone inhibits basal apoptosis in fetal membranes by altering expression of both pro- and anti-apoptotic proteins


      Progesterone supplementation prevents preterm birth (PTB) in some high-risk women, but its mechanism of action is unknown. One third of PTB is associated with preterm premature rupture of membranes (PPROM). We have previously shown that progesterone inhibits basal and TNF α-induced apoptosis in fetal membranes (Luo et al. Reprod Sci 2010;17:532). This study investigates the molecular mechanisms responsible for this progesterone-mediated inhibition of apoptosis in the fetal membranes.

      Study Design

      Fetal membranes (amniochorion) were collected at elective cesarean at term (no labor, no infection [n=6]), washed, cultured in DMEM/Ham F-12 medium with/without progesterone (500 ng/mL) for 24h and Opti-MEM medium for 48h, harvested and homogenized. Apoptosis was determined by evaluating caspase-3 activity using Caspase-Glo assay (Promega).Activity in relative light units was measured on a luminometer and corrected for total protein. Data was analyzed by ANOVA. The effect of progesterone on levels of intracellular pro-apoptotic (BAX, BID) and anti-apoptotic (XIAP, FLIP, Bcl-2) proteins were measured by western blot.


      In keeping with our prior observations, results of caspase-3 activity assay confirmed that progesterone significantly inhibits basal apoptosis in term fetal membranes. XIAP and Bcl-2 levels increased significantly and BID levels decreased significantly in response to progesterone stimulation (p<0.05 for all); no change was seen in BAX or FLIP expression.


      Progesterone-mediated inhibition of basal apoptosis in term fetal membranes is mediated through the upregulation of the anti-apoptotic proteins, XIAP and Bcl-2, and suppression of the pro-apoptotic protein, BID. These data explain at least in part the molecular mechanisms by which progesterone supplementation prevents PPROM and PTB in some high-risk women, and have have important implications also for the onset of normal labor at term.