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36: Toll like receptor 4 (TLR-4) is essential for fetal neuronal injury in inflammation-induced preterm birth

      Objective

      Inflammation-induced preterm birth (IIPB) is a major cause of adverse neurological outcome (ANO). ANO has been linked to white matter and glial damage. Recently, we have demonstrated that IIPB results specifically in neuronal injury. The activation of TLR-4 is implicated in inflammation-induced brain injury in both neonatal and adult animal models but has not been investigated in fetal injury from preterm birth. This study investigates whether TLR-4 is essential for fetal neuronal injury in IIPB.

      Study Design

      TLR-4 mutant mice, C3H/HEJ, were mated and HEJ embryos transferred to pseudopregnant CD-1 mice. OUJ and CD-1 embryos were used as controls. CD-1 dams pregnant with CD, OUJ or HEJ embryos were randomized to intrauterine LPS or saline using our mouse model of preterm birth on E15. The presence of LPS in amniotic fluid and maternal serum was assessed with LAL assay. Neuronal morphology from exposed and non-exposed fetal brains from HEJ and controls was investigated using cortical culture technique with confocal microscopy at division day 3 (DD3). TLR4, GFAP, and PLP expression in wild type neuronal and glial cultures was assessed by QPCR.

      Results

      LPS was present in amniotic fluid and maternal serum within 3 hrs after treatment. QPCR revealed that TLR-4 was present on astrocytes, but not in neurons in wild type on E15. Wild type fetuses exposed to in vivo LPS demonstrated significant disruptions in neuronal morphology with decreased aggregation and number of dendritic processes. In contrast, cortical cultures from LPS exposed HEJ brains did not demonstrate any of these morphological differences and had similar number of dendritic processes on DD3 (P>0.05) as saline exposed CD and HEJ fetuses.

      Conclusion

      Activation of TLR-4 is a critical mechanism by which neuronal injury occurs in preterm births. Neuronal injury in II PTB appears to be secondary to LPS activating TLR-4 on astrocytes and subsequent astrocyte-neuronal interaction. Targeting TLR-4 may serve as a potential therapeutic option to prevent neuronal injury in the setting of preterm birth.