Decoding the amniotic membrane transcriptome during equine ascending placentitis.

Despite its critical role in protecting the fetus, the amniotic membrane remains poorly understood in the context of disease response. The equine amniotic membrane is an important physical barrier to the amniotic compartment, and there is evidence that it may contribute to surfactant synthesis. Surfactants are essential for normal fetal lung development, and disruptions in its availability may be linked to future neonatal complications. Therefore, understanding the molecular changes that occur in fetal-maternal tissues during placentitis would clarify how this condition leads to abortion, preterm delivery, and stillbirth, and identify new strategies to manage the adverse outcomes. Thus, we used RNA sequencing, bioinformatic methods, and immunohistochemistry to characterize the equine amniotic membrane gene expression during experimentally induced ascending placentitis (placentitis group, n = 6) compared to gestationally matched control groups (control group, n = 6) at 288 days of gestation. We identified 288 differentially expressed genes (DEG) in the placentitis group compared to the control group. Placentitis was associated with the upregulation of toll-like receptors (TLR4), prostaglandin synthesis (PTGS2 and PTGES), apoptosis (MMP9 and CASP3), and hypoxia-associated genes (SOD2, BNIP3, and HMOX1). Our RNA sequencing results were supported by the visual identification of two of those proteins (TLR4 and PTGS2) in the immunohistochemistry analysis. Functional annotation revealed significant enrichment between the DEGs and the toll receptor signaling pathway, which may be a key factor negatively affecting placental functions. In conclusion, our study revealed that the amniotic membrane is not only a physical barrier but also plays an active role in immune response during ascending placentitis.