Human placental proteomics and exon variant studies link AAT/SERPINA1 with spontaneous preterm birth

Background Preterm birth is defined as live birth before 37 completed weeks of pregnancy, and it is a major problem worldwide. The molecular mechanisms that lead to onset of spontaneous preterm birth are incompletely understood. Prediction and evaluation of the risk of preterm birth is challenging as there is a lack of accurate biomarkers. In this study, our aim was to identify placental proteins that associate with spontaneous preterm birth. Methods We analyzed the proteomes from placentas to identify proteins that associate with both gestational age and spontaneous labor. Next, rare and potentially damaging gene variants of the identified protein candidates were sought for from our whole exome sequencing data. Further experiments we performed on placental samples and placenta-associated cells to explore the location and function of the spontaneous preterm labor-associated proteins in placentas. Results Exome sequencing data revealed rare damaging variants in SERPINA1 in families with recurrent spontaneous preterm deliveries. Protein and mRNA levels of alpha-1 antitrypsin/SERPINA1 from the maternal side of the placenta were downregulated in spontaneous preterm births. Alpha-1 antitrypsin was expressed by villous trophoblasts in the placenta, and immunoelectron microscopy showed localization in decidual fibrinoid deposits in association with specific extracellular proteins. siRNA knockdown in trophoblast-derived HTR8/SVneo cells revealed that SERPINA1 had a marked effect on regulation of the actin cytoskeleton pathway, Slit-Robo signaling, and extracellular matrix organization. Conclusions Alpha-1 antitrypsin is a protease inhibitor. We propose that loss of the protease inhibition effects of alpha-1 antitrypsin renders structures critical to maintaining pregnancy susceptible to proteases and inflammatory activation. This may lead to spontaneous premature birth.

Automated summary

This study aimed to identify placental proteins associated with spontaneous preterm birth. We found rare damaging variants in the SERPINA1 gene in families with recurrent spontaneous preterm deliveries. The protein and mRNA levels of alpha-1 antitrypsin/SERPINA1 were downregulated in spontaneous preterm births, and it played a role in regulating actin cytoskeleton pathway, Slit-Robo signaling, and extracellular matrix organization. Loss of the protease inhibition effects of alpha-1 antitrypsin may render structures critical to maintaining pregnancy susceptible to proteases and inflammatory activation, leading to spontaneous premature birth.