Term labor in humans is associated with increased oxidative stress (OS) -induced senescence and damages to amnion epithelial cells (AECs). Senescent fetal cells release alarmin high-mobility group box 1 (HMGB1) and cell-free fetal telomere fragments (cffTF) which can be carried by exosomes to other uterine tissues to produce parturition-associated inflammatory changes. This study characterized AEC-derived exosomes under normal and OS conditions and their packaging of HMGB1 and cffTF. Primary AECs were treated with either standard media or oxidative stress-induced media (exposure to cigarette smoke extract for 48h). Senescence was determined, and exosomes were isolated and characterized. To colocalize HMGB1 and cffTF in amnion exosomes, immunofluorescent staining and in situ hybridization were performed, followed by confocal microscopy. Next generation sequencing (NGS) determined exosomal cffTF and other cell-free amnion cell DNA specificity. Regardless of condition, primary AECs produce exosomes with a classic size, shape, and markers. OS and senescence caused the translocation of HMGB1 and cffTF from AECs' nuclei to cytoplasm compared to untreated cells, which was inhibited by antioxidant N-acetyl cysteine (NAC). Linescans confirmed colocalization of HMGB1 and cffTF in exosomes were higher in the cytoplasm after CSE treatment compared to untreated AECs. NGS determined that besides cffTF, AEC exosomes also carry genomic and mitochondrial DNA, regardless of growth conditions. Sterile inflammatory markers HMGB1 and cffTF from senescent fetal cells are packaged inside exosomes. We postulate that this exosomal cargo can act as a fetal signal at term and can cause labor-associated changes in neighboring tissues.
Keywords: Amniochorion; DAMPs; Fetal signals; Inflammation; Microvesicles; Parturition.
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