"Whole genome bisulfite sequencing of serum extracellular vesicle DNA identifies alterations in mitochondrial DNA methylation in early onset preeclampsia".

Early-onset preeclampsia (EOPE) is a serious pregnancy complication. Understanding its underlying mechanisms could lead to improved diagnosis and management. Genome-wide DNA methylation changes in circulating Extracellular Vesicle DNA (EV-DNA) from women with EOPE could serve as a non-invasive approach to identify key regions and genes that could serve as biomarkers to understand placental pathophysiology. In this case-control study, serum extracellular vesicles were isolated from 3rd trimester pregnant women and characterized using Nanoparticle Tracking Analysis and Transmission Electron Microscopy. The circulating EV-DNA samples were subjected to Whole Genome Bisulfite Sequencing analysis (WGBS) to identify differentially methylated CpGs (DMCs) sites in EOPE cases compared to control. A total of 154 DMCs were identified in EV-DNA, of which 131 were hypomethylated and 23 were hypermethylated. Majority of DMCs were of mitochondrial origin. Previously, it has been reported that oxidative stress, decreased trophoblast differentiation, and invasion are linked to preeclampsia pathogenesis and are related to mitochondrial dysfunction. Therefore, DMCs of the mitochondrial genes like MT-ND1, MT-ND4, MT-CO2, MT-CO3, and MT-RNR1 were selected for validation and showed a similar trend by pyrosequencing. The expression of these genes were also altered in circulating extracellular vesicles. Our study shows changes in the DNA methylation patterns of circulating EV-DNA in women with EOPE. These changes, especially in mitochondrial genes, could lead to mitochondrial dysfunction and contribute EOPE pathogenesis. These findings suggest that these alterations could be explored as non-invasive approach to better understand placental health and improve disease management.