Investigating the role of placental microbiome in the pathogenesis of early- and late-onset pre-eclampsia.

Abstract

Pre-eclampsia (PE) is a multifactorial pregnancy disorder characterised by new-onset hypertension and proteinuria, often accompanied by end-organ damage and foetal growth restriction. The removal of proteinuria from the diagnostic criteria has further complicated clinical differentiation. Despite extensive research, the precise pathophysiology of PE remains unclear, limiting effective diagnostic and therapeutic strategies. Recent advances suggest that the placental microbiome plays a crucial role in pregnancy outcomes, influencing immune modulation, angiogenesis, and systemic maternal endothelial function. This study explores the potential contributions of the placental microbiome in PE pathogenesis, focusing on microbial profiles, inflammatory mediators, immune response, and epigenetic influences. Thirty age-matched normotensive and early-onset as well as age-matched normotensive and late-onset pre-eclamptic women were recruited. After informed consent was obtained, blood samples were collected through venipuncture, while the placental tissues were obtained at the end of the pregnancy through cesarean section with sterile and standardised clinical procedures. DNA was extracted, and microbiome analysis was conducted using targeted 16S rRNA gene sequencing and shotgun metagenomic sequencing (NGS). The reads were analysed using bioinformatics. In addition, serum was obtained from blood samples, and RNA was extracted. ELISA and qPCR were used to determine histone deacetylase-2 (HDAC-2) and acetate levels, and human leucocyte antigen-DRA (HLADRA) levels, respectively. Findings from 16S analysis revealed low biomass, classified as Actinobacteria, Firmicutes, Bacteroidetes, and Proteobacteria, with Proteobacteria dominated by the classes Pseudomonadales and Gammaproteobacteria, and smaller amounts of Actinobacteria and Bacteroidetes. NGS revealed low biomass, classified as Cutibacterium acnes, Staphylococcus epidermidis, and Bradyrhizobium species. Further analysis found no significant difference in bacterial species between placental samples from women with early- or late-onset pre-eclamptic women and age-matched normotensive controls. Similarly, there was no significant difference in bacterial species between placental samples from EOPE and LOPE. Additionally, there were significant differences in HDAC-2 and acetate levels between the EOPE and NORM groups. Similarly, HLA-DRA levels were significantly higher in EOPE than in the NORM group. The study therefore demonstrates a low number of reads, which might further indicate that the placental samples had very low levels of bacteria, and there is no correlation between placental samples from normotensive individuals and those with early- or late-onset PE. The data also highlight epigenetic dysregulation, immune activation, and metabolic alterations associated with PE, particularly in EOPE cases. The findings provide preliminary evidence supporting the role of placental epigenetics, microbial metabolites, and immune dysregulation in PE pathophysiology. Further large-scale approaches are warranted to determine whether HDAC2, HLA-DRA, and acetate could serve as potential diagnostic biomarkers or therapeutic targets for PE management.