Environmental Endocrine Disruptors Activate CBX2 to Disrupt Cholesterol Homeostasis in PCOS

Polycystic ovary syndrome (PCOS) is a common endocrine disorder influenced by genetic and environmental factors, yet the molecular mechanisms linking endocrine-disrupting chemicals (EDCs) to ovarian dysfunction remain unclear. Here, we establish a letrozole-induced PCOS-like rat model and integrate bulk RNA-seq, single-cell RNA-seq of human granulosa cells (GCs), and functional validation to identify CBX2 as a critical epigenetic regulator connecting EDC exposure to PCOS pathogenesis. Transcriptomic profiling revealed dysregulated cell cycle progression, disrupted cholesterol homeostasis, and chronic inflammation in PCOS ovaries. Of these, cholesterol biosynthesis genes (e.g., Ebp, Dhcr7) were broadly suppressed, while efflux (Abca1) and metabolism-related (Cyp27a1) genes showed opposing alterations. Cross-species analysis identified CBX2 as consistently upregulated in both rat and human PCOS GCs, where it strongly correlated with accelerated cell proliferation and impaired cholesterol homeostasis. Mechanistically, exposure to EDCs (BPA and DDT) significantly induced CBX2 expression in human GCs. ChIP-seq analysis demonstrated that CBX2 directly binds to and represses genes from cholesterol-homeostasis-associated transcriptional networks-including CSRNP1, DDIT3, and FOSL1-through H3K27me3-mediated epigenetic silencing. Functional validation showed that CBX2 knockdown suppressed GCs proliferation, reduced lipid droplet accumulation while restoring normal cell cycle distribution. Single-cell RNA-seq confirmed elevated CBX2 activity specifically in PCOS GCs, particularly during G2/M phase, where it exhibited the strongest negative correlation with cholesterol homeostasis signatures (rs = -0.23). These findings reveal a novel EDC-CBX2-H3K27me3 epigenetic axis that decouples GC proliferation from metabolic support functions, establishing CBX2 as both a molecular biomarker and potential therapeutic target for environment-associated PCOS.