Epigenetics in osteoarthritis: emerging mechanistic and translational landscape.

Epigenetic mechanisms are implicated in osteoarthritis (OA) as they regulate the expression of several key genes involved in OA disease progression. This mini-review highlights major epigenetic studies in OA from the past 25 years, focusing on mechanistic and therapeutic perspectives. We discuss how DNA methylation, histone modifications, and non-coding RNAs (ncRNAs) impact OA, highlighting preclinical studies targeting epigenetic mechanisms in mouse models. Indeed, existing studies demonstrate that DNA methylation regulates the expression of OA-related genes through DNA methyltransferases, and targeting their activity has shown promise in restoring cartilage homeostasis. EZH2 and DOT1L are key methyltransferases involved in histone methylation with opposing roles in OA: high EZH2 promotes disease progression and is a potential therapeutic target, whereas DOT1L exerts protective effects, partly by suppressing Wnt signaling. Additionally, targeting enzymes that catalyze histone acetylation (PCAF, BRD4) and deacetylation (HDAC1/2) has demonstrated therapeutic potential in preclinical OA models. ncRNAs-including miRNAs, circRNAs, and lncRNAs-regulate gene expression in OA tissues at multiple levels. Several miRNAs (e.g. miR-17, miR-27b-3p) influence cartilage homeostasis and OA pathogenesis, while circRNAs (e.g. circPDE4B) and lncRNAs (e.g. ELDR) have emerged as important disease regulators, offering new therapeutic avenues. Despite significant advancements in OA-related epigenetic mechanisms, clinical translation remains challenging due to the complexity of epigenetic regulation, patient heterogeneity, and limited success of preclinical studies. Importantly, epigenetic alterations are often context-specific, necessitating nuanced interpretation to accurately discern their role in OA. Future research should prioritize identifying specific epigenetic markers linked to clinical outcomes (e.g. structural changes, functional impairment, pain) and developing more selective and potent epigenetic modulators for therapeutic use.