NAT10-mediated ac4C modification of KDM1B drives osteoarthritis progression through epigenetic suppression of SOX9.

Histone methylation acts as a crucial regulator of diverse pathophysiological processes in humans. However, the involvement of histone methylation modification enzymes in osteoarthritis (OA) remains poorly characterized. Here, we delineated lysine demethylase 1B (KDM1B) as a nodal epigenetic effector driving OA pathobiology through an integrated strategy that combined data mining, bioinformatics analysis, and experimental validation. Gain-of-function studies revealed that chondrocyte - specific KDM1B overexpression amplified IL-1β-induced chondrocyte injury primarily through the inhibition of SRY-box transcription factor 9 (SOX9). Conversely, KDM1B knockdown inhibited IL-1β-induced chondrocyte damage in vitro and significantly alleviated OA progression in vivo by upregulating SOX9. Mechanistically, NAT10-catalyzed ac4C epitranscriptomic editing to KDM1B mRNA stabilization, leading to its overexpression in osteoarthritic chondrocytes. Elevated KDM1B subsequently binds to the promoter region of the SOX9 and catalyzes the demethylation of H3K4me2 to suppress SOX9 expression in osteoarthritic chondrocytes. Furthermore, our data also demonstrated that chondrocyte-specific NAT10 knockdown attenuated IL-1β-induced chondrocyte injury by modulating the KDM1B/SOX9 axis. Collectively, our findings unveil a novel NAT10/KDM1B/SOX9 regulatory cascade in OA pathogenesis, highlighting the potential of targeting epigenetic regulators to restore chondrocyte function and mitigate OA progression.