Lactylome-based investigation of osteoarthritic subchondral bone reveals cell-specific differential expression of histone H4K12 lactylation: an experimental study

BACKGROUND: Osteoarthritis (OA) is a progressive joint disorder in which subchondral bone remodeling plays a central role in its pathogenesis. We employed high-resolution proteomic and lactylome analyses to explore metabolic and epigenetic alterations in OA subchondral bone, focusing on lysine lactylation as a novel post-translational modification. METHODS AND RESULTS: A total of 668 lactylated proteins were identified, with 48 lactylation sites on 45 proteins showing significantly increased modification levels and 55 sites on 39 proteins showing decreased levels in OA samples compared to controls. These differentially lactylated proteins were primarily associated with extracellular matrix remodeling and metabolic regulation. Notably, lactylation of histone H4 at lysine 12 (H4K12la) was markedly elevated in OA subchondral bone and correlated with abnormal bone remodeling. Cell-specific analysis revealed increased H4K12la levels in osteoblasts but reduced levels in osteoclasts, despite elevated lactate production by osteoclasts. Exogenous sodium lactate increased H4K12la levels and osteogenic markers, effects that were attenuated by the p300 inhibitor (used to inhibit lactylation) and the MCT1 inhibitor (used to block lactate uptake). To further explore the role of lactate transport in OA, we used Syrosingopine, a dual MCT1/MCT4 inhibitor, to inhibit lactate efflux and uptake. Syrosingopine significantly reduced lactate transport in vitro and alleviated subchondral bone sclerosis in the anterior cruciate ligament transection-induced OA rat model, further supporting the involvement of lactate metabolism in the pathogenesis of OA. CONCLUSIONS: This study delineates a lactate-epigenetic axis in which osteoclast-derived lactate, transported via MCT1/MCT4, enters osteoblasts and activates osteogenic transcriptional programs through H4K12la, driving osteogenic activation and subchondral sclerosis. These findings provide novel insights into the molecular basis of subchondral bone remodeling in OA and suggest potential therapeutic targets involving lactate metabolism, lactate transport, and H4K12la-mediated epigenetic regulation to modulate OA-related subchondral bone remodeling.