Inhibiting EZH2 Alleviates Osteoarthritis and Pain in an Experimental Murine Model Through Modulating Synovial and Macrophage Inflammation, Axon Guidance, and Osteoclastogenesis

Enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, has gained attention as a promising therapeutic target in osteoarthritis (OA) due to its central role in modulating inflammation, catabolism, and hypertrophy within chondrocytes. Previous studies have further demonstrated that EZH2 inhibition can slow OA progression in surgically induced mouse models, highlighting its potential in reducing joint degradation. However, the precise mechanisms by which EZH2 influences other key cell types in OA pathology remain poorly understood. In this study, we aimed to evaluate the effects of EZH2 inhibition in an alternative OA model and investigate its broader impact on cellular and molecular pathways across various tissues involved in OA progression and joint pain. OA was induced in mice via intra-articular injection of monosodium iodoacetate (MIA), with disease progression evaluated by histological and behavioral assessments. In parallel, human synoviocytes and bone marrow-derived cells were isolated from OA patients. Synoviocytes were stimulated with interleukin-1β (IL-1β) in the presence or absence of the EZH2 inhibitor EPZ-6438 (Tazemetostat), and ChIP-Seq and proteomic analyses were conducted to identify genomic and proteomic targets of EZH2. Additionally, the effects of EZH2 inhibition on M1 macrophage polarization and osteoclast differentiation were analyzed. Results revealed that EZH2 inhibition attenuated both OA progression and joint pain in the MIA-induced mouse model. IL-1β stimulation significantly upregulated EZH2 expression in synoviocytes, and treatment with the EZH2 inhibitor reduced the expression of genes linked to inflammation, pain, and catabolism while promoting autophagy. Proteomic analysis highlighted significant alterations in pathways related to IL-1β signaling, matrix metalloproteinase (MMP) activation, and autophagy, as well as changes in proteins associated with metabolic regulation and axon guidance. Importantly, EZH2 inhibition decreased M1 macrophage polarization and osteoclast formation, cellular processes that contribute to OA pain and inflammation. In conclusion, this study underscores the pivotal role of the histone methyltransferase EZH2 in the pathophysiology of osteoarthritis and associated joint pain. Our findings reveal that EZH2 inhibition not only attenuates inflammation in synovial cells and macrophages but also modulates axon guidance and osteoclastogenesis, both critical in OA progression and pain. These insights position EZH2 inhibition as a promising, multi-targeted therapeutic approach for addressing the complex cellular interactions underlying osteoarthritis, offering new hope for effective treatment strategies in this debilitating condition.