Inhibition of ezh2 slows the progression of osteoarthritis by reducing inflammation, catabolism and hypertrophy in chondrocytes, and improves motor functions of oa mice

Purpose: Previous studies have shown that epigenetics play a major role in joint cells and during OA development. For instance, the expression of Enhancer of Zest Homolog 2 (EZH2), a histone methyltransferase which adds a methyl group (-CH3) on the lysine 27 of the histone 3 (H3K27), is upregulated in cartilage from OA patients, and its inhibition reduces chondrocyte hypertrophy, suggesting that EZH2 inhibition may reduce OA progression. However, a recent study showed that, at contrary, conditional knockout of EZH2 aggravates osteoarthritis development. Thus, the objective of this study was to determine whether epigenetic therapy targeting the histone methyltransferase EZH2 could reduce OA progression. The in vitro role of EZH2 in human chondrocytes and the in vivo effects of its inhibition on OA progression (cartilage degradation and functional disability) were investigated. Methods: In vitro, gain and loss of EZH2 function were performed in human articular OA chondrocytes stimulated with IL-1β (inflammation model) or TGFb1 (hypertrophy model). The expression of collagen type X and the Wnt pathway were analyzed to assess hypertrophy. The expression of NO, PGE2, IL-6, NGF and MMPs was assessed by RT-PCR and ELISA for evaluate inflammation, pain and catabolism. Cultures of cartilage explants were also performed to estimate catabolism. In vivo, the effects of EZH2 inhibition were investigated on medial meniscectomy (MMX) OA mouse model. The tissue alterations were assayed by histology and the functional disabilities of the mice by actimetry and running wheel. Results: In vitro, EZH2 inhibition by a pharmacological inhibitor, EPZ-6438, reduced chondrocyte hypertrophy. In addition, EPZ-6428 and DZNep (another inhibitor of histone methylation) reduced IL-1β effects. At contrary, EZH2 overexpression exacerbated the action of this proinflammatory cytokine increasing the expression of genes involved in inflammation, pain (NO, PGE2, IL6, NGF) and catabolism (MMPs) in chondrocytes. Ex vivo, EZH2 inhibition decreased IL-1β-induced degradation of cartilage. In vivo, intra-articular injections of the EZH2 inhibitor reduced cartilage degradation and improved motor functions of OA mice. Conclusions: This study demonstrates that the pharmacological inhibition of the histone methyl-transferase EZH2 slows the progression of osteoarthritis and improves motor functions in an experimental OA model, suggesting that EZH2 could be an effective target for the treatment of OA by reducing catabolism, hypertrophy, inflammation and pain.