Innate immune sensor NOD2 promotes cartilage degradation and osteoarthritis progression by stabilizing TRAF6 in chondrocytes.

Inflammation driven by the innate immune response plays a crucial role in osteoarthritis (OA) pathogenesis, yet the underlying mechanisms remain incompletely understood. Moreover, current antiinflammatory therapies primarily offer symptomatic relief without altering disease progression. Nucleotide-binding oligomerization domain 2 (NOD2) is an intracellular pattern recognition receptor that detects a broad range of microbial and damage-associated stimuli and has been implicated in several inflammatory conditions. In this study, we investigated the role of NOD2 in OA-associated inflammation and cartilage degradation. Elevated NOD2 expression was observed in both human and mouse osteoarthritic cartilage. Conditional KO of Nod2 in chondrocytes suppressed inflammation-induced catabolic responses in vitro and protected against cartilage degradation in mouse OA models. Mechanistically, we identified tumor necrosis factor receptor-associated factor 6 (TRAF6) as a key downstream mediator through which NOD2 promotes chondrocyte catabolism. Furthermore, we showed that pharmacological inhibition of NOD2 using 2 independent small-molecule inhibitors significantly attenuated OA progression in vivo. Collectively, these findings establish NOD2 as a critical regulator of OA-associated inflammation and cartilage degradation, and they highlight its potential as a therapeutic target for disease-modifying OA treatment.