<p>Osteoarthritis (OA) is a degenerative joint disorder with the destruction of the joint’s structural and functional which affects the entire joint. An important feature of OA is the progressive degeneration of articular cartilage due to an imbalance between extracellular matrix synthesis and degradation. While the molecular basis of OA remains unclear, microRNAs (miRNAs) have been recognized as key factors in controlling cartilage homeostasis and inflammation. Of these, miR-221 and miR-222 are implicated in inflammatory and degenerative disease, but their exact role in OA has yet to be determined. This study aims to assess the impact of miR-221/222 cluster knockout (KO) on mouse OA models and to explore its underlying mech</p><p>anisms. OA was induced in miR-221/222 KO mice utilizing the destabilization of the medial meniscus (DMM) model. Joint pathology was examined by X-ray, histological scoring, immunofluorescence, and biochemical assays. In addition, in vitro studies were performed using IL-1β-treated chondrocytes. Gain-of-function experiments were performed using miR-221/222 agomir. OA tissues of mice and mouse primary chondrocytes treated with IL-1β showed a decrease in miR-221 and miR-222 expression as compared with the shamed mice. However, miR-221/222 KO mice exhibited significant osteophyte formation and cartilage degradation, with a marked increase in collagen I, MMP-13 levels, and a significant decrease in COL2A1 levels. In vitro, miR-221/222 KO led to increased inflammatory mediators like IL-6 and TNF-α, which promoted chondrocyte apoptosis and activated the MAPK signaling pathway, thereby exacerbating OA progression. Conversely, treatment with miR-221/222 agomir attenuated OA progression in vivo. These findings suggest that loss of the miR-221 cluster contributes to OA progression by promoting inflammation, apoptosis, and matrix degradation, partly through MAPK signaling. Restoring miR-221/222 may hold therapeutic potential, but human studies are needed for validation.</p>