Tacrolimus attenuates BCL-2/BAX-mediated chondrocyte apoptosis and cartilage matrix degradation in experimental osteoarthritis

Osteoarthritis is a progressive whole-joint disease characterized by cartilage matrix degradation, synovial inflammation and impaired chondrocyte survival. Current pharmacological treatments mainly relieve symptoms and do not reliably prevent structural progression. Here, we investigated whether tacrolimus, a clinically used immunomodulatory drug, could be repurposed as an intra-articular therapy for osteoarthritis. Network pharmacology identified multiple osteoarthritis-related tacrolimus targets associated with inflammation, apoptosis and metabolic regulation. In cultured chondrocytes, tacrolimus showed a safe working range at low micromolar concentrations and promoted matrix-associated gene expression, increasing COL2A1 and ACAN while reducing MMP13. Under IL-1β-induced inflammatory stress, tacrolimus reduced reactive oxygen species production, restored the BCL-2/BAX expression balance and attenuated apoptosis-associated molecular changes. Mechanistically, molecular docking suggested a potential interaction between tacrolimus and BCL-2, and BCL-2 knockdown partially reversed the effects of tacrolimus on BAX, SOX9, collagen II (COL-II) and MMP13, supporting a functional role for BCL-2-dependent survival signaling. Tacrolimus also modulated macrophage polarization by suppressing M1-associated inflammatory markers and enhancing M2-associated markers. In the ACLT+pMMx-induced OA model, intra-articular tacrolimus preserved proteoglycan-rich cartilage matrix, maintained COL-II expression and reduced synovitis, with histological protection greater than dexamethasone and approaching the sham condition. These findings support tacrolimus as a potential steroid-sparing, cartilage-protective candidate for osteoarthritis, acting primarily through regulation of chondrocyte survival and inflammatory joint microenvironments.