Corticosteroid-induced alterations in cytoskeletal organization and mechanosensing of osteoarthritic synoviocytes.

BACKGROUND: Fibroblast-like synoviocytes (FLSs) are key effector cells in osteoarthritis (OA), contributing to joint degeneration through inflammatory and mechanobiological mechanisms. Triamcinolone acetonide (TA) is widely used as an intra-articular therapy for OA; however, its effects on synoviocyte mechanobiology remain poorly defined. This study investigated TA-induced changes in FLS viability, cytoskeletal organization, biomechanical properties, mechanically evoked Ca²⁺ signaling, and mechanotransduction-related gene expression. METHODS: Primary FLSs isolated from the synovial tissue of patients with osteoarthritis (N = 3) were treated with increasing concentrations of TA. Cell morphology and viability were assessed by cytooskelton laelling andflow cytometry. Cellular stiffness was measured by atomic force microscopy (AFM). Mechanically evoked Ca²⁺ responses were assessed by combining AFM-based single-cell stimulation with live-cell calcium imaging. Mechanotransduction-associated transcripts were quantified by qPCR, while PIEZO1, PIEZO2 and TRPV4 protein expression was evaluated by immunolabelling and ELISA. RESULTS: TA induced concentration-dependent alterations in FLS morphology and viability, with marked cytotoxicity above 0.35 mM. At sub-cytotoxic levels, TA significantly increased cellular stiffness at 0.2 mM (p = 0.0219), while 0.35 mM showed a non-significant increase. Mechanically evoked Ca²⁺ signaling was enhanced following TA treatment, particularly at lower concentrations, with notable inter-donor variability. Immunolabelling revealed PIEZO1, PIEZO2 and TRPV4 distribution across all conditions, while quantitative ELISA showed increased protein expression following TA exposure despite only modest changes in the transcript levels. CONCLUSIONS: TA exerts concentration-dependent effects on OA-derived FLSs, modulating cytoskeletal organization, biomechanical properties, mechanically evoked Ca²⁺ responses and mechanosensitive ion-channel regulation. These findings suggest that TA modulates FLSs mechanobiology beyond its established anti-inflammatory effects.