Articular chondrocytes isolated from the knee and ankle joints of human tissue donors demonstrate similar redox-regulated MAP kinase and Akt signaling

Objective: To compare key intracellular redox-regulated signaling pathways in chondrocytes derived from knee joint femoral cartilage and ankle joint talar cartilage in order to determine if differences exist that might contribute to the lower prevalence of ankle osteoarthritis (OA). Methods: Femoral and talar chondrocytes were treated with H ₂ O ₂ generators (menadione or 2-3-dimethoxy-1,4-napthoquinone (DMNQ), fragments of fibronectin (FN-f)) to stimulate MAP kinase signaling (MAPK), or with IGF-1 to stimulate the Akt signaling pathway. Hyperoxidation of the peroxiredoxins, used as a measure of redox status, and phosphorylation of proteins pertinent to MAPK (p38, ERK, JNK, c-Jun) and Akt (Akt, PRAS40) signaling cascades were detected by immunoblotting. Results: Treatment of femoral and talar chondrocytes with menadione, DMNQ or FN-f led to a time dependent increase in extracellular-regulated kinase (ERK) and p38 phosphorylation. DMNQ and FN-f stimulation enhanced phosphorylation of JNK and its downstream substrate, c-Jun. Menadione treatment did not stimulate JNK activity but hyperoxidized the peroxiredoxins and inhibited IGF-1-induced Akt activation. In all experiments, chondrocytes derived from the femur and talar joints displayed comparable MAP kinase responses after treatment with various catabolic stimuli, as well as similar Akt signaling responses after IGF-1 treatment. Conclusions: MAP kinase and Akt signaling in response to factors that modulate the intracellular redox status were similar in chondrocytes from knee and ankle joints suggesting that redox signaling differences do not explain differences in OA prevalence. Talar chondrocytes, when isolated from their native matrix, can be used to examine redox-regulated cell signaling events relevant to OA in either joint.