Vitamin D Modulates PAR-4 Expression in an in Vitro Model of Osteoarthritis

Abstract Osteoarthritis (OA) encompasses degeneration of articular cartilage, subchondral bone erosions and sclerosis. Chondrocyte apoptosis and an oxygen-deprived microenvironment are essential factors in OA pathogenesis. PAR-4 (Prostate apoptosis response-4) is a pro-apoptotic protein implicated in many pathologies as well as in chondrocyte cell death mechanism. Vitamin D supplementation has been identified as a therapeutic tool for a variety of inflammatory pathologies. In the present manuscript, we investigated whether first, PAR-4 expression is influenced by chondrocytes in a model of OA, in vitro, and second, whether vitamin D modulates PAR-4 expression in the same model. To test our hypothesis, we used the primary culture of murine chondrocytes isolated from the femoral and tibial condyles of wistar rats. The expression of the pro-inflammatory effect interleukin IL-1β was evaluated in the presence and absence of vitamin D. Western blot and immunofluorescence analysis confirmed protein expression. In the normoxia condition, the chondrocytes expressed PAR-4 in the cell nucleus, and in the hypoxic condition, PAR-4 was expressed in the cell cytoplasm. We disclosed that the treatment with Vitamin D decreased PAR-4 (p= 0.0137) and caspase-3 (p= 0.0007) expression. Thus, the results suggested that PAR-4 and caspase-3 proteins could be potential targets for OA.However, we believe that research is needed to identify the mechanisms implicated in the regulation of PAR-4 in OA.