1,25-dihydroxyvitamin D3 Activates MMP13 Gene Expression in Chondrocytes through p38 MARK Pathway

Osteoarthritis (OA) is the most prevalent degenerative joint disease. The highly regulated balance of matrix synthesis and degradation is disrupted in OA, leading to progressive breakdown of articular cartilage. The molecular events and pathways involved in chondrocyte disfunction of cartilage in OA are not fully understood. It is known that 1,25-dihydroxyvitamin D-3 (1,25-(OH)(2)D-3) is synthesized by macrophages derived from synovial fluid of patients with inflammatory arthritis. Vitmain D receptor is expressed in chondrocytes within osteoarthritic cartilage, suggesting a contributory role of 1,25-(OH)(2)D-3 in the aberrant behavior of chondrocytes in OA. However, the physiological function of 1,25-(OH)(2)D-3 on chondrocytes in OA remains obscure. Effect of 1,25-(OH)(2)D-3 on gene expression in chondrocytes was investigated in this study. We found that 1,25-(OH)(2)D-3 activated MMP13 expression in a dose-dependent and time-dependent manner, a major enzyme that targets cartilage for degradation. Interestingly, a specific mitogen-activated protein kinase p38 inhibitor SB203580, but not JNK kinase inhibitor SP600125, abrogated 1,25-(OH)(2)D-3 activation of MMP13 expression. 1,25-(OH)(2)D-3-induced increase in MMP13 protein level was in parallel with the phosphorylation of p38 in chondrocytes. To further address the effect of 1,25-(OH)(2)D-3 on MMP13 expression, transfection assays were used to show that 1,25-(OH)(2)D-3 activated the MMP13 promoter reporter expression. MMP13 is known to target type II collagen and aggrecan for degradation, two major components of cartilage matrix. We observed that the treatment of 1,25-(OH)(2)D-3 in chondrocytes results in downregulation of both type II collagen and aggrecan while MMP13 was upregulated. Taken together, we provide the first evidence to demonstrate that 1,25-(OH)(2)D-3 activates MMP13 expression through p38 pathway in chondrocytes. Since MMP13 plays a major role in cartilage degradation in OA, we speculate that the ability of 1,25-(OH)(2)D-3 to potentiate MMP13 expression might facilitate cartilage erosion at the site of inflammatory arthritis.