To investigate the mechanism how Transforming growth factor-(TGF-) represses Interleukin-1 (IL-1)-induced Proteinase-Activated Receptor-2 (PAR-2) expression in human primary synovial cells (hPSCs). Human chondrocytes and hPSCs isolated from cartilages and synovium of Osteoarthritis (OA) patients were cultured with 10% fetal bovine serum media or serum free media before treatment with IL-1, TGF-1, or Connective tissue growth factor (CTGF). The expression of PAR-2 was detected using reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Collagen zymography was performed to assess the activity of Matrix metalloproteinases-13 (MMP-13). It was demonstrated that IL-1 induces PAR-2 expression via p38 pathway in hPSCs. This induction can be repressed by TGF- and was observed to persist for at least 48 hrs, suggesting that TGF- inhibits PAR-2 expression through multiple pathways. First of all, TGF- was able to inhibit PAR-2 activity by inhibiting IL-1-induced p38 signal transduction and secondly the inhibition was also indirectly due to MMP-13 inactivation. Finally, TGF- was able to induce CTGF, and in turn CTGF represses PAR-2 expression by inhibiting IL-1-induced phospho-p38 level. TGF- could prevent OA from progression with the anabolic ability to induce CTGF production to maintain extracellular matrix (ECM) integrity and to down regulate PAR-2 expression, and the anti-catabolic ability to induce Tissue inhibitors of metalloproteinase-3 (TIMP-3) production to inhibit MMPs leading to avoid PAR-2 over-expression. Because IL-1-induced PAR-2 expressed in hPSCs might play a significantly important role in early phase of OA, PAR-2 repression by exogenous TGF- or other agents might be an ideal therapeutic target to prevent OA from progression.
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