Transforming growth factor-ß stimulates nerve growth factor production in osteoarthritic synovium.

ABSTRACT

BACKGROUND: Nerve growth factor (NGF) contributes to pain in knee osteoarthritis (KOA) patients. Transforming growth factor-beta (TGF-ß) stimulates NGF expression in chondrocytes from KOA patients. However, the correlation between synovial TGF-ß and NGF levels has not been sufficiently studied in human KOA patients. Further, the mechanism governing NGF regulation by TGF-ß in synovial cells is unclear. METHODS: During total knee arthroplasty, we extracted the synovial tissue (SYT) of 107 subjects with unilateral Kellgren/Lawrence grade 3-4 KOA confirmed by radiography. We examined the distribution of TGF-ß and NGF using immunohistochemistry, and analyzed the relationship between NGF and TGFB mRNA levels. Cultured synovial cells extracted from SYT were exposed to culture medium (control), human recombinant TGF-ß (rhTGF-ß), rhTGF-ß + ALK5 inhibitor SB505124, rhTGF-ß + transforming growth factor activating kinase 1 (TAK1) inhibitor (5Z)-7-oxozeaenol, or rhTGF-ß + p38 inhibitor SB203580 for 30 min, 6 h and 24 h. NGF mRNA expressed by the cultured cells and NGF protein levels in the cell supernatant were detected by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Phosphorylation of p38 was evaluated by western blotting. RESULTS: NGF mRNA levels were positively correlated with those of TGFB. Cells expressing TGF-ß and NGF protein were observed in the lining layer of SYT. TGF-ß stimulated increased NGF mRNA expression and NGF protein production. The ALK5 inhibitor completely suppressed the TGF-ß-mediated increase in NGF expression and NGF production in synovial cells. ALK5, TAK1 and p38 inhibitors inhibited the TGF-ß-induced phosphorylation of p38, and TAK1 and p38 inhibitors partially inhibited the TGF-ß-mediated increase in NGF expression and NGF production in synovial cells. CONCLUSION: TGF-ß regulates NGF production via the TGF-ß/ALK5 signaling pathway in osteoarthritic synovium. This effect may partially occur through inhibition of the TAK1/p38 pathway in the SYT of KOA patients.