To investigate the expression of growth differentiation factor-5 (GDF-5) in chondrocytes (HC) and fibroblast-like synoviocytes (FLS) from humans with rheumatoid arthritis (RA) when stimulated with proinflammatory cytokines and to explore whether GDF-5 plays a role in regulating the differentiation of FLS-RA into chondrocytes.
Expression of GDF-5 in synovium and cartilage in RA and osteoarthritis (OA) was assessed by immunohistochemistry. GDF-5 production in FLS-RA and HC-RA was examined through real-time quantitative RT-PCR (Q-PCR) and western blotting. Expressions of GDF-associated receptors on FLS-RA were determined by semiquantitative-PCR, and MTT assay was used to study the effects on FLS-RA proliferation. Effect of GDF-5 and TGF-beta3 on in vitro chondrogenic ability of FLS-RA was investigated using pellet-culture system, Q-PCR and histological analysis.
Immunohistochemical analysis demonstrated that GDF-5 expression in the synovium and cartilage from joints of RA patients was much lower than that of OA patients. Addition of IL-1beta or TNF-alpha appeared to downregulate the expression of GDF-5 in HC-RA and FLS-RA. Inhibition of GDF-5 expression by IL-1beta in RA-FLS was attenuated by pretreatment with MEK1/2 inhibitor. GDF-5-associated receptors were expressed in FLS-RA, but GDF-5 had no effect on FLS-RA proliferation. GDF-5 had a strong chondrogenic-promoting effect on TGF-beta3-induced chondrocyte differentiation in FLS-RA.
GDF-5 is expressed in FLS-RA and HC-RA, and its expression is strongly downregulated by proinflammatory cytokines. MEK-ERK pathway is a negative regulator of GDF-5 expression in FLS-RA. In FLS-RA, synergy between GDF-5 and TGF-beta3 enhances chondrogenesis. Anti-inflammatory drugs combined with GDF-5 might be a new therapeutic treatment for RA.