Background Rheumatoid arthritis (RA) is characterized by the aggressive synovial expansion due to angiogenesis and subsequent destruction of the underlying cartilage and bone. New blood vessel formation is critically important for synovial expansion in RA. Hepatocyte growth factor (HGF) enhances angiogenesis and impairs bone formations. Therefore, the abrogation of HGF receptor (c-Met)-mediated signaling events appears to be a promising strategy for the prevention of synovial cell proliferations and bone destructions.
Objectives In the present study we examined the role of HGF receptor (c-Met) signaling pathway for synovial cell function and osteoblast differentiation using human synovial cell line and mouse myoblastic cell line which differentiate into osteoblast in vitro.
Methods HGF or c-Met expressions in synovial tissues were examined by immunohistochemistry using either anti-HGF Ab or anti-c-Met Ab. Human MH7A synovial cell line was established by transfection with SV40 T antigen to synovial cells which were isolated from knee joint intraarticular soft tissue of RA patients. IL-6, prostaglandin (PG) E2, and matrix metalloproteinase (MMP)-3 production from MH7A cells was determined by ELISA. C2C12 mouse myoblast cell line was cultured with bone morphogenic protein (BMP)-2 and alkaline phosphatase (ALP) activity in the cells was determined using an ALP staining kit. Osteocalcin production by C2C12 cells was determined by ELISA. Extracellular signal-regulated kinase (ERK) 1/2 phosphorylation was determined by Western blot analysis. The effect of MEK1/2 inhibitor or c-Met kinase inhibitor was examined by the treatment of the cells with either U0126 or SU11274, respectively.
Results HGF and c-Met expressions in RA synovium were increased comparing to those in osteoarthritis synovium, suggesting the increased HGF receptor signaling in RA synovial cells. We also detected HGF and c-Met expressions in MH7A and C2C12 cells. TNF-alpha significantly enhanced the production of IL-6, PGE2, and MMP-3 by MH7A cells. The blocking of c-Met signaling pathway by c-Met kinase inhibitor slightly enhanced TNF-alpha-induced IL-6 and PGE2 production but significantly inhibited MMP-3 production by MH7A cells. In addition, c-Met kinase inhibitor significantly enhanced ALP and osteocalcin production by BMP-2 stimulated C2C12 cells. These c-Met kinase inhibitor effects were resucued by MEK1/2 inhibitor, indicating that c-Met signaling pathway activates ERK1/2.
Conclusions These results indicate that c-Met signaling pathway activates ERK1/2 and enhances MMP-3 production by synovial cells and inhibits osteoblast differentiation. Blocking the c-Met signaling pathway may inhibits synovial expansion and enhances osteoblast differentiation and become a new therapeutic approach for the treatment of RA.
Disclosure of Interest None Declared
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