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Hepatocyte growth factor induction of macrophage chemoattractant protein‐1 and osteophyte‐inducing factors in osteoarthritis

In osteoarthritis (OA), hepatocyte growth factor (HGF) is supposed to play a role in cartilage repair. Because the development of osteophytes is a major characteristic of OA and thought to be part of an attempted repair process, the purpose of this study was to determine whether HGF may be involved in osteophyte formation. HGF levels in synovial fluids from 41 patients assessed by enzyme immunosorbant assay were correlated with disease severity and osteophyte formation, evaluated by anteroposterior weight‐bearing radiographs. Detection of HGF, c‐Met, and CD68 in cartilage and synovial tissues was assessed by immunohistochemistry. Effects of HGF on the secretion of TGF‐β1 and BMP‐2 by chondrocytes, fibroblast‐like synovial cells (FLS), and macrophages as well as HGF‐induced secretion of MCP‐1 by FLS and chondrocytes were determined by ELISA. HGF was detected in all synovial fluids and concentrations correlated highly with disease severity and osteophyte formation (p < 0.001). Immunohistochemistry revealed weak synovial staining for HGF, whereas increasing numbers of HGF expressing chondrocytes were detected depending on disease severity. In addition, an increased number of macrophages in synovial specimens was observed, which was likewise severity dependent. In a series of subsequent in vitro studies, HGF remarkable induced MCP‐1 secretion by FLS in a dose‐dependent manner. No effect on TGF‐β1 and BMP‐2 secretion by FLS and chondrocytes was evident upon HGF stimulation, whereas secretion of these growth factors by PMA‐differentiated THP‐1 cells was significantly increased by HGF. The results indicate that HGF may facilitate osteophyte development by promoting MCP‐1‐mediated entry of monocytes/macrophages into the OA‐affected joint and/or by stimulating macrophage‐derived growth factors. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:569–577, 2007