Objective and design: Transforming growth factor- beta (TGF-beta) has not only a fibrogenic role, but also monocyte/ macrophage chemotactic properties in a synovial joint. However, little is known about the effects of TGF-beta on monocyte chemoattractant protein-1 (MCP-1) expression in human synovial cells under inflammatory status. The aim of this study was to determine whether TGF-modulates MCP-1 production under the chronic inflammation, and to elucidate the cell signaling mechanism involved.
Materials and methods: Human synovial cells were exposed to IL-1beta, which mimics the environment of chronic inflammation. Production of MCP-1 protein and expression of MCP-1 mRNA were determined by ELISA and real-time PCR.
Results: TGF-beta upregulated the expression of MCP-1 mRNA and protein with or without IL-1beta. TGF-beta and IL-1beta synergistically enhanced MCP-1 gene expression, and an AP-1 binding site was involved in the signal transduction. In addition, MEK inhibitor completely suppressed TGF-beta-induced MCP-1 production.
Conclusions: TGF-beta and IL-1beta synergistically enhance MCP-1 gene expression through the activation of the MEK/ERK1/2 pathways, which leads to AP-1 activation. The impairment of MCP-1 regulation by TGF-beta in resident synovial cells might represent an important mechanism of chronic inflammation and tissue fibrosis in a synovial joint. MCP-1 should be considered a valid target for therapeutic intervention.