RGD Reference Report - Chemokine receptors CCR2 and CX3CR1 regulate skin fibrosis in the mouse model of cytokine-induced systemic sclerosis. - Rat Genome Database
BACKGROUND: Skin fibrotic disorders such as systemic sclerosis (SSc) are characterized by an excessive accumulation of extracellular matrix (ECM), and develop under the influence of certain cytokines. We previously established a mouse model of skin fibrosis induced by exogenous application of cytokines. We have revealed that both the number of macrophages and the levels of macrophage chemoattractant protein-1 (MCP-1) mRNA positively correlate with the extent of skin fibrosis. Macrophages can be divided into two subsets, the first expressing CCR2, and the second expressing CX3CR1. OBJECTIVE: To elucidate the role of skin infiltrating macrophages based on CCR2 and CX3CR1 in this cytokine-induced murine fibrosis model. METHODS: We examined the amounts of collagen deposited in granulation tissues, the numbers of macrophages and the levels of several mRNA in wild type (WT) mice, CCR2(-/-) mice, and CX3CR1(-/-) mice during injections of transforming growth factor-beta (TGF-beta) followed by injections of connective tissue growth factor (CTGF). RESULTS: TGF-beta injection increased the expressions of MCP-1, fractalkine, CCR2 and CX3CR1 mRNA in WT mice. The overproduction of collagen induced by TGF-beta was significantly reduced by CCR2 deficiency, while collagen contents induced by CTGF were restored to wild-type levels. In contrast, overproduction of collagen in CX3CR1-deficient mice decreased nearly 50% by both TGF-beta and CTGF stimulations. CONCLUSION: The involvement of CCR2/MCP-1 interaction (CCR2-dependent loop) was during the TGF-beta phase. In contrast, the fractalkine/CX3CR1 interaction contributes to the initiation of fibrosis by TGF-beta and its maintenance by CTGF. Collectively, two subsets of macrophages both cooperatively and independently play important roles in the development of fibrosis.