Monocyte chemoattractant protein 1 released from glycosaminoglycans mediates its profibrotic effects in systemic sclerosis via the release of interleukin‐4 from T cells

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Abstract
Objective: Monocyte chemoattractant protein 1 (MCP‐1; CCL2) has been implicated in the pathogenesis of fibrotic diseases and is up‐regulated in patients with systemic sclerosis (SSc). The aim of the present study was to examine the mechanisms by which MCP‐1 mediates its profibrotic effects in the setting of SSc.Methods: The expression of receptors for MCP‐1 on dermal fibroblasts was analyzed by real‐time polymerase chain reaction and fluorescence‐activated cell sorting. The ability of extracellular matrix proteins to bind and release MCP‐1 was quantified by enzyme‐linked immunosorbent assay. Th0 cells were isolated using a magnetic‐activated cell sorting system and were stimulated twice in the presence of MCP‐1. The synthesis of collagen was measured using the Sircol collagen assay kit.Results: The glycosaminoglycan chondroitin sulfate, but not fibronectin or collagens, bound and released MCP‐1 in a time‐dependent manner. MCP‐1 that was released from chondroitin sulfate induced the differentiation of interleukin‐4 (IL‐4)–producing T cells in a dose‐dependent manner. In turn, dermal fibroblasts from patients with SSc expressed IL‐4 receptor, and stimulation with IL‐4 significantly increased the production of collagen in dermal fibroblasts. In contrast, CCR2a and CCR2b, as well as D6 and US28 (other potential receptors of MCP‐1), were not detectable in SSc and normal fibroblasts, and their expression was not induced by platelet‐derived growth factor, IL‐1β, or IL‐4. In addition, MCP‐1 had no direct effects on collagen production by fibroblasts.Conclusion: MCP‐1 has no direct effects on dermal fibroblasts but contributes to fibrosis in patients with SSc by inducing the differentiation of IL‐4–producing T cells. Because MCP‐1 has both proinflammatory and profibrotic effects, pharmacologic targeting of MCP‐1 could be a promising therapeutic approach in SSc.