To determine the gene‐expression profile in dermal fibroblasts from type 1 tight‐skin (Tsk1) mice, and to examine the expression and potential fibrotic activity of monocyte chemoattractant protein 3 (MCP‐3) in Tsk1 mouse and human systemic sclerosis (SSc) skin.

Complementary DNA microarrays (Atlas 1.2) were used to compare Tsk1 fibroblasts with non‐Tsk1 littermate cells at 10 days, 6 weeks, and 12 weeks of age. Expression of MCP‐3 protein was assessed by Western blotting of fibroblast culture supernatants, and localized in the mouse and human skin biopsy samples by immunohistochemistry. Activation of collagen reporter genes by MCP‐3 was explored in transgenic mouse fibroblasts and by transient transfection assays.

MCP‐3 was highly overexpressed by neonatal Tsk1 fibroblasts and by fibroblasts cultured from the lesional skin of patients with early‐stage diffuse cutaneous SSc. Immunolocalization confirmed increased expression of MCP‐3 in the dermis of 4 of 5 Tsk1 skin samples and 14 of 28 lesional SSc skin samples, compared with that in matched healthy mice (n = 5) and human controls (n = 11). Proα2(I) collagen promoter–reporter gene constructs were activated by MCP‐3 in transgenic mice and by transient transfection assays. This response was maximal between 16 and 24 hours of culture and mediated via sequences within the proximal promoter. The effects of MCP‐3 could be diminished by a neutralizing antibody to transforming growth factor β.

We demonstrate, for the first time, overexpression of MCP‐3 in early‐stage SSc and in Tsk1 skin, and suggest a novel role for this protein as a fibrotic mediator activating extracellular matrix gene expression in addition to promoting leukocyte trafficking. This chemokine may be an important early member of the cytokine cascade driving the pathogenesis of SSc.