An acute bleomycin inflammatory and fibrotic mouse model of morphea is dependent upon CXCL9 and CXCR3

Abstract Morphea, or localized scleroderma, is characterized by an inflammatory phase followed by cutaneous fibrosis, which may lead to disfigurement and/or disability. Previous work from our group showed that the CXCR3 ligands CXCL9 and CXCL10 are highly upregulated in lesional skin of morphea patients. Here, we used an acute inflammatory and fibrotic bleomycin mouse model of morphea to examine the role of the CXCR3 chemokine axis in pathogenesis. We first characterized which cells produce the CXCR3 ligands in the skin using the Reporter of Expression of CXCR3 ligands mouse (REX3). We found that fibroblasts contribute the bulk of CXCL9 and CXCL10, whereas endothelial cells are key dual chemokine producers. Macrophages, which have high MFI of chemokine expression, upregulated CXCL9 production over time, fibroblasts CXCL10 production, and T cells dual chemokine expression. To determine whether bleomycin treatment could directly induce expression of these chemokines, we treated cultured REX3 mouse dermis monolayers in vitro with bleomycin or IFNγ with TNF and found that bleomycin could induce low amounts of CXCL9 directly in fibroblasts, whereas the cytokines were required for optimal CXCL9 and CXCL10 production. To determine whether these chemokines are mechanistically involved in pathogenesis, we induced fibrosis in CXCL9, CXCL10, or CXCR3 deficient mice and found that fibrosis is dependent on CXCL9 and CXCR3. Addition of recombinant CXCL9, but not CXCL10, to cultured mouse fibroblasts induces collagen 1a1 mRNA expression, indicating the chemokine itself can contribute to fibrosis. Taken together, our studies provide evidence that acute intradermal bleomycin administration in mice can model inflammatory morphea, and that CXCL9 and its receptor CXCR3 are mechanistically involved in pathogenesis. One Sentence SummaryCXCL9 drives acute morphea pathogenesis in mice.