Inhibition of the Progression of Skin Inflammation, Fibrosis, and Vascular Injury by Blockade of the CX3CL1/CX3CR1 Pathway in Experimental Mouse Models of Systemic Sclerosis

Objective To assess the preclinical efficacy and mechanism of action of an anti-CX(3)CL1 monoclonal antibody (mAb) in systemic sclerosis (SSc). Methods Cultured human dermal fibroblasts were used to evaluate the direct effect of anti-CX(3)CL1 mAb on fibroblasts. In addition, bleomycin-induced and growth factor-induced models of SSc were used to investigate the effect of anti-CX(3)CL1 mAb on leukocyte infiltration, collagen deposition, and vascular damage in the skin. Results Anti-CX(3)CL1 mAb treatment significantly inhibited Smad3 phosphorylation (P < 0.05) and expression of type I collagen and fibronectin 1 (P < 0.01) in dermal fibroblasts stimulated with transforming growth factor beta 1 (TGF beta 1). In the bleomycin model, daily subcutaneous bleomycin injection increased serum CX(3)CL1 levels (P < 0.05) and augmented lesional CX(3)CL1 expression. Simultaneous administration of anti-CX(3)CL1 mAb or CX(3)CR1 deficiency significantly suppressed the dermal thickness, collagen content, and capillary loss caused by bleomycin (P < 0.05). Injection of bleomycin induced expression of pSmad3 and TGF beta 1 in the skin, which was inhibited by anti-CX(3)CL1 mAb. Further, the dermal infiltration of CX(3)CR1+ cells, macrophages (inflammatory and alternatively activated [M2-like] subsets), and CD3+ cells significantly decreased following anti-CX(3)CL1 mAb therapy (P < 0.05), as did the enhanced skin expression of fibrogenic molecules, such as thymic stromal lymphopoietin and secreted phosphoprotein 1 (P < 0.05). However, the treatment did not significantly reduce established skin fibrosis. In the second model, simultaneous anti-mCX(3)CL1 mAb therapy significantly diminished the skin fibrosis induced by serial subcutaneous injection of TGF beta and connective tissue growth factor (P < 0.01). Conclusion Anti-CX(3)CL1 mAb therapy may be a novel approach for treating early skin fibrosis in inflammation-driven fibrotic skin disorders such as SSc.