Thy-1 (CD90) is a well-known marker of fibroblasts implicated in organ fibrosis, but its contribution to skin fibrosis remains unknown. We examined Thy-1 expression in scleroderma skin and its potential role as a biomarker and pathogenic factor in animal models of skin fibrosis. Skin from patients with systemic sclerosis demonstrates markedly elevated Thy-1 expression compared to controls, co-localizes with fibroblast activator protein (FAP) in the deep dermis, and is correlated with the severity of skin involvement (MRSS). Serial imaging of skin from Thy-1 YFP reporter mice by IVIS showed an increase in Thy-1 expression which correlated with onset and progression of fibrosis. In contrast to lung fibrosis, Thy-1 KO mice had attenuated skin fibrosis in both bleomycin and Tsk-1 murine models. Moreover, Thy-1 regulated key pathogenic pathways involved in fibrosis including inflammation, myofibroblast differentiation, apoptosis and multiple additional canonical fibrotic pathways. Therefore, while Thy-1 deficiency leads to exacerbated lung fibrosis, in skin it is protective. Moreover, Thy-1 may serve as a longitudinal marker to assess skin fibrosis.
Roberta G. Marangoni, Poulami Datta, Ananta Paine, Stacey Duemmel, Marc A. Nuzzo, Laura Sherwood, John Varga, Christopher Ritchlin, Benjamin D. Korman