Tracy Frech

Objectives Eph/Ephrin cell‐cell signaling is emerging as a key player in tissue fibrogenesis. The aim of this study was to test the hypothesis that the receptor tyrosine kinase EphB2 mediates dermal fibrosis in systemic sclerosis (SSc). Methods We assessed normal and SSc human skin biopsies for EphB2 expression. The in vivo role of EphB2 in skin fibrosis was investigated by subjecting Ephb2 ‐knockout mice to both bleomycin‐induced and tight skin ( Tsk1 /+) genetic mouse models of skin fibrosis. EphB2 kinase‐dead and overactive point mutant mice were used to evaluate the role of EphB2 forward signaling in bleomycin‐induced dermal fibrosis. In vitro studies were performed on dermal fibroblasts from SSc patients and healthy controls, which was followed by in vivo analysis of fibroblast‐specific Ephb2 ‐deficient mice. Results Expression of EphB2 is upregulated in SSc skin tissue and explanted SSc dermal fibroblasts compared to healthy controls. EphB2 expression is elevated in two animal models of dermal fibrosis. In mice, EphB2 drives dermal fibrosis in both the bleomycin and the Tsk1/+ models of skin fibrosis. EphB2 forward signaling is a critical mediator of dermal fibrosis. Transforming growth factor‐β (TGF‐β) cytokines upregulate EphB2 in dermal fibroblasts via non‐canonical TGF‐β/SMAD signaling and silencing EPHB2 in human dermal fibroblasts is sufficient to dampen TGFβ‐induced fibroblast‐to‐myofibroblasts differentiation. Moreover, mice with fibroblast‐specific deletion of Ephb2 showed impaired fibroblast‐to‐myofibroblasts differentiation and reduced skin fibrosis upon bleomycin challenge. Conclusion Our data implicate TGF‐β regulation of EphB2 overexpression and kinase‐mediated forward signaling in the development of dermal fibrosis in SSc. EphB2 thus represents a potential new therapeutic target for SSc.