Contribution of activin receptor-like kinase 5 (Transforming growth factor β receptor type I) signaling to the fibrotic phenotype of scleroderma fibroblasts

Objective. To use a specific transforming growth factor beta receptor type I (TGF beta RI; activin receptor-like kinase 5 [ALK-5]) kinase inhibitor (SD208) to determine the role of activation of the TGF beta RI kinase (ALK-5) in maintaining the profibrotic phenotype of dermal fibroblasts in systemic sclerosis (SSc). Methods. The effect of SD208 on the expression of key biochemical markers of the fibrotic phenotype was compared in fibroblasts cultured from clinically involved (lesional) and clinically uninvolved skin of patients with diffuse cutaneous SSc (dcSSc) and in fibroblasts from healthy controls matched for age, sex, and anatomic site. Protein expression was compared together with the ability of fibroblasts to adhere to the extracellular matrix and to remodel and contract a free-floating fibroblast-populated type I collagen lattice. Results. Inhibiting TGF beta RI kinase reduced the expression of a cohort of fibrotic markers by dermal fibroblasts from patients with dcSSC, including type I collagen and beta 1 integrin. Moreover, inhibition also attenuated the elevated adhesive and contractile abilities of dcSSc fibroblasts. Conclusion. Our data suggest that some of the key profibrotic features of lesional SSc fibroblasts are dependent upon ALK-5 activity. Thus, TGF beta RI kinase-mediated signaling may contribute to dermal fibrosis in dcSSc.