Progranulin Promotes Bleomycin-Induced Skin Sclerosis by Enhancing Transforming Growth Factor-β/Smad3 Signaling through Up-Regulation of Transforming Growth Factor-β Type I Receptor.

Progranulin (PGRN) is an autocrine growth factor with numerous physiological and pathologic roles. Previous reports demonstrated PGRN could increase dermal fibroblasts in wound healing and activate cancer-associated fibroblasts in some cancers. Because systemic sclerosis (SSc) is a prototypical fibrosis-related disorder, here, the aim was to clarify the role and mechanism of PGRN in bleomycin (BLM)-induced model of SSc for the first time. It was observed that the serum PGRN levels were increased in SSc patients compared with healthy controls. Immunohistology and quantitative RT-PCR demonstrated that PGRN was also elevated in the lesion from the mice model of BLM-induced dermal fibrosis. In addition, in BLM-treated mice, PGRN deficiency not only attenuated dermal fibrosis but also decreased the differentiation of myofibroblasts. The reduced progression of skin sclerosis in PGRN-deficient mice was associated with down-regulation of transforming growth factor (TGF)-β receptor I (TβR I) and decreased level of phosphorylated Smad3, with correspondingly impaired expression of its downstream target gene connective tissue growth factor (CTGF) in skin lesion. In contrast, exogenous PGRN significantly increased the level of TβR I and phosphorylated Smad3 in cultured mouse fibroblasts. This study demonstrates that PGRN plays a promoting role in the development of dermal fibrosis through the activation of the TGF-β/Smad3 signaling via up-regulation of TβR I. PGRN may be a new therapeutic target in SSc.