Attenuation of Fibroblast Activation and Fibrosis by Adropin in Systemic Sclerosis (SSc)

Fibrotic diseases impose a major socioeconomic challenge on modern societies with limited treatment options. Adropin, a peptide hormone encoded by the energy-homeostasis-associated (ENHO) gene, is implicated in metabolism and vascular homeostasis, but its role in the pathogenesis of fibrosis remains enigmatic. Here, we used machine learning approaches in combination with functional in vitro and in vivo experiments to characterize Adropin/ENHO as a potential regulator involved in fibroblast activation and tissue fibrosis in systemic sclerosis (SSc). We demonstrated consistent downregulation of Adropin/ENHO in SSc skin across different SSc cohorts. The prototypical profibrotic cytokine TGFβ reduced Adropin/ENHO expression in a JNK-dependent manner. Restoration of Adropin signaling by therapeutic application of bioactive Adropin34-76 peptides in turn inhibited TGFβ-induced fibroblast activation and fibrotic tissue remodeling in primary human dermal fibroblasts, three-dimensional full-thickness skin equivalents, the mouse models of bleomycin-induced pulmonary fibrosis and sclerodermatous chronic graft-versus-host-disease (sclGvHD), and precision-cut human skin slices (PCSS). Knockdown of GPR19, receptor of Adropin, abrogated the antifibrotic effects of Adropin in fibroblasts. RNA-seq demonstrated that the antifibrotic effects of Adropin34-76 were functionally linked to deactivation of GLI1 dependent profibrotic transcriptional networks, which was experimentally confirmed in vitro, in vivo and ex vivo. ChIP-seq confirmed Adropin34-76-induced changes in TGFβ/GLI1 signaling. Our study thus characterizes the TGFβ-induced downregulation of Adropin/ENHO expression as a potential pathomechanism of SSc as a prototypical systemic fibrotic disease that unleashes uncontrolled activation of profibrotic GLI1 signaling. We also provide evidence in multiple preclinical models that Adropin34-76 might offer potential for the treatment of fibrosis.