β-carboline derivative Z86 alleviates pulmonary fibrosis via suppressing TGF-β/Smad signaling

Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant fibroblast proliferation and excessive expression and deposition of extracellular matrix (ECM) by myofibroblasts, ultimately resulting in progressive and irreversible disorder or even loss of the pulmonary function. IPF is incurable with limited therapeutic options and low survival rate, thus the discovery of the therapeutic potential agents for IPF is in urgent need. Here, we identified isopropyl 9-ethyl-1-(naphthalen-1-yl)-9H-pyrido[3,4-b] indole-3-carboxylate (Z86) as a promising bioactive agent against Bleomycin (BLM) induced pulmonary fibrotic mice with the lung abnormalities including histological alteration, accumulation of ECM, as well as markers of EMT (epithelial-mesenchymal transition) were all relieved upon Z86 treatment in C57BL/6 mice. Consistent to the activity in vivo, Z86 decreased TGF-β induced cell migration, fibrotic marker expression, and myofibroblast activation in A549 and HFL1 cells. In further mechanism of action study of Z86 against IPF, we found TGF-β (transforming growth factor β) /Smad2/3 signaling pathway was substantially attenuated in TGF-β treated A549 and HFL1 cells, with remarkably decreased protein level of Smad2/3. Further, we identified Z86 as a novel USP15 inhibitor. Correspondingly, Z86 interacted with USP15, promoted the ubiquitination and degradation of Smad2/3 and disrupted TGF-β/Smad2/3 signaling pathway. Taken together, our findings demonstrated that Z86 suppressed TGF-β induced pulmonary fibrosis in A549 and HFL cells and BLM induced pulmonary fibrotic mice through inhibiting TGF-β/Smad2/3 signaling, and provided the possibility of USP15 inhibitors as the potential drug candidates for idiopathic pulmonary fibrosis.