Regulation of Transforming Growth Factor-/Smad-mediated Epithelial-Mesenchymal Transition by Celastrol Provides Protection against Bleomycin-induced Pulmonary Fibrosis

The respiratory disease pulmonary fibrosis (PF), which is characterized by scar formation throughout the lung, imposes a serious health burden. No effective drug without side effects has been proven to prevent this fatal lung disease. In this context, this study was undertaken to elucidate the protective effect of celastrol, a quinine methide pentacyclic triterpenoid from a Chinese medicinal plant thunder god vine' against bleomycin (BLM)-induced PF. We also attempted to study how the cytokine transforming growth factor- (TGF-) stimulates fibrosis through the induction of epithelial-mesenchymal transition (EMT) and the role of celastrol in regulating EMT. TGF- (5 ng/ml) was administered to human alveolar epithelial adenocarcinoma A549 cells to induce fibrotic response in cells. Induction of EMT was analysed in cells through morphological analysis and expression of epithelial and mesenchymal markers by Western blotting. Bleomycin at a concentration of 3 U/Kg b.w was used to induce fibrosis in adult male rat lungs. Celastrol (5 mg/kg b.w) was given to rats twice a week after BLM administration for a period of 28 days. Western blot and immunofluorescence analyses were performed with lung tissue sample to find out the potential of celastrol in regulating EMT during the progression of fibrosis. TGF- induces EMT in A549 cells as demonstrated by changes in epithelial cell morphology and expression of epithelial and mesenchymal marker proteins. The expressions of epithelial marker proteins E-cadherin and claudin were found to be reduced in the BLM-induced group of rats. Expression of mesenchymal markers, such as N-cadherin, snail, slug, vimentin and -catenin, was enhanced in BLM-induced rat lungs. Celastrol reverts these cellular changes in rat lungs, and it was found that celastrol regulates EMT through the inhibition of heat shock protein 90 (HSP 90). Together, the results indicate that EMT is a crucial phenomenon for the progression of fibrosis, and celastrol provides protection against PF through the regulation of EMT.