Isorhamnetin protects against bleomycin-induced pulmonary fibrosis by inhibiting endoplasmic reticulum stress and epithelial-mesenchymal transition.

The present study aimed to determine whether isorhamnetin (Isor), a natural antioxidant polyphenol, has antifibrotic effects in a murine model of bleomycin‑induced pulmonary fibrosis. A C57 mouse model of pulmonary fibrosis was established by intraperitoneal injection of a single dose of bleomycin (3.5 U/kg), and then Isor (10 and 30 mg/kg) was administered intragastrically. The level of fibrosis was assessed by hematoxylin and eosin and Sirius red staining. α‑smooth muscle actin and type I collagen levels in lung tissues were determined by western blotting and immunohistochemistry (IHC). Epithelial‑mesenchymal transition (EMT), endoplasmic reticulum stress (ERS) and related signaling pathways were examined by western blotting and IHC. In vitro, human bronchial epithelial cells (HBECs) and A549 cells were treated with transforming growth factor (TGF)β1 with or without Isor, and collagen deposition and the expression levels of EMT‑ and ERS‑related genes or proteins were analyzed by reverse transcription‑quantitative polymerase chain reaction, western blotting, and immunofluorescence. The results demonstrated that Isor inhibited bleomycin‑induced collagen deposition, reduced type I collagen and α‑SMA expression, and alleviated EMT and ERS in vivo. Furthermore, incubation of HBECs and A549 cells with TGFβ1 activated EMT and ERS, and this effect was reversed by Isor. In conclusion, Isor treatment attenuated bleomycin‑induced EMT and pulmonary fibrosis and suppressed bleomycin‑induced ERS and the activation of PERK signaling.