Ac-SDKP Ameliorates Bleomycin-Induced Pulmonary Fibrosis By Inhibiting Endoplasmic Reticulum Stress Induced Epithelial-Mesenchymal Transition

Objective:The study investigated the effect of Ac-SDKP on reduction of endoplasmic reticulum stress(ERS)induced by epithelial-mesenchymal transition(EMT)in vivo and in vitro.Methods:In vivo:Twenty-four male C57BL/6 mice were randomly allocated into 3 groups:(i)Sham-operated group(n=8): instilled with 0.9% saline.(ii)BLM group(n=8): injected with bleomycin intratracheally at a dose of 5 mg/kg.(iii)BLM+Ac-SDKP group(n=8): same as the BLM group but Ac-SDKP was administered(800 ?g/kg.d)i.p.for 21 days after BLM until day 42.Mice were euthanized with pentobarbitone overdose.HE staining?Masson staining and measured the content of hydroxyproline in the lung tissues to evaluate histological changes in lungs.Protein expressions of GRP78,CHOP,E-cadherin and Vimentin were assessed by Immunohistochemistry and Western Blot.In vitro:Human type II alveolar epithelial cells(A549 cells)intervened by with 5 ng/ml of TGF-? were used to detect morphological evidence of EMT by phase-contrast microscopy.qRT-PCR was used to examine changes in mRNA levels of GRP78,CHOP,E-cadherin and Vimentin.Results:In vivo:On day 21,histopathological findings of fibrosis induced in BLM group showed alveolar/bronchiolar walls thickening and extracellular collagen deposition,which were eventually moderated by Ac-SDKP.The hydroxyprotein level in mice of BLM group was significantly upregulated(P<0.05),while significantly lower in BLM+ Ac-SDKP group than BLM group(P<0.05).Compared with Sham-operated group,protein expressions of CHOP,GRP78 and Vimentin are higher in BLM group(P<0.05),while E-cadherin was lower in BLM group(P<0.05).The expressions of these markers in BLM+Ac-SDKP group were between Sham-operated and BLM groups.In vitro:The results demonstrated that A549 cells became spindle-like when exposed to TGF-?.E-cadherin showed decreased mRNA levels,while those of Vimentin,GRP78 and CHOP were increased.Conclusion:Ac-SDKP inhibits the process of ERS through EMT,which plays an important role in anti-pulmonary fibrosis.