Melatonin Alleviates Endoplasmic Reticulum Stress At Early Stage During Bleomycin-induced Lung Fibrosis In Mice

Objective Discuss about melatonin(MT) alleviates endoplasmic reticulum(ER) stress at early stage of bleomycin(BLM)-induced lung fibrosis in mice.Methods Adult healthy male ICR mice were divided randomly into control group, MT group, BLM group and MT+BLM group. In MT group, mice had saline treatment 30 minutes after having intraperitoneal(i.p.) injection MT(10 mg·kg-1) and had intraperitoneally(i.p.) injected MT once in the following every 24 hours. In BLM group, mice were intratracheally injected with a single dose of BLM(5 mg·kg-1). In MT+BLM group, mice had intraperitoneally injected BLM 30 minutes after having MT and had injected MT once in the following every 24 hours. In control group, mice received the same level of saline treatment by the same method. All mice were dissected for collecting the tissue of lungs at different times(24h, 72h) after BLM treatment. Inflammatory cell infiltration of lungs was determined by HE staining. The level of ER stress related proteins(GRP78, p-e IF2α, p-IRE1α) in lungs were determined using Western blot. The distribution of ER stress related proteins(GRP78, p-IRE1α, ATF6α, p-PERK) in lungs were detected by immunohistochemistry.Results The model of BLM-induced acute inflammatory of lung fibrosis in mice have been successfully constructed. After BLM treatment, lung weight, lung weight ratio and inflammatory cell infiltration are significantly increased with significant correlation between time and effectiveness. After MT treatment, lung weight, lung weight ratio and inflammatory cell infiltration are significantly reduced. The results of western blot show that MT pretreatment not only prevent increase of BLM-induced GRP78 protein significantly, but also restrain the phosphorylation of e IF2α and IRE1α in mouse lungs. Immunohistochemistry also shows that MT pretreatment reduced the expression of GRP78, p-IRE1α, ATF6α and p-PERK.Conclusion MT alleviates ER stress effectively at early stage of BLM-induced lung fibrosis in mice.