Effects of celastrol on autophagy and endoplasmic reticulum stress-mediated apoptosis in a mouse model of nonalcoholic fatty liver disease

Abstract

Objective: To investigate the effect of celastrol (CEL) on autophagy and endoplasmic reticulum stress-mediated apoptosis in a mouse model of nonalcoholic fatty liver disease (NAFLD). Methods: Eighteen male C57BL/6J mice were randomly divided into normal control (NC, n=6), high-fat diet (HFD, n=6) and celastrol group (HFD+CEL, n=6). The normal control group was fed with regular diet, and the high-fat diet and celastrol group were fed with high-fat diet for 12 weeks. After successful modeling, celastrol group were injected with 100 μg⋅kg-1⋅d-1 celastrol intraperitoneally for 4 weeks, and NC and HFD group were injected intraperitoneally with the same doses of normal saline. Serum concentrations of alanine aminotransferase (ALT), aspartate aminotransferase (AST), triglyceride (TG), total cholesterol (TC), high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C) were measured in mouse after 4-weeks of intervention. HE and Oil Red O staining were used to observe the pathomorphological changes and lipid droplet deposition in mouse liver, and the findings were scored according to NAFLD activity score (NAS). Western blot was used to detect the expression levels of liver microtubule associated protein 1 light chain 3 (LC3), P62, glucose-regulated protein 78 (GRP78), protein kinase R-like endoplasmic reticulum kinase (PERK), phosphorylated PERK (p-PERK), activated transcription factor 4 (ATF4), C/EBP homologous protein (CHOP), cleaved Caspase-3(cleaved caspase-3), B-cell lymphoma-2 (Bcl-2) and Bcl-2 related X protein (Bax).TUNEL staining was used to observe the apoptosis of hepatocytes. One-way analysis of variance was used for the intergroup comparison. Results: Serum levels of ALT (68.71±8.57) U/L, AST (209.63±28.64) U/L, TG (0.97±0.14) mmol/L, TC (4.12±0.64) mmol/L, and LDL -C (0.40±0.06) mmol/L were lower in celastrol group mouse than HFD group [(110.19±10.79) U/L, (399.72±73.47) U/L, (1.44±0.13) mmol/L, (5.65±0.54) mmol /L, (0.61±0.07) mmol/L] (P<0.05); while the serum HDL-C level (1.29±0.17) mmol/L was higher in celastrol than HFD group (0.72±0.13) mmol/L (P<0.05). HE and Oil Red O staining showed that lipid deposition and intralobular inflammation were apparent in the liver tissue of HFD group mouse, and the NAS score was significantly increased, while the hepatocyte steatosis and intralobular inflammation were alleviated after celastrol intervention, and the NAS score was decreased significantly (P<0.05). Compared with HFD group, the ratio of LC3II/I was significantly increased in the liver of celastrol group mouse, and the P62 was significantly decreased (P<0.05). Meanwhile, the expression level of GRP78, p-PERK/PERK , ATF4, and CHOP was significantly lower in celastrol than HFD group (P<0.05). In addition, the expressions of cleaved caspase-3 and Bax were significantly lower in celastrol than HFD group, and the expression of Bcl-2 was significantly increased (P<0.05). At the same time, the apoptosis rate of hepatocytes was also significantly lower in celastrol than HFD group (P<0.05). Conclusion: Celastrol can effectively alleviate the lipid deposition, protect hepatocytes and delay the progression of non-alcoholic fatty liver disease in mouse liver with non-alcoholic fatty liver disease. In addition, its mechanism of action may be related to the induction of autophagy, inhibition of endoplasmic reticulum stress PERK/ATF4/CHOP pathway and its mediated apoptosis.