| Objective : Through establish a high-fat diet(HFD) induced mouse model of Nonalcoholic Fatty Liver Disease(NAFLD),the hepatic Zinc alpha2 glycoprotein(ZAG)expression was observed in NAFLD mouse.Over-expression of ZAG in liver of NAFLD mice through tail-vein injection of Ad-ZAG-GFP was used to investigate the effect and mechanism of ZAG on lipid metabolism.Methods:Male C57BL/6(n=32) mice aged 8 weeks were randomly divided into SD(n=8), HFD(n=8), HFD+ZAG(n=8) and HFD+GFP group(n=8).After adaptive feeding for one week, mice in SD group were fed standard diet while mice in the rest three groups were free access to a high-fat chow for 18 weeks. At the 16 th week, HFD+ZAG group mice were injected Ad-ZAG-GFP(2×109vg per mouse) through tail-vein, while the HFD+GFP group mice were injected Ad-GFP in same volume respectively. After one week,the function of pancreatic was measured byintroperitoneal glucose tolerance test(IPGTT) and introperitoneal insulin tolerance test(IPITT).At the 18 th week, blood and liver tissues of mice were collected after sacrificed. The liver tissues of mice were stained by H&E staining for histological analysis. The serum TG, TC, LDL, HDL,ALT, AST and hepatic triglyceride content were assayed by biochemistry analyzer or ELISA kit. The protein expression levels of genes involving ZAG, metabolic nuclear receptors(FXR、PPARα、LXR and SREBP-1c),fatty acids(TG) synthesis(FAS 、 ACC 、 SCD-1), intake(CD36),β-oxidation(CPT-1A) and adipokines(Adiponectin) were detected by western blot.Results:1. The protein level of heptatic ZAG in HFD group mice was reduced(P<0.05) compared with SD group.2. At the end of the 18 th week, compared with SD group, the liver index, hepatic triglyceride content and the level of TG、TC、LDL、HDL、AST 、 ALT were increased significantly in HFD group and HFD+GFP group(P<0.01). While compared with HFD+GFP group,the liver index,hepatic triglyceride content and the level of AST in ZAG over-expression mice were decreased significantly(P<0.01) as well as the level of ALT、TG and LDL(P<0.05),however, the level of HDL and TC were not decreased significantly(P>0.05).3. H&E staining showed that compared with the SD group,there werea large number of lipid droplets, liver cell edema and partial course ballooning degeneration in hepatocytes of HFD and HFD+GFP group mice compared with SD group. Lipid droplets in hepatocytes of HFD+ZAG group mice were decreased significantly in the number or morphology, and fewer ballooning degeneration compared with HFD+GFP group.4. Compared with SD group, the corresponding area under the curve of IPGTT and IPITT in HFD group was lager(P<0.01), the protein level of hepatic adiponectin, FXR, PPARα and CPT-1A was decreased significantly(P<0.01). Moreover, the protein level of hepatic SREBP-1c,LXR, FAS, ACC, SCD-1 and CD36 was increased significantly(P<0.01).Compared with HFD+GFP group, the corresponding area under the curve of IPGTT and IPITT hasn’t statistical significance(P>0.05), the protein level of hepatic FXR, PPARα in HFD+ZAG group was increased(P<0.05) and the protein level of hepatic adiponectin and CPT-1A was increased significantly(P<0.01). Additionaly, the protein level of hepatic SREBP-1c and CD36 was decreased(P<0.05) as well as the protein level of hepatic LXR, FAS, ACC, SCD-1(P<0.01).Conclusion:1. High-fat diet could induce insulin resistance and down-regulate the protein level of ZAG, FXR, PPARα, CPT-1A and adiponectin in mice,while the expression of LXR, SREBP-1c, FAS, ACC, SCD-1 and CD36 were increased.2. Over-expression of hepatic ZAG could recuce liver index as well as the lever of serum TG and LDL, alleviate deposition of lipid, improve liver function, but ZAG couldn’t improve insulin resisitance.3.Over-expression of hepatic ZAG could improve high fat diet induced NAFLD through increasing fatty acids β-oxidation, decreasing fatty acids synthesis and intake, which may be due to up-regulation of FXR, PPARα,CPT-1A and adiponectin expression and down-regulation of LXR,SREBP-1c, FAS, ACC, SCD-1 and CD36 expression. |
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