Abstract:

Objective To discuss the effect of angiopoietin-like protein 6 （ANGPTL6） on improving liver lipid accumulation induced by methionine- and choline-deficient （MCD） diet in the mice， and to clarify its possible mechanism. Methods Forty-two six-week-old C57BL/6 mice were randomly divided into control group， model group and ANGPTL6 overexpression group （ANGPTL6 group）， with 14 mice in each group. After one week of adaptive feeding， the mice in control group were fed normal diet， and the mice in model group and ANGPTL6 group were fed with MCD diet for 8 weeks. One week after starting the MCD diet， adeno-associated virus serotype 8（AAV8）-green fluorescent protein （GFP） empty vector and AAV8-ANGPTL6 overexpression vector were injected into the mice in model group and ANGPTL6 group via the tail vein， respectively. The steatosis model in HepG2 cells was induced by a mixture of oleic acid（OA） and palmitic acid（PA）， and the cells were divided into blank control group （BSA group）， model group （OD group）， ANGPTL6-treated group （OAD group） and mammalian target of rapamycin （mTOR） agonist group （OAM group）. HE staining and oil red O staining were used to evaluate the liver tissue morphology and lipid deposition in the mice in various groups； kits were used to detect the levels of total cholesterol （TC） and triglyceride （TG） in liver tissue of the mice in various groups and in HepG2 cells in various groups； real-time fluorescence quantitative PCR （RT-qPCR） method was used to detect the mRNA expression levels of lipid metabolism-related genes in liver tissue of the mice in various groups and in HepG2 cells in various groups； Western blotting method was used to detect the expression levels of ANGPTL6， mTOR and phosphorylated mTOR （p-mTOR） proteins in liver tissue of the mice in various groups and in the HepG2 cells in various groups. Results Compared with control group， the livers of the mice in model and ANGPTL groups showed severe vacuolar degeneration and abnormal lipid accumulation， and the expression levels of ANGPTL6 protein in the liver tissue were decreased （P<0.05）. Compared with model group， the vacuolar degeneration and lipid accumulation in liver tissue of the mice in ANGPTL6 group were alleviated， the TG level in liver tissue was decreased （P<0.05）； the expression levels of lipid synthesis-related genes sterol regulatory element binding factor 1 （SREBF1） and fatty acid synthase （FASN） mRNA in liver tissue were decreased （P<0.05）， and the expression levels of lipid decomposition-related genes adipose triglyceride lipase （ATGL） and carnitine palmitoyltransferase 1A （CPT1A） mRNA in liver tissue were increased （P<0.05）； the expression levels of mTOR and p-mTOR proteins in liver tissue were decreased （P<0.05）. Compared with BSA group， the TG level， the expression levels of FASN and acetyl-CoA carboxylase alpha （ACACA） mRNA， and the expression levels of mTOR and p-mTOR proteins in the cells in OD group were all increased （P<0.05）； compared with OD group， the TG level， the expression levels of FASN and ACACA mRNA， and the expression levels of mTOR and p-mTOR proteins in the cells in OAD group were all decreased （P<0.05）； compared with OAD group， the TG level， the expression levels of FASN and ACACA mRNA， and the expression levels of mTOR and p-mTOR proteins in the cells in OAM group were all increased （P<0.05）. Conclusion ANGPTL6 can improve MCD diet-induced liver lipid accumulation in the mice， and its mechanism may be related to the inhibition of mTOR signaling pathway activity.

Key words: Angiopoietin-like protein 6, Metabolic dysfunction-associated fatty liver disease, Mammalian target of rapamycin, Lipid metabolism, Mice，C57BL/6