| The development of our society has increased the average age of today’s population and thereby also changed the lifestyle of people.Non-alcoholic fatty liver disease(NAFLD)has been common in chronic liver injury.NAFLD is,in a way,a lifestyle disease.The disease spectrum of NAFLD includes changes ranging from steatosis to steatohepatitis,as well as those ranging from cirrhosis to hepatocellular carcinoma.This common disease is also associated with symptoms,such as insulin resistance(IR),type 2 diabetes,and obesity.Previous studies have found that glycerol-3-phosphate acyltransferase-4(GPAT4)is highly expressed in the adipose tissue and liver of mice and plays a role in triglyceride synthesis.Gene overexpression and gene knockout experiments have confirmed that GPAT4 is important in the development of obesity,liver steatosis,and IR.GPAT4 mapping in the endoplasmic reticulum,and it is involved in the synthesis of endoplasmic reticulum lipids.Related studies have confirmed that endoplasmic reticulum stress(ERS)is possibly involved in the pathogenesis of IR and NAFLD.To further explore whether there is an association among IR,NAFLD pathogenesis,and GPAT4,in this study,a mouse model with a GPAT4 knockout in the liver was built to observe the differences in phenotypes between mice with the GAPT4 knockout and those without it upon administration of the D09100301 diet-a special high-fat diet rich in trans fatty acids.Moreover,possible mechanisms of action were explored by detecting ERS-related signaling molecules so as to deepen our understanding of the pathogenesis of IR and NAFLD and provide a theoretical basis for the development of therapeutic drugs in the future.Objective: To explore the role of GPAT4 in the pathogenesis of diet-induced hepatic steatosis and IR in mice.Methods:1.The establishment and identification of the liver GPAT4 knockout model: the mouse model with a GPAT4 knockout in liver was established using the Cre/lox P recombinase system.The specificity and efficiency of GPAT4 knockout in the liver were verified through genotyping,quantitative real-time PCR(q RT-PCR),and western blotting.2.The establishment of the dietary induction model: male and female GPAT4-knockout mice aged 6 weeks were selected for the experimental group(GPAT4-LKO group,n = 10),and littermate flox mice having the GPAT4 gene loxp marker were selected for the control group(GPAT4-FLOX group,n = 10).The mice were fed the D09100301 diet,which contains 40%fat(30% of which is made up by trans fatty acids),20% fructose,and 2% cholesterol.Then,IR and NAFLD were induced in the mice to establish the IR and NAFLD models.3.The detection of the metabolic index and ERS: for both the GPAT4-LKO group and the GPAT4-FLOX group,a glucose tolerance test was conducted on the 10 th week after the mice were fed the D09100301 diet.After the 12 th week,serum was collected and insulin,blood lipid,liver lipid,and liver function indicators were tested.The liver tissue was stained with Oil Red O and HE,and a pathological evaluation was performed for comparison.The ERS indicators of hepatocytes were detected through q RT-PCR.Results:1.The mice were fed the D09100301 diet for 12 weeks,and their weights were recorded every week.During this period,there was no significant difference in body weight between the GPAT4-LKO group and the GPAT4-FLOX group,and no significant storage of visceral fat was observed.Compared to those in the GPAT4-FLOX group,the indicators of fasting blood glucose,glucose tolerance test results,and HOMA-IR in the mice in the experimental group were significantly reduced(P<0.05,P<0.01).2.Compared to those in the GPAT4-FLOX group,the contents of liver lysophosphatidic acid(LPA),glycerol diester(DAG),and triglyceride(TAG)in the GPAT4-LKO group were significantly reduced(P<0.05,P<0.01)in female mice by 17.16%,8.09%,and 11.55%,respectively,and in male mice by 24.68%,16.08%,and 18.11% respectively.Liver injury was alleviated in the GPAT4-LKO group,and the AST indicators were significantly different from those in the GPAT4-FLOX group(GPAT4-LKO vs.GPAT4-FLOX: 214.92 vs.369.97 IU/L,P<0.05).Significant hepatic ballooning degeneration and inflammatory cell infiltration were observed in the liver pathological sections of the GPAT4-FLOX group.Six out of the 10 mice in the GPAT4-FLOX group were found to have jaundice and splenomegaly.3.q RT-PCR was used to detect the expression of mRNAs in three signaling pathways of ERS in the two groups.Compared to that in the GPAT4-FLOX group,the mRNA expression of GRP78,CHOP,ATF6,XBP-1,eIF2α,and ATF4 in the livers of the mice in the GPAT4-LKO group was significantly decreased(P<0.05).Conclusion:1.The D09100301 diet can induce hepatic steatosis and IR in mice,while the knockout of liver GPAT4 can significantly improve D09100301 diet-induced hyperglycemia and insulin resistance and reduce hepatic steatosis in mice.2.The mechanism of the alleviation of diet-induced NAFLD and IR in mice with a knockout of liver GPAT4 may involve the down-regulation of ERS-related signaling molecules. |
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