Research On The Safeguarding Efficiency And Mechanism Of GLP-1 Mediated High-protein Diet On Abnormal Lipid Metabolism Of Liver In OVX Mice

Objective:Design a diet with different gradient protein concentrations,and keep ovariectomy(OVX)female mice for a long time,and observe the morphological changes of the liver,subcutaneous and retroperitoneal adipose tissue in each group of mice,and the change of glucagon-like peptide-1(GLP-1),Fibroblast growth factor-21(FGF-21)in the serum of mice.To explore the effect of long-term high-protein diet on liver lipid metabolism and white adipose tissue in OVX mice and the possible mechanism of this process.Methods:Thirty-two 8-week-old C57BL/6 female mice were randomly divided into control group,model group,high-protein group and low-protein group,with 8 mice in each group.Model group,high-protein group,low-protein group after ovariectomy were respectively given a standard diet,a high protein diet,a low protein diet.The control group underwent the same operation to preserve their ovaries and were given a standard diet.The experiment lasted for 6 months,all the mice were free to eat and drink water.Record the weight change of mice every week,after the mice were killed at the end of sixth month,the tissues of liver,colon and subcutaneous and retroperitoneal adipose tissue were taken and weighed white adipose tissue.HE staining was used to observe the pathological changes of liver and white adipose tissue,oil red O staining to observe the distribution of lipid droplets in liver cells.The content of GLP-1 and FGF-21 in serum was determined by enzyme-linked immunosorbent assay(ELISA).The expression of FGF-21,liver kinase B1(LKB1),liver sterol regulatory element binding protein-1c(SREBP-1c),atty acid synthase(FAS),and GLP-1 mRNA in colon tissues were detected by real-time quantitative PCR.Immunohistochemical staining was used to detect the expression of SREBP-1c protein in the liver.Results:1.Compared with the control group,the model group gained weight,increased subcutaneous fat in the groin and retroperitoneal fat tissue,compared with the model group,the high-protein group had a lower body weight,and significantly decreased subcutaneous fat in the groin and retroperitoneal fat.There was no statistically significant difference between the low protein group and the model group.2.Both HE staining and Oil Red O staining of the model group showed a large number of lipid droplets,long-term high-protein diet can reduce liver steatosis in OVX mice,The effect of low-protein diet is not obvious.3.The cell volume of adipose tissue in the groin and retroperitoneum of the model group was significantly larger than that of the control group and the volume of fat cells in the high-protein group was significantly smaller than that in the model group were observed in the HE staining,low protein group changes are not obvious.4.Compared with the control group,the expression of GLP-1mRNA in the colon tissue of the model group was decreased,and the content of GLP-1 in the serum was reduced.The high-protein diet can promote the expression of GLP-1mRNA in the colon tissue of OVX mice and increase the GLP-1 protein content in the serum.There was no statistically significant difference between the low protein group and the model group.5.Compared with the control group,the expression of FGF-21 mRNA in the liver tissue and the content of FGF-21 protein in the serum increased in the model group.The long-term high-protein diet can significantly down-regulate the expression of FGF-21 mRNA in the liver tissue and reduce the FGF-21 protein in serum of OVX mice.6.The expression of SREBP-1cmRNA,protein and FAS mRNA in the liver tissues of the model group were higher than those of in the control group,while the expression of LKB1 mRNA decreased.the long-term high-protein diet can reverse the changes above in the OVX mice,there is no statistically significant difference between the low protein group and the model group.Conclusion:After long-term administration of a high-protein diet to OVX mice,the weight gain of the mice slowed down,the liver steatosis was improved,and the accumulation of fat in the groin and retroperitoneum was reduced.It is suggested that long-term high-protein diet can play a role similar to estrogen,and it may be related to the mechanism of high-protein diet promoting intestinal secretion of GLP-1,improving FGF-21 resistance,and upregulating LKB1 to activate AMPK pathway reduces the expression of SERBP-1c mRNA and protein in the liver and reduces lipid synthesis.