Abstract:

The purpose of this study is to investigate the changes in mitochondrial function and energy metabolism in the liver during the entire process of insulin resistance by establishing a mouse model. A total of 60 male C57BL6 mice were randomly selected and divided into three groups: a control group (Con group) fed with normal maintenance feed; a high-fat diet group (HFD group) fed with high-fat feed. The model was established by randomly selecting six mice from each group at weeks 4, 6, 8, 10, and 12 of feeding. The successful establishment of the whole-process model of insulin resistance was confirmed by insulin resistance assessment and histopathological examination. At the 8th and 12th weeks of the experiment, blood was collected from the tail of the mice for IGTT and ITTs. At weeks 4, 6, 8, 10, and 12 of the experiment, serum and liver tissue samples were collected from the mice for testing: 1) fasting blood glucose and serum content were measured; 2) The contents of Srebp-1c enzyme, PFK1, and COX-I in liver tissues were detected by ELISA. 3) Biochemical detection of ALT and AST levels in serum; 4) Western blot was used to detect expression level of PI3K, Akt, P-Akt, GLUT4, GSK-3β, P-GSK-3 β, FOXO1, P-FOXO1, SIRT1, AMPK, P-AMPK, and PGC-1 α protein in liver tissue; 5) Transmission electron microscopy, HE staining, oil red O staining, and PAS staining were used to detect changes in the pathological organization and structure of the liver. The results showed that: 1) 12 weeks of high-fat diet caused obesity and increased HOMA-IR in mice, and oil red O staining showed significant fat deposition, successfully inducing a model of insulin resistance in the entire mouse. During insulin resistance, the levels of ALT and AST in mice increased, and HE results showed significant lipid droplet vacuoles and structural disorder of liver cells. 3) After the fourth week of feeding a high-fat diet, the upstream signaling of insulin in the liver began to be affected; Compared with the Con-6 group, the expression of GLUT4 protein and the ratio of P-FOXO1/FOXO1 as well as the content of PFK1 in the liver of HFD-6 group mice significantly decreased (P < 0.01); Compared with the Con-4 group, the GSK-3β expression in the liver of the HFD-4 group mice Phosphorylation and Srebp-1c enzyme levels gradually decreased (P < 0.05); The PAS results showed that from the 8th week, the glycogen content in the liver cells of HFD mice decreased; Compared with the Con-4 group, the AMPK, P-AMPK, and SIRT1 contents in the liver of the HFD-4 group significantly decreased (P < 0.01 and P < 0.001); 6) In the HFD group, the expression of Mfn2 in the liver increased at week 10, while the expression of Drp1 protein showed a trend of decrease first and then increase. Compared with the HFD-6 group, the PINK1 and Parkin proteins in the liver of the HFD-6 group mice decreased significantly (P < 0.05). In summary, the liver, as the main organ of metabolism, undergoes selective insulin resistance after feeding 60% high-fat feed. After resistance, overall energy catabolism decreases, mitochondrial damage increases, and autophagy, which clears damaged mitochondria, weakens. In addition, there is a brief increase in mitochondrial biogenesis and fusion at weeks 8 and 10, indicating a temporary compensatory effect due to energy deficiency in the liver. This study explains the characteristics and regularities of energy metabolism in hepatic insulin resistance from the perspective of the entire process, providing a reference for further studying the mechanism of excess nutrients affecting cellular energy metabolism.

Key words: high fat diet (HFD), insulin resistance, liver, mitochondria, energy metabolism, mice