The Mechanism Of High Altitude Hypoxia Effect On Mitochondrial Function In Obese Mice

Obesity is one of the diseases threatening human health,it leads to the growing popularity of related complications,such as insulin resistance,type 2 diabetes mellitus and Nonalcoholic fatty liver disease.As to obesity,high-calorie diet and a sedentary lifestyle are the most common factors.Globally,the prevalence of obesity is on the rise.In China,the latest epidemiology investigation shows that the incidence of obesity varies with geographical location,the prevalence of obesity in high altitude significantly below the plains.There are similar reports abroad,epidemiological data have shown that the incidence of overweight and obesity is inversely related to altitude,with the prevalence of besity significantly higher among adults individuals living at altitudes of 0–499 m compared to those living at 3000 m above sea level.Insulin resistance is one of the most common complications of obesity,and a growing number of studies have shown a close relationship between mitochondrial function and insulin resistance.Skeletal muscle is an important target organ of insulin,and mitochondria dysfunction leads to glucose and lipid metabolism disorder,induces glucose and lipid toxicity,and further affects the insulin signaling pathway.NAFLD is another common complication of obesity.Insulin resistance elevates the flux of free fatty acids(FFAs)into hepatocytes and increases the synthesis of FFAs in liver.Steatosis develops if these FFAs are incompletely oxidized or if they are secreted.Hepatic steatosis makes the liver susceptible to mitochondrial dysfunction,imbalance of lipid homeostasis,reactive oxygen species(ROS)production,and so on.Numerous studies have indicated that hepatic mitochondria play a vital role in the pathogenesis of NAFLD.Adenosine 5'-monophosphate-activated protein kinase(AMPK)is an energy sensor that regulates energy metabolism and maintains mitochondrial homeostasis.AMPK activation promotes mitochondrial biogenesis and fatty acid oxidation.Based on the above studies,this study investigated the mechanisms of changes in body weight,insulin sensitivity and lipid metabolism,skeletal muscle mitochondrial function and liver mitochondrial function in obese mice with high altitude chronic hypoxia,and further explained the effects of high altitude chronic hypoxia on obesity-related metabolic diseases.Part I Effects of high altitude hypoxia on body weight,insulin sensitivity and lipid metabolism in obese miceObjective: To investigate the changes of body weight,insulin sensitivity and lipid metabolism in obese mice at different altitudes.Methods: 60 male C57 BL / 6J mice were randomly divided into four groups: Control group,high-altitude hypoxia(CHH)group,high-fat diet(HFD)group and high-fat diet under high-altitude hypoxia group,with 15 mice in each group.The Control group and CHH group were fed with normal diet(10% energy).The HFD group and HFD-CHH group were fed high-fat diet(60% energy).Control and HFD groups were raised altitude 50 m.CHH and HFD-CHH groups were raised altitude 4,300 m.Body weight and food intake were measured weekly,After 8 weeks,glucose tolerance test and insulin tolerance test were measured.hemoglobin(Hb),red blood cell(RBC)count and hematocrit,fasting serum insulin,serum triglycerides and free fatty acids were measured,HOMA-IR index was calculated,and epididymal visceral adipose tissue were weighed and were performed with hematoxylin and eosin stain.Results: Compared with the control group,there were no significant changes in body weight,glucose tolerance,insulin sensitivity,triglycerides,free fatty acids and HOMA-IR in the high-altitude hypoxia group(CHH group)at 8 weeks.Compared with plain HFD group,body weight of HFD-CHH group mice decreased,glucose tolerance and insulin tolerance improved,triglycerides,free fatty acids and HOMA-IR index after 8 weeks.Conclusion: High altitude hypoxia reduced the weight of HFD-induced obese mice,enhanced glucose uptake and clearance,enhanced insulin sensitivity and improved lipid metabolism.Part II Effects of high altitude hypoxia on skeletal muscle mitochondrial function and insulin signaling pathway in obese miceObjective: To investigate the changes of skeletal muscle mitochondria in obese mice with high altitude hypoxia and further effected on insulin signaling pathway.Methods: After 8 weeks of feeding,the mitochondrial respiratory function of skeletal muscle fibers were measured and permeabilized.Morphological and molecular biology experiments were used to observe the changes of lipid deposition under microscope,mitochondrial structure and quantity under electron microscope in skeletal muscle tissue,and the expression levels of P-AMPK,lipid content,lipid metabolism-related genes,mitochondrial biogenesis-related genes and AKT in skeletal muscle tissue were measured.Results: Compared with HFD group,skeletal muscle tissue lipid deposition was reduced,AMPK was activated,and mitochondrial biogenesis function was improved.Skeletal muscle tissue mitochondria showed increased oxygen availability,mitochondrial activity and promoted the expression of AKT in the insulin signaling pathway.Conclusion: High altitude hypoxia improved mitochondrial function,reduced lipid deposition,promoted the expression of AKT related to insulin signaling pathway in HFD-induced obese mice.Part III Effects of high altitude hypoxia on mitochondrial function and lipid deposition in liver of obese miceObjective: To investigate the changes of mitochondria function and lipid deposition in liver with mice under high altitude hypoxia.Methods: Mitochondrial respiratory function of liver homogenate were measured on site after 8 weeks.Morphological and molecular biology experiments were used to observe the changes of lipid deposition under microscope,and detected the expression levels of P-AMPK,lipid content,lipid metabolism related genes.Mitochondrial respiratory control ratio,coupling efficiency,mitochondrial biogenesis pathway related genes,mitochondrial DNA content,ROS and other relevant indicators were measured.Results: Under high-altitude hypoxia,the liver AMPK of obese mice was activated,fatty acid oxidation was enhanced,mitochondrial biogenesis was improved,antioxidant capacity was enhanced,and lipid deposition was reduced.Conclusion: High altitude hypoxia improve mitochondrial function and lipid deposition in the liver of obese mice.