The Mechanism Of Chemerin In Aerobic Exercise-induced Improvement Of Glucose Metabolism In Diabetic Mice

Object The previous research of our group has shown that as an adipokine and an inflammatory factor,chemerin exerts important roles in the occurrence and progression of obesity and type 2 diabetes mellitus(T2DM).And the decrease of chemerin caused by aerobic exercise plays an important role in improving the glucose metabolism in T2 DM mice.However,it has not yet been fully elucidated that how does the decrease of chemerin improves glucose metabolism.In recent years,Glucagon-like peptide-1(GLP-1)has been found to play an important role in the prevention and treatment of T2 DM.And its receptor agonist liraglutide has been used for the clinical treatment of T2 DM.GLP-1 is mainly secreted by intestinal L cells and has the effects of promoting the production of islet beta cells,inhibiting the apoptosis of beta cells,and improving the function of beta cells.In view of the expression of chemerin in the colon and the ability of chemerin to regulate the gut microbiota and inflammatory bowel disease,we speculate that the effect of chemerin on the regulation of glucose metabolism may be caused by the increase of GLP-1 and the improvement of islet function and structure.Therefore,the main purpose of this article is to use exogenous chemerin to investigate whether the mechanism that the decrease of chemerin improves the glucose metabolism of T2 DM mice is related to the change of GLP-1.At present,there are no reports on the regulation of GLP-1 by chemerin in vivo and in vitro.Therefore,another purpose of this study is to explore the changes of GLP-1 levels in adipose tissue-specific chemerin gene knockout mice fed with normal and high-fat diet.In another word,we verify whether chemerin has a regulatory effect on GLP-1 by determining the effect of chemerin knockdown or knockout on the level and function of GLP-1 in the colon and serum of mice.Furthermore,we study the regulatory effect of aerobic exercise on the level and function of GLP-1 in adipose tissue-specific chemerin gene knockout mice,to determine whether the role of reducing chemerin in improving glucose metabolism is related to the regulation of GLP-1.Methods Part 1.Effects of exogenous chemerin on the GLP-1 level and islet structure of diabetic mice with exercise.1.Modeling of diabetic mice 50 male ICR mice at the age of six weeks were randomly divided into control group(Con,n=6),and diabetes model group(n=44).Mice in the control group were fed with normal diet.And mice in the diabetes model group were intraperitoneally injected with a small dose of streptozotocin(STZ,100 mg/kg)after six weeks of highfat diet(HFD).Fasting blood glucose(FBG)was measured on the 3rd and 7th days after the injection.And the diabetes modeling was determined to be successful if both FBG were greater than 11.1 mmol/L.2.The plan of grouping,exercise,and chemerin injected in Diabetic mice All the successfully established diabetic mice were divided into diabetes group(DM,n=6),diabetes plus exercise group(EDM,n=6),and diabetes plus exercise and exogenous chemerin group(EDMC,n=6).All the mice in EDM and EDMC groups participated in a six-week modest intensity treadmill running exercise with gradually increased load,six days per week and one time per day.And all the mice in the EDMC group were intraperitoneally injected with exogenous chemerin(with the dose of 8 ng/g)from the 4th week of the exercise period,six days per week,and one time per day.Part 2.The changes of adipose tissue-specific chemerin gene knockout mice in the level of GLP-1 and the function and structure of islet,and the regulatory effect of exercise on it.1.Modeling of adipose tissue-specific chemerin gene knockout mice Shanghai model organisms were commissioned to construct adipose tissuespecific chemerin gene knockout mice by using the Cre-lox P system.Newborn mice were raised to 2 weeks of age,and their tails were cut out about 0.5 cm for DNA detection to screen adipose tissue-specific chemerin gene knockout mice.2.The changes of adipose tissue-specific chemerin gene knockout mice fed with normal and high-fat diet in the level of GLP-1 and the function and structure of islet Animal grouping: Wild type C57 mice fed with normal diet(Con-ND),chemerin knockout heterozygote mice fed with normal diet [chemerin(+/-)-ND],and chemerin knockout homozygotes mice group [chemerin(-/-)-ND].All mice were fed with normal diet for 11 weeks.In addition,the other three groups similar to the groups above were also set with the HFD.Totally,there are 6 groups with four mice each group.3.Effects of aerobic exercise on adipose tissue-specific chemerin gene knockout mice fed with HFD in the level of GLP-1 and the function and structure of islet 8-week-old male Wild type C57 mice and chemerin knockout homozygotes mice were fed with HFD for 5 weeks,and then randomly divided into four groups: control group(Control),control group plus exercise(Control+E),chemerin knockout homozygotes group [chemerin(-/-)] and chemerin knockout homozygotes plus exercise group [chemerin(-/-)+E],with 4 mice in each group.The mice in each group continued to be fed with HFD,while the mice in the chemerin(-/-)group and chemerin(-/-)+E group were given treadmill aerobic exercise for 6 weeks.The detection indexes and methods are the same as above.4.Detection index and method After the mice of each group were executed under anesthesia,the samples such as colon,pancreas,and serum were collected.The m RNA level of GLP-1 in the colon was detected by real-time PCR.And the protein level of GLP-1 in the colon was detected by western blot.ELISA was used to detect the total GLP-1 level in serum.Pancreatic HE staining was used to observe the structure of islets.Results Part 1.Exogenous supplementation of chemerin reverses the effects of aerobic exercise on diabetic mice in the level of GLP-1 and the structure of islet 1.Exogenous supplementation of chemerin reverses the effects of aerobic exercise on the level of GLP-1 in the colon and serum of diabetic mice Aerobic exercise significantly increased the m RNA and protein levels of GLP-1 in the colon of diabetic mice,which could be reversed by exogenous chemerin.In addition,exogenous chemerin tended to reduce the level of GLP-1 in the serum of diabetic mice with exercise,but there was no statistical significance.2.Exogenous chemerin reverses the effect of aerobic exercise on the islet structure of diabetic mice Aerobic exercise can improve the structure of islets in diabetic mice,which is characterized by the decrease of vacuolar degenerative cells and the decrease of shrinking islets.On the other hand,exogenous chemerin led to the shrinkage of the islet,unclear boundary,uneven distribution of islet cells,vacuolar degeneration of some cells.Part 2.Adipose tissue-specific chemerin gene knockout mice are increased in the level of GLP-1 in colon and serum,and the regulatory effect of exercise on it.1.The level of colonic chemerin in adipose tissue-specific chemerin gene knockout mice is decreased The m RNA level of colonic chemerin in the chemerin knockout homozygotes mice fed with normal diet was significantly lower than that in the control group.And the m RNA level of colonic chemerin in the chemerin knockout heterozygote and homozygote mice fed with HFD was significantly lower than that in the control group.2.Adipose tissue-specific chemerin gene knockout mice fed with normal and high-fat diet are increased in the level of GLP-1 in colon and serum The m RNA level of colonic GLP-1 in the chemerin knockout heterozygote mice fed with normal and high-fat diet was both significantly higher than that in the control group.The protein level of colonic GLP-1 in the chemerin knockout homozygote mice fed with HFD was significantly higher than that in the control.And the level of total GLP-1 in the serum of the chemerin knockout homozygote mice fed with both normal and high-fat diet was significantly higher than that in the control group.3.Functional and structural of islets is changed in adipose tissue-specific chemerin gene knockout mice Compared with the control group,after 60 min of oral glucose in the OGTT test,the blood glucose concentration of adipose tissue-specific chemerin gene knockout mice fed with both normal and high-fat diet are significantly decreased.In addition,the structure of the islet in the control mice fed with HFD was damaged,which was characterized by islet atrophy,reduced volume,reduced number,sparse distribution,irregular shape,unclear boundary,and disordered arrangement.On the other hand,the structure of islet in adipose tissue-specific chemerin gene knockout mice fed with HFD was almost normal,which was characterized by a clear structure,regular shape,and clear boundary.These results suggest that the knockout of chemerin in adipose can improve the function and structure of islets in HFD mice,which often have glucose metabolism disorder.4.Effects of aerobic exercise on adipose tissue-specific chemerin gene knockout mice fed with HFD in the level of GLP-1 and the function and structure of islet Aerobic exercise significantly increased the m RNA level of GLP-1 in the colon of mice.And the knockout of chemerin in adipose can further increase the level of GLP-1 in the colon and serum of exercise mice fed with HFD.In addition,both exercise and the knockout of chemerin could significantly improve the hypoglycemic function and the structure of islets in mice.Exercise could further improve the structure of islet in adipose tissue-specific chemerin gene knockout mice,but did not further enhance their hypoglycemic function of the islet.Conclusion 1.The decrease of chemerin induced plays an important role in improving glucose metabolism in diabetic mice,and this effect may be related to that the decrease of chemerin up-regulates the level of GLP-1 and further improves the function and structure of islet.2.The knockout of chemerin in adipose can increase the level of GLP-1 in colon and serum and improve the function and structure of islets in mice fed with HFD,indicating that chemerin can regulate the level and function of GLP-1.3.Aerobic exercise increased the level of colonic GLP-1 in mice fed with HFD,while the knockout of chemerin in adipose further increased the level of GLP-1 levels in colon and serum in exercise mice fed with HFD.