| Background:Obesity has become a global problem endangering public health.Most western countries have entered the later stages of a healthy transition.High-fat,high-cholesterol,high-sugar,high-energy,low-fiber diets and sedentary lifestyles are common,and energy consumption has been significantly reduced,leading to obesity.Over the past three decades,the prevalence of obesity in China has also increased sharply due to rapid economic growth,social development,and urbanization.Although obesity itself is not directly life-threatening,its occurrence is often accompanied by disturbances in the metabolic functions of tissues and organs in the body,leading to the occurrence of multiple diseases such as cardiovascular disease,type 2 diabetes,asthma,sleep apnea,fatty liver disease,etc.Therefore,the prevention and treatment of obesity is still very important.Objective:TGR5 is a member of G-protein-coupled receptors(GPCRs).Because it can be activated by bile acids,it is also called G-protein-coupled bile acid receptor,GPBAR1).It is expressed in human and animal multi-tissue organs.TGR5 receptors can not only be activated by bile acids to participate in bile concentration and secretion processes,but also play an important role in many pathways of human glucose metabolism,lipid metabolism,and energy metabolism.Previous studies have shown that after TGR5 is activated by bile acid stimulation,it can increase the energy consumption of brown fat in mice,and alleviate the fat accumulation caused by a high-fat diet.TGR5 activation can increase c AMP levels in brown adipose tissue of mice,thereby enhancing type II deiodinase(D2)-mediated conversion of thyroid hormone(T4)to3,5,3’-triiodothyronine(T3)This process enhances the expression of uncoupling protein(UCP),thereby increasing brown fat energy consumption.AQP8 is a member of the aquaporin(AQP)family.As a membrane channel protein,AQP8 can mediate the transport of water,ammonia,hydrogen peroxide,etc.,and exhibit a variety of biological functions.The results of our previous studies showed that,under the induction of high-fat food intake,obesity formation in AQP8 gene knockout mice increased significantly,and liver fat metabolism was significantly enhanced.However,it is unclear how the function of peripheral brown adipose tissue in obese mice changes.In this experiment,wild-type C57 BL / 6J(C57)mice and AQP8 gene knockout C57BL/ 6J(AQP8-/-)mice were used to establish an obesity model by feeding on a high-fat diet,and to observe changes in bile secretion and brown adipose tissue function.To explore the role of brown adipose tissue in the process of AQP8 gene deletion and obesity exacerbation,and provide a new theoretical basis for the formation and prevention of obesity.Methods:1.Preparation of mouse obesity model: Four-year-old wild-type C57 BL / 6J(C57)mice and AQP8 gene knockout C57 BL / 6J(AQP8-/-)mice were selected.High-fat diet was fed for 8 weeks and the body weight and body fat rate of the mice were measured.2.After the body fat percentage of the mice was measured at the end of 8 weeks of feeding,some C57 mice and some AQP8-/-mice were randomly selected,and the gallbladder was removed to collect bile after anesthesia.The remaining C57 and AQP8-/-mice were sacrificed after blood extraction,and liver,brown adipose tissue,and intestinal feces were collected from the mice.ELISA method was used to determine the bile acid content of liver,gallbladder bile,serum and intestinal feces in two groups of mice and the content of T3 in brown fat;Western blot and real-time quantitative PCR were used to determine TGR5,UCP1,and type II deiodination in brown fat Enzyme nucleic acid and protein expression levels.Results:1.The body weight and body fat percentage of AQP8-/-mice after high-fat feeding were significantly higher than those of C57 mice.After 8 weeks of high-fat feeding,the body weight and body fat percentage of mice in the AQP8-/-group were significantly higher than those in the C57 group(P<0.01,P<0.01).2.After high-fat feeding in AQP8-/-mice,the amount of bile in the gallbladder was significantly reduced compared with the C57 group control group(P <0.01),but the total bile acid content was not significantly different.In addition,the total bile acid content of different tissues and organs also changed significantly.Compared with the wild control group,the total bile acid content in the liver of AQP8-/-mice was significantly increased(P <0.01),the total bile acid content in serum was significantly reduced(P <0.05),and the total bile acid content in intestinal feces was significantly reduced.(P <0.01).3.The m RNA expression of bile acid membrane receptor TGR5 in brown adipose tissue cells of AQP8-/-mice after high-fat feeding was significantly down-regulated(P<0.01).4.The content of triiodothyronine(T3)in brown adipose tissue of AQP8-/-mice after high-fat feeding was significantly decreased(P <0.01).Compared with C57 mice,m RNA and protein expression of type II deiodinase(D2)in brown adipose tissue did not change significantly.5.After high-fat feeding of AQP8-/-mice,the m RNA and protein expressions of UCP1 in brown adipose tissue were significantly down-regulated compared with wild control mice(P <0.05,P <0.05).Conclusions:After AQP8 gene is knocked out,high-fat food intake can increase obesity in mice.The decline of brown adipose tissue function is an important cause of exacerbating the formation of obesity.The mechanism may be that the deletion of the AQP8 gene leads to a decrease in the intestinal and serum bile acid content of mice,which in turn leads to a decrease in the expression of TGR5,a decrease in T3 content,a decrease in UCP1 expression,and a decrease in energy consumption in brown adipose tissue of mice,thereby exacerbating obesity formation. |
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