| BackgroundIn recent years,with the improvement of people’s living standards and changes in people’s diet,the number of overweight people in the world has increased significantly.It has been predicted that more than 57.8%adults worldwide will suffer from overweight or obesity problems by 2030,which will become a major threat to people’s health and bring a heavy burden to society.Obesity has been officially listed as a disease by the World Health Organization in 2000.Obesity,as the basic diseases related to many metabolic diseases,its pathophysiological mechanism is still unclear.Besides,there are still no effective therapy strategies for obesity treatment.Therefore,the researches based on the underline pathogenesis for obesity are of great significance.The energy intake is greater than the expenditure in obesity patients and excessive energy is stored in the form of triglycerides（TAG）in adipose tissue,leading to adipocyte hypertrophy.Except for serving as an energy storage organ,adipose tissue also acts as an endocrine organ that secrets adipokines to regulate metabolism.Whereas the hypertrophic adipocytes are dysfunctional which result in abnormal adipokines secretion,further promoting the development of obesity.Therefore,inhibit adipocyte hypertrophy and improve adipose function can be effective therapeutic strategies for obesity and related metabolic disorders.The renin-angiotensin system（RAS）has been known for more than 120 years and its classic physiological effect is to regulate blood pressure and fluid and electrolyte metabolic balance.However,recent studies have confirmed the important role of RAS in the occurrence and development of obesity and other metabolic diseases.Researches showed that RAS is over-activated and the serum angiotensin II（Ang II）level is higher in obesity patients than that in the normal population,while the correlation between Ang II and obesity has not been established.As the predominant peptide of RAS,Ang II exerts biological effects mainly by binding with angiotensin type 1 receptor（AT1R）.Therefore,a rat model with AT1aR gene knockout were established in our present study to explore the role of adipose AT1R in diet-induced obesity and related metabolic disorders.Objective:Obesity is basic disease of many chronic metabolic diseases that endangering human health.Therefor,the underline mechanism for the occurrence of obesity has received more and more attention.As the main receptor of AngⅡ,the special role of angiotensin II type 1 receptor（AT1R）in obesity is less studied and the findings are controversial.Therefore,this study aims to explore the role of AT1aR in high-fat diet obesity and insulin resistance with focus on adipose tissue.Methods:1.Wild-type（WT）and AT1aR gene knockout(AT1aR-/-)SD rats were fed with normal chow diet and 60%high-fat diet for 12 weeks respectively and body weight changes were recorded weekly.2.After 12 weeks of fedding,fasting blood glucose,insulin tolerance test（ITT）and oral glucose tolerance test（OGTT）were measured.3.Blood pressuere was measured by carotid artery cannulation.4.Blood was collected from the abdominal aorta and then centrifuged for serum.The serum levels of insulin and indicators related to lipid metabolism were detected with commercial kits.5.The bilateral epididymal adipose tissue were isolated and weighed,and the morphology of adipocytes were visualized by HE staining.6.RT-PCR was used to detect the transcriptional expressions of key enzymes related to lipid synthesis such as acetyl-Co A carboxylase and fatty acid synthase and correlation factors responsible for adipogenic differentiation and energy metabolism like fatty acid oxidation in adipose tissue.7.The levels of non-esterified fatty acids（NEFAs）and glycerol that released from adipose tissue within 24 h were measured with commercial kits.8.Protein expressions of lipolysis rate-limiting enzymes such as adipose triglyceride lipase and hormone sensitive lipase,protein kinase A（PKA）,protein kinase C（PKC）and proteins related to insulin signaling in adipose tissue were assayed with western blot.9.ELISA was used to detect the level of cyclic adenosine monophosphate（cAMP）in adipose tissue homogenate.Results:1.AT1aR knockout reduced body weight and epididymal fat weight.The cross-sectional area of adipocyte in high-fat diet AT1aR-/-rats was smaller than that in WT rats,demonstrating that AT1aR knockout improved adipocyte hypertrophy induced by high-fat diet.2.The levels of serum total cholesterol（T-CHO）,triglyceride（TG）,free fatty acids（NEFAs）,glycerol（Glycerol）and low-density lipoprotein（LDL）in AT1aR-/-rats with high-fat diet were much lower than those of WT rats,indicating that AT1aR deficiency improved dyslipidemia caused by high-fat diet.3.The gene knockout of AT1aR increased gene expressions of adipogenic differentiation-related factors PPARγand SREBP-1c.4.AT1aR knockout promoted adipose lipolysis by upregulating protein expressions of lipolysis-related key enzymes such as adipose triglyceride lipase（ATGL）and hormone sensitive lipase（HSL）,and thus increased the levels of glycerol and NEFAs released from adipose tissue within 24 h compared with WT rats.However,there were no changes in gene expressions of lipid synthesis-related enzymes like fatty acid synthase（FAS）and acetyl-Co A carboxylase（ACC）between WT and AT1aR-/-rats,demonstrating that AT1aR knockout improved adipocyte hypertrophy via elevating adipose lipolysis.5.AT1aR knockout elevated energy metabolism and fatty acids oxidation in adipose tissue.6.The cyclic adenosine monophosphate（cAMP）contents and protein expressions of PKA in the adipose tissue of AT1aR-/-rats were increased,indicative of activating the cAMP/PKA pathway.7.Fasting blood glucose,serum insulin level and insulin resistance index（HOMA-IR）were significantly reduced in high-fat diet AT1aR-/-rats.In response to glucose load or insulin injection,the area under the curve（AUC）in high-fat diet AT1aR-/-rats was significantly lower than that in the HFD-fed WT rats,indicating AT1aR-/-improved OGTT and ITT.8.AT1aR knockout improved insulin signal transduction in the adipose tissue of high-fat diet rats.9.AT1aR knockout reduced PKCα,PKCεand PKCηprotein expressionss in adipose tissue.Conclusion:The gene knockout of AT1aR promoted adipogenic differentiation and accelerated adipose lipolysis by activating the cAMP/PKA pathway and thereby significantly inhibited high-fat diet-induced adipocyte hypertrophy.Besides,AT1aR knockout improved insulin signal transduction and inhibited PKCs protein expressions in adipose tissue,and thus significantly improved high-fat diet induced insulin resistance. |
PDF Full Text Request