The Regulation Effect Of Liraglutide On Myocardial Autophagy In Rats Induced By A High-fat Diet

Autophagy means self-eating,that means the cell digests and clears intracellular components.It is an evolutionarily conserved metabolic pathway.Autophagy is a kind of basic cellular process.It functions to degrade and recycle some long lived-proteins and damaged organelles,mainly maintain the cellular homeostasis and survival.Autophagy is believed to play an important role in the maintenance of cell activity,it meets the needs of the cell metabolism and organelles update.It also reacts to the changes of internal and external environmental pressure,maintaining the normal cellular function.Under normal physiological condition,if autophagy is suppressed can lead to the accumulation of harmful substances,while excessive autophagy will destroy the normal structure of cell.So either overexpression or defection of autophagy will cause cellular damage.As a common life phenomenon,autophagy participates in broadly various of physiological and pathological processes.Since autophagy is full of significance in many pathologic conditions,regulating autophagy may become the targets in certain human diseases.Myocardial cell is a kind of long life and anaphase cell,with limited differentiation regeneration ability.Myocardial cell autophagy plays an important role in the maintenance of cardiac function and activity.In a variety of heart diseases,including myocardial infarction(MI),and dilated cardiomyopathy(DCM),there exists accumulation of protein aggregates and dysfunctional organelles,implying that autophagy may be insufficient in these diseases.Research has been shown that autophagy can affect myocardial remodeling and other heart diseases,thus regulating autophagy may become one of the potential targets for prevention and control of cardiovascular disease.Glucagon like peptide 1(GLP-1)is one of the physiologic peptide hormone secreted by small intestine L cells.It can promote insulin cell proliferation and differentiation to increase the synthesis and secretion of insulin.It involves in many cell process and attracts more and more interests.Now researchers are not only focuses on pancreas.Many studies showed that GLP-1 protects important organs such as heart,kidney and so on,experiment on cells demonstrated that GLP-1 is associated with the changes in the level of autophagy in islet cell.But whether it affects the myocardial autophagy as well is unknown.In our study,we will observe the effect of liraglutide on the myocardial autophagy in high-fat-diet rats,and further explore the mechanisms.Objective: Examining the effect of liraglutide on the myocardial autophagy in high-fat-diet rats,assaying the expression of autophagy-related molecules,and further to explore the potential mechanisms.Method and Materials: Totally 48 Sprague Dawldy(SD)rats were randomly divided into five groups: normal control group(Con),high-fat diet group(HF),high-fat diet with 3 doses of liraglutide.Rats in normal diet group were given a normal diet,and the rats in high-fat diet group were provided with a high-fat diet.Each group contents eight rats.Liraglutide diluted with saline to obtain a mixture,each experimental group were subcutaneously injected with corresponding concentration,the normal and high-fat-diet group received saline.Body weight was monitored weekly.After 12 weeks,the rats were killed by abdominal aorta bleeding.Serum fasting blood glucose,triglyceride(TG),total cholesterol(TC),LDL-C and HDL-C were detected.ELISA kits were performed to analysis B-type natriuretic peptide(BNP)levels.The expression of Beclin 1,LC3-?,ATG7 and p62 mRNA in each group were determined by Real-Time polymerase chain reaction,the protein expression of Beclin1,LC3-B,AMPK,P-AMPK,mTOR and P-mTOR were detected by Western-blot.Results:1 Effect of Liraglutide on body weight:After 12 weeks,the Body weight of HF group showed a significant increase compared to Con group(P<0.05),and the body weight in liraglutide group was decreased markedly than HF group(P<0.05),but there are no difference between each liraglutide group(P>0.05)2 Effect of Liraglutide on blood glucose and blood lipid level: At the end of 12 th week,blood glucose and TG in HF group were significantly higher than in Con group(P<0.05),treatment with different amounts of liraglutide had decreased the content of blood glucose and TG in serum(P<0.05),3 Effect of the level of BNP:At 12 th week,compared with normal control group,the level of BNP of HF group showed significant increased difference(P<0.05),and the level of BNP was decreased markedly than HF group(P<0.05),While no difference was observed between each treatment group(P>0.05).High amount of Liraglutide had decreased the content of TC in serum(P<0.05);4 The gene and protein expression of autophagy-related molecules: At the end of the research,in HF group the protein expression of Beclin 1 and LC-3B were notably decreased(P<0.05),after drug intervention the protein of Beclin 1 and LC-3? were up-regulated(P<0.05).The mRNA expression of Beclin 1 and LC3-? were significantly increased by liraglutide(P<0.05),which was consistent with the protein expression.The ATG7 mRNA expression was obviously down-regulated in HF group(P<0.05),and the p62 mRNA expression was markedly increased in HF group(P<0.05).We observed the opposite results in liraglutide.5 The protein expression of AMPK-mTOR signaling pathway in myocardial tissue: There was no significant difference among groups in protein expression of AMPK and mTOR(P>0.05).The protein expression of P-AMPK was down-regulated in HF group compared with the Con group(P<0.05),the expression of P-mTOR were significantly up-regulated by liraglutide(P<0.05).Compared with the HF group,protein expression of P-AMPK were up-regulated in intervention group(P<0.05);and after the intervention of liraglutide the protein expression of P-mTOR was up-regulated(P<0.05).Conclusions:1 The high-fat-diet can damage the function of heart in rats,increasing the level of BNP,and liraglutide intervention improved the impaired condition.2 Autophagy activated the AMPK,inturn inhibited the m-TOR to increase the level of autophagy in high-fat-diet rats,thus improving the heart function of high-fat-diet rats.