| Objective:Diabetes mellitus (DM) is a group of systemic metabolic syndromes mainly characterized by sugar metabolic disorder which caused by both genetic and environmental factors. In recent years, studies have confirmed that diabetic cardiomyopathy (DCM) is one of the main reasons that lead diabetes patients to heart failure. Myocardial apoptosis is one of the main pathogenesises of DCM. Synthetic peptide glucagon-like peptide-1(GLP-1) receptor agonist liraglutide (LR) is a new drug to cure diabetes mellitus which has cardiovascular protective effect. The early experiments of this study found that LR can inhibit myocardial apoptosis, but the specific mechanism was unclear. It is thought that the cardiovascular protective effect of LR was mainly mediated by the GLP-1receptor. GLP-1receptor is one of the G protein coupled receptors which can improve the level of intracellular cyclic adenosine monophosphate (cAMP) when activated. The downstream signaling molecules of cAMP include protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). Previous studies thought that anti-apoptotic effect of cAMP was mainly mediated by PKA signaling pathway, however, in recent years, the anti-apoptotic role of Epac signaling pathway has been noted gradually. Researches also showed that activation of Epacl can activate the protein kinase B (Akt), while the activation of Akt is associated with the regulation of cell apoptosis. Thus, this study investigated whether the GLP-1receptor agonist LR inhibit apoptosis of diabetic myocardial cells by activating Epac/Akt signaling pathway.Methods:36clean grade inbred male Wistar rats were reared in single cage in specific pathogen-free conditions. After fed adaptively for1week,10of Wistar rats were selected randomly as normal group (N group) and fed with normal animal feeds. Other26Wistar rats were fed with fatty feeds and sugary stuff.8weeks later,26rats which were fed with fatty feeds and sugary stuff were injected with streptozocin diluted with citrate buffe via the tail vein to induce animal model of type2diabetes. N group rats were injected with equal citrate buffer solution. Only22rats survived after modeling, and they were randomly divided into liraglutide intervention group (LR group)(n=11) and diabetes group (DM group)(n=11). LR group rats were administered with LR (400μg·kg-1) by subcutaneous injection daily, and N group and DM group rats were subcutaneous injected with physiological saline in the same amount. Rats were continued to be fed for12weeks. At the end of the experiment, there were10rats left in each group. Recorded body weight of the rats. Rats in each group were killed and taken blood to detect biochemical indicators. Some myocardial tissue was cut out and kept in-80℃refrigerator to make the following test:Detected the expressions of Epacl, Akt and P-Akt(Ser473) in each group by Western Blotting. Calculated relative expressions of the target proteins with GAPDH as internal control.Results:There were expressions of Epacl, Akt, and P-Akt(Ser473) in myocardial tissue of N group, DM group and LR group. Compared with N group, the expressions of Epacl, P-Akt(Ser473)/Akt in DM group decreased obviously. The difference was statistically significant (P<0.05). Compared with DM group, the expressions of Epacl, P-Akt(Ser473)/Akt in LR group increased obviously, but it didn’t recover to normal level. The difference was statistically significant (P<0.05).Conclusions:(1) Compared with N group rats, the expressions of Epacl, P-Akt(Ser473)/Akt in DM rats myocardium all decreased obviously, suggesting that down-regulated expression of Epac/Akt signaling transduction pathway may play a role in the apoptosis of DCM myocardial cells.(2) Compared with DM group rats, the expressions of Epacl, P-Akt(Ser473)/Akt in LR intervention group all increased obviously, suggesting that Epac/Akt signaling pathway is one of the molecular mechanisms that GLP-1receptor agonist LR inhibit apoptosis of myocardial cells. |
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