The Mechanism Of Opening MitoK_ATP To Improve Cardiac Function During Diabetic Cardiomyopathy In Mice

Background: Diabetic cardiomyopathy is the main reason for the decline of cardiac function in patients with diabetes mellitus, and seriously does harm to human health. The pathogenesis of diabetic cardiomyopathy is mainly associated with microvascular disease, insulin resistance and metabolic product accumulation in present.In previous studies, we found that phosphorylation of AKT-Foxo1 was decreased in diabetic cardiomyopathy mice, and the phenomenon was closely related to the occurrence of insulin resistance and apoptosis. Mitochondrial ATP-sensitive potassium channels (mitoKATp) is an inward rectifier potassium channel which locates in the mitochondrial inner membrane, whose function is to improve the energy metabolism,inhibit the apoptosis, relieve the overload of Ca2+ and stabilize the internal environment.Recent studies have showed that opening of mitoKATP increased the expression of phosphorylated AKT (p-AKT) and thereafter alleviated the reperfusion injury in myocardium. In this sudy, we hypothesize that opening of mitoKATp probably regulates AKT-Foxo1 signaling pathway and increases the expression of p-AKT and p-Foxo1,which plays a role in reducing insulin resistance, inhibiting apoptosis and improving cardiac function.Objective: To study the mechanism of opening mitoKATp to improve cardiac function during diabetic cardiomyopathy.Methods: Ten db/m mice with the same age, weight and genetic backgroung were selected as the control group, thirty db/db mice with the same age were randomly assigned to three groups with different drugs intervention, which included 2%DMSO,2%DMSO + DZX (5mg/kg), 2%DMSO + 5-HD (5mg/kg) + DZX (5mg/kg), control group with only 2%DMSO, all animals received an intraperitoneal injection in every morning for 4 weeks. The effects of opening mitoKATp on cardiac function in mice were evaluated by Echocardiography and serum NT-ProBNP levels, and the effects of opening mitoKATP on myocardial hypertrophy and apoptosis were detected by HE and Tunel staining, respectively. Cultured cardiomyocytes were divided into five groups with different drugs intervention,which included insulin (100nmol/L) for 24h to induce insulin resistance; DZX (100?mol/L) + insulin (100nmol/L) for 24h; 5-HD (100?mol/L)+ DZX (100?mol/L) + insulin (100nmol/L) for 24h; MK-2206 (5?mol/L) + DZX(100?mol/L) + insulin (100nmol/L) for 24h; Control group with only solvent intervention, DZX, 5-HD and MK-2206 were given for 30min in advance.Mitochondrial membrane potential (??m) was measured to evaluate energy metabolism.The protein expressions of pro-caspase 3, cleaved-caspase 3, total AKT (t-AKT),total Foxo1 (t-Foxo1), p-AKT and phosphorylated Foxo1 (p-Foxo1) were determined by western blotting to evaluate the effects of opening mitoKA-TP on apoptosis and the AKT-Foxo1 signaling pathway.Results: (1) Compared with the control group, twenty-week-old db/db mice had already appeared cardiac dysfunction characterized by the decrease of left ventricular ejection fraction (LVEF), shorten of axis shortening (FS),the decrease of left ventricular weight to body weight (LVW/BW) and cardiac index (CI), whereas the increase of left ventricular internal dimension in systole (LVDs) (P<0.05); Compared with the DMSO group, the values of LVEF, FS and CI were significantly increased, whereas the LVDs and serum NT-ProBNP levels were decreased in DZX group (P<0.05),and the cross-sectional area, apoptotic rate and the expression of cleaved-caspase 3 in cardiomyocytes were also significantly decreased in DZX group (P<0.05), while the expressions of p-AKT and p-Foxol were significantly increased in DZX group (P<0.05).However, the above effects of DZX were blocked by mitoKATP inhibitor 5-HD. (2)Insulin resistance in cultured cardiomyocytes was induced by incubated with 100nmol/L insulin for 24h. Compared with control group, the expression of NT-ProBNP in cultured supernatant and BNP mRNA expression in cardiomyocytes was increased significantly(P<0.05). Compared with the insulin group, the expression of NT-ProBNP in cultured supernatant and BNP mRNA expression was decreased in DZX+insulin group (P<0.05),meanwhile, the expression of cleaved-caspase 3 and caspase 3 activity was also declined (P<0.05), whereas the mitochondrial membrane potential (??m) and the expression of p-AKT and p-Foxo1 were increased significantly in DZX+insulin group(P<0.05). The above effects of DZX also were blocked by 5-HD. (3) Compared with the DZX+insulin group, the effects of opening mitoKATP on the increase of p-AKT and p-Foxol expression were blocked by specific AKT inhibitor MK-2206. Furthermore,the rise of ??m, the improvement of energy metabolism, the inhibition of apoptosis,and the decrease of heart failure biomarkers by opening mitoKATP were also blocked by MK-2206 (P<0.05),which has the similar potency of 5-HD (P>0.05).Conclusion: (1) Opening of mitoKATp improves cardiac function during diabetic cardiomyopathy in mice and decreases the expression of heart failure biomarkers when mimicked insulin resistance in cultured cardiomyocytes. (2) Opening of mitoKATP increases ??m, improves energy metabolism, and inhibits myocardial hypertrophy and apoptosis during insulin resistance. (3) The effects of opening mitoKATP on the improvement of cardiac function may be associated with the improvement of energy metabolism and the inhibition of apoptosis. (4) The regulation of opening mitoKATP on the AKT-Foxol signaling pathway plays an important role in increasing ??m,improving energy metabolism, inhibiting apoptosis, and reducing the expression of heart failure markers. (5) MitoKATP may be a potential target for early treatment during diabetic cardiomyopathy.