Regulatory Mechanisms Of Sirt1 In Phenotypic Transformation Of Diabetic Cardiac Fibroblasts: Role Of Sirt1/Akt/α-SMA Axis

Objective Cardiac remodelling in diabetes,including microvascular damage,cardiomyocyte hypertrophy and cardiac fibrosis.The prevalence of cardiac fibrosis increases with the prevalence of diabetes mellitus.The process by which cardiac fibroblasts shift from a resting to an activated state and undergo phenotypic transdifferentiation is the main pathological mechanism of cardiac fibrosis.Cardiac fibrosis involves multiple complex fibrillogenic pathways in diabetic heart disease,the specific regulatory mechanisms of which are unclear.Sirt1,a class III histone deacetyltransferase,is involved in multiple metabolic pathways to regulate body function.Evidence from ongoing studies on Sirtuin1(Sirt1)has demonstrated its protective role in pathophysiological processes associated with cardiovascular disease,but its effect on the progression of cardiac fibrosis in diabetic cardiomyopathy and the mechanisms involved are unclear.The aim of this paper is to investigate,the role of Sirt1 on fibroblast transdifferentiation in the diabetic heart and the possible mechanisms.Methods1.Animal model studies: Male 6-week-old C57BL/6 mice weighing between 15-20 g were injected intraperitoneally with streptozotocin(STZ,50 mg/kg/d)for 3 consecutive days to establish the required diabetic mouse model,and Sirt1 activity was increased using drug levels of the Sirt1 activator resveratrol.The percentage of survival,body weight and heart weight of the experimental mice were recorded;cardiac ultrasound was used to assess the cardiac function of the mice;HE staining and SR staining were used to assess the degree of central muscle fibrosis in the tissue sections;western-blot assay was used to detect the protein expression levels of Sirt1,P-Akt,α-SMA and type I collagen in the heart tissues.2.In vitro cellular studies: primary mouse cardiac fibroblasts were cultured at a concentration of30 mmol/L glucose,while Sirt1 activity was increased by drug levels of the Sirt1 activator resveratrol,and protein kinase B(Akt)activity was inhibited by Wortmannin.Protein expression levels of Sirt1,P-Akt,α-SMA and type I collagen were measured.ResultsAccording to the results of animal experiments,the percentage of diabetic mice surviving decreased,body weight decreased,heart weight to body weight ratio increased,cardiac function decreased,cardiac fibrosis increased,Sirt1 protein expression level in heart tissue decreased,phosphorylated Akt expression decreased,fibroblast phenotype differentiation specific proteinα-SMA,type I collagen expression increased.In contrast,Sirt1 activator resveratrol upregulated the expression of Sirt1,increased the expression of phosphorylated Akt and decreased the expression of fibroblast phenotype-specific protein α-SMA and type I collagen,effectively reducing the extent of cardiac fibrosis and improving cardiac function in diabetic mice.According to the knowledge of cell experiments,primary cardiac fibroblasts were treated with high glucose environment and the expression levels of Sirt1,P-Akt,α-SMA and type I collagen were detected by western-blot method.The results showed that Sirt1 protein expression decreased in primary cardiac fibroblasts treated with high glucose,and fibroblasts activated and changed to myofibroblasts,so the protein expression levels of α-SMA and type I collagen increased.The Sirt1 activator resveratrol upregulated the expression of Sirt1 protein at the pharmacological level,and the expression of α-SMA and collagen type I,which are specific for the phenotypic transition from cardiac fibroblasts to myofibroblasts,decreased.The cascade relationship between Sirt1/Akt/α-SMA axis was clarified.ConclusionDiabetes causes downregulation of Sirt1 protein expression in cardiac fibroblasts,leading to reduced phosphorylation levels of Akt,which promotes activation and transdifferentiation of cardiac fibroblasts and high expression of α-SMA,positively regulating the expression levels of fibrosis-associated type I collagen,promoting the pathogenesis of cardiac fibrosis and mediating the development and progression of diabetic heart disease.