Type 1 diabetic cardiomyopathy in the Akita (Ins2WT/C96Y) mouse model is characterized by lipotoxicity and diastolic dysfunction with preserved systolic function

Abstract

Diabetic cardiomyopathy is an important contributor to diastolic and systolic heart failure. We examined the nature and mechanism of the cardiomyopathy in Akita ( Ins2WT/C96Y) mice, a model of genetic nonobese type 1 diabetes that recapitulates human type 1 diabetes. Cardiac function was evaluated in male Ins2WT/C96Yand their littermate control ( Ins2WT/WT) mice using echocardiography and tissue Doppler imaging, in vivo hemodynamic measurements, as well as ex vivo working heart preparation. At 3 and 6 mo of age, Ins2WT/C96Ymice exhibited preserved cardiac systolic function compared with Ins2WT/WTmice, as evaluated by ejection fraction, fractional shortening, left ventricular (LV) end-systolic pressure and maximum rate of increase in LV pressure in vivo, cardiac work, cardiac power, and rate-pressure product ex vivo. Despite the unaltered systolic function, Ins2WT/C96Ymice exhibited significant and progressive diastolic dysfunction at 3 and 6 mo of age compared with Ins2WT/WTmice as assessed by tissue and pulse Doppler imaging (E-wave velocity, isovolumetric relaxation time) and by in vivo hemodynamic measurements (LV end-diastolic pressure, time constant of LV relaxation, and maximum rate of decrease in LV pressure). We found no evidence of myocardial hypertrophy or fibrosis in the Ins2WT/C96Ymyocardium. Consistent with the lack of fibrosis, expression of procollagen-α type I, procollagen-α type III, and fibronectin were not increased in these hearts. Ins2WT/C96Yhearts showed significantly reduced sarcoplasmic reticulum Ca2+-ATPase 2a (cardiac sarcoplasmic reticulum Ca2+pump) levels, elevated β-myosin heavy chain isoform, increased long-chain fatty acids, and triacylglycerol with evidence of lipotoxicity, as indicated by a significant rise in ceramide, diacylglycerol, and lipid deposits in the myocardium. Consistent with metabolic perturbation, and a switch to fatty acid oxidation from glucose oxidation in Ins2WT/C96Yhearts, expression of mitochondrial long-chain acyl-CoA dehydrogenase and pyruvate dehydrogenase kinase isoform 4 were increased. Insulin treatment reversed the diastolic dysfunction, the elevated B-type natriuretic peptide and β-myosin heavy chain, and the reduced sarcoplasmic reticulum Ca2+-ATPase 2a levels with abolition of cardiac lipotoxicity. We conclude that early type 1 diabetic cardiomyopathy is characterized by diastolic dysfunction associated with lipotoxic cardiomyopathy with preserved systolic function in the absence of interstitial fibrosis and hypertrophy.