Mice With Cardiac Overexpression of Peroxisome Proliferator–Activated Receptor (cid:1) Have Impaired Repolarization and Spontaneous Fatal Ventricular Arrhythmias

Background —Diabetes mellitus and obesity, which confer an increased risk of sudden cardiac death, are associated with cardiomyocyte lipid accumulation and altered cardiac electric properties, manifested by prolongation of the QRS duration and QT interval. It is difficult to distinguish the contribution of cardiomyocyte lipid accumulation from the contribution of global metabolic defects to the increased incidence of sudden death and electric abnormalities. Methods and Results —In order to study the effects of metabolic abnormalities on arrhythmias without the complex systemic effects of diabetes mellitus and obesity, we studied transgenic mice with cardiac-specific overexpression of peroxisome proliferator–activated receptor (cid:1) 1 (PPAR (cid:1) 1) via the cardiac (cid:2) -myosin heavy-chain promoter. The PPAR (cid:1) transgenic mice develop abnormal accumulation of intracellular lipids and die as young adults before any significant reduction in systolic function. Using implantable ECG telemeters, we found that these mice have prolongation of the QRS and QT intervals and spontaneous ventricular arrhythmias, including polymorphic ventricular tachycardia and ventricular fibrillation. Isolated cardiomyocytes demonstrated prolonged action potential duration caused by reduced expression and function of the potassium channels responsible for repolarization. Short-term exposure to pioglitazone, a PPAR (cid:1) agonist, had no effect on mortality or rhythm in WT mice but further exacerbated the arrhythmic phenotype and increased the mortality in the PPAR (cid:1) transgenic mice. Conclusions —Our findings support an important link between PPAR (cid:1) activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality. ( Circulation . 2011;124:2812-2821.) test with equal variances was used for comparisons of larger groups. A 2-tailed value of P (cid:3) 0.05 was considered statistically significant, except for ECG intervals and premature ventricular complexes (PVCs) burden where the Bonferroni correction was used for multiple comparisons. Linear regression analysis was performed using GraphPad Software. and ventricular fibrillation. Isolated cardiomyocytes demonstrated prolonged action potential duration caused by reduced potassium currents, which are responsible for repolarization. Short-term exposure to pioglitazone, a PPAR (cid:1) agonist, had no effect on mortality or rhythm in wild-type mice but further exacerbated the arrhythmic phenotype and increased mortality in the PPAR (cid:1) mice. Our findings support an important link between PPAR (cid:1) activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality. This mouse model may help identify the molecular mechanisms leading to sudden death in diabetic and/or obese patients. with 0.3% H 2 O 2 to block endogenous peroxidase. Sections were incubated with rabbit polyclonal antibodies against Cx43 (1:200 dilution, Invitrogen Corp.) or non-immune rabbit polyclonal IgG at the same concentration, at 4˚C overnight. For DAB staining, after exposure to anti-rabbit swine antibody conjugated to biotin (1:500, DakoCytomation Denmark A/S, Glostrup, Denmark) for 1 hr in room temperature, the sections were treated with peroxidase-labeled ABC (VECTASATIN ABC Kit, Vector Laboratories, Inc., Burlingame, CA) and developed with DAB solution (ImmPACT DAB Peroxidase Substrate, Vector Laboratories, Inc.). After the reaction, the sections were counterstained with hematoxylin and observed by a light microscope. For immunofluorescent staining, after reaction with anti-rabbit donkey antibody conjugated to Alexa Fluor 488 (1:500, Invitrogen Corp.), the sections were counterstained with DAPI and observed by a fluorescent microscope. Tissues from two mice in each group (PPAR γ overexpression and WT littermates) were used. Slides were photographed with a digital camera. Signal intensity was quantified using ImageJ software (NIH).