High-fat diet-induced juvenile obesity leads to cardiomyocyte dysfunction and upregulation of Foxo3a transcription factor independent of lipotoxicity and apoptosis

Background: Obesity is associated with dyslipidemia, which leads to elevated triglyceride and ceramide levels, apoptosis and compromised cardiac function. Methods: To determine the role of high-fat diet-induced obesity on cardiomyocyte function, weanling male Sprague-Dawley rats were fed diets incorporating 10% of kcal or 45% of kcal from fat. Mechanical function of ventricular myocytes was evaluated including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening and relengthening (+/- dl/dt). Intracellular Ca2+ properties were assessed using fluorescent microscopy. Results: High-fat diet induced hyperinsulinemic insulin-resistant obesity with depressed PS, +/- dl/dt, prolonged TPS/TR90 reduced intracellular Ca2+ release and Ca2+ clearing rate in the absence of hypertension, diabetes, lipotoxicity and apoptosis. Myocyte responsiveness to increased stimulus frequency and extracellular Ca2+ was compromised. SERCA2a and phospholamban levels were increased, whereas phosphorylated phospholamban and potassium channel (Kv1,2) were reduced in high-fat diet group. High-fat diet upregulated the forkhead transcription factor Foxo3a, and suppressed mitochondrial aconitase activity without affecting expression of the caloric sensitive gene silent information regulator 2 (Sir2), protein nitrotyrosine formation, lipid peroxidation and apoptosis. Levels of endothelial nitric oxide synthase (NOS), inducible NOS, triglycerides and ceramide were similar between the two groups. Conclusions: Collectively, our data show that high-fat diet-induced obesity resulted in impaired cardiomyocyte function, upregulated Foxo3a transcription factor and mitochondrial damage without overt lipotoxicity or apoptosis.