In addition to fatty acids, glucose and lactate are important myocardial substrates under physiological and stress conditions. They are metabolized to pyruvate that enters mitochondria via the mitochondrial pyruvate carrier (MPC) for citric acid cycle (CAC) metabolism. Here, we show that MPC-mediated mitochondrial pyruvate utilization is essential for the partitioning of glucose-derived cytosolic metabolic intermediates, which modulate myocardial stress adaptation. Mice with cardiomyocyte-restricted deletion of subunit 1 of MPC (cMPC1 −/− ) developed age-dependent pathologic cardiac hypertrophy, transitioning to a dilated cardiomyopathy and premature death. Hypertrophied hearts accumulated lactate, pyruvate, and glycogen and displayed increased protein O-GlcNacylation (O-GlcNAc), which was prevented by increasing availability of non-glucose substrates in vivo by ketogenic (KD) or high-fat (HFD) diets, which reversed the structural, metabolic and functional remodeling of non-stressed cMPC1 −/− hearts. While concurrent short-term KD did not rescue cMPC1 −/− hearts from rapid decompensation and early mortality following pressure overload, 3-week of KD prior to TAC was sufficient to rescue this phenotype. Together, our results highlight the centrality of pyruvate metabolism to myocardial metabolism and function.

Since the initial use of ketogenic diets (KD) as adjunctive treatment for epilepsy, these diets are being increasingly used to promote weight loss and to reduce the risk of metabolic sequelae of obesity. Typical KD are very low in carbohydrate and high in fat, promoting hepatic production of ketone bodies. Few studies have evaluated gender differences in response to KD, and many animal studies tend to be performed in male mice. To explore sex differences in response to KD, female and male wild type mice on the C57BL/6J background were fed either a control diet (CD- 7% fat, 47% carb., 19% protein) or KD (75% fat, 3% carb., 8% protein), following weaning. Females on the CD manifested higher levels of circulating β-hydroxybutyrate (β-HB) than males (2.86-fold, p<0.05). Circulating β-HB concentrations increased with KD in males and females (1.30-fold and 5.05-fold, p<10-4 and p<0.01 respectively) with higher concentrations in females. After 8 weeks, females on KD displayed an increase in body weight (1.07-fold KD vs. CD, p<0.05) while body weight declined in males (0.88-fold, p<0.05). Nuclear magnetic resonance analysis revealed elevated lean mass in females (1.07-fold, p<0.05), but a significant reduction in fat mass in males (0.49-fold, p<0.05) relative to sex-matched mice on CD. The female mice on KD developed impaired glucose tolerance with a 1.35-fold increase in glucose tolerance test area under the curve (GTT AUC) relative to females on CD (p<0.001). In contrast, fasting glucose levels were lower in males on KD (131.8 ± 12.5 mg/ dl vs. 169.2 ± 6.3 mg/dl, p<0.05). Despite no significant change in GTT AUC, the male mice on KD displayed elevated blood glucose concentrations 30 minutes after injection relative to males on CD (344.9 ± 18.7 mg/dl vs. 272.0 ± 10.3 mg/dl, p<0.05). However, after 120 minutes, blood glucose levels returned to initial fasting levels. In conclusion, significant sex differences exist in terms of body composition and metabolism in response to ketogenic diets via mechanisms that remain to be elucidated. Disclosure J. Cochran: None. P.V. Taufalele: None. K.D. Lin: None. Y. Zhang: None. E. Abel: None.

Molecular mechanisms underlying cardiac dysfunction and subsequent heart failure in diabetic cardiomyopathy are incompletely understood. Initially we intended to test the role of GRK2, a potential mediator of cardiac dysfunction in diabetic cardiomyopathy, but found that control animals on HFD did not develop cardiomyopathy. Cardiac function was preserved in both wildtype and GRK2 knockout animals fed high fat diet as indicated by preserved left ventricular ejection fraction (LVEF) although heart mass was increased. The absence of cardiac dysfunction led us to rigorously evaluate the utility of diet-induced obesity to model diabetic cardiomyopathy in mice. Using pure C57BL/6J animals and various diets formulated with different sources of fat- lard (32% saturated fat, 68% unsaturated fat) or hydrogenated coconut oil (95% saturated fat), we consistently observed left ventricular hypertrophy, preserved LVEF and preserved contractility measured by invasive hemodynamics in animals fed high fat diet. Gene expression patterns that characterize pathological hypertrophy were not induced but a modest induction of various collagen isoforms and matrix metalloproteinases were observed in heart with high fat diet feeding. PPARa-target genes that enhance lipid utilization such as Pdk4, CD36, AcadL and Cpt1b were induced, but mitochondrial energetics were not impaired. These results suggest while long-term fat feeding in mice induces cardiac hypertrophy and increases cardiac fatty acid metabolism, it may not be sufficient to activate pathological hypertrophic mechanisms that impair cardiac function or induce cardiac fibrosis. Thus, additional factors that are currently not understood may contribute to the cardiac abnormalities previously reported by many groups.