Background-Diabetes-associated cardiac dysfunction is associated with mitochondrial dysfunction and oxidative stress, which may contribute to left ventricular dysfunction. The contribution of altered myocardial insulin action, independent of associated changes in systemic metabolism, is incompletely understood. The present study tested the hypothesis that perinatal loss of insulin signaling in the heart impairs mitochondrial function. Methods and Results-In 8-week-old mice with cardiomyocyte deletion of insulin receptors (CIRKO), inotropic reserves were reduced, and mitochondria manifested respiratory defects for pyruvate that was associated with proportionate reductions in catalytic subunits of pyruvate dehydrogenase. Progressive age-dependent defects in oxygen consumption and ATP synthesis with the substrate glutamate and the fatty acid derivative palmitoyl-carnitine were observed. Mitochondria also were uncoupled when exposed to palmitoyl-carnitine, in part as a result of increased reactive oxygen species production and oxidative stress. Although proteomic and genomic approaches revealed a reduction in subsets of genes and proteins related to oxidative phosphorylation, no reductions in maximal activities of mitochondrial electron transport chain complexes were found. However, a disproportionate reduction in tricarboxylic acid cycle and fatty acid oxidation proteins in mitochondria suggests that defects in fatty acid and pyruvate metabolism and tricarboxylic acid flux may explain the mitochondrial dysfunction observed. Conclusions-Impaired myocardial insulin signaling promotes oxidative stress and mitochondrial uncoupling, which, together with reduced tricarboxylic acid and fatty acid oxidative capacity, impairs mitochondrial energetics. This study identifies specific contributions of impaired insulin action to mitochondrial dysfunction in the heart. (Circulation. 2009; 119:1272-1283.)Key Words: insulin Ⅲ metabolism Ⅲ mitochondria Ⅲ oxidative stress R ecent studies have suggested that impaired mitochondrial energetics may contribute to cardiac dysfunction in obesity and diabetes mellitus. [1][2][3][4][5][6][7] The pathogenesis of mitochondrial dysfunction in obesity or diabetes-related heart disease is likely multifactorial but includes fatty acid (FA)-mediated mitochondrial uncoupling and oxidative damage. 3,4,8 -11 A commonly associated finding in the heart in experimental models of obesity and diabetes mellitus is myocardial insulin resistance. [12][13][14][15][16] However, it is not known whether myocardial insulin resistance per se contributes directly to the pathogenesis of myocardial mitochondrial dysfunction. Clinical Perspective p 1283The effects of myocardial insulin signaling on the acute regulation of myocardial metabolism are well known 17,18 and include increasing glucose uptake and glycolysis via regulation of GLUT4 translocation 19,20 and activation of 6-phosphofructo-1-kinase. 21 In perfused hearts, insulin increases glucose oxidation and reduces FA oxidation. 13 In vivo, the antilipolytic ef...

OBJECTIVE-Fatty acid-induced mitochondrial uncoupling and oxidative stress have been proposed to reduce cardiac efficiency and contribute to cardiac dysfunction in type 2 diabetes. We hypothesized that mitochondrial uncoupling may also contribute to reduced cardiac efficiency and contractile dysfunction in the type 1 diabetic Akita mouse model (Akita). RESEARCH DESIGN AND METHODS-Cardiac function andsubstrate utilization were determined in isolated working hearts and in vivo function by echocardiography. Mitochondrial function and coupling were determined in saponin-permeabilized fibers, and proton leak kinetics was determined in isolated mitochondria. Hydrogen peroxide production and aconitase activity were measured in isolated mitochondria, and total reactive oxygen species (ROS) were measured in heart homogenates. RESULTS-Resting cardiac function was normal in Akita mice, and myocardial insulin sensitivity was preserved. Although Akita hearts oxidized more fatty acids, myocardial O 2 consumption was not increased, and cardiac efficiency was not reduced. ADP-stimulated mitochondrial oxygen consumption and ATP synthesis were decreased, and mitochondria showed grossly abnormal morphology in Akita. There was no evidence of oxidative stress, and despite a twofold increase in uncoupling protein 3 (UCP3) content, ATP-to-O ratios and proton leak kinetics were unchanged, even after perfusion of Akita hearts with 1 mmol/l palmitate.

The receptors for IGF-I (IGF-IR) and insulin (IR) have been implicated in physiological cardiac growth, but it is unknown whether IGF-IR or IR signaling are critically required. We generated mice with cardiomyocyte-specific knockout of IGF-IR (CIGF1RKO) and compared them with cardiomyocyte-specific insulin receptor knockout (CIRKO) mice in response to 5 wk exercise swim training. Cardiac development was normal in CIGF1RKO mice, but the hypertrophic response to exercise was prevented. In contrast, despite reduced baseline heart size, the hypertrophic response of CIRKO hearts to exercise was preserved. Exercise increased IGF-IR content in control and CIRKO hearts. Akt phosphorylation increased in exercise-trained control and CIRKO hearts and, surprisingly, in CIGF1RKO hearts as well. In exercise-trained control and CIRKO mice, expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) and glycogen content were both increased but were unchanged in trained CIGF1RKO mice. Activation of AMP-activated protein kinase (AMPK) and its downstream target eukaryotic elongation factor-2 was increased in exercise-trained CIGF1RKO but not in CIRKO or control hearts. In cultured neonatal rat cardiomyocytes, activation of AMPK with 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) prevented IGF-I/insulin-induced cardiomyocyte hypertrophy. These studies identify an essential role for IGF-IR in mediating physiological cardiomyocyte hypertrophy. IGF-IR deficiency promotes energetic stress in response to exercise, thereby activating AMPK, which leads to phosphorylation of eukaryotic elongation factor-2. These signaling events antagonize Akt signaling, which although necessary for mediating physiological cardiac hypertrophy, is insufficient to promote cardiac hypertrophy in the absence of myocardial IGF-I signaling.

Rationale Pressure overload cardiac hypertrophy, a risk factor for heart failure, is associated with reduced mitochondrial fatty acid oxidation (FAO) and oxidative phosphorylation (OXPHOS) proteins that correlate in rodents with reduced PGC-1α expression. Objective To determine the role of PGC-1β in maintaining mitochondrial energy metabolism and contractile function in pressure overload hypertrophy. Methods and Results PGC-1β deficient (KO) mice and wildtype controls (WT) were subjected to transverse aortic constriction (TAC). Although LV function was modestly reduced in young KO hearts, there was no further decline with age so that LV function was similar between KO and WT when TAC was performed. WT – TAC mice developed relatively compensated LVH, despite reduced mitochondrial function and repression of OXPHOS and FAO genes. In non-stressed KO hearts, OXPHOS gene expression and palmitoyl-carnitine supported mitochondrial function were reduced to the same extent as banded WT, but FAO gene expression was normal. Following TAC, KO mice progressed more rapidly to heart failure and developed more severe mitochondrial dysfunction, despite a similar overall pattern of repression of OXPHOS and FAO genes as WT – TAC. However, relative to WT TAC, PGC-1β deficient mice exhibited greater degrees of oxidative stress, decreased cardiac efficiency, lower rates of glucose metabolism and repression of hexokinase II protein. Conclusions PGC-1β plays an important role in maintaining baseline mitochondrial function and cardiac contractile function following pressure overload hypertrophy by preserving glucose metabolism and preventing oxidative stress.

Physiological cardiac hypertrophy is associated with mitochondrial adaptations that are characterized by activation of PGC-1alpha and increased fatty acid oxidative (FAO) capacity. It is widely accepted that phosphatidylinositol 3-kinase (PI3K) signaling to Akt1 is required for physiological cardiac growth. However, the signaling pathways that coordinate physiological hypertrophy and metabolic remodeling are incompletely understood. We show here that activation of PI3K is sufficient to increase myocardial FAO capacity and that inhibition of PI3K signaling prevents mitochondrial adaptations in response to physiological hypertrophic stimuli despite increased expression of PGC-1alpha. We also show that activation of the downstream kinase Akt is not required for the mitochondrial adaptations that are secondary to PI3K activation. Thus, in physiological cardiac growth, PI3K is an integrator of cellular growth and metabolic remodeling. Although PI3K signaling to Akt1 is required for cellular growth, Akt-independent pathways mediate the accompanying mitochondrial adaptations.