In failing and nonfailing donor human myocardium, there is a combined decrease of CK activity and creatine that may impair the ability to deliver ATP to energy-consuming systems.

Rationale: Mitochondrial dysfunction plays a pivotal role in the development of heart failure. Animal studies suggest that impaired mitochondrial biogenesis attributable to downregulation of the peroxisome proliferator-activated receptor ␥ coactivator (PGC)-1 transcriptional pathway is integral of mitochondrial dysfunction in heart failure. Objective: The study sought to define mechanisms underlying the impaired mitochondrial biogenesis and function in human heart failure. Methods and Results: We collected left ventricular tissue from end-stage heart failure patients and from nonfailing hearts (n‫,32؍‬ and 19, respectively). The mitochondrial DNA (mtDNA) content was decreased by >40% in the failing hearts, after normalization for a moderate decrease in citrate synthase activity (P<0.05). This was accompanied by reductions in mtDNA-encoded proteins (by 25% to 80%) at both mRNA and protein level (P<0.05). The mRNA levels of PGC-1␣/␤ and PRC (PGC-1-related coactivator) were unchanged, whereas PGC-1␣ protein increased by 58% in the failing hearts. Among the PGC-1 coactivating targets, the expression of estrogen-related receptor ␣ and its downstream genes decreased by up to 50% (P<0.05), whereas peroxisome proliferator-activated receptor ␣ and its downstream gene expression were unchanged in the failing hearts. The formation of D-loop in the mtDNA was normal but D-loop extension, which dictates the replication process of mtDNA, was decreased by 75% in the failing hearts. Furthermore, DNA oxidative damage was increased by 50% in the failing hearts. Conclusions: Mitochondrial biogenesis is severely impaired as evidenced by reduced mtDNA replication and depletion of mtDNA in the human failing heart. These defects are independent of the downregulation of the PGC-1 expression suggesting novel mechanisms for mitochondrial dysfunction in heart failure. (Circ Res. 2010;106:1541-1548.)Key Words: mtDNA Ⅲ mitochondrial biogenesis Ⅲ human heart failure Ⅲ PGC-1 Ⅲ oxidative damage M itochondrial dysfunction has been observed in a variety of cardiac diseases, including myocardial ischemia, diabetic cardiomyopathy and heart failure. Accumulating evidence have suggested that mitochondrial dysfunction accounts for impaired myocardial energetics and increased cell death during myocardial injury and the development of heart failure. 1,2 However, the molecular mechanisms responsible for the mitochondrial dysfunction under these pathological conditions are poorly understood making it difficult to develop mitochondriatargeted therapy.Recent studies have revealed a central role of peroxisome proliferator-activated receptor ␥ coactivator (PGC)-1 family proteins in mitochondrial biogenesis and function in multiple organs including the heart. 3-5 Downregulation of PGC-1␣ and its target genes have been observed in a number of rodent models of heart failure raising the intriguing possibility that impaired mitochondrial biogenesis can be a causal mechanism for mitochondrial dysfunction in heart failure. 6,7 However, despite strong evidence sugges...

Abstract-Glycolysis increases in hypertrophied hearts but the mechanisms are unknown. We studied the regulation of glycolysis in hearts with pressure-overload LV hypertrophy (LVH), a model that showed marked increases in the rates of glycolysis (by 2-fold) and insulin-independent glucose uptake (by 3-fold). Although the V max of the key glycolytic enzymes was unchanged in this model, concentrations of free ADP, free AMP, inorganic phosphate (P i ), and fructose-2,6-bisphosphate (F-2,6-P 2 ), all activators of the rate-limiting enzyme phosphofructokinase (PFK), were increased (up to 10-fold). Concentrations of the inhibitors of PFK, ATP, citrate, and H ϩ were unaltered in LVH. Thus, our findings show that increased glucose entry and activation of the rate-limiting enzyme PFK both contribute to increased flux through the glycolytic pathway in hypertrophied hearts. Moreover, our results also suggest that these changes can be explained by increased intracellular free [ADP] and [AMP], due to decreased energy reserve in LVH, activating the AMP-activated protein kinase cascade. This, in turn, results in enhanced synthesis of F-2,6-P 2 and increased sarcolemma localization of glucose transporters, leading to coordinated increases in glucose transport and activation of PFK. Key Words: cardiac function Ⅲ hypertrophy Ⅲ protein kinases Ⅲ cardiac metabolism Ⅲ cyclic AMP G lucose utilization is increased in hypertrophied and failing hearts, 1-4 but the underlying mechanisms are poorly understood. Increased glycolytic flux in the hypertrophied myocardium is important because ATP synthesis via glucose utilization may compensate for decreased capacity for ATP synthesis via other pathways. 5,6 In hearts with chronic pressure overload hypertrophy, it was recently reported that chronic depletion of the energy reserve compound PCr coupled with large changes in the ratio of PCr to free creatine led to activation of AMP-activated protein kinase (AMPK) by elevated AMP concentrations. 7 AMPK acts as a low-on-fuel sensor and, when the cytosolic AMP concentration increases, AMPK activates enzymes in pathways that synthesize ATP and inhibits enzymes in pathways that use ATP. 8,9 Among the many consequences of activated AMPK is increased localization of glucose transporters in the sarcolemma and hence increased glucose uptake by an insulinindependent mechanism. 10,11 In addition, in a study of acute myocardial ischemia, AMPK was found to phosphorylate and thereby activate heart phosphofructokinase-2 (PFK-2), leading to increased production of fructose-2,6-bisphosphate (F-2,6-P 2 ), a potent activator of the rate-limiting glycolytic enzyme phosphofructokinase (PFK). 12 In the present study, we tested the hypothesis that increased glycolysis in hypertrophied hearts occurs as a consequence of chronic decreases in the energy reserve and activation of AMPK.Using a model of pressure overload left ventricular hypertrophy (LVH) of the rat heart, in which reduced energy reserve, increased AMPK activity, and increased insulin-independent glucose upt...

Increased [ADP] contributes to diastolic dysfunction in LVH, possibly due to slowed cross-bridge cycling. Decreased capacity of the creatine kinase reaction to rephosphorylate ADP is a likely contributing mechanism to the failure to maintain a low [ADP] in LVH.