Extreme Acetylation of the Cardiac Mitochondrial Proteome Does Not Promote Heart Failure.

RATIONALE: Circumstantial evidence links the development of heart failure to posttranslational modifications of mitochondrial proteins, including lysine acetylation (Kac). Nonetheless, direct evidence that Kac compromises mitochondrial performance remains sparse. OBJECTIVE: This study sought to explore the premise that mitochondrial Kac contributes to heart failure by disrupting oxidative metabolism. METHODS AND RESULTS: A DKO (dual knockout) mouse line with deficiencies in CrAT (carnitine acetyltransferase) and Sirt3 (sirtuin 3)-enzymes that oppose Kac by buffering the acetyl group pool and catalyzing lysine deacetylation, respectively-was developed to model extreme mitochondrial Kac in cardiac muscle, as confirmed by quantitative acetyl-proteomics. The resulting impact on mitochondrial bioenergetics was evaluated using a respiratory diagnostics platform that permits comprehensive assessment of mitochondrial function and energy transduction. Susceptibility of DKO mice to heart failure was investigated using transaortic constriction as a model of cardiac pressure overload. The mitochondrial acetyl-lysine landscape of DKO hearts was elevated well beyond that observed in response to pressure overload or Sirt3 deficiency alone. Relative changes in the abundance of specific acetylated lysine peptides measured in DKO versus Sirt3 KO hearts were strongly correlated. A proteomics comparison across multiple settings of hyperacetylation revealed ≈86% overlap between the populations of Kac peptides affected by the DKO manipulation as compared with experimental heart failure. Despite the severity of cardiac Kac in DKO mice relative to other conditions, deep phenotyping of mitochondrial function revealed a surprisingly normal bioenergetics profile. Thus, of the >120 mitochondrial energy fluxes evaluated, including substrate-specific dehydrogenase activities, respiratory responses, redox charge, mitochondrial membrane potential, and electron leak, we found minimal evidence of oxidative insufficiencies. Similarly, DKO hearts were not more vulnerable to dysfunction caused by transaortic constriction-induced pressure overload. CONCLUSIONS: The findings challenge the premise that hyperacetylation per se threatens metabolic resilience in the myocardium by causing broad-ranging disruption to mitochondrial oxidative machinery.

Muscle-specific deletion of carnitine acetyltransferase compromises glucose tolerance and metabolic flexibility.

The concept of "metabolic inflexibility" was first introduced to describe the failure of insulin-resistant human subjects to appropriately adjust mitochondrial fuel selection in response to nutritional cues. This phenomenon has since gained increasing recognition as a core component of the metabolic syndrome, but the underlying mechanisms have remained elusive. Here, we identify an essential role for the mitochondrial matrix enzyme, carnitine acetyltransferase (CrAT), in regulating substrate switching and glucose tolerance. By converting acetyl-CoA to its membrane permeant acetylcarnitine ester, CrAT regulates mitochondrial and intracellular carbon trafficking. Studies in muscle-specific Crat knockout mice, primary human skeletal myocytes, and human subjects undergoing L-carnitine supplementation support a model wherein CrAT combats nutrient stress, promotes metabolic flexibility, and enhances insulin action by permitting mitochondrial efflux of excess acetyl moieties that otherwise inhibit key regulatory enzymes such as pyruvate dehydrogenase. These findings offer therapeutically relevant insights into the molecular basis of metabolic inflexibility.

Lethal cardiac tachyarrhythmia in a patient with neonatal carnitine-acylcarnitine translocase deficiency.

Carnitine-acylcarnitine translocase (CACT) deficiency is an inherited defect of the co-transport of free and esterified carnitine across the inner mitochondrial membrane. We report a case of CACT deficiency in a newborn who died at 72 h of age from severe, intractable cardiac tachyarrhythmia, despite an improvement in his neurological and biochemical status. Postmortem examination showed marked steatosis of myocardium, liver, and kidney. In addition, electron microscopic studies showed virtually complete elimination of mitochondria from cardiomyocytes. It appears that the correction of the acute metabolic derangements in this condition may not prevent rapid progression to death, suggesting that the rhythm disturbances in CACT deficiency result from prior and ongoing accumulation of toxic metabolites, rather than from an acute metabolic derangement. Furthermore, we speculate that the choice of anti-arrhythmic agent in this patient may paradoxically have contributed to his death.

[Mitochondrial myopathies and encephalomyopathies. Neuromuscular and central nervous system diseases caused by defects in mitochondrial oxidative metabolism]. / Mitochondriale Myopathien und Enzephalomyopathien. Neuromuskuläre und zentralnervöse Erkrankungen infolge von Defekten des mitochondrialen oxydativen Stoffwechsels.

In this review the clinical data and biochemical findings of disorders of oxidative metabolism in the mitochondria are summarized. Defects in pyruvate metabolism, the citric acid circle, the respiratory chain and less well defined disorders of energy transfer are discussed.

Myoencephalopathies with abnormal mitochondria: a review.

Myoencephalopathies with abnormal mitochondria comprise a heterogeneous group of diseases and syndromes with a large diversity of clinical signs. Thus, their identification and classification pose many difficulties. The underlying biochemical disorders of energy metabolism evoke non-specific structural alterations of the mitochondria in skeletal muscle and brain, but also in other organs. In this paper the morphologic and biochemical background of confirmed cases is reviewed and the position of these cases within the concept of mitochondriopathy is discussed.

Fatal ataxic encephalopathy and carnitine acetyltransferase deficiency: a functional defect of pyruvate oxidation?

A 3-year 8-month-old girl died after 14 months of illness characterized by episodes of intermittent ataxia associated with oculomotor palsy, hypotonia, mental confusion, and disturbances of consciousness. In the last 4 months of life, there were signs of liver dysfunction. Pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase activities were normal in autopsy brain specimens and in cultured fibroblasts from the patient. Carnitine acetyltransferase was deficient in liver, brain, kidney, and cultured fibroblasts. Medium- and long-chain carnitine acyltransferase activities were normal. It is proposed that a functional defect of acetyl-coenzyme A (acetyl-CoA) utilization in brain mitochondria accompanies the carnitine acetyltransferase deficiency.