Michael J. Goldenthal

Abnormal cardiac and skeletal muscle mitochondrial function in pacing-induced cardiac failure

BACKGROUND Previous studies have shown that marked changes in myocardial mitochondrial structure and function occur in human cardiac failure. To further understand the cellular events and to clarify their role in the pathology of cardiac failure, we have examined mitochondrial enzymatic function and peptide content, and mitochondrial DNA (mtDNA) integrity in a canine model of pacing-induced cardiac failure. METHODS Myocardium and skeletal muscle tissues were evaluated for levels of respiratory complex I-V and citrate synthase activities, large-scale mtDNA deletions as well as peptide content of specific mitochondrial enzyme subunits. Levels of circulating and cardiac tumor necrosis factor-alpha (TNF-alpha), and of total aldehyde content in left ventricle were also assessed. RESULTS Specific activity levels of complex III and V were significantly lower in both myocardial and skeletal muscle tissues of paced animals compared to controls. In contrast, activity levels of complex I, II, IV and citrate synthase were unchanged, as was the peptide content of specific mitochondrial enzyme subunits. Large-scale mtDNA deletions were found to be more likely present in myocardial tissue of paced as compared to control animals, albeit at a relatively low proportion of mtDNA molecules (<0.01% of wild-type). In addition, the reduction in complex III and V activities was correlated with elevated plasma and cardiac TNF-alpha levels. Significant increases in left ventricle aldehyde levels were also found. CONCLUSIONS Our data show reductions in specific mitochondrial respiratory enzyme activities in pacing-induced heart failure which is not likely due to overall decreases in mitochondrial number, or necrosis. Our findings suggest a role for mitochondrial dysfunction in the pathogenesis of cardiac failure and may indicate a commonality in the signaling for pacing-induced mitochondrial dysfunction in myocardial and skeletal muscle. Increased levels of TNF-alpha and oxidative stress appear to play a contributory role.

Mitochondrial pathology in cardiac failure

Time for primary review 34 days. The heart is highly dependent for its function on oxidative energy generated in mitochondria, primarily by fatty acid β-oxidation, respiratory electron chain and oxidative phosphorylation (OXPHOS). In this review, we survey the available evidence that mitochondrial dysfunction may play a pivotal role in cardiac failure. We also discuss how mitochondrial dysfunction may be related to other critical cellular and molecular changes found in cardiac hypertrophy and failure, including dysfunctional structural and cytoskeletal proteins, apoptosis, calcium flux and handling, and signalling pathways. The review also focuses on the biochemical and molecular changes in severe heart failure secondary to primary cardiomyopathy (dilated/hypertrophic) in humans as well as findings in animal models of heart failure related to volume and/or pressure overload. Mitochondria are abundant in energy-demanding cardiac tissue constituting 20–40% of cellular volume (greater proportion than in skeletal muscle). Mitochondrial energy production depends on genetic factors which modulate normal mitochondrial function including enzyme activity and cofactor availability and on environmental factors including the availability of fuels (e.g. sugars, fats and proteins) and oxygen. Fatty acids are the primary energy substrate for heart muscle ATP generation by OXPHOS and the mitochondrial respiratory chain, the most important supply of cardiac energy. The supply of ATP from other sources, e.g. glycolytic metabolism is limited in normal cardiac tissue. Fatty acid β-oxidation and the oxidation of carbohydrates through the TCA cycle generate the majority of intramitochondrial NADH and FADH which are the direct source of electrons for the electron transport chain (and produce as well a small proportion of the ATP supply) (Fig. 1) [1]. The heart also maintains stored high-energy phosphates (e.g. ATP and phosphocreatine pools). Fig. 1 Mitochondrial bioenergetic pathways in cardiac failure. Mitochondrial inner-membrane localized respiratory complexes I–V (hatched circles) with associated electron-transfer components, CoQ and Cyt c, are … * Corresponding author. Tel.: +1-732-220-1719; fax: +1-732-220-2992 tmci{at}worldnet.att.net

Mitochondrial centrality in heart failure

A number of observations have shown that mitochondria are at the center of the pathophysiology of the failing heart and mitochondrial-based oxidative stress (OS), myocardial apoptosis, and cardiac bioenergetic dysfunction are implicated in the progression of heart failure (HF), as shown by both clinical studies and animal models. In this manuscript, we review the body of evidence that multiple defects in mitochondria are central and primary to HF progression. In addition, novel approaches to therapeutic targeting of mitochondrial bioenergetic, biogenic, and signaling abnormalities that can impact HF are discussed.

Bioenergetic remodeling of heart mitochondria by thyroid hormone

Changes in thyroid status are associated with profound alterations in biochemical and physiological functioning of cardiac muscle impacting metabolic rate, contractility and structural hypertrophy. Using an in vivo model of chronic treatment with thyroid hormone (T4, 0.3 mg/kg/day), we evaluated how mitochondria are regulated in response to T4, and assessed the relationship of T4-induced mitochondrial biogenesis and bioenergetics to overall cardiac hypertrophy. The role of thyroid hormone in cardiac bioenergetic remodeling was addressed in rats treated with T4 for 5, 10 and 15 days. Over that time, myocardial oxygen consumption substantially increased as did cardiac hypertrophy. Myocardial levels of mitochondrial enzyme activities, mitochondrial DNA (mtDNA), specific proteins and transcript were assessed. Activity levels of respiratory complexes I-V and citrate synthase significantly increased with 15 but not with 5 or 10-day T4 treatment. Myocardial levels of mtDNA, mitochondrial proteins (e.g. cytochrome c, cytochrome b, ATPase subunits, MnSOD) and the global transcription factor PPARα were significantly elevated with 15-day T4. Transcript analysis revealed increased expression of transcription factors and cofactors involved in mitochondrial biogenesis including PPARα, mtTFA, ErbAα and PGC-1α. Our findings indicate parallel increases in myocardial mitochondrial bioenergetic capacity, oxygen consumption and markers of mitochondrial biogenesis with 15-day T4; these changes were not present with 10-day T4 even with significant cardiac hypertrophy. The marked, parallel increases in PPARα levels suggest its potential involvement in mediating myocardial-specific remodeling of mitochondria in response to T4. (Mol Cell Biochem xxx: 97–106, 2004)

Mitochondria play a critical role in cardioprotection

BACKGROUND There is increasing evidence documenting the capacity of myocardial cells exposed to a variety of insults to mount a cardioprotective response. Although this cardioprotection has been most well characterized with respect to ischemic preconditioning, other chemical and metabolic stressors have been shown to share features of the ischemic preconditioning model, including the involvement of mitochondria in the triggering, signaling, and mediation of the cardioprotective response. METHODS In this article, we review the evidence showing that mitochondria play a critical role in cardioprotection from multiple (often interrelated) standpoints: its primary function in producing the cellular bioenergetic supply, its control over events in apoptosis, its contribution to myocardial signal transducing processes, and its role in producing reactive oxidative species and in providing an appropriate antioxidant response to a variety of cellular insults. CONCLUSIONS Although our understanding of cytoprotection has increased substantially within the last few years, the mechanisms mediating mitochondrial resistance to insults leading to cardiac protection remain to be fully delineated, and represents a significant approach in the clinical treatment of heart disease.

5q14.3 Deletion Manifesting as Mitochondrial Disease and Autism: Case Report

Mitochondrial disorders are usually associated with defects of 1 or more of the 5 complexes (I to V) of the electron transport chain, or respiratory chain. Complex I and IV are the 2 most frequent abnormalities of the electron transport chain in humans. The authors report the case of a 12-year-old boy with dysmorphic facies, mental retardation, autism, epilepsy, and leg weakness. Buccal swab electron transport chain analysis revealed severe decrease in complex IV and mild reduction in complex I activity levels. Chromosomal microarray studies, using array-based comparative genomic hybridization, revealed a 1-Mb deletion in the 5q14.3 region. This case illustrates that this deletion can be associated with complex I and IV deficits, hence manifesting as a mitochondrial disease. It could be hypothesized that genes that either encode or regulate the expression and/or assembly of complex IV or I subunits are located within the deleted region of 5q14.3.

Mitochondrial Dysfunction in Autism

Using data of the current prevalence of autism as 200:10,000 and a 1:2000 incidence of definite mitochondrial (mt) disease, if there was no linkage of autism spectrum disorder (ASD) and mt disease, it would be expected that 1 in 110 subjects with mt disease would have ASD and 1 in 2000 individuals with ASD would have mt disease. The co-occurrence of autism and mt disease is much higher than these figures, suggesting a possible pathogenetic relationship. Such hypothesis was initially suggested by the presence of biochemical markers of abnormal mt metabolic function in patients with ASD, including elevation of lactate, pyruvate, or alanine levels in blood, cerebrospinal fluid, or brain; carnitine level in plasma; and level of organic acids in urine, and by demonstrating impaired mt fatty acid β-oxidation. More recently, mtDNA genetic mutations or deletions or mutations of nuclear genes regulating mt function have been associated with ASD in patients or in neuropathologic studies on the brains of patients with autism. In addition, the presence of dysfunction of the complexes of the mt respiratory chain or electron transport chain, indicating abnormal oxidative phosphorylation, has been reported in patients with ASD and in the autopsy samples of brains. Possible pathogenetic mechanisms linking mt dysfunction and ASD include mt activation of the immune system, abnormal mt Ca(2+) handling, and mt-induced oxidative stress. Genetic and epigenetic regulation of brain development may also be disrupted by mt dysfunction, including mt-induced oxidative stress. The role of the purinergic system linking mt dysfunction and ASD is currently under investigation. In summary, there is genetic and biochemical evidence for a mitochondria (mt) role in the pathogenesis of ASD in a subset of children. To determine the prevalence and type of genetic and biochemical mt defects in ASD, there is a need for further research using the latest genetic technology such as next-generation sequencing, microarrays, bioinformatics, and biochemical assays. Because of the availability of potential therapeutic options for mt disease, successful research results could translate into better treatment and outcome for patients with mt-associated ASD. This requires a high index of suspicion of mt disease in children with autism who are diagnosed early.

La mitocondria y el corazón

The heart is highly dependent for its function on oxidative energy generated in mitochondria, primarily by fatty acid β-oxidation, respiratory electron chain and oxidative phosphorylation. Defects in mitochondrial structure and function have been found in association with cardiovascular diseases such as dilated and hypertrophy cardiomyopathy, cardiac conduction defects and sudden death, ischemic and alcoholic cardiomyopathy, as well as myocarditis. While a subset of these mitochondrial abnormalities have a defined genetic basis (e.g. mitochondrial DNA changes leading to oxidative phosphorylation dysfunction,fatty acid β-oxidation defects due to specific nuclear DNA mutations), other abnormalities appear to be due to a more sporadic or environmental cardiotoxic insult or have not yet been characterized. This review focuses on abnormalities in mitochondrial bioenergetic function and mitochondrial DNA defects associated with cardiovascular diseases, their significance in cardiac pathogenesis as well as on the available diagnostic and therapeutic options. A concise background concerning mitochondrial biogenesis and bioenergetic pathways during cardiac growth,development and aging will also be provided.

Fatty acid metabolism in cardiac failure: biochemical, genetic and cellular analysis

Time for primary review 29 days. Despite the abundant literature dealing with the metabolism of fatty acid in the heart, there is a limited understanding (and to the best of our knowledge no comprehensive review) concerning the role that cardiac lipid and fatty acid metabolism plays in the genesis and progression of cardiac failure. What is presently known is: 1. Fatty acids and associated lipids play an important role in cardiomyocytes structure and function. There is considerable evidence that in the post-natal and adult mammalian heart, fatty acid β oxidation is the preferred pathway for the energy that is required for efficient cardiac pumping. 2. Specific defects (either inherited or acquired) in mitochondrial fatty acid metabolism may cause cardiomyopathy and arrhythmias that can lead to cardiac failure. In this review, we discuss the information available concerning the molecular and cellular basis of fatty acid and lipid metabolic perturbations which can lead to cardiac failure. In this context, we will focus on the molecular and biochemical players as well as the events that occur in both the genetic abnormalities in fatty acid metabolism that lead to cardiomyopathy and cardiac failure, as well as in cardiac hypertrophy and apoptosis. The term cardiac failure is broadly used as a pathophysiologic state where the heart is unable to meet the metabolic requirements of the body. Most of this review is directed to our understanding of the mechanisms, diagnosis and treatment of fatty acid defects occurring in human cardiac failure. Experimental findings of defects in fatty acid metabolism are also discussed with respect to current and future use of animal models. Since the literature is abundant (including numerous reviews) on the subject of acquired and inherited lipid disorders in the development of coronary artery disease and stroke (e.g., cholesterol, the apolipoproteins and HDL/LDL), we have omitted these … * Corresponding author. Tel.: +1-732-22017-19; fax: +1-732-220-2992

Regional Distribution of Mitochondrial Dysfunction and Apoptotic Remodeling in Pacing-Induced Heart Failure

BACKGROUND Specific myocardial mitochondrial enzymatic dysfunction and apoptotic remodeling occur in pacing-induced heart failure. We sought to define their regional distribution and molecular basis in the failing heart. METHODS AND RESULTS Enzyme dysfunction was assessed in mitochondrial subpopulations and immunoblot analysis was performed using homogenate proteins from the left atria (LA) and left ventricle (LV) of paced and control mongrel dogs. A greater range of enzymatic defects (complex I, III, and V) was found in mitochondria subpopulations from the LV as compared with the LA (where only complex V was defective). Analysis of paced LV proteins demonstrated a downregulated expression of both mitochondrial genes (eg, cytochrome b) and nuclear genes (eg, ATP synthase beta subunit, mitochondrial creatine kinase). Protease-activated products of both mitochondrial (eg, apoptosis inducing factor) and cytosolic (eg, caspase-3) apoptogenic proteins were increased in both the LA and LV. Nuclear-localized apoptotic markers (eg, p53, p21) were also significantly increased in the LV of paced dogs. CONCLUSION Abnormal activity of several mitochondrial enzymes and increased apoptogenic pathway appear to be mediated, at least in part, by an orchestrated shift in expression (both nuclear and mitochondrial DNA) of respiratory chain subunits (eg, cyt b, ATP-beta), mitochondrial bioenergetic enzymes (eg, mitochondrial creatine kinase), global transcription factor (eg, PGC-1), and apoptotic proteins (eg, p53, p21) with distinct differences in their regional distribution and in the subpopulations of mitochondria affected.