A case of severe hypermetabolism of nonthyroid origin with a defect in the maintenance of mitochondrial respiratory control: a correlated clinical, biochemical, and morphological study

De Toni-Debré-Fanconi syndrome in a patient with Kearns-Sayre syndrome: a case report

Introduction

Kearns-Sayre syndrome is a mitochondrial myopathy that demonstrates chronic progressive ophthalmoplegia with onset before the age of 20 and pigmentary degeneration of the retina.

Case presentation

We report the case of an 18-year-old Romanian man with short stature, external ophthalmoplegia, palpebral ptosis, myopathy, sensorineural hearing impairment, cerebellar ataxia, cardiac conduction defect, diabetes mellitus, hypoparathyroidism and hyperaldosteronism. The patient's evolution showed progressive insufficiency of the renal tubule: hyperphosphaturia, hyperaminoaciduria and, later, glucosuria (de Toni-Debré-Fanconi syndrome), a syndrome, to date, rarely diagnosed in association with complete Kearns-Sayre syndrome. The final diagnosis was delayed for several years and was only established when he developed diabetes mellitus. Southern blot analysis and polymerase chain reaction amplification revealed the presence of a deletion in the mitochondrial DNA.

Conclusion

Despite the rarity of this syndrome, the diagnosis was easily made due to the presence of the classic triad: external ophthalmoplegia, pigmentary retinopathy and onset in a patient younger than 20 years old. In our opinion, a search for Kearns-Sayre syndrome in all patients with de Toni-Debré-Fanconi syndrome is a valuable medical routine.

Clinical characteristics of patients with non-specific and non-categorized mitochondrial diseases

AIM

Mitochondrial disease is a heterogeneous disorder entity induced by defects in mitochondrial respiratory chain complex (MRC). A significant portion of patients with MRC defect will not conform to a specific, known syndrome. We have analysed the clinical features of 108 Korean paediatric patients with non-specific and non-categorized mitochondrial disease.

METHODS

We retrospectively reviewed the clinical and laboratory features of 108 paediatrics patients with non-specific and non-categorized mitochondrial diseases who showed defects in MRC activity, confirmed by spectrophotometric biochemical enzyme assay of their muscles.

RESULTS

Neuromuscular involvement was noted in all patients, with developmental delay and seizure accounting for 92.6% and 77.8% of total patients respectively. Various extraneurological symptoms were observed. Most patients exhibited MRC I defect, accounting for 100 (92.6%) patients. The most common brain magnetic resonance imaging (MRI) finding was diffuse cerebral atrophy. However, in 23.1% of patients, no notable changes were visible on MRI.

CONCLUSIONS

Mitochondrial respiratory chain complex I defect was the most common finding in this study. Though neuromuscular symptoms predominated, with presence of numerous extraneurological findings, we could not find any novel symptoms that might be unique to this category of mitochondrial disease. But, comparatively, more patients presented with unremarkable birth histories and normal brain MRI findings.

Mitochondria: new drug targets for oxidative stress-induced diseases

The identification of the mitochondrion as the gatekeeper of the life and death of a cell and the appreciation of the role of mitochondrial dysfunction in a range of clinical disease processes have made the mitochondrion a target for drug delivery. Accordingly, strategies are being developed for the targeted delivery of antioxidants to mitochondria. Recent studies show that triphenylphosphonium-based antioxidants and amino acid- and peptide-based antioxidants protect mitochondria against oxidative insult. Future studies will undoubtedly exploit the unique biophysical and biochemical properties of mitochondria, including mitochondrial activation of prodrugs, for the targeted delivery of cytoprotective agents.

The role of mitochondria in health and disease

Mitochondria play a key role in energy metabolism in many tissues, including skeletal muscle and liver. Inherent disorders of mitochondria such as DNA deletions cause major disruption of metabolism and can result in severe impairment or death. However, the occurrence of such disorders is extremely rare and cannot account for the majority of metabolic disease. Recently, mitochondrial dysfunction of a more subtle nature in skeletal muscle has been implicated in the pathology of chronic metabolic disease characterized by insulin resistance such as obesity, type 2 diabetes mellitus, and aging. This hypothesis has been substantiated by work from Shulman and colleagues, showing that reduced mitochondrial oxidative capacity underlies the accumulation of intramuscular fat causing insulin resistance with aging. However, recent work by Nair and coworkers has demonstrated that mitochondrial activity may actually be higher in persons exposed to high-calorie diet leading to obesity, suggesting that the accumulation of intramuscular fat and associated fatty acid metabolites may be directly responsible for the development of insulin resistance, independent of mitochondrial function. These inconsistent findings have promoted ongoing investigation into mitochondrial function to determine whether impaired function is a cause or consequence of metabolic disorders.

The pathophysiology of mitochondrial disease as modeled in the mouse

It is now clear that mitochondrial defects are associated with a plethora of clinical phenotypes in man and mouse. This is the result of the mitochondria's central role in energy production, reactive oxygen species (ROS) biology, and apoptosis, and because the mitochondrial genome consists of roughly 1500 genes distributed across the maternal mitochondrial DNA (mtDNA) and the Mendelian nuclear DNA (nDNA). While numerous pathogenic mutations in both mtDNA and nDNA mitochondrial genes have been identified in the past 21 years, the causal role of mitochondrial dysfunction in the common metabolic and degenerative diseases, cancer, and aging is still debated. However, the development of mice harboring mitochondrial gene mutations is permitting demonstration of the direct cause-and-effect relationship between mitochondrial dysfunction and disease. Mutations in nDNA-encoded mitochondrial genes involved in energy metabolism, antioxidant defenses, apoptosis via the mitochondrial permeability transition pore (mtPTP), mitochondrial fusion, and mtDNA biogenesis have already demonstrated the phenotypic importance of mitochondrial defects. These studies are being expanded by the recent development of procedures for introducing mtDNA mutations into the mouse. These studies are providing direct proof that mtDNA mutations are sufficient by themselves to generate major clinical phenotypes. As more different mtDNA types and mtDNA gene mutations are introduced into various mouse nDNA backgrounds, the potential functional role of mtDNA variation in permitting humans and mammals to adapt to different environments and in determining their predisposition to a wide array of diseases should be definitively demonstrated.

[Metabolic myopathies - an overview]

Metabolic disorders of energy production characterise the group of rare, mainly autosomal recessively inherited metabolic muscular diseases which are often associated with multi-systemic symptoms. In this report, an update on the clinics, pathophysiology, pathomorphology and current treatment options of metabolic myopathies will be given. Beyond classic phenotypes of these disorders, one should be aware of oligosymptomatic patients who can be easily missed. The relevant gene mutations and the pathophysiology and pathomorphology they cause are now known for almost all these metabolic diseases. Establishing the correct diagnosis has become even more important since highly specific therapy options are now available for at least some of these inherited disorders, e.g. enzyme replacement therapy in Pompe disease.

Morphological Methods in the Diagnosis of Mitochondrial Encephalomyopathies: The Role of Electron Microscopy

Mitochondrial encephalomyopathies (MEs) encompass a heterogeneous group of disorders that frequently present a diagnostic challenge to clinicians. Historically, MEs were diagnosed by finding ragged red fibers in the muscle biopsy and confirmatory evidence was provided by the presence of numerical and/or ultrastructural abnormalities in mitochondria. In most centers diagnosis involves clinical evaluation and the morphological, histochemical, and biochemical investigation of a skeletal muscle biopsy. However, with the availability of mitochondrial DNA analysis, the necessity and role of morphological methods and, in particular, electron microscopy has been questioned. The aim of this study was to delineate the role of electron microscopy in the diagnosis of MEs.

Myocardial overexpression of Mecr, a gene of mitochondrial FAS II leads to cardiac dysfunction in mouse

It has been recently recognized that mammalian mitochondria contain most, if not all, of the components of fatty acid synthesis type II (FAS II). Among the components identified is 2-enoyl thioester reductase/mitochondrial enoyl-CoA reductase (Etr1/Mecr), which catalyzes the NADPH-dependent reduction of trans-2-enoyl thioesters, generating saturated acyl-groups. Although the FAS type II pathway is highly conserved, its physiological role in fatty acid synthesis, which apparently occurs simultaneously with breakdown of fatty acids in the same subcellular compartment in mammals, has remained an enigma. To study the in vivo function of the mitochondrial FAS in mammals, with special reference to Mecr, we generated mice overexpressing Mecr under control of the mouse metallothionein-1 promoter. These Mecr transgenic mice developed cardiac abnormalities as demonstrated by echocardiography in vivo, heart perfusion ex vivo, and electron microscopy in situ. Moreover, the Mecr transgenic mice showed decreased performance in endurance exercise testing. Our results showed a ventricular dilatation behind impaired heart function upon Mecr overexpression, concurrent with appearance of dysmorphic mitochondria. Furthermore, the data suggested that inappropriate expression of genes of FAS II can result in the development of hereditary cardiomyopathy.

Dynamic organization of mitochondria in human heart and in myocardial disease

Heart mitochondria, which, depending on their location within cardiomyofibers, are classified as either subsarcolemmal or interfibrillar, are the major sources of the high energy compound, adenosine triphosphate. Physiological differences between these two populations are reflected by differences in the morphology of their cristae, with those of subsarcolemmal mitochondria being mostly lamelliform, and those of interfibrillar mitochondria being mostly tubular. What determines the configuration of cristae, not only in cardiac mitochondria but in mitochondria in general, is unclear. The morphology of cardiac mitochondria, as well as their physiology, is responsive to the exigencies posed by a large variety of pathological situations. Giant cardiac mitochondria make an appearance in certain types of cardiomyopathy and as a result of dietary, pharmacological, and toxicological manipulation; such megamitochondria probably arise by a combination of fusion and true growth. Some of these enlarged organelles occasionally contain a membrane-bound deposit of beta-glycogen. Those giant mitochondria induced by experimental treatment usually can be restored to normal dimensions simply by supplying the missing nutrient or by deleting the noxious substance. In some conditions, such as endurance training and ischemia, the mitochondrial matrices become pale. Dense rods or plates are present in the outer compartment of mitochondria under certain conditions. Biochemical alterations in cardiac mitochondria appear to be important in heart failure. In aging, only interfibrillar mitochondria exhibit such changes, with the subsarcolemmal mitochondria unaffected. In certain heart afflictions, biochemical defects are not accompanied by obvious morphological transformations. Mitochondria clearly play a cardinal role in homeostasis of the heart.

Mitochondrial NADH-dehydrogenase subunit 3 (ND3) polymorphism (A10398G) and sporadic breast cancer in Poland

Mitochondria are subcellular organelles that produce adenosine triphosphate (ATP) through oxidative phosphorylation (OXPHOS). As suggested over 70 years ago by Otto Warburg and recently confirmed with molecular techniques, alterations in respiratory activity and mitochondrial DNA (mtDNA) appear to be common features of malignant cells. Somatic mtDNA mutations have been reported in many types of cancer cells, but very few reports document the prevalence of inherited mitochondrial DNA polymorphisms in cancer patients compared to healthy control populations. Here we report the abundance of the 10398G polymorphism in a Polish breast cancer population and its frequency in controls. Amongst individuals with breast cancer the G single nucleotide polymorphism (SNP) is present in 23% of affected females compared to 3% of controls. This difference is highly statistically significant (P = 0.0008). It is therefore possible that the 10398G SNP constitutes an inherited predisposition factor for the development of breast cancer.

Pathogenic mutations of nuclear genes associated with mitochondrial disorders

Mitochondrial disorders are clinical phenotypes associated with mitochondrial dysfunction, which can be caused by mutations in mitochondrial DNA (mtDNA) or nuclear genes. In this review, we summarized the pathogenic mutations of nuclear genes associated with mitochondrial disorders. These nuclear genes encode, components of mitochondrial translational machinery and structural subunits and assembly factors of the oxidative phosphorylation, that complex. The molecular mechanisms, that nuclear modifier genes modulate the phenotypic expression of mtDNA mutations, are discussed in detail.

The neurodegenerative mitochondriopathies

Mitochondria are physically or functionally altered in many neurodegenerative diseases. This is the case for very rare neurodegenerative disorders as well as extremely common age-related ones such as Alzheimer's disease and Parkinson's disease. In some disorders very specific patterns of altered mitochondrial function or systemic mitochondrial dysfunction are demonstrable. Some disorders arise from mitochondrial DNA mutation, some from nuclear gene mutation, and for some the etiology is not definitively known. This review classifies neurodegenerative diseases using mitochondrial dysfunction as a unifying feature, and in doing so defines a group of disorders called the neurodegenerative mitochondriopathies. It discusses what mitochondrial abnormalities have been identified in various neurodegenerative diseases, what is currently known about the mitochondria-neurodegeneration nexus, and speculates on the significance of mitochondrial function in some disorders not classically thought of as mitochondriopathies.

Pathogenesis and treatment of mitochondrial disorders

In the past 50 years, our understanding of the biochemical and molecular causes of mitochondrial diseases, defined restrictively as disorders due to defects of the mitochondrial respiratory chain (RC), has made great strides. Mitochondrial diseases can be due to mutations in mitochondrial DNA (mtDNA) or in nuclear DNA (nDNA) and each group can be subdivided into more specific classes. Thus, mtDNA-related disorders can result from mutations in genes affecting protein synthesis in toto or mutations in protein-coding genes. Mendelian mitochondrial disorders can be attributed to mutations in genes that (i) encode subunits of the RC ("direct hits"); (ii) encode assembly proteins or RC complexes ("indirect hits"); (iii) encode factors needed for mtDNA maintenance, replication, or translation (intergenomic signaling); (iv) encode components of the mitochondrial protein import machinery; (v) control the synthesis and composition of mitochondrial membrane phospholipids; and (vi) encode proteins involved in mitochondrial dynamics.In contrast to this wealth of knowledge about etiology, our understanding of pathogenic mechanism is very limited. We discuss pathogenic factors that can influence clinical expression, especially ATP shortage and reactive oxygen radicals (ROS) excess. Therapeutic options are limited and fall into three modalities: (i) symptomatic interventions, which are palliative but crucial for day-to-day management; (ii) radical approaches aimed at correcting the biochemical or molecular error, which are interesting but still largely experimental; and (iii) pharmacological means of interfering with the pathogenic cascade of events (e.g. boosting ATP production or scavenging ROS), which are inconsistently and incompletely effective, but can be safe and helpful.

Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes: basic concepts, clinical phenotype, and therapeutic management of MELAS syndrome

Since the initial description almost 25 years ago, the syndrome of mitochondrial encephalopathy, lactic acidosis, and strokelike episodes (MELAS) has been a useful model to study the complex interplay of factors that define mitochondrial disease. This syndrome, most commonly caused by an A-to-G transition mutation at position 3243 of the mitochondrial genome, is typified by characteristic neurological manifestations including seizures, encephalopathy, and strokelike episodes, as well as other frequent secondary manifestations including short stature, cognitive impairment, migraines, depression, cardiomyopathy, cardiac conduction defects, and diabetes mellitus. In this review, we discuss the history, pathogenesis, clinical features, and diagnostic and management strategies of mitochondrial disease in general and of MELAS in particular. We explore features of mitochondrial genetics, including the concepts of heteroplasmy, mitotic segregation, and threshold effect, as a basis for understanding the variability and complicated inheritance patterns seen with this group of diseases. We also describe systemic manifestations of MELAS-associated mutations, including cardiac, renal, endocrine, gastrointestinal, and endothelial abnormalities and pathology, as well as the hypothetical role of derangements to COX enzymatic function in driving the unique pathology and clinical manifestations of MELAS. Although therapeutic options for MELAS and other mitochondrial diseases remain limited, and recent trials have been disappointing, we also consider current and potential therapeutic modalities.

Avaliação audiológica na doença mitocondrial: relato de dois casos

TEMA: audição e mitocondriopatia. PROCEDIMENTOS: este relato de caso teve como objetivo descrever os resultados da avaliação audiológica de duas crianças atendidas no ambulatório de audiologia clínica da Universidade Federal de São Paulo - Escola Paulista de Medicina (UNIFESP/EPM), com diagnóstico de doença mitocondrial, correlacionando os achados desta avaliação com a fisiopatologia subjacente. As crianças deste estudo, filhas de pais consangüíneos, foram encaminhadas para o ambulatório de audiologia clínica da UNIFESP-EPM pelo ambulatório de doenças metabólicas da mesma instituição em março de 2006 para realizar avaliação audiológica completa. As crianças foram submetidas à audiometria tonal, audiometria vocal, observação comportamental, medidas da imitância acústica e emissões otoacústicas. RESULTADOS: as avaliações comportamental e fisiológica revelaram que as crianças apresentam deficiência auditiva neurossensorial de grau leve a moderadamente severo e presença de sobressalto com ausência de habituação, indicando assim, comprometimento auditivo central. CONCLUSÃO: estes relatos de casos ressaltam a importância de ser considerada a associação entre os fatores de risco para deficiência auditiva no planejamento da reabilitação dos pacientes.

Medication-induced mitochondrial damage and disease

Since the first mitochondrial dysfunction was described in the 1960s, the medicine has advanced in its understanding the role mitochondria play in health and disease. Damage to mitochondria is now understood to play a role in the pathogenesis of a wide range of seemingly unrelated disorders such as schizophrenia, bipolar disease, dementia, Alzheimer's disease, epilepsy, migraine headaches, strokes, neuropathic pain, Parkinson's disease, ataxia, transient ischemic attack, cardiomyopathy, coronary artery disease, chronic fatigue syndrome, fibromyalgia, retinitis pigmentosa, diabetes, hepatitis C, and primary biliary cirrhosis. Medications have now emerged as a major cause of mitochondrial damage, which may explain many adverse effects. All classes of psychotropic drugs have been documented to damage mitochondria, as have stain medications, analgesics such as acetaminophen, and many others. While targeted nutrient therapies using antioxidants or their precursors (e. g., N-acetylcysteine) hold promise for improving mitochondrial function, there are large gaps in our knowledge. The most rational approach is to understand the mechanisms underlying mitochondrial damage for specific medications and attempt to counteract their deleterious effects with nutritional therapies. This article reviews our basic understanding of how mitochondria function and how medications damage mitochondria to create their occasionally fatal adverse effects.

Muscle 3243A-->G mutation load and capacity of the mitochondrial energy-generating system

OBJECTIVE

The mitochondrial energy-generating system (MEGS) encompasses the mitochondrial enzymatic reactions from oxidation of pyruvate to the export of adenosine triphosphate. It is investigated in intact muscle mitochondria by measuring the pyruvate oxidation and adenosine triphosphate production rates, which we refer to as the "MEGS capacity." Currently, little is known about MEGS pathology in patients with mutations in the mitochondrial DNA. Because MEGS capacity is an indicator for the overall mitochondrial function related to energy production, we searched for a correlation between MEGS capacity and 3243A-->G mutation load in muscle of patients with the MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes) syndrome.

METHODS

In muscle tissue of 24 patients with the 3243A-->G mutation, we investigated the MEGS capacity, the respiratory chain enzymatic activities, and the 3243A-->G mutation load. To exclude coinciding mutations, we sequenced all 22 mitochondrial transfer RNA genes in the patients, if possible.

RESULTS

We found highly significant differences between patients and control subjects with respect to the MEGS capacity and complex I, III, and IV activities. MEGS-related measurements correlated considerably better with the mutation load than respiratory chain enzyme activities. We found no additional mutations in the mitochondrial transfer RNA genes of the patients.

INTERPRETATION

The results show that MEGS capacity has a greater sensitivity than respiratory chain enzymatic activities for detection of subtle mitochondrial dysfunction. This is important in the workup of patients with rare or new mitochondrial DNA mutations, and with low mutation loads. In these cases we suggest to determine the MEGS capacity.

Energy utilization for control

When, on addition of a suitable substrate, a chemical potential is applied to an enzymic process such as glycolysis or respiration, whether in solution or membrane-bound, all components of the process pass into a nonequilibrium state, which might be steady or non-steady and which produces the following phenomena: (1) The reactants of each enzymic reaction are displaced from their equilibrium concentration, and energy is dissipated; (2) Part of each enzyme is transferred to a transition state of its catalytic function as well as isosteric and allosteric controlling functions, displaying local and gross conformation changes, and a rate-controlling state is generated; (3) In cyclic portions of a process futile events and chemical interconversion may occur; (4) In self- and cross-coupled portions of a process, oscillation with periodic changes of states and spatial propagation as well as instabilities may be observed; (5) At each step of a process, depending on the rate of flux and the specific enzymic function, a varying proportion of the free energy changes--which are concentration-dependent and derived from the overall potential of the system-is contributed to the control of flux rates. This will be exemplified for enzymes of bioenergetic pathways.

Fatigue in human metabolic myopathy

The ability of muscle fibres to sustain force can be related to their economy of energy utilization and to their capacity to regenerate energy under the prevailing conditions (aerobic or anaerobic) of contraction. The pathophysiology of muscle fatigue is analysed in patients with thyroid dysfunction and with impaired glycogenolysis, and in a patient with abnormal mitochondrial function. Muscle from hypothyroid patients, like cooled muscle, is slow in relaxing and shows a reduced energy requirement (energy economy) and reduced fatiguability, whereas muscle of hyperthyroid patients may show the opposite features. In myophosphorylase deficiency the energy economy is normal in the fresh state and increases as contraction proceeds; however, fatigue is premature and associated with impaired excitation rather than an overall depletion of energy stores. With abnormal mitochondrial function the muscle tends to be effectively anaerobic and fatigue is associated with impaired excitation-contraction coupling. This appears to result from either muscle ischaemia or the dominant use of anaerobic metabolism for energy regeneration. Fatigue in these disorders of energy metabolism may ultimately be due to a reduced supply of ATP but direct evidence of this is lacking and, if it occurs, its physiological expression is probably variable.

The efficiency of cellular energy transduction and its implications for obesity

We assess the existence, mechanism, and functions of less-than-maximal coupling efficiency of mitochondrial oxidative phosphorylation and its potential as a target for future antiobesity interventions. Coupling efficiency is the proportion of oxygen consumption used to make adenosine triphosphate (ATP) and do useful work. High coupling efficiency may lead to fat deposition; low coupling efficiency to a decrease in fat stores. We review obligatory and facultative energy expenditure and the role of a futile cycle of proton pumping and proton leak across the mitochondrial inner membrane in dissipating energy. Basal proton conductance is catalyzed primarily by the adenine nucleotide translocase but can be mimicked by chemical uncouplers. Inducible proton conductance is catalyzed by specific uncoupling proteins. We discuss the opportunities and pitfalls of targeting these processes as a treatment for obesity by decreasing coupling efficiency and increasing energy expenditure, either directly or through central mechanisms of energy homeostasis.

Links between thyroid hormone action, oxidative metabolism, and diabetes risk?

A key phenotype associated with type 2 diabetes in humans is impaired mitochondrial oxidative metabolism in skeletal muscle, a pattern potentially contributing to increased lipid accumulation and impaired metabolic flexibility-in turn, central features of both insulin resistance and diabetes. Since thyroid hormone regulates mitochondrial gene expression and function in skeletal muscle, reductions in T3-mediated transcription may contribute to diabetes-related impairments in oxidative metabolism. We review the evidence for relationships between thyroid hormone action and diabetes risk, and discuss potential mechanisms linking intracellular thyroid hormone availability, thyroid receptor action, and the transcriptional coactivator PGC1 in regulating oxidative metabolism.

Neuropsychologic Profile of a High-functioning Family With a Mitochondrial Cytopathy

OBJECTIVE

To examine the neuropsychologic profile of 3 family members diagnosed with the same mitochondrial cytopathy corresponding to a defect in the respiratory chain.

BACKGROUND

The neuropsychologic functioning of patients with mitochondrial cytopathies has been largely unexamined in the literature. These mitochondrial defects often result in cell death and the failure of whole systems, including the brain. There are over 40 known types of mitochondrial cytopathies, which vary greatly in their genetic, clinical, and behavioral manifestations.

METHOD

The following project describes the neuropsychologic profiles of a family (a mother and her 2 children) afflicted by the same mitochondrial cytopathy possibly associated with nucleotide 15,924. Standardized tests of premorbid intelligence estimation, attention, executive function, language, verbal and visual memory, visuospatial functioning, motor functioning, visual acuity, mood, and activities of daily living were administered.

RESULTS

Participants' profiles were characterized by estimated intellectual ability in the average to superior range with marked variability on a number of assessments, making it difficult to identify a distinct pattern. General trends, however, were reflective of executive function impairment associated with dysfunction of frontal-subcortical systems.

CONCLUSIONS

Mitochondrial disorders are extremely complicated and variable in their presentation. A multifactor approach should be adopted when examining neuropsychologic profiles.

Foreword: Mitochondrial Medicine

Mitochondrion is currently known to play major roles in many disease processes: neuromuscular disorders, neurodegenerative conditions (i.e. Parkinson's and Alzheimer's diseases), diabetes mellitus, aging, programmed cell death, and carcinogenesis, to name a few. In this background, the Department of Neuroscience of the University of Pisa (Italy) has organised a scientific meeting on October 25th, 2006, to discuss recent progress in the field of mitochondriology.

Mitochondria-specific nanotechnology

Mitochondrial research has made an enormous leap since mitochondrial DNA mutations were identified as a primary cause for human diseases in 1988 and the organelle’s crucial role in apoptosis was identified during the 1990s. Considerable progress has been made in identifying the molecular components of the mitochondrial machinery responsible for life and cell death; however, effective therapies for diseases caused by mitochondrial dysfunction remain elusive. An impediment to manipulating, probing and assessing the functional components of mammalian mitochondria within living cells is their limited accessibility to direct physical, biochemical and pharmacological manipulation. Recent advances in nanotechnology hold the promise of helping to overcome these obstacles. New tools will undoubtedly emerge, creating new avenues for the diagnosis and therapy of mitochondrial disorders. This review briefly discusses current efforts to merge nanobiotechnology with mitochondrial medicine.

Approche diagnostique des maladies mitochondriales à présentation neurologique

Mitochondrial respiratory chain abnormalities are a cause of neuromuscular diseases. They present with very diverse clinical presentations,involving either the central nervous system, the peripheral nervous system, or skeletal muscle, and may be due to mutations either in mitochondrial or nuclear genome. The aim of this review is to familiarise the clinician with these diseases, to evoke main syndromes, and to give guidelines for their diagnostic investigation.

Mitochondrial dysfunction and molecular pathways of disease

Since the first mitochondrial dysfunction was described in the 1960s, the medicine has advanced in its understanding the role mitochondria play in health, disease, and aging. A wide range of seemingly unrelated disorders, such as schizophrenia, bipolar disease, dementia, Alzheimer's disease, epilepsy, migraine headaches, strokes, neuropathic pain, Parkinson's disease, ataxia, transient ischemic attack, cardiomyopathy, coronary artery disease, chronic fatigue syndrome, fibromyalgia, retinitis pigmentosa, diabetes, hepatitis C, and primary biliary cirrhosis, have underlying pathophysiological mechanisms in common, namely reactive oxygen species (ROS) production, the accumulation of mitochondrial DNA (mtDNA) damage, resulting in mitochondrial dysfunction. Antioxidant therapies hold promise for improving mitochondrial performance. Physicians seeking systematic treatments for their patients might consider testing urinary organic acids to determine how best to treat them. If in the next 50 years advances in mitochondrial treatments match the immense increase in knowledge about mitochondrial function that has occurred in the last 50 years, mitochondrial diseases and dysfunction will largely be a medical triumph.

Keshan disease and mitochondrial cardiomyopathy

Keshan disease (KD) is a potentially fatal form of cardiomyopathy (disease of the heart muscle) endemic in certain areas of China. From 1984 to 1986, a national comprehensive scientific investigation on KD in Chuxiong region of Yunnan Province in the southwest China was conducted. The investigation team was composed of epidemiologists, clinic doctors, pathologists, biochemists, biophysicists and specialists in ecological environment. Results of pathological, biochemical and biophysical as well as clinical studies showed: an obvious increase of enlarged and swollen mitochondria with distended crista membranes in myocardium from patients with KD; significant reductions in the activity of oxidative phosphorylation (succinate dehydrogenase, cytochrome oxidase, succinate oxidase, H(+)-ATPase) of affected mitochondria; decrease in CoQ, cardiolipin, Se and GSHPx activity, while obvious increase in the Ca2+ content. So, it was suggested that mitochondria are the predominant target of the pathogenic factors of KD. Before Chuxiong KD survey only a few cases of mitochondrial cardiomyopathy were studied. During the multidisciplinary scientific investigation on KD in Chuxiong a large amount of samples from KD cases and the positive controls were examined. On the basis of the results obtained it was suggested that KD might be classified as a "Mitochondrial Cardiomyopathy" endemic in China. This is one of the achievements in the three years' survey in Chuxiong and is valuable not only to the deeper understanding of pathogenic mechanism of KD but also to the study of mitochondrial cardiomyopathy in general. Keshan disease is not a genetic disease, but is closely related to the malnutrition (especially microelement Se deficiency). KD occurs along a low Se belt, and Se supplementation has been effective in prevention of such disease. The incidence of KD has sharply decreased along with the steady raise of living standard and realization of preventive measures. At present, patients of KD are very sparse. In recent years the research on the non-KD mitochondrial cardiomyopathy has progressed rapidly. Given the advances in this aspect a minireview is written to evaluate the classification of KD as a kind of mitochondrial cardiomyopathy.

Overexpression of peroxisome proliferator-activated receptor gamma co-activator-1alpha leads to muscle atrophy with depletion of ATP

Peroxisome proliferator-activated receptor-gamma co-activator-1alpha (PGC-1alpha) is a key nuclear receptor co-activator for mitochondrial biogenesis. Here we report that overexpression of PGC-1alpha in skeletal muscles increased mitochondrial number and caused atrophy of skeletal muscle, especially type 2B fiber-rich muscles (gastrocnemius, quadriceps, and plantaris). Muscle atrophy became evident at 25 weeks of age, and a portion of the muscle was replaced by adipocytes. Mice showed increased energy expenditure and reduced body weight; thyroid hormone levels were normal. Mitochondria exhibited normal respiratory chain activity per mitochondrion; however, mitochondrial respiration was not inhibited by an ATP synthase inhibitor, oligomycin, clearly indicating that oxidative phosphorylation was uncoupled. Accordingly, ATP content in gastrocnemius was markedly reduced. A similar phenotype is observed in Luft's disease, a mitochondrial disorder that involves increased uncoupling of respiration and muscle atrophy. Our results indicate that overexpression of PGC-1alpha in skeletal muscle increases not only mitochondrial biogenesis but also uncoupling of respiration, resulting in muscle atrophy.

Assaying the probabilities of obtaining maternally inherited heteroplasmy as the basis for modeling OXPHOS diseases in animals

Gross alterations in cell energy metabolism underlie manifestations of hereditary OXPHOS (oxidative phosphorylation) diseases, many of which depend on proportion of mutant mitochondrial DNA (mtDNA) in tissues. An animal model of OXPHOS disease with maternal inheritance of mitochondrial heteroplasmy might help understanding the peculiarities of abnormal mtDNA distribution and its effect on pre- and postnatal development. Previously we obtained mice that carry human mtDNA in some tissues. It co-existed with murine mtDNA (heteroplasmy) and was transmitted maternally to the progeny of animals developed from zygotes injected with human mitochondria. To analyze the probability of obtaining heteroplasmic mice we increased the number of experiments with early embryos and obtained more specimens from F1. About 33% of zygotes injected with human mtDNA developed into post-implantation embryos (7th-13th days). Lower amount of such developed into neonate mice (ca. 21%). Among post-implantation embryos and in generations F0 and F1 percentages of human mtDNA-carriers were ca. 14-16%. Such percentages are sufficient for modeling maternally inherited heteroplasmy in small animal groups. More data are needed to understand the regularities of anomalous mtDNA distribution among cells and tissues and whether heart and muscles frequently carrying human mtDNA in our experiments are particularly susceptible to heteroplasmy.

Redox regulation of heat shock protein expression by signaling involving nitric oxide and carbon monoxide: relevance to brain aging, neurodegenerative disorders, and longevity

Increased free radical generation and decreased efficiency of the reparative/degradative mechanisms both primarily contribute to age-related elevation in the level of oxidative stress and brain damage. Excess formation of reactive oxygen and nitrogen species can cause proteasomal dysfunction and protein overloading. The major neurodegenerative diseases are all associated with the presence of abnormal proteins. Different integrated responses exist in the brain to detect oxidative stress which is controlled by several genes termed vitagenes, including the heat shock protein (HSP) system. Of the various HSPs, heme oxygenase-I (HO-1), by generating the vasoactive molecule carbon monoxide and the potent antioxidant bilirubin, could represent a protective system potentially active against brain oxidative injury. The HO-1 gene is redox regulated and its expression is modulated by redox active compounds, including nutritional antioxidants. Given the broad cytoprotective properties of the heat shock response, there is now strong interest in discovering and developing pharmacological agents capable of inducing the heat shock response. These findings have opened up new neuroprotective strategies, as molecules inducing this defense mechanism can be a therapeutic target to minimize the deleterious consequences associated with accumulation of conformationally aberrant proteins to oxidative stress, such as in neurodegenerative disorders and brain aging, with resulting prolongation of a healthy life span.

Mitochondrial myopathies: diagnosis, exercise intolerance, and treatment options

Mitochondrial myopathies are caused by genetic mutations that directly influence the functioning of the electron transport chain (ETC). It is estimated that 1 of 8,000 people have pathology inducing mutations affecting mitochondrial function. Diagnosis often requires a multifaceted approach with measurements of serum lactate and pyruvate, urine organic acids, magnetic resonance spectroscopy (MRS), muscle histology and ultrastructure, enzymology, genetic analysis, and exercise testing. The ubiquitous distribution of the mitochondria in the human body explains the multiple organ involvement. Exercise intolerance is a common but often an overlooked hallmark of mitochondrial myopathies. The muscle consequences of ETC dysfunction include increased reliance on anaerobic metabolism (lactate generation, phosphocreatine degradation), enhanced free radical production, reduced oxygen extraction and electron flux through ETC, and mitochondrial proliferation or biogenesis (see article by Hood in current issue). Treatments have included antioxidants (vitamin E, alpha lipoic acid), electron donors and acceptors (coenzyme Q10, riboflavin), alternative energy sources (creatine monohydrate), lactate reduction strategies (dichloroacetate) and exercise training. Exercise is a particularly important modality in diagnosis as well as therapy (see article by Taivassalo in current issue). Increased awareness of these disorders by exercise physiologists and sports medicine practitioners should lead to more accurate and more rapid diagnosis and the opportunity for therapy and genetic counseling.