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PubMed1997

Oxidative phosphorylation defects and Alzheimer's disease.

Abnormalities in cellular bioenergetics have been identified in patients with Alzheimer's disease (AD) as well as in patients with other neurodegenerative diseases. The most commonly reported enzyme abnormalities are in the pyruvate dehydrogenase complex, the alpha-ketoglutarate dehydrogenase complex, and oxidative phosphorylation (OXPHOS). Although genetic evidence supporting primary OXPHOS defects as a cause for AD is weak, functionally important reductions in OXPHOS enzyme activities appear to occur in AD and may be related to beta-amyloid accumulation or other neurodegenerative processes. Since reduced neuronal ATP may enhance susceptibility to glutamate toxicity, OXPHOS defects could play an important role in the pathophysiology of AD.

Alzheimer Disease↗
PubMed1995

The role of thyroid hormone and promoter diversity in the regulation of nuclear encoded mitochondrial proteins.

Thyroid hormone regulates the in vivo expression of a selected set of rat nuclear genes encoding mitochondrial inner membrane proteins. Certain mRNAs, such as that for cytochrome c1, are increased as much as 20-50-fold, while others, such as core protein 1 of Complex III and the F1-ATPase beta-subunit do not respond. The promoter region of human cytochrome c1 also supports thyroid hormone induction of a reporter gene in transient transfection experiments. Thus, thyroid hormone regulates only selected genes, even for subunits within the same complex and in widely varying species. By contrast, growth activation of quiescent NIH3T3 cells, a second paradigm used for stimulating mitochondrial biogenesis, does not increase cytochrome c1 mRNA but does increase F1-ATPase beta-subunit mRNA. These findings suggest that nuclear OXPHOS genes are not necessarily expressed in a coordinated manner, and that multiple regulatory circuits might exist which are linked to different physiological stimuli. Analysis of the promoters of several OXPHOS genes reveals a great diversity and heterogeneity of transfactor binding elements. No single regulatory feature exists which could account for a coordinated expression of all OXPHOS genes. The potential diversity for regulating expression of nuclear OXPHOS genes raises the possibility for the existence of disease states linked to regulatory defects.

3T3 Cells↗
PubMed2006

Mitochondrial medicine: a metabolic perspective on the pathology of oxidative phosphorylation disorders.

The final steps in the production of adenosine triphosphate (ATP) in mitochondria are executed by a series of multisubunit complexes and electron carriers, which together constitute the oxidative phosphorylation (OXPHOS) system. OXPHOS is under dual genetic control, with communication between the nuclear and mitochondrial genomes essential for optimal assembly and function of the system. We describe the current understanding of the metabolic consequences of pathological OXPHOS defects, based on analyses of patients and of genetically engineered model systems. Understanding the metabolic consequences of OXPHOS disease is of key importance for elucidating pathogenic mechanisms, guiding diagnosis and developing therapies.

Animals↗
PubMed2005

Drosophila simulans as a novel model for studying mitochondrial metabolism and aging.

Mitochondria generate much of the cellular energy through the process of oxidative phosphorylation (OXPHOS). OXPHOS function may be affected by a mutation in any of the mitochondrial (mt) DNA encoded genes and/or nuclear encoded genes that produce proteins imported into the mitochondrion that form (or assemble) the five complexes located on the inner mitochondrial membrane. Decreasing mitochondrial OXPHOS efficiency, defined as the amount of inorganic phosphate incorporated into ATP per mole of oxygen consumed (ADP:O ratio), results in an increase in the production of reactive oxygen species (ROS). ROS damages mtDNA, cell membranes, and lipids and, according to the free radical theory of aging, the rate of its accumulation is a major factor affecting lifespan. In humans, studies of age-specific cohorts suggest that extended longevity is associated with specific mtDNA types (mitotypes). However, the influence of each mitotype appears to be dependent on the nuclear genetic background in which it resides. These association studies are intuitively appealing, but since the age groups are necessarily from different cohorts there is no rigorous means of eliminating spurious associations due to accidents of sampling or environment. The critical need is to determine the extent to which (i) mitochondrial encoded genes, (ii) nuclear encoded genes whose products are imported into the mitochondrion, and (iii) interactions among mtDNA and nuclear (mitonuclear) encoded proteins, influence mitochondrial metabolism and life history traits including survival. This need can be efficiently accomplished in the fly Drosophila simulans owing to its (i) high mtDNA diversity, (ii) ease of genetic and experimental manipulations, (iii) sequence of multiple complete genomes, (iv) short generation time, (v) ease of collection and (vi) ability to raise large numbers so that sex and age-specific effects can be determined. The utility of the fly model is supported by the conservation of the OXPHOS pathway and the mitochondrial genome in humans, mice and Drosophila.

Aging↗
PubMed2006

Defect in oxidative phosphorylation in LV papillary muscle mitochondria of patients undergoing mitral valve replacement.

Mitochondria play a pivotal role in cellular metabolism, especially in energy production. Myocardial function depends on adenosine triphosphate (ATP) supplied by oxidation of several substrates. In the adult heart, this energy is obtained primarily from fatty acid oxidation through oxidative phosphorylation (OXPHOS). With this in view, we studied OXPHOS, Total-ATPase and cytochrome content in the mitochondria of the left ventricular (LV) papillary muscles in excised mitral valves of patients who underwent mitral valve replacement (MVR). The mitochondrial OXPHOS, cytochrome content and ATPase activity were studied in 70 patients (ranging from 22 to 40 years) operated on for mitral valve disease. Control study includes 25 normal mitral valves removed at necropsy from patients who died of extracardiac causes. In the presence of glutamate and succinate as substrates, the rate of mitochondrial oxygen consumption was significantly lower in LV papillary muscles of pathological mitral valves (P<0.001) by using with and without addition of ADP. The ADP/O ratio indices for glutamate and succinate were not significantly affected. Using glutamate as substrate, respiratory control index was significantly raised (P<0.05) as compared with control. A significant reduction of total cytochrome content and ATPase activity (P<0.001) was noted in LV papillary muscles of patients operated for mitral valve disease. Our results showed that OXPHOS, cytochromes 'a', 'b', 'c+c(1)' and ATP activity are significantly impaired in LV papillary muscles in patients with pathological mitral valve. Cardiac mitochondrial oxygen consumption is a very valuable tool to investigate the regulation of cardiac mitochondrial energy metabolism. There is increasing evidence that mitochondrial diseases, such as mitochondrial cardiomyopathy, valvular disease and some myopathies, can be responsive to treatment with metabolic intermediates such as coenzyme Q(10), thiamine, prednisone, and vitamin therapy.

Adenosine Triphosphatases↗
PubMed2001

Respiratory chain defects in hereditary spastic paraplegias.

Hereditary Spastic Paraplegias (HSPs) are heterogeneous neurodegenerative disorders whose etiopathogenesis is still unclear. The identification of pathogenic mutations in a gene (SPG7) encoding a mitochondrial metalloprotease suggested that oxidative phosphorylation (OXPHOS) alterations might underlie HSP in a subgroup of patients. We performed clinical, morphological, biochemical, and molecular genetic studies in six HSP patients and in six sporadic patients to investigate OXPHOS in muscle biopsies. Complicated and pure forms were included in our study. Morphological alterations of the type seen in OXPHOS-related disorders were found in three patients. Five patients showed an isolated defect of complex I activity. No mutations in the SPG7 gene were detected. Our results suggest that OXPHOS defects in HSP patients are more common than previously believed.

Adolescent↗
PubMed2006

Defining the mitochondrial proteomes from five rat organs in a physiologically significant context using 2D blue-native/SDS-PAGE.

In accordance with their manifold tasks, various dysfunctions of mitochondria are critically involved in a large number of diseases and the aging process. This has inspired considerable efforts to identify all the mitochondrial proteins by denaturing approaches, notably, the standard gel-based method employing isoelectric focusing. Because a significant part of the mitochondrial proteome is membrane-associated and/or functions as homo- or heterooligomeric protein complexes, there is an urgent need to detect and identify mitochondrial proteins, both membranous and soluble ones, under conditions preserving protein-protein interactions. Here, we investigated mitochondria of five different rat organs (kidney, liver, heart, skeletal muscle, and brain) solubilized with digitonin, enabling the quantitative extraction of the five oxidative phosphorylation (OXPHOS) complexes. The analysis by blue-native (BN)-PAGE recovered the OXPHOS complexes to a large extent as supercomplexes and separated many other protein complexes and individual proteins which were resolved by subsequent 2D SDS-PAGE revealing the tissue-diverse mitochondrial proteomes. Using MS peptide mass fingerprinting, we identified in all five organs 92 nonredundant soluble and membrane-embedded non-OXPHOS proteins, among them, many as constituents of known mitochondrial protein complexes as well as novel ones such as the putative "stomatin-like protein 2 complex" with an apparent mass of ca. 1800 kDa. Interestingly, the identification list included 36 proteins known or presumed to be localized to nonmitochondrial compartments, for example, glycolytic enzymes, clathrin heavy chain, valosin-containing protein/p97, VoV1-ATPase, and Na,K-ATPase. We expect that more than 200 distinct non-OXPHOS proteins of digitonin-solubilized rat mitochondria separated by 2D BN/SDS-PAGE, representing a partial "protein interactome" map, can be identified.

Animals↗
PubMed1997

Oxidative phosphorylation enzymes in normal and neoplastic cell growth.

Cancer cells, despite growing aerobically, have the propension to utilize the glycolytic pathway as energy source. This biochemical phenotype is accompanied by a decreased content of mitochondria and, paradoxically, by enhanced transcription of nuclear and mitochondrial-encoded genes for the enzymes of oxidative phosphorylation (OXPHOS). The role of OXPHOS enzymes in normal and neoplastic cell growth has been studied in liver regeneration and human hepatocellular carcinoma. In early liver regeneration characterized by active mtDNA replication, a decrease in the content and activity of ATP synthase occurs while transcription of the ATPsyn beta nuclear gene is activated. Translation of ATP synthase subunits seems, on the contrary, to be less effective in this phase. In the second replicative phase of liver regeneration, the repression of ATPsyn beta translation is relieved and normal cell growth starts. In this replicative phase the recovery of the liver mass appears to be directly related to the recovery of the OXPHOS capacity. Mitochondria isolated from biopsies of human hepatocellular carcinoma exhibit a decreased rate of respiratory ATP synthesis (OXPHOS) and a decreased ATPase activity. The decline in the activity of the ATP synthase is found to be associated with a decreased content of the ATPsyn beta in the inner mitochondrial membrane. In neoplastic tissue the ATPase inhibitor protein (IF1) is overexpressed. This could contribute to prevent hydrolysis of glycolytic ATP in cancer cells. A peptide segment of IF1 (IF1-(42-58)-peptide), constructed by chemical synthesis, proved to be equally effective as IF1 in inhibiting the ATPase activity of the ATP synthase complex in the mitochondrial membrane deprived of IF1. The synthetic peptide might turn out to be a useful tool to develop immunological approaches for the control of neoplastic growth.

Adenosine Triphosphatases↗
PubMed2006

Mitochondrial mutations in cancer.

The metabolism of solid tumors is associated with high lactate production while growing in oxygen (aerobic glycolysis) suggesting that tumors may have defects in mitochondrial function. The mitochondria produce cellular energy by oxidative phosphorylation (OXPHOS), generate reactive oxygen species (ROS) as a by-product, and regulate apoptosis via the mitochondrial permeability transition pore (mtPTP). The mitochondria are assembled from both nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) genes. The mtDNA codes for 37 genes essential of OXPHOS, is present in thousands of copies per cell, and has a very high mutations rate. In humans, severe mtDNA mutations result in multisystem disease, while some functional population-specific polymorphisms appear to have permitted humans to adapt to new environments. Mutations in the nDNA-encoded mitochondrial genes for fumarate hydratase and succinate dehydrogenase have been linked to uterine leiomyomas and paragangliomas, and cancer cells have been shown to induce hexokinase II which harnesses OXPHOS adenosine triphosphate (ATP) production to drive glycolysis. Germline mtDNA mutations at nucleotides 10398 and 16189 have been associated with breast cancer and endometrial cancer. Tumor mtDNA somatic mutations range from severe insertion-deletion and chain termination mutations to mild missense mutations. Surprisingly, of the 190 tumor-specific somatic mtDNA mutations reported, 72% are also mtDNA sequence variants found in the general population. These include 52% of the tumor somatic mRNA missense mutations, 83% of the tRNA mutations, 38% of the rRNA mutations, and 85% of the control region mutations. Some associations might reflect mtDNA sequencing errors, but analysis of several of the tumor-specific somatic missense mutations with population counterparts appear legitimate. Therefore, mtDNA mutations in tumors may fall into two main classes: (1) severe mutations that inhibit OXPHOS, increase ROS production and promote tumor cell proliferation and (2) milder mutations that may permit tumors to adapt to new environments. The former may be lost during subsequent tumor oxygenation while the latter may become fixed. Hence, mitochondrial dysfunction does appear to be a factor in cancer etiology, an insight that may suggest new approaches for diagnosis and treatment.

Cell Nucleus↗
PubMed2001

An introduction: oxidative phosphorylation diseases.

Oxidative phosphorylation (OXPHOS) is responsible for producing much of the adenosine triphosphate that is required by cells. The OXPHOS pathway incorporates over 100 polypeptides whose genes are located in either the nuclear DNA or the mitochondrial DNA (mtDNA). The expression of these genes and the assembly of the five OXPHOS enzyme complexes (complexes I to V) is a highly ordered and coordinated process. A broad array of human diseases result from mutations in either the nuclear or mtDNA genes or even in the systems that coordinate their interactions. Consequently, OXPHOS diseases can have complex inheritance patterns and a wide spectrum of clinical presentations.

Education, Medical, Continuing↗
PubMed2004

Erralpha and Gabpa/b specify PGC-1alpha-dependent oxidative phosphorylation gene expression that is altered in diabetic muscle.

Recent studies have shown that genes involved in oxidative phosphorylation (OXPHOS) exhibit reduced expression in skeletal muscle of diabetic and prediabetic humans. Moreover, these changes may be mediated by the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha). By combining PGC-1alpha-induced genome-wide transcriptional profiles with a computational strategy to detect cis-regulatory motifs, we identified estrogen-related receptor alpha (Erralpha) and GA repeat-binding protein alpha as key transcription factors regulating the OXPHOS pathway. Interestingly, the genes encoding these two transcription factors are themselves PGC-1alpha-inducible and contain variants of both motifs near their promoters. Cellular assays confirmed that Erralpha and GA-binding protein a partner with PGC-1alpha in muscle to form a double-positive-feedback loop that drives the expression of many OXPHOS genes. By using a synthetic inhibitor of Erralpha, we demonstrated its key role in PGC-1alpha-mediated effects on gene regulation and cellular respiration. These results illustrate the dissection of gene regulatory networks in a complex mammalian system, elucidate the mechanism of PGC-1alpha action in the OXPHOS pathway, and suggest that Erralpha agonists may ameliorate insulin-resistance in individuals with type 2 diabetes mellitus.

Animals↗
PubMed1999

Up-regulation of nuclear and mitochondrial genes in the skeletal muscle of mice lacking the heart/muscle isoform of the adenine nucleotide translocator.

Mice deficient in the heart/muscle specific isoform of the adenine nucleotide translocator (ANT1) exhibit many of the hallmarks of human oxidative phosphorylation (OXPHOS) disease, including a dramatic proliferation of skeletal muscle mitochondria. Because many of the genes necessary for mitochondrial biosynthesis, OXPHOS function, and response to OXPHOS disease might be expected to be up-regulated in the Ant1(-/-) mouse, we used differential display reverse transcription-polymerase chain reaction techniques in an effort to identify these genes. 17 genes were identified as up-regulated in Ant1-deficient mice, and they fall into four categories: 1) nuclear and mitochondrial genes encoding OXPHOS components, 2) mitochondrial tRNA and rRNA genes, 3) genes involved in intermediary metabolism, and 4) an eclectic group of other genes. Among the latter genes, we identified the gene encoding anti-apoptotic Mcl-1, the Skd3 gene, and the WS-3 gene, which were previously unknown to be related to mitochondrial function. These results indicate that identification of genes up-regulated in the skeletal muscle of the Ant1-deficient mouse provides a novel method for identifying mammalian genes required for mitochondrial biogenesis.

Adenosine Triphosphatases↗
PubMed1999

Coordinate induction of energy gene expression in tissues of mitochondrial disease patients.

We have examined the transcript levels of a variety of oxidative phosphorylation (OXPHOS) and associated bioenergetic genes in tissues of a patient carrying the myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) A3243G mitochondrial DNA (mtDNA) mutation and the skeletal muscles of 14 patients harboring other pathogenic mtDNA mutations. The patients' tissues, which harbored 88% or more mutant mtDNA, had increased levels of mtDNA transcripts, increased nuclear OXPHOS gene transcripts including the ATP synthase beta subunit and the heart-muscle isoform of the adenine nucleotide translocator, and increased ancillary gene transcripts including muscle mitochondrial creatine phosphokinase, muscle glycogen phosphorylase, hexokinase I, muscle phosphofructokinase, the E1alpha subunit of pyruvate dehydrogenase, and the ubiquinone oxidoreductase. A similar coordinate induction of bioenergetic genes was observed in the muscle biopsies of severe pathologic mtDNA mutations. The more significant coordinated expression was found in muscle from patients with the MELAS, myoclonic epilepsy with ragged red fibers, and chronic progressive external ophthalmoplegia deletion syndromes, with ragged red muscle fibers and mitochondrial paracrystalline inclusions. High levels of mutant mtDNAs were linked to a high induction of the mtDNA and nuclear OXPHOS genes and of several associated bioenergetic genes. These observations suggest that human tissues attempt to compensate for OXPHOS defects associated with mtDNA mutations by stimulating mitochondrial biogenesis, possibly mediated through redox-sensitive transcription factors.

Adolescent↗
PubMed2002

Nutrient-gene interactions in mitochondrial function: vitamin A needs are increased in BHE/Cdb rats.

The BHE/Cdb rat has a maternally inherited mutation in the ATPase 6 mitochondrial gene that associates with impaired oxidative phosphorylation (OXPHOS) and glucose intolerance. A longevity study revealed that feeding an egg-rich (vitamin A-rich) diet delayed the onset of impaired glucose tolerance. Two experiments were conducted to test the hypothesis that BHE/Cdb rats require more dietary vitamin A than normal rats. Experiment 1 was a dose-response study examining OXPHOS in BHE/Cdb rats fed one of six levels of vitamin A. In experiment 2 BHE/Cdb and Sprague-Dawley rats were used. The rats were depleted of retinol stores, then repleted with 4 or 12 IU vitamin A/g diet. Vitamin A status was assessed in depleted, never depleted, and depleted/repleted rats. OXPHOS was optimized at 4 IU/g diet for the Sprague-Dawley rats and 12 IU/g diet for the BHE/Cdb rats. These results suggested that the criteria for vitamin intake adequacy in the BHE/Cdb rats is the optimization of mitochondrial OXPHOS. Using this criteria, we conclude that diabetes-prone BHE/Cdb rats require more dietary vitamin A than normal rats.

Adenosine Triphosphatases↗
PubMed2003

New insights into the bioenergetics of mitochondrial disorders using intracellular ATP reporters.

Mutations in mitochondrial DNA (mtDNA) cause impairment of ATP synthesis. It was hypothesized that high-energy compounds, such as ATP, are compartmentalized within cells and that different cell functions are sustained by different pools of ATP, some deriving from mitochondrial oxidative phosphorylation (OXPHOS) and others from glycolysis. Therefore, an OXPHOS dysfunction may affect different cell compartments to different extents. To address this issue, we have used recombinant forms of the ATP reporter luciferase localized in different cell compartments- the cytosol, the subplasma membrane region, the mitochondrial matrix, and the nucleus- of cells containing either wild-type or mutant mtDNA. We found that with glycolytic substrates, both wild-type and mutant cells were able to maintain adequate ATP supplies in all compartments. Conversely, with the OXPHOS substrate pyruvate ATP levels collapsed in all cell compartments of mutant cells. In wild-type cells normal levels of ATP were maintained with pyruvate in the cytosol and in the subplasma membrane region, but, surprisingly, they were reduced in the mitochondria and, to a greater extent, in the nucleus. The severe decrease in nuclear ATP content under "OXPHOS-only" conditions implies that depletion of nuclear ATP plays an important, and hitherto unappreciated, role in patients with mitochondrial dysfunction.

Adenosine Triphosphate↗
PubMed2002

Low mitochondrial respiratory chain content correlates with tumor aggressiveness in renal cell carcinoma.

A mechanism decreasing oxidative metabolism during normal cell division and growth is expected to direct substrates toward biosyntheses rather than toward complete oxidation to CO(2). Hence, any event decreasing oxidative phosphorylations (OXPHOS) could provide a proliferating advantage to a transformed or tumor cell in an oxidative tissue. To test this hypothesis, we studied mitochondrial enzymes, DNA and OXPHOS protein content in three types of renal tumors from 25 patients. Renal cell carcinomas (RCCs) of clear cell type (CCRCCs) originate from the proximal tubule and are most aggressive. Chromophilic RCCs, from similar proximal origin, are less aggressive. The benign renal oncocytomas originate from collecting duct cells. Mitochondrial enzyme and DNA contents in all tumor types or grades differed significantly from normal tissue. Mitochondrial impairment increased from the less aggressive to the most aggressive RCCs, and correlated with a considerably decreased content of OXPHOS complexes (complexes II, III, and IV of the respiratory chain, and ATPase/ATP synthase) rather than to the mitochondrial content (citrate synthase and mitochondrial (mt)DNA). In benign oncocytoma, some mitochondrial parameters (mtDNA, citrate synthase, and complex IV) were increased 4- to 7-fold, and some were slightly increased by a factor of 2 (complex V) or close to normal (complexes II and III). A low content of complex V protein was found in all CCRCC and chromophilic tumors studied. However F(1)-ATPase activity was not consistently decreased and its impairment was associated with increased aggressiveness in CCRCCs. Immunodetection of free F(1)-sector of complex V demonstrated a disturbed assembly/stability of complex V in several CCRCC and chromophilic tumors. All results are in agreement with the hypothesis that a decreased OXPHOS capacity favors faster growth or increased invasiveness.

Base Sequence↗
PubMed2000

Oxidative phosphorylation-dependent and -independent oxygen consumption by individual preimplantation mouse embryos.

The self-referencing electrode technique was employed to noninvasively measure gradients of dissolved oxygen in the medium immediately surrounding developing mouse embryos and, thereby, characterized changes in oxygen consumption and utilization during development. A gradient of depleted oxygen surrounded each embryo and could be detected >50 microm from the embryo. Blastocysts depleted the surrounding medium of 0.6+/-0.1 microM of oxygen, whereas early cleavage stage embryos depleted the medium of only 0.3+/-0.1 microM of oxygen, suggesting a twofold increase in oxygen consumption at the blastocyst stage. Mitochondrial oxidative phosphorylation (OXPHOS) accounted for 60-70% of the oxygen consumed by blastocysts, while it accounted for only 30% of the total oxygen consumed by cleavage-stage embryos. The amount of oxygen consumed by non-OXPHOS mechanisms remained relatively constant throughout preimplantation development. By contrast, the amount of oxygen consumed by OXPHOS in blastocysts is greater than that consumed by OXPHOS in cleavage-stage embryos. The amount of oxygen consumed by one-cell embryos was modulated by the absence of pyruvate from the culture medium. Treatment of one-cell embryos and blastocysts with diamide, an agent known to induce cell death in embryos, resulted in a decline in oxygen consumption, such that the medium surrounding dying embryos was not as depleted of oxygen as that surrounding untreated control embryos. Together these results validate the self-referencing electrode technique for analyzing oxygen consumption and utilization by preimplantation embryos and demonstrate that changes in oxygen consumption accompany important physiological events, such as development, response to medium metabolites, or cell death.

Animals↗
PubMed1999

Oxidative phosphorylation disease diagnosis.

Although the mtDNA encodes only 13 polypeptide subunits of the OXPHOS enzymes, approximately 1,000 proteins are estimated to be necessary for proper OXPHOS function. Over the past 10 years a wide variety of adult and pediatric OXPHOS diseases were found to be caused by or associated with mitochondrial DNA (mtDNA) mutations and nuclear DNA mutations. These advances enhanced the ability to definitively diagnose patients, develop management plans, and provide genetic counseling. Recently described nuclear DNA and mtDNA mutations are enhancing our understanding of this complex group of diseases. The impact of these advances on our understanding of OXPHOS disease pathogenesis will be reviewed.

Adult↗