Biomedical subjects

Yves Malthièry

Publications and source records attributed to Yves Malthièry.

At least 19 recordsLinked to original sources

PubMed2006

Influence of intensity of food restriction on skeletal muscle mitochondrial energy metabolism in rats.

Variable durations of food restriction (FR; lasting weeks to years) and variable FR intensities are applied to animals in life span-prolonging studies. A reduction in mitochondrial proton leak is suggested as a putative mechanism linking such diet interventions and aging retardation. Early mechanisms of mitochondrial metabolic adaptation induced by FR remain unclear. We investigated the influence of different degrees of FR over 3 days on mitochondrial proton leak and mitochondrial energy metabolism in rat hindlimb skeletal muscle. Animals underwent 25, 50, and 75% and total FR compared with control rats. Proton leak kinetics and mitochondrial functions were investigated in two mitochondrial subpopulations, intermyofibrillar (IMF) and subsarcolemmal (SSM) mitochondria. Regardless of the degree of restriction, skeletal muscle mass was not affected by 3 days of FR. Mitochondrial basal proton conductance was significantly decreased in 50% restricted rats in both mitochondrial subpopulations (46 and 40% for IMF and SSM, respectively) but was unaffected in other groups compared with controls. State 3 and uncoupled state 3 respiration rates were decreased in SSM mitochondria only for 50% restricted rats when pyruvate + malate was used as substrate (-34.5 and -38.9% compared with controls, P < 0.05). IMF mitochondria respiratory rates remained unchanged. Three days of FR, particularly at 50% FR, were sufficient to lower mitochondria energetic metabolism in both mitochondrial populations. Our study highlights an early step in mitochondrial adaptation to FR and the influence of the severity of restriction on this adaptation. This step may be involved in an aging-retardation process.

Adenosine Triphosphate↗

PubMed2006

mtDNA controls expression of the Death Associated Protein 3.

The Death Associated Protein 3 (DAP3), a GTP-binding constituent of the small subunit of the mitochondrial ribosome, is implicated in the TNFalpha and IFNgamma apoptotic pathways of the cell and is involved in the maintenance of the mitochondrial network. We have investigated the mitochondrial role of DAP3 by analyzing its mRNA and protein expression in transformed and non-transformed cell lines presenting various levels of mtDNA. The 3 mtDNA-less (rho degrees ) cell lines showed a complete absence of DAP3, whereas the mRNA expression was conserved. In HepG2 cells treated with increasing doses of ddCTP, the depletion of mtDNA was accompanied by the reduced expression of DAP3. However, the expression of the corresponding mRNA was maintained, suggesting the existence of a post-transcriptional mechanism responsible for the depletion of the DAP3. Compared to the parental cells, the 3 rho degrees cell lines displayed partial resistance to staurosporin-induced cell death. The absence of pro-apoptotic DAP3 in these mtDNA-less cells could explain their reduced apoptotic capacity. Our results suggest that the mtDNA content plays a role in cell apoptosis by mediating the expression of DAP3.

Apoptosis↗

PubMed2005

Dinitrophenol-induced mitochondrial uncoupling in vivo triggers respiratory adaptation in HepG2 cells.

Here, we show that 3 days of mitochondrial uncoupling, induced by low concentrations of dinitrophenol (10 and 50 microM) in cultured human HepG2 cells, triggers cellular metabolic adaptation towards oxidative metabolism. Chronic respiratory uncoupling of HepG2 cells induced an increase in cellular oxygen consumption, oxidative capacity and cytochrome c oxidase activity. This was associated with an upregulation of COXIV and ANT3 gene expression, two nuclear genes that encode mitochondrial proteins involved in oxidative phosphorylation. Glucose consumption, lactate and pyruvate production and growth rate were unaffected, indicating that metabolic adaptation of HepG2 cells undergoing chronic respiratory uncoupling allows continuous and efficient mitochondrial ATP production without the need to increase glycolytic activity. In contrast, 3 days of dinitrophenol treatment did not change the oxidative capacity of human 143B.TK(-) cells, but it increased glucose consumption, lactate and pyruvate production. Despite a large increase in glycolytic metabolism, the growth rate of 143B.TK(-) cells was significantly reduced by dinitrophenol-induced mitochondrial uncoupling. We propose that chronic respiratory uncoupling may constitute an internal bioenergetic signal, which would initiate a coordinated increase in nuclear respiratory gene expression, which ultimately drives mitochondrial metabolic adaptation within cells.

2,4-Dinitrophenol↗

PubMed2005

Increase of mitochondrial DNA content and transcripts in early bovine embryogenesis associated with upregulation of mtTFA and NRF1 transcription factors.

BACKGROUND: Recent work has shown that mitochondrial biogenesis and mitochondrial functions are critical determinants of embryonic development. However, the expression of the factors controlling mitochondrial biogenesis in early embryogenesis has received little attention so far. METHODS: We used real-time quantitative PCR to quantify mitochondrial DNA (mtDNA) in bovine oocytes and in various stages of in vitro produced embryos. To investigate the molecular mechanisms responsible for the replication and the transcriptional activation of mtDNA, we quantified the mRNA corresponding to the mtDNA-encoded cytochrome oxidase 1 (COX1), and two nuclear-encoded factors, i.e. the Nuclear Respiratory Factor 1 (NRF1), and the nuclear-encoded Mitochondrial Transcription Factor A (mtTFA). RESULTS: Unlike findings reported in mouse embryos, the mtDNA content was not constant during early bovine embryogenesis. We found a sharp, 60% decrease in mtDNA content between the 2-cell and the 4/8-cell stages. COX1 mRNA was constant until the morula stage after which it increased dramatically. mtTFA mRNA was undetectable in oocytes and remained so until the 8/16-cell stage; it began to appear only at the morula stage, suggesting de novo synthesis. In contrast, NRF1 mRNA was detectable in oocytes and the quantity remained constant until the morula stage. CONCLUSION: Our results revealed a reduction of mtDNA content in early bovine embryos suggesting an active process of mitochondrial DNA degradation. In addition, de novo mtTFA expression associated with mitochondrial biogenesis activation and high levels of NRF1 mRNA from the oocyte stage onwards argue for the essential function of these factors during the first steps of bovine embryogenesis.

Animals↗

PubMed2005

OPA1 R445H mutation in optic atrophy associated with sensorineural deafness.

The heterozygous R445H mutation in OPA1 was found in five patients with optic atrophy and deafness. Audiometry suggested that the sensorineural deafness resulted from auditory neuropathy. Skin fibroblasts showed hyperfragmentation of the mitochondrial network, decreased mitochondrial membrane potential, and adenosine triphosphate synthesis defect. In addition, OPA1 was found to be widely expressed in the sensory and neural cochlear cells of the guinea pig. Thus, optic atrophy and deafness may be related to energy defects due to a fragmented mitochondrial network.

Adolescent↗

PubMed2005

eOPA1: an online database for OPA1 mutations.

Autosomal dominant optic atrophy (ADOA), also known as Kjer disease, is characterized by moderate to severe loss of visual acuity with an insidious onset in early childhood, blue-yellow dyschromatopsia, and central scotoma. An optic atrophy gene, called OPA1, has been identified in most cases of the disease. A total of 83 OPA1 mutations, often family-specific, have been reported so far, and the observations support the hypothesis that haploinsufficiency and the functional loss of a single allele may lead to ADOA. We have developed a new locus-specific database (LSDB), eOPA1 (http://lbbma.univ-angers.fr/eOPA1/) aimed at collecting published and unpublished sequence variations in OPA1. The database has been designed to incorporate new submissions rapidly and will provide a secured online catalog of OPA1 mutations and nonpathogenic sequence variants (NPSVs). The LSDB should prove useful for molecular diagnosis, large-scale mutation statistics, and the determination of original genotype-phenotype correlations in studies on ADOA.

Base Sequence↗

PubMed2005

ANT2 expression under hypoxic conditions produces opposite cell-cycle behavior in 143B and HepG2 cancer cells.

Under hypoxic conditions, mitochondrial ATP production ceases, leaving cells entirely dependent on their glycolytic metabolism. The cytoplasmic and intramitochondrial ATP/ADP ratios, partly controlled by the adenine nucleotide translocator (ANT), are drastically modified. In dividing and growing cells that have a predominantly glycolytic metabolism, the ANT isoform 2, which has kinetic properties allowing ATP import into mitochondria, is over-expressed in comparison to control cells. We studied the cellular metabolic and proliferative response to hypoxia in two transformed human cell lines with different metabolic backgrounds: HepG2 and 143B, and in their rho(o) derivatives, i.e., cells with no mitochondrial DNA. Transformed 143B and rho(o) cells continued their proliferation whereas HepG2 cells, with a more differentiated phenotype, arrested their cell-cycle at the G(1)/S checkpoint. Hypoxia induced an increase in glycolytic activity, correlated to an induction of VEGF and hexokinase II (HK II) expression. Thus, according to their tumorigenicity, transformed cells may adopt one of two distinct behaviors to support hypoxic stress, i.e., proliferation or quiescence. Our study links the constitutive glycolytic activity and ANT2 expression levels of transformed cells with the loss of cell-cycle control after oxygen deprivation. ATP import by ANT2 allows cells to maintain their mitochondrial integrity while acquiring insensitivity to any alterations in the proteins involved in oxidative phosphorylation. This loss of cell dependence on oxidative metabolism is an important factor in the development of tumors.

Adenine Nucleotide Translocator 2↗

PubMed2005

ANT2 isoform required for cancer cell glycolysis.

The three adenine nucleotide translocator (ANT1 to ANT3) isoforms, differentially expressed in human cells, play a crucial role in cell bioenergetics by catalyzing ADP and ATP exchange across the mitochondrial inner membrane. In contrast to differentiated tissue cells, transformed cells, and their rho(0) derivatives, i.e. cells deprived of mitochondrial DNA, sustain a high rate of glycolysis. We compared the expression pattern of ANT isoforms in several transformed human cell lines at different stages of the cell cycle. The level of ANT2 expression and glycolytic ATP production in these cell lines were in keeping with their metabolic background and their state of differentiation. The sensitivity of the mitochondrial inner membrane potential (Deltapsi) to several inhibitors of glycolysis and oxidative phosphorylation confirmed this relationship. We propose a new model for ATP uptake in cancer cells implicating the ANT2 isoform, in conjunction with hexokinase II and the beta subunit of mitochondrial ATP synthase, in the Deltapsi maintenance and in the aggressiveness of cancer cells.

Adenine Nucleotide Translocator 2↗

PubMed2005

Maternal smoking is associated with mitochondrial DNA depletion and respiratory chain complex III deficiency in placenta.

Maternal smoking during pregnancy is often associated with a decrease in placental function, which might lead to intrauterine growth retardation. Because tobacco is known to alter the mitochondrial respiratory function in cardiomyocytes and lung tissue, we hypothesized that placental mitochondrial function could be altered by maternal smoking. Placental mitochondria from 9 smoking and 19 nonsmoking mothers were isolated by differential centrifugation. Mitochondrial oxygen consumption was measured by polarography, and the enzymatic activity of each complex of the electron transport chain was assessed by spectrophotometry. In addition, the relative content in mitochondrial DNA (mtDNA) was determined by real-time quantitative PCR in placentas from seven smoking and seven nonsmoking mothers. We observed a 29% reduction in the enzymatic activity of complex III in the placental mitochondria from smokers compared with nonsmokers (P = 0.03). The relative content of mtDNA (with respect to the beta-globin gene) was reduced by 37% in the placental tissue from smokers compared with nonsmokers (P < 0.02). Both the enzymatic activity of complex III and mtDNA content were inversely related with the daily consumption of cigarettes, and mtDNA content was correlated with cord blood insulin-like growth factor-binding protein-3 (r = 0.74, P < 0.01), a marker of fetal growth. These results show that maternal smoking is associated with placental mitochondrial dysfunction, which might contribute to restricted fetal growth by limiting energy availability in cells.

Adult↗

PubMed2004

Kinetics and control of oxidative phosphorylation in rat liver mitochondria after dexamethasone treatment.

The present investigation was undertaken in order to evaluate the contributions of ATP synthesis and proton leak reactions to the rate of active respiration of liver mitochondria, which is altered following dexamethasone treatment (1.5 mg/kg per day for 5 days). We applied top-down metabolic control analysis and its extension, elasticity analysis, to gain insight into the mechanisms of glucocorticoid regulation of mitochondrial bioenergetics. Liver mitochondria were isolated from dexamethasone-treated, pair-fed and control rats when in a fed or overnight fasted state. Injection of dexamethasone for 5 days resulted in an increase in the fraction of the proton cycle of phosphorylating liver mitochondria, which was associated with a decrease in the efficiency of the mitochondrial oxidative phosphorylation process in liver. This increase in proton leak activity occurred with little change in the mitochondrial membrane potential, despite a significant decrease in the rate of oxidative phosphorylation. Regulation analysis indicates that mitochondrial membrane potential homoeostasis is achieved by equal inhibition of the mitochondrial substrate oxidation and phosphorylation reactions in rats given dexamethasone. Our results also suggest that active liver mitochondria from dexamethasone-treated rats are capable of maintaining phosphorylation flux for cellular purposes, despite an increase in the energetic cost of mitochondrial ATP production due to increased basal proton permeability of the inner membrane. They also provide a complete description of the effects of dexamethasone treatment on liver mitochondrial bioenergetics.

Adenosine Triphosphate↗

PubMed2004

Mitochondrial diseases preferentially involve proteins with prokaryote homologues.

The comparison of each of the 393 nuclear-encoded human mitochondrial proteins annotated in the SwissProt databank with 256,953 proteins from 94 prokaryote species showed that two thirds of the mitochondrial proteome were homologous with prokaryotic proteins, whereas one third was not. Prokaryotic mitochondrial proteins differ markedly from eukaryotic proteins, particularly in regard to their size, localization, function, and mitochondrial-targeting N-terminal sequence. Remarkably, the majority of nuclear genes implicated in respiratory chain mitochondrial diseases were found to be of prokaryotic ancestry. Our study indicates that the investigation of the co-evolution of eukaryotic and prokaryotic mitochondrial proteins should lead to a better understanding of mitochondrial diseases.

Humans↗

PubMed2004

Transcriptional profiling reveals coordinated up-regulation of oxidative metabolism genes in thyroid oncocytic tumors.

Oncocytomas are large cell tumors characterized by an abnormal proliferation of mitochondria. To investigate this phenomenon in thyroid oncocytomas, we determined gene expression profiles of 87 samples using microarrays of 6720 PCR products from cDNA clones. Samples included 29 thyroid oncocytomas and six papillary carcinomas, the remainder representing other thyroid pathologies or mitochondria-rich tumor samples, normal thyroid samples, and two thyroid cell lines. Hierarchical clustering and supervised analysis identified two specific oncocytic clusters and 163 distinctly regulated genes between oncocytoma and normal thyroid. Differential expression of five selected genes (APOD, BCL-2, COX, CTSB, and MAP2) was confirmed by immunohistochemistry. The two specific oncocytic clusters were rich in mitochondrial genes and revealed coordinated expression of nuclear and mitochondrial respiratory chain genes. We also observed the up-regulation of genes involved in mitochondrial biogenesis, such as nuclear respiratory factor 1 and the endothelial nitric oxide synthase. Several oxidative metabolism genes were overexpressed in oncocytomas, including those from the tricarboxylic acid cycle (MDH1) and cytosolic glycolysis (GAPD, ENO1, and GPI). On the contrary, the lactate dehydrogenase A gene, involved in anaerobic metabolism, was down-regulated. Our results suggest that, unlike a large number of solid tumors, thyroid oncocytomas produce energy through an aerobic pathway.

Adenoma, Oxyphilic↗

PubMed2004

Decreased expression of thyrotropin receptor gene suggests a high-risk subgroup for oncocytic adenoma.

OBJECTIVE: The malignancy of thyroid oncocytic tumours, or oncocytomas, is higher than that of follicular tumours. The aim of this study was to investigate the role of thyroid-specific genes in oncocytic tumours and papillary carcinomas. DESIGN AND METHODS: We compared 29 oncocytic tumours with 12 papillary carcinomas. Real-time quantitative PCR was used to measure the expression of thyroid-specific differentiation markers (thyrotrophin-stimulation hormone receptor (TSHR), thyroglobulin (TG) and Na(+)/I(-) symporter (NIS)), transcription factors (thyroid transcription factor-1 (TTF-1) and paired box gene-8 (PAX8)) and nuclear receptors (peroxisome proliferator-activated receptor (PPARgamma1) and thyroid hormone receptor (TRbeta1)) involved in thyroid carcinogenesis. RESULTS: TSHR, TTF-1 and TRbeta1 levels were significantly lower in oncocytic tumours than in papillary carcinomas, as a result of specific biological changes in oncocytic tumours. However, PAX8 and PPARgamma1 did not seem to be involved in the process. Applying the criterion of the underexpression of the thyroid-specific differentiation markers, TSHR, TG and NIS, we classified the oncocytic tumours and papillary carcinomas into three groups. In the first, all three markers were underexpressed; in the second, TSHR was normal while TG and NIS were underexpressed; and in the third, only NIS was underexpressed. The expression patterns revealed that 13 of the 24 oncocytic adenomas underexpressing TSHR in our study, as did four of the five oncocytic carcinomas. CONCLUSION: Cases of oncocytic adenoma associated with low levels of TSHR could be putative oncocytic carcinomas and should therefore receive adequate follow-up [corrected].

Adenocarcinoma, Follicular↗

PubMed2003

PGC-1-related coactivator and targets are upregulated in thyroid oncocytoma.

Thyroid oncocytomas are tumors characterized by dense mitochondrial accumulation, the cause of which is currently unknown. Members of the PGC-1 coactivator family have been identified as important mediators of mitochondrial biogenesis because of their ability to activate nuclear genes encoding mitochondrial proteins. We have investigated the influence of the PGC-1 related coactivator (PRC) on the high mitochondrial content observed in oncocytoma by quantifying the transcripts of PRC, the nuclear respiratory factor 1 (NRF-1) and the mitochondrial transcription factor A (TFAM), in 30 oncocytic tumors and corresponding normal tissues. The three genes studied were found to be significantly overexpressed in thyroid oncocytomas, concomitantly with an increase in cytochrome oxidase activity and mitochondrial DNA (mtDNA) content. However, no mtDNA variant in the D-loop region appeared to be involved in oncocytic development. We conclude that overexpression of the PRC pathway is responsible for mitochondrial proliferation in the context of thyroid oncocytoma.

Adenoma↗

PubMed2003

Fourteen novel OPA1 mutations in autosomal dominant optic atrophy including two de novo mutations in sporadic optic atrophy.

The OPA1 gene, encoding a dynamin-related GTPase that plays a role in mitochondrial biogenesis, is implicated in most cases of autosomal dominant optic atrophy (ADOA). Sixty-nine pathogenic OPA1 mutations have been reported so far. Most of these are truncating mutations located in the GTPase domain coding region (exons 8-16) and at the 3'-end (exons 27-28). We screened 44 patients with typical ADOA using PCR-sequencing. We also tested 20 sporadic cases of bilateral optic atrophy compatible with ADOA. Of the 18 OPA1 mutations found, 14 have never been previously reported. The novel mutations include one nonsense mutation, 3 missense mutations, 6 deletions, one insertion and 3 exon-skipping mutations. Two of these are de novo mutations, which were found in 2 patients with sporadic optic atrophy. The recurrent c.2708_2711delTTAG mutation was found in 2 patients with a severe congenital presentation of the disease. These results suggest that screening for OPA1 gene mutations may be useful for patients with optic atrophy who have no affected relatives, or when the presentation of the disease is atypical as in the case of early onset optic atrophy.

Alternative Splicing↗

PubMed2002

Oxygen consumption and expression of the adenine nucleotide translocator in cells lacking mitochondrial DNA.

It has been shown previously that human rho degrees cells, deprived of mitochondrial DNA and consequently of functional oxidative phosphorylation, maintain a mitochondrial membrane potential, which is necessary for their growth. The goal of our study was to determine the precise origin of this membrane potential in three rho degrees cell lines originating from the human HepG2, 143B, and HeLa S3 cell lines. Residual cyanide-sensitive oxygen consumption suggests the persistence of residual mitochondrial respiratory chain activity, about 8% of that of the corresponding parental cells. The fluorescence emitted by the three rho degrees cell lines in the presence of a mitochondrial specific fluorochrome was partially reduced by a protonophore, suggesting the existence of a proton gradient. The mitochondrial membrane potential is maintained both by a residual proton gradient (up to 45 to 50% of the potential) and by other ion movements such as the glycolytic ATP(4-) to mitochondrial ADP(3-) exchange. The ANT2 gene, encoding isoform 2 of the adenine nucleotide translocator, is overexpressed in rho degrees HepG2 and 143B cells strongly dependent on glycolytic ATP synthesis, as compared to the corresponding parental cells, which present a more oxidative metabolism. In rho degrees HeLa S3 cells, originating from the HeLa S3 cell line, which already displays a glycolytic energy status, ANT2 gene expression was not higher as in parental cells. Mitochondrial oxygen consumption and ANT2 gene overexpression vary in opposite ways and this suggests that these two parameters have complementary roles in the maintenance of the mitochondrial membrane potential in rho degrees cells.

DNA, Mitochondrial↗

PubMed2002

Leigh-like encephalopathy complicating Leber's hereditary optic neuropathy.

Leber's hereditary optic neuropathy is a mitochondrial disease caused by point mutations in mitochondrial DNA. It usually presents as severe bilateral visual loss in young adults. We report on a neurological disorder resembling Leigh syndrome, which complicated Leber's hereditary optic neuropathy in three unrelated male patients harboring mitochondrial DNA mutations at nucleotide positions 3460, 14459, and 14484, respectively. This Leigh-like encephalopathy appears to be associated with a much more severe outcome than isolated Leber's hereditary optic neuropathy.

Adult↗

PubMed2002

Structure and chromosomal distribution of human mitochondrial pseudogenes.

Nuclear mitochondrial pseudogenes (Numts) have been found in the genome of many eukaryote species, including humans. Using a BLAST approach, we found 1105 DNA sequences homologous to mitochondrial DNA (mtDNA) in the August 2001 Goldenpath human genome database. We assembled these sequences manually into 286 pseudogenes on the basis of single insertion events and constructed a chromosomal map of these Numts. Some pseudogenes appeared highly modified, containing inversions, deletions, duplications, and displaced sequences. In the case of four randomly selected Numts, we used PCR tests on cells lacking mtDNA to ensure that our technique was free from genome-sequencing artifacts. Furthermore, phylogenetic investigation suggested that one Numt, apparently inserted into the nuclear genome 25-30 million years ago, had been duplicated at least 10 times in various chromosomes during the course of evolution. Thus, these pseudogenes should be very useful in the study of ancient mtDNA and nuclear genome evolution.

Chromosome Mapping↗