Biomedical subjects

Paule Bénit

Publications and source records attributed to Paule Bénit.

12 recordsLinked to original sources

PubMed2006

Loss of Aif function causes cell death in the mouse embryo, but the temporal progression of patterning is normal.

Apoptosis-inducing factor (AIF) is an evolutionarily conserved, ubiquitously expressed flavoprotein with NADH oxidase activity that is normally confined to mitochondria. In mammalian cells, AIF is released from mitochondria in response to apoptotic stimuli and translocates to the nucleus where it is thought to bind DNA and contribute to chromatinolysis and cell death in a caspase-independent manner. Here we describe the consequences of inactivating Aif in the early mouse embryo. Unexpectedly, we found that both the apoptosis-dependent process of cavitation in embryoid bodies and apoptosis associated with embryonic neural tube closure occur in the absence of AIF, indicating that Aif function is not required for apoptotic cell death in early mouse embryos. By embryonic day 9 (E9), loss of Aif function causes abnormal cell death, presumably because of reduced mitochondrial respiratory chain complex I activity. Because of this cell death, Aif null embryos fail to increase significantly in size after E9. Remarkably, patterning processes continue on an essentially normal schedule, such that E10 Aif null embryos with only approximately 1/10 the normal number of cells have the same somite number as their wild-type littermates. These observations show that pattern formation in the mouse can occur independent of embryo size and cell number.

Animals↗

PubMed2006

Three spectrophotometric assays for the measurement of the five respiratory chain complexes in minuscule biological samples.

BACKGROUND: The measurement of the activities of the five complexes comprising the respiratory chain has proven to be a major challenge when a limiting amount of biological material is available. Here we report a set of three convenient assays that allows this measurement under such circumstances. METHODS: One assay relies on the sequential addition of reagents to measure first complex IV activity, followed by complex II+III, and then glycerol-3-phosphate dehydrogenase+complex III activities and finally isolated complex III activity. A second assay measures the activity of complex II followed by glycerol-3-phosphate dehydrogenase and isocitrate dehydrogenase. A third assay measures rotenone-sensitive complex I activity and subsequently oligomycin-sensitive complex V activity. RESULTS: These assays have been successfully used on extracts of small numbers of human cells displaying various defects in the respiratory chain, and on frozen tissue homogenates of retina and very early mouse embryos. CONCLUSIONS: The strength of this set of assays lies both in its rapid and simple execution and its capacity for immediate detection of partial defects, because each activity can be compared with one or two other activities measured in the same sample.

Animals↗

PubMed2005

Mitochondrial succinate is instrumental for HIF1alpha nuclear translocation in SDHA-mutant fibroblasts under normoxic conditions.

The genes encoding succinate dehydrogenase (SDH) subunits B, C and D, act as tumour suppressors in neuro-endocrine tissues. Tumour formation has been associated with succinate accumulation. In paraganglioma cells, two forms of SDHA (type I, II) were found which might preclude significant succinate accumulation in the case of a mutation in either form. In fibroblasts only SDHA type I is found. In these cells, SDHA type I mutation leads to SDH deficiency, succinate accumulation and hypoxia-inducible factor 1alpha(HIF1alpha) nuclear translocation. HIF1alpha nuclear translocation was not observed in ATPase-deficient fibroblasts with increased superoxide production and was found to be independent of cellular iron availability in SDHA-mutant cells. This suggests that neither superoxides nor iron were causative of HIF1alpha nuclear translocation. Conversely, alpha-ketoglutarate (alpha-KG) inhibits this nuclear translocation. Therefore, the pseudo-hypoxia pathway in SDH-deficient cells depends on the HIF1alphaprolyl hydroxylase product/substrate (succinate/alpha-KG) equilibrium. In SDH deficiency, organic acids thus appear instrumental in the HIF1alpha-dependent cascade suggesting a direct link between SDH and tumourigenesis.

Blotting, Western↗

PubMed2005

Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy.

Cardiac and skeletal muscle critically depend on mitochondrial energy metabolism for their normal function. Recently, we showed that apoptosis-inducing factor (AIF), a mitochondrial protein implicated in programmed cell death, plays a role in mitochondrial respiration. However, the in vivo consequences of AIF-regulated mitochondrial respiration resulting from a loss-of-function mutation in Aif are not known. Here, we report tissue-specific deletion of Aif in the mouse. Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I. Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain. Isolated hearts from mutant animals exhibit poor contractile performance in response to a respiratory chain-dependent energy substrate, but not in response to glucose, supporting the notion that impaired heart function in mutant animals results from defective mitochondrial energy metabolism. These data provide genetic proof that the previously defined cell death promoter AIF has a second essential function in mitochondrial respiration and aerobic energy metabolism required for normal heart function and skeletal muscle homeostasis.

Animals↗

PubMed2004

Respiratory chain defects: what do we know for sure about their consequences in vivo?

The function and the structure of mitochondria have been the subject of intensive research since the discovery of these organelles. Yet, the investigation of patients with mitochondrial disease reveals that we do not understand a large part of the underlying pathogenic processes. This has disastrous consequences in terms of the therapy possibly proposed to the patients and their family. An attempt is made in this short review to question our present ideas on the potential consequences of mitochondrial dysfunctions and to enlighten new observations which might be valuable in the understanding of the physiopathology of these diseases.

Adenosine Triphosphate↗

PubMed2004

AIF deficiency compromises oxidative phosphorylation.

Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein that, after apoptosis induction, translocates to the nucleus where it participates in apoptotic chromatinolysis. Here, we show that human or mouse cells lacking AIF as a result of homologous recombination or small interfering RNA exhibit high lactate production and enhanced dependency on glycolytic ATP generation, due to severe reduction of respiratory chain complex I activity. Although AIF itself is not a part of complex I, AIF-deficient cells exhibit a reduced content of complex I and of its components, pointing to a role of AIF in the biogenesis and/or maintenance of this polyprotein complex. Harlequin mice with reduced AIF expression due to a retroviral insertion into the AIF gene also manifest a reduced oxidative phosphorylation (OXPHOS) in the retina and in the brain, correlating with reduced expression of complex I subunits, retinal degeneration, and neuronal defects. Altogether, these data point to a role of AIF in OXPHOS and emphasize the dual role of AIF in life and death.

Adenosine Triphosphate↗

PubMed2004

Processing of the 24 kDa subunit mitochondrial import signal is not required for assembly of functional complex I in Yarrowia lipolytica.

A small deletion in the second intron of human NDUFV2 (IVS2+5_+8delGTAA) has been shown to cause hypertrophic cardiomyopathy and encephalomyopathy [Bénit, P., Beugnot, R., Chretien, D., Giurgea, I., de Lonlay-Debeney, P., Issartel, J.P., Kerscher, S., Rustin, P., Rötig, A. & Munnich, A. (2003) Human Mutat.21, 582-586]. Skipping of exon 2 results in a partial deletion of the mitochondrial targeting sequence of the precursor for the 24 kDa subunit of respiratory chain complex I. Immunoreactivity of the 24 kDa subunit and complex I activity, both present at 30-50% of normal levels in patient mitochondria, raised the question of how the mutant 24 kDa subunit precursor can be imported and assembled into functional complex I. In the present study, we have remodelled the human NDUFV2 mutation by deleting codons 17-32 from the orthologous NUHM gene of the obligate aerobic yeast Yarrowia lipolytica. The resulting mutant enzyme was indistinguishable from parental complex I with regard to activity, inhibitor sensitivity and EPR signature. Size, isoelectric point and presumably also N-terminal acetylation were altered, indicating that the residual targeting sequence was retained on the mature 24 kDa protein. Complete removal of the NUHM presequence resulted in the absence of complex I activity, strongly arguing against the presence of an internal mitochondrial targeting sequence within the 24 kDa protein.

Amino Acid Sequence↗

PubMed2003

Genotyping microsatellite DNA markers at putative disease loci in inbred/multiplex families with respiratory chain complex I deficiency allows rapid identification of a novel nonsense mutation (IVS1nt -1) in the NDUFS4 gene in Leigh syndrome.

Complex I deficiency, the most common cause of mitochondrial disorders, accounts for a variety of clinical symptoms and its genetic heterogeneity makes identification of the disease genes particularly tedious. Indeed, most of the 43 complex I subunits are encoded by nuclear genes, only seven of them being mitochondrially encoded. In order to offer urgent prenatal diagnosis, we have studied an inbred/multiplex family with complex I deficiency by using microsatellite DNA markers flanking the putative disease loci. Microsatellite DNA markers have allowed us to exclude the NDUFS7, NDUFS8, NDUFV1 and NDUFS1 genes and to find homozygosity at the NDUFS4 locus. Direct sequencing has led to identification of a homozygous splice acceptor site mutation in intron 1 of the NDUFS4 gene (IVS1nt -1, G-->A); this was not found in chorion villi of the ongoing pregnancy. We suggest that genotyping microsatellite DNA markers at putative disease loci in inbred/multiplex families helps to identify the disease-causing mutation. More generally, we suggest giving consideration to a more systematic microsatellite analysis of putative disease loci for identification of disease genes in inbred/multiplex families affected with genetically heterogeneous conditions.

Codon, Nonsense↗

PubMed2003

Assay of mitochondrial respiratory chain complex I in human lymphocytes and cultured skin fibroblasts.

Respiratory chain complex I (NADH:ubiquinone oxidoreductase) deficiency is one of the most frequent causes of mitochondrial disease in humans. The activity of this complex can be confidently measured in most tissue samples, but not in cultured skin fibroblasts or circulating lymphocytes. Highly contaminating non-mitochondrial NADH-quinone oxidoreductase activity in fibroblasts and the limited access of substrates to complex I in lymphocytes hinder its measurement in permeabilized cells. Complex I assay in these cells requires the isolation of mitochondria, which in turn necessitates large quantities of cells and is not feasible when studying circulating lymphocytes. Here we report a simple method to measure complex I activity in a minute amount of either cell type. The procedure strongly reduces contaminating NADH:quinone oxidoreductase activity and permits measuring high rates of rotenone-sensitive complex I activity thanks to effective cell permeabilization.

Cells, Cultured↗

PubMed2003

Mutant NDUFV2 subunit of mitochondrial complex I causes early onset hypertrophic cardiomyopathy and encephalopathy.

Respiratory chain complex I deficiencies represent a genetically heterogeneous group of diseases resulting from mutations in either mitochondrial or nuclear DNA. Combination of denaturing high performance liquid chromatography and sequence analysis allowed us to show that a 4-bp deletion in intron 2 (IVS2+5_+8delGTAA) of the NDUFV2 gene (encoding NADH dehydrogenase ubiquinone flavoprotein 2) causes complex I deficiency and early onset hypertrophic cardiomyopathy with trunk hypotonia in three affected sibs of a consanguineous family. The homozygous mutation altering the consensus splice-donor site of exon 2 resulted in 70% decreased NDUFV2 protein and complex I deficiency. While mutation in a number of genes encoding complex I subunits essentially result in neurological symptoms, this first mutation in NDUFV2 is strikingly associated with cardiomyopathy, as previously observed in the unique case of NDFUS2 mutations.

Age of Onset↗

PubMed2002

Cell complementation using Genebridge 4 human:rodent hybrids for physical mapping of novel mitochondrial respiratory chain deficiency genes.

The mapping and identification of respiratory chain deficiency genes is particularly tedious owing to the large number of genes encoding catalytic subunits and involved in respiratory chain (RC) assembly and maintenance. We have developed a functional complementation approach by: (i) growing the patient's fibroblasts in a highly selective medium; and (ii) transferring human chromosome fragments into RC-deficient fibroblasts by microcell-mediated transfer. In the absence of carbohydrates in the culture medium, the deficient cells rapidly disappeared unless they were rescued by a chromosome fragment carrying the disease gene. Microcells prepared from human:rodent Genebridge 4 panel of whole genome radiation hybrids were fused with fibroblast strains of two patients with complex II or I+IV deficiency and allowed to map the disease-causing genes to small intervals (4 and 12 Mb) on chromosomes 12p13 and 7p21, respectively. These intervals are similar to that obtained by genetic linkage analyses in large informative families. The recovery of normal RC enzyme activity in deficient skin fibroblasts supported the relevance of the transferred chromosome fragment in the disease. This approach makes the physical mapping of the disease genes feasible in some sporadic cases of RC deficiency.

Animals↗

PubMedDate not supplied

Coenzyme Q(10) and idebenone in the therapy of respiratory chain diseases: rationale and comparative benefits.

While there have been major advances in both the identification of the molecular basis and our understanding of mitochondrial pathology, the clinical management of patients with mitochondrial respiratory chain disease is still essentially supportive. Quinones are the only pharmacological agents that have proven some efficacy when, and only when, given to patients presenting with quite specific respiratory chain defects. In this article, after a short presentation of the coenzyme Q(10) molecule, its origin and distribution in human body, we summarize our present knowledge on its several physiological functions. We next discuss the rational that justifies using different types of quinones in the therapy of mitochondrial disorders. We finally briefly review the available data obtained in the therapy of mitochondrial disorders by using quinones as either substitutive electron carriers or antioxidant compounds.

Antioxidants↗