Publications by authors named "Pierre Rustin"

157 Publications

Cell Metabolic Alterations due to Mcph1 Mutation in Microcephaly.

Cell Rep 2020 04;31(2):107506

Université de Paris, NeuroDiderot, Inserm, 75019 Paris, France. Electronic address:

A distinctive feature of neocortical development is the highly coordinated production of different progenitor cell subtypes, which are critical for ensuring adequate neurogenic outcome and the development of normal neocortical size. To further understand the mechanisms that underlie neocortical growth, we focused our studies on the microcephaly gene Mcph1, and we report here that Mcph1 (1) exerts its functions in rapidly dividing apical radial glial cells (aRGCs) during mouse neocortical development stages that precede indirect neurogenesis; (2) is expressed at mitochondria; and (3) controls the proper proliferation and survival of RGCs, potentially through crosstalk with cellular metabolic pathways involving the stimulation of mitochondrial activity via VDAC1/GRP75 and AKT/HK2/VDAC1 and glutaminolysis via ATF4/PCK2. We currently report the description of a MCPH-gene implication in the interplay between bioenergetic pathways and neocortical growth, thus pointing to alterations of cellular metabolic pathways, in particular glutaminolysis, as a possible cause of microcephalic pathogenesis.
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http://dx.doi.org/10.1016/j.celrep.2020.03.070DOI Listing
April 2020

Succinate detection using in vivo H-MR spectroscopy identifies germline and somatic SDHx mutations in paragangliomas.

Eur J Nucl Med Mol Imaging 2020 06 13;47(6):1510-1517. Epub 2019 Dec 13.

Université de Paris, PARCC, INSERM, Equipe Labellisée par la Ligue contre le Cancer, F-75015, Paris, France.

Purpose: Germline mutations in genes encoding succinate dehydrogenase (SDH) are frequent in patients with pheochromocytoma and paraganglioma (PPGL). They lead to SDH inactivation, mediating a massive accumulation of succinate, which constitutes a highly specific biomarker of SDHx-mutated tumors when measured in vitro. In a recent pilot study, we showed that magnetic resonance spectroscopy (H-MRS) optimized for succinate detection (SUCCES) could detect succinate in vivo in both allografted mouse models and PPGL patients. The objective of this study was to prospectively assess the diagnostic performances of H-MRS SUCCES sequence for the identification of SDH deficiency in PPGL patients.

Methods: Forty-nine patients presenting with 50 PPGLs were prospectively enrolled in our referral center for H-MRS SUCCES. Two observers blinded to the clinical characteristics and genetic status analyzed the presence of a succinate peak and confronted the results to a composite gold standard combining PPGL genetic testing and/or in vitro protein analyses in the tumor.

Results: A succinate peak was observed in 20 tumors, all of which had proven SDH deficiency using the gold standard (17 patients with germline SDHx mutations, 2 with a somatic SDHD mutation, and 1 with negative SDHB IHC and SDH loss of function). A false negative result was observed in 3 tumors. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of H-MRS SUCCES were respectively 87%, 100%, 100%, 90%, and 94%.

Conclusions: Detection of succinate using H-MRS is a highly specific and sensitive hallmark of SDH-deficiency in PPGLs.
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http://dx.doi.org/10.1007/s00259-019-04633-9DOI Listing
June 2020

Evolutionarily conserved susceptibility of the mitochondrial respiratory chain to SDHI pesticides and its consequence on the impact of SDHIs on human cultured cells.

PLoS One 2019 7;14(11):e0224132. Epub 2019 Nov 7.

Université de Paris, NeuroDiderot, INSERM, Paris, France.

Succinate dehydrogenase (SDH) inhibitors (SDHIs) are used worldwide to limit the proliferation of molds on plants and plant products. However, as SDH, also known as respiratory chain (RC) complex II, is a universal component of mitochondria from living organisms, highly conserved through evolution, the specificity of these inhibitors toward fungi warrants investigation. We first establish that the human, honeybee, earthworm and fungal SDHs are all sensitive to the eight SDHIs tested, albeit with varying IC50 values, generally in the micromolar range. In addition to SDH, we observed that five of the SDHIs, mostly from the latest generation, inhibit the activity of RC complex III. Finally, we show that the provision of glucose ad libitum in the cell culture medium, while simultaneously providing sufficient ATP and reducing power for antioxidant enzymes through glycolysis, allows the growth of RC-deficient cells, fully masking the deleterious effect of SDHIs. As a result, when glutamine is the major carbon source, the presence of SDHIs leads to time-dependent cell death. This process is significantly accelerated in fibroblasts derived from patients with neurological or neurodegenerative diseases due to RC impairment (encephalopathy originating from a partial SDH defect) and/or hypersensitivity to oxidative insults (Friedreich ataxia, familial Alzheimer's disease).
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0224132PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6837341PMC
March 2020

Arabidopsis thaliana alternative dehydrogenases: a potential therapy for mitochondrial complex I deficiency? Perspectives and pitfalls.

Orphanet J Rare Dis 2019 10 29;14(1):236. Epub 2019 Oct 29.

UMR1141, PROTECT, INSERM, Université de Paris, Paris, France.

Background: Complex I (CI or NADH:ubiquinone oxidoreductase) deficiency is the most frequent cause of mitochondrial respiratory chain defect. Successful attempts to rescue CI function by introducing an exogenous NADH dehydrogenase, such as the NDI1 from Saccharomyces cerevisiae (ScNDI1), have been reported although with drawbacks related to competition with CI. In contrast to ScNDI1, which is permanently active in yeast naturally devoid of CI, plant alternative NADH dehydrogenases (NDH-2) support the oxidation of NADH only when the CI is metabolically inactive and conceivably when the concentration of matrix NADH exceeds a certain threshold. We therefore explored the feasibility of CI rescue by NDH-2 from Arabidopsis thaliana (At) in human CI defective fibroblasts.

Results: We showed that, other than ScNDI1, two different NDH-2 (AtNDA2 and AtNDB4) targeted to the mitochondria were able to rescue CI deficiency and decrease oxidative stress as indicated by a normalization of SOD activity in human CI-defective fibroblasts. We further demonstrated that when expressed in human control fibroblasts, AtNDA2 shows an affinity for NADH oxidation similar to that of CI, thus competing with CI for the oxidation of NADH as opposed to our initial hypothesis. This competition reduced the amount of ATP produced per oxygen atom reduced to water by half in control cells.

Conclusions: In conclusion, despite their promising potential to rescue CI defects, due to a possible competition with remaining CI activity, plant NDH-2 should be regarded with caution as potential therapeutic tools for human mitochondrial diseases.
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http://dx.doi.org/10.1186/s13023-019-1185-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6821020PMC
October 2019

Induced pluripotent stem cells-derived neurons from patients with Friedreich ataxia exhibit differential sensitivity to resveratrol and nicotinamide.

Sci Rep 2019 10 10;9(1):14568. Epub 2019 Oct 10.

INSERM UMR 861, I-STEM, AFM, 91100, Corbeil-Essonnes, France.

Translation of pharmacological results from in vitro cell testing to clinical trials is challenging. One of the causes that may underlie these discrepant results is the lack of the phenotypic or species-specific relevance of the tested cells; today, this lack of relevance may be reduced by relying on cells differentiated from human pluripotent stem cells. To analyse the benefits provided by this approach, we chose to focus on Friedreich ataxia, a neurodegenerative condition for which the recent clinical testing of two compounds was not successful. These compounds, namely, resveratrol and nicotinamide, were selected because they had been shown to stimulate the expression of frataxin in fibroblasts and lymphoblastoid cells. Our results indicated that these compounds failed to do so in iPSC-derived neurons generated from two patients with Friedreich ataxia. By comparing the effects of both molecules on different cell types that may be considered to be non-relevant for the disease, such as fibroblasts, or more relevant to the disease, such as neurons differentiated from iPSCs, a differential response was observed; this response suggests the importance of developing more predictive in vitro systems for drug discovery. Our results demonstrate the value of utilizing human iPSCs early in drug discovery to improve translational predictability.
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http://dx.doi.org/10.1038/s41598-019-49870-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6787055PMC
October 2019

Report on three additional patients and genotype-phenotype correlation in SLC25A22-related disorders group.

Eur J Hum Genet 2019 11 8;27(11):1692-1700. Epub 2019 Jul 8.

Département de Génétique Médicale, Maladies Rares et Médecine Personnalisée, Centre de Référence Anomalies du Développement et Syndromes Malformatifs, Université de Montpellier, CHU de Montpellier, France.

Early infantile epileptic encephalopathy (EIEE) is a heterogeneous group of severe forms of age-related developmental and epileptic encephalopathies with onset during the first weeks or months of life. The interictal electroencephalogram (EEG) shows a "suppression burst" (SB) pattern. The prognosis is usually poor and most children die within the first two years or survive with very severe intellectual disabilities. EIEE type 3 is caused by variants affecting function, in SLC25A22, which is also responsible for epilepsy of infancy with migrating focal seizures (EIMFS). We report a family with a less severe phenotype of EIEE type 3. We performed exome sequencing and identified two unreported variants in SLC25A22 in the compound heterozygous state: NM_024698.4: c.[813_814delTG];[818 G>A] (p.[Ala272Glnfs*144];[Arg273Lys]). Functional studies in cultured skin fibroblasts from a patient showed that glutamate oxidation was strongly defective, based on a literature review. We clustered the 18 published patients (including those from this family) into three groups according to the severity of the SLC25A22-related disorders. In an attempt to identify genotype-phenotype correlations, we compared the variants according to the location depending on the protein domains. We observed that patients with two variants located in helical transmembrane domains presented a severe phenotype, whereas patients with at least one variant outside helical transmembrane domains presented a milder phenotype. These data are suggestive of a continuum of disorders related to SLC25A22 that could be called SLC25A22-related disorders. This might be a first clue to enable geneticists to outline a prognosis based on genetic molecular data regarding the SLC25A22 gene.
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http://dx.doi.org/10.1038/s41431-019-0433-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6871179PMC
November 2019

Distinctive Krebs cycle remodeling in iPSC-derived neural and mesenchymal stem cells.

Biochem Biophys Res Commun 2019 04 27;511(3):658-664. Epub 2019 Feb 27.

INSERM UMR 1141, Hôpital Robert Debré, 48 Boulevard Sérurier, 75019, Paris, France; Université Paris Diderot, Paris, France. Electronic address:

Mitochondria play a vital role in proliferation and differentiation and their remodeling in the course of differentiation is related to the variable energy and metabolic needs of the cell. In this work, we show a distinctive mitochondrial remodeling in human induced pluripotent stem cells differentiated into neural or mesenchymal progenitors. While leading to upregulation of the citrate synthase-α-ketoglutarate dehydrogenase segment of the Krebs cycle and increased respiratory chain activities and respiration in the mesenchymal stem cells, the remodeling in the neural stem cells resulted in downregulation of α-ketoglutarate dehydrogenase, upregulation of isocitrate dehydrogenase 2 and the accumulation of α-ketoglutarate. The distinct, lineage-specific changes indicate an involvement of these Krebs cycle enzymes in cell differentiation.
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http://dx.doi.org/10.1016/j.bbrc.2019.02.033DOI Listing
April 2019

Lipin1 deficiency causes sarcoplasmic reticulum stress and chaperone-responsive myopathy.

EMBO J 2019 01 12;38(1). Epub 2018 Nov 12.

Institut Necker-Enfants Malades, Paris, France

As a consequence of impaired glucose or fatty acid metabolism, bioenergetic stress in skeletal muscles may trigger myopathy and rhabdomyolysis. Genetic mutations causing loss of function of the LPIN1 gene frequently lead to severe rhabdomyolysis bouts in children, though the metabolic alterations and possible therapeutic interventions remain elusive. Here, we show that lipin1 deficiency in mouse skeletal muscles is sufficient to trigger myopathy. Strikingly, muscle fibers display strong accumulation of both neutral and phospholipids. The metabolic lipid imbalance can be traced to an altered fatty acid synthesis and fatty acid oxidation, accompanied by a defect in acyl chain elongation and desaturation. As an underlying cause, we reveal a severe sarcoplasmic reticulum (SR) stress, leading to the activation of the lipogenic SREBP1c/SREBP2 factors, the accumulation of the Fgf21 cytokine, and alterations of SR-mitochondria morphology. Importantly, pharmacological treatments with the chaperone TUDCA and the fatty acid oxidation activator bezafibrate improve muscle histology and strength of lipin1 mutants. Our data reveal that SR stress and alterations in SR-mitochondria contacts are contributing factors and potential intervention targets of the myopathy associated with lipin1 deficiency.
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http://dx.doi.org/10.15252/embj.201899576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6315296PMC
January 2019

Alternative respiratory chain enzymes: Therapeutic potential and possible pitfalls.

Biochim Biophys Acta Mol Basis Dis 2019 04 17;1865(4):854-866. Epub 2018 Oct 17.

Faculty of Medicine and Life Sciences, BioMediTech Institute and Tampere University Hospital, FI-33014, University of Tampere, Finland; Institute of Biotechnology, FI-00014, University of Helsinki, Finland. Electronic address:

The alternative respiratory chain (aRC), comprising the alternative NADH dehydrogenases (NDX) and quinone oxidases (AOX), is found in microbes, fungi and plants, where it buffers stresses arising from restrictions on electron flow in the oxidative phosphorylation system. The aRC enzymes are also found in species belonging to most metazoan phyla, including some chordates and arthropods species, although not in vertebrates or in Drosophila. We postulated that the aRC enzymes might be deployed to alleviate pathological stresses arising from mitochondrial dysfunction in a wide variety of disease states. However, before such therapies can be contemplated, it is essential to understand the effects of aRC enzymes on cell metabolism and organismal physiology. Here we report and discuss new findings that shed light on the functions of the aRC enzymes in animals, and the unexpected benefits and detriments that they confer on model organisms. In Ciona intestinalis, the aRC is induced by hypoxia and by sulfide, but is unresponsive to other environmental stressors. When expressed in Drosophila, AOX results in impaired survival under restricted nutrition, in addition to the previously reported male reproductive anomalies. In contrast, it confers cold resistance to developing and adult flies, and counteracts cell signaling defects that underlie developmental dysmorphologies. The aRC enzymes may also influence lifespan and stress resistance more generally, by eliciting or interfering with hormetic mechanisms. In sum, their judicious use may lead to major benefits in medicine, but this will require a thorough characterization of their properties and physiological effects.
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http://dx.doi.org/10.1016/j.bbadis.2018.10.012DOI Listing
April 2019

CHCHD2 accumulates in distressed mitochondria and facilitates oligomerization of CHCHD10.

Hum Mol Genet 2019 01;28(2):349

Inherited Movement Disorders Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.

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http://dx.doi.org/10.1093/hmg/ddy340DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6322067PMC
January 2019

CHCHD2 accumulates in distressed mitochondria and facilitates oligomerization of CHCHD10.

Hum Mol Genet 2018 11;27(22):3881-3900

Inherited Movement Disorders Unit, Neurogenetics Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD USA.

Mutations in paralogous mitochondrial proteins CHCHD2 and CHCHD10 cause autosomal dominant Parkinson Disease (PD) and Amyotrophic Lateral Sclerosis/Frontotemporal Dementia (ALS/FTD), respectively. Using newly generated CHCHD2, CHCHD10 and CHCHD2/10 double knockout cell lines, we find that the proteins are partially functionally redundant, similarly distributed throughout the mitochondrial cristae, and form heterodimers. Unexpectedly, we also find that CHCHD2/CHCHD10 heterodimerization increases in response to mitochondrial stress. This increase is driven by differences in the proteins' stability and mutual affinity: CHCHD2 is preferentially stabilized by loss of mitochondrial membrane potential, and CHCHD10 oligomerization depends on CHCHD2 expression. Exploiting the dependence of CHCHD10 oligomerization on CHCHD2, we developed a heterodimer incorporation assay and demonstrate that CHCHD2 and CHCHD10 with disease-causing mutations readily form heterodimers. As we also find that both proteins are highly expressed in human Substantia nigra and cortical pyramidal neurons, mutant CHCHD2 and CHCHD10 may directly interact with their wild-type paralogs in the context of PD and ALS/FTD pathogenesis. Together, these findings demonstrate that differences in the stability and mutual affinity of CHCHD2 and CHCHD10 regulate their heterodimerization in response to mitochondrial distress, revealing an unanticipated link between PD and ALS/FTD pathogenesis.
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http://dx.doi.org/10.1093/hmg/ddy270DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6216204PMC
November 2018

mutations: A novel phenotype associating severe optic atrophy and spastic paraplegia.

Neurol Genet 2018 Apr 20;4(2):e225. Epub 2018 Mar 20.

Department of Neurology (C.M., B.C.), Gui de Chauliac Montpellier University Hospital; EA7402 Institut Universitaire de Recherche Clinique (C.M., L.L., M.K., C.G.), and Laboratoire de Génétique Moléculaire, University Hospital; Maladies Sensorielles Génétiques (C.H., M.Q., C.D., E.S.), CHRU; INSERM U1051 (C.H., M.Q., C.D., E.S.), Institute for Neurosciences of Montpellier; Université Montpellier (C.H., M.Q., C.D., E.S.), France; INSERM UMR 1141 (D.C., P.R.), PROTECT, INSERM, Université Paris Diderot, Sorbonne Paris Cité, France.

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http://dx.doi.org/10.1212/NXG.0000000000000225DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5860906PMC
April 2018

Mitochondria are physiologically maintained at close to 50 °C.

PLoS Biol 2018 01 25;16(1):e2003992. Epub 2018 Jan 25.

INSERM UMR1141, Hôpital Robert Debré, Paris, France.

In endothermic species, heat released as a product of metabolism ensures stable internal temperature throughout the organism, despite varying environmental conditions. Mitochondria are major actors in this thermogenic process. Part of the energy released by the oxidation of respiratory substrates drives ATP synthesis and metabolite transport, but a substantial proportion is released as heat. Using a temperature-sensitive fluorescent probe targeted to mitochondria, we measured mitochondrial temperature in situ under different physiological conditions. At a constant external temperature of 38 °C, mitochondria were more than 10 °C warmer when the respiratory chain (RC) was fully functional, both in human embryonic kidney (HEK) 293 cells and primary skin fibroblasts. This differential was abolished in cells depleted of mitochondrial DNA or treated with respiratory inhibitors but preserved or enhanced by expressing thermogenic enzymes, such as the alternative oxidase or the uncoupling protein 1. The activity of various RC enzymes was maximal at or slightly above 50 °C. In view of their potential consequences, these observations need to be further validated and explored by independent methods. Our study prompts a critical re-examination of the literature on mitochondria.
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http://dx.doi.org/10.1371/journal.pbio.2003992DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5784887PMC
January 2018

An Effective, Versatile, and Inexpensive Device for Oxygen Uptake Measurement.

J Clin Med 2017 Jun 8;6(6). Epub 2017 Jun 8.

INSERM UMR 1141, Hôpital Robert Debré, 75019 Paris, France.

In the last ten years, the use of fluorescent probes developed to measure oxygen has resulted in several marketed devices, some unreasonably expensive and with little flexibility. We have explored the use of the effective, versatile, and inexpensive Redflash technology to determine oxygen uptake by a number of different biological samples using various layouts. This technology relies on the use of an optic fiber equipped at its tip with a membrane coated with a fluorescent dye (www.pyro-science.com). This oxygen-sensitive dye uses red light excitation and lifetime detection in the near infrared. So far, the use of this technology has mostly been used to determine oxygen concentration in open spaces for environmental studies, especially in aquatic media. The oxygen uptake determined by the device can be easily assessed in small volumes of respiration medium and combined with the measurement of additional parameters, such as lactate excretion by intact cells or the membrane potential of purified mitochondria. We conclude that the performance of by this technology should make it a first choice in the context of both fundamental studies and investigations for respiratory chain deficiencies in human samples.
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http://dx.doi.org/10.3390/jcm6060058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5483868PMC
June 2017

Acute and chronic mitochondrial respiratory chain deficiency differentially regulate lysosomal biogenesis.

Sci Rep 2017 03 27;7:45076. Epub 2017 Mar 27.

Institute of Cellular Biology, University Medical Center Goettingen, Goettingen, Germany.

Mitochondria are key cellular signaling platforms, affecting fundamental processes such as cell proliferation, differentiation and death. However, it remains unclear how mitochondrial signaling affects other organelles, particularly lysosomes. Here, we demonstrate that mitochondrial respiratory chain (RC) impairments elicit a stress signaling pathway that regulates lysosomal biogenesis via the microphtalmia transcription factor family. Interestingly, the effect of mitochondrial stress over lysosomal biogenesis depends on the timeframe of the stress elicited: while RC inhibition with rotenone or uncoupling with CCCP initially triggers lysosomal biogenesis, the effect peaks after few hours and returns to baseline. Long-term RC inhibition by long-term treatment with rotenone, or patient mutations in fibroblasts and in a mouse model result in repression of lysosomal biogenesis. The induction of lysosomal biogenesis by short-term mitochondrial stress is dependent on TFEB and MITF, requires AMPK signaling and is independent of calcineurin signaling. These results reveal an integrated view of how mitochondrial signaling affects lysosomes, which is essential to fully comprehend the consequences of mitochondrial malfunction, particularly in the context of mitochondrial diseases.
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http://dx.doi.org/10.1038/srep45076DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5366864PMC
March 2017

Paradoxical Inhibition of Glycolysis by Pioglitazone Opposes the Mitochondriopathy Caused by AIF Deficiency.

EBioMedicine 2017 Mar 16;17:75-87. Epub 2017 Feb 16.

INSERM UMR 1141, PROTECT, INSERM, Université Paris Diderot, Sorbonne Paris Cité, Paris, France. Electronic address:

Mice with the hypomorphic AIF-Harlequin mutation exhibit a highly heterogeneous mitochondriopathy that mostly affects respiratory chain complex I, causing a cerebral pathology that resembles that found in patients with AIF loss-of-function mutations. Here we describe that the antidiabetic drug pioglitazone (PIO) can improve the phenotype of a mouse Harlequin (Hq) subgroup, presumably due to an inhibition of glycolysis that causes an increase in blood glucose levels. This glycolysis-inhibitory PIO effect was observed in cultured astrocytes from Hq mice, as well as in human skin fibroblasts from patients with AIF mutation. Glycolysis inhibition by PIO resulted from direct competitive inhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Moreover, GAPDH protein levels were reduced in the cerebellum and in the muscle from Hq mice that exhibited an improved phenotype upon PIO treatment. Altogether, our results suggest that excessive glycolysis participates to the pathogenesis of mitochondriopathies and that pharmacological inhibition of glycolysis may have beneficial effects in this condition.
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http://dx.doi.org/10.1016/j.ebiom.2017.02.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5360583PMC
March 2017

Broad AOX expression in a genetically tractable mouse model does not disturb normal physiology.

Dis Model Mech 2017 02 14;10(2):163-171. Epub 2016 Dec 14.

Max Planck Institute for Heart and Lung Research, Cardiac Development and Remodelling (Department I), Bad Nauheim D-61231, Germany.

Plants and many lower organisms, but not mammals, express alternative oxidases (AOXs) that branch the mitochondrial respiratory chain, transferring electrons directly from ubiquinol to oxygen without proton pumping. Thus, they maintain electron flow under conditions when the classical respiratory chain is impaired, limiting excess production of oxygen radicals and supporting redox and metabolic homeostasis. AOX from Ciona intestinalis has been used to study and mitigate mitochondrial impairments in mammalian cell lines, Drosophila disease models and, most recently, in the mouse, where multiple lentivector-AOX transgenes conferred substantial expression in specific tissues. Here, we describe a genetically tractable mouse model in which Ciona AOX has been targeted to the Rosa26 locus for ubiquitous expression. The AOX mouse exhibited only subtle phenotypic effects on respiratory complex formation, oxygen consumption or the global metabolome, and showed an essentially normal physiology. AOX conferred robust resistance to inhibitors of the respiratory chain in organello; moreover, animals exposed to a systemically applied LD50 dose of cyanide did not succumb. The AOX mouse is a useful tool to investigate respiratory control mechanisms and to decipher mitochondrial disease aetiology in vivo.
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http://dx.doi.org/10.1242/dmm.027839DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312010PMC
February 2017

QIL1 mutation causes MICOS disassembly and early onset fatal mitochondrial encephalopathy with liver disease.

Elife 2016 09 13;5. Epub 2016 Sep 13.

UMR1141, PROTECT, INSERM, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France.

Previously, we identified QIL1 as a subunit of mitochondrial contact site (MICOS) complex and demonstrated a role for QIL1 in MICOS assembly, mitochondrial respiration, and cristae formation critical for mitochondrial architecture (Guarani et al., 2015). Here, we identify QIL1 null alleles in two siblings displaying multiple clinical symptoms of early-onset fatal mitochondrial encephalopathy with liver disease, including defects in respiratory chain function in patient muscle. QIL1 absence in patients' fibroblasts was associated with MICOS disassembly, abnormal cristae, mild cytochrome c oxidase defect, and sensitivity to glucose withdrawal. QIL1 expression rescued cristae defects, and promoted re-accumulation of MICOS subunits to facilitate MICOS assembly. MICOS assembly and cristae morphology were not efficiently rescued by over-expression of other MICOS subunits in patient fibroblasts. Taken together, these data provide the first evidence of altered MICOS assembly linked with a human mitochondrial disease and confirm a central role for QIL1 in stable MICOS complex formation.
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http://dx.doi.org/10.7554/eLife.17163DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5021520PMC
September 2016

The environmental carcinogen benzo[a]pyrene induces a Warburg-like metabolic reprogramming dependent on NHE1 and associated with cell survival.

Sci Rep 2016 08 4;6:30776. Epub 2016 Aug 4.

Institut national de la santé et de la recherche médicale (Inserm), Institut de recherche en santé, environnement et travail (Irset - Inserm UMR 1085), F-35043 Rennes, France.

Cancer cells display alterations in many cellular processes. One core hallmark of cancer is the Warburg effect which is a glycolytic reprogramming that allows cells to survive and proliferate. Although the contributions of environmental contaminants to cancer development are widely accepted, the underlying mechanisms have to be clarified. Benzo[a]pyrene (B[a]P), the prototype of polycyclic aromatic hydrocarbons, exhibits genotoxic and carcinogenic effects, and it is a human carcinogen according to the International Agency for Research on Cancer. In addition to triggering apoptotic signals, B[a]P may induce survival signals, both of which are likely to be involved in cancer promotion. We previously suggested that B[a]P-induced mitochondrial dysfunctions, especially membrane hyperpolarization, might trigger cell survival signaling in rat hepatic epithelial F258 cells. Here, we further characterized these dysfunctions by focusing on energy metabolism. We found that B[a]P promoted a metabolic reprogramming. Cell respiration decreased and lactate production increased. These changes were associated with alterations in the tricarboxylic acid cycle which likely involve a dysfunction of the mitochondrial complex II. The glycolytic shift relied on activation of the Na(+)/H(+) exchanger 1 (NHE1) and appeared to be a key feature in B[a]P-induced cell survival related to changes in cell phenotype (epithelial-to-mesenchymal transition and cell migration).
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http://dx.doi.org/10.1038/srep30776DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4973274PMC
August 2016

[Heart failure from mitochondrial origin: a matter of diet?].

Med Sci (Paris) 2016 May 25;32(5):458-60. Epub 2016 May 25.

Inserm UMR1141, Hôpital Robert Debré, 48, boulevard Sérurier, 75019 Paris, France.

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http://dx.doi.org/10.1051/medsci/20163205011DOI Listing
May 2016

Idebenone in Friedreich ataxia and Leber's hereditary optic neuropathy: close mechanisms, similar therapy?

Brain 2016 07 19;139(Pt 7):e39. Epub 2016 Apr 19.

1 Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche 1141, Hôpital Robert Debré, 48 Boulevard Sérurier, 75019 Paris, France 2 Faculté de Médecine Denis Diderot, Université Paris Diderot - Paris 7, Site Robert Debré, 48 Boulevard Sérurier, 75019 Paris, France

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http://dx.doi.org/10.1093/brain/aww085DOI Listing
July 2016

Expression of the alternative oxidase mitigates beta-amyloid production and toxicity in model systems.

Free Radic Biol Med 2016 07 14;96:57-66. Epub 2016 Apr 14.

INSERM UMR 1141 and Université Paris 7, Faculté de Médecine Denis Diderot, Hôpital Robert Debré, 48, Boulevard Sérurier, 75019 Paris, France.

Mitochondrial dysfunction has been widely associated with the pathology of Alzheimer's disease, but there is no consensus on whether it is a cause or consequence of disease, nor on the precise mechanism(s). We addressed these issues by testing the effects of expressing the alternative oxidase AOX from Ciona intestinalis, in different models of AD pathology. AOX can restore respiratory electron flow when the cytochrome segment of the mitochondrial respiratory chain is inhibited, supporting ATP synthesis, maintaining cellular redox homeostasis and mitigating excess superoxide production at respiratory complexes I and III. In human HEK293-derived cells, AOX expression decreased the production of beta-amyloid peptide resulting from antimycin inhibition of respiratory complex III. Because hydrogen peroxide was neither a direct product nor substrate of AOX, the ability of AOX to mimic antioxidants in this assay must be indirect. In addition, AOX expression was able to partially alleviate the short lifespan of Drosophila models neuronally expressing human beta-amyloid peptides, whilst abrogating the induction of markers of oxidative stress. Our findings support the idea of respiratory chain dysfunction and excess ROS production as both an early step and as a pathologically meaningful target in Alzheimer's disease pathogenesis, supporting the concept of a mitochondrial vicious cycle underlying the disease.
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http://dx.doi.org/10.1016/j.freeradbiomed.2016.04.006DOI Listing
July 2016

Translocator Protein-Mediated Stabilization of Mitochondrial Architecture during Inflammation Stress in Colonic Cells.

PLoS One 2016 7;11(4):e0152919. Epub 2016 Apr 7.

Sorbonne Universités - Université Pierre et Marie Curie Université de Paris VI, École Normale Supérieure - PSL Research University, Département de Chimie, CNRS UMR 7203 LBM, 4 Place Jussieu, F-75005, Paris, France.

Unlabelled: Chronic inflammation of the gastrointestinal tract increasing the risk of cancer has been described to be linked to the high expression of the mitochondrial translocator protein (18 kDa; TSPO). Accordingly, TSPO drug ligands have been shown to regulate cytokine production and to improve tissue reconstruction. We used HT-29 human colon carcinoma cells to evaluate the role of TSPO and its drug ligands in tumor necrosis factor (TNF)-induced inflammation. TNF-induced interleukin (IL)-8 expression, coupled to reactive oxygen species (ROS) production, was followed by TSPO overexpression. TNF also destabilized mitochondrial ultrastructure, inducing cell death by apoptosis. Treatment with the TSPO drug ligand PK 11195 maintained the mitochondrial ultrastructure, reducing IL-8 and ROS production and cell death. TSPO silencing and overexpression studies demonstrated that the presence of TSPO is essential to control IL-8 and ROS production, so as to maintain mitochondrial ultrastructure and to prevent cell death. Taken together, our data indicate that inflammation results in the disruption of mitochondrial complexes containing TSPO, leading to cell death and epithelia disruption.

Significance: This work implicates TSPO in the maintenance of mitochondrial membrane integrity and in the control of mitochondrial ROS production, ultimately favoring tissue regeneration.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0152919PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4824355PMC
August 2016

Mitochondrial cytochrome c oxidase deficiency.

Clin Sci (Lond) 2016 Mar;130(6):393-407

Institut National de la Santé et de la Recherche Médicale Unité Mixte de Recherche 1141, Hôpital Robert Debré, 48 Boulevard Sérurier, 75019 Paris, France Faculté de Médecine Denis Diderot, Université Paris Diderot-Paris 7, Site Robert Debré, 48 Boulevard Sérurier, 75019 Paris, France

As with other mitochondrial respiratory chain components, marked clinical and genetic heterogeneity is observed in patients with a cytochrome c oxidase deficiency. This constitutes a considerable diagnostic challenge and raises a number of puzzling questions. So far, pathological mutations have been reported in more than 30 genes, in both mitochondrial and nuclear DNA, affecting either structural subunits of the enzyme or proteins involved in its biogenesis. In this review, we discuss the possible causes of the discrepancy between the spectacular advances made in the identification of the molecular bases of cytochrome oxidase deficiency and the lack of any efficient treatment in diseases resulting from such deficiencies. This brings back many unsolved questions related to the frequent delay of clinical manifestation, variable course and severity, and tissue-involvement often associated with these diseases. In this context, we stress the importance of studying different models of these diseases, but also discuss the limitations encountered in most available disease models. In the future, with the possible exception of replacement therapy using genes, cells or organs, a better understanding of underlying mechanism(s) of these mitochondrial diseases is presumably required to develop efficient therapy.
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http://dx.doi.org/10.1042/CS20150707DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4948581PMC
March 2016

Imbalanced OPA1 processing and mitochondrial fragmentation cause heart failure in mice.

Science 2015 Dec;350(6265):aad0116

Institute for Genetics, University of Cologne, 50674 Cologne, Germany. Max-Planck-Institute for Biology of Aging, Cologne, Germany. Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD), University of Cologne, Cologne, Germany. Center for Molecular Medicine (CMMC), University of Cologne, Cologne, Germany.

Mitochondrial morphology is shaped by fusion and division of their membranes. Here, we found that adult myocardial function depends on balanced mitochondrial fusion and fission, maintained by processing of the dynamin-like guanosine triphosphatase OPA1 by the mitochondrial peptidases YME1L and OMA1. Cardiac-specific ablation of Yme1l in mice activated OMA1 and accelerated OPA1 proteolysis, which triggered mitochondrial fragmentation and altered cardiac metabolism. This caused dilated cardiomyopathy and heart failure. Cardiac function and mitochondrial morphology were rescued by Oma1 deletion, which prevented OPA1 cleavage. Feeding mice a high-fat diet or ablating Yme1l in skeletal muscle restored cardiac metabolism and preserved heart function without suppressing mitochondrial fragmentation. Thus, unprocessed OPA1 is sufficient to maintain heart function, OMA1 is a critical regulator of cardiomyocyte survival, and mitochondrial morphology and cardiac metabolism are intimately linked.
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http://dx.doi.org/10.1126/science.aad0116DOI Listing
December 2015

Diiron centre mutations in Ciona intestinalis alternative oxidase abolish enzymatic activity and prevent rescue of cytochrome oxidase deficiency in flies.

Sci Rep 2015 Dec 17;5:18295. Epub 2015 Dec 17.

BioMediTech and Tampere University Hospital, University of Tampere, FI-33014, Finland.

The mitochondrial alternative oxidase, AOX, carries out the non proton-motive re-oxidation of ubiquinol by oxygen in lower eukaryotes, plants and some animals. Here we created a modified version of AOX from Ciona instestinalis, carrying mutations at conserved residues predicted to be required for chelation of the diiron prosthetic group. The modified protein was stably expressed in mammalian cells or flies, but lacked enzymatic activity and was unable to rescue the phenotypes of flies knocked down for a subunit of cytochrome oxidase. The mutated AOX transgene is thus a potentially useful tool in studies of the physiological effects of AOX expression.
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http://dx.doi.org/10.1038/srep18295DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4682143PMC
December 2015

In Vitro and In Vivo Modulation of Alternative Splicing by the Biguanide Metformin.

Mol Ther Nucleic Acids 2015 Nov 3;4:e262. Epub 2015 Nov 3.

INSERM/UEVE UMR 861, Evry Cedex, France.

Major physiological changes are governed by alternative splicing of RNA, and its misregulation may lead to specific diseases. With the use of a genome-wide approach, we show here that this splicing step can be modified by medication and demonstrate the effects of the biguanide metformin, on alternative splicing. The mechanism of action involves AMPK activation and downregulation of the RBM3 RNA-binding protein. The effects of metformin treatment were tested on myotonic dystrophy type I (DM1), a multisystemic disease considered to be a spliceopathy. We show that this drug promotes a corrective effect on several splicing defects associated with DM1 in derivatives of human embryonic stem cells carrying the causal mutation of DM1 as well as in primary myoblasts derived from patients. The biological effects of metformin were shown to be compatible with typical therapeutic dosages in a clinical investigation involving diabetic patients. The drug appears to act as a modifier of alternative splicing of a subset of genes and may therefore have novel therapeutic potential for many more diseases besides those directly linked to defective alternative splicing.
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http://dx.doi.org/10.1038/mtna.2015.35DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4877444PMC
November 2015

In Vivo Detection of Succinate by Magnetic Resonance Spectroscopy as a Hallmark of SDHx Mutations in Paraganglioma.

Clin Cancer Res 2016 Mar 21;22(5):1120-9. Epub 2015 Oct 21.

INSERM, UMR970, Paris Cardiovascular Research Center, Paris, France. Université Paris Descartes, Sorbonne Paris Cité, Faculté de Médecine, Paris, France. Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Service de Radiologie, Paris, France.

Purpose: Germline mutations in genes encoding mitochondrial succinate dehydrogenase (SDH) are found in patients with paragangliomas, pheochromocytomas, gastrointestinal stromal tumors, and renal cancers. SDH inactivation leads to a massive accumulation of succinate, acting as an oncometabolite and which levels, assessed on surgically resected tissue are a highly specific biomarker of SDHx-mutated tumors. The aim of this study was to address the feasibility of detecting succinate in vivo by magnetic resonance spectroscopy.

Experimental Design: A pulsed proton magnetic resonance spectroscopy ((1)H-MRS) sequence was developed, optimized, and applied to image nude mice grafted with Sdhb(-/-) or wild-type chromaffin cells. The method was then applied to patients with paraganglioma carrying (n = 5) or not (n = 4) an SDHx gene mutation. Following surgery, succinate was measured using gas chromatography/mass spectrometry, and SDH protein expression was assessed by immunohistochemistry in resected tumors.

Results: A succinate peak was observed at 2.44 ppm by (1)H-MRS in all Sdhb(-/-)-derived tumors in mice and in all paragangliomas of patients carrying an SDHx gene mutation, but neither in wild-type mouse tumors nor in patients exempt of SDHx mutation. In one patient, (1)H-MRS results led to the identification of an unsuspected SDHA gene mutation. In another case, it helped define the pathogenicity of a variant of unknown significance in the SDHB gene.

Conclusions: Detection of succinate by (1)H-MRS is a highly specific and sensitive hallmark of SDHx mutations. This noninvasive approach is a simple and robust method allowing in vivo detection of the major biomarker of SDHx-mutated tumors.
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http://dx.doi.org/10.1158/1078-0432.CCR-15-1576DOI Listing
March 2016