Publications by authors named "Yan Burelle"

62 Publications

A recurrent de novo ATP5F1A substitution associated with neonatal complex V deficiency.

Eur J Hum Genet 2021 Sep 6. Epub 2021 Sep 6.

Metabolics and Newborn Screening, Children's Hospital of Eastern Ontario, Ottawa, ON, Canada.

Mitochondrial disorders are a heterogeneous group of rare, degenerative multisystem disorders affecting the cell's core bioenergetic and signalling functions. Spontaneous improvement is rare. We describe a novel neonatal-onset mitochondriopathy in three infants with failure to thrive, hyperlactatemia, hyperammonemia, and apparent clinical resolution before 18 months. Exome sequencing showed all three probands to be identically heterozygous for a recurrent de novo substitution, c.620G>A [p.(Arg207His)] in ATP5F1A, encoding the α-subunit of complex V. Patient-derived fibroblasts exhibited multiple deficits in complex V function and expression in vitro. Structural modelling predicts the observed substitution to create an abnormal region of negative charge on ATP5F1A's β-subunit-interacting surface, adjacent to the nearby β subunit's active site. This disorder, which presents with life-threatening neonatal manifestations, appears to follow a remitting course; the long-term prognosis remains unknown.
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http://dx.doi.org/10.1038/s41431-021-00956-0DOI Listing
September 2021

Adaptive optimization of the OXPHOS assembly line partially compensates lrpprc-dependent mitochondrial translation defects in mice.

Commun Biol 2021 08 19;4(1):989. Epub 2021 Aug 19.

Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.

Mouse models of genetic mitochondrial disorders are generally used to understand specific molecular defects and their biochemical consequences, but rarely to map compensatory changes allowing survival. Here we took advantage of the extraordinary mitochondrial resilience of hepatic Lrpprc knockout mice to explore this question using native proteomics profiling and lipidomics. In these mice, low levels of the mtRNA binding protein LRPPRC induce a global mitochondrial translation defect and a severe reduction (>80%) in the assembly and activity of the electron transport chain (ETC) complex IV (CIV). Yet, animals show no signs of overt liver failure and capacity of the ETC is preserved. Beyond stimulation of mitochondrial biogenesis, results show that the abundance of mitoribosomes per unit of mitochondria is increased and proteostatic mechanisms are induced in presence of low LRPPRC levels to preserve a balance in the availability of mitochondrial- vs nuclear-encoded ETC subunits. At the level of individual organelles, a stabilization of residual CIV in supercomplexes (SCs) is observed, pointing to a role of these supramolecular arrangements in preserving ETC function. While the SC assembly factor COX7A2L could not contribute to the stabilization of CIV, important changes in membrane glycerophospholipid (GPL), most notably an increase in SC-stabilizing cardiolipins species (CLs), were observed along with an increased abundance of other supramolecular assemblies known to be stabilized by, and/or participate in CL metabolism. Together these data reveal a complex in vivo network of molecular adjustments involved in preserving mitochondrial integrity in energy consuming organs facing OXPHOS defects, which could be therapeutically exploited.
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http://dx.doi.org/10.1038/s42003-021-02492-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8376967PMC
August 2021

Oxidative stress-induced senescence mediates inflammatory and fibrotic phenotypes in fibroblasts from systemic sclerosis patients.

Rheumatology (Oxford) 2021 Jun 11. Epub 2021 Jun 11.

Faculty of Pharmacy, Université de Montréal, Québec, Canada.

Objective: Systemic sclerosis (SSc) is an autoimmune connective tissue disorder characterized by inflammation and fibrosis. Although constitutive activation of fibroblasts is proposed to be responsible for the fibrotic and inflammatory features of the disease, the underlying mechanism remains elusive and, effective therapeutic targets are still lacking. The aim of this study was to evaluate the role of oxidative stress-induced senescence and its contribution to the pro-fibrotic and pro-inflammatory phenotypes of fibroblasts from SSc patients.

Methods: Dermal fibroblasts were isolated from SSc (n = 13) and healthy (n = 10) donors. Fibroblast's intracellular and mitochondrial reactive oxygen species were determined by flow cytometry. Mitochondrial function measured by Seahorse XF24 analyzer. Fibrotic and inflammatory gene expressions were assessed by qPCR and key pro-inflammatory components of the fibroblasts' secretome (interleukin (IL) 6 and IL8) were quantified by ELISA.

Results: Compared to healthy fibroblasts, SSc fibroblasts displayed higher levels of both intracellular and mitochondrial ROS. Oxidative stress in SSc fibroblasts induced the expression of fibrotic genes and activated the transforming growth factor-β-activated kinase 1 (TAK1) -IκB kinase β (IKKβ)- interferon regulatory factor 5 (IRF5) inflammatory signaling cascade. These cellular responses paralleled the presence of a DNA damage response, a senescence-associated secretory phenotype and a fibrotic response. Treatment of SSc fibroblasts with ROS scavengers reduced their pro-inflammatory secretome production and fibrotic gene expression.

Conclusions: Oxidative stress-induced cellular senescence in SSc fibroblasts underlies their pro-inflammatory and pro-fibrotic phenotypes. Targeting redox imbalance of SSc fibroblasts enhances their in vitro functions and could be of relevance for SSc therapy.
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http://dx.doi.org/10.1093/rheumatology/keab477DOI Listing
June 2021

Proteomics characterization of mitochondrial-derived vesicles under oxidative stress.

FASEB J 2021 04;35(4):e21278

Interdisciplinary School of Health Sciences, Faculty of Health Sciences, University of Ottawa, Ottawa, ON, Canada.

Mitochondria share attributes of vesicular transport with their bacterial ancestors given their ability to form mitochondrial-derived vesicles (MDVs). MDVs are involved in mitochondrial quality control and their formation is enhanced with stress and may, therefore, play a potential role in mitochondrial-cellular communication. However, MDV proteomic cargo has remained mostly undefined. In this study, we strategically used an in vitro MDV budding/reconstitution assay on cardiac mitochondria, followed by graded oxidative stress, to identify and characterize the MDV proteome. Our results confirmed previously identified cardiac MDV markers, while also revealing a complete map of the MDV proteome, paving the way to a better understanding of the role of MDVs. The oxidative stress vulnerability of proteins directed the cargo loading of MDVs, which was enhanced by antimycin A (Ant-A). Among OXPHOS complexes, complexes III and V were found to be Ant-A-sensitive. Proteins from metabolic pathways such as the TCA cycle and fatty acid metabolism, along with Fe-S cluster, antioxidant response proteins, and autophagy were also found to be Ant-A sensitive. Intriguingly, proteins containing hyper-reactive cysteine residues, metabolic redox switches, including professional redox enzymes and those that mediate iron metabolism, were found to be components of MDV cargo with Ant-A sensitivity. Last, we revealed a possible contribution of MDVs to the formation of extracellular vesicles, which may indicate mitochondrial stress. In conclusion, our study provides an MDV proteomics signature that delineates MDV cargo selectivity and hints at the potential for MDVs and their novel protein cargo to serve as vital biomarkers during mitochondrial stress and related pathologies.
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http://dx.doi.org/10.1096/fj.202002151RDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8252493PMC
April 2021

Regulates Skeletal Muscle Mitochondrial Structure and Autophagy.

Front Physiol 2021 5;12:604210. Epub 2021 Mar 5.

Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.

Glutathione is an important antioxidant that regulates cellular redox status and is disordered in many disease states. Glutaredoxin 2 () is a glutathione-dependent oxidoreductase that plays a pivotal role in redox control by catalyzing reversible protein deglutathionylation. As oxidized glutathione (GSSG) can stimulate mitochondrial fusion, we hypothesized that may contribute to the maintenance of mitochondrial dynamics and ultrastructure. Here, we demonstrate that deletion results in decreased GSH:GSSG, with a marked increase of GSSG in primary muscle cells isolated from C57BL/6 mice. The altered glutathione redox was accompanied by increased mitochondrial length, consistent with a more fused mitochondrial reticulum. Electron microscopy of skeletal muscle fibers revealed decreased mitochondrial surface area, profoundly disordered ultrastructure, and the appearance of multi-lamellar structures. Immunoblot analysis revealed that autophagic flux was augmented in muscle as demonstrated by an increase in the ratio of LC3II/I expression. These molecular changes resulted in impaired complex I respiration and complex IV activity, a smaller diameter of muscle, and decreased body weight in deficient mice. Together, these are the first results to show that regulates skeletal muscle mitochondrial structure, and autophagy.
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http://dx.doi.org/10.3389/fphys.2021.604210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7982873PMC
March 2021

Mitophagy: A New Player in Stem Cell Biology.

Biology (Basel) 2020 Dec 19;9(12). Epub 2020 Dec 19.

Center for Neuromuscular Disease, Department of Biochemistry, Microbiology and Immunology, Faculty of Medicine, Ottawa Institute of Systems Biology (OISB), University of Ottawa, Ottawa, ON K1H 8M5, Canada.

The fundamental importance of functional mitochondria in the survival of most eukaryotic cells, through regulation of bioenergetics, cell death, calcium dynamics and reactive oxygen species (ROS) generation, is undisputed. However, with new avenues of research in stem cell biology these organelles have now emerged as signaling entities, actively involved in many aspects of stem cell functions, including self-renewal, commitment and differentiation. With this recent knowledge, it becomes evident that regulatory pathways that would ensure the maintenance of mitochondria with state-specific characteristics and the selective removal of organelles with sub-optimal functions must play a pivotal role in stem cells. As such, mitophagy, as an essential mitochondrial quality control mechanism, is beginning to gain appreciation within the stem cell field. Here we review and discuss recent advances in our knowledge pertaining to the roles of mitophagy in stem cell functions and the potential contributions of this specific quality control process on to the progression of aging and diseases.
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http://dx.doi.org/10.3390/biology9120481DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7766552PMC
December 2020

Protein O-GlcNAcylation levels are regulated independently of dietary intake in a tissue and time-specific manner during rat postnatal development.

Acta Physiol (Oxf) 2021 03 16;231(3):e13566. Epub 2020 Oct 16.

Université de Nantes, CHU Nantes, CNRS, INSERM, l'institut du thorax, Nantes, France.

Aim: Metabolic sources switch from carbohydrates in utero, to fatty acids after birth and then a mix once adults. O-GlcNAcylation (O-GlcNAc) is a post-translational modification considered as a nutrient sensor. The purpose of this work was to assess changes in protein O-GlcNAc levels, regulatory enzymes and metabolites during the first periods of life and decipher the impact of O-GlcNAcylation on cardiac proteins.

Methods: Heart, brain and liver were harvested from rats before and after birth (D-1 and D0), in suckling animals (D12), after weaning with a standard (D28) or a low-carbohydrate diet (D28F), and adults (D84). O-GlcNAc levels and regulatory enzymes were evaluated by western blots. Mass spectrometry (MS) approaches were performed to quantify levels of metabolites regulating O-GlcNAc and identify putative cardiac O-GlcNAcylated proteins.

Results: Protein O-GlcNAc levels decrease drastically and progressively from D-1 to D84 (13-fold, P < .05) in the heart, whereas the changes were opposite in liver and brain. O-GlcNAc levels were unaffected by weaning diet in any tissues. Changes in expression of enzymes and levels of metabolites regulating O-GlcNAc were tissue-dependent. MS analyses identified changes in putative cardiac O-GlcNAcylated proteins, namely those involved in the stress response and energy metabolism, such as ACAT1, which is only O-GlcNAcylated at D0.

Conclusion: Our results demonstrate that protein O-GlcNAc levels are not linked to dietary intake and regulated in a time and tissue-specific manner during postnatal development. We have identified by untargeted MS putative proteins with a particular O-GlcNAc signature across the development process suggesting specific role of these proteins.
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http://dx.doi.org/10.1111/apha.13566DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7988603PMC
March 2021

Effects of (-)-epicatechin on mitochondria.

Nutr Rev 2021 01;79(1):25-41

Interdisciplinary School of Health Sciences, Faculty of Health Sciences, University of Ottawa, Ontario; and Department of Molecular and Cellular Medicine, Faculty of Medicine, University of Ottawa, Ontario, Canada.

Mitochondrial dysfunction is observed in a broad range of human diseases, including rare genetic disorders and complex acquired pathologies. For this reason, there is increasing interest in identifying safe and effective strategies to mitigate mitochondrial impairments. Natural compounds are widely used for multiple indications, and their broad healing properties suggest that several may improve mitochondrial function. This review focuses on (-)-epicatechin, a monomeric flavanol, and its effects on mitochondria. The review summarizes the available data on the effects of acute and chronic (-)-epicatechin supplementation on mitochondrial function, outlines the potential mechanisms involved in mitochondrial biogenesis induced by (-)-epicatechin supplementation and discusses some future therapeutic applications.
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http://dx.doi.org/10.1093/nutrit/nuaa094DOI Listing
January 2021

Mitochondrial Psychobiology: Foundations and Applications.

Curr Opin Behav Sci 2019 Aug 14;28:142-151. Epub 2019 Jun 14.

Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.

Mitochondrial psychobiology is the study of the interactions between psychological states and the biological processes that take place within mitochondria. It also examines how mitochondrial behavior influence neural, endocrine, and immune systems known to transduce psychological experiences into health outcomes. Unlike traditional biological outcomes and mediators, mitochondria are dynamic and multifunctional living organisms. By leveraging a variety of laboratory tools including omics, scientists can now map mitochondrial behavior at multiple levels of complexity - from isolated molecular markers to dynamic functional and signaling outcomes. Here we discuss current efforts to develop relevant measures of mitochondrial behavior in accessible human tissues, increase their biological specificity by applying precise measurements in defined cell populations, create composite indices reflecting mitochondrial health, and integrate these approaches with psycho-neuro-endocrino-immune outcomes. This systematic inter-disciplinary effort will help move the field of mitochondrial psychobiology towards a predictive science explaining how, and to what extent, mitochondria contribute to the biological embedding of stress and other psychological states.
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http://dx.doi.org/10.1016/j.cobeha.2019.04.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7339630PMC
August 2019

MCL-1 maintains neuronal survival by enhancing mitochondrial integrity and bioenergetic capacity under stress conditions.

Cell Death Dis 2020 05 5;11(5):321. Epub 2020 May 5.

University of Ottawa Brain and Mind Research Institute, Department of Cellular and Molecular medicine, University of Ottawa, Ottawa, ON, Canada.

Mitochondria play a crucial role in neuronal survival through efficient energy metabolism. In pathological conditions, mitochondrial stress leads to neuronal death, which is regulated by the anti-apoptotic BCL-2 family of proteins. MCL-1 is an anti-apoptotic BCL-2 protein localized to mitochondria either in the outer membrane (OM) or inner membrane (Matrix), which have distinct roles in inhibiting apoptosis and promoting bioenergetics, respectively. While the anti-apoptotic role for Mcl1 is well characterized, the protective function of MCL-1 remains poorly understood. Here, we show MCL-1 and MCL-1 prevent neuronal death through distinct mechanisms. We report that MCL-1 functions to preserve mitochondrial energy transduction and improves respiratory chain capacity by modulating mitochondrial oxygen consumption in response to mitochondrial stress. We show that MCL-1 protects neurons from stress by enhancing respiratory function, and by inhibiting mitochondrial permeability transition pore opening. Taken together, our results provide novel insight into how MCL-1 may confer neuroprotection under stress conditions involving loss of mitochondrial function.
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http://dx.doi.org/10.1038/s41419-020-2498-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7200794PMC
May 2020

Fiber-specific and whole-muscle LRP130 expression in rested, exercised, and fasted human skeletal muscle.

Pflugers Arch 2020 03 17;472(3):375-384. Epub 2020 Feb 17.

School of Kinesiology and Health Studies, Queen's University, Kingston, Ontario, Canada.

Leucine-rich pentatricopeptide repeat motif-containing protein (LRP130) is implicated in the control of mitochondrial gene expression and oxidative phosphorylation in the liver, partly due to its interaction with peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α). To investigate LRP130's role in healthy human skeletal muscle, we examined LRP130's fiber-type distribution and subcellular localization (n = 6), as well as LRP130's relationship with PGC-1α protein and citrate synthase (CS) maximal activity (n = 33) in vastus lateralis samples obtained from young males. The impact of an acute bout of exercise (endurance [END] and sprint interval training [SIT]) and fasting (8 h) on LRP130 and PGC-1α expression was also determined (n = 10). LRP130 protein content paralleled fiber-specific succinate dehydrogenase activity (I > IIA) and strongly correlated with the mitochondrially localized protein apoptosis-inducing factor in type I (r = 0.75) and type IIA (r = 0.85) fibers. Whole-muscle LRP130 protein content was positively related to PGC-1α protein (r = 0.49, p < 0.01) and CS maximal activity (r = 0.42, p < 0.01). LRP130 mRNA expression was unaltered (p > 0.05) following exercise, despite ~ 6.6- and ~ 3.8-fold increases (p < 0.01) in PGC-1α mRNA expression after END and SIT, respectively. Although unchanged at the group level (p > 0.05), moderate-to-strong positive correlations were apparent between individual changes in LRP130 and PGC-1α expression at the mRNA (r = 0.63, p < 0.05) and protein (r = 0.59, p = 0.07) level in response to fasting. Our findings support a potential role for LRP130 in the maintenance of basal mitochondrial phenotype in human skeletal muscle. LRP130's importance for mitochondrial remodeling in exercised and fasted human skeletal muscle requires further investigation.
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http://dx.doi.org/10.1007/s00424-020-02359-4DOI Listing
March 2020

Lipidomics unveils lipid dyshomeostasis and low circulating plasmalogens as biomarkers in a monogenic mitochondrial disorder.

JCI Insight 2019 07 25;4(14). Epub 2019 Jul 25.

Department of Nutrition and.

Mitochondrial dysfunction characterizes many rare and common age-associated diseases. The biochemical consequences, underlying clinical manifestations, and potential therapeutic targets, remain to be better understood. We tested the hypothesis that lipid dyshomeostasis in mitochondrial disorders goes beyond mitochondrial fatty acid β-oxidation, particularly in liver. This was achieved using comprehensive untargeted and targeted lipidomics in a case-control cohort of patients with Leigh syndrome French-Canadian variant (LSFC), a mitochondrial disease caused by mutations in LRPPRC, and in mice harboring liver-specific inactivation of Lrpprc (H-Lrpprc-/-). We discovered a plasma lipid signature discriminating LSFC patients from controls encompassing lower levels of plasmalogens and conjugated bile acids, which suggest perturbations in peroxisomal lipid metabolism. This premise was reinforced in H-Lrpprc-/- mice, which compared with littermates recapitulated a similar, albeit stronger peroxisomal metabolic signature in plasma and liver including elevated levels of very-long-chain acylcarnitines. These mice also presented higher transcript levels for hepatic markers of peroxisome proliferation in addition to lipid remodeling reminiscent of nonalcoholic fatty liver diseases. Our study underscores the value of lipidomics to unveil unexpected mechanisms underlying lipid dyshomeostasis ensuing from mitochondrial dysfunction herein implying peroxisomes and liver, which likely contribute to the pathophysiology of LSFC, but also other rare and common mitochondrial diseases.
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http://dx.doi.org/10.1172/jci.insight.123231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6675547PMC
July 2019

Hybrid Clear/Blue Native Electrophoresis for the Separation and Analysis of Mitochondrial Respiratory Chain Supercomplexes.

J Vis Exp 2019 05 19(147). Epub 2019 May 19.

Interdisciplinary School of Health Science, Faculty of Health Sciences and Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa;

Complexes of the oxidative phosphorylation machinery form supramolecular protein arrangements named supercomplexes (SCs), which are believed to confer structural and functional advantages to mitochondria. SCs have been identified in many species, from yeast to mammal, and an increasing number of studies report disruption of their organization in genetic and acquired human diseases. As a result, an increasing number of laboratories are interested in analyzing SCs, which can be methodologically challenging. This article presents an optimized protocol that combines the advantages of Blue- and Clear-Native PAGE methods to resolve and analyze SCs in a time-effective manner. With this hybrid CN/BN-PAGE method, mitochondrial SCs extracted with optimal amounts of the mild detergent digitonin are exposed briefly to the anionic dye Coomassie Blue (CB) at the beginning of the electrophoresis, without exposure to other detergents. This short exposure to CB allows to separate and resolve SCs as effectively as with traditional BN-PAGE methods, while avoiding the negative impact of high CB levels on in-gel activity assays, and labile protein-protein interactions within SCs. With this protocol it is thus possible to combine precise and rapid in gel activity measurements with analytical techniques involving 2D electrophoresis, immuno-detection, and/or proteomics for advanced analysis of SCs.
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http://dx.doi.org/10.3791/59294DOI Listing
May 2019

A Linear Fragment of Unacylated Ghrelin (UAG) Protects Against Myocardial Ischemia/Reperfusion Injury in Mice in a Growth Hormone Secretagogue Receptor-Independent Manner.

Front Endocrinol (Lausanne) 2018 11;9:798. Epub 2019 Jan 11.

Faculté de pharmacie, Université de Montréal, Montréal, QC, Canada.

Unacylated ghrelin (UAG), the most abundant form of ghrelin in circulation, has been shown to exert cardioprotective effect in experimental cardiopathies. The present study aimed to investigate the cardioprotective effect of a linear bioactive fragment of UAG against myocardial ischemia-induced injury and dysfunction in C57BL/6 wild type mice and the mechanisms involved. Treatments were administered at doses of 100 (UAG), 1,000 and 3,000 (UAG) nmol/kg at 12 h interval during 14 days prior to 30 min left coronary artery ligation and reperfusion for a period of 6 or 48 h. The infarct area was decreased in a dose-dependent manner at 48 h of reperfusion, with a reduction of 54% at the highest dose of UAG tested. Myocardial hemodynamics were improved as demonstrated by an increase in cardiac output, maximum first derivative of left ventricular pressure, and preload recruitable stroke work, a load-independent contractility index. Six hours after reperfusion, circulating levels of IL-6 and TNF-α pro-inflammatory cytokines were reduced, and the effect was maintained at 48 h for TNF-α. 5' AMP-activated protein kinase (AMPK) was activated, while acetyl-CoA carboxylase (ACC) activity was inhibited, along with a decrease in apoptotic protein levels. In isolated hearts, the effect of UAG was unaffected by the presence of D-Lys-GHRP-6, a ghrelin receptor (GHSR1a) antagonist, suggesting that the peptide acted through a GHSR1a-independent pathway. The results support the therapeutic application of UAG bioactive peptide fragments against myocardial ischemia/reperfusion injury.
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http://dx.doi.org/10.3389/fendo.2018.00798DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6340090PMC
January 2019

Mitochondrial quality control in the cardiac system: An integrative view.

Biochim Biophys Acta Mol Basis Dis 2019 04 22;1865(4):782-796. Epub 2018 Nov 22.

Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada; Interdisciplinary School of Health Sciences, Faculty of Health Sciences, University of Ottawa, Ottawa, ON, Canada. Electronic address:

Recent studies have led to the discovery of multiple mitochondrial quality control (mQC) processes that operate at various scales, ranging from the degradation of proteins by mitochondrial proteases to the degradation of selected cargos or entire organelles in lysosomes. While the mechanisms governing these mQC processes are progressively being delineated, their role and importance remain unclear. Converging evidence however point to a complex system whereby multiple and partly overlapping processes are recruited to orchestrate a cell type specific mQC response that is adapted to the physiological state and level of stress encountered. Knowledge gained from basic model systems of mQC therefore need to be integrated within organ-specific (patho)physiological frameworks. Building on this notion, this article focuses on mQC in the heart, where developmental metabolic reprogramming, sustained contraction, and multiple pathophysiological conditions pose broadly different constraints. We provide an overview of current knowledge of mQC processes, and discuss their implication in cardiac mQC under normal and diseased conditions.
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http://dx.doi.org/10.1016/j.bbadis.2018.11.018DOI Listing
April 2019

Protective role of Parkin in skeletal muscle contractile and mitochondrial function.

J Physiol 2018 07 30;596(13):2565-2579. Epub 2018 May 30.

Departments of Critical Care and Medicine, McGill University Health Centre and Meakins-Christie Laboratories, Department of Medicine, McGill University, Montreal, Quebec, Canada.

Key Points: Parkin, an E3 ubiquitin ligase encoded by the Park2 gene, has been implicated in the regulation of mitophagy, a quality control process in which defective mitochondria are degraded. The exact physiological significance of Parkin in regulating mitochondrial function and contractility in skeletal muscle remains largely unexplored. Using Park2 mice, we show that Parkin ablation causes a decrease in muscle specific force, a severe decrease in mitochondrial respiration, mitochondrial uncoupling and an increased susceptibility to opening of the permeability transition pore. These results demonstrate that Parkin plays a protective role in the maintenance of normal mitochondrial and contractile functions in skeletal muscles.

Abstract: Parkin is an E3 ubiquitin ligase encoded by the Park2 gene. Parkin has been implicated in the regulation of mitophagy, a quality control process in which defective mitochondria are sequestered in autophagosomes and delivered to lysosomes for degradation. Although Parkin has been mainly studied for its implication in neuronal degeneration in Parkinson disease, its role in other tissues remains largely unknown. In the present study, we investigated the skeletal muscles of Park2 knockout (Park2 ) mice to test the hypothesis that Parkin plays a physiological role in mitochondrial quality control in normal skeletal muscle, a tissue highly reliant on mitochondrial content and function. We first show that the tibialis anterior (TA) of Park2 mice display a slight but significant decrease in its specific force. Park2 muscles also show a trend for type IIB fibre hypertrophy without alteration in muscle fibre type proportion. Compared to Park2 muscles, the mitochondrial function of Park2 skeletal muscles was significantly impaired, as indicated by the significant decrease in ADP-stimulated mitochondrial respiratory rates, uncoupling, reduced activities of respiratory chain complexes containing mitochondrial DNA (mtDNA)-encoded subunits and increased susceptibility to opening of the permeability transition pore. Muscles of Park2 mice also displayed a decrease in the content of the mitochondrial pro-fusion protein Mfn2 and an increase in the pro-fission protein Drp1 suggesting an increase in mitochondrial fragmentation. Finally, Park2 ablation resulted in an increase in basal autophagic flux in skeletal muscles. Overall, the results of the present study demonstrate that Parkin plays a protective role in the maintenance of normal mitochondrial and contractile functions in normal skeletal muscles.
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http://dx.doi.org/10.1113/JP275604DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6023825PMC
July 2018

A Mitochondrial Health Index Sensitive to Mood and Caregiving Stress.

Biol Psychiatry 2018 07 3;84(1):9-17. Epub 2018 Feb 3.

Department of Psychiatry, University of California-San Francisco, San Francisco, California.

Background: Chronic life stress, such as the stress of caregiving, can promote pathophysiology, but the underlying cellular mechanisms are not well understood. Chronic stress may induce recalibrations in mitochondria leading to changes either in mitochondrial content per cell, or in mitochondrial functional capacity (i.e., quality).

Methods: Here we present a functional index of mitochondrial health (MHI) for human leukocytes that can distinguish between these two possibilities. The MHI integrates nuclear and mitochondrial DNA-encoded respiratory chain enzymatic activities and mitochondrial DNA copy number. We then use the MHI to test the hypothesis that daily emotional states and caregiving stress influence mitochondrial function by comparing healthy mothers of a child with an autism spectrum disorder (high-stress caregivers, n = 46) with mothers of a neurotypical child (control group, n = 45).

Results: The MHI outperformed individual mitochondrial function measures. Elevated positive mood at night was associated with higher MHI, and nightly positive mood was also a mediator of the association between caregiving and MHI. Moreover, MHI was correlated to positive mood on the days preceding, but not following the blood draw, suggesting for the first time in humans that mitochondria may respond to proximate emotional states within days. Correspondingly, the caregiver group, which had higher perceived stress and lower positive and greater negative daily affect, exhibited lower MHI. This effect was not explained by a mismatch between nuclear and mitochondrial genomes.

Conclusions: Daily mood and chronic caregiving stress are associated with mitochondrial functional capacity. Mitochondrial health may represent a nexus between psychological stress and health.
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http://dx.doi.org/10.1016/j.biopsych.2018.01.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6014908PMC
July 2018

Mitochondrial Oxidative Stress Reduces the Immunopotency of Mesenchymal Stromal Cells in Adults With Coronary Artery Disease.

Circ Res 2018 01 7;122(2):255-266. Epub 2017 Nov 7.

From the Department of Anatomy and Cell Biology (O.K.M.), Department of Physiology (U.S.), Divisions of Cardiac Surgery and Surgical Research, Department of Surgery (D.S.T.), Division of Rheumatology, Department of Medicine (I.C., M.L.) McGill University, Montreal, Quebec, Canada; Shriners Hospital for Children (R.H.); Department of Cellular and Molecular Medicine, Faculty of Medicine (A.C., Y.B.), University of Ottawa, Ontario, Canada; and Faculty of Pharmacy (M.J.S.), University of Montreal, Quebec, Canada.

Rationale: Mesenchymal stromal cells (MSCs) are promising therapeutic strategies for coronary artery disease; however, donor-related variability in cell quality is a main cause of discrepancies in preclinical studies. In vitro, MSCs from individuals with coronary artery disease have reduced ability to suppress activated T-cells. The mechanisms underlying the altered immunomodulatory capacity of MSCs in the context of atherosclerosis remain elusive.

Objective: The aim of this study was to assess the role of mitochondrial dysfunction in the impaired immunomodulatory properties of MSCs from patients with atherosclerosis.

Methods And Results: Adipose tissue-derived MSCs were isolated from atherosclerotic (n=38) and nonatherosclerotic (n=42) donors. MSCs:CD4T-cell suppression was assessed in allogeneic coculture systems. Compared with nonatherosclerotic-MSCs, atherosclerotic-MSCs displayed higher levels of both intracellular (=0.006) and mitochondrial (=0.03) reactive oxygen species reflecting altered mitochondrial function. The increased mitochondrial reactive oxygen species levels of atherosclerotic-MSCs promoted a phenotypic switch characterized by enhanced glycolysis and an altered cytokine secretion (interleukin-6 <0.0001, interleukin-8/C-X-C motif chemokine ligand 8 =0.04, and monocyte chemoattractant protein-1/chemokine ligand 2 =0.01). Furthermore, treatment of atherosclerotic-MSCs with the reactive oxygen species scavenger N-acetyl-l-cysteine reduced the levels of interleukin-6, interleukin-8/C-X-C motif chemokine ligand 8, and monocyte chemoattractant protein-1/chemokine ligand 2 in the MSC secretome and improved MSCs immunosuppressive capacity (=0.03).

Conclusions: An impaired mitochondrial function of atherosclerotic-MSCs underlies their altered secretome and reduced immunopotency. Interventions aimed at restoring the mitochondrial function of atherosclerotic-MSCs improve their in vitro immunosuppressive ability and may translate into enhanced therapeutic efficiency.
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http://dx.doi.org/10.1161/CIRCRESAHA.117.311400DOI Listing
January 2018

Adiponectin has a pivotal role in the cardioprotective effect of CP-3(iv), a selective CD36 azapeptide ligand, after transient coronary artery occlusion in mice.

FASEB J 2018 02 4;32(2):807-818. Epub 2018 Jan 4.

Faculty of Pharmacy, Université de Montréal, Montreal, Quebec, Canada.

CD36 is a multiligand receptor involved in lipid metabolism. We investigated the mechanisms underlying the cardioprotective effect of CP-3(iv), an azapeptide belonging to a new class of selective CD36 ligands. The role of CP-3(iv) in mediating cardioprotection was investigated because CD36 signaling leads to activation of peroxisome proliferator-activated receptor-γ, a transcriptional regulator of adiponectin. CP-3(iv) pretreatment reduced infarct size by 54% and preserved hemodynamics in C57BL/6 mice subjected to 30 min coronary ligation and reperfusion but had no effect in CD36-deficient mice. The effects of CP-3(iv) were associated with an increase in circulating adiponectin levels, epididymal fat adiponectin gene expression, and adiponectin transcriptional regulators ( Pparg, Cebpb, Sirt1) after 6 h of reperfusion. Reduced myocardial oxidative stress and apoptosis were observed along with an increase in expression of myocardial adiponectin target proteins, including cyclooxygenase-2, phospho-AMPK, and phospho-Akt. Moreover, CP-3(iv) increased myocardial performance in isolated hearts, whereas blockade of adiponectin with an anti-adiponectin antibody abrogated it. CP-3(iv) exerts cardioprotection against myocardial ischemia and reperfusion (MI/R) injury and dysfunction, at least in part, by increasing circulating and myocardial adiponectin levels. Hence, both paracrine and endocrine effects of adiponectin may contribute to reduced reactive oxygen species generation and apoptosis after MI/R, in a CD36-dependent manner.-Huynh, D. N., Bessi, V. L., Ménard, L., Piquereau, J., Proulx, C., Febbraio, M., Lubell, W. D., Carpentier, A. C., Burelle, Y., Ong, H., Marleau, S. Adiponectin has a pivotal role in the cardioprotective effect of CP-3(iv), a selective CD36 azapeptide ligand, after transient coronary artery occlusion in mice.
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http://dx.doi.org/10.1096/fj.201700505RDOI Listing
February 2018

Loss of hepatic LRPPRC alters mitochondrial bioenergetics, regulation of permeability transition and trans-membrane ROS diffusion.

Hum Mol Genet 2017 08;26(16):3186-3201

Faculty of Pharmacy, University of Montreal, Montreal, QC H3C 3J7, Canada.

The French-Canadian variant of Leigh Syndrome (LSFC) is an autosomal recessive oxidative phosphorylation (OXPHOS) disorder caused by a mutation in LRPPRC, coding for a protein involved in the stability of mitochondrially-encoded mRNAs. Low levels of LRPPRC are present in all patient tissues, but result in a disproportionately severe OXPHOS defect in the brain and liver, leading to unpredictable subacute metabolic crises. To investigate the impact of the OXPHOS defect in the liver, we analyzed the mitochondrial phenotype in mice harboring an hepatocyte-specific inactivation of Lrpprc. Loss of LRPPRC in the liver caused a generalized growth delay, and typical histological features of mitochondrial hepatopathy. At the molecular level, LRPPRC deficiency caused destabilization of polyadenylated mitochondrial mRNAs, altered mitochondrial ultrastructure, and a severe complex IV (CIV) and ATP synthase (CV) assembly defect. The impact of LRPPRC deficiency was not limited to OXPHOS, but also included impairment of long-chain fatty acid oxidation, a striking dysregulation of the mitochondrial permeability transition pore, and an unsuspected alteration of trans-membrane H2O2 diffusion, which was traced to the ATP synthase assembly defect, and to changes in the lipid composition of mitochondrial membranes. This study underscores the value of mitochondria phenotyping to uncover complex and unexpected mechanisms contributing to the pathophysiology of mitochondrial disorders.
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http://dx.doi.org/10.1093/hmg/ddx202DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5886084PMC
August 2017

Regulation of ULK1 Expression and Autophagy by STAT1.

J Biol Chem 2017 02 23;292(5):1899-1909. Epub 2016 Dec 23.

From the Departments of Critical Care and Medicine, McGill University Health Centre and Meakins-Christie Laboratories, McGill University, Montreal, Quebec H4A 3J1, Canada. Electronic address:

Autophagy involves the lysosomal degradation of cytoplasmic contents for regeneration of anabolic substrates during nutritional or inflammatory stress. Its initiation occurs rapidly after inactivation of the protein kinase mammalian target of rapamycin (mTOR) (or mechanistic target of rapamycin), leading to dephosphorylation of Unc-51-like kinase 1 (ULK1) and autophagosome formation. Recent studies indicate that mTOR can, in parallel, regulate the activity of stress transcription factors, including signal transducer and activator of transcription-1 (STAT1). The current study addresses the role of STAT1 as a transcriptional suppressor of autophagy genes and autophagic activity. We show that STAT1-deficient human fibrosarcoma cells exhibited enhanced autophagic flux as well as its induction by pharmacological inhibition of mTOR. Consistent with enhanced autophagy initiation, ULK1 mRNA and protein levels were increased in STAT1-deficient cells. By chromatin immunoprecipitation, STAT1 bound a putative regulatory sequence in the ULK1 5'-flanking region, the mutation of which increased ULK1 promoter activity, and rendered it unresponsive to mTOR inhibition. Consistent with an anti-apoptotic effect of autophagy, rapamycin-induced apoptosis and cytotoxicity were blocked in STAT1-deficient cells but restored in cells simultaneously exposed to the autophagy inhibitor ammonium chloride. In vivo, skeletal muscle ULK1 mRNA and protein levels as well as autophagic flux were significantly enhanced in STAT1-deficient mice. These results demonstrate a novel mechanism by which STAT1 negatively regulates ULK1 expression and autophagy.
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http://dx.doi.org/10.1074/jbc.M116.771584DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5290961PMC
February 2017

The rise of mitochondria in medicine.

Mitochondrion 2016 09 14;30:105-16. Epub 2016 Jul 14.

Faculty of Pharmacy, Université de Montreal, Montreal, QC, Canada.

Once considered exclusively the cell's powerhouse, mitochondria are now recognized to perform multiple essential functions beyond energy production, impacting most areas of cell biology and medicine. Since the emergence of molecular biology and the discovery of pathogenic mitochondrial DNA defects in the 1980's, research advances have revealed a number of common human diseases which share an underlying pathogenesis involving mitochondrial dysfunction. Mitochondria undergo function-defining dynamic shape changes, communicate with each other, regulate gene expression within the nucleus, modulate synaptic transmission within the brain, release molecules that contribute to oncogenic transformation and trigger inflammatory responses systemically, and influence the regulation of complex physiological systems. Novel mitopathogenic mechanisms are thus being uncovered across a number of medical disciplines including genetics, oncology, neurology, immunology, and critical care medicine. Increasing knowledge of the bioenergetic aspects of human disease has provided new opportunities for diagnosis, therapy, prevention, and in connecting various domains of medicine. In this article, we overview specific aspects of mitochondrial biology that have contributed to - and likely will continue to enhance the progress of modern medicine.
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http://dx.doi.org/10.1016/j.mito.2016.07.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5023480PMC
September 2016

Parkinson's Disease-Related Proteins PINK1 and Parkin Repress Mitochondrial Antigen Presentation.

Cell 2016 Jul 23;166(2):314-327. Epub 2016 Jun 23.

Département de Pathologie et Biologie Cellulaire, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal, QC H3C 3J7, Canada. Electronic address:

Antigen presentation is essential for establishing immune tolerance and for immune responses against infectious disease and cancer. Although antigen presentation can be mediated by autophagy, here we demonstrate a pathway for mitochondrial antigen presentation (MitAP) that relies on the generation and trafficking of mitochondrial-derived vesicles (MDVs) rather than on autophagy/mitophagy. We find that PINK1 and Parkin, two mitochondrial proteins linked to Parkinson's disease (PD), actively inhibit MDV formation and MitAP. In absence of PINK1 or Parkin, inflammatory conditions trigger MitAP in immune cells, both in vitro and in vivo. MitAP and the formation of MDVs require Rab9 and Sorting nexin 9, whose recruitment to mitochondria is inhibited by Parkin. The identification of PINK1 and Parkin as suppressors of an immune-response-eliciting pathway provoked by inflammation suggests new insights into PD pathology.
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http://dx.doi.org/10.1016/j.cell.2016.05.039DOI Listing
July 2016

Formation of mitochondrial-derived vesicles is an active and physiologically relevant mitochondrial quality control process in the cardiac system.

J Physiol 2016 09 24;594(18):5343-62. Epub 2016 Jul 24.

Faculty of Pharmacy, Université de Montréal, Montréal, Québec, Canada.

Key Points: Mitochondrial-derived vesicle (MDV) formation occurs under baseline conditions and is rapidly upregulated in response to stress-inducing conditions in H9c2 cardiac myoblasts. In mice formation of MDVs occurs readily in the heart under normal healthy conditions while mitophagy is comparatively less prevalent. In response to acute stress induced by doxorubicin, mitochondrial dysfunction develops in the heart, triggering MDV formation and mitophagy. MDV formation is thus active in the cardiac system, where it probably constitutes a baseline housekeeping mechanism and a first line of defence against stress.

Abstract: The formation of mitochondrial-derived vesicles (MDVs), a process inherited from bacteria, has emerged as a potentially important mitochondrial quality control (QC) mechanism to selectively deliver damaged material to lysosomes for degradation. However, the existence of this mechanism in various cell types, and its physiological relevance, remains unknown. Our aim was to investigate the dynamics of MDV formation in the cardiac system in vitro and in vivo. Immunofluorescence in cell culture, quantitative transmission electron microscopy and electron tomography in vivo were used to study MDV production in the cardiac system. We show that in cardiac cells MDV production occurs at baseline, is commensurate with the dependence of cells on oxidative metabolism, is more frequent than mitophagy and is up-regulated on the time scale of minutes to hours in response to prototypical mitochondrial stressors (antimycin-A, xanthine/xanthine oxidase). We further show that MDV production is up-regulated together with mitophagy in response to doxorubicin-induced mitochondrial and cardiac dysfunction. Here we provide the first quantitative data demonstrating that MDV formation is a mitochondrial QC operating in the heart.
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http://dx.doi.org/10.1113/JP272703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5023710PMC
September 2016

Cyclosporine A Treatment Inhibits Abcc6-Dependent Cardiac Necrosis and Calcification following Coxsackievirus B3 Infection in Mice.

PLoS One 2015 16;10(9):e0138222. Epub 2015 Sep 16.

Department of Human Genetics and Complex Traits Group, McGill University, Montreal, Canada.

Coxsackievirus type B3 (CVB3) is a cardiotropic enterovirus. Infection causes cardiomyocyte necrosis and myocardial inflammation. The damaged tissue that results is replaced with fibrotic or calcified tissue, which can lead to permanently altered cardiac function. The extent of pathogenesis among individuals exposed to CVB3 is dictated by a combination of host genetics, viral virulence, and the environment. Here, we aimed to identify genes that modulate cardiopathology following CVB3 infection. 129S1 mice infected with CVB3 developed increased cardiac pathology compared to 129X1 substrain mice despite no difference in viral burden. Linkage analysis identified a major locus on chromosome 7 (LOD: 8.307, P<0.0001) that controlled the severity of cardiac calcification and necrosis following infection. Sub-phenotyping and genetic complementation assays identified Abcc6 as the underlying gene. Microarray expression profiling identified genotype-dependent regulation of genes associated with mitochondria. Electron microscopy examination showed elevated deposition of hydroxyapatite-like material in the mitochondrial matrices of infected Abcc6 knockout (Abcc6-/-) mice but not in wildtype littermates. Cyclosporine A (CsA) inhibits mitochondrial permeability transition pore opening by inhibiting cyclophilin D (CypD). Treatment of Abcc6 -/- mice with CsA reduced cardiac necrosis and calcification by more than half. Furthermore, CsA had no effect on the CVB3-induced phenotype of doubly deficient CypD-/-Abcc6-/- mice. Altogether, our work demonstrates that mutations in Abcc6 render mice more susceptible to cardiac calcification following CVB3 infection. Moreover, we implicate CypD in the control of cardiac necrosis and calcification in Abcc6-deficient mice, whereby CypD inhibition is required for cardioprotection.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0138222PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4574283PMC
June 2016

Interdependence of Parkin-Mediated Mitophagy and Mitochondrial Fission in Adult Mouse Hearts.

Circ Res 2015 Jul 2;117(4):346-51. Epub 2015 Jun 2.

From the Center for Pharmacogenomics, Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO (M.S., G.G., S.J.M., G.W.D.); Department of Biomedical Sciences, University of Montreal, Quebec, Canada (Y.B.); Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA (A.B.G.); and Departments of Medicine (Cardiology) and Cell Biology, and Wilf Family Cardiovascular Research Institute, Albert Einstein College of Medicine, Bronx, NY (R.N.K.).

Rationale: The role of Parkin in hearts is unclear. Germ-line Parkin knockout mice have normal hearts, but Parkin is protective in cardiac ischemia. Parkin-mediated mitophagy is reportedly either irrelevant, or a major factor, in the lethal cardiomyopathy evoked by cardiac myocyte-specific interruption of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission.

Objective: To understand the role of Parkin-mediated mitophagy in normal and mitochondrial fission-defective adult mouse hearts.

Methods And Results: Parkin mRNA and protein were present at low levels in normal mouse hearts, but were upregulated after cardiac myocyte-directed Drp1 gene deletion in adult mice. Alone, forced cardiac myocyte Parkin overexpression activated mitophagy without adverse effects. Likewise, cardiac myocyte-specific Parkin deletion evoked no adult cardiac phenotype, revealing no essential function for, and tolerance of, Parkin-mediated mitophagy in normal hearts. Concomitant conditional Parkin deletion with Drp1 ablation in adult mouse hearts prevented Parkin upregulation in mitochondria of fission-defective hearts, also increasing 6-week survival, improving ventricular ejection performance, mitigating adverse cardiac remodeling, and decreasing cardiac myocyte necrosis and replacement fibrosis. Underlying the Parkin knockout rescue was suppression of Drp1-induced hyper-mitophagy, assessed as ubiquitination of mitochondrial proteins and mitochondrial association of autophagosomal p62/sequestosome 1 (SQSTM1) and processed microtubule-associated protein 1 light chain 3 (LC3-II). Consequently, mitochondrial content of Drp1-deficient hearts was preserved. Parkin deletion did not alter characteristic mitochondrial enlargement of Drp1-deficient cardiac myocytes.

Conclusions: Parkin is rare in normal hearts and dispensable for constitutive mitophagic quality control. Ablating Drp1 in adult mouse cardiac myocytes not only interrupts mitochondrial fission, but also markedly upregulates Parkin, thus provoking mitophagic mitochondrial depletion that contributes to the lethal cardiomyopathy.
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http://dx.doi.org/10.1161/CIRCRESAHA.117.306859DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4522211PMC
July 2015

Mitochondrial vulnerability and increased susceptibility to nutrient-induced cytotoxicity in fibroblasts from leigh syndrome French canadian patients.

PLoS One 2015 2;10(3):e0120767. Epub 2015 Apr 2.

Montreal Heart Institute, Montreal, Canada; Department of Nutrition, Faculty of Medicine, Université de Montréal, Montreal, Canada.

Mutations in LRPPRC are responsible for the French Canadian variant of Leigh Syndrome (LSFC), a severe disorder characterized biochemically by a tissue-specific deficiency of cytochrome c oxidase (COX) and clinically by the occurrence of severe and deadly acidotic crises. Factors that precipitate these crises remain unclear. To better understand the physiopathology and identify potential treatments, we performed a comprehensive analysis of mitochondrial function in LSFC and control fibroblasts. Furthermore, we have used this cell-based model to screen for conditions that promote premature cell death in LSFC cells and test the protective effect of ten interventions targeting well-defined aspects of mitochondrial function. We show that, despite maintaining normal ATP levels, LSFC fibroblasts present several mitochondrial functional abnormalities under normal baseline conditions, which likely impair their capacity to respond to stress. This includes mitochondrial network fragmentation, impaired oxidative phosphorylation capacity, lower membrane potential, increased sensitivity to Ca2+-induced permeability transition, but no changes in reactive oxygen species production. We also show that LSFC fibroblasts display enhanced susceptibility to cell death when exposed to palmitate, an effect that is potentiated by high lactate, while high glucose or acidosis alone or in combination were neutral. Furthermore, we demonstrate that compounds that are known to promote flux through the electron transport chain independent of phosphorylation (methylene blue, dinitrophenol), or modulate fatty acid (L-carnitine) or Krebs cycle metabolism (propionate) are protective, while antioxidants (idebenone, N-acetyl cysteine, resveratrol) exacerbate palmitate plus lactate-induced cell death. Collectively, beyond highlighting multiple alterations in mitochondrial function and increased susceptibility to nutrient-induced cytotoxicity in LSFC fibroblasts, these results raise questions about the nature of the diets, particularly excess fat intake, as well as on the use of antioxidants in patients with LSFC and, possibly, other COX defects.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120767PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4383560PMC
March 2016

Mechanical ventilation triggers abnormal mitochondrial dynamics and morphology in the diaphragm.

J Appl Physiol (1985) 2015 May 12;118(9):1161-71. Epub 2015 Mar 12.

Meakins-Christie Laboratories, McGill University Health Centre Research Institute, Montreal, Quebec, Canada; Critical Care and Respiratory Divisions, McGill University Health Centre, Montreal, Quebec, Canada;

The diaphragm is a unique skeletal muscle designed to be rhythmically active throughout life, such that its sustained inactivation by the medical intervention of mechanical ventilation (MV) represents an unanticipated physiological state in evolutionary terms. Within a short period after initiating MV, the diaphragm develops muscle atrophy, damage, and diminished strength, and many of these features appear to arise from mitochondrial dysfunction. Notably, in response to metabolic perturbations, mitochondria fuse, divide, and interact with neighboring organelles to remodel their shape and functional properties-a process collectively known as mitochondrial dynamics. Using a quantitative electron microscopy approach, here we show that diaphragm contractile inactivity induced by 6 h of MV in mice leads to fragmentation of intermyofibrillar (IMF) but not subsarcolemmal (SS) mitochondria. Furthermore, physical interactions between adjacent organellar membranes were less abundant in IMF mitochondria during MV. The profusion proteins Mfn2 and OPA1 were unchanged, whereas abundance and activation status of the profission protein Drp1 were increased in the diaphragm following MV. Overall, our results suggest that mitochondrial morphological abnormalities characterized by excessive fission-fragmentation represent early events during MV, which could potentially contribute to the rapid onset of mitochondrial dysfunction, maladaptive signaling, and associated contractile dysfunction of the diaphragm.
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http://dx.doi.org/10.1152/japplphysiol.00873.2014DOI Listing
May 2015

The relationship between muscle fiber type-specific PGC-1α content and mitochondrial content varies between rodent models and humans.

PLoS One 2014 14;9(8):e103044. Epub 2014 Aug 14.

Department of Critical Care, McGill University Health Centre and Department of Medicine, McGill University, Montréal, Québec, Canada; Department of Kinesiology and Physical Education, McGill University, Montréal, Québec, Canada.

PGC-1α regulates critical processes in muscle physiology, including mitochondrial biogenesis, lipid metabolism and angiogenesis. Furthermore, PGC-1α was suggested as an important regulator of fiber type determination. However, whether a muscle fiber type-specific PGC-1α content exists, whether PGC-1α content relates to basal levels of mitochondrial content, and whether such relationships are preserved between humans and classically used rodent models are all questions that have been either poorly addressed or never investigated. To address these issues, we investigated the fiber type-specific content of PGC-1α and its relationship to basal mitochondrial content in mouse, rat and human muscles using in situ immunolabeling and histochemical methods on muscle serial cross-sections. Whereas type IIa fibers exhibited the highest PGC-1α in all three species, other fiber types displayed a hierarchy of type IIx>I>IIb in mouse, type I = IIx> IIb in rat, and type IIx>I in human. In terms of mitochondrial content, we observed a hierarchy of IIa>IIx>I>IIb in mouse, IIa >I>IIx> IIb in rat, and I>IIa> IIx in human skeletal muscle. We also found in rat skeletal muscle that type I fibers displayed the highest capillarization followed by type IIa >IIx>IIb. Finally, we found in human skeletal muscle that type I fibers display the highest lipid content, followed by type IIa>IIx. Altogether, our results reveal that (i) the fiber type-specific PGC-1α and mitochondrial contents were only matched in mouse, (ii) the patterns of PGC-1α and mitochondrial contents observed in mice and rats do not correspond to that seen in humans in several respects, and (iii) the classical phenotypes thought to be regulated by PGC-1α do not vary exclusively as a function of PGC-1α content in rat and human muscles.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0103044PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4133187PMC
April 2015
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