bims-cytox1 2019-03-10 papers

Issue of 2019–03–10
seven papers selected by
Gavin McStay, Staffordshire University

Biochim Biophys Acta Mol Basis Dis. 2019 Apr 01. pii: S0925-4439(18)30318-1. [Epub ahead of print]1865(4): 810-821

The role of mitochondrial cardiolipin in heart function and its implication in cardiac disease.

Jan Dudek, Magnus Hartmann, Peter Rehling.

Mitochondria play an essential role in the energy metabolism of the heart. Many of the essential functions are associated with mitochondrial membranes and oxidative phosphorylation driven by the respiratory chain. Mitochondrial membranes are unique in the cell as they contain the phospholipid cardiolipin. The important role of cardiolipin in cardiovascular health is highlighted by several cardiac diseases, in which cardiolipin plays a fundamental role. Barth syndrome, Sengers syndrome, and Dilated cardiomyopathy with ataxia (DCMA) are genetic disorders, which affect cardiolipin biosynthesis. Other cardiovascular diseases including ischemia/reperfusion injury and heart failure are also associated with changes in the cardiolipin pool. Here, we summarize molecular functions of cardiolipin in mitochondrial biogenesis and morphology. We highlight the role of cardiolipin for the respiratory chain, metabolite carriers, and mitochondrial metabolism and describe links to apoptosis and mitochondria specific autophagy (mitophagy) with possible implications in cardiac disease.

Keywords: Barth syndrome; Cardiolipin; Mitochondria; Respiratory chain; Sengers syndrome

DOI: https://doi.org/10.1016/j.bbadis.2018.08.025

J Med Case Rep. 2019 Mar 06. 13(1): 63

Chorea-ballism as a dominant clinical manifestation in heteroplasmic mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome with A3251G mutation in mitochondrial genome: a case report.

Durjoy Lahiri, Vishal Madhukar Sawale, Subhadeep Banerjee, Souvik Dubey, Biman Kanti Roy, Shyamal Kumar Das.

BACKGROUND: Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes, the most common maternally inherited mitochondrial disease, can present with a wide range of neurological manifestations including both central and peripheral nervous system involvement. The most frequent genetic mutation reported in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome is A3243G in MT-TL1 gene. Stroke-like episodes, dementia, epilepsy, lactic acidemia, myopathy, recurrent headaches, hearing impairment, diabetes, and short stature constitute the known presentations in this syndrome. Among the abnormal involuntary movements in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome, myoclonus is the commonest. Other movement disorders, including chorea, are rarely reported in this disorder.
CASE PRESENTATION: A 14-year-old South Asian boy from rural Bengal (India), born of a second degree consanguineous marriage, with normal birth and development history, presented with abnormal brief jerky movements involving his trunk and limbs, with recurrent falls for 10 months. We present here a case of heteroplasmic mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome with A3251G mutation, in which the clinical picture was dominated by a host of involuntary abnormal movements including chorea-ballism, myoclonus, and oromandibular dystonia in a backdrop of cognitive decline, seizure, and stroke-like episode. A final diagnosis was established by muscle biopsy and genetic study. Haloperidol was administered to control the involuntary movements along with introduction of co-enzyme Q, besides symptomatic management for his focal seizures. Six months into follow-up his seizures and abnormal movements were controlled significantly with slight improvement of cognitive abilities.
CONCLUSION: The dominance of hyperkinetic movements in the clinical scenario and the finding of a point mutation A3251G in MT-TL1 gene make this a rare presentation.

Keywords: A3251G mutation; Ballism; Chorea; Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)

DOI: https://doi.org/10.1186/s13256-018-1936-0

J Vis Exp. 2019 Feb 12.

Analysis of Mitochondrial Respiratory Chain Complexes in Cultured Human Cells using Blue Native Polyacrylamide Gel Electrophoresis and Immunoblotting.

Svetlana Konovalova.

Mitochondrial respiration is performed by oxidative phosphorylation (OXPHOS) complexes within mitochondria. Internal and environmental factors can perturb the assembly and stability of OXPHOS complexes. This protocol describes the analysis of mitochondrial respiratory chain complexes by blue native polyacrylamide gel electrophoresis (BN-PAGE) in application to cultured human cells. First, mitochondria are extracted from the cells using digitonin, then using lauryl maltoside, the intact OXPHOS complexes are isolated from the mitochondrial membranes. The OXPHOS complexes are then resolved by gradient gel electrophoresis in the presence of the negatively charged dye, Coomassie blue, which prevents protein aggregation and ensures electrophoretic mobility of protein complexes towards the cathode. Finally, the OXPHOS complexes are detected by standard immunoblotting. Thus, BN-PAGE is a convenient and inexpensive technique that can be used to evaluate the assembly of entire OXPHOS complexes, in contrast to the basic SDS-PAGE allowing the study of only individual OXPHOS complex subunits.

DOI: https://doi.org/10.3791/59269

Front Genet. 2019 ;10 130

Age Dependent Dysfunction of Mitochondrial and ROS Metabolism Induced by Mitonuclear Mismatch.

Nicolas Pichaud, Roxanne Bérubé, Geneviève Côté, Claude Belzile, France Dufresne, Geneviève Morrow, Robert M Tanguay, David M Rand, Pierre U Blier.

Mitochondrial and nuclear genomes have to coevolve to ensure the proper functioning of the different mitochondrial complexes that are assembled from peptides encoded by both genomes. Mismatch between these genomes is believed to be strongly selected against due to the consequent impairments of mitochondrial functions and induction of oxidative stress. Here, we used a Drosophila model harboring an incompatibility between a mitochondrial tRNAtyr and its nuclear-encoded mitochondrial tyrosine synthetase to assess the cellular mechanisms affected by this incompatibility and to test the relative contribution of mitonuclear interactions and aging on the expression of impaired phenotypes. Our results show that the mitochondrial tRNA mutation caused a decrease in mitochondrial oxygen consumption in the incompatible nuclear background but no effect with the compatible nuclear background. Mitochondrial DNA copy number increased in the incompatible genotype but that increase failed to rescue mitochondrial functions. The flies harboring mismatch between nuclear and mitochondrial genomes had almost three times the relative mtDNA copy number and fifty percent higher rate of hydrogen peroxide production compared to other genome combinations at 25 days of age. We also found that aging exacerbated the mitochondrial dysfunctions. Our results reveal the tight interactions linking mitonuclear mismatch to mitochondrial dysfunction, mitochondrial DNA regulation, ROS production and aging.

Keywords: Drosophila; aging; mitochondrial respiration; mitonuclear incompatibility; reactive oxygen species; replication; tRNA

DOI: https://doi.org/10.3389/fgene.2019.00130

PLoS One. 2019 ;14(3): e0213283

Concentration of mitochondrial DNA mutations by cytoplasmic transfer from platelets to cultured mouse cells.

Kaori Ishikawa, Kohei Kobayashi, Akihito Yamada, Moe Umehara, Toshihiko Oka, Kazuto Nakada.

Accumulation of mutations in mitochondrial DNA (mtDNA) is thought to be responsible for mitochondrial, and other, diseases and biological phenomena, such as diabetes, cancer, neurodegenerative diseases, and aging. Mouse models may elucidate the relationship between mutations in mtDNA and these abnormalities. However, because of the difficulty of mtDNA manipulation, generation of mouse models has not sufficiently progressed to enable such studies. To overcome this difficulty and to establish a source of diverse mtDNA mutations, we here generated cultured mouse cells containing mtDNA derived from an mtDNA mutator mouse that accumulates random mtDNA mutations with age. Mutation analysis of the obtained transmitochondrial cytoplasmic hybrid cells (cybrids) revealed that the cells harbored diverse mtDNA mutations occurring at a higher frequency than in mouse tissues, and exhibited severe respiration defects that would be lethal in tissues or organs. Abnormal respiratory complex formation and high stress on the mitochondrial protein quality control system appeared to be involved in these severe respiration defects. The mutation rates of the majority of highly accumulated mutations converged to either approximately 5%, 10%, or 40%, suggesting that these mutations are linked on the respective mtDNA molecules, and mtDNA in cybrid cells likely consisted of mtDNA molecules clonally expanded from the small population of introduced mtDNAs. Thus, the linked mutations in these cybrid cells cannot be evaluated individually. In addition, mtDNA mutations homologous to confirmed pathogenic mutations in human were rarely observed in our generated cybrids. However, the transmitochondrial cybrids constitute a useful tool for concentrating pathogenic mtDNA mutations and as a source of diverse mtDNA mutations to elucidate the relationship between mtDNA mutations and diseases.

DOI: https://doi.org/10.1371/journal.pone.0213283

mSphere. 2019 Mar 06. pii: e00644-18. [Epub ahead of print]4(2):

Disruption of the Putative Ribosome-Binding Motif of a Scaffold Protein Impairs Cytochrome c Oxidase Subunit Expression in Leishmania major.

Daviel Cardenas, Charity Sylvester, Bo Cao, Catherine S Nation, Juan C Pizarro, Hua Lu, Jessie Guidry, Edward J Wojcik, Ben L Kelly.

During their parasitic life cycle, through sandflies and vertebrate hosts, Leishmania parasites confront strikingly different environments, including abrupt changes in pH and temperature, to which they must rapidly adapt. These adaptations include alterations in Leishmania gene expression, metabolism, and morphology, allowing them to thrive as promastigotes in the sandfly and as intracellular amastigotes in the vertebrate host. A critical aspect of Leishmania metabolic adaptation to these changes is maintenance of efficient mitochondrial function in the hostile vertebrate environment. Such functions, including generation of ATP, depend upon the expression of many mitochondrial proteins, including subunits of cytochrome c oxidase (COX). Significantly, under mammalian temperature conditions, expression of Leishmania major COX subunit IV (LmCOX4) and virulence are dependent upon two copies of LACK, a gene that encodes the ribosome-associated scaffold protein, LACK (Leishmania ortholog of RACK1 [receptor for activated C kinase]). Targeted replacement of an endogenous LACK copy with a putative ribosome-binding motif-disrupted variant (LACKR34D35G36→LACKD34D35E36) resulted in thermosensitive parasites that showed diminished LmCOX4 expression, mitochondrial fitness, and replication in macrophages. Surprisingly, despite these phenotypes, LACKD34D35E36 associated with monosomes and polysomes and showed no major impairment of global protein synthesis. Collectively, these data suggest that wild-type (WT) LACK orchestrates robust LmCOX4 expression and mitochondrial fitness to ensure parasite virulence, via optimized functional interactions with the ribosome.IMPORTANCE Leishmania parasites are trypanosomatid protozoans that persist in infected human hosts to cause a spectrum of pathologies, from cutaneous and mucocutaneous manifestations to visceral leishmaniasis caused by Leishmania donovani The latter is usually fatal if not treated. Persistence of L. major in the mammalian host depends upon maintaining gene-regulatory programs to support essential parasite metabolic functions. These include expression and assembly of mitochondrial L. major cytochrome c oxidase (LmCOX) subunits, important for Leishmania ATP production. Significantly, under mammalian conditions, WT levels of LmCOX subunits require threshold levels of the Leishmania ribosome-associated scaffold protein, LACK. Unexpectedly, we find that although disruption of LACK's putative ribosome-binding motif does not grossly perturb ribosome association or global protein synthesis, it nonetheless impairs COX subunit expression, mitochondrial function, and virulence. Our data indicate that the quality of LACK's interaction with Leishmania ribosomes is critical for LmCOX subunit expression and parasite mitochondrial function in the mammalian host. Collectively, these findings validate LACK's ribosomal interactions as a potential therapeutic target.

Keywords: LACK; Leishmania ; RACK1; cytochrome c oxidase; mitochondria; parasite; ribosome; translation

DOI: https://doi.org/10.1128/mSphere.00644-18

FASEB J. 2019 Mar 08. fj201801591R

Increased dNTP pools rescue mtDNA depletion in human POLG-deficient fibroblasts.

Cora Blázquez-Bermejo, Lidia Carreño-Gago, David Molina-Granada, Josu Aguirre, Javier Ramón, Javier Torres-Torronteras, Raquel Cabrera-Pérez, Miguel Ángel Martín, Cristina Domínguez-González, Xavier de la Cruz, Anne Lombès, Elena García-Arumí, Ramon Martí, Yolanda Cámara.

Polymerase γ catalytic subunit ( POLG) gene encodes the enzyme responsible for mitochondrial DNA (mtDNA) synthesis. Mutations affecting POLG are the most prevalent cause of mitochondrial disease because of defective mtDNA replication and lead to a wide spectrum of clinical phenotypes characterized by mtDNA deletions or depletion. Enhancing mitochondrial deoxyribonucleoside triphosphate (dNTP) synthesis effectively rescues mtDNA depletion in different models of defective mtDNA maintenance due to dNTP insufficiency. In this study, we studied mtDNA copy number recovery rates following ethidium bromide-forced depletion in quiescent fibroblasts from patients harboring mutations in different domains of POLG. Whereas control cells spontaneously recovered initial mtDNA levels, POLG-deficient cells experienced a more severe depletion and could not repopulate mtDNA. However, activation of deoxyribonucleoside (dN) salvage by supplementation with dNs plus erythro-9-(2-hydroxy-3-nonyl) adenine (inhibitor of deoxyadenosine degradation) led to increased mitochondrial dNTP pools and promoted mtDNA repopulation in all tested POLG-mutant cells independently of their specific genetic defect. The treatment did not compromise POLG fidelity because no increase in multiple deletions or point mutations was detected. Our study suggests that physiologic dNTP concentration limits the mtDNA replication rate. We thus propose that increasing mitochondrial dNTP availability could be of therapeutic interest for POLG deficiency and other conditions in which mtDNA maintenance is challenged.-Blázquez-Bermejo, C., Carreño-Gago, L., Molina-Granada, D., Aguirre, J., Ramón, J., Torres-Torronteras, J., Cabrera-Pérez, R., Martín, M. Á., Domínguez-González, C., de la Cruz, X., Lombès, A., García-Arumí, E., Martí, R., Cámara, Y. Increased dNTP pools rescue mtDNA depletion in human POLG-deficient fibroblasts.

Keywords: deoxynucleosides; mitochondria; mitochondrial DNA replication; polymerase γ; therapy

DOI: https://doi.org/10.1096/fj.201801591R