bims-cytox1 Biomed News
on Cytochrome oxidase subunit 1
Issue of 2020–07–12
eight papers selected by
Gavin McStay, Staffordshire University
  1. Maternally inherited mitochondrial respiratory disorders: from pathogenetic principles to therapeutic implications.
  2. COX deficiency and leukoencephalopathy due to a novel homozygous APOPT1/COA8 mutation.
  3. Transfer of xenomitochondria containing the entire mouse mitochondrial genome into a genetically modified yeast expressing mitochondrial transcription factor A.
  4. Secondary manifestations of mitochondrial disorders.
  5. Mitochondrial genome editing gets precise.
  6. A bacterial cytidine deaminase toxin enables CRISPR-free mitochondrial base editing.
  7. Scientists make precise gene edits to mitochondrial DNA for first time.
  8. Functional role of respiratory supercomplexes in mice: SCAF1 relevance and segmentation of the Qpool.
  1. Mol Genet Metab. 2020 Jun 27. pii: S1096-7192(20)30150-5. [Epub ahead of print]
    Maternally inherited mitochondrial respiratory disorders: from pathogenetic principles to therapeutic implications.
    Martine Uittenbogaard, Anne Chiaramello.
      Maternally inherited mitochondrial respiratory disorders are rare, progressive, and multi-systemic diseases that remain intractable, with no effective therapeutic interventions. Patients share a defective oxidative phosphorylation pathway responsible for mitochondrial ATP synthesis, in most cases due to pathogenic mitochondrial variants transmitted from mother to child or to a rare de novo mutation or large-scale deletion of the mitochondrial genome. The clinical diagnosis of these mitochondrial diseases is difficult due to exceptionally high clinical variability, while their genetic diagnosis has improved with the advent of next-generation sequencing. The mechanisms regulating the penetrance of the mitochondrial variants remain unresolved with the patient's nuclear background, epigenomic regulation, heteroplasmy, mitochondrial haplogroups, and environmental factors thought to act as rheostats. The lack of animal models mimicking the phenotypic manifestations of these disorders has hampered efforts toward curative therapies. Patient-derived cellular paradigms provide alternative models for elucidating the pathogenic mechanisms and screening pharmacological small molecules to enhance mitochondrial function. Recent progress has been made in designing promising approaches to curtail the negative impact of dysfunctional mitochondria and alleviate clinical symptoms: 1) boosting mitochondrial biogenesis; 2) shifting heteroplasmy; 3) reprogramming metabolism; and 4) administering hypoxia-based treatment. Here, we discuss their varying efficacies and limitations and provide an outlook on their therapeutic potential and clinical application.
    Keywords:  Hypoxia-directed intervention; Metabolic reprogramming; Mitochondrial genetics; Mitochondrial genome editing; Mitochondrial homeostasis; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.ymgme.2020.06.011
  2. Neurol Genet. 2020 Aug;6(4): e464
    COX deficiency and leukoencephalopathy due to a novel homozygous APOPT1/COA8 mutation.
    Carola Hedberg-Oldfors, Niklas Darin, Christer Thomsen, Christopher Lindberg, Anders Oldfors.
       Objective: To describe the long-term follow-up and pathogenesis in a child with leukoencephalopathy and cytochrome c oxidase (COX) deficiency due to a novel homozygous nonsense mutation in APOPT1/COA8.
    Methods: The patient was clinically investigated at 3, 5, 9, and 25 years of age. Brain MRI, repeat muscle biopsies with biochemical, morphologic, and protein expression analyses were performed, and whole-genome sequencing was used for genetic analysis.
    Results: Clinical investigation revealed dysarthria, dysphagia, and muscle weakness following pneumonia at age 3 years. There was clinical regression leading to severe loss of ambulation, speech, swallowing, hearing, and vision. The clinical course stabilized after 2.5 years and improved over time. The MRI pattern in the patient demonstrated cavitating leukoencephalopathy, and muscle mitochondrial investigations showed COX deficiency with loss of complex IV subunits and ultrastructural abnormalities. Genetic analysis revealed a novel homozygous mutation in the APOPT1/COA8 gene, c.310T>C; p.(Gln104*).
    Conclusions: We describe a novel nonsense mutation in APOPT1/COA8 and provide additional experimental evidence for a COX assembly defect in human muscle causing the complex IV deficiency. The long-term outcome of the disease seems in general to be favorable, and the characteristic MRI pattern with cavitating leukoencephalopathy in combination with COX deficiency should prompt for testing of the APOPT1/COA8 gene.
    DOI:  https://doi.org/10.1212/NXG.0000000000000464
  3. J Microbiol Biotechnol. 2020 Jul 06.
    Transfer of xenomitochondria containing the entire mouse mitochondrial genome into a genetically modified yeast expressing mitochondrial transcription factor A.
    Young Geol Yoon.
      Recently, it was reported that entire mammalian mtDNA genomes could be transplanted into the mitochondrial networks of yeast, where they were accurately and stably maintained without rearrangement as intact genomes. Here, it was found that engineered mtDNA genomes could be readily transferred to and steadily maintained in the mitochondria of genetically modified yeast expressing the mouse mitochondrial transcription factor A (Tfam), one of the mitochondrial nucleoid proteins. The transferred mtDNA genomes were stably retained in the Tfam-expressing yeast cells for many generations. These results indicated that the engineered mouse mtDNA genomes introduced in yeast mitochondria could be relocated into the mitochondria of other cells and that the transferred genomes could be maintained within a mitochondrial environment that is highly amenable to mimicry of the biological conditions in mammalian mitochondria.
    Keywords:  N-ethylmaleimide; Tfam; mitochondrial transcription factor A; mtDNA; spheroplast; xenomitochondria
    DOI:  https://doi.org/10.4014/jmb.2004.04033
  4. J Zhejiang Univ Sci B. 2020 Jul;21(7): 590-592
    Secondary manifestations of mitochondrial disorders.
    Josef Finsterer.
      Mitochondrial disorders (MIDs) are a heterogeneous group of genetic metabolic diseases due to mutations in the mitochondrial DNA (mtDNA) or in the nuclear DNA (nDNA) (Rahman and Rahman, 2018). Some affected genes encode proteins with various functions, or structural RNAs such as transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs). MIDs may also be caused by mutations in non-coding regions (e.g., D-loop of mtDNA) (Rahman and Rahman, 2018). Proteins involved in MIDs include enzymes, assembling factors, transport proteins, signaling proteins, pore proteins, and fusion/fission proteins (Gorman et al., 2016). The pathways most frequently affected by mutations in "mitochondrial genes" are the respiratory chain and the oxidative phosphorylation. Dysfunction of many other pathways (e.g., β-oxidation, pyruvate-dehydrogenase complex, and heme synthesis) may also manifest as MIDs (Hu et al., 2019). The estimated prevalence of MIDs is at least 1:5000 (Ng and Turnbull, 2016).
    Keywords:  Mitochondrial disorder; nDNA; Multiple mtDNA deletions; Phenotype; Multisystem involvement
    DOI:  https://doi.org/10.1631/jzus.B2000010
  5. Nature. 2020 Jul 08.
    Mitochondrial genome editing gets precise.
    Magomet Aushev, Mary Herbert.
      
    Keywords:  Biotechnology; Gene therapy
    DOI:  https://doi.org/10.1038/d41586-020-01974-6
  6. Nature. 2020 Jul 08.
    A bacterial cytidine deaminase toxin enables CRISPR-free mitochondrial base editing.
    Beverly Y Mok, Marcos H de Moraes, Jun Zeng, Dustin E Bosch, Anna V Kotrys, Aditya Raguram, FoSheng Hsu, Matthew C Radey, S Brook Peterson, Vamsi K Mootha, Joseph D Mougous, David R Liu.
      Bacterial toxins represent a vast reservoir of biochemical diversity that can be repurposed for biomedical applications. Such proteins include a group of predicted interbacterial toxins of the deaminase superfamily, members of which have found application in gene-editing techniques1,2. Because previously described cytidine deaminases operate on single-stranded nucleic acids3, their use in base editing requires the unwinding of double-stranded DNA (dsDNA)-for example by a CRISPR-Cas9 system. Base editing within mitochondrial DNA (mtDNA), however, has thus far been hindered by challenges associated with the delivery of guide RNA into the mitochondria4. As a consequence, manipulation of mtDNA to date has been limited to the targeted destruction of the mitochondrial genome by designer nucleases9,10.Here we describe an interbacterial toxin, which we name DddA, that catalyses the deamination of cytidines within dsDNA. We engineered split-DddA halves that are non-toxic and inactive until brought together on target DNA by adjacently bound programmable DNA-binding proteins. Fusions of the split-DddA halves, transcription activator-like effector array proteins, and a uracil glycosylase inhibitor resulted in RNA-free DddA-derived cytosine base editors (DdCBEs) that catalyse C•G-to-T•A conversions in human mtDNA with high target specificity and product purity. We used DdCBEs to model a disease-associated mtDNA mutation in human cells, resulting in changes in respiration rates and oxidative phosphorylation. CRISPR-free DdCBEs enable the precise manipulation of mtDNA, rather than the elimination of mtDNA copies that results from its cleavage by targeted nucleases, with broad implications for the study and potential treatment of mitochondrial disorders.
    DOI:  https://doi.org/10.1038/s41586-020-2477-4
  7. Nature. 2020 Jul 08.
    Scientists make precise gene edits to mitochondrial DNA for first time.
    Heidi Ledford.
      
    Keywords:  Biological techniques; CRISPR-Cas9 genome editing; Genetics; Metabolism
    DOI:  https://doi.org/10.1038/d41586-020-02054-5
  8. Sci Adv. 2020 Jun;6(26): eaba7509
    Functional role of respiratory supercomplexes in mice: SCAF1 relevance and segmentation of the Qpool.
    Enrique Calvo, Sara Cogliati, Pablo Hernansanz-Agustín, Marta Loureiro-López, Adela Guarás, Rafael A Casuso, Fernando García-Marqués, Rebeca Acín-Pérez, Yolanda Martí-Mateos, J C Silla-Castro, Marta Carro-Alvarellos, Jesús R Huertas, Jesús Vázquez, J A Enríquez.
      Mitochondrial respiratory complexes assemble into supercomplexes (SC). Q-respirasome (III2 + IV) requires the supercomplex assembly factor (SCAF1) protein. The role of this factor in the N-respirasome (I + III2 + IV) and the physiological role of SCs are controversial. Here, we study C57BL/6J mice harboring nonfunctional SCAF1, the full knockout for SCAF1, or the wild-type version of the protein and found that exercise performance is SCAF1 dependent. By combining quantitative data-independent proteomics, 2D Blue native gel electrophoresis, and functional analysis of enriched respirasome fractions, we show that SCAF1 confers structural attachment between III2 and IV within the N-respirasome, increases NADH-dependent respiration, and reduces reactive oxygen species (ROS). Furthermore, the expression of AOX in cells and mice confirms that CI-CIII superassembly segments the CoQ in two pools and modulates CI-NADH oxidative capacity.
    DOI:  https://doi.org/10.1126/sciadv.aba7509
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