bims-mitmed Biomed News
on Mitochondrial medicine
Issue of 2021‒12‒26
twenty-four papers selected by
Dario Brunetti
Fondazione IRCCS Istituto Neurologico
  1. Unlocking the Complexity of Mitochondrial DNA: A Key to Understanding Neurodegenerative Disease Caused by Injury.
  2. Clinical Diagnosis and Treatment of Leigh Syndrome Based on SURF1: Genotype and Phenotype.
  3. Forecasting stroke-like episodes and outcomes in mitochondrial disease.
  4. Saccharomyces cerevisiae as a Tool for Studying Mutations in Nuclear Genes Involved in Diseases Caused by Mitochondrial DNA Instability.
  5. Differential effects of mTOR inhibition and dietary ketosis in a mouse model of subacute necrotizing encephalomyelopathy.
  6. ATAD3A has a scaffolding role regulating mitochondria inner membrane structure and protein assembly.
  7. Identification of Novel Therapeutic Targets for Polyglutamine Diseases That Target Mitochondrial Fragmentation.
  8. Mitochondrial DNA damage as driver of cellular outcomes.
  9. A novel MRPS34 gene mutation with combined OXPHOS deficiency in an adult patient with Leigh syndrome.
  10. Mitochondrial dysfunction and mitochondrial therapies in heart failure.
  11. Protein Quality Control at the Mitochondrial Surface.
  12. Metabolic reprogramming during hyperammonemia targets mitochondrial function and postmitotic senescence.
  13. Genetically modified large animal models for investigating neurodegenerative diseases.
  14. Reanalysis of Exome Data Identifies Novel SLC25A46 Variants Associated with Leigh Syndrome.
  15. Inactivity of Peptidase ClpP Causes Primary Accumulation of Mitochondrial Disaggregase ClpX with Its Interacting Nucleoid Proteins, and of mtDNA.
  16. Mitophagy in neurological disorders.
  17. The Dynamin-Related Protein 1 is Decreased and the Mitochondrial Network is Altered in Friedreich's Ataxia Cardiomyopathy.
  18. Development of Leigh syndrome with a high probability of cardiac manifestations in infantile-onset patients with m.14453G>A.
  19. Nrf2 for protection against oxidant generation and mitochondrial damage in cardiac injury.
  20. Induced Pluripotent Stem Cells (iPSCs) and Gene Therapy: A New Era for the Treatment of Neurological Diseases.
  21. N-Acetylcysteine Reverses the Mitochondrial Dysfunction Induced by Very Long-Chain Fatty Acids in Murine Oligodendrocyte Model of Adrenoleukodystrophy.
  22. Mito-TIPTP Increases Mitochondrial Function by Repressing the Rubicon-p22phox Interaction in Colitis-Induced Mice.
  23. Mitochondrial neurogastrointestinal encephalomyopathy: Clinical and biochemical impact of allogeneic stem cell transplantation in a Greek patient with one novel TYMP mutation.
  24. Recurrent erosion of COA1/MITRAC15 exemplifies conditional gene dispensability in oxidative phosphorylation.
  1. Cells. 2021 Dec 08. pii: 3460. [Epub ahead of print]10(12):
    Unlocking the Complexity of Mitochondrial DNA: A Key to Understanding Neurodegenerative Disease Caused by Injury.
    Larry N Singh, Shih-Han Kao, Douglas C Wallace.
      Neurodegenerative disorders that are triggered by injury typically have variable and unpredictable outcomes due to the complex and multifactorial cascade of events following the injury and during recovery. Hence, several factors beyond the initial injury likely contribute to the disease progression and pathology, and among these are genetic factors. Genetics is a recognized factor in determining the outcome of common neurodegenerative diseases. The role of mitochondrial genetics and function in traditional neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, is well-established. Much less is known about mitochondrial genetics, however, regarding neurodegenerative diseases that result from injuries such as traumatic brain injury and ischaemic stroke. We discuss the potential role of mitochondrial DNA genetics in the progression and outcome of injury-related neurodegenerative diseases. We present a guide for understanding mitochondrial genetic variation, along with the nuances of quantifying mitochondrial DNA variation. Evidence supporting a role for mitochondrial DNA as a risk factor for neurodegenerative disease is also reviewed and examined. Further research into the impact of mitochondrial DNA on neurodegenerative disease resulting from injury will likely offer key insights into the genetic factors that determine the outcome of these diseases together with potential targets for treatment.
    Keywords:  evolution; genetics; genomics; ischaemic stroke; mitochondria; traumatic brain injury
    DOI:  https://doi.org/10.3390/cells10123460
  2. Antioxidants (Basel). 2021 Dec 05. pii: 1950. [Epub ahead of print]10(12):
    Clinical Diagnosis and Treatment of Leigh Syndrome Based on SURF1: Genotype and Phenotype.
    Inn-Chi Lee, Kuo-Liang Chiang.
      SURF1 encodes the assembly factor for maintaining the antioxidant of cytochrome c oxidase (COX) stability in the human electron respiratory chain. Mutations in SURF1 can cause Leigh syndrome (LS), a subacute neurodegenerative encephalopathy, characterized by early onset (infancy), grave prognosis, and predominant symptoms presenting in the basal ganglia, thalamus, brainstem, cerebellum, and peripheral nerves. To date, more than sixty different SURF1 mutations have been found to cause SURF1-associated LS; however, the relationship between genotype and phenotype is still unclear. Most SURF1-associated LS courses present as typical LS and cause early mortality (before the age of ten years). However, 10% of the cases present with atypical courses with milder symptoms and increased life expectancy. One reason for this inconsistency may be due to specific duplications or mutations close to the C-terminus of the SURF1 protein appearing to cause less protein decay. Furthermore, the treatment for SURF1-associated LS is unsatisfactory. A ketogenic diet is most often prescribed and has proven to be effective. Supplementing with coenzyme Q and other cofactors is also a common treatment option; however, the results are inconsistent. Importantly, anti-epileptic drugs such as valproate-which cause mitochondrial dysfunction-should be avoided in patients with SURF1-associated LS presenting with seizures.
    Keywords:  Leigh syndrome; complex IV assembly; mitochondrial disorders
    DOI:  https://doi.org/10.3390/antiox10121950
  3. Brain. 2021 Dec 20. pii: awab353. [Epub ahead of print]
    Forecasting stroke-like episodes and outcomes in mitochondrial disease.
    Yi Shiau Ng, Nichola Z Lax, Alasdair P Blain, Daniel Erskine, Mark R Baker, Tuomo Polvikoski, Rhys H Thomas, Christopher M Morris, Ming Lai, Roger G Whittaker, Alasdair Gebbels, Amy Winder, Julie Hall, Catherine Feeney, Maria Elena Farrugia, Claire Hirst, Mark Roberts, Charlotte Lawthom, Alexia Chrysostomou, Kevin Murphy, Tracey Baird, Paul Maddison, Callum Duncan, Joanna Poulton, Victoria Nesbitt, Michael G Hanna, Robert D S Pitceathly, Robert W Taylor, Emma L Blakely, Andrew M Schaefer, Doug M Turnbull, Robert McFarland, Gráinne S Gorman.
      In this retrospective, multicentre, observational cohort study, we sought to determine the clinical, radiological, EEG, genetics and neuropathological characteristics of mitochondrial stroke-like episodes and to identify associated risk predictors. Between January 1998 and June 2018, we identified 111 patients with genetically-determined mitochondrial disease who developed stroke-like episodes. Post-mortem cases of mitochondrial disease (n = 26) were identified from Newcastle Brain Tissue Resource. The primary outcome was to interrogate the clinic-radio-pathological correlates and prognostic indicators of stroke-like episode in patients with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes syndrome. The secondary objective was to develop a multivariable prediction model to forecast stroke-like episode risk. The most common genetic cause of stroke-like episodes was the m.3243A>G variant in MT-TL1 (n = 66), followed by recessive pathogenic POLG variants (n = 22), and 11 other rarer pathogenic mitochondrial DNA (mtDNA) variants (n = 23). The age of first stroke-like episode was available for 105 patients (mean [SD] age: 31.8 [16.1]); a total of 35 patients (32%) presented with their first stroke-like episode ≥40 years of age. The median interval (interquartile range) between first and second stroke-like episodes was 1.33 (2.86) years; 43% of patients developed recurrent stroke-like episodes within 12 months. Clinico-radiological, electrophysiological and neuropathological findings of stroke-like episodes were consistent with the hallmarks of medically refractory epilepsy. Patients with POLG-related stroke-like episodes demonstrated more fulminant disease trajectories than cases of m.3243A>G and other mtDNA pathogenic variants, in terms of the frequency of refractory status epilepticus, rapidity of progression and overall mortality. In multivariate analysis, baseline factors of body mass index, age-adjusted blood m.3243A>G heteroplasmy, sensorineural hearing loss and serum lactate were significantly associated with risk of stroke-like episodes in patients with the m.3243A>G variant. These factors informed the development of a prediction model to assess the risk of developing stroke-like episodes that demonstrated good overall discrimination (area under the curve = 0.87, 95% CI 0.82-0.93; c-statistic = 0.89). Significant radiological and pathological features of neurodegeneration was more evident in patients harbouring pathogenic mtDNA variants compared with POLG: brain atrophy on cranial MRI (90% vs 44%, p < 0.001) and reduced mean brain weight [SD] (1044 g [148] vs 1304 g [142], p = 0.005). Our findings highlight the often idiosyncratic clinical, radiological and EEG characteristics of mitochondrial stroke-like episodes. Early recognition of seizures and aggressive instigation of treatment may help circumvent or slow neuronal loss and abate increasing disease burden. The risk-prediction model for the m.3243A>G variant can help inform more tailored genetic counselling and prognostication in routine clinical practice.
    Keywords:  MELAS; mitochondrial DNA (mtDNA); neuropathology; prognostic modelling; seizures
    DOI:  https://doi.org/10.1093/brain/awab353
  4. Genes (Basel). 2021 Nov 24. pii: 1866. [Epub ahead of print]12(12):
    Saccharomyces cerevisiae as a Tool for Studying Mutations in Nuclear Genes Involved in Diseases Caused by Mitochondrial DNA Instability.
    Alexandru Ionut Gilea, Camilla Ceccatelli Berti, Martina Magistrati, Giulia di Punzio, Paola Goffrini, Enrico Baruffini, Cristina Dallabona.
      Mitochondrial DNA (mtDNA) maintenance is critical for oxidative phosphorylation (OXPHOS) since some subunits of the respiratory chain complexes are mitochondrially encoded. Pathological mutations in nuclear genes involved in the mtDNA metabolism may result in a quantitative decrease in mtDNA levels, referred to as mtDNA depletion, or in qualitative defects in mtDNA, especially in multiple deletions. Since, in the last decade, most of the novel mutations have been identified through whole-exome sequencing, it is crucial to confirm the pathogenicity by functional analysis in the appropriate model systems. Among these, the yeast Saccharomyces cerevisiae has proved to be a good model for studying mutations associated with mtDNA instability. This review focuses on the use of yeast for evaluating the pathogenicity of mutations in six genes, MPV17/SYM1, MRM2/MRM2, OPA1/MGM1, POLG/MIP1, RRM2B/RNR2, and SLC25A4/AAC2, all associated with mtDNA depletion or multiple deletions. We highlight the techniques used to construct a specific model and to measure the mtDNA instability as well as the main results obtained. We then report the contribution that yeast has given in understanding the pathogenic mechanisms of the mutant variants, in finding the genetic suppressors of the mitochondrial defects and in the discovery of molecules able to improve the mtDNA stability.
    Keywords:  MPV17/SYM1; MRM2/MRM2; OPA1/MGM1; POLG/MIP1; RRM2B/RNR2; SLC25A4 (ANT1)/AAC2; diseases associated with mtDNA deletions; drug repurposing; mtDNA depletion syndromes; yeast model
    DOI:  https://doi.org/10.3390/genes12121866
  5. Neurobiol Dis. 2021 Dec 20. pii: S0969-9961(21)00343-0. [Epub ahead of print]163 105594
    Differential effects of mTOR inhibition and dietary ketosis in a mouse model of subacute necrotizing encephalomyelopathy.
    Rebecca Bornstein, Katerina James, Julia Stokes, Kyung Yeon Park, Ernst-Bernhard Kayser, John Snell, Angela Bard, Yihan Chen, Franck Kalume, Simon C Johnson.
      Genetic mitochondrial diseases are the most frequent cause of inherited metabolic disorders and one of the most prevalent causes of heritable neurological disease. Leigh syndrome is the most common clinical presentation of pediatric mitochondrial disease, typically appearing in the first few years of life, and involving severe multisystem pathologies. Clinical care for Leigh syndrome patients is difficult, complicated by the wide range of symptoms including characteristic progressive CNS lesion, metabolic sequelae, and epileptic seizures, which can be intractable to standard management. While no proven therapies yet exist for the underlying mitochondrial disease, a ketogenic diet has led to some reports of success in managing mitochondrial epilepsies, with ketosis reducing seizure risk and severity. The impact of ketosis on other aspects of disease progression in Leigh syndrome has not been studied, however, and a rigorous study of the impact of ketosis on seizures in mitochondrial disease is lacking. Conversely, preclinical efforts have identified the intracellular nutrient signaling regulator mTOR as a promising therapeutic target, with data suggesting the benefits are mediated by metabolic changes. mTOR inhibition alleviates epilepsies arising from defects in TSC, an mTOR regulator, but the therapeutic potential of mTOR inhibition in seizures related to primary mitochondrial dysfunction is unknown. Given that ketogenic diet is used clinically in the setting of mitochondrial disease, and mTOR inhibition is in clinical trials for intractable pediatric epilepsies of diverse causal origins, a direct experimental assessment of their effects is imperative. Here, we define the impact of dietary ketosis on survival and CNS disease in the Ndufs4(KO) mouse model of Leigh syndrome and the therapeutic potential of both dietary ketosis and mTOR inhibition on seizures in this model. These data provide timely insight into two important clinical interventions.
    Keywords:  Epilepsy; Ketogenic diet; Ketosis; Mitochondrial disease; Seizure; mTOR
    DOI:  https://doi.org/10.1016/j.nbd.2021.105594
  6. Cell Rep. 2021 Dec 21. pii: S2211-1247(21)01635-1. [Epub ahead of print]37(12): 110139
    ATAD3A has a scaffolding role regulating mitochondria inner membrane structure and protein assembly.
    Tania Arguello, Susana Peralta, Hana Antonicka, Gabriel Gaidosh, Francisca Diaz, Ya-Ting Tu, Sofia Garcia, Ramin Shiekhattar, Antonio Barrientos, Carlos T Moraes.
      The ATPase Family AAA Domain Containing 3A (ATAD3A), is a mitochondrial inner membrane protein conserved in metazoans. ATAD3A has been associated with several mitochondrial functions, including nucleoid organization, cholesterol metabolism, and mitochondrial translation. To address its primary role, we generated a neuronal-specific conditional knockout (Atad3 nKO) mouse model, which developed a severe encephalopathy by 5 months of age. Pre-symptomatic mice showed aberrant mitochondrial cristae morphogenesis in the cortex as early as 2 months. Using a multi-omics approach in the CNS of 2-to-3-month-old mice, we found early alterations in the organelle membrane structure. We also show that human ATAD3A associates with different components of the inner membrane, including OXPHOS complex I, Letm1, and prohibitin complexes. Stochastic Optical Reconstruction Microscopy (STORM) shows that ATAD3A is regularly distributed along the inner mitochondrial membrane, suggesting a critical structural role in inner mitochondrial membrane and its organization, most likely in an ATPase-dependent manner.
    Keywords:  ATAD3; cardiolipin; cristae; inner membrane; mitochondria
    DOI:  https://doi.org/10.1016/j.celrep.2021.110139
  7. Int J Mol Sci. 2021 Dec 14. pii: 13447. [Epub ahead of print]22(24):
    Identification of Novel Therapeutic Targets for Polyglutamine Diseases That Target Mitochondrial Fragmentation.
    Annika Traa, Emily Machiela, Paige D Rudich, Sonja K Soo, Megan M Senchuk, Jeremy M Van Raamsdonk.
      Huntington's disease (HD) is one of at least nine polyglutamine diseases caused by a trinucleotide CAG repeat expansion, all of which lead to age-onset neurodegeneration. Mitochondrial dynamics and function are disrupted in HD and other polyglutamine diseases. While multiple studies have found beneficial effects from decreasing mitochondrial fragmentation in HD models by disrupting the mitochondrial fission protein DRP1, disrupting DRP1 can also have detrimental consequences in wild-type animals and HD models. In this work, we examine the effect of decreasing mitochondrial fragmentation in a neuronal C. elegans model of polyglutamine toxicity called Neur-67Q. We find that Neur-67Q worms exhibit mitochondrial fragmentation in GABAergic neurons and decreased mitochondrial function. Disruption of drp-1 eliminates differences in mitochondrial morphology and rescues deficits in both movement and longevity in Neur-67Q worms. In testing twenty-four RNA interference (RNAi) clones that decrease mitochondrial fragmentation, we identified eleven clones-each targeting a different gene-that increase movement and extend lifespan in Neur-67Q worms. Overall, we show that decreasing mitochondrial fragmentation may be an effective approach to treating polyglutamine diseases and we identify multiple novel genetic targets that circumvent the potential negative side effects of disrupting the primary mitochondrial fission gene drp-1.
    Keywords:  C. elegans; DRP1; Huntington’s disease; genetics; mitochondria; mitochondrial dynamics; polyglutamine diseases
    DOI:  https://doi.org/10.3390/ijms222413447
  8. Am J Physiol Cell Physiol. 2021 Dec 22.
    Mitochondrial DNA damage as driver of cellular outcomes.
    Cristina A Nadalutti, Sylvette Ayala-Peña, Janine H Santos.
      Mitochondria are primarily involved in energy production through the process of oxidative phosphorylation (OXPHOS). Increasing evidence has shown that mitochondrial function impacts a plethora of different cellular activities, including metabolism, epigenetics and innate immunity. Like the nucleus, mitochondria own their genetic material, which is maternally inherited. The mitochondrial DNA (mtDNA) encodes 37 genes that are solely involved in OXPHOS. Maintenance of mtDNA, through replication and repair, requires the import of nuclear DNA encoded proteins. Thus, mitochondria completely rely on the nucleus to prevent mitochondrial genetic alterations. As every cell contains hundreds to thousands of mitochondria, it follows that the shear number of organelles allow for the buffering of dysfunction - at least to some extent - before tissue homeostasis becomes impaired. Only red blood cells lack mitochondria entirely. Impaired mitochondrial function is a hallmark of aging and is involved in a number of different disorders, including neurodegenerative diseases, diabetes, cancer, and autoimmunity. While alterations in mitochondrial processes unrelated to OXPHOS, such as fusion and fission, contribute to aging and disease, maintenance of mtDNA integrity is critical for proper organellar function. Here, we focus on how mtDNA damage contributes to cellular dysfunction and health outcomes.
    Keywords:  DNA repair; cellular outcomes; mitochondrial dysfunction; mtDNA damage
    DOI:  https://doi.org/10.1152/ajpcell.00389.2021
  9. Mol Genet Metab Rep. 2022 Mar;30 100830
    A novel MRPS34 gene mutation with combined OXPHOS deficiency in an adult patient with Leigh syndrome.
    L Lenzini, M Carecchio, E Iori, A Legati, E Lamantea, A Avogaro, N Vitturi.
      We report a novel pathogenic variant (c.223G > C; p.Gly75Arg) in the gene encoding the small mitoribosomal subunit protein mS34 in a long-surviving patient with Leigh Syndrome who was genetically diagnosed at age 34 years. The patient presented with delayed motor milestones and a stepwise motor deterioration during life, along with brain MRI alterations involving the subcortical white matter, deep grey nuclei and in particular the internal globi pallidi, that appeared calcified on CT scan. The novel variant is associated with a reduction of mS34 protein levels and of the OXPHOS complex I and IV subunits in peripheral blood mononuclear cells of the case. This study expands the number of variants that, by affecting the stability of the mitoribosome, may cause an OXPHOS deficiency in Leigh Syndrome and reports, for the first time, an unusual long survival in a patient with a homozygous MRPS34 pathogenic variant.
    DOI:  https://doi.org/10.1016/j.ymgmr.2021.100830
  10. Pharmacol Res. 2021 Dec 17. pii: S1043-6618(21)00622-8. [Epub ahead of print]175 106038
    Mitochondrial dysfunction and mitochondrial therapies in heart failure.
    Chennan Wu, Zhen Zhang, Weidong Zhang, Xia Liu.
      Cardiovascular diseases remain the leading cause of death worldwide in the last decade, accompanied by immense health and economic burdens. Heart failure (HF), as the terminal stage of many cardiovascular diseases, is a common, intractable, and costly medical condition. Despite significant improvements in pharmacologic and device therapies over the years, life expectancy for this disease remains poor. Current therapies have not reversed the trends in morbidity and mortality as expected. Thus, there is an urgent need for novel potential therapeutic agents. Although the pathophysiology of the failing heart is extraordinarily complex, targeting mitochondrial dysfunction can be an effective approach for potential treatment. Increasing evidence has shown that mitochondrial abnormalities, including altered metabolic substrate utilization, impaired mitochondrial oxidative phosphorylation (OXPHOS), increased reactive oxygen species (ROS) formation, and aberrant mitochondrial dynamics, are closely related to HF. Here, we reviewed the findings on the role of mitochondrial dysfunction in HF, along with novel mitochondrial therapeutics and their pharmacological effects.
    Keywords:  Energy metabolism; Heart failure; Mitochondrial dynamics; Mitochondrial dysfunction; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.phrs.2021.106038
  11. Front Cell Dev Biol. 2021 ;9 795685
    Protein Quality Control at the Mitochondrial Surface.
    Fabian den Brave, Arushi Gupta, Thomas Becker.
      Mitochondria contain two membranes, the outer and inner membrane. The outer membrane fulfills crucial functions for the communication of mitochondria with the cellular environment like exchange of lipids via organelle contact sites, the transport of metabolites and the formation of a signaling platform in apoptosis and innate immunity. The translocase of the outer membrane (TOM complex) forms the entry gate for the vast majority of precursor proteins that are produced on cytosolic ribosomes. Surveillance of the functionality of outer membrane proteins is critical for mitochondrial functions and biogenesis. Quality control mechanisms remove defective and mistargeted proteins from the outer membrane as well as precursor proteins that clog the TOM complex. Selective degradation of single proteins is also an important mode to regulate mitochondrial dynamics and initiation of mitophagy pathways. Whereas inner mitochondrial compartments are equipped with specific proteases, the ubiquitin-proteasome system is a central player in protein surveillance on the mitochondrial surface. In this review, we summarize our current knowledge about the molecular mechanisms that govern quality control of proteins at the outer mitochondrial membrane.
    Keywords:  Cdc48; TOM complex; mitochondria; protein quality control; protein sorting
    DOI:  https://doi.org/10.3389/fcell.2021.795685
  12. JCI Insight. 2021 Dec 22. pii: e154089. [Epub ahead of print]6(24):
    Metabolic reprogramming during hyperammonemia targets mitochondrial function and postmitotic senescence.
    Avinash Kumar, Nicole Welch, Saurabh Mishra, Annette Bellar, Rafaella Nasciemento Silva, Ling Li, Shashi Shekhar Singh, Mary Sharkoff, Alexis Kerr, Aruna Kumar Chelluboyina, Jinendiran Sekar, Amy H Attaway, Charles Hoppel, Belinda Willard, Gangarao Davuluri, Srinivasan Dasarathy.
      Ammonia is a cytotoxic metabolite with pleiotropic molecular and metabolic effects, including senescence induction. During dysregulated ammonia metabolism, which occurs in chronic diseases, skeletal muscle becomes a major organ for nonhepatocyte ammonia uptake. Muscle ammonia disposal occurs in mitochondria via cataplerosis of critical intermediary metabolite α-ketoglutarate, a senescence-ameliorating molecule. Untargeted and mitochondrially targeted data were analyzed by multiomics approaches. These analyses were validated experimentally to dissect the specific mitochondrial oxidative defects and functional consequences, including senescence. Responses to ammonia lowering in myotubes and in hyperammonemic portacaval anastomosis rat muscle were studied. Whole-cell transcriptomics integrated with whole-cell, mitochondrial, and tissue proteomics showed distinct temporal clusters of responses with enrichment of oxidative dysfunction and senescence-related pathways/proteins during hyperammonemia and after ammonia withdrawal. Functional and metabolic studies showed defects in electron transport chain complexes I, III, and IV; loss of supercomplex assembly; decreased ATP synthesis; increased free radical generation with oxidative modification of proteins/lipids; and senescence-associated molecular phenotype-increased β-galactosidase activity and expression of p16INK, p21, and p53. These perturbations were partially reversed by ammonia lowering. Dysregulated ammonia metabolism caused reversible mitochondrial dysfunction by transcriptional and translational perturbations in multiple pathways with a distinct skeletal muscle senescence-associated molecular phenotype.
    Keywords:  Cell Biology; Cellular senescence; Hepatology; Mitochondria; Skeletal muscle
    DOI:  https://doi.org/10.1172/jci.insight.154089
  13. Cell Biosci. 2021 Dec 21. 11(1): 218
    Genetically modified large animal models for investigating neurodegenerative diseases.
    Weili Yang, Xiusheng Chen, Shihua Li, Xiao-Jiang Li.
      Neurodegenerative diseases represent a large group of neurological disorders including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease. Although this group of diseases show heterogeneous clinical and pathological phenotypes, they share important pathological features characterized by the age-dependent and progressive degeneration of nerve cells that is caused by the accumulation of misfolded proteins. The association of genetic mutations with neurodegeneration diseases has enabled the establishment of various types of animal models that mimic genetic defects and have provided important insights into the pathogenesis. However, most of genetically modified rodent models lack the overt and selective neurodegeneration seen in the patient brains, making it difficult to use the small animal models to validate the effective treatment on neurodegeneration. Recent studies of pig and monkey models suggest that large animals can more faithfully recapitulate pathological features of neurodegenerative diseases. In this review, we discuss the important differences in animal models for modeling pathological features of neurodegenerative diseases, aiming to assist the use of animal models to better understand the pathogenesis and to develop effective therapeutic strategies.
    Keywords:  Animal models; CRISPR/Cas9; Neurodegeneration; Pathogenesis; Species
    DOI:  https://doi.org/10.1186/s13578-021-00729-8
  14. J Pers Med. 2021 Dec 02. pii: 1277. [Epub ahead of print]11(12):
    Reanalysis of Exome Data Identifies Novel SLC25A46 Variants Associated with Leigh Syndrome.
    Qifei Li, Jill A Madden, Jasmine Lin, Jiahai Shi, Samantha M Rosen, Klaus Schmitz-Abe, Pankaj B Agrawal.
      SLC25A46 (solute carrier family 25 member 46) mutations have been linked to various neurological diseases with recessive inheritance, including Leigh syndrome, optic atrophy, and lethal congenital pontocerebellar hypoplasia. SLC25A46 is expressed in the outer membrane of mitochondria, where it plays a critical role in mitochondrial dynamics. A deceased 7-month-old female infant was suspected to have Leigh syndrome. Clinical exome sequencing was non-diagnostic, but research reanalysis of the sequencing data identified two novel variants in SLC25A46: a missense (c.1039C>T, p.Arg347Cys; NM_138773, hg19) and a donor splice region variant (c.283+5G>A) in intron 1. Both variants were predicted to be damaging. Sanger sequencing of cDNA detected a single missense allele in the patient compared to control, and the SLC25A46 transcript levels were also reduced due to the splice region variant. Additionally, Western blot analysis of whole-cell lysate showed a decrease of SLC25A46 expression in proband fibroblasts, relative to control cells. Further, analysis of mitochondrial morphology revealed evidence of increased fragmentation of the mitochondrial network in proband fibroblasts, compared to control cells. Collectively, our findings suggest that these novel variants in SLC24A46, the donor splice one and the missense variant, are the cause of the neurological phenotype in this proband.
    Keywords:  Leigh syndrome; SLC25A46; mitochondria; optic atrophy; reanalysis
    DOI:  https://doi.org/10.3390/jpm11121277
  15. Cells. 2021 Nov 29. pii: 3354. [Epub ahead of print]10(12):
    Inactivity of Peptidase ClpP Causes Primary Accumulation of Mitochondrial Disaggregase ClpX with Its Interacting Nucleoid Proteins, and of mtDNA.
    Jana Key, Sylvia Torres-Odio, Nina C Bach, Suzana Gispert, Gabriele Koepf, Marina Reichlmeir, A Phillip West, Holger Prokisch, Peter Freisinger, William G Newman, Stavit Shalev, Stephan A Sieber, Ilka Wittig, Georg Auburger.
      Biallelic pathogenic variants in CLPP, encoding mitochondrial matrix peptidase ClpP, cause a rare autosomal recessive condition, Perrault syndrome type 3 (PRLTS3). It is characterized by primary ovarian insufficiency and early sensorineural hearing loss, often associated with progressive neurological deficits. Mouse models showed that accumulations of (i) its main protein interactor, the substrate-selecting AAA+ ATPase ClpX, (ii) mitoribosomes, and (iii) mtDNA nucleoids are the main cellular consequences of ClpP absence. However, the sequence of these events and their validity in human remain unclear. Here, we studied global proteome profiles to define ClpP substrates among mitochondrial ClpX interactors, which accumulated consistently in ClpP-null mouse embryonal fibroblasts and brains. Validation work included novel ClpP-mutant patient fibroblast proteomics. ClpX co-accumulated in mitochondria with the nucleoid component POLDIP2, the mitochondrial poly(A) mRNA granule element LRPPRC, and tRNA processing factor GFM1 (in mouse, also GRSF1). Only in mouse did accumulated ClpX, GFM1, and GRSF1 appear in nuclear fractions. Mitoribosomal accumulation was minor. Consistent accumulations in murine and human fibroblasts also affected multimerizing factors not known as ClpX interactors, namely, OAT, ASS1, ACADVL, STOM, PRDX3, PC, MUT, ALDH2, PMPCB, UQCRC2, and ACADSB, but the impact on downstream metabolites was marginal. Our data demonstrate the primary impact of ClpXP on the assembly of proteins with nucleic acids and show nucleoid enlargement in human as a key consequence.
    Keywords:  ClpB; ERAL1; HARS2; LARS2; Parkinson’s disease; TWNK; ataxia; leukodystrophy
    DOI:  https://doi.org/10.3390/cells10123354
  16. J Neuroinflammation. 2021 Dec 22. 18(1): 297
    Mitophagy in neurological disorders.
    Lijun Zhang, Lei Dai, Deyuan Li.
      Selective autophagy is an evolutionarily conserved mechanism that removes excess protein aggregates and damaged intracellular components. Most eukaryotic cells, including neurons, rely on proficient mitophagy responses to fine-tune the mitochondrial number and preserve energy metabolism. In some circumstances (such as the presence of pathogenic protein oligopolymers and protein mutations), dysfunctional mitophagy leads to nerve degeneration, with age-dependent intracellular accumulation of protein aggregates and dysfunctional organelles, leading to neurodegenerative disease. However, when pathogenic protein oligopolymers, protein mutations, stress, or injury are present, mitophagy prevents the accumulation of damaged mitochondria. Accordingly, mitophagy mediates neuroprotective effects in some forms of neurodegenerative disease (e.g., Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic lateral sclerosis) and acute brain damage (e.g., stroke, hypoxic-ischemic brain injury, epilepsy, and traumatic brain injury). The complex interplay between mitophagy and neurological disorders suggests that targeting mitophagy might be applicable for the treatment of neurodegenerative diseases and acute brain injury. However, due to the complexity of the mitophagy mechanism, mitophagy can be both harmful and beneficial, and future efforts should focus on maximizing its benefits. Here, we discuss the impact of mitophagy on neurological disorders, emphasizing the contrast between the positive and negative effects of mitophagy.
    Keywords:  Alzheimer's disease; Autophagy; Huntington's disease; Mitophagy; Neurological diseases; Stroke
    DOI:  https://doi.org/10.1186/s12974-021-02334-5
  17. Int J Biochem Cell Biol. 2021 Dec 16. pii: S1357-2725(21)00218-1. [Epub ahead of print] 106137
    The Dynamin-Related Protein 1 is Decreased and the Mitochondrial Network is Altered in Friedreich's Ataxia Cardiomyopathy.
    Bojjibabu Chidipi, Mariana Burgos Angulo, Syed Islamuddin Shah, Michelle Rieser, Ganim Ullah, Thomas V McDonald, Sami F Noujaim.
      Friedreich ataxia is an autosomal recessive congenital neurodegenerative disease caused by a deficiency in the frataxin protein and is often diagnosed in young adulthood. An expansion of guanine-adenine-adenine repeats in the first intron of the FXN gene leads to decreased frataxin expression. Frataxin plays an essential role in mitochondrial metabolism. Most Friedreich ataxia patients are diagnosed with left ventricular hypertrophic cardiomyopathy, and 60% of patients die with hypertrophic cardiomyopathy. However, the mitochondrial anatomy in Friedreich ataxia hypertrophic cardiomyopathy is still poorly understood. We investigated mitochondrial fission, fusion, and function using biochemical, microscopy, and computational stochastic analysis in human induced pluripotent stem cell derived cardiomyocytes from a patient with Friedreich ataxia hypertrophic cardiomyopathy and a healthy individual. We found a significantly higher mitochondrial footprint, decreased mitochondrial fission protein dynamin-related protein, and mitochondrial fission rate over fusion with more giant mitochondrial clusters in human induced pluripotent stem cell derived cardiomyocytes from a patient with Friedreich ataxia hypertrophic cardiomyopathy, compared to an unaffected individual. We also found significantly depolarized mitochondrial membrane potential and higher reactive oxygen species levels in Friedreich ataxia human induced pluripotent stem cell cardiomyocytes. Our results show that frataxin's depletion may dampen the mitochondrial fission machinery by reducing dynamin-related protein1. The loss of mitochondrial fission might lead to elevated reactive oxygen species and depolarized mitochondrial membrane potential, which may cause oxidative damage in Friedreich ataxia hypertrophic cardiomyopathy. Further investigations are needed to identify the mechanism of downregulating dynamin-related protein1 due to the frataxin deficiency in Friedreich ataxia hypertrophic cardiomyopathy.
    Keywords:  DRP1; Friedreich ataxia; hypertrophic cardiomyopathy; mitochondrial fusion and fission
    DOI:  https://doi.org/10.1016/j.biocel.2021.106137
  18. Mitochondrion. 2021 Dec 18. pii: S1567-7249(21)00172-0. [Epub ahead of print]
    Development of Leigh syndrome with a high probability of cardiac manifestations in infantile-onset patients with m.14453G>A.
    Masaru Shimura, Takanori Onuki, Yohei Sugiyama, Tetsuro Matsuhashi, Tomohiro Ebihara, Takuya Fushimi, Makiko Tajika, Keiko Ichimoto, Ayako Matsunaga, Tomoko Tsuruoka, Kazuhiro R Nitta, Atsuko Imai-Okazaki, Yukiko Yatsuka, Yoshihito Kishita, Akira Ohtake, Yasushi Okazaki, Kei Murayama.
      The m.14453G>A mutation in MT-ND6 has been described in a few patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes or Leigh syndrome.However, the clinical spectrum and molecular characteristics are unclear.Here, we present four infantile-onset patients with m.14453G>A-associated Leigh syndrome. All four patients had brainstem lesions with basal ganglia lesions, and two patients had cardiac manifestations. Decreased ND6 protein expression and immunoreactivity were observed in patient-derived samples. There was no clear correlation between heteroplasmy levels and onset age or between heteroplasmy levels and phenotype; however, infantile onset was associated with Leigh syndrome.
    Keywords:  Leigh syndrome; Wolff-Parkinson-White syndrome; brainstem lesion; hypertrophic cardiomyopathy; mitochondrial NADH-ubiquinone oxidoreductase chain 6 gene
    DOI:  https://doi.org/10.1016/j.mito.2021.12.005
  19. Free Radic Biol Med. 2021 Dec 15. pii: S0891-5849(21)00852-2. [Epub ahead of print]
    Nrf2 for protection against oxidant generation and mitochondrial damage in cardiac injury.
    Qin M Chen.
      Myocardial infarction is the most common form of acute coronary syndrome. Blockage of a coronary artery due to blood clotting leads to ischemia and subsequent cell death in the form of necrosis, apoptosis, necroptosis and ferroptosis. Revascularization by coronary artery bypass graft surgery or non-surgical percutaneous coronary intervention combined with pharmacotherapy is effective in relieving symptoms and decreasing mortality. However, reactive oxygen species (ROS) are generated from damaged mitochondria, NADPH oxidases, xanthine oxidase, and inflammation. Impairment of mitochondria is shown as decreased metabolic activity, increased ROS production, membrane permeability transition, and release of mitochondrial proteins into the cytoplasm. Oxidative stress activates Nrf2 transcription factor, which in turn mediates the expression of mitofusin 2 (Mfn 2) and proteasomal genes. Increased expression of Mfn2 and inhibition of mitochondrial fission due to decreased Drp1 protein by proteasomal degradation contribute to mitochondrial hyperfusion. Damaged mitochondria can be removed by mitophagy via Parkin or p62 mediated ubiquitination. Mitochondrial biogenesis compensates for the loss of mitochondria, but requires mitochondrial DNA replication and initiation of transcription or translation of mitochondrial genes. Experimental evidence supports a role of Nrf2 in mitophagy, via up-regulation of PINK1 or p62 gene expression; and in mitochondrial biogenesis, by influencing the expression of PGC-1α, NResF1, NResF2, TFAM and mitochondrial genes. Oxidative stress causes Nrf2 activation via Keap1 dissociation, de novo protein translation, and nuclear translocation related to inactivation of GSK3β. The mechanism of Keap 1 mediated Nrf2 activation has been hijacked for Nrf2 activation by small molecules derived from natural products, some of which have been shown capable of mitochondrial protection. Multiple lines of evidence support the importance of Nrf2 in protecting mitochondria and preserving or renewing energy metabolism following tissue injury.
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2021.12.001
  20. Int J Mol Sci. 2021 Dec 20. pii: 13674. [Epub ahead of print]22(24):
    Induced Pluripotent Stem Cells (iPSCs) and Gene Therapy: A New Era for the Treatment of Neurological Diseases.
    Giulia Paolini Sguazzi, Valentina Muto, Marco Tartaglia, Enrico Bertini, Claudia Compagnucci.
      To date, gene therapy has employed viral vectors to deliver therapeutic genes. However, recent progress in molecular and cell biology has revolutionized the field of stem cells and gene therapy. A few years ago, clinical trials started using stem cell replacement therapy, and the induced pluripotent stem cells (iPSCs) technology combined with CRISPR-Cas9 gene editing has launched a new era in gene therapy for the treatment of neurological disorders. Here, we summarize the latest findings in this research field and discuss their clinical applications, emphasizing the relevance of recent studies in the development of innovative stem cell and gene editing therapeutic approaches. Even though tumorigenicity and immunogenicity are existing hurdles, we report how recent progress has tackled them, making engineered stem cell transplantation therapy a realistic option.
    Keywords:  CRISPR-Cas9 gene editing; gene therapy; iPSCs; neurodegeneration; non-viral vector; pediatric diseases; stem cells; viral vector
    DOI:  https://doi.org/10.3390/ijms222413674
  21. Biomedicines. 2021 Dec 03. pii: 1826. [Epub ahead of print]9(12):
    N-Acetylcysteine Reverses the Mitochondrial Dysfunction Induced by Very Long-Chain Fatty Acids in Murine Oligodendrocyte Model of Adrenoleukodystrophy.
    Jie Zhou, Marcia R Terluk, Paul J Orchard, James C Cloyd, Reena V Kartha.
      The accumulation of saturated very long-chain fatty acids (VLCFA, ≥C22:0) due to peroxisomal impairment leads to oxidative stress and neurodegeneration in X-linked adrenoleukodystrophy (ALD). Among the neural supporting cells, myelin-producing oligodendrocytes are the most sensitive to the detrimental effect of VLCFA. Here, we characterized the mitochondrial dysfunction and cell death induced by VLFCA, and examined whether N-acetylcysteine (NAC), an antioxidant, prevents the cytotoxicity. We exposed murine oligodendrocytes (158 N) to hexacosanoic acid (C26:0, 1-100 µM) for 24 h and measured reactive oxygen species (ROS) and cell death. Low concentrations of C26:0 (≤25 µM) induced a mild effect on cell survival with no alterations in ROS or total glutathione (GSH) concentrations. However, analysis of the mitochondrial status of cells treated with C26:0 (25 µM) revealed depletion in mitochondrial GSH (mtGSH) and a decrease in the inner membrane potential. These results indicate that VLCFA disturbs the mitochondrial membrane potential causing ROS accumulation, oxidative stress, and cell death. We further tested whether NAC (500 µM) can prevent the mitochondria-specific effects of VLCFA in C26:0-treated oligodendrocytes. Our results demonstrate that NAC improves mtGSH levels and mitochondrial function in oligodendrocytes, indicating that it has potential use in the treatment of ALD and related disorders.
    Keywords:  N-acetylcysteine (NAC); adrenoleukodystrophy (ALD); antioxidant; glutathione (GSH); mitochondrial GSH (mtGSH); mitochondrial dysfunction; oligodendrocytes; very long-chain fatty acids (VLCFA)
    DOI:  https://doi.org/10.3390/biomedicines9121826
  22. Antioxidants (Basel). 2021 Dec 06. pii: 1954. [Epub ahead of print]10(12):
    Mito-TIPTP Increases Mitochondrial Function by Repressing the Rubicon-p22phox Interaction in Colitis-Induced Mice.
    Jae-Sung Kim, Ye-Ram Kim, Sein Jang, Sang Geon Wang, Euni Cho, Seok-Jun Mun, Hye-In Jeon, Hyo-Keun Kim, Sun-Joon Min, Chul-Su Yang.
      The run/cysteine-rich-domain-containing Beclin1-interacting autophagy protein (Rubicon) is essential for the regulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase by interacting with p22phox to trigger the production of reactive oxygen species (ROS) in immune cells. In a previous study, we demonstrated that the interaction of Rubicon with p22phox increases cellular ROS levels. The correlation between Rubicon and mitochondrial ROS (mtROS) is poorly understood. Here, we report that Rubicon interacts with p22phox in the outer mitochondrial membrane in macrophages and patients with human ulcerative colitis. Upon lipopolysaccharide (LPS) activation, the binding of Rubicon to p22phox was elevated, and increased not only cellular ROS levels but also mtROS, with an impairment of mitochondrial complex III and mitochondrial biogenesis in macrophages. Furthermore, increased Rubicon decreases mitochondrial metabolic flux in macrophages. Mito-TIPTP, which is a p22phox inhibitor containing a mitochondrial translocation signal, enhances mitochondrial function by inhibiting the association between Rubicon and p22phox in LPS-primed bone-marrow-derived macrophages (BMDMs) treated with adenosine triphosphate (ATP) or dextran sulfate sodium (DSS). Remarkably, Mito-TIPTP exhibited a therapeutic effect by decreasing mtROS in DSS-induced acute or chronic colitis mouse models. Thus, our findings suggest that Mito-TIPTP is a potential therapeutic agent for colitis by inhibiting the interaction between Rubicon and p22phox to recover mitochondrial function.
    Keywords:  Rubicon; colitis; mitochondria; p22phox; reactive oxygen species
    DOI:  https://doi.org/10.3390/antiox10121954
  23. Mol Genet Metab Rep. 2022 Mar;30 100829
    Mitochondrial neurogastrointestinal encephalomyopathy: Clinical and biochemical impact of allogeneic stem cell transplantation in a Greek patient with one novel TYMP mutation.
    A Paisiou, M Rogalidou, R Pons, E Ioannidou, K Dimakou, A Papadopoulou, F M Vaz, G Vessalas, S M I Goorden, J Roelofsen, A Zoetekouw, M M Nieman, E Dimitriou, M Moraitou, I Peristeri, H Michelakakis, A B P van Kuilenburg.
      We describe the case of a Greek female patient with the Classic form of the ultra- rare and fatal autosomal recessive disorder Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and the impact of allogeneic hematopoietic stem cell transplantation on the biochemical and clinical aspects of the disease. The patient presented at the age of 15 years with severe gastrointestinal symptoms, cachexia, peripheral neuropathy and diffuse leukoencephalopathy. The diagnosis of MNGIE disease was established by the increased levels of thymidine and deoxyuridine in plasma and the complete deficiency of thymidine phosphorylase activity. The novel c.[978dup] (p.Ala327Argfs*?) variant and the previously described variant c.[417 + 1G > A] were identified in TYMP. The donor for the allogeneic hematopoietic stem cell transplantation was her fully compatible sister, a carrier of the disease. The patient had a completely uneventful post- transplant period and satisfactory PB chimerism levels. A marked and rapid decrease in thymidine and deoxyuridine plasma levels and an increase of the thymidine phosphorylase activity to the levels measured in her donor sister was observed and is still present sixteen months post-transplant. Disease symptoms stabilized and some improvement was also observed both in her neurological and gastrointestinal symptoms. Follow up studies will be essential for determining the long term impact of allogeneic hematopoietic stem cell transplantation in our patient.
    Keywords:  AHSCT, allogeneic hematopoietic stem cell transplantation;; Allogeneic hematopoietic stem cell transplantation, AHSCT; CSF, cerebrospinal fluid;; GVHD, Graft Versus Host Disease;; HSCT, hematopoietic stem cell transplantation;; MNGIE; MNGIE, mitochondrial neurogastrointestinal encephalomyopathy;; Mitochondrial neurogastrointestinal encephalomyopathy; Mutation analysis; OLT, orthotopic liver transplantation;; PB, peripheral blood;; PLT, platelet;; TP, thymidine phosphorylase;; TPN, total parenteral nutrition;; TYMP, thymidine phosphorylase gene;; VLCFA, very long chain fatty acids; dThd, thymidine;; dUrd, 2′-deoxyuridine;; mtDNA, mitochondrial DNA;
    DOI:  https://doi.org/10.1016/j.ymgmr.2021.100829
  24. Sci Rep. 2021 Dec 24. 11(1): 24437
    Recurrent erosion of COA1/MITRAC15 exemplifies conditional gene dispensability in oxidative phosphorylation.
    Sagar Sharad Shinde, Sandhya Sharma, Lokdeep Teekas, Ashutosh Sharma, Nagarjun Vijay.
      Skeletal muscle fibers rely upon either oxidative phosphorylation or the glycolytic pathway with much less reliance on oxidative phosphorylation to achieve muscular contractions that power mechanical movements. Species with energy-intensive adaptive traits that require sudden bursts of energy have a greater dependency on glycolytic fibers. Glycolytic fibers have decreased reliance on OXPHOS and lower mitochondrial content compared to oxidative fibers. Hence, we hypothesized that gene loss might have occurred within the OXPHOS pathway in lineages that largely depend on glycolytic fibers. The protein encoded by the COA1/MITRAC15 gene with conserved orthologs found in budding yeast to humans promotes mitochondrial translation. We show that gene disrupting mutations have accumulated within the COA1 gene in the cheetah, several species of galliform birds, and rodents. The genomic region containing COA1 is a well-established evolutionary breakpoint region in mammals. Careful inspection of genome assemblies of closely related species of rodents and marsupials suggests two independent COA1 gene loss events co-occurring with chromosomal rearrangements. Besides recurrent gene loss events, we document changes in COA1 exon structure in primates and felids. The detailed evolutionary history presented in this study reveals the intricate link between skeletal muscle fiber composition and the occasional dispensability of the chaperone-like role of the COA1 gene.
    DOI:  https://doi.org/10.1038/s41598-021-04077-y
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