bims-mitdis Biomed News
on Mitochondrial Disorders
Issue of 2021‒07‒04
fifty-seven papers selected by
Catalina Vasilescu
University of Helsinki
  1. Loss of Individual Mitochondrial Ribonuclease P Complex Proteins Differentially Affects Mitochondrial tRNA Processing In Vivo.
  2. The mitochondrial single-stranded DNA binding protein is essential for initiation of mtDNA replication.
  3. Epilepsy in Mitochondrial Diseases-Current State of Knowledge on Aetiology and Treatment.
  4. Dominant Optic Atrophy (DOA): Modeling the Kaleidoscopic Roles of OPA1 in Mitochondrial Homeostasis.
  5. Leber's Hereditary Optic Neuropathy: A Report on Novel mtDNA Pathogenic Variants.
  6. Increased mitochondrial protein import and cardiolipin remodelling upon early mtUPR.
  7. Mitochondrial nanomedicine: Subcellular organelle-specific delivery of molecular medicines.
  8. Mitochondrial Cristae Architecture and Functions: Lessons from Minimal Model Systems.
  9. mtDNA Heteroplasmy: Origin, Detection, Significance, and Evolutionary Consequences.
  10. Novel biallelic mutations in POLG gene: large deletion and missense variant associated with PEO.
  11. The Role of Mitochondrial Mutations and Chronic Inflammation in Diabetes.
  12. Strategies for mitochondrial gene editing.
  13. Quantifying Mitochondrial Dynamics in Patient Fibroblasts with Multiple Developmental Defects and Mitochondrial Disorders.
  14. Mitochondrial Protein Abundance Gradients Require the Distribution of Separated Mitochondria.
  15. Polymerase Gamma Mitochondrial DNA Depletion Syndrome Initially Presenting as Disproportionate Respiratory Distress in a Moderately Premature Neonate: A Case Report.
  16. Neuroprotection in Glaucoma: NAD+/NADH Redox State as a Potential Biomarker and Therapeutic Target.
  17. Increased levels of mitochondrial import factor Mia40 prevent the aggregation of polyQ proteins in the cytosol.
  18. Therapy Prospects for Mitochondrial DNA Maintenance Disorders.
  19. Mitochondrial O-GlcNAc Transferase Interacts with and Modifies Many Proteins and Its Up-Regulation Affects Mitochondrial Function and Cellular Energy Homeostasis.
  20. The Mystery of Extramitochondrial Proteins Lysine Succinylation.
  21. Prospective diagnosis of MT-ATP6-related mitochondrial disease by newborn screening.
  22. Development of Peptide-Based Nanoparticles for Mitochondrial Plasmid DNA Delivery.
  23. Structural perspectives on H2S homeostasis.
  24. Evidence for the Role of Mitochondrial DNA Release in the Inflammatory Response in Neurological Disorders.
  25. Miro1-dependent mitochondrial dynamics in parvalbumin Interneurons.
  26. Innate immunity in mutator mice.
  27. TAT-Conjugated NDUFS8 Can Be Transduced into Mitochondria in a Membrane-Potential-Independent Manner and Rescue Complex I Deficiency.
  28. Mechanisms of the effect of oxidative phosphorylation deficiencies on the skeletal muscle bioenergetic system in patients with mitochondrial myopathies.
  29. The Influence of Mitochondrial Dynamics and Function on Retinal Ganglion Cell Susceptibility in Optic Nerve Disease.
  30. NAD+-Precursor Supplementation With L-Tryptophan, Nicotinic Acid, and Nicotinamide Does Not Affect Mitochondrial Function or Skeletal Muscle Function in Physically Compromised Older Adults.
  31. Modulation of mitochondrial nucleoid structure during aging and by mtDNA content in Drosophila.
  32. Experimental evolution improves mitochondrial genome quality control in Saccharomyces cerevisiae and extends its replicative lifespan.
  33. Mitochondria-targeted hydroxyurea inhibits OXPHOS and induces antiproliferative and immunomodulatory effects.
  34. Mitochondrial Transplantation in Cardiomyocytes: foundation, methods, and outcomes.
  35. Mitochondrial DNA Copy Number and Developmental Origins of Health and Disease (DOHaD).
  36. Immunonutrition for the acute treatment of MELAS syndrome.
  37. Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS) Syndrome: Frequency, Clinical Features, Imaging, Histopathologic, and Molecular Genetic Findings in a Third-level Health Care Center in Mexico.
  38. Mitochondria in Myelinating Oligodendrocytes: Slow and Out of Breath?
  39. STING1 Promotes Ferroptosis Through MFN1/2-Dependent Mitochondrial Fusion.
  40. Translation stress and collided ribosomes are co-activators of cGAS.
  41. Plasma Gelsolin Reinforces the Diagnostic Value of FGF-21 and GDF-15 for Mitochondrial Disorders.
  42. NADH Fluorescence Lifetime Imaging Microscopy Reveals Selective Mitochondrial Dysfunction in Neurons Overexpressing Alzheimer's Disease-Related Proteins.
  43. Systemic Treatment with Nicotinamide Riboside Is Protective in Two Mouse Models of Retinal Ganglion Cell Damage.
  44. A Novel Variation in the Mitochondrial Complex I Assembly Factor NDUFAF5 Causes Isolated Bilateral Striatal Necrosis in Childhood.
  45. Discovering Cellular Mitochondrial Heteroplasmy Heterogeneity with Single Cell RNA and ATAC Sequencing.
  46. Efficient C•G-to-G•C base editors developed using CRISPRi screens, target-library analysis, and machine learning.
  47. Epilepsy Associated With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes.
  48. Protective Effect of Optic Atrophy 1 on Cardiomyocyte Oxidative Stress: Roles of Mitophagy, Mitochondrial Fission, and MAPK/ERK Signaling.
  49. Editorial: Autophagy and Mitophagy in Skeletal Muscle Health and Disease.
  50. Advanced Fiber Type-Specific Protein Profiles Derived from Adult Murine Skeletal Muscle.
  51. Pervasive inflammatory activation in patients with deficiency in very-long-chain acyl-coA dehydrogenase (VLCADD).
  52. Coenzyme Q10 Phytosome Formulation Improves CoQ10 Bioavailability and Mitochondrial Functionality in Cultured Cells.
  53. Treatment of ARS deficiencies with specific amino acids.
  54. Coenzyme Q Biosynthesis: An Update on the Origins of the Benzenoid Ring and Discovery of New Ring Precursors.
  55. LRRK2 recruitment, activity, and function in organelles.
  56. Quantification and molecular imaging of fatty acid isomers from complex biological samples by mass spectrometry.
  57. Western Diet Decreases the Liver Mitochondrial Oxidative Flux of Succinate: Insight from a Murine NAFLD Model.
  1. Int J Mol Sci. 2021 Jun 04. pii: 6066. [Epub ahead of print]22(11):
    Loss of Individual Mitochondrial Ribonuclease P Complex Proteins Differentially Affects Mitochondrial tRNA Processing In Vivo.
    Maithili Saoji, Aditya Sen, Rachel T Cox.
      Over a thousand nucleus-encoded mitochondrial proteins are imported from the cytoplasm; however, mitochondrial (mt) DNA encodes for a small number of critical proteins and the entire suite of mt:tRNAs responsible for translating these proteins. Mitochondrial RNase P (mtRNase P) is a three-protein complex responsible for cleaving and processing the 5'-end of mt:tRNAs. Mutations in any of the three proteins can cause mitochondrial disease, as well as mutations in mitochondrial DNA. Great strides have been made in understanding the enzymology of mtRNase P; however, how the loss of each protein causes mitochondrial dysfunction and abnormal mt:tRNA processing in vivo has not been examined in detail. Here, we used Drosophila genetics to selectively remove each member of the complex in order to assess their specific contributions to mt:tRNA cleavage. Using this powerful model, we find differential effects on cleavage depending on which complex member is lost and which mt:tRNA is being processed. These data revealed in vivo subtleties of mtRNase P function that could improve understanding of human diseases.
    Keywords:  Drosophila; mitochondria; mtDNA; mtRNase P; tRNA
    DOI:  https://doi.org/10.3390/ijms22116066
  2. Sci Adv. 2021 Jul;pii: eabf8631. [Epub ahead of print]7(27):
    The mitochondrial single-stranded DNA binding protein is essential for initiation of mtDNA replication.
    Min Jiang, Xie Xie, Xuefeng Zhu, Shan Jiang, Dusanka Milenkovic, Jelena Misic, Yonghong Shi, Nirwan Tandukar, Xinping Li, Ilian Atanassov, Louise Jenninger, Emily Hoberg, Sara Albarran-Gutierrez, Zsolt Szilagyi, Bertil Macao, Stefan J Siira, Valerio Carelli, Jack D Griffith, Claes M Gustafsson, Thomas J Nicholls, Aleksandra Filipovska, Nils-Göran Larsson, Maria Falkenberg.
      We report a role for the mitochondrial single-stranded DNA binding protein (mtSSB) in regulating mitochondrial DNA (mtDNA) replication initiation in mammalian mitochondria. Transcription from the light-strand promoter (LSP) is required both for gene expression and for generating the RNA primers needed for initiation of mtDNA synthesis. In the absence of mtSSB, transcription from LSP is strongly up-regulated, but no replication primers are formed. Using deep sequencing in a mouse knockout model and biochemical reconstitution experiments with pure proteins, we find that mtSSB is necessary to restrict transcription initiation to optimize RNA primer formation at both origins of mtDNA replication. Last, we show that human pathological versions of mtSSB causing severe mitochondrial disease cannot efficiently support primer formation and initiation of mtDNA replication.
    DOI:  https://doi.org/10.1126/sciadv.abf8631
  3. Children (Basel). 2021 Jun 22. pii: 532. [Epub ahead of print]8(7):
    Epilepsy in Mitochondrial Diseases-Current State of Knowledge on Aetiology and Treatment.
    Dorota Wesół-Kucharska, Dariusz Rokicki, Aleksandra Jezela-Stanek.
      Mitochondrial diseases are a heterogeneous group of diseases resulting from energy deficit and reduced adenosine triphosphate (ATP) production due to impaired oxidative phosphorylation. The manifestation of mitochondrial disease is usually multi-organ. Epilepsy is one of the most common manifestations of diseases resulting from mitochondrial dysfunction, especially in children. The onset of epilepsy is associated with poor prognosis, while its treatment is very challenging, which further adversely affects the course of these disorders. Fortunately, our knowledge of mitochondrial diseases is still growing, which gives hope for patients to improve their condition in the future. The paper presents the pathophysiology, clinical picture and treatment options for epilepsy in patients with mitochondrial disease.
    Keywords:  antiepileptic drugs (AED); epilepsy; mitochondrial disorders; mtDNA; nDNA; treatment
    DOI:  https://doi.org/10.3390/children8070532
  4. Front Neurol. 2021 ;12 681326
    Dominant Optic Atrophy (DOA): Modeling the Kaleidoscopic Roles of OPA1 in Mitochondrial Homeostasis.
    Valentina Del Dotto, Valerio Carelli.
      In the year 2000, the discovery of OPA1 mutations as causative for dominant optic atrophy (DOA) was pivotal to rapidly expand the field of mitochondrial dynamics and describe the complex machinery governing this pathway, with a multitude of other genes and encoded proteins involved in neurodegenerative disorders of the optic nerve. OPA1 turned out to be a much more complex protein than initially envisaged, connecting multiple pathways beyond its strict role in mitochondrial fusion, such as sensing of OXPHOS needs and mitochondrial DNA maintenance. As a consequence, an increasing need to investigate OPA1 functions at multiple levels has imposed the development of multiple tools and models that are here reviewed. Translational mitochondrial medicine, with the ultimate objective of translating basic science necessary to understand pathogenic mechanisms into therapeutic strategies, requires disease modeling at multiple levels: from the simplest, like in yeast, to cell models, including the increasing use of reprogrammed stem cells (iPSCs) from patients, to animal models. In the present review, we thoroughly examine and provide the state of the art of all these approaches.
    Keywords:  OPA1; OPA1 mutations; cell models; dominant optic atrophy; iPSCs; mitochondria; mouse models; retinal ganglion cells
    DOI:  https://doi.org/10.3389/fneur.2021.681326
  5. Front Neurol. 2021 ;12 657317
    Leber's Hereditary Optic Neuropathy: A Report on Novel mtDNA Pathogenic Variants.
    Lorenzo Peverelli, Alessia Catania, Silvia Marchet, Paola Ciasca, Gabriella Cammarata, Lisa Melzi, Antonella Bellino, Roberto Fancellu, Eleonora Lamantea, Mariantonietta Capristo, Leonardo Caporali, Chiara La Morgia, Valerio Carelli, Daniele Ghezzi, Stefania Bianchi Marzoli, Costanza Lamperti.
      Leber's hereditary optic neuropathy (LHON) is due to missense point mutations affecting mitochondrial DNA (mtDNA); 90% of cases harbor the m.3460G>A, m.11778G>A, and m.14484T>C primary mutations. Here, we report and discuss five families with patients affected by symptomatic LHON, in which we found five novel mtDNA variants. Remarkably, these mtDNA variants are located in complex I genes, though without strong deleterious effect on respiration in cellular models: this finding is likely linked to the tissue specificity of LHON. This study observes that in the case of a strong clinical suspicion of LHON, it is recommended to analyze the whole mtDNA sequence, since new rare mtDNA pathogenic variants causing LHON are increasingly identified.
    Keywords:  LHON; Leber optic atrophy; complex I; mitochondrial respiratory chain; transmitochondrial cybrids
    DOI:  https://doi.org/10.3389/fneur.2021.657317
  6. PLoS Genet. 2021 Jul 02. 17(7): e1009664
    Increased mitochondrial protein import and cardiolipin remodelling upon early mtUPR.
    Daniel Poveda-Huertes, Asli Aras Taskin, Ines Dhaouadi, Lisa Myketin, Adinarayana Marada, Lukas Habernig, Sabrina Büttner, F-Nora Vögtle.
      Mitochondrial defects can cause a variety of human diseases and protective mechanisms exist to maintain mitochondrial functionality. Imbalances in mitochondrial proteostasis trigger a transcriptional program, termed mitochondrial unfolded protein response (mtUPR). However, the temporal sequence of events in mtUPR is unclear and the consequences on mitochondrial protein import are controversial. Here, we have quantitatively analyzed all main import pathways into mitochondria after different time spans of mtUPR induction. Kinetic analyses reveal that protein import into all mitochondrial subcompartments strongly increases early upon mtUPR and that this is accompanied by rapid remodelling of the mitochondrial signature lipid cardiolipin. Genetic inactivation of cardiolipin synthesis precluded stimulation of protein import and compromised cellular fitness. At late stages of mtUPR upon sustained stress, mitochondrial protein import efficiency declined. Our work clarifies the enigma of protein import upon mtUPR and identifies sequential mtUPR stages, in which an early increase in protein biogenesis to restore mitochondrial proteostasis is followed by late stages characterized by a decrease in import capacity upon prolonged stress induction.
    DOI:  https://doi.org/10.1371/journal.pgen.1009664
  7. Nanomedicine. 2021 Jun 24. pii: S1549-9634(21)00065-4. [Epub ahead of print] 102422
    Mitochondrial nanomedicine: Subcellular organelle-specific delivery of molecular medicines.
    Lara Milane, Saket Dolare, Tanjheela Jahan, Mansoor Amiji.
      As mitochondria network together to act as the master sensors and effectors of apoptosis, ATP production, reactive oxygen species management, mitophagy/autophagy, and homeostasis; this organelle is an ideal target for pharmaceutical manipulation. Mitochondrial dysfunction contributes to many diseases, for example, β-amyloid has been shown to interfere with mitochondrial protein import and induce apoptosis in Alzheimer's Disease while some forms of Parkinson's Disease are associated with dysfunctional mitochondrial PINK1 and Parkin proteins. Mitochondrial medicine has applications in the treatment of an array of pathologies from cancer to cardiovascular disease. A challenge of mitochondrial medicine is directing therapies to a sub-cellular target. Nanotechnology based approaches combined with mitochondrial targeting strategies can greatly improve the clinical translation and effectiveness of mitochondrial medicine. This review discusses mitochondrial drug delivery approaches and applications of mitochondrial nanomedicines. Nanomedicine approaches have the potential to drive the success of mitochondrial therapies into the clinic.
    Keywords:  Drug delivery; Mitochondria; Mitochondriotropic; Nanomedicine
    DOI:  https://doi.org/10.1016/j.nano.2021.102422
  8. Membranes (Basel). 2021 Jun 23. pii: 465. [Epub ahead of print]11(7):
    Mitochondrial Cristae Architecture and Functions: Lessons from Minimal Model Systems.
    Frédéric Joubert, Nicolas Puff.
      Mitochondria are known as the powerhouse of eukaryotic cells. Energy production occurs in specific dynamic membrane invaginations in the inner mitochondrial membrane called cristae. Although the integrity of these structures is recognized as a key point for proper mitochondrial function, less is known about the mechanisms at the origin of their plasticity and organization, and how they can influence mitochondria function. Here, we review the studies which question the role of lipid membrane composition based mainly on minimal model systems.
    Keywords:  cardiolipin; cone-shaped lipid asymmetry; cristae; curvature-based sorting; mitochondria; nonbilayer structures
    DOI:  https://doi.org/10.3390/membranes11070465
  9. Life (Basel). 2021 Jun 29. pii: 633. [Epub ahead of print]11(7):
    mtDNA Heteroplasmy: Origin, Detection, Significance, and Evolutionary Consequences.
    Maria-Eleni Parakatselaki, Emmanuel D Ladoukakis.
      Mitochondrial DNA (mtDNA) is predominately uniparentally transmitted. This results in organisms with a single type of mtDNA (homoplasmy), but two or more mtDNA haplotypes have been observed in low frequency in several species (heteroplasmy). In this review, we aim to highlight several aspects of heteroplasmy regarding its origin and its significance on mtDNA function and evolution, which has been progressively recognized in the last several years. Heteroplasmic organisms commonly occur through somatic mutations during an individual's lifetime. They also occur due to leakage of paternal mtDNA, which rarely happens during fertilization. Alternatively, heteroplasmy can be potentially inherited maternally if an egg is already heteroplasmic. Recent advances in sequencing techniques have increased the ability to detect and quantify heteroplasmy and have revealed that mitochondrial DNA copies in the nucleus (NUMTs) can imitate true heteroplasmy. Heteroplasmy can have significant evolutionary consequences on the survival of mtDNA from the accumulation of deleterious mutations and for its coevolution with the nuclear genome. Particularly in humans, heteroplasmy plays an important role in the emergence of mitochondrial diseases and determines the success of the mitochondrial replacement therapy, a recent method that has been developed to cure mitochondrial diseases.
    Keywords:  NUMTs; heteroplasmy; mtDNA; paternal leakage; selection
    DOI:  https://doi.org/10.3390/life11070633
  10. Neurol Sci. 2021 Jun 29.
    Novel biallelic mutations in POLG gene: large deletion and missense variant associated with PEO.
    Yan Lin, Jixiang Du, Wei Wang, Hong Ren, Dandan Zhao, Fuchen Liu, Pengfei Lin, Kunqian Ji, Yuying Zhao, Chuanzhu Yan.
      BACKGROUND: Mitochondrial disorders are clinically heterogeneous diseases associated with impaired oxidative phosphorylation (OXPHOS) activity. POLG, which encodes the DNA polymerase-γ (Polγ) catalytic subunit, is the most commonly mutated nuclear gene associated with mitochondrial disorders.METHODS: We carried out whole-exome sequencing (WES) to identify the gene associated with progressive external ophthalmoplegia (PEO). We then performed histopathological analyses, assessed mitochondrial biology, and executed functional studies to evaluate the potential pathogenicity of the identified genetic mutations.
    RESULTS: Novel biallelic POLG mutations, including a large deletion mutation (exons 7-21) and a missense variant c.1796C>T (p.Thr599Ile) were detected in the proband. Histopathological analysis of a biopsied muscle sample from this patient revealed the presence of approximately 20% COX-negative fibers. Bioinformatics analyses confirmed that the detected mutations were pathogenic. Furthermore, levels of mitochondrial complex I, II, and IV subunit protein expressions were found to be decreased in the proband, and marked impairment of mitochondrial respiration was evident in cells harboring these mutations.
    CONCLUSION: This study expands the spectrum of known POLG variants associated with PEO and advances current understanding regarding the structural and functional impacts of these mutations.
    Keywords:  Large deletion; Missense variant; Mitochondrial disease; PEO; POLG
    DOI:  https://doi.org/10.1007/s10072-021-05380-2
  11. Int J Mol Sci. 2021 Jun 23. pii: 6733. [Epub ahead of print]22(13):
    The Role of Mitochondrial Mutations and Chronic Inflammation in Diabetes.
    Siarhei A Dabravolski, Varvara A Orekhova, Mirza S Baig, Evgeny E Bezsonov, Antonina V Starodubova, Tatyana V Popkova, Alexander N Orekhov.
      Diabetes mellitus and related disorders significantly contribute to morbidity and mortality worldwide. Despite the advances in the current therapeutic methods, further development of anti-diabetic therapies is necessary. Mitochondrial dysfunction is known to be implicated in diabetes development. Moreover, specific types of mitochondrial diabetes have been discovered, such as MIDD (maternally inherited diabetes and deafness) and DAD (diabetes and Deafness). Hereditary mitochondrial disorders are caused by certain mutations in the mitochondrial DNA (mtDNA), which encodes for a substantial part of mitochondrial proteins and mitochondrial tRNA necessary for mitochondrial protein synthesis. Study of mtDNA mutations is challenging because the pathogenic phenotype associated with such mutations depends on the level of its heteroplasmy (proportion of mtDNA copies carrying the mutation) and can be tissue-specific. Nevertheless, modern sequencing methods have allowed describing and characterizing a number of mtDNA mutations associated with human disorders, and the list is constantly growing. In this review, we provide a list of mtDNA mutations associated with diabetes and related disorders and discuss the mechanisms of their involvement in the pathology development.
    Keywords:  MIDD; diabetes; mitochondria; mtDNA mutations; oxidative stress
    DOI:  https://doi.org/10.3390/ijms22136733
  12. Comput Struct Biotechnol J. 2021 ;19 3319-3329
    Strategies for mitochondrial gene editing.
    Xingbo Yang, Jiacheng Jiang, Zongyu Li, Jiayi Liang, Yaozu Xiang.
      Mitochondria, as the energy factory of cells, participate in metabolism processes and play a critical role in the maintenance of human life activities. Mitochondria belong to semi-automatic organelles, which have their own genome different from nuclear genome. Mitochondrial DNA (mtDNA) mutations can cause a series of diseases and threaten human health. However, an effective approach to edit mitochondrial DNA, though long-desired, is lacking. In recent years, gene editing technologies, represented by restriction endonucleases (RE) technology, zinc finger nuclease (ZFN) technology, transcription activator-like effector nuclease (TALEN) technology, CRISPR system and pAgo-based system have been comprehensively explored, but the application of these technologies in mitochondrial gene editing is still to be explored and optimized. The present study highlights the progress and limitations of current mitochondrial gene editing technologies and approaches, and provides insights for development of novel strategies for future attempts.
    Keywords:  Gene editing; Mitochondria; mtDNA
    DOI:  https://doi.org/10.1016/j.csbj.2021.06.003
  13. Int J Mol Sci. 2021 Jun 10. pii: 6263. [Epub ahead of print]22(12):
    Quantifying Mitochondrial Dynamics in Patient Fibroblasts with Multiple Developmental Defects and Mitochondrial Disorders.
    Ajibola B Bakare, Julienne Daniel, Joshua Stabach, Anapaula Rojas, Austin Bell, Brooke Henry, Shilpa Iyer.
      Mitochondria are dynamic organelles that undergo rounds of fission and fusion and exhibit a wide range of morphologies that contribute to the regulation of different signaling pathways and various cellular functions. It is important to understand the differences between mitochondrial structure in health and disease so that therapies can be developed to maintain the homeostatic balance of mitochondrial dynamics. Mitochondrial disorders are multisystemic and characterized by complex and variable clinical pathologies. The dynamics of mitochondria in mitochondrial disorders is thus worthy of investigation. Therefore, in this study, we performed a comprehensive analysis of mitochondrial dynamics in ten patient-derived fibroblasts containing different mutations and deletions associated with various mitochondrial disorders. Our results suggest that the most predominant morphological signature for mitochondria in the diseased state is fragmentation, with eight out of the ten cell lines exhibiting characteristics consistent with fragmented mitochondria. To our knowledge, this is the first comprehensive study that quantifies mitochondrial dynamics in cell lines with a wide array of developmental and mitochondrial disorders. A more thorough analysis of the correlations between mitochondrial dynamics, mitochondrial genome perturbations, and bioenergetic dysfunction will aid in identifying unique morphological signatures of various mitochondrial disorders in the future.
    Keywords:  mitochondrial disorders; mitochondrial dynamics; mitochondrial fission; mitochondrial fusion; mitochondrial membrane potential; mitochondrial morphology
    DOI:  https://doi.org/10.3390/ijms22126263
  14. Biology (Basel). 2021 Jun 23. pii: 572. [Epub ahead of print]10(7):
    Mitochondrial Protein Abundance Gradients Require the Distribution of Separated Mitochondria.
    Franziska Bollmann, Jan-Niklas Dohrke, Christian A Wurm, Daniel C Jans, Stefan Jakobs.
      Mitochondria are highly dynamic organelles that interchange their contents mediated by fission and fusion. However, it has previously been shown that the mitochondria of cultured human epithelial cells exhibit a gradient in the relative abundance of several proteins, with the perinuclear mitochondria generally exhibiting a higher protein abundance than the peripheral mitochondria. The molecular mechanisms that are required for the establishment and the maintenance of such inner-cellular mitochondrial protein abundance gradients are unknown. We verified the existence of inner-cellular gradients in the abundance of clusters of the mitochondrial outer membrane protein Tom20 in the mitochondria of kidney epithelial cells from an African green monkey (Vero cells) using STED nanoscopy and confocal microscopy. We found that the Tom20 gradients are established immediately after cell division and require the presence of microtubules. Furthermore, the gradients are abrogated in hyperfused mitochondrial networks. Our results suggest that inner-cellular protein abundance gradients from the perinuclear to the peripheral mitochondria are established by the trafficking of individual mitochondria to their respective cellular destination.
    Keywords:  image analysis; inner-cellular heterogeneity; nanoscopy; protein distribution; super-resolution microscopy
    DOI:  https://doi.org/10.3390/biology10070572
  15. Front Genet. 2021 ;12 664278
    Polymerase Gamma Mitochondrial DNA Depletion Syndrome Initially Presenting as Disproportionate Respiratory Distress in a Moderately Premature Neonate: A Case Report.
    Andrew D Franklin, Bimal P Chaudhari, Daniel C Koboldt, Kerri Z Machut.
      A 32-week premature infant presented with respiratory failure, later progressing to pulmonary hypertension (PH), liver failure, lactic acidosis, and encephalopathy. Using exome sequencing, this patient was diagnosed with a rare Polymerase Gamma (POLG)-related mitochondrial DNA (mtDNA) depletion syndrome. This case demonstrates that expanding the differential to uncommon diagnoses is important for complex infants, even in premature neonates whose condition may be explained partially by their gestational age (GA). It also shows that patients with complex neonatal diseases with significant family history may benefit from exome sequencing for diagnosis.
    Keywords:  case report; mitochondria DNA depletion; polymerase gamma; pulmonary hypertension; whole exome sequencing
    DOI:  https://doi.org/10.3389/fgene.2021.664278
  16. Cells. 2021 Jun 05. pii: 1402. [Epub ahead of print]10(6):
    Neuroprotection in Glaucoma: NAD+/NADH Redox State as a Potential Biomarker and Therapeutic Target.
    Bledi Petriti, Pete A Williams, Gerassimos Lascaratos, Kai-Yin Chau, David F Garway-Heath.
      Glaucoma is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with age and the level of intraocular pressure (IOP). IOP reduction is currently the only therapeutic modality shown to slow glaucoma progression. However, patients still lose vision despite best treatment, suggesting that other factors confer susceptibility. Several studies indicate that mitochondrial function may underlie both susceptibility and resistance to developing glaucoma. Mitochondria meet high energy demand, in the form of ATP, that is required for the maintenance of optimum retinal ganglion cell (RGC) function. Reduced nicotinamide adenine dinucleotide (NAD+) levels have been closely correlated to mitochondrial dysfunction and have been implicated in several neurodegenerative diseases including glaucoma. NAD+ is at the centre of various metabolic reactions culminating in ATP production-essential for RGC function. In this review we present various pathways that influence the NAD+(H) redox state, affecting mitochondrial function and making RGCs susceptible to degeneration. Such disruptions of the NAD+(H) redox state are generalised and not solely induced in RGCs because of high IOP. This places the NAD+(H) redox state as a potential systemic biomarker for glaucoma susceptibility and progression; a hypothesis which may be tested in clinical trials and then translated to clinical practice.
    Keywords:  ATP; NAD+/NADH redox state; glaucoma; mitochondrial dysfunction; neurodegenerative disease; nicotinamide adenine dinucleotide (NAD+); retinal ganglion cell (RGC)
    DOI:  https://doi.org/10.3390/cells10061402
  17. EMBO J. 2021 Jun 30. e107913
    Increased levels of mitochondrial import factor Mia40 prevent the aggregation of polyQ proteins in the cytosol.
    Anna M Schlagowski, Katharina Knöringer, Sandrine Morlot, Ana Sánchez Vicente, Tamara Flohr, Lena Krämer, Felix Boos, Nabeel Khalid, Sheraz Ahmed, Jana Schramm, Lena M Murschall, Per Haberkant, Frank Stein, Jan Riemer, Benedikt Westermann, Ralf J Braun, Konstanze F Winklhofer, Gilles Charvin, Johannes M Herrmann.
      The formation of protein aggregates is a hallmark of neurodegenerative diseases. Observations on patient samples and model systems demonstrated links between aggregate formation and declining mitochondrial functionality, but causalities remain unclear. We used Saccharomyces cerevisiae to analyze how mitochondrial processes regulate the behavior of aggregation-prone polyQ protein derived from human huntingtin. Expression of Q97-GFP rapidly led to insoluble cytosolic aggregates and cell death. Although aggregation impaired mitochondrial respiration only slightly, it considerably interfered with the import of mitochondrial precursor proteins. Mutants in the import component Mia40 were hypersensitive to Q97-GFP, whereas Mia40 overexpression strongly suppressed the formation of toxic Q97-GFP aggregates both in yeast and in human cells. Based on these observations, we propose that the post-translational import of mitochondrial precursor proteins into mitochondria competes with aggregation-prone cytosolic proteins for chaperones and proteasome capacity. Mia40 regulates this competition as it has a rate-limiting role in mitochondrial protein import. Therefore, Mia40 is a dynamic regulator in mitochondrial biogenesis that can be exploited to stabilize cytosolic proteostasis.
    Keywords:  Mia40; huntingtin; mitochondria; protein aggregation; protein translocation
    DOI:  https://doi.org/10.15252/embj.2021107913
  18. Int J Mol Sci. 2021 Jun 16. pii: 6447. [Epub ahead of print]22(12):
    Therapy Prospects for Mitochondrial DNA Maintenance Disorders.
    Javier Ramón, Ferran Vila-Julià, David Molina-Granada, Miguel Molina-Berenguer, Maria Jesús Melià, Elena García-Arumí, Javier Torres-Torronteras, Yolanda Cámara, Ramon Martí.
      Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.
    Keywords:  depletion; gene therapy; mitochondria; mtDNA; multiple deletions; nucleoside; replication; therapy
    DOI:  https://doi.org/10.3390/ijms22126447
  19. Cancers (Basel). 2021 Jun 12. pii: 2956. [Epub ahead of print]13(12):
    Mitochondrial O-GlcNAc Transferase Interacts with and Modifies Many Proteins and Its Up-Regulation Affects Mitochondrial Function and Cellular Energy Homeostasis.
    Paweł Jóźwiak, Piotr Ciesielski, Piotr K Zakrzewski, Karolina Kozal, Joanna Oracz, Grażyna Budryn, Dorota Żyżelewicz, Stéphanie Flament, Anne-Sophie Vercoutter-Edouart, Fabrice Bray, Tony Lefebvre, Anna Krześlak.
      O-GlcNAcylation is a cell glucose sensor. The addition of O-GlcNAc moieties to target protein is catalyzed by the O-Linked N-acetylglucosamine transferase (OGT). OGT is encoded by a single gene that yields differentially spliced OGT isoforms. One of them is targeted to mitochondria (mOGT). Although the impact of O-GlcNAcylation on cancer cells biology is well documented, mOGT's role remains poorly investigated. We performed studies using breast cancer cells with up-regulated mOGT or its catalytic inactive mutant to identify proteins specifically modified by mOGT. Proteomic approaches included isolation of mOGT protein partners and O-GlcNAcylated proteins from mitochondria-enriched fraction followed by their analysis by mass spectrometry. Moreover, we analyzed the impact of mOGT dysregulation on mitochondrial activity and cellular metabolism using a variety of biochemical assays. We found that mitochondrial OGT expression is glucose-dependent. Elevated mOGT expression affected the mitochondrial transmembrane potential and increased intramitochondrial ROS generation. Moreover, mOGT up-regulation caused a decrease in cellular ATP level. We identified many mitochondrial proteins as mOGT substrates. Most of these proteins are localized in the mitochondrial matrix and the inner mitochondrial membrane and participate in mitochondrial respiration, fatty acid metabolism, transport, translation, apoptosis, and mtDNA processes. Our findings suggest that mOGT interacts with and modifies many mitochondrial proteins, and its dysregulation affects cellular bioenergetics and mitochondria function.
    Keywords:  O-GlcNAc; breast cancer; energy metabolism; glucose; mOGT; mitochondria
    DOI:  https://doi.org/10.3390/cancers13122956
  20. Int J Mol Sci. 2021 Jun 04. pii: 6085. [Epub ahead of print]22(11):
    The Mystery of Extramitochondrial Proteins Lysine Succinylation.
    Christos Chinopoulos.
      Lysine succinylation is a post-translational modification which alters protein function in both physiological and pathological processes. Mindful that it requires succinyl-CoA, a metabolite formed within the mitochondrial matrix that cannot permeate the inner mitochondrial membrane, the question arises as to how there can be succinylation of proteins outside mitochondria. The present mini-review examines pathways participating in peroxisomal fatty acid oxidation that lead to succinyl-CoA production, potentially supporting succinylation of extramitochondrial proteins. Furthermore, the influence of the mitochondrial status on cytosolic NAD+ availability affecting the activity of cytosolic SIRT5 iso1 and iso4-in turn regulating cytosolic protein lysine succinylations-is presented. Finally, the discovery that glia in the adult human brain lack subunits of both alpha-ketoglutarate dehydrogenase complex and succinate-CoA ligase-thus being unable to produce succinyl-CoA in the matrix-and yet exhibit robust pancellular lysine succinylation, is highlighted.
    Keywords:  fatty acid oxidation; ketoglutarate dehydrogenase complex; lysine; peroxisomes; post-translational modification; succinyl-CoA
    DOI:  https://doi.org/10.3390/ijms22116085
  21. Mol Genet Metab. 2021 Jun 24. pii: S1096-7192(21)00736-8. [Epub ahead of print]
    Prospective diagnosis of MT-ATP6-related mitochondrial disease by newborn screening.
    Ryan H Peretz, Nicholas Ah Mew, Hilary J Vernon, Rebecca D Ganetzky.
      Elevated citrulline and C5-OH levels are reported as part of the newborn screening of core and secondary disorders on the Recommended Uniform Screening Panel (RUSP). Additionally, some state laboratory newborn screening programs report low citrulline levels, which may be observed in proximal urea cycle disorders. We report six patients who were found on newborn screening to have low citrulline and/or elevated C5-OH levels in whom confirmatory testing showed the combination of these two abnormal analytes. Mitochondrial sequencing revealed known pathogenic variants in MT-ATP6 at high heteroplasmy levels in all cases. MT-ATP6 at these heteroplasmy levels is associated with Leigh syndrome, a progressive neurodegenerative disease. Patients were treated with supplemental citrulline and, in some cases, mitochondrial cofactor therapy. These six patients have not experienced metabolic crises or developmental regression, and early diagnosis and management may help prevent the neurological sequelae of Leigh syndrome. The affected mothers and siblings are asymptomatic or paucisymptomatic (e.g intellectual disability, depression, migraines, obsessive-compulsive disorder, and poor balance) despite high heteroplasmy or apparent homoplasmy of the familial variant, thus expanding the clinical spectrum seen in pathogenic variants of MT-ATP6. Confirmatory plasma amino acid analysis and acylcarnitine profiling should be ordered in a patient with either low citrulline and/or elevated C5-OH, as this combination appears specific for pathogenic variants in MT-ATP6.
    Keywords:  Acylcarnitine; Amino acids; Citrulline; Leigh syndrome; Mitochondrial disease; Newborn screening
    DOI:  https://doi.org/10.1016/j.ymgme.2021.06.007
  22. Polymers (Basel). 2021 Jun 01. pii: 1836. [Epub ahead of print]13(11):
    Development of Peptide-Based Nanoparticles for Mitochondrial Plasmid DNA Delivery.
    Rúben Faria, Eric Vivés, Prisca Boisguerin, Angela Sousa, Diana Costa.
      A mitochondrion is a cellular organelle able to produce cellular energy in the form of adenosine triphosphate (ATP). As in the nucleus, mitochondria contain their own genome: the mitochondrial DNA (mtDNA). This genome is particularly susceptible to mutations that are at the basis of a multitude of disorders, especially those affecting the heart, the central nervous system and muscles. Conventional clinical practice applied to mitochondrial diseases is very limited and ineffective; a clear need for innovative therapies is demonstrated. Gene therapy seems to be a promising approach. The use of mitochondrial DNA as a therapeutic, optimized by peptide-based complexes with mitochondrial targeting, can be seen as a powerful tool in the reestablishment of normal mitochondrial function. In line with this requirement, in this work and for the first time, a mitochondrial-targeting sequence (MTS) has been incorporated into previously researched peptides, to confer on them a targeting ability. These peptides were then considered to complex a plasmid DNA (pDNA) which contains the mitochondrial gene ND1 (mitochondrially encoded NADH dehydrogenase 1 protein), aiming at the formation of peptide-based nanoparticles. Currently, the ND1 plasmid is one of the most advanced bioengineered vectors for conducting research on mitochondrial gene expression. The formed complexes were characterized in terms of pDNA complexation capacity, morphology, size, surface charge and cytotoxic profile. These data revealed that the developed carriers possess suitable properties for pDNA delivery. Furthermore, in vitro studies illustrated the mitochondrial targeting ability of the novel peptide/pDNA complexes. A comparison between the different complexes revealed the most promising ones that complex pDNA and target mitochondria. This may contribute to the optimization of peptide-based non-viral systems to target mitochondria, instigating progress in mitochondrial gene therapy.
    Keywords:  biocompatibility; cell-penetrating peptides; mitochondria targeting; mitochondrial DNA diseases; nano-delivery systems; plasmid DNA
    DOI:  https://doi.org/10.3390/polym13111836
  23. Curr Opin Struct Biol. 2021 Jun 29. pii: S0959-440X(21)00079-8. [Epub ahead of print]71 27-35
    Structural perspectives on H2S homeostasis.
    Aaron P Landry, Joseph Roman, Ruma Banerjee.
      The enzymes involved in H2S homeostasis regulate its production from sulfur-containing amino acids and its oxidation to thiosulfate and sulfate. Two gatekeepers in this homeostatic circuit are cystathionine beta-synthase, which commits homocysteine to cysteine, and sulfide quinone oxidoreductase, which commits H2S to oxidation via a mitochondrial pathway. Inborn errors at either locus affect sulfur metabolism, increasing homocysteine-derived H2S synthesis in the case of CBS deficiency and reducing complex IV activity in the case of SQOR deficiency. In this review, we focus on structural perspectives on the reaction mechanisms and regulation of these two enzymes, which are key to understanding H2S homeostasis in health and its dysregulation and potential targeting in disease.
    DOI:  https://doi.org/10.1016/j.sbi.2021.05.010
  24. Int J Mol Sci. 2021 Jun 29. pii: 7030. [Epub ahead of print]22(13):
    Evidence for the Role of Mitochondrial DNA Release in the Inflammatory Response in Neurological Disorders.
    Gonzalo E Moya, Phillip D Rivera, Kristin E Dittenhafer-Reed.
      Mitochondria are regarded as the metabolic centers of cells and are integral in many other cell processes, including the immune response. Each mitochondrion contains numerous copies of mitochondrial DNA (mtDNA), a small, circular, and bacterial-like DNA. In response to cellular damage or stress, mtDNA can be released from the mitochondrion and trigger immune and inflammatory responses. mtDNA release into the cytosol or bloodstream can occur as a response to hypoxia, sepsis, traumatic injury, excitatory cytotoxicity, or drastic mitochondrial membrane potential changes, some of which are hallmarks of neurodegenerative and mood disorders. Released mtDNA can mediate inflammatory responses observed in many neurological and mood disorders by driving the expression of inflammatory cytokines and the interferon response system. The current understanding of the role of mtDNA release in affective mood disorders and neurodegenerative diseases will be discussed.
    Keywords:  inflammation; mitochondria; mitochondrial DNA (mtDNA); neurodegenerative disease; neuropsychiatric disorder; reactive oxygen species (ROS)
    DOI:  https://doi.org/10.3390/ijms22137030
  25. Elife. 2021 Jun 30. pii: e65215. [Epub ahead of print]10
    Miro1-dependent mitochondrial dynamics in parvalbumin Interneurons.
    Georgina Kontou, Pantelis Antonoudiou, Marina Podpolny, Blanka R Szulc, I Lorena Arancibia-Carcamo, Nathalie F Higgs, Guillermo Lopez-Domenech, Patricia C Salinas, Edward Mann, Josef T Kittler.
      The spatiotemporal distribution of mitochondria is crucial for precise ATP provision and calcium buffering required to support neuronal signaling. Fast-spiking GABAergic interneurons expressing parvalbumin (PV) have a high mitochondrial content reflecting their large energy utilization. The importance for correct trafficking and precise mitochondrial positioning remains poorly elucidated in inhibitory neurons. Miro1 is a Ca²⁺-sensing adaptor protein that links mitochondria to the trafficking apparatus, for their microtubule-dependent transport along axons and dendrites, in order to meet the metabolic and Ca2+-buffering requirements of the cell. Here, we explore the role of Miro1 in parvalbumin interneurons and how changes in mitochondrial trafficking could alter network activity in the mouse brain. By employing live and fixed imaging, we found that the impairments in Miro1-directed trafficking in PV+ interneurons altered their mitochondrial distribution and axonal arborization while PV+ interneuron mediated inhibition remained intact. These changes were accompanied by an increase in the ex vivo hippocampal γ-oscillation (30 - 80 Hz) frequency and promoted anxiolysis. Our findings show that precise regulation of mitochondrial dynamics in PV+ interneurons is crucial for proper neuronal signaling and network synchronization.
    Keywords:  cell biology; mouse; neuroscience
    DOI:  https://doi.org/10.7554/eLife.65215
  26. Lab Anim (NY). 2021 07;50(7): 167
    Innate immunity in mutator mice.
    Ellen P Neff.
      
    DOI:  https://doi.org/10.1038/s41684-021-00809-9
  27. Int J Mol Sci. 2021 Jun 17. pii: 6524. [Epub ahead of print]22(12):
    TAT-Conjugated NDUFS8 Can Be Transduced into Mitochondria in a Membrane-Potential-Independent Manner and Rescue Complex I Deficiency.
    Bo-Yu Lin, Gui-Teng Zheng, Kai-Wen Teng, Juan-Yu Chang, Chao-Chang Lee, Pin-Chao Liao, Mou-Chieh Kao.
      NADH dehydrogenase (ubiquinone) Fe-S protein 8 (NDUFS8) is a nuclear-encoded core subunit of human mitochondrial complex I. Defects in NDUFS8 are associated with Leigh syndrome and encephalomyopathy. Cell-penetrating peptide derived from the HIV-1 transactivator of transcription protein (TAT) has been successfully applied as a carrier to bring fusion proteins into cells without compromising the biological function of the cargoes. In this study, we developed a TAT-mediated protein transduction system to rescue complex I deficiency caused by NDUFS8 defects. Two fusion proteins (TAT-NDUFS8 and NDUFS8-TAT) were exogenously expressed and purified from Escherichia coli for transduction of human cells. In addition, similar constructs were generated and used in transfection studies for comparison. The results showed that both exogenous TAT-NDUFS8 and NDUFS8-TAT were delivered into mitochondria and correctly processed. Interestingly, the mitochondrial import of TAT-containing NDUFS8 was independent of mitochondrial membrane potential. Treatment with TAT-NDUFS8 not only significantly improved the assembly of complex I in an NDUFS8-deficient cell line, but also partially rescued complex I functions both in the in-gel activity assay and the oxygen consumption assay. Our current findings suggest the considerable potential of applying the TAT-mediated protein transduction system for treatment of complex I deficiency.
    Keywords:  HIV-1 transactivator of transcription peptide (TAT); NDUFS8; complex I; enzyme replacement therapy; mitochondria; mitochondrial membrane potential; mitochondrial targeting sequence; protein transduction domain
    DOI:  https://doi.org/10.3390/ijms22126524
  28. J Appl Physiol (1985). 2021 Jul 01.
    Mechanisms of the effect of oxidative phosphorylation deficiencies on the skeletal muscle bioenergetic system in patients with mitochondrial myopathies.
    Bernard Korzeniewski.
      Simulations carried out using a previously-developed model of the skeletal muscle bioenergetic system, involving the "Pi double-threshold" mechanism of muscle fatigue, lead to the conclusion that a decrease in the oxidative phosphorylation (OXPHOS) activity, caused by mutations in mitochondrial or nuclear DNA, is the main mechanism underlying the changes in the kinetic properties of the system in mitochondrial myopathies (MM). These changes generally involve the very-heavy-exercise-like behavior and exercise termination because of fatigue at low work intensities. In particular, a sufficiently large (at a given work intensity) decrease in OXPHOS activity leads to slowing of the primary phase II of the V̇O2 on-kinetics, decrease in V̇O2max, appearance of the slow component of the V̇O2 on-kinetics, exercise intolerance and lactic acidosis at relatively low power outputs encountered in experimental studies in MM patients. Thus, the "Pi double-threshold" mechanism of muscle fatigue is able to account, at least semi-quantitatively, for various kinetic effects of inborn OXPHOS deficiencies of the skeletal muscle bioenergetic system. Exercise can be potentially lengthened and V̇O2max elevated in MM patients through an increase in peak Pi (Pipeak), at which exercise is terminated because of fatigue. Generally, a mechanism underlying the kinetic effects of OXPHOS deficiencies on the skeletal muscle bioenergetic system in MM is proposed that was absent in the literature.
    Keywords:  OXPHOS deficiencies; V̇O2 on-kinetics; mitochondrial myopathies; slow component
    DOI:  https://doi.org/10.1152/japplphysiol.00196.2021
  29. Cells. 2021 Jun 25. pii: 1593. [Epub ahead of print]10(7):
    The Influence of Mitochondrial Dynamics and Function on Retinal Ganglion Cell Susceptibility in Optic Nerve Disease.
    Nicole A Muench, Sonia Patel, Margaret E Maes, Ryan J Donahue, Akihiro Ikeda, Robert W Nickells.
      The important roles of mitochondrial function and dysfunction in the process of neurodegeneration are widely acknowledged. Retinal ganglion cells (RGCs) appear to be a highly vulnerable neuronal cell type in the central nervous system with respect to mitochondrial dysfunction but the actual reasons for this are still incompletely understood. These cells have a unique circumstance where unmyelinated axons must bend nearly 90° to exit the eye and then cross a translaminar pressure gradient before becoming myelinated in the optic nerve. This region, the optic nerve head, contains some of the highest density of mitochondria present in these cells. Glaucoma represents a perfect storm of events occurring at this location, with a combination of changes in the translaminar pressure gradient and reassignment of the metabolic support functions of supporting glia, which appears to apply increased metabolic stress to the RGC axons leading to a failure of axonal transport mechanisms. However, RGCs themselves are also extremely sensitive to genetic mutations, particularly in genes affecting mitochondrial dynamics and mitochondrial clearance. These mutations, which systemically affect the mitochondria in every cell, often lead to an optic neuropathy as the sole pathologic defect in affected patients. This review summarizes knowledge of mitochondrial structure and function, the known energy demands of neurons in general, and places these in the context of normal and pathological characteristics of mitochondria attributed to RGCs.
    Keywords:  dominant optic atrophy; glaucoma; metabolism; mitochondria; neurodegeneration; optic nerve; retinal ganglion cells
    DOI:  https://doi.org/10.3390/cells10071593
  30. J Nutr. 2021 Jun 30. pii: nxab193. [Epub ahead of print]
    NAD+-Precursor Supplementation With L-Tryptophan, Nicotinic Acid, and Nicotinamide Does Not Affect Mitochondrial Function or Skeletal Muscle Function in Physically Compromised Older Adults.
    N J Connell, L Grevendonk, C E Fealy, E Moonen-Kornips, Y M H Bruls, V B Schrauwen-Hinderling, J de Vogel, R Hageman, J Geurts, R Zapata-Perez, R H Houtkooper, B Havekes, J Hoeks, P Schrauwen.
      BACKGROUND: Boosting NAD+ via supplementation with niacin equivalents has been proposed as a potential modality capable of promoting healthy aging and negating age-dependent declines of skeletal muscle mass and function.OBJECTIVES: We investigated the efficacy of NAD+-precursor supplementation (tryptophan, nicotinic acid, and nicotinamide) on skeletal muscle mitochondrial function in physically compromised older adults.
    METHODS: A randomized, double-blind, controlled trial was conducted in 14 (female/male: 4/10) community-dwelling, older adults with impaired physical function [age, 72.9 ± 4.0 years; BMI, 25.2 ± 2.3 kg/m2]. Participants were supplemented with 207.5 mg niacin equivalents/day [intervention (INT)] and a control product (CON) that did not contain niacin equivalents, each for 32 days. The primary outcomes tested were mitochondrial oxidative capacity and exercise efficiency, analyzed by means of paired Student's t-tests. Secondary outcomes, such as NAD+ concentrations, were analyzed accordingly.
    RESULTS: Following supplementation, skeletal muscle NAD+ concentrations [7.5 ± 1.9 compared with 7.9 ± 1.6 AU, respectively] in INT compared with CON conditions were not significantly different compared to the control condition, whereas skeletal muscle methyl-nicotinamide levels were significantly higher under NAD+-precursor supplementation [INT, 0.098 ± 0.063 compared with CON, 0.025 ± 0.014; P = 0.001], suggesting an increased NAD+ metabolism. Conversely, neither ADP-stimulated [INT, 82.1 ± 19.0 compared with CON, 84.0 ± 19.2; P = 0.716] nor maximally uncoupled mitochondrial respiration [INT, 103.4 ± 30.7 compared with CON, 108.7 ± 33.4; P = 0.495] improved under NAD+-precursor supplementation, nor did net exercise efficiency during the submaximal cycling test [INT, 20.2 ± 2.77 compared with CON, 20.8 ± 2.88; P = 0.342].
    CONCLUSIONS: Our findings are consistent with previous findings on NAD+ efficacy in humans, and we show in community-dwelling, older adults with impaired physical function that NAD+-precursor supplementation through L-tryptophan, nicotinic acid, and nicotinamide does not improve mitochondrial or skeletal muscle function. This study was registered at clinicaltrials.gov as NCT03310034.
    Keywords:  NAD+-precursors; metabolism; mitochondrial function; muscle health; older adults; skeletal muscle
    DOI:  https://doi.org/10.1093/jn/nxab193
  31. Biol Open. 2021 Jun 15. pii: bio058553. [Epub ahead of print]10(6):
    Modulation of mitochondrial nucleoid structure during aging and by mtDNA content in Drosophila.
    Li-Jie Wang, Tian Hsu, Hsiang-Ling Lin, Chi-Yu Fu.
      Mitochondrial DNA (mtDNA) encodes gene products that are essential for oxidative phosphorylation. They organize as higher order nucleoid structures (mtNucleoids) that were shown to be critical for the maintenance of mtDNA stability and integrity. While mtNucleoid structures are associated with cellular health, how they change in situ under physiological maturation and aging requires further investigation. In this study, we investigated the mtNucleoid assembly at an ultrastructural level in situ using the TFAM-Apex2 Drosophila model. We found that smaller and more compact TFAM-nucleoids are populated in the mitochondria of indirect flight muscle of aged flies. Furthermore, mtDNA transcription and replication were cross-regulated in the mtTFB2-knockdown flies as in the mtRNAPol-knockdown flies that resulted in reductions in mtDNA copy numbers and nucleoid-associated TFAM. Overall, our study reveals that the modulation of TFAM-nucleoid structure under physiological aging, which is critically regulated by mtDNA content.
    Keywords:  Mitochondrial DNA; Mitochondrial RNA polymerase (mtRNAPol); Mitochondrial nucleoid; Mitochondrial transcription factor B2 (mtTFB2); Transcription factor A (TFAM)
    DOI:  https://doi.org/10.1242/bio.058553
  32. Curr Biol. 2021 Jun 23. pii: S0960-9822(21)00821-6. [Epub ahead of print]
    Experimental evolution improves mitochondrial genome quality control in Saccharomyces cerevisiae and extends its replicative lifespan.
    Ahmed A A Amine, Chia-Wei Liao, Po-Chen Hsu, Florica J G Opoc, Jun-Yi Leu.
      The mitochondrion is an ancient endosymbiotic organelle that performs many essential functions in eukaryotic cells.1-3 Mitochondrial impairment often results in physiological defects or diseases.2-8 Since most mitochondrial genes have been copied into the nuclear genome during evolution,9 the regulatory and interaction mechanisms between the mitochondrial and nuclear genomes are very complex. Multiple mechanisms, including antioxidant, DNA repair, mitophagy, and mitochondrial biogenesis pathways, have been shown to monitor the quality and quantity of mitochondria.10-12 Nonetheless, it remains unclear if these pathways can be further modified to enhance mitochondrial stability. Previously, experimental evolution has been used to adapt cells to novel growth conditions. By analyzing the resulting evolved populations, insights have been gained into the underlying molecular mechanisms.13 Here, we experimentally evolved yeast cells under conditions that selected for efficient respiration while continuously assaulting the mitochondrial genome (mtDNA) with ethidium bromide (EtBr). We found that the ability to maintain functional mtDNA was enhanced in most of the evolved lines when challenged with mtDNA-damaging reagents. We identified mutations of the mitochondrial NADH dehydrogenase NDE1 in most of the evolved lines, but other pathways are also involved. Finally, we show that cells displaying enhanced mtDNA retention also exhibit a prolonged replicative lifespan. Our work reveals potential evolutionary trajectories by which cells can maintain functional mitochondria in response to mtDNA stress, as well as the physiological implications of such adaptations.
    Keywords:  experimental evolution; mitochondrial DNA; mitochondrial quality control; replicative lifespan; yeast genomics
    DOI:  https://doi.org/10.1016/j.cub.2021.06.026
  33. iScience. 2021 Jun 25. 24(6): 102673
    Mitochondria-targeted hydroxyurea inhibits OXPHOS and induces antiproliferative and immunomodulatory effects.
    Gang Cheng, Micael Hardy, Paytsar Topchyan, Ryan Zander, Peter Volberding, Weiguo Cui, Balaraman Kalyanaraman.
      Hydroxyurea (HU), an FDA-approved drug for treating sickle cell disease, is used as an antitumor drug alone and together with conventional chemotherapeutics or radiation therapy. HU is used primarily to treat myeloproliferative diseases because it inhibits the enzyme ribonucleotide reductase involved in DNA synthesis. The hydroxyl group in HU is considered critical for its antiproliferative and chemotherapeutic effects. Here, we substituted the hydroxyl group in HU with a triphenylphosphonium cation attached to an alkyl group with different chain lengths, forming a new class of mitochondria-targeted HU (Mito-HU). Elongating the alkyl side chain length increased the hydrophobicity of Mito-HUs, inhibition of oxidative phosphorylation, and antiproliferative effects in tumor cells. Both mitochondrial complex I- and complex III-induced oxygen consumption decreased with the increasing hydrophobicity of Mito-HUs. The more hydrophobic Mito-HUs also potently inhibited the monocytic myeloid-derived suppressor cells and suppressive neutrophils, and stimulated T cell response, implicating their potential antitumor immunomodulatory mechanism.
    Keywords:  Biological sciences; Drugs; Immunology; Organic chemistry
    DOI:  https://doi.org/10.1016/j.isci.2021.102673
  34. Am J Physiol Cell Physiol. 2021 06 30.
    Mitochondrial Transplantation in Cardiomyocytes: foundation, methods, and outcomes.
    Paria Ali Pour, Sina Hosseinian, Arash Kheradvar.
      Mitochondrial Transplantation is emerging as a novel cellular biotherapy to alleviate mitochondrial damage and dysfunction. Mitochondria play a crucial role in establishing cellular homeostasis and providing cell with the energy necessary to accomplish its function. Owing to its endosymbiotic origin, mitochondria share many features with their bacterial ancestors. Unlike the nuclear DNA, which is packaged into nucleosomes and protected from adverse environmental effects; mitochondrial DNA are more prone to harsh environmental effects, in particular that of the reactive oxygen species (ROS). Mitochondrial damage and dysfunction are implicated in many diseases ranging from metabolic diseases to cardiovascular and neurodegenerative diseases, among others. While it was once thought that transplantation of mitochondria would not be possible due to its semi-autonomous nature and reliance on the nucleus, recent advances have shown that it is possible to transplant viable functional intact mitochondria from autologous, allogenic, and xenogeneic sources into different cell types. Moreover, current research suggests that the transplantation could positively modulate bioenergetics and improve disease outcome. Mitochondrial transplantation techniques and consequences of transplantation in cardiomyocytes are the theme of this review. First, we outline the different mitochondrial isolation and transfer techniques. Second, we detail the consequences of mitochondrial transplantation in the cardiovascular system, more specifically in the context of cardiomyopathies and ischemia. Lastly, we elaborate our vision on how mitochondrial transplantation may mitigate other cardiac conditions secondary to mitochondrial damage and dysfunction, such as atherosclerosis and ST-elevated myocardial infarction.
    Keywords:  Bioenergetics; Ischemia Reperfusion Injury; Mitochondiral transplantation; Mitochondrial Cardiomyopathy; Mitochondrial Transfer
    DOI:  https://doi.org/10.1152/ajpcell.00152.2021
  35. Int J Mol Sci. 2021 Jun 21. pii: 6634. [Epub ahead of print]22(12):
    Mitochondrial DNA Copy Number and Developmental Origins of Health and Disease (DOHaD).
    Hisanori Fukunaga.
      Mitochondrial dysfunction is known to contribute to mitochondrial diseases, as well as to a variety of aging-based pathologies. Mitochondria have their own genomes (mitochondrial DNA (mtDNA)) and the abnormalities, such as point mutations, deletions, and copy number variations, are involved in mitochondrial dysfunction. In recent years, several epidemiological studies and animal experiments have supported the Developmental Origin of Health and Disease (DOHaD) theory, which states that the environment during fetal life influences the predisposition to disease and the risk of morbidity in adulthood. Mitochondria play a central role in energy production, as well as in various cellular functions, such as apoptosis, lipid metabolism, and calcium metabolism. In terms of the DOHaD theory, mtDNA copy number may be a mediator of health and disease. This paper summarizes the results of recent epidemiological studies on the relationship between environmental factors and mtDNA copy number during pregnancy from the perspective of DOHaD theory. The results of these studies suggest a hypothesis that mtDNA copy number may reflect environmental influences during fetal life and possibly serve as a surrogate marker of health risks in adulthood.
    Keywords:  DOHaD; environmental stress; mitochondrial DNA copy number; pregnancy; risk management
    DOI:  https://doi.org/10.3390/ijms22126634
  36. Endocrinol Diabetes Nutr. 2021 Jun 28. pii: S2530-0164(21)00151-8. [Epub ahead of print]
    Immunonutrition for the acute treatment of MELAS syndrome.
    Elizabeth Pérez-Cruz, Carolina González-Rivera, Luz Del Carmen Gabriela Valencia-Olvera.
      MELAS syndrome (Mitochondrial Encephalopathy, Lactic Acidosis and Stroke-like episodes) is one of the most frequent mitochondrial pathologies. Its diagnosis is based on the classic triad of symptoms its acronym stands for and the presence of ragged red fibres. There is currently no curative therapy for MELAS, and treatment focuses on managing complications that affect specific organs and functions. However, some immunonutrients can be used as a therapeutic alternative in patients with MELAS. We present a scientific literature review accompanied by the clinical case of a patient with dementia and seizures admitted to the intensive care unit.
    Keywords:  Arginina; Arginine; Carnitina; Carnitine; Immunonutrition; Inmunonutrición; MELAS syndrome; Síndrome MELAS
    DOI:  https://doi.org/10.1016/j.endinu.2021.03.004
  37. Neurologist. 2021 Jul 06. 26(4): 143-148
    Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes (MELAS) Syndrome: Frequency, Clinical Features, Imaging, Histopathologic, and Molecular Genetic Findings in a Third-level Health Care Center in Mexico.
    Javier A Galnares-Olalde, Juan C López-Hernández, Edmar O Benitez-Alonso, David J D-O de Montellano, Raúl N May-Mas, María E Briseño-Godínez, Esther Y Pérez-Valdez, Enrique Pérez-Jovel, Francisca Fernández-Valverde, Elizabeth León-Manríquez, Edwin S Vargas-Cañas.
      INTRODUCTION: Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, is a multisystemic entity of mitochondrial inheritance. To date, there is no epidemiological information on MELAS syndrome in Mexico.CASE SERIES: A retrospective, cross-sectional design was employed to collect and analyze the data. The clinical records of patients with mitochondrial cytopathies in the period ranging from January 2018 to March 2020 were reviewed. Patients who met definitive Yatsuga diagnostic criteria for MELAS syndrome were included to describe frequency, clinical, imaging, histopathologic, and molecular studies. Of 56 patients diagnosed with mitochondrial cytopathy, 6 patients met definitive Yatsuga criterion for MELAS (10.7%). The median age at diagnosis was 34 years (30 to 34 y), 2 females and the median time from onset of symptoms at diagnosis 3.5 years (1 to 10 y). The median of the number of stroke-like episodes before the diagnosis was 3 (range, 2 to 3). The main findings in computed tomography were basal ganglia calcifications (33%), whereas in magnetic resonance imaging were a lactate peak in the spectroscopy sequence in 2 patients. Five patients (84%) had red-ragged fibers and phantom fibers in the Cox stain in the muscle biopsy. Four patients (67%) had presence of 3243A>G mutation in the mitochondrial MT-TL1 gene. One patient died because of status epilepticus.
    CONCLUSIONS: MELAS syndrome represents a common diagnostic challenge for clinicians, often delaying definitive diagnosis. It should be suspected in young patients with stroke of undetermined etiology associated with other systemic and neurological features.
    DOI:  https://doi.org/10.1097/NRL.0000000000000331
  38. Metabolites. 2021 Jun 05. pii: 359. [Epub ahead of print]11(6):
    Mitochondria in Myelinating Oligodendrocytes: Slow and Out of Breath?
    Niklas Meyer, Johanne Egge Rinholm.
      Myelin is a lipid-rich membrane that wraps around axons and facilitates rapid action potential propagation. In the brain, myelin is synthesized and maintained by oligodendrocytes. These cells have a high metabolic demand that requires mitochondrial ATP production during the process of myelination, but they rely less on mitochondrial respiration after myelination is complete. Mitochondria change in morphology and distribution during oligodendrocyte development. Furthermore, the morphology and dynamic properties of mitochondria in mature oligodendrocytes seem different from any other brain cell. Here, we first give a brief introduction to oligodendrocyte biology and function. We then review the current knowledge on oligodendrocyte metabolism and discuss how the available data on mitochondrial morphology and mobility as well as transcriptome and proteome studies can shed light on the metabolic properties of oligodendrocytes.
    Keywords:  ATP; glycolysis; metabolism; mitochondria; myelination; oligodendrocyte; oligodendrocyte precursor cell (OPC); oxidative phosphorylation; proteome; transcriptome
    DOI:  https://doi.org/10.3390/metabo11060359
  39. Front Cell Dev Biol. 2021 ;9 698679
    STING1 Promotes Ferroptosis Through MFN1/2-Dependent Mitochondrial Fusion.
    Changfeng Li, Jiao Liu, Wen Hou, Rui Kang, Daolin Tang.
      Ferroptosis is a type of iron-dependent regulated cell death caused by the disruption that occurs when oxidative stress and antioxidant defenses interact, and then driven by lipid peroxidation and subsequent plasma membrane ruptures. The regulation of ferroptosis involves many factors, including the crosstalk between subcellular organelles, such as mitochondria, endoplasmic reticulum (ER), lysosomes, lipid droplets, and peroxisomes. Here, we show that the ER protein STING1 (also known as STING or TMEM173) promotes ferroptosis in human pancreatic cancer cell lines by increasing MFN1/2-dependent mitochondrial fusion, but not mitophagy-mediated mitochondrial removal. The classic ferroptosis inducer erastin, but not sulfasalazine, induces the accumulation of STING1 in the mitochondria, where it binds to MFN1/2 to trigger mitochondrial fusion, leading to subsequent reactive oxygen species production and lipid peroxidation. Consequently, in vitro or xenograft mouse models show that the genetic depletion of STING1 or MFN1/2 (but not the mitophagy regulator PINK1 or PRKN) reduces the sensitivity of pancreatic cancer cells to ferroptosis. These findings not only establish a new mitochondrial fusion-dependent cell death mechanism, but also indicate a potential strategy for enhancing ferroptosis-based therapy.
    Keywords:  MFN1/2; STING1; dynamic; ferroptosis; mitochondria
    DOI:  https://doi.org/10.3389/fcell.2021.698679
  40. Mol Cell. 2021 Jul 01. pii: S1097-2765(21)00402-0. [Epub ahead of print]81(13): 2808-2822.e10
    Translation stress and collided ribosomes are co-activators of cGAS.
    Li Wan, Szymon Juszkiewicz, Daniel Blears, Prashanth Kumar Bajpe, Zhong Han, Peter Faull, Richard Mitter, Aengus Stewart, Ambrosius P Snijders, Ramanujan S Hegde, Jesper Q Svejstrup.
      The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway senses cytosolic DNA and induces interferon-stimulated genes (ISGs) to activate the innate immune system. Here, we report the unexpected discovery that cGAS also senses dysfunctional protein production. Purified ribosomes interact directly with cGAS and stimulate its DNA-dependent activity in vitro. Disruption of the ribosome-associated protein quality control (RQC) pathway, which detects and resolves ribosome collision during translation, results in cGAS-dependent ISG expression and causes re-localization of cGAS from the nucleus to the cytosol. Indeed, cGAS preferentially binds collided ribosomes in vitro, and orthogonal perturbations that result in elevated levels of collided ribosomes and RQC activation cause sub-cellular re-localization of cGAS and ribosome binding in vivo as well. Thus, translation stress potently increases DNA-dependent cGAS activation. These findings have implications for the inflammatory response to viral infection and tumorigenesis, both of which substantially reprogram cellular protein synthesis.
    Keywords:  ASCC3; IRF3; STING; ZNF598; cGAS; innate immunity; interferon signalling; mRNA translation; ribosome collision; ribosome-associated protein quality control
    DOI:  https://doi.org/10.1016/j.molcel.2021.05.018
  41. Int J Mol Sci. 2021 Jun 15. pii: 6396. [Epub ahead of print]22(12):
    Plasma Gelsolin Reinforces the Diagnostic Value of FGF-21 and GDF-15 for Mitochondrial Disorders.
    Ana Peñas, Miguel Fernández-De la Torre, Sara Laine-Menéndez, David Lora, María Illescas, Alberto García-Bartolomé, Montserrat Morales-Conejo, Joaquín Arenas, Miguel A Martín, María Morán, Cristina Domínguez-González, Cristina Ugalde.
      Mitochondrial disorders (MD) comprise a group of heterogeneous clinical disorders for which non-invasive diagnosis remains a challenge. Two protein biomarkers have so far emerged for MD detection, FGF-21 and GDF-15, but the identification of additional biomarkers capable of improving their diagnostic accuracy is highly relevant. Previous studies identified Gelsolin as a regulator of cell survival adaptations triggered by mitochondrial defects. Gelsolin presents a circulating plasma isoform (pGSN), whose altered levels could be a hallmark of mitochondrial dysfunction. Therefore, we investigated the diagnostic performance of pGSN for MD relative to FGF-21 and GDF-15. Using ELISA assays, we quantified plasma levels of pGSN, FGF-21, and GDF-15 in three age- and gender-matched adult cohorts: 60 genetically diagnosed MD patients, 56 healthy donors, and 41 patients with unrelated neuromuscular pathologies (non-MD). Clinical variables and biomarkers' plasma levels were compared between groups. Discrimination ability was calculated using the area under the ROC curve (AUC). Optimal cut-offs and the following diagnostic parameters were determined: sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios, and efficiency. Comprehensive statistical analyses revealed significant discrimination ability for the three biomarkers to classify between MD and healthy individuals, with the best diagnostic performance for the GDF-15/pGSN combination. pGSN and GDF-15 preferentially discriminated between MD and non-MD patients under 50 years, whereas FGF-21 best classified older subjects. Conclusion: pGSN improves the diagnosis accuracy for MD provided by FGF-21 and GDF-15.
    Keywords:  FGF-21; GDF-15; OXPHOS deficiency; biomarkers; mitochondrial disorders; plasma GSN
    DOI:  https://doi.org/10.3390/ijms22126396
  42. Front Mol Biosci. 2021 ;8 671274
    NADH Fluorescence Lifetime Imaging Microscopy Reveals Selective Mitochondrial Dysfunction in Neurons Overexpressing Alzheimer's Disease-Related Proteins.
    Moritz A Niederschweiberer, Patrick M Schaefer, Larry N Singh, Ludwig Lausser, Devyani Bhosale, Raphael Hesse, Enrico Calzia, Hans A Kestler, Angelika Rueck, Douglas C Wallace, Bjoern von Einem, Christine A F von Arnim.
      Alzheimer's disease (AD), the most prevalent form of dementia, affects globally more than 30 million people suffering from cognitive deficits and neuropsychiatric symptoms. Substantial evidence for the involvement of mitochondrial dysfunction in the development and/or progression of AD has been shown in addition to the pathological hallmarks amyloid beta (Aβ) and tau. Still, the selective vulnerability and associated selective mitochondrial dysfunction cannot even be resolved to date. We aimed at optically quantifying mitochondrial function on a single-cell level in primary hippocampal neuron models of AD, unraveling differential involvement of cell and mitochondrial populations in amyloid precursor protein (APP)-associated mitochondrial dysfunction. NADH lifetime imaging is a highly sensitive marker-free method with high spatial resolution. However, deciphering cellular bioenergetics of complex cells like primary neurons has still not succeeded yet. To achieve this, we combined highly sensitive NADH lifetime imaging with respiratory inhibitor treatment, allowing characterization of mitochondrial function down to even the subcellular level in primary neurons. Measuring NADH lifetime of the same neuron before and after respiratory treatment reveals the metabolic delta, which can be taken as a surrogate for cellular redox capacity. Correlating NADH lifetime delta with overexpression strength of Aβ-related proteins on the single-cell level, we could verify the important role of intracellular Aβ-mediated mitochondrial toxicity. Subcellularly, we could demonstrate a higher respiration in neuronal somata in general than dendrites, but a similar impairment of somatic and dendritic mitochondria in our AD models. This illustrates the power of NADH lifetime imaging in revealing mitochondrial function on a single and even subcellular level and its potential to shed light into bioenergetic alterations in neuropsychiatric diseases and beyond.
    Keywords:  Alzheimer’s disease; NADH; amyloid beta; energy metabolism; mitochondria; redox imaging
    DOI:  https://doi.org/10.3389/fmolb.2021.671274
  43. Pharmaceutics. 2021 Jun 16. pii: 893. [Epub ahead of print]13(6):
    Systemic Treatment with Nicotinamide Riboside Is Protective in Two Mouse Models of Retinal Ganglion Cell Damage.
    Xian Zhang, Nan Zhang, Micah A Chrenek, Preston E Girardot, Jiaxing Wang, Jana T Sellers, Eldon E Geisert, Charles Brenner, John M Nickerson, Jeffrey H Boatright, Ying Li.
      Glaucoma etiology often includes retinal ganglion cell (RGC) death associated with elevated intraocular pressure (IOP). However, even when IOP is managed well, disease can progress. It is thus important to develop therapeutic approaches that directly protect RGCs in an IOP-independent manner. Compromised nicotinamide adenine dinucleotide (NAD+) metabolism occurs in neurodegenerative diseases, including models of glaucoma. Here we report testing the protective effects of prophylactically systemically administered nicotinamide riboside (NR), a NAD+ precursor, in a mouse model of acute RGC damage (optic nerve crush (ONC)), and in a chronic model of RGC degeneration (ocular hypertension induced by intracameral injection of microbeads). For both models, treatment enhanced RGC survival, assessed by counting cells in retinal flatmounts immunostained for Brn3a+. In the ONC model, treatment preserved RGC function, as assessed by pattern electroretinogram, and suppressed retinal inflammation, as assessed by immunofluorescence staining of retinal fixed sections for glial fibrillary acidic protein (GFAP). This is the first study to demonstrate that systemic treatment with NR is protective in acute and chronic models of RGC damage. The protection is significant and, considering that NR is highly bioavailable in and well-tolerated by humans, may support the proposition of prospective human subject studies.
    Keywords:  ERG; microbead; neuroprotection; nicotinamide riboside; optic nerve crush; retinal ganglion cell
    DOI:  https://doi.org/10.3390/pharmaceutics13060893
  44. Front Neurol. 2021 ;12 675616
    A Novel Variation in the Mitochondrial Complex I Assembly Factor NDUFAF5 Causes Isolated Bilateral Striatal Necrosis in Childhood.
    Hongyan Bi, Hui Guo, Qianfei Wang, Xiao Zhang, Yaming Zhao, Jimei Li, Weiqin Zhao, Houzhen Tuo, Yongbo Zhang.
      Background: Bilateral striatal necrosis (BSN) is characterized by symmetrical degeneration, predominantly of the caudate and putamen nucleus, in the basal ganglia. It is associated with numerous acquired and hereditary neuro-developmental and motor dysfunction-related pathological conditions. BSN results in high morbidity and mortality among infants and children, and its diagnosis is clinically challenging due to several overlapping disease phenotypes. Therefore, a precise genetic diagnosis is urgently needed for accurate genetic counseling and improved prognostic outcomes as well. Objective: To identify novel missense mutations in the NDUFAF5 gene as a cause of childhood BSN in members of a Chinese family and summarize the clinical characteristics of patients with the NDUFAF5 gene mutations. Methods: This study included a large family living in a remote northwestern area of China. Three siblings developed a neurological disorder characterized by generalized dystonia within the first decade of their lives. Cerebral computed tomography (CT) and magnetic resonance imaging (MRI) showed bilateral lesions of the putamen. Biochemical and genetic approaches were used to identify the cause of BSN. Results: Sequence analysis showed no pathogenic variation in PANK2, SLC25A19, SLC19A3, and NUP62 genes and in the entire mitochondrial genome as well. Whole-exome sequencing revealed compound heterozygous mutations consisting of NDUFAF5:c.425A > C(p.E142A) and c.836T > G (p.M279R). The father, a healthy sister, and a healthy brother of the affected siblings carried the c.836T > G mutation, and the mother carried the c.425A > C mutation. These variants were absent in 100 ethnically matched non-BSN controls. In silico analysis demonstrated that the E142A and M279R mutations in NDUFAF5 protein significantly perturbed the normal conformation of the protein due to alterations in the hydrogen bonding patterns around the evolutionarily conserved catalytic domains, leading to its loss of function in the early stage of mitochondrial complex I assembly. Conclusions: We identified a novel compound heterozygous mutation (c.425A > C and c.836T > G) in the NDUFAF5 gene as the potential cause of autosomal recessive childhood BSN, which extended the pathogenic variation spectrum of the NDUFAF5 gene. This study provides substantial evidence for further improvement of genetic counseling and better clinical management of BSN affected individuals.
    Keywords:  NDUFAF5; bilateral striatal necrosis; mitochondrial complex I deficiency; novel variation; whole-exome sequencing
    DOI:  https://doi.org/10.3389/fneur.2021.675616
  45. Biology (Basel). 2021 Jun 05. pii: 503. [Epub ahead of print]10(6):
    Discovering Cellular Mitochondrial Heteroplasmy Heterogeneity with Single Cell RNA and ATAC Sequencing.
    Aidan S Marshall, Nick S Jones.
      Next-generation sequencing technologies have revolutionised the study of biological systems by enabling the examination of a broad range of tissues. Its application to single-cell genomics has generated a dynamic and evolving field with a vast amount of research highlighting heterogeneity in transcriptional, genetic and epigenomic state between cells. However, compared to these aspects of cellular heterogeneity, relatively little has been gleaned from single-cell datasets regarding cellular mitochondrial heterogeneity. Single-cell sequencing techniques can provide coverage of the mitochondrial genome which allows researchers to probe heteroplasmies at the level of the single cell, and observe interactions with cellular function. In this review, we give an overview of two popular single-cell modalities-single-cell RNA sequencing and single-cell ATAC sequencing-whose throughput and widespread usage offers researchers the chance to probe heteroplasmy combined with cell state in detailed resolution across thousands of cells. After summarising these technologies in the context of mitochondrial research, we give an overview of recent methods which have used these approaches for discovering mitochondrial heterogeneity. We conclude by highlighting current limitations of these approaches and open problems for future consideration.
    Keywords:  heterogeneity; heteroplasmy; mitochondria; scATAC-seq; scRNA-seq
    DOI:  https://doi.org/10.3390/biology10060503
  46. Nat Biotechnol. 2021 Jun 28.
    Efficient C•G-to-G•C base editors developed using CRISPRi screens, target-library analysis, and machine learning.
    Luke W Koblan, Mandana Arbab, Max W Shen, Jeffrey A Hussmann, Andrew V Anzalone, Jordan L Doman, Gregory A Newby, Dian Yang, Beverly Mok, Joseph M Replogle, Albert Xu, Tyler A Sisley, Jonathan S Weissman, Britt Adamson, David R Liu.
      Programmable C•G-to-G•C base editors (CGBEs) have broad scientific and therapeutic potential, but their editing outcomes have proved difficult to predict and their editing efficiency and product purity are often low. We describe a suite of engineered CGBEs paired with machine learning models to enable efficient, high-purity C•G-to-G•C base editing. We performed a CRISPR interference (CRISPRi) screen targeting DNA repair genes to identify factors that affect C•G-to-G•C editing outcomes and used these insights to develop CGBEs with diverse editing profiles. We characterized ten promising CGBEs on a library of 10,638 genomically integrated target sites in mammalian cells and trained machine learning models that accurately predict the purity and yield of editing outcomes (R = 0.90) using these data. These CGBEs enable correction to the wild-type coding sequence of 546 disease-related transversion single-nucleotide variants (SNVs) with >90% precision (mean 96%) and up to 70% efficiency (mean 14%). Computational prediction of optimal CGBE-single-guide RNA pairs enables high-purity transversion base editing at over fourfold more target sites than achieved using any single CGBE variant.
    DOI:  https://doi.org/10.1038/s41587-021-00938-z
  47. Front Neurol. 2021 ;12 675816
    Epilepsy Associated With Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes.
    Jiaai Li, Wuqiong Zhang, Zhitao Cui, Zhaoran Li, Ting Jiang, Hongmei Meng.
      Objectives: The present study explored the clinical characteristics and prognostic factors of epilepsy in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). Methods: Thirty-four MELAS patients were included in the present study. They were diagnosed by clinical characteristics, genetic testing, muscle biopsy, and retrospective analysis of other clinical data. The patients were divided into three groups according to the effects of treatment after at least 2 years of follow-up. Results: Epilepsy was more common in male MELAS patients than in females (20/14). The age of onset ranged from 0.5 to 57 years, with an average of 22.6 years. Patients with epilepsy and MELAS had various forms of seizures. Focal seizures were the most common type affecting 58.82% of patients, and some patients had multiple types of seizures. The abnormal EEG waves were mainly concentrated in the occipital (69.57%), frontal (65.22%) and temporal lobes (47.83%). Overall, the prognosis of patients with epilepsy and MELAS was poor. Poor prognosis was associated with brain atrophy (P = 0.026), status epilepticus (P < 0.001), and use of anti-seizure medications with high mitochondrial toxicity (P = 0.015). Interpretation: Avoiding the application of anti-seizure medications with high mitochondrial toxicity, controlling seizures more actively and effectively, and delaying the occurrence and progression of brain atrophy as much as possible are particularly important to improve the prognosis of patients with MELAS and epilepsy.
    Keywords:  EEG; MELAS; epilepsy; influencing factors; prognosis
    DOI:  https://doi.org/10.3389/fneur.2021.675816
  48. Oxid Med Cell Longev. 2021 ;2021 3726885
    Protective Effect of Optic Atrophy 1 on Cardiomyocyte Oxidative Stress: Roles of Mitophagy, Mitochondrial Fission, and MAPK/ERK Signaling.
    Yue Wang, Zhihua Han, Zuojun Xu, Junfeng Zhang.
      Myocardial infarction is associated with oxidative stress and mitochondrial damage. However, the regulatory mechanisms underlying cardiomyocyte oxidative stress during myocardial infarction are not fully understood. In the present study, we explored the cardioprotective action of optic atrophy 1- (Opa1-) mediated mitochondrial autophagy (mitophagy) in oxidative stress-challenged cardiomyocytes, with a focus on mitochondrial homeostasis and the MAPK/ERK pathway. Our results demonstrated that overexpression of Opa1 in cultured rat H9C2 cardiomyocytes, a procedure that stimulates mitophagy, attenuates oxidative stress and increases cellular antioxidant capacity. Activation of Opa1-mediated mitophagy suppressed cardiomyocyte apoptosis by downregulating Bax, caspase-9, and caspase-12 and upregulating Bcl-2 and c-IAP. Using mitochondrial tracker staining and a reactive oxygen species indicator, our assays showed that Opa1-mediated mitophagy attenuated mitochondrial fission and reduced ROS production in cardiomyocytes. In addition, we found that inhibition of the MAPK/ERK pathway abolished the antioxidant action of Opa1-mediated mitophagy in these cells. Taken together, our data demonstrate that Opa1-mediated mitophagy protects cardiomyocytes against oxidative stress damage through inhibition of mitochondrial fission and activation of MAPK/ERK signaling. These findings reveal a critical role for Opa1 in the modulation of cardiomyocyte redox balance and suggest a potential target for the treatment of myocardial infarction.
    DOI:  https://doi.org/10.1155/2021/3726885
  49. Front Physiol. 2021 ;12 703458
    Editorial: Autophagy and Mitophagy in Skeletal Muscle Health and Disease.
    Sabah N A Hussain, Marco Sandri, Gilles Gouspillou.
      
    Keywords:  atrophy; autophagy; mitophagy; proteolysis; skeletal muscles; sympathethic nervous system
    DOI:  https://doi.org/10.3389/fphys.2021.703458
  50. Proteomes. 2021 Jun 08. pii: 28. [Epub ahead of print]9(2):
    Advanced Fiber Type-Specific Protein Profiles Derived from Adult Murine Skeletal Muscle.
    Britta Eggers, Karin Schork, Michael Turewicz, Katalin Barkovits, Martin Eisenacher, Rolf Schröder, Christoph S Clemen, Katrin Marcus.
      Skeletal muscle is a heterogeneous tissue consisting of blood vessels, connective tissue, and muscle fibers. The last are highly adaptive and can change their molecular composition depending on external and internal factors, such as exercise, age, and disease. Thus, examination of the skeletal muscles at the fiber type level is essential to detect potential alterations. Therefore, we established a protocol in which myosin heavy chain isoform immunolabeled muscle fibers were laser microdissected and separately investigated by mass spectrometry to develop advanced proteomic profiles of all murine skeletal muscle fiber types. All data are available via ProteomeXchange with the identifier PXD025359. Our in-depth mass spectrometric analysis revealed unique fiber type protein profiles, confirming fiber type-specific metabolic properties and revealing a more versatile function of type IIx fibers. Furthermore, we found that multiple myopathy-associated proteins were enriched in type I and IIa fibers. To further optimize the assignment of fiber types based on the protein profile, we developed a hypothesis-free machine-learning approach, identified a discriminative peptide panel, and confirmed our panel using a public data set.
    Keywords:  fiber types; laser microdissection; neuromuscular disorders; proteomics; skeletal muscle
    DOI:  https://doi.org/10.3390/proteomes9020028
  51. Clin Transl Immunology. 2021 ;10(6): e1304
    Pervasive inflammatory activation in patients with deficiency in very-long-chain acyl-coA dehydrogenase (VLCADD).
    Abbe N Vallejo, Henry J Mroczkowski, Joshua J Michel, Michael Woolford, Harry C Blair, Patricia Griffin, Elizabeth McCracken, Stephanie J Mihalik, Miguel Reyes-Mugica, Jerry Vockley.
      Objectives: Very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a disorder of fatty acid oxidation. Symptoms are managed by dietary supplementation with medium-chain fatty acids that bypass the metabolic block. However, patients remain vulnerable to hospitalisations because of rhabdomyolysis, suggesting pathologic processes other than energy deficit. Since rhabdomyolysis is a self-destructive process that can signal inflammatory/immune cascades, we tested the hypothesis that inflammation is a physiologic dimension of VLCADD.Methods: All subjects (n = 18) underwent informed consent/assent. Plasma cytokine and cytometry analyses were performed. A prospective case analysis was carried out on a patient with recurrent hospitalisation. Health data were extracted from patient medical records.
    Results: Patients showed systemic upregulation of nine inflammatory mediators during symptomatic and asymptomatic periods. There was also overall abundance of immune cells with high intracellular expression of IFNγ, IL-6, MIP-1β (CCL4) and TNFα, and the transcription factors p65-NFκB and STAT1 linked to inflammatory pathways. A case analysis of a patient exhibited already elevated plasma cytokine levels during diagnosis in early infancy, evolving into sustained high systemic levels during recurrent rhabdomyolysis-related hospitalisations. There were corresponding activated leukocytes, with higher intracellular stores of inflammatory molecules in monocytes compared to T cells. Exposure of monocytes to long-chain free fatty acids recapitulated the cytokine signature of patients.
    Conclusion: Pervasive plasma cytokine upregulation and pre-activated immune cells indicate chronic inflammatory state in VLCADD. Thus, there is rationale for practical implementation of clinical assessment of inflammation and/or translational testing, or adoption, of anti-inflammatory intervention(s) for personalised disease management.
    Keywords:  fatty acid oxidation; inflammation; lymphocytes; monocytes; rhabdomyolysis; very‐long‐chain acyl‐CoA dehydrogenase deficiency
    DOI:  https://doi.org/10.1002/cti2.1304
  52. Antioxidants (Basel). 2021 Jun 07. pii: 927. [Epub ahead of print]10(6):
    Coenzyme Q10 Phytosome Formulation Improves CoQ10 Bioavailability and Mitochondrial Functionality in Cultured Cells.
    Nicola Rizzardi, Irene Liparulo, Giorgia Antonelli, Francesca Orsini, Antonella Riva, Christian Bergamini, Romana Fato.
      Coenzyme Q10 (CoQ10) is a lipid-soluble molecule with a dual role: it transfers electrons in the mitochondrial transport chain by promoting the transmembrane potential exploited by the ATPase to synthesize ATP and, in its reduced form, is a membrane antioxidant. Since the high CoQ10 hydrophobicity hinders its bioavailability, several formulations have been developed to facilitate its cellular uptake. In this work, we studied the bioenergetic and antioxidant effects in I407 and H9c2 cells of a CoQ10 phytosome formulation (UBIQSOME®, UBQ). We investigated the cellular and mitochondrial content of CoQ10 and its redox state after incubation with UBQ. We studied different bioenergetic parameters, such as oxygen consumption, ATP content and mitochondrial potential. Moreover, we evaluated the effects of CoQ10 incubation on oxidative stress, membrane lipid peroxidation and ferroptosis and highlighted the connection between the intracellular concentration of CoQ10 and its antioxidant potency. Finally, we focused on the cellular mechanism that regulates UBQ internalization. We showed that the cell lines used in this work share the same uptake mechanism for UBQ, although the intestinal cell line was less efficient. Given the limitations of an in vitro model, the latter result supports that intestinal absorption is a critical step for the oral administration of Coenzyme Q10 formulations.
    Keywords:  ATP; Coenzyme Q10; Ubiqsome®; antioxidant; ferroptosis; mitochondria; phytosome
    DOI:  https://doi.org/10.3390/antiox10060927
  53. Genet Med. 2021 Jun 30.
    Treatment of ARS deficiencies with specific amino acids.
    Gautam Kok, Laura Tseng, Imre F Schene, Monique E Dijsselhof, Gajja Salomons, Marisa I Mendes, Desiree E C Smith, Arnaud Wiedemann, Marie Canton, François Feillet, Tom J de Koning, Megan Boothe, Joy Dean, Rachel Kassel, Elise A Ferreira, Margreet van den Born, Edward E S Nieuwenhuis, Holger Rehmann, Suzanne W J Terheggen-Lagro, Clara D M van Karnebeek, Sabine A Fuchs.
      PURPOSE: Recessive cytosolic aminoacyl-tRNA synthetase (ARS) deficiencies are severe multiorgan diseases, with limited treatment options. By loading transfer RNAs (tRNAs) with their cognate amino acids, ARS are essential for protein translation. However, it remains unknown why ARS deficiencies lead to specific symptoms, especially early life and during infections. We set out to increase pathophysiological insight and improve therapeutic possibilities.METHODS: In fibroblasts from patients with isoleucyl-RS (IARS), leucyl-RS (LARS), phenylalanyl-RS-beta-subunit (FARSB), and seryl-RS (SARS) deficiencies, we investigated aminoacylation activity, thermostability, and sensitivity to ARS-specific amino acid concentrations, and developed personalized treatments.
    RESULTS: Aminoacylation activity was reduced in all patients, and further diminished at 38.5/40 °C (PLARS and PFARSB), consistent with infectious deteriorations. With lower cognate amino acid concentrations, patient fibroblast growth was severely affected. To prevent local and/or temporal deficiencies, we treated patients with corresponding amino acids (follow-up: 1/2-2 2/3rd years), and intensified treatment during infections. All patients showed beneficial treatment effects, most strikingly in growth (without tube feeding), head circumference, development, coping with infections, and oxygen dependency.
    CONCLUSION: For these four ARS deficiencies, we observed a common disease mechanism of episodic insufficient aminoacylation to meet translational demands and illustrate the power of amino acid supplementation for the expanding ARS patient group. Moreover, we provide a strategy for personalized preclinical functional evaluation.
    DOI:  https://doi.org/10.1038/s41436-021-01249-z
  54. Metabolites. 2021 Jun 14. pii: 385. [Epub ahead of print]11(6):
    Coenzyme Q Biosynthesis: An Update on the Origins of the Benzenoid Ring and Discovery of New Ring Precursors.
    Lucía Fernández-Del-Río, Catherine F Clarke.
      Coenzyme Q (ubiquinone or CoQ) is a conserved polyprenylated lipid essential for mitochondrial respiration. CoQ is composed of a redox-active benzoquinone ring and a long polyisoprenyl tail that serves as a membrane anchor. A classic pathway leading to CoQ biosynthesis employs 4-hydroxybenzoic acid (4HB). Recent studies with stable isotopes in E. coli, yeast, and plant and animal cells have identified CoQ intermediates and new metabolic pathways that produce 4HB. Stable isotope labeling has identified para-aminobenzoic acid as an alternate ring precursor of yeast CoQ biosynthesis, as well as other natural products, such as kaempferol, that provide ring precursors for CoQ biosynthesis in plants and mammals. In this review, we highlight how stable isotopes can be used to delineate the biosynthetic pathways leading to CoQ.
    Keywords:  4-hydroxybenzoic acid; biosynthesis; coenzyme Q; kaempferol; natural products; p-aminobenzoic acid; polyphenols; stable isotopes; ubiquinone
    DOI:  https://doi.org/10.3390/metabo11060385
  55. FEBS J. 2021 Jul 01.
    LRRK2 recruitment, activity, and function in organelles.
    Luis Bonet-Ponce, Mark R Cookson.
      Protein coding mutations in Leucine-rich repeat kinase 2 (LRRK2) cause familial Parkinson's disease (PD) and non-coding variations around the gene increase the risk of developing sporadic PD. It is generally accepted that pathogenic LRRK2 mutations increase LRRK2 kinase activity, resulting in a toxic hyperactive protein that is inferred to lead to the PD phenotype. LRRK2 has long been linked to different membrane trafficking events, but the specific role of LRRK2 in these events has been difficult to resolve. Recently, several papers have reported the activation and translocation of LRRK2 to cellular organelles under specific conditions, which suggests that LRRK2 may influence intracellular membrane trafficking. Here, we review what is known about the role of LRRK2 at various organelle compartments.
    Keywords:  Endomembranes; Leucine-rich repeat kinase 2; Lysosome; Membrane trafficking; Neurodegeneration; Parkinson’s disease
    DOI:  https://doi.org/10.1111/febs.16099
  56. Chem Sci. 2021 May 04. 12(23): 8115-8122
    Quantification and molecular imaging of fatty acid isomers from complex biological samples by mass spectrometry.
    Hua Zhang, Meng Xu, Xudong Shi, Yuan Liu, Zihui Li, Justin C Jagodinsky, Min Ma, Nathan V Welham, Zachary S Morris, Lingjun Li.
      Elucidating the isomeric structure of free fatty acids (FAs) in biological samples is essential to comprehend their biological functions in various physiological and pathological processes. Herein, we report a novel approach of using peracetic acid (PAA) induced epoxidation coupled with mass spectrometry (MS) for localization of the C[double bond, length as m-dash]C bond in unsaturated FAs, which enables both quantification and spatial visualization of FA isomers from biological samples. Abundant diagnostic fragment ions indicative of the C[double bond, length as m-dash]C positions were produced upon fragmentation of the FA epoxides derived from either in-solution or on-tissue PAA epoxidation of free FAs. The performance of the proposed approach was evaluated by analysis of FAs in human cell lines as well as mapping the FA isomers from cancer tissue samples with MALDI-TOF/TOF-MS. Merits of the newly developed method include high sensitivity, simplicity, high reaction efficiency, and capability of spatial characterization of FA isomers in tissue samples.
    DOI:  https://doi.org/10.1039/d1sc01614h
  57. Int J Mol Sci. 2021 Jun 27. pii: 6908. [Epub ahead of print]22(13):
    Western Diet Decreases the Liver Mitochondrial Oxidative Flux of Succinate: Insight from a Murine NAFLD Model.
    Pavla Staňková, Otto Kučera, Eva Peterová, Moustafa Elkalaf, David Rychtrmoc, Jan Melek, Miroslav Podhola, Veronika Zubáňová, Zuzana Červinková.
      Mitochondria play an essential role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Previously, we found that succinate-activated respiration was the most affected mitochondrial parameter in mice with mild NAFLD. In this study, we focused on the role of succinate dehydrogenase (SDH) in NAFLD pathogenesis. To induce the progression of NAFLD to nonalcoholic steatohepatitis (NASH), C57BL/6J mice were fed a Western-style diet (WD) or control diet for 30 weeks. NAFLD severity was evaluated histologically and the expression of selected proteins and genes was assessed. Mitochondrial respiration was measured by high-resolution respirometry. Liver redox status was assessed using glutathione, malondialdehyde, and mitochondrial production of reactive oxygen species (ROS). Metabolomic analysis was performed by GC/MS. WD consumption for 30 weeks led to reduced succinate-activated respiration. We also observed decreased SDH activity, decreased expression of the SDH activator sirtuin 3, decreased gene expression of SDH subunits, and increased levels of hepatic succinate, an important signaling molecule. Succinate receptor 1 (SUCNR1) gene and protein expression were reduced in the livers of WD-fed mice. We did not observe signs of oxidative damage compared to the control group. The changes observed in WD-fed mice appear to be adaptive to prevent mitochondrial respiratory chain overload and massive ROS production.
    Keywords:  mitochondria; nonalcoholic fatty liver disease; oxidative phosphorylation; respirometry; succinate; succinate dehydrogenase
    DOI:  https://doi.org/10.3390/ijms22136908
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