bims-mitdis Biomed News
on Mitochondrial disorders
Issue of 2024–10–20
48 papers selected by
Catalina Vasilescu, Helmholz Munich
  1. Quantifying constraint in the human mitochondrial genome.
  2. Molecular mechanisms of mitochondrial dynamics.
  3. Clinical and Genetic Spectrum of Patients With Mitochondrial Disease in a Pediatric Egyptian Cohort: Novel Variants and Phenotypic Expansion.
  4. Optogenetic Control of the Mitochondrial Protein Import in Mammalian Cells.
  5. Direct mitochondrial import of lactate supports resilient carbohydrate oxidation.
  6. Resolving Phenotypic Variability in Mitochondrial Diseases: Preliminary Findings of a Proteomic Approach.
  7. Hypoxia-mediated rescue of retinal ganglion cells deficient in mitochondrial complex I is independent of the hypoxia-inducible factor pathway.
  8. Analyzing Mitochondrial Calcium Influx in Isolated Mitochondria.
  9. Post-transcriptional methylation of mitochondrial-tRNA differentially contributes to mitochondrial pathology.
  10. LETMD1 regulates mitochondrial protein synthesis and import to guard brown fat mitochondrial integrity and function.
  11. Critically unwell infants and children with mitochondrial disorders diagnosed by ultra-rapid genomic sequencing.
  12. Brown fat ATP-citrate lyase links carbohydrate availability to thermogenesis and guards against metabolic stress.
  13. Mitophagy as a guardian against cellular aging.
  14. A viable hypomorphic mutation in the mitochondrial ribosome subunit, MRPS-31, exhibits mitochondrial dysfunction in C. elegans.
  15. Mitochondrial transfer in the progression and treatment of cardiac disease.
  16. MICU1 and MICU2, two peas in a pod or entirely different fruits?
  17. Mitochondrial transplantation: a promising strategy for treating degenerative joint diseases.
  18. Clinical and genetic landscape of optic atrophy in 826 families: insights from 50 nuclear genes.
  19. Cardiolipin deficiency disrupts CoQ redox state and induces steatohepatitis.
  20. The mitochondrial long non-coding RNA lncMtloop regulates mitochondrial transcription and suppresses Alzheimer's disease.
  21. Distinct roles for the domains of the mitochondrial aspartate/glutamate carrier citrin in organellar localization and substrate transport.
  22. Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates.
  23. An integrated multi-omics approach allowed ultra-rapid diagnosis of a deep intronic pathogenic variant in PDHX and precision treatment in a neonate critically ill with lactic acidosis.
  24. Protein kinase 2 of the giant sarcomeric protein UNC-89 regulates mitochondrial morphology and function.
  25. Single-cell mitochondrial sequencing reveals low-frequency mitochondrial mutations in naturally aging mice.
  26. Integrative study of skeletal muscle mitochondrial dysfunction in a murine pancreatic cancer-induced cachexia model.
  27. Quantitative dynamics of intracellular NMN by genetically encoded biosensor.
  28. Direct targeting of mitochondria by cisplatin leads to cytotoxicity in zebrafish lateral-line hair cells.
  29. An Unusual Presentation of Leber Hereditary Optic Neuropathy-Plus Case Caused by a Novel DNAJC30 Variant.
  30. Cytosolic acetyl-CoA synthesis shields mitochondria from stress in brown adipocytes.
  31. Outer mitochondrial membrane E3 Ub ligase MARCH5 controls de novo peroxisome biogenesis.
  32. Biallelic variants in MRPL49 cause variable clinical presentations, including sensorineural hearing loss, leukodystrophy, and ovarian insufficiency.
  33. Ndufs4 knockout mice with isolated complex I deficiency engage a futile adaptive brain response.
  34. The Spectrum of clinical manifestations in newborns with the COQ4 mutation: case series and literature review.
  35. Cross-Species Studies Reveal That Dysregulated Mitochondrial Gene Expression and Electron Transport Complex I Activity Are Crucial for Sarcopenia.
  36. Autophagy, aging, and age-related neurodegeneration.
  37. Acute contractile activity induces the activation of the mitochondrial integrated stress response and the transcription factor ATF4.
  38. Ubiquitin ligase MARCH5 controls the formation of mitochondria-derived pre-peroxisomes.
  39. Deciphering the intracellular forces shaping mitochondrial motion.
  40. Visualizing VDAC1 in live cells using a tetracysteine tag.
  41. Structural basis of respiratory complex adaptation to cold temperatures.
  42. A Comprehensive Approach to the Diagnosis of Leigh Syndrome Spectrum.
  43. An Orai1 gain-of-function tubular aggregate myopathy mouse model phenocopies key features of the human disease.
  44. A mitochondrial unfolded protein response-independent role of DVE-1 in longevity regulation.
  45. Itaconate drives mtRNA-mediated type I interferon production through inhibition of succinate dehydrogenase.
  46. Quantification of nutrient fluxes during acute exercise in mice.
  47. Paroxysmal Non-Kinesigenic Dyskinesias Associated with Biallelic POLG Variants: A Case Report.
  48. Dramatic changes in mitochondrial subcellular location and morphology accompany activation of the CO2 concentrating mechanism.
  1. Nature. 2024 Oct 16.
    Quantifying constraint in the human mitochondrial genome.
    Nicole J Lake, Kaiyue Ma, Wei Liu, Stephanie L Battle, Kristen M Laricchia, Grace Tiao, Daniela Puiu, Kenneth K Ng, Justin Cohen, Alison G Compton, Shannon Cowie, John Christodoulou, David R Thorburn, Hongyu Zhao, Dan E Arking, Shamil R Sunyaev, Monkol Lek.
      Mitochondrial DNA (mtDNA) has an important yet often overlooked role in health and disease. Constraint models quantify the removal of deleterious variation from the population by selection and represent powerful tools for identifying genetic variation that underlies human phenotypes1-4. However, nuclear constraint models are not applicable to mtDNA, owing to its distinct features. Here we describe the development of a mitochondrial genome constraint model and its application to the Genome Aggregation Database (gnomAD), a large-scale population dataset that reports mtDNA variation across 56,434 human participants5. Specifically, we analyse constraint by comparing the observed variation in gnomAD to that expected under neutrality, which was calculated using a mtDNA mutational model and observed maximum heteroplasmy-level data. Our results highlight strong depletion of expected variation, which suggests that many deleterious mtDNA variants remain undetected. To aid their discovery, we compute constraint metrics for every mitochondrial protein, tRNA and rRNA gene, which revealed a range of intolerance to variation. We further characterize the most constrained regions within genes through regional constraint and identify the most constrained sites within the entire mitochondrial genome through local constraint, which showed enrichment of pathogenic variation. Constraint also clustered in three-dimensional structures, which provided insight into functionally important domains and their disease relevance. Notably, we identify constraint at often overlooked sites, including in rRNA and noncoding regions. Last, we demonstrate that these metrics can improve the discovery of deleterious variation that underlies rare and common phenotypes.
    DOI:  https://doi.org/10.1038/s41586-024-08048-x
  2. Nat Rev Mol Cell Biol. 2024 Oct 17.
    Molecular mechanisms of mitochondrial dynamics.
    Luis-Carlos Tábara, Mayuko Segawa, Julien Prudent.
      Mitochondria not only synthesize energy required for cellular functions but are also involved in numerous cellular pathways including apoptosis, calcium homoeostasis, inflammation and immunity. Mitochondria are dynamic organelles that undergo cycles of fission and fusion, and these transitions between fragmented and hyperfused networks ensure mitochondrial function, enabling adaptations to metabolic changes or cellular stress. Defects in mitochondrial morphology have been associated with numerous diseases, highlighting the importance of elucidating the molecular mechanisms regulating mitochondrial morphology. Here, we discuss recent structural insights into the assembly and mechanism of action of the core mitochondrial dynamics proteins, such as the dynamin-related protein 1 (DRP1) that controls division, and the mitofusins (MFN1 and MFN2) and optic atrophy 1 (OPA1) driving membrane fusion. Furthermore, we provide an updated view of the complex interplay between different proteins, lipids and organelles during the processes of mitochondrial membrane fusion and fission. Overall, we aim to present a valuable framework reflecting current perspectives on how mitochondrial membrane remodelling is regulated.
    DOI:  https://doi.org/10.1038/s41580-024-00785-1
  3. Am J Med Genet A. 2024 Oct 14. e63881
    Clinical and Genetic Spectrum of Patients With Mitochondrial Disease in a Pediatric Egyptian Cohort: Novel Variants and Phenotypic Expansion.
    Hebatallah M Hassaan, Angela Pyle, Nihal Almenabawy, Fiona M Robertson, Nour Elkhateeb, Marian Y Girgis, Iman Gamal El Din Mahmoud, Fawzia Amer, Mona Samaha, Yara Shaheen, Walaa ElNaggar, Doaa Abdoh, Dina Ahmed Mehaney, Iman Ehsan Abdel Meguid, Robert W Taylor, Robert McFarland, Laila Selim.
      Mitochondrial disorders exhibit clinical and genetic diversity. Nearly 400 distinct genes, located in both the mitochondrial and nuclear genomes, harbor pathogenic variants that can produce a broad spectrum of mitochondrial diseases. This work aims to explore the genetic etiology of a cohort of Egyptian pediatric patients who were clinically suspected of having a mitochondrial disorder. A total of 49 patients from 44 unrelated families were studied. Selection criteria included age below 18 years and meeting Morava criteria (a score ≥ 3). The mitochondrial disease criteria (MDC) have been developed to quantify the clinical picture and evaluate the probability of an underlying mitochondrial disorder Exome sequencing, including mitochondrial genome sequencing, was carried out for each participant. Causative variants likely responsible for the phenotypes were identified in 68% of the study population. The mitochondrial subgroup constituted 41% of the studied population with a median age of 4 years. No primary pathogenic variants in mitochondrial DNA were detected. Pathogenic or likely pathogenic variants in eight mitochondrial genes were identified in 78% of the mitochondrial cohort. Additionally, seven novel variants were identified. Nonmitochondrial diagnoses accounted for 27% of the study population. In 32% of cases, disease-causing variants were not identified. The current study underscores the diverse phenotypic and genetic landscape of mitochondrial disorders among Egyptian patients.
    Keywords:  exome sequencing; gene; mitochondrial diseases; variants
    DOI:  https://doi.org/10.1002/ajmg.a.63881
  4. Cells. 2024 Oct 09. pii: 1671. [Epub ahead of print]13(19):
    Optogenetic Control of the Mitochondrial Protein Import in Mammalian Cells.
    Lukas F J Althoff, Markus M Kramer, Benjamin Bührer, Denise Gaspar, Gerald Radziwill.
      Mitochondria provide cells with energy and regulate the cellular metabolism. Almost all mitochondrial proteins are nuclear-encoded, translated on ribosomes in the cytoplasm, and subsequently transferred to the different subcellular compartments of mitochondria. Here, we developed OptoMitoImport, an optogenetic tool to control the import of proteins into the mitochondrial matrix via the presequence pathway on demand. OptoMitoImport is based on a two-step process: first, light-induced cleavage by a TEV protease cuts off a plasma membrane-anchored fusion construct in close proximity to a mitochondrial targeting sequence; second, the mitochondrial targeting sequence preceding the protein of interest recruits to the outer mitochondrial membrane and imports the protein fused to it into mitochondria. Upon reaching the mitochondrial matrix, the matrix processing peptidase cuts off the mitochondrial targeting sequence and releases the protein of interest. OptoMitoImport is available as a two-plasmid system as well as a P2A peptide or IRES sequence-based bicistronic system. Fluorescence studies demonstrate the release of the plasma membrane-anchored protein of interest through light-induced TEV protease cleavage and its localization to mitochondria. Cell fractionation experiments confirm the presence of the peptidase-cleaved protein of interest in the mitochondrial fraction. The processed product is protected from proteinase K treatment. Depletion of the membrane potential across the inner mitochondria membrane prevents the mitochondrial protein import, indicating an import of the protein of interest by the presequence pathway. These data demonstrate the functionality of OptoMitoImport as a generic system with which to control the post-translational mitochondrial import of proteins via the presequence pathway.
    Keywords:  CRY2; LOV domain; MTS; TEV; matrix peptidases; mitochondrial import; optogenetics
    DOI:  https://doi.org/10.3390/cells13191671
  5. bioRxiv. 2024 Oct 08. pii: 2024.10.07.617073. [Epub ahead of print]
    Direct mitochondrial import of lactate supports resilient carbohydrate oxidation.
    Ahmad A Cluntun, Joseph R Visker, Jesse N Velasco-Silva, Marisa J Lang, Luis Cedeño-Rosario, Thirupura S Shankar, Rana Hamouche, Jing Ling, Ji Eon Kim, Ashish G Toshniwal, Hayden K Low, Corey N Cunningham, James Carrington, Jonathan Leon Catrow, Quentinn Pearce, Mi-Young Jeong, Alex J Bott, Álvaro J Narbona-Pérez, Claire E Stanley, Qing Li, David R Eberhardt, Jeffrey T Morgan, Tarun Yadav, Chloe E Wells, Dinesh K A Ramadurai, Wojciech I Swiatek, Dipayan Chaudhuri, Jeffery D Rothstein, Deborah M Muoio, Joao A Paulo, Steven P Gygi, Steven A Baker, Sutip Navankasattusas, James E Cox, Katsuhiko Funai, Stavros G Drakos, Jared Rutter, Gregory S Ducker.
      Lactate is the highest turnover circulating metabolite in mammals. While traditionally viewed as a waste product, lactate is an important energy source for many organs, but first must be oxidized to pyruvate for entry into the tricarboxylic acid cycle (TCA cycle). This reaction is thought to occur in the cytosol, with pyruvate subsequently transported into mitochondria via the mitochondrial pyruvate carrier (MPC). Using 13 C stable isotope tracing, we demonstrated that lactate is oxidized in the myocardial tissue of mice even when the MPC is genetically deleted. This MPC-independent lactate import and mitochondrial oxidation is dependent upon the monocarboxylate transporter 1 (MCT1/ Slc16a1 ). Mitochondria isolated from the myocardium without MCT1 exhibit a specific defect in mitochondrial lactate, but not pyruvate, metabolism. The import and subsequent mitochondrial oxidation of lactate by mitochondrial lactate dehydrogenase (LDH) acts as an electron shuttle, generating sufficient NADH to support respiration even when the TCA cycle is disrupted. In response to diverse cardiac insults, animals with hearts lacking MCT1 undergo rapid progression to heart failure with reduced ejection fraction. Thus, the mitochondrial import and oxidation of lactate enables carbohydrate entry into the TCA cycle to sustain cardiac energetics and maintain myocardial structure and function under stress conditions.
    DOI:  https://doi.org/10.1101/2024.10.07.617073
  6. Int J Mol Sci. 2024 Oct 05. pii: 10731. [Epub ahead of print]25(19):
    Resolving Phenotypic Variability in Mitochondrial Diseases: Preliminary Findings of a Proteomic Approach.
    Michela Cicchinelli, Guido Primiano, Serenella Servidei, Michelangelo Ardito, Anna Percio, Andrea Urbani, Federica Iavarone.
      The introduction of new sequencing approaches into clinical practice has radically changed the diagnostic approach to mitochondrial diseases, significantly improving the molecular definition rate in this group of neurogenetic disorders. At the same time, there have been no equal successes in the area of in-depth understanding of disease mechanisms and few innovative therapeutic approaches have been proposed recently. In this regard, the identification of the molecular basis of phenotypic variability in primary mitochondrial disorders represents a key aspect for deciphering disease mechanisms with important therapeutic implications. In this study, we present data from proteomic investigations in two subjects affected by mitochondrial disease characterized by a different clinical severity and associated with the same variant in the TWNK gene, encoding the mitochondrial DNA and RNA helicase with a specific role in the mtDNA replisome. Heterozygous pathogenic variants in this gene are associated with progressive external ophthalmoplegia and ptosis, usually with adult onset. The overall results suggest an imbalance in glucose metabolism and ROS production/regulation, with possible consequences on the phenotypic manifestations of the enrolled subjects. Although the data will need to be validated in a large cohort, proteomic investigations have proven to be a valid approach for a deep understanding of these neurometabolic disorders.
    Keywords:  PEO; mitochondria; mitochondrial diseases; omics technologies; proteomics
    DOI:  https://doi.org/10.3390/ijms251910731
  7. Sci Rep. 2024 10 15. 14(1): 24114
    Hypoxia-mediated rescue of retinal ganglion cells deficient in mitochondrial complex I is independent of the hypoxia-inducible factor pathway.
    Alexander M Warwick, Howard M Bomze, Luyu Wang, Ying Hao, Sandra S Stinnett, Sidney M Gospe.
      Continuous exposure to environmental hypoxia (11% O2) has been shown to markedly slow the progressive degeneration of retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy with RGC-specific deletion of the key mitochondrial complex I accessory subunit ndufs4. As a first step toward identifying the therapeutic mechanism of hypoxia in this model, we conducted a series of experiments to investigate the role of the hypoxia-inducible factor (HIF) regulatory pathway in RGC neuroprotection. Vglut2-Cre; ndufs4loxP/loxP mice were crossed with strains bearing floxed alleles of the negative HIF regulatory vhl or of the two major HIF α-subunit isoforms, Hif1α and Hif2α. Deletion of vhl within ndufs4-deficient RGCs failed to prevent RGC degeneration under normoxia, indicating that HIF activation is not sufficient to achieve RGC rescue. Furthermore, the rescue of ndufs4-deficient RGCs by hypoxia remained robust despite genetic inactivation of Hif1α and Hif2α. Our findings demonstrate that the HIF pathway is entirely dispensable to the rescue of RGCs by hypoxia. Future efforts to uncover key HIF-independent molecular pathways induced by hypoxia in this mouse model may be of therapeutic relevance to mitochondrial optic neuropathies such as Leber hereditary optic neuropathy.
    Keywords:  Complex I; Hypoxia; Hypoxia-inducible factor; Leber hereditary optic neuropathy; Mitochondria; Retinal ganglion cell
    DOI:  https://doi.org/10.1038/s41598-024-75916-x
  8. Methods Mol Biol. 2025 ;2861 155-164
    Analyzing Mitochondrial Calcium Influx in Isolated Mitochondria.
    Nasab Ghazal, Jennifer Q Kwong.
      Mitochondria play a crucial role in Ca2+ signaling and homeostasis and can contribute to shaping the cytosolic Ca2+ landscape as well as regulate a variety of pathways including energy production and cell death. Dysregulation of mitochondrial Ca2+ homeostasis promotes pathologies including neurodegenerative diseases, cardiovascular disorders, and metabolic syndromes. The significance of mitochondria to Ca2+ signaling and regulation underscores the value of methods to assess mitochondrial Ca2+ import. Here we present a plate reader-based method using the Ca2+-sensitive fluorescent probe calcium green-5 N to measure mitochondrial Ca2+ import in isolated cardiac mitochondria. This technique can be expanded to measure Ca2+ uptake in mitochondria isolated from other tissue types and from cultured cells.
    Keywords:  Calcium; Heart; Mitochondria; Mitochondrial permeability transition pore; Signaling; Uniporter
    DOI:  https://doi.org/10.1007/978-1-0716-4164-4_12
  9. Nat Commun. 2024 Oct 18. 15(1): 9008
    Post-transcriptional methylation of mitochondrial-tRNA differentially contributes to mitochondrial pathology.
    Sunita Maharjan, Howard Gamper, Yuka Yamaki, Thomas Christian, Robert Y Henley, Nan-Sheng Li, Takeo Suzuki, Tsutomu Suzuki, Joseph A Piccirilli, Meni Wanunu, Erin Seifert, Douglas C Wallace, Ya-Ming Hou.
      Human mitochondrial tRNAs (mt-tRNAs), critical for mitochondrial biogenesis, are frequently associated with pathogenic mutations. These mt-tRNAs have unusual sequence motifs and require post-transcriptional modifications to stabilize their fragile structures. However, whether a modification that stabilizes a wild-type (WT) mt-tRNA would also stabilize its pathogenic variants is unknown. Here we show that the N1-methylation of guanosine at position 9 (m1G9) of mt-Leu(UAA), while stabilizing the WT tRNA, has a destabilizing effect on variants associated with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). This differential effect is further demonstrated, as removal of the m1G9 methylation, while damaging to the WT tRNA, is beneficial to the major pathogenic variant, improving the structure and activity of the variant. These results have therapeutic implications, suggesting that the N1-methylation of mt-tRNAs at position 9 is a determinant of pathogenicity and that controlling the methylation level is an important modulator of mt-tRNA-associated diseases.
    DOI:  https://doi.org/10.1038/s41467-024-53318-x
  10. iScience. 2024 Oct 18. 27(10): 110944
    LETMD1 regulates mitochondrial protein synthesis and import to guard brown fat mitochondrial integrity and function.
    Madigan Snyder, Yi-Kai Liu, Renjie Shang, Haowei Xu, Charlie Thrift, Xiyue Chen, Jingjuan Chen, Kun Ho Kim, Jiamin Qiu, Pengpeng Bi, W Andy Tao, Shihuan Kuang.
      Thermogenic brown adipocytes (BAs) catabolize lipids to generate heat, representing powerful agents against the growing global obesity epidemic. We and others reported recently that LETMD1 is a BA-specific protein essential for mitochondrial structure and function, but the mechanisms of action remain unclear. We performed sequential digestion to demonstrate that LETMD1 is a trans-inner mitochondrial membrane protein. We then generated UCP1Cre-driven BA-specific Letmd1 knockout (Letmd1 UKO ) mice to show that Letmd1 UKO leads to protein aggregation, reactive oxidative stress, hyperpolarization, and mitophagy in BAs. We further employed TurboID proximity labeling to identify LETMD1-interacting proteins. Many candidate proteins are associated with mitochondrial ribosomes, protein import machinery, and electron transport chain complexes (ETC-I and ETC-IV). Using quantitative proteomics, we confirmed the elevated aggregations of ETC and mitochondrial ribosomal proteins, impairing mitochondrial protein synthesis in the Letmd1 UKO BAs. Therefore, LETMD1 may function to maintain mitochondrial proteostasis through regulating import of nuclear-encoded proteins and local protein translation in brown fat mitochondria.
    Keywords:  Cell; Cell biology; Cellular physiology; Molecular biology
    DOI:  https://doi.org/10.1016/j.isci.2024.110944
  11. Genet Med. 2024 Oct 14. pii: S1098-3600(24)00227-2. [Epub ahead of print] 101293
    Critically unwell infants and children with mitochondrial disorders diagnosed by ultra-rapid genomic sequencing.
    Megan Ball, Sophie E Bouffler, Christopher B Barnett, Mary-Louise Freckmann, Matthew F Hunter, Benjamin Kamien, Karin S Kassahn, Sebastian Lunke, Chirag V Patel, Jason Pinner, Tony Roscioli, Sarah A Sandaradura, Hamish S Scott, Tiong Y Tan, Mathew Wallis, Alison G Compton, David R Thorburn, Zornitza Stark, John Christodoulou.
       PURPOSE: To characterize the diagnostic and clinical outcomes of a cohort of critically ill infants and children with suspected mitochondrial disorders (MD) undergoing ultra-rapid genomic testing as part of a national program.
    METHODS: Ultra-rapid genomic sequencing was performed in 454 families (genome sequencing: n=290, exome sequencing +/- mitochondrial DNA sequencing: n=164). In 91 individuals, MD was considered, prompting analysis using an MD virtual gene panel. These individuals were reviewed retrospectively and scored according to modified Nijmegen Mitochondrial Disease Criteria.
    RESULTS: A diagnosis was achieved in 47% (43/91) of individuals, 40% (17/43) of whom had an MD. Seven additional individuals in whom an MD was not suspected were diagnosed with an MD following broader analysis. Gene-agnostic analysis led to the discovery of two novel disease genes, with pathogenicity validated through targeted functional studies (CRLS1 and MRPL39). Functional studies enabled diagnosis in another four individuals. Of the 24 individuals ultimately diagnosed with an MD, 79% had a change in management, which included 53% whose care was redirected to palliation.
    CONCLUSION: Ultra-rapid genetic diagnosis of MD in acutely unwell infants and children is critical for guiding decisions about the need for additional investigations and clinical management.
    Keywords:  Mitochondrial disorders; Neonatal; Paediatric; Rapid Genomics
    DOI:  https://doi.org/10.1016/j.gim.2024.101293
  12. Nat Metab. 2024 Oct 14.
    Brown fat ATP-citrate lyase links carbohydrate availability to thermogenesis and guards against metabolic stress.
    Ekaterina D Korobkina, Camila Martinez Calejman, John A Haley, Miranda E Kelly, Huawei Li, Maria Gaughan, Qingbo Chen, Hannah L Pepper, Hafsah Ahmad, Alexander Boucher, Shelagh M Fluharty, Te-Yueh Lin, Anoushka Lotun, Jessica Peura, Sophie Trefely, Courtney R Green, Paula Vo, Clay F Semenkovich, Jason R Pitarresi, Jessica B Spinelli, Ozkan Aydemir, Christian M Metallo, Matthew D Lynes, Cholsoon Jang, Nathaniel W Snyder, Kathryn E Wellen, David A Guertin.
      Brown adipose tissue (BAT) engages futile fatty acid synthesis-oxidation cycling, the purpose of which has remained elusive. Here, we show that ATP-citrate lyase (ACLY), which generates acetyl-CoA for fatty acid synthesis, promotes thermogenesis by mitigating metabolic stress. Without ACLY, BAT overloads the tricarboxylic acid cycle, activates the integrated stress response (ISR) and suppresses thermogenesis. ACLY's role in preventing BAT stress becomes critical when mice are weaned onto a carbohydrate-plentiful diet, while removing dietary carbohydrates prevents stress induction in ACLY-deficient BAT. ACLY loss also upregulates fatty acid synthase (Fasn); yet while ISR activation is not caused by impaired fatty acid synthesis per se, deleting Fasn and Acly unlocks an alternative metabolic programme that overcomes tricarboxylic acid cycle overload, prevents ISR activation and rescues thermogenesis. Overall, we uncover a previously unappreciated role for ACLY in mitigating mitochondrial stress that links dietary carbohydrates to uncoupling protein 1-dependent thermogenesis and provides fundamental insight into the fatty acid synthesis-oxidation paradox in BAT.
    DOI:  https://doi.org/10.1038/s42255-024-01143-3
  13. Autophagy. 2024 Oct 14. 1-3
    Mitophagy as a guardian against cellular aging.
    Tetsushi Kataura, Niall Wilson, Gailing Ma, Viktor I Korolchuk.
      Mitophagy, the selective autophagic clearance of damaged mitochondria, is considered vital for maintaining mitochondrial quality and cellular homeostasis; however, its molecular mechanisms, particularly under basal conditions, and its role in cellular physiology remain poorly characterized. We recently demonstrated that basal mitophagy is a key feature of primary human cells and is downregulated by immortalization, suggesting its dependence on the primary cell state. Mechanistically, we demonstrated that the PINK1-PRKN-SQSTM1 pathway regulates basal mitophagy, with SQSTM1 sensing superoxide-enriched mitochondria through its redox-sensitive cysteine residues, which mediate SQSTM1 oligomerization and mitophagy activation. We developed STOCK1N-57534, a small molecule that targets and promotes this SQSTM1 activation mechanism. Treatment with STOCK1N-57534 reactivates mitophagy downregulated in senescent and naturally aged donor-derived primary cells, improving cellular senescence(-like) phenotypes. Our findings highlight that basal mitophagy is protective against cellular senescence and aging, positioning its pharmacological reactivation as a promising anti-aging strategy.Abbreviation: IR: ionizing radiation; ROS: reactive oxygen species; SARs: selective autophagy receptors.
    Keywords:  Aging; SQSTM1/p62; autophagy; mitochondria; mitophagy; senescence
    DOI:  https://doi.org/10.1080/15548627.2024.2414461
  14. MicroPubl Biol. 2024 ;2024
    A viable hypomorphic mutation in the mitochondrial ribosome subunit, MRPS-31, exhibits mitochondrial dysfunction in C. elegans.
    Kylie M Jozwik, James P Held, Chloe A Hecht, Maulik R Patel.
      The mitochondrial ribosome (mitoribosome) translates mitochondrial genome encoded proteins essential for cellular energy production. Given this critical role, defects in the mitoribosome can cause mitochondrial stress and manifest as multisystemic diseases. In a screen for unique activators of the mitochondrial unfolded protein response (UPR mt ) in Caenorhabditis elegans , we recovered a strain harboring a missense mutation in the gene encoding mitochondrial ribosome protein S31 ( MRPS-31 )-a component of the mitoribosome small subunit. Herein, we confirm causality of the mrps-31 allele and characterize its induction of UPR mt and impact on organismal development, providing a valuable model for further study of the mitoribosome.
    DOI:  https://doi.org/10.17912/micropub.biology.001344
  15. Life Sci. 2024 Oct 10. pii: S0024-3205(24)00709-4. [Epub ahead of print]358 123119
    Mitochondrial transfer in the progression and treatment of cardiac disease.
    Yaqing Huang, Wanling Li, Hongyu Sun, Xin Guo, Yue Zhou, Jun Liu, Feila Liu, Yonghong Fan.
      Mitochondria are the primary site for energy production and play a crucial role in supporting normal physiological functions of the human body. In cardiomyocytes (CMs), mitochondria can occupy up to 30 % of the cell volume, providing sufficient energy for CMs contraction and relaxation. However, some pathological conditions such as ischemia, hypoxia, infection, and the side effect of drugs, can cause mitochondrial dysfunction in CMs, leading to various myocardial injury-related diseases including myocardial infarction (MI), myocardial hypertrophy, and heart failure. Self-control of mitochondria quality and conversion of metabolism pathway in energy production can serve as the self-rescue measure to avoid autologous mitochondrial damage. Particularly, mitochondrial transfer from the neighboring or extraneous cells enables to mitigate mitochondrial dysfunction and restore their biological functions in CMs. Here, we described the homeostatic control strategies and related mechanisms of mitochondria in injured CMs, including autologous mitochondrial quality control, mitochondrial energy conversion, and especially the exogenetic mitochondrial donation. Additionally, this review emphasizes on the therapeutic effects and potential application of utilizing mitochondrial transfer in reducing myocardial injury. We hope that this review can provide theoretical clues for the developing of advanced therapeutics to treat cardiac diseases.
    Keywords:  Cardiac diseases; Cardiomyocyte; Mitochondrial quality control; Mitochondrial therapy; Mitochondrial transfer
    DOI:  https://doi.org/10.1016/j.lfs.2024.123119
  16. Cell Calcium. 2024 Oct 08. pii: S0143-4160(24)00117-9. [Epub ahead of print]124 102959
    MICU1 and MICU2, two peas in a pod or entirely different fruits?
    Jiuzhou Huo, Jeffery D Molkentin.
      Fluctuations in mitochondrial matrix Ca2+ plays a critical role in matching energy production to cellular demand through direct effects on oxidative phosphorylation and ATP production. Disruption in mitochondrial Ca2+ homeostasis, particularly under pathological conditions such as ischemia or heart failure, can lead to mitochondrial dysfunction, energy deficit, and eventually death of cardiomyocytes. The primary channel regulating acute mitochondrial Ca2+ influx is the mitochondrial Ca2+ uniporter (mtCU), which is regulated by the mitochondrial Ca2+ uptake (MICU) proteins that were examined here.
    DOI:  https://doi.org/10.1016/j.ceca.2024.102959
  17. J Transl Med. 2024 Oct 15. 22(1): 941
    Mitochondrial transplantation: a promising strategy for treating degenerative joint diseases.
    Hong Luo, Yue Lai, Weili Tang, Guoyou Wang, Jianlin Shen, Huan Liu.
      The prevalence of age-related degenerative joint diseases, particularly intervertebral disc degeneration and osteoarthritis, is increasing, thereby posing significant challenges for the elderly population. Mitochondrial dysfunction is a critical factor in the etiology and progression of these disorders. Therapeutic interventions that incorporate mitochondrial transplantation exhibit considerable promise by increasing mitochondrial numbers and improving their functionality. Existing evidence suggests that exogenous mitochondrial therapy improves clinical outcomes for patients with degenerative joint diseases. This review elucidates the mitochondrial abnormalities associated with degenerative joint diseases and examines the mechanisms of mitochondrial intercellular transfer and artificial mitochondrial transplantation. Furthermore, therapeutic strategies for mitochondrial transplantation in degenerative joint diseases are synthesized, and the concept of engineered mitochondrial transplantation is proposed.
    Keywords:  Degenerative joint diseases; Engineered mitochondria; Intervertebral disc degeneration; Mitochondrial transplantation; Osteoarthritis
    DOI:  https://doi.org/10.1186/s12967-024-05752-0
  18. Brain. 2024 Oct 18. pii: awae324. [Epub ahead of print]
    Clinical and genetic landscape of optic atrophy in 826 families: insights from 50 nuclear genes.
    Yuxi Zheng, Panfeng Wang, Shiqiang Li, Yuxi Long, Yi Jiang, Dongwei Guo, Xiaoyun Jia, Mengchu Liu, Yiyan Zeng, Xueshan Xiao, J Fielding Hejtmancik, Qingjiong Zhang, Wenmin Sun.
      Hereditary optic neuropathies (HON) are a group of diseases due to genetic defects either in mitochondria or in nuclear genomes. The increasing availability of genetic testing has expanded a broader genetic and phenotypic spectrum of HON than previously recognized. To provide systematic insight into the genetic and phenotypic landscape of HON attributed to 50 nuclear genes, we conducted genetic analysis on part of 4776 index patients with clinical diagnosis of HON following our previous study on 1516 probands with Leber hereditary optic neuropathy (LHON) and mitochondrial DNA variants. Exome sequencing was performed in 473 patients diagnosed with nuclear gene-related HON (nHON) and 353 cases with unsolved LHON. Sequencing and variant interpretation in 50 causative nuclear genes indicated that the diagnostic yield of exome sequencing for nHON was 31.50% (149/473), while it was markedly lower at 1.42% (5/353) for LHON patients without primary mtDNA mutations. The top five implicated genes causing nHON in our in-house cohort, OPA1, WFS1, FDXR, ACO2, and AFG3L2, account for 82.46% of mutations. Although OPA1 was the most prevalent causative gene of nHON in both our cohort (53.25%) and literature review (37.09%), the prevalence of OPA1, WFS1, and FDXR differed significantly between our in-house cohort and the literature review (P-adjusted<0.001). Fundus changes in nHON could be stratified into three categories, the most common is optic atrophy at the examination (78.79%), the rarest is LHON-like optic atrophy (3.64%), and the intermediate is optic atrophy with concurrent retinal degeneration (17.57%), which was an independent risk factor for visual prognosis in nHON. A systematic genotype-phenotype analysis highlighted different genetic contributions for ocular, extraocular neurological, and extraocular non-neurological phenotypes. In addition, systemic variant analysis at the individual gene level suggested a revised interpretation of the pathogenicity of a WFS1 heterozygous truncation variant. This study provides a panoramic summary of both the genetic and phenotypic profiles of HON in real-world studies and literature. The category for nHON fundus phenotypes is built for future studies on molecular mechanisms underlying HON and targeted therapies. In addition to routine ophthalmic examinations, careful examination of the extraocular symptoms and meaningful genetic counseling are warranted for patients with nHON.
    Keywords:  Leber hereditary optic neuropathy; dominant optic atrophy; hereditary optic neuropathy; mitochondrial
    DOI:  https://doi.org/10.1093/brain/awae324
  19. bioRxiv. 2024 Oct 10. pii: 2024.10.10.617517. [Epub ahead of print]
    Cardiolipin deficiency disrupts CoQ redox state and induces steatohepatitis.
    Marisa J Brothwell, Guoshen Cao, J Alan Maschek, Annelise M Poss, Alek D Peterlin, Liping Wang, Talia B Baker, Justin L Shahtout, Piyarat Siripoksup, Quentinn J Pearce, Jordan M Johnson, Fabian M Finger, Alexandre Prola, Sarah A Pellizzari, Gillian L Hale, Allison M Manuel, Shinya Watanabe, Edwin R Miranda, Kajsa E Affolter, Trevor S Tippetts, Linda S Nikolova, Ran Hee Choi, Stephen T Decker, Mallikarjun Patil, J Leon Catrow, William L Holland, Sara M Nowinski, Daniel S Lark, Kelsey H Fisher-Wellman, Patrice N Mimche, Kimberley J Evason, James E Cox, Scott A Summers, Zach Gerhart-Hines, Katsuhiko Funai.
      Metabolic dysfunction-associated steatotic liver disease (MASLD) is a progressive disorder marked by lipid accumulation, leading to steatohepatitis (MASH). A key feature of the transition to MASH involves oxidative stress resulting from defects in mitochondrial oxidative phosphorylation (OXPHOS). Here, we show that pathological alterations in the lipid composition of the inner mitochondrial membrane (IMM) directly instigate electron transfer inefficiency to promote oxidative stress. Specifically, cardiolipin (CL) was downregulated across four mouse models of MASLD. Hepatocyte-specific CL synthase knockout (CLS-LKO) led to spontaneous MASH with elevated mitochondrial electron leak. Loss of CL interfered with the ability of coenzyme Q (CoQ) to transfer electrons, promoting leak primarily at sites II F and III Q0 . Data from human liver biopsies revealed a highly robust correlation between mitochondrial CL and CoQ, co-downregulated with MASH. Thus, reduction in mitochondrial CL promotes oxidative stress and contributes to pathogenesis of MASH.
    DOI:  https://doi.org/10.1101/2024.10.10.617517
  20. EMBO J. 2024 Oct 18.
    The mitochondrial long non-coding RNA lncMtloop regulates mitochondrial transcription and suppresses Alzheimer's disease.
    Wandi Xiong, Kaiyu Xu, Jacquelyne Ka-Li Sun, Siling Liu, Baizhen Zhao, Jie Shi, Karl Herrup, Hei-Man Chow, Lin Lu, Jiali Li.
      Maintaining mitochondrial homeostasis is crucial for cell survival and organismal health, as evidenced by the links between mitochondrial dysfunction and various diseases, including Alzheimer's disease (AD). Here, we report that lncMtDloop, a non-coding RNA of unknown function encoded within the D-loop region of the mitochondrial genome, maintains mitochondrial RNA levels and function with age. lncMtDloop expression is decreased in the brains of both human AD patients and 3xTg AD mouse models. Furthermore, lncMtDloop binds to mitochondrial transcription factor A (TFAM), facilitates TFAM recruitment to mtDNA promoters, and increases mitochondrial transcription. To allow lncMtDloop transport into mitochondria via the PNPASE-dependent trafficking pathway, we fused the 3'UTR localization sequence of mitochondrial ribosomal protein S12 (MRPS12) to its terminal end, generating a specified stem-loop structure. Introducing this allotropic lncMtDloop into AD model mice significantly improved mitochondrial function and morphology, and ameliorated AD-like pathology and behavioral deficits of AD model mice. Taken together, these data provide insights into lncMtDloop as a regulator of mitochondrial transcription and its contribution to Alzheimer's pathogenesis.
    Keywords:   lncMtDloop ; Alzheimer’s Disease; Mitochondrial Homeostasis; TFAM; mtDNA
    DOI:  https://doi.org/10.1038/s44318-024-00270-7
  21. Mol Metab. 2024 Oct 15. pii: S2212-8778(24)00178-9. [Epub ahead of print] 102047
    Distinct roles for the domains of the mitochondrial aspartate/glutamate carrier citrin in organellar localization and substrate transport.
    Sotiria Tavoulari, Denis Lacabanne, Gonçalo C Pereira, Chancievan Thangaratnarajah, Martin S King, Jiuya He, Roy Chowdhury, Lisa Tilokani, Shane M Palmer, Julien Prudent, John E Walker, Edmund R S Kunji.
       OBJECTIVE: Citrin, the mitochondrial aspartate/glutamate carrier isoform 2, is structurally and mechanistically the most complex SLC25 family member, because it consists of three-domains and forms a homodimer. Each protomer has an N-terminal calcium-binding domain with EF-hands, followed by a substrate-transporting carrier domain and a C-terminal domain with an amphipathic helix. The absence or dysfunction of citrin leads to citrin deficiency, a highly prevalent pan-ethnic mitochondrial disease. Here, we aim to understand the role of different citrin domains and how they contribute to pathogenic mechanisms in citrin deficiency.
    METHODS: We have employed structural modelling and functional reconstitution of purified proteins in proteoliposomes to assess the transport activity and calcium regulation of wild-type citrin and pathogenic variants associated with citrin deficiency. We have also developed a double knock-out of citrin and aralar (AGC1), the two paralogs of the mitochondrial aspartate/glutamate carrier, in HAP1 cells to perform mitochondrial imaging and to investigate mitochondrial localisation.
    RESULTS: Using 33 pathogenic variants of citrin we clarify determinants of sub-cellular localization and transport mechanism. We identify crucial elements of the carrier domain that are required for transport, including those involved in substrate binding, network formation and dynamics. We show that the N-terminal domain is not involved in calcium regulation of transport, as previously thought, but when mutated causes a mitochondrial import defect.
    CONCLUSIONS: Our work introduces a new role for the N-terminal domain of citrin and demonstrates that dysfunction of the different domains contributes to distinct pathogenic mechanisms in citrin deficiency.
    Keywords:  SLC25; calcium regulation; citrin deficiency; transport; urea cycle disorders
    DOI:  https://doi.org/10.1016/j.molmet.2024.102047
  22. EMBO J. 2024 Oct 17.
    Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates.
    Zi Yang, Saori R Yoshii, Yuji Sakai, Jing Zhang, Haruka Chino, Roland L Knorr, Noboru Mizushima.
      During PINK1- and Parkin-mediated mitophagy, autophagy adaptors are recruited to damaged mitochondria to promote their selective degradation. Autophagy adaptors such as optineurin (OPTN) and NDP52 facilitate mitophagy by recruiting the autophagy-initiation machinery, and assisting engulfment of damaged mitochondria through binding to ubiquitinated mitochondrial proteins and autophagosomal ATG8 family proteins. Here, we demonstrate that OPTN and NDP52 form sheet-like phase-separated condensates with liquid-like properties on the surface of ubiquitinated mitochondria. The dynamic and liquid-like nature of OPTN condensates is important for mitophagy activity, because reducing the fluidity of OPTN-ubiquitin condensates suppresses the recruitment of ATG9 vesicles and impairs mitophagy. Based on these results, we propose a dynamic liquid-like, rather than a stoichiometric, model of autophagy adaptors to explain the interactions between autophagic membranes (i.e., ATG9 vesicles and isolation membranes) and mitochondrial membranes during Parkin-mediated mitophagy. This model underscores the importance of liquid-liquid phase separation in facilitating membrane-membrane contacts, likely through the generation of capillary forces.
    Keywords:  Autophagy; Liquid–Liquid Phase Separation; Mitophagy; Optineurin; Wetting
    DOI:  https://doi.org/10.1038/s44318-024-00272-5
  23. Mitochondrion. 2024 Oct 14. pii: S1567-7249(24)00131-4. [Epub ahead of print] 101973
    An integrated multi-omics approach allowed ultra-rapid diagnosis of a deep intronic pathogenic variant in PDHX and precision treatment in a neonate critically ill with lactic acidosis.
    Rodrigo T Starosta, Austin A Larson, Naomi J L Meeks, Sara Gracie, Marisa W Friederich, Sommer M Gaughan, Peter R Baker, Kelly G Knupp, Cole R Michel, Richard Reisdorph, Daniella H Hock, David A Stroud, Tim Wood, Johan L K Van Hove.
      The diagnosis of mitochondrial disorders is complex. Rapid whole genome sequencing is a first line test for critically ill neonates and infants allowing rapid diagnosis and treatment. Standard genomic technology and bioinformatic pipelines still have an incomplete diagnostic yield requiring complementary approaches. There are currently limited options for rapid additional tests to continue a diagnostic work-up after a negative rapid whole-genome sequencing result, reflecting a gap in clinical practice. Multi-modal integrative diagnostic approaches derived from systems biology including proteomics and transcriptomics show promise in suspected mitochondrial disorders. In this article, we report the case of a neonate who presented with severe lactic acidosis on the second day of life, for whom an initial report of ultra-rapid genome sequencing was negative. The patient was started on dichloroacetate as an emergency investigational new drug (eIND), with a sharp decline in lactic acid levels and clinical stabilization. A proteomics-based approach identified a complete absence of PDHX protein, leading to a re-review of the genome data for the PDHX gene in which a homozygous deep intronic pathogenic variant was identified. Subsequent testing in the following months confirmed the diagnosis with deficient pyruvate dehydrogenase enzyme activity, reduced protein levels of E3-binding protein, and confirmed by mRNA sequencing to lead to the inclusion of a cryptic exon and a premature stop codon. This case highlights the power of rapid proteomics in guiding genomic analysis. It also shows a promising role for dichloroacetate treatment in controlling lactic acidosis related to PDHX-related pyruvate dehydrogenase complex deficiency.
    Keywords:  Dichloroacetate; Hereditary orotic aciduria; Lactic acidosis; Proteomics; Pyruvate dehydrogenase; Whole genome sequencing
    DOI:  https://doi.org/10.1016/j.mito.2024.101973
  24. Commun Biol. 2024 Oct 17. 7(1): 1342
    Protein kinase 2 of the giant sarcomeric protein UNC-89 regulates mitochondrial morphology and function.
    Yohei Matsunaga, Hiroshi Qadota, Nasab Ghazal, Leila Lesanpezeshki, Till Dorendorf, Jasmine C Moody, Arnaud Ahier, Courtney J Matheny, Siva A Vanapalli, Steven Zuryn, Olga Mayans, Jennifer Q Kwong, Guy M Benian.
      UNC-89 is a giant sarcomeric M-line protein required for sarcomere organization and optimal muscle function. UNC-89 contains two protein kinase domains, PK1 and PK2, separated by an elastic region. Here we show that PK2 is a canonical kinase expected to be catalytically active. C. elegans expressing UNC-89 with a lysine to alanine (KtoA) mutation to inactivate PK2 have normally organized sarcomeres and SR, and normal muscle function. PK2 KtoA mutants have fragmented mitochondria, correlated with more mitochondrially-associated DRP-1. PK2 KtoA mutants have increased ATP levels, increased glycolysis and altered levels of electron transport chain complexes. Muscle mitochondria show increased complex I and decreased complex II basal respiration, each of which cannot be uncoupled. This suggests that mutant mitochondria are already uncoupled, possibly resulting from an increased level of the uncoupling protein, UCP-4. Our results suggest signaling from sarcomeres to mitochondria, to help match energy requirements with energy production.
    DOI:  https://doi.org/10.1038/s42003-024-07042-3
  25. Aging Cell. 2024 Sep;23(9): e14242
    Single-cell mitochondrial sequencing reveals low-frequency mitochondrial mutations in naturally aging mice.
    Fuyan Liu, Xiaolin Sun, Cai Wei, Liu Ji, Yali Song, Chenlu Yang, Yue Wang, Xin Liu, Daqing Wang, Jingmin Kang.
      Mitochondria play a crucial role in numerous biological processes; however, limited methods and research have focused on revealing mitochondrial heterogeneity at the single-cell level. In this study, we optimized the DNBelab C4 single-cell ATAC (assay for transposase-accessible chromatin) sequencing workflow for single-cell mitochondrial sequencing (C4_mtscATAC-seq). We validated the effectiveness of our C4_mtscATAC-seq protocol by sequencing the HEK-293T cell line with two biological replicates, successfully capturing both mitochondrial content (~68% of total sequencing data) and open chromatin status simultaneously. Subsequently, we applied C4_mtscATAC-seq to investigate two mouse tissues, spleen and bone marrow, obtained from two mice aged 2 months and two mice aged 23 months. Our findings revealed higher mitochondrial DNA (mtDNA) content in young tissues compared to more variable mitochondrial content in aged tissues, consistent with higher activity scores of nuclear genes associated with mitochondrial replication and transcription in young tissues. We detected a total of 22, 15, and 21 mtDNA mutations in the young spleen, aged spleen, and bone marrow, respectively, with most variant allele frequencies (VAF) below 1%. Moreover, we observed a higher number of mtDNA mutations with higher VAF in aged tissues compared to young tissues. Importantly, we identified three mtDNA variations (m.9821A>T, m.15219T>C, and m.15984C>T) with the highest VAF in both aged spleen and aged bone marrow. By comparing cells with and without these mtDNA variations, we analyzed differential open chromatin status to identify potential genes associated with these mtDNA variations, including transcription factors such as KLF15 and NRF1. Our study presents an alternative single-cell mitochondrial sequencing method and provides crude insights into age-related single-cell mitochondrial variations.
    Keywords:  ATAC; aging; mitochondrial DNA (mtDNA); mitochondrial mutation; single cell sequencing
    DOI:  https://doi.org/10.1111/acel.14242
  26. Elife. 2024 Oct 18. pii: RP93312. [Epub ahead of print]13
    Integrative study of skeletal muscle mitochondrial dysfunction in a murine pancreatic cancer-induced cachexia model.
    Tristan Gicquel, Fabio Marchiano, Gabriela Reyes-Castellanos, Stephane Audebert, Luc Camoin, Bianca H Habermann, Benoit Giannesini, Alice Carrier.
      Pancreatic ductal adenocarcinoma (PDAC), the most common pancreatic cancer, is a deadly cancer, often diagnosed late and resistant to current therapies. PDAC patients are frequently affected by cachexia characterized by muscle mass and strength loss (sarcopenia) contributing to patient frailty and poor therapeutic response. This study assesses the mechanisms underlying mitochondrial remodeling in the cachectic skeletal muscle, through an integrative exploration combining functional, morphological, and omics-based evaluation of gastrocnemius muscle from KIC genetically engineered mice developing autochthonous pancreatic tumor and cachexia. Cachectic PDAC KIC mice exhibit severe sarcopenia with loss of muscle mass and strength associated with reduced muscle fiber's size and induction of protein degradation processes. Mitochondria in PDAC atrophied muscles show reduced respiratory capacities and structural alterations, associated with deregulation of oxidative phosphorylation and mitochondrial dynamics pathways. Beyond the metabolic pathways known to be altered in sarcopenic muscle (carbohydrates, proteins, and redox), lipid and nucleic acid metabolisms are also affected. Although the number of mitochondria per cell is not altered, mitochondrial mass shows a twofold decrease and the mitochondrial DNA threefold, suggesting a defect in mitochondrial genome homeostasis. In conclusion, this work provides a framework to guide toward the most relevant targets in the clinic to limit PDAC-induced cachexia.
    Keywords:  cachexia; cancer biology; energy metabolism; mitochondria; mouse; muscle wasting; pancreatic cancer
    DOI:  https://doi.org/10.7554/eLife.93312
  27. Biosens Bioelectron. 2024 Oct 10. pii: S0956-5663(24)00849-2. [Epub ahead of print]267 116842
    Quantitative dynamics of intracellular NMN by genetically encoded biosensor.
    Liuqing Chen, Pei Wang, Guan Huang, Wenxiang Cheng, Kaijing Liu, Qiuliyang Yu.
      Nicotinamide mononucleotide (NMN) is the direct precursor and a major booster of NAD+ with increasing applications in NAD+- and aging-related pathologies. However, measuring live cell NMN dynamics was not possible, leaving key questions in NMN uptake and intracellular regulation unanswered. Here we developed genetically encoded bioluminescent and fluorescent sensors to quantify subcellular NMN in live cells by engineering specific NMN-responsive protein scaffolds fused to luciferase and fluorescent proteins. The sensor dissected the multimechanistic uptake of exogenous NMN and nicotinamide riboside (NR) in live cells and further measured the NMN levels across different subcellular compartments, as well as the perturbed NMN/NAD+ ratios by external supplements. Moreover, we measured the NMN regulation by NAD(H) hydrolase Nudts and peroxisomal carrier Pxmp2 and identified Slc25a45 as a potential mitochondrial NMN regulator for its unique fingerprint on the local NMN/NAD+ ratio. Collectively, the genetically encoded sensors provide a useful tool for visualizing NMN metabolism.
    Keywords:  Biosensor; Metabolism; NAD(+); NMN; Subcellular
    DOI:  https://doi.org/10.1016/j.bios.2024.116842
  28. iScience. 2024 Oct 18. 27(10): 110975
    Direct targeting of mitochondria by cisplatin leads to cytotoxicity in zebrafish lateral-line hair cells.
    David S Lee, Angela Schrader, Jiaoxia Zou, Wee Han Ang, Mark E Warchol, Lavinia Sheets.
      Cisplatin is a chemotherapy drug that causes permanent hearing loss by injuring cochlear hair cells. Hair cell mitochondria have emerged as potential mediators of hair cell cytotoxicity. Using in vivo live imaging of hair cells in the zebrafish lateral-line organ expressing a genetically encoded indicator of cumulative mitochondrial activity, we first demonstrate that greater redox history increases susceptibility to cisplatin. Next, we conducted time-lapse imaging to understand dynamic changes in mitochondrial homeostasis and observe elevated mitochondrial and cytosolic calcium that surge prior to hair cell death. Furthermore, using a localized probe that fluoresces in the presence of cisplatin, we show that cisplatin directly accumulates in hair cell mitochondria, and this accumulation occurs before mitochondrial dysregulation and apoptosis. Our findings provide evidence that cisplatin directly targets hair cell mitochondria and support that the mitochondria are integral to cisplatin cytotoxicity in hair cells.
    Keywords:  biological sciences; cancer systems biology; natural sciences; pharmacology; systems biology
    DOI:  https://doi.org/10.1016/j.isci.2024.110975
  29. Am J Med Genet A. 2024 Oct 15. e63902
    An Unusual Presentation of Leber Hereditary Optic Neuropathy-Plus Case Caused by a Novel DNAJC30 Variant.
    Hüseyin Bahadır Şenol, Didem Soydemir, Ayşe İpek Polat, Adem Aydın, Ayşe Semra Hız, Uluç Yiş.
      Leber hereditary optic neuropathy (LHON) is characterized by vision loss due to the degeneration of retinal ganglion cells. LHON-Plus refers to LHON with additional extraocular findings. Neurological conditions observed in LHON-Plus include seizures, encephalopathy, movement disorders, neuropathy, and myopathy. Herein, we present a case with atypical LHON-Plus caused by a novel DNAJC30 disease-causing gene variant. A 15-year-old boy presented with acute headache, and blurred and decreased vision in both eyes. Although initial evaluation pointed toward idiopathic intracranial hypertension, the subsequent diagnostic process revealed unusual features like area postrema syndrome and T2 hyperintensity in brain magnetic resonance imaging. Consequently, antibody-negative neuromyelitis optica spectrum disorder (NMOSD) was diagnosed and treatment was commenced. Recurrent episodes of elevated intracranial pressure necessitated the insertion of a ventriculoperitoneal shunt. Exome sequencing (ES) revealed a novel homozygous variant in the DNAJC30 gene 2 years after symptom onset. Atypical LHON presentations due to nuclear gene mutations may mimic other neuroinflammatory conditions like NMOSD, necessitating thorough clinical evaluation and genetic testing. ES plays a crucial role in diagnosing complex neurological cases, enabling the identification of novel genetic variants associated with LHON and related disorders.
    Keywords:  Leber hereditary optic neuropathy; exome sequencing; idiopathic intracranial hypertension; neuromyelitis optica spectrum disorder; ventriculoperitoneal shunt
    DOI:  https://doi.org/10.1002/ajmg.a.63902
  30. Nat Metab. 2024 Oct 15.
    Cytosolic acetyl-CoA synthesis shields mitochondria from stress in brown adipocytes.
      
    DOI:  https://doi.org/10.1038/s42255-024-01152-2
  31. Dev Cell. 2024 Oct 15. pii: S1534-5807(24)00538-0. [Epub ahead of print]
    Outer mitochondrial membrane E3 Ub ligase MARCH5 controls de novo peroxisome biogenesis.
    Nicolas Verhoeven, Yumiko Oshima, Etienne Cartier, Claudia Christiane Bippes, Albert Neutzner, Liron Boyman, Mariusz Karbowski.
      We report that the outer mitochondrial membrane (OMM)-associated E3 Ub ligase MARCH5 is vital for generating mitochondria-derived pre-peroxisomes. In human immortalized cells, MARCH5 knockout leads to the accumulation of immature peroxisomes, reduced fatty-acid-induced peroxisomal biogenesis, and abnormal peroxisome biogenesis in MARCH5/Pex14 and MARCH5/Pex3 dko cells. Upon fatty-acid-induced peroxisomal biogenesis, MARCH5 redistributes to peroxisomes, and ubiquitination activity-deficient mutants of MARCH5 accumulate on peroxisomes containing high levels of the OMM protein Tom20 (mitochondria-derived pre-peroxisomes). Similarly, depletion of peroxisome biogenesis factor Pex14 leads to the accumulation of MARCH5- and Tom20-positive pre-peroxisomes, whereas no peroxisomes are detected in MARCH5/Pex14 dko cells. Inconsistent with MARCH5 merely acting as a quality factor, mitochondrial decline is not evident in tested models. Furthermore, reduced expression of peroxisomal proteins is detected in MARCH5-/- cells, whereas some of these proteins are stabilized in peroxisome biogenesis deficiency models lacking MARCH5 expression. Thus, MARCH5 is central for mitochondria-dependent peroxisome biogenesis.
    Keywords:  MARCH5; Pex14; Pex3; Ub E3 ligase; biogenesis; metabolic adaptation; mitochondria; mitochondria-derived pre-peroxisomes; peroxisomes
    DOI:  https://doi.org/10.1016/j.devcel.2024.09.010
  32. medRxiv. 2024 Oct 11. pii: 2024.10.10.24315152. [Epub ahead of print]
    Biallelic variants in MRPL49 cause variable clinical presentations, including sensorineural hearing loss, leukodystrophy, and ovarian insufficiency.
    Huw B Thomas, Leigh A M Demain, Alfredo Cabrera-Orefice, Isabelle Schrauwen, Hanan E Shamseldin, Alessandro Rea, Thashi Bharadwaj, Thomas B Smith, Monika Oláhová, Kyle Thompson, Langping He, Namanpreet Kaur, Anju Shukla, Musaad Abukhalid, Muhammad Ansar, Sakina Rehman, Saima Riazuddin, Firdous Abdulwahab, Janine M Smith, Zornitza Stark, Samantha Carrera, Wyatt W Yue, Kevin J Munro, Fowzan S Alkuraya, Peter Jamieson, Zubair M Ahmed, Suzanne M Leal, Robert W Taylor, Ilka Wittig, Raymond T O'Keefe, William G Newman.
      Combined oxidative phosphorylation deficiency (COXPD) is a rare multisystem disorder which is clinically and genetically heterogeneous. Genome sequencing identified biallelic MRPL49 variants in individuals from five unrelated families with presentations ranging from Perrault syndrome (primary ovarian insufficiency and sensorineural hearing loss) to severe childhood onset of leukodystrophy, learning disability, microcephaly and retinal dystrophy. Complexome profiling of fibroblasts from affected individuals revealed reduced levels of the small and, a more pronounced reduction of, the large mitochondrial ribosomal subunits. There was no evidence of altered mitoribosomal assembly. The reductions in levels of OXPHOS enzyme complexes I and IV are consistent with a form of COXPD associated with biallelic MRPL49 variants, expanding the understanding of how disruption of the mitochondrial ribosomal large subunit results in multi-system phenotypes.
    DOI:  https://doi.org/10.1101/2024.10.10.24315152
  33. Biochim Biophys Acta Proteins Proteom. 2024 Oct 10. pii: S1570-9639(24)00062-1. [Epub ahead of print] 141055
    Ndufs4 knockout mice with isolated complex I deficiency engage a futile adaptive brain response.
    Melissa A E van de Wal, Cenna Doornbos, Janne Bibbe, Judith R Homberg, Clara van Karnebeek, Martijn A Huynen, Jaap Keijer, Evert M van Schothorst, Peter A C 't Hoen, Mirian C H Janssen, Merel J W Adjobo-Hermans, Mariusz R Wieckowski, Werner J H Koopman.
      Paediatric Leigh syndrome (LS) is an early-onset and fatal neurodegenerative disorder lacking treatment options. LS is frequently caused by mutations in the NDUFS4 gene, encoding an accessory subunit of mitochondrial complex I (CI), the first complex of the oxidative phosphorylation (OXPHOS) system. Whole-body Ndufs4 knockout (KO) mice (WB-KO mice) are widely used to study isolated CI deficiency, LS pathology and interventions. These animals develop a brain-specific phenotype via an incompletely understood pathomechanism. Here we performed a quantitative analysis of the sub-brain proteome in six-weeks old WB-KO mice vs. wildtype mice. Brain regions comprised of a brain slice (BrSl), cerebellum (CB), cerebral cortex (CC), hippocampus (HC), inferior colliculus (IC), and superior colliculus (SC). Proteome analysis demonstrated similarities between CC/HC, and between IC/SC, whereas BrSl and CB differed from these two groups and each other. All brain regions displayed greatly reduced levels of two CI structural subunits (NDUFS4, NDUFA12) and an increased level of the CI assembly factor NDUFAF2. The level of CI-Q module subunits was significantly more reduced in IC/SC than in BrSl/CB/CC/HC, whereas other OXPHOS complex levels were not reduced. Gene ontology and pathway analysis demonstrated specific and common proteome changes between brain regions. Across brain regions, upregulation of cold-shock-associated proteins, mitochondrial fatty acid (FA) oxidation and synthesis (mtFAS) were the most prominent. FA-related pathways were predominantly upregulated in CB and HC. Based upon these results, we argue that stimulation of these pathways is futile and pro-pathological and discuss alternative strategies for therapeutic intervention in LS. SIGNIFICANCE: The Ndufs4 knockout mouse model is currently the most relevant and most widely used animal model to study the brain-linked pathophysiology of human Leigh Syndrome (LS) and intervention strategies. We demonstrate that the Ndufs4 knockout brain engages futile and pro-pathological responses. These responses explain both negative and positive outcomes of intervention studies in Leigh Syndrome mice and patients, thereby guiding novel intervention opportunities.
    Keywords:  Brain; Fatty acids; Leigh syndrome; Pathomechanism; Proteomics
    DOI:  https://doi.org/10.1016/j.bbapap.2024.141055
  34. Front Pediatr. 2024 ;12 1410133
    The Spectrum of clinical manifestations in newborns with the COQ4 mutation: case series and literature review.
    Pianpian Pan, Na Zhou, Yi Sun, Zhengrong Chen, Jin Han, Wei Zhou.
       Background: Coenzyme Q10 (CoQ10) plays an important role in the electron transport chain within the human mitochondrial respiratory chain. The manifestations of this deficiency exhibit a diverse range. This study investigates the clinical manifestations of primary coenzyme Q10 deficiency in neonates with the COQ4 mutation to improve the diagnosis of the disease and the prognosis through targeted treatment.
    Methods: We report 4 patients with primary coenzyme Q10 deficiency by COQ4 variants in neonates. A comprehensive literature search and review for original articles and case reports with COQ4 mutation published from January 1989 to November 2023 was performed through Pubmed. We review clinical manifestations, diagnostic approaches, and treatment monitoring in these and 20 previously reported patients.
    Results: Within the cohort of four cases examined, three females and one male were identified from two distinct families. Specifically, case 1 and 2 consisted of monoamniotic twins. Cases 3 and 4 were siblings. A comprehensive review of 20 cases involving neonatal-onset COQ4 mutation was conducted. Half of the cases are Chinese. There was no statistically significant difference in the mortality between Chinese (9/12, 75%) and other regions (11/12, 91.7%) (P = 0.27). The survival time for the 24 cases was 60.0 ± 98.0 days (95% confidence interval CI: 0-252.0 days). The incidence of prenatal abnormalities in preterm infants was significantly higher than that in full-term infants (66.7% vs. 16.7%, P = 0.02). Hyperlactatemia was one of the most common manifestations, accounting for 75% of cases (18/24). Twenty of the 24 cases were diagnosed by whole exome sequencing. Only 9 patients received exogenous coenzyme Q10 treatment, and all the 4 surviving patients received coenzyme Q10 supplementation.
    Conclusion: The prognosis of COQ4 mutation in the neonatal period indicates a low survival rate and an poor prognosis. This may be due to the incomplete understanding of the mechanism of how COQ4 gene defects lead to coenzyme Q10 deficiency and why CoQ10 supplementation does not respond well to treatment. To improve the diagnostic rate, in addition to genetic testing, mitochondrial functional verification should be prioritized in southern China, where the incidence is relatively high. It will facilitate more in-depth mechanistic studies.
    Keywords:  COQ4; CoQ10; mitochondrial disorder; newborn; primary coenzyme Q10 deficiency
    DOI:  https://doi.org/10.3389/fped.2024.1410133
  35. Int J Mol Sci. 2024 Sep 25. pii: 10302. [Epub ahead of print]25(19):
    Cross-Species Studies Reveal That Dysregulated Mitochondrial Gene Expression and Electron Transport Complex I Activity Are Crucial for Sarcopenia.
    Ji-Yoon Lee, Su-Kyung Shin, Ji-Won Han, Eun-Young Kwon, Heekyong R Bae.
      The significance of complex I of the electron transport chain (ETC) in the aging process is widely acknowledged; however, its specific impact on the development of sarcopenia in muscle remains poorly understood. This study elucidated the correlation between complex I inhibition and sarcopenia by conducting a comparative analysis of skeletal muscle gene expression in sarcopenia phenotypes from rats, mice, and humans. Our findings reveal a common mechanistic link across species, particularly highlighting the correlation between the suppression of complex I of ETC activity and dysregulated mitochondrial transcription and translation in sarcopenia phenotypes. Additionally, we observed macrophage dysfunction alongside abnormal metabolic processes within skeletal muscle tissues across all species, implicating their pathogenic role in the onset of sarcopenia. These discoveries underscore the importance of understanding the shared mechanisms associated with complex I of ETC in sarcopenia development. The identified correlations provide valuable insights into potential targets for therapeutic interventions aimed at mitigating the impact of sarcopenia, a condition with substantial implications for aging populations.
    Keywords:  aging; electron transport complex I; macrophage; mitochondria; muscle; sarcopenia; skeletal
    DOI:  https://doi.org/10.3390/ijms251910302
  36. Neuron. 2024 Oct 08. pii: S0896-6273(24)00663-9. [Epub ahead of print]
    Autophagy, aging, and age-related neurodegeneration.
    Jennifer E Palmer, Niall Wilson, Sung Min Son, Pawel Obrocki, Lidia Wrobel, Matea Rob, Michael Takla, Viktor I Korolchuk, David C Rubinsztein.
      Autophagy is a conserved mechanism that degrades damaged or superfluous cellular contents and enables nutrient recycling under starvation conditions. Many neurodegeneration-associated proteins are autophagy substrates, and autophagy upregulation ameliorates disease in many animal models of neurodegeneration by enhancing the clearance of toxic proteins, proinflammatory molecules, and dysfunctional organelles. Autophagy inhibition also induces neuronal and glial senescence, a phenomenon that occurs with increasing age in non-diseased brains as well as in response to neurodegeneration-associated stresses. However, aging and many neurodegeneration-associated proteins and mutations impair autophagy. This creates a potentially detrimental feedback loop whereby the accumulation of these disease-associated proteins impairs their autophagic clearance, facilitating their further accumulation and aggregation. Thus, understanding how autophagy interacts with aging, senescence, and neurodegenerative diseases in a temporal, cellular, and genetic context is important for the future clinical application of autophagy-modulating therapies in aging and neurodegeneration.
    Keywords:  Alzheimer’s disease; Huntington’s disease; Parkinson’s disease; aging; autophagy; frontotemporal dementia; motor neuron disease; neurodegeneration; senescence
    DOI:  https://doi.org/10.1016/j.neuron.2024.09.015
  37. J Appl Physiol (1985). 2024 Oct 17.
    Acute contractile activity induces the activation of the mitochondrial integrated stress response and the transcription factor ATF4.
    Victoria C Sanfrancesco, David A Hood.
      Skeletal muscle relies on mitochondria to produce energy and support its metabolic flexibility. The function of the mitochondrial pool is regulated by quality control (MQC) processes. The integrated stress response (ISR), a MQC pathway, is activated in response to various cellular stressors. The transcription factor ATF4, the main effector of the ISR, ameliorates cellular stress by upregulating protective genes, such as CHOP and ATF5. Recent literature has shown that the ISR is activated upon mitochondrial stress, however, whether this includes acute exercise-induced stress is poorly defined. To investigate this, a mouse in situ hindlimb protocol was utilized to acutely stimulate muscles at 0.25, 0.5 and 1 tetanic contraction/per second for 9 mins, followed by a 1-hour recovery period. CAMKII and JNK2 were robustly activated 6-fold immediately following the protocol. ISR activation, denoted as the ratio of phosphorylated to total-eIF2a protein levels, was also elevated following recovery. Downstream, contractile activity induced an increase in the nuclear localization of ATF4. Robust 2-fold increases in the mRNA expression of ATF4 and CHOP were also observed following the recovery period. Changes in ATF4 mRNA were independent of transcriptional activation, as assessed using an ATF4 promoter-reporter plasmid. Instead, mRNA decay assays revealed an increase in ATF4 mRNA stability post-contractile activity, as a result of enhanced stabilization by the RNA binding protein, HuR. Thus, acute contractile activity is sufficient to induce mitochondrial stress and activate the ISR, corresponding to the induction of ATF4 with potential consequences for mitochondrial phenotype adaptations in response to repeated exercise.
    Keywords:  Adaptations; Exercise; Mitochondrial Biogenesis; Skeletal Muscle; eIF2α
    DOI:  https://doi.org/10.1152/japplphysiol.00307.2024
  38. Dev Cell. 2024 Oct 14. pii: S1534-5807(24)00600-2. [Epub ahead of print]
    Ubiquitin ligase MARCH5 controls the formation of mitochondria-derived pre-peroxisomes.
    Jun Zheng, Jing Chen, Zhihe Cao, Kaichen Wu, Jinhui Wang, Yusong Guo, Min Zhuang.
      Peroxisome biogenesis involves two pathways: growth and division from pre-existing mature peroxisomes and de novo biogenesis from the endoplasmic reticulum, with a contribution from mitochondria, particularly in human peroxisome-deficient cells. However, the essential components that control peroxisome de novo biogenesis are largely unknown. Dual organelle localized ubiquitin ligase MARCH5 functions on peroxisomes to control pexophagy. Here, we show that mitochondria-localized MARCH5 is essential for the formation of vesicles in the de novo biogenesis of peroxisomes from mitochondria in human cell lines. Loss of MARCH5 specifically impedes the budding of PEX3-containing vesicles from mitochondria, thereby blocking the formation of pre-peroxisomes. Overall, our study highlights the function of MARCH5 for mitochondria-derived pre-peroxisomes, emphasizing MARCH5 as one regulator to maintain peroxisome homeostasis.
    Keywords:  MARCH5; MDVs; PEX3; de nono biogenesis; mitochondria-derived vesicles; peroxisome
    DOI:  https://doi.org/10.1016/j.devcel.2024.09.029
  39. Sci Rep. 2024 10 13. 14(1): 23914
    Deciphering the intracellular forces shaping mitochondrial motion.
    Agustina Belén Fernández Casafuz, Azul Marí A Brigante, Marí A Cecilia De Rossi, Alejandro Gabriel Monastra, Luciana Bruno.
      We propose a novel quantitative method to explore the forces affecting mitochondria within living cells in an almost non-invasive fashion. This new tool enables the detection of localized mechanical impulses on these organelles that occur amidst the stationary fluctuations caused by the thermal jittering in the cytoplasm. Recent experimental evidence shows that the action of mechanical forces has important effects on the dynamics, morphology and distribution of mitochondria in cells. In particular, their crosstalk with the cytoskeleton has been found to alter these organelles function; however, the mechanisms underlying this phenomenon are largely unknown. Our results highlight the different functions that cytoskeletal networks play in shaping mitochondrial dynamics. This work presents a novel technique to extend our knowledge of how the impact of mechanical cues can be quantified at the single organelle level. Moreover, this approach can be expanded to the study of other organelles or biopolymers.
    DOI:  https://doi.org/10.1038/s41598-024-74734-5
  40. PLoS One. 2024 ;19(10): e0311107
    Visualizing VDAC1 in live cells using a tetracysteine tag.
    Johannes Pilic, Furkan E Oflaz, Benjamin Gottschalk, Yusuf C Erdogan, Wolfgang F Graier, Roland Malli.
      The voltage-dependent anion channel 1 (VDAC1) is a crucial gatekeeper in the outer mitochondrial membrane, controlling metabolic and energy homeostasis. The available methodological approaches fell short of accurate visualization of VDAC1 in living cells. To permit precise VDAC1 imaging, we utilized the tetracysteine (TC)-tag and visualized VDAC1 dynamics in living cells. TC-tagged VDAC1 had a cluster-like distribution on mitochondria. The labeling of TC-tagged VDAC1 was validated with immunofluorescence. The majority of VDAC1-TC-clusters were localized at endoplasmic reticulum (ER)-mitochondria contact sites. Notably, VDAC1 colocalized with BCL-2 Antagonist/Killer (BAK)-clusters upon apoptotic stimulation. Using this new tool, we were able to observe VDAC1-TC at mitochondrial fission sites. These findings highlight the suitability of the TC-tag for live-cell imaging of VDAC1, shedding light on the roles of VDAC1 in cellular processes.
    DOI:  https://doi.org/10.1371/journal.pone.0311107
  41. Cell. 2024 Oct 03. pii: S0092-8674(24)01087-0. [Epub ahead of print]
    Structural basis of respiratory complex adaptation to cold temperatures.
    Young-Cheul Shin, Pedro Latorre-Muro, Amina Djurabekova, Oleksii Zdorevskyi, Christopher F Bennett, Nils Burger, Kangkang Song, Chen Xu, Joao A Paulo, Steven P Gygi, Vivek Sharma, Maofu Liao, Pere Puigserver.
      In response to cold, mammals activate brown fat for respiratory-dependent thermogenesis reliant on the electron transport chain. Yet, the structural basis of respiratory complex adaptation upon cold exposure remains elusive. Herein, we combined thermoregulatory physiology and cryoelectron microscopy (cryo-EM) to study endogenous respiratory supercomplexes from mice exposed to different temperatures. A cold-induced conformation of CI:III2 (termed type 2) supercomplex was identified with a ∼25° rotation of CIII2 around its inter-dimer axis, shortening inter-complex Q exchange space, and exhibiting catalytic states that favor electron transfer. Large-scale supercomplex simulations in mitochondrial membranes reveal how lipid-protein arrangements stabilize type 2 complexes to enhance catalytic activity. Together, our cryo-EM studies, multiscale simulations, and biochemical analyses unveil the thermoregulatory mechanisms and dynamics of increased respiratory capacity in brown fat at the structural and energetic level.
    Keywords:  CIII(2) rotation; brown adipose tissue; cellular adaptation; electron transport chain; membrane lipid remodeling; respiratory complexes
    DOI:  https://doi.org/10.1016/j.cell.2024.09.029
  42. Diagnostics (Basel). 2024 Sep 25. pii: 2133. [Epub ahead of print]14(19):
    A Comprehensive Approach to the Diagnosis of Leigh Syndrome Spectrum.
    Manuela Schubert Baldo, Luísa Azevedo, Margarida Paiva Coelho, Esmeralda Martins, Laura Vilarinho.
       BACKGROUND: Leigh syndrome spectrum (LSS) is a novel nomenclature that encompasses both classical Leigh syndrome and Leigh-like phenotypes. Given the heterogeneity of disease presentation, a new consensus published recently addressed the main issues and proposed general guidelines towards diagnosis. Based on these recommendations, we developed a simple pipeline that can be useful in the diagnosis of LSS.
    METHODS: We combined previously published criteria with our own experience to achieve a diagnostic framework that can provide faster satisfactory results with fewer resources.
    RESULTS: We suggest adding basic biochemical tests for amino acids, acylcarnitine, and urinary organic acids as parallel investigations, as these results can be obtained in a short time. This approach characterized 80% of our cohort and promoted specific intervention in 10% of confirmed cases.
    CONCLUSIONS: Genetic studies are crucial in the diagnosis of LSS, but they are time-consuming and might delay tailored interventions. Therefore, we suggest adding more affordable and less complex biochemical studies as primary tests when investigating treatable causes of LSS.
    Keywords:  Leigh syndrome spectrum; diagnosis; mitochondrial disorder; neurodegeneration
    DOI:  https://doi.org/10.3390/diagnostics14192133
  43. EMBO J. 2024 Oct 17.
    An Orai1 gain-of-function tubular aggregate myopathy mouse model phenocopies key features of the human disease.
    Nan Zhao, Antonio Michelucci, Laura Pietrangelo, Sundeep Malik, Linda Groom, Jennifer Leigh, Thomas N O'Connor, Takahiro Takano, Paul D Kingsley, James Palis, Simona Boncompagni, Feliciano Protasi, Robert T Dirksen.
      Tubular aggregate myopathy (TAM) is a heritable myopathy primarily characterized by progressive muscle weakness, elevated levels of creatine kinase (CK), hypocalcemia, exercise intolerance, and the presence of tubular aggregates (TAs). Here, we generated a knock-in mouse model based on a human gain-of-function mutation which results in a severe, early-onset form of TAM, by inducing a glycine-to-serine point mutation in the ORAI1 pore (Orai1G100S/+ or GS mice). By 8 months of age, GS mice exhibited significant muscle weakness, exercise intolerance, elevated CK levels, hypocalcemia, and robust TA presence. Unexpectedly, constitutive Ca2+ entry in mutant mice was observed in muscle only during early development and was abolished in adult skeletal muscle, partly due to reduced ORAI1 expression. Consistent with proteomic results, significant mitochondrial damage and dysfunction was observed in skeletal muscle of GS mice. Thus, GS mice represent a powerful model for investigation of the pathophysiological mechanisms that underlie key TAM symptoms, as well as those compensatory responses that limit the damaging effects of uncontrolled ORAI1-mediated Ca2+ influx.
    Keywords:  Calcium Signaling; Mitochondria; Muscle Disease; ORAI1; Proteomics
    DOI:  https://doi.org/10.1038/s44318-024-00273-4
  44. Cell Rep. 2024 Oct 16. pii: S2211-1247(24)01240-3. [Epub ahead of print]43(11): 114889
    A mitochondrial unfolded protein response-independent role of DVE-1 in longevity regulation.
    Yi Sheng, Adriana Abreu, Zachary Markovich, Pearl Ebea, Leah Davis, Eric Park, Peike Sheng, Mingyi Xie, Sung Min Han, Rui Xiao.
      The special AT-rich sequence-binding (SATB) protein DVE-1 is widely recognized for its pivotal involvement in orchestrating the retrograde mitochondrial unfolded protein response (mitoUPR) in C. elegans. In our study of downstream factors contributing to lifespan extension in sensory ciliary mutants, we find that DVE-1 is crucial for this longevity effect independent of its canonical mitoUPR function. Additionally, DVE-1 also influences lifespan under conditions of dietary restriction and germline loss, again distinct from its role in mitoUPR. Mechanistically, while mitochondrial stress typically prompts nuclear accumulation of DVE-1 to initiate the transcriptional mitoUPR program, these long-lived mutants reduce DVE-1 nuclear accumulation, likely by enhancing its cytosolic translocation. This observation suggests a cytosolic role for DVE-1 in lifespan extension. Overall, our study implies that, in contrast to the more narrowly defined role of the mitoUPR-related transcription factor ATFS-1, DVE-1 may possess broader functions than previously recognized in modulating longevity and defending against stress.
    Keywords:  ATFS-1; C. elegans; CP: Cell biology; CP: Molecular biology; DVE-1; cilia; dietary restriction; germline signaling; longevity; mitoUPR
    DOI:  https://doi.org/10.1016/j.celrep.2024.114889
  45. Nat Metab. 2024 Oct 15.
    Itaconate drives mtRNA-mediated type I interferon production through inhibition of succinate dehydrogenase.
    Shane M O'Carroll, Christian G Peace, Juliana E Toller-Kawahisa, Yukun Min, Alexander Hooftman, Sara Charki, Louise Kehoe, Maureen J O'Sullivan, Aline Zoller, Anne F Mcgettrick, Emily A Day, Maria Simarro, Neali Armstrong, Justin P Annes, Luke A J O'Neill.
      Itaconate is one of the most highly upregulated metabolites in inflammatory macrophages and has been shown to have immunomodulatory properties. Here, we show that itaconate promotes type I interferon production through inhibition of succinate dehydrogenase (SDH). Using pharmacological and genetic approaches, we show that SDH inhibition by endogenous or exogenous itaconate leads to double-stranded mitochondrial RNA (mtRNA) release, which is dependent on the mitochondrial pore formed by VDAC1. In addition, the double-stranded RNA sensors MDA5 and RIG-I are required for IFNβ production in response to SDH inhibition by itaconate. Collectively, our data indicate that inhibition of SDH by itaconate links TCA cycle modulation to type I interferon production through mtRNA release.
    DOI:  https://doi.org/10.1038/s42255-024-01145-1
  46. Cell Metab. 2024 Oct 11. pii: S1550-4131(24)00374-7. [Epub ahead of print]
    Quantification of nutrient fluxes during acute exercise in mice.
    Jessie Axsom, Tara TeSlaa, Won Dong Lee, Qingwei Chu, Alexis Cowan, Marc R Bornstein, Michael D Neinast, Caroline R Bartman, Megan C Blair, Kristina Li, Chelsea Thorsheim, Joshua D Rabinowitz, Zoltan Arany.
      Despite the known metabolic benefits of exercise, an integrated metabolic understanding of exercise is lacking. Here, we use in vivo steady-state isotope-labeled infusions to quantify fuel flux and oxidation during exercise in fasted, fed, and exhausted female mice, revealing several novel findings. Exercise strongly promoted glucose fluxes from liver glycogen, lactate, and glycerol, distinct from humans. Several organs spared glucose, a process that broke down in exhausted mice despite concomitant hypoglycemia. Proteolysis increased markedly, also divergent from humans. Fatty acid oxidation dominated during fasted exercise. Ketone production and oxidation rose rapidly, seemingly driven by a hepatic bottleneck caused by gluconeogenesis-induced cataplerotic stress. Altered fuel consumption was observed in organs not directly involved in muscle contraction, including the pancreas and brown fat. Several futile cycles surprisingly persisted during exercise, despite their energy cost. In sum, we provide a comprehensive, integrated, holistic, and quantitative accounting of metabolism during exercise in an intact organism.
    Keywords:  TCA cycle; circulating metabolites; energy metabolism; exercise; in vivo flux quantification; isotope tracing; skeletal muscle
    DOI:  https://doi.org/10.1016/j.cmet.2024.09.010
  47. Mov Disord. 2024 Oct 15.
    Paroxysmal Non-Kinesigenic Dyskinesias Associated with Biallelic POLG Variants: A Case Report.
    Barbara Castellotti, Cinzia Gellera, Davide Caputo, Federica Rachele Danti, Giuliana Messina, Marinella Corbetta, Stefania Magri, Franco Taroni, Holger Prokisch, Michael Zech, Giovanna Zorzi.
      
    Keywords:  DNA polymerase gamma (POLG); next generation sequencing (NGS); paroxysmal non‐kinesigenic dystinesias (PNKD)
    DOI:  https://doi.org/10.1002/mds.30029
  48. Proc Natl Acad Sci U S A. 2024 Oct 22. 121(43): e2407548121
    Dramatic changes in mitochondrial subcellular location and morphology accompany activation of the CO2 concentrating mechanism.
    Justin Findinier, Lydia-Marie Joubert, Neda Fakhimi, Michael F Schmid, Andrey V Malkovskiy, Wah Chiu, Adrien Burlacot, Arthur R Grossman.
      Dynamic changes in intracellular ultrastructure can be critical for the ability of organisms to acclimate to environmental conditions. Microalgae, which are responsible for ~50% of global photosynthesis, compartmentalize their Ribulose 1,5 Bisphosphate Carboxylase/Oxygenase (Rubisco) into a specialized structure known as the pyrenoid when the cells experience limiting CO2 conditions; this compartmentalization is a component of the CO2 Concentrating Mechanism (CCM), which facilitates photosynthetic CO2 fixation as environmental levels of inorganic carbon (Ci) decline. Changes in the spatial distribution of mitochondria in green algae have also been observed under CO2 limitation, although a role for this reorganization in CCM function remains unclear. We used the green microalga Chlamydomonas reinhardtii to monitor changes in mitochondrial position and ultrastructure as cells transition between high CO2 and Low/Very Low CO2 (LC/VLC). Upon transferring cells to VLC, the mitochondria move from a central to a peripheral cell location and orient in parallel tubular arrays that extend along the cell's apico-basal axis. We show that these ultrastructural changes correlate with CCM induction and are regulated by the CCM master regulator CIA5. The apico-basal orientation of the mitochondrial membranes, but not the movement of the mitochondrion to the cell periphery, is dependent on microtubules and the MIRO1 protein, with the latter involved in membrane-microtubule interactions. Furthermore, blocking mitochondrial respiration in VLC-acclimated cells reduces the affinity of the cells for Ci. Overall, our results suggest that mitochondrial repositioning functions in integrating cellular architecture and energetics with CCM activities and invite further exploration of how intracellular architecture can impact fitness under dynamic environmental conditions.
    Keywords:  CO2 concentrating mechanism; Chlamydomonas; fluorescence microscopy; microalgae; mitochondria
    DOI:  https://doi.org/10.1073/pnas.2407548121
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