bims-mitdyn Biomed News
on Mitochondrial dynamics: mechanisms
Issue of 2021–03–07
23 papers selected by
Edmond Chan, Queen’s University, School of Medicine
  1. Actin cables and comet tails organize mitochondrial networks in mitosis.
  2. Mitochondrial arginase-2 is essential for IL-10 metabolic reprogramming of inflammatory macrophages.
  3. Deletion of the mitochondria-shaping protein Opa1 during early thymocyte maturation impacts mature memory T cell metabolism.
  4. Complexome profile of Toxoplasma gondii mitochondria identifies divergent subunits of respiratory chain complexes including new subunits of cytochrome bc1 complex.
  5. Protease OMA1 modulates mitochondrial bioenergetics and ultrastructure through dynamic association with MICOS complex.
  6. ATAD3B is a mitophagy receptor mediating clearance of oxidative stress-induced damaged mitochondrial DNA.
  7. OXPHOS deficiency activates global adaptation pathways to maintain mitochondrial membrane potential.
  8. MFN2 interacts with Nuage-associated proteins and is essential for male germ cell development by controlling mRNA fate during spermatogenesis.
  9. MITOL-dependent ubiquitylation negatively regulates the entry of PolγA into mitochondria.
  10. Mitochondria as Signaling Organelles Control Mammalian Stem Cell Fate.
  11. Quality control of the mitochondrion.
  12. A conserved arginine residue is critical for stabilizing the N2 FeS cluster in mitochondrial complex I.
  13. Mitochondrial fission is a critical modulator of mutant APP-induced neural toxicity.
  14. Machine learning-based classification of mitochondrial morphology in primary neurons and brain.
  15. IUBMB focused meeting/FEBS workshop: Crosstalk between nucleus and mitochondria in human disease (CrossMitoNus).
  16. Keep your macrophages fit for healthy aging.
  17. Pharmacological advances in mitochondrial therapy.
  18. The translocator protein (TSPO) is prodromal to mitophagy loss in neurotoxicity.
  19. Challenges in Studying Stem Cell Metabolism.
  20. Mitochondrial Respiratory Measurements in Patient-derived Fibroblasts.
  21. Live Mitochondrial or Cytosolic Calcium Imaging Using Genetically-encoded Cameleon Indicator in Mammalian Cells.
  22. Oxygen Consumption Measurements in Caenorhabditis elegans Using the Seahorse XF24.
  23. Quantification of Mitochondrial Dynamics in Fission Yeast.
  1. Nature. 2021 Mar 03.
    Actin cables and comet tails organize mitochondrial networks in mitosis.
    Andrew S Moore, Stephen M Coscia, Cory L Simpson, Fabian E Ortega, Eric C Wait, John M Heddleston, Jeffrey J Nirschl, Christopher J Obara, Pedro Guedes-Dias, C Alexander Boecker, Teng-Leong Chew, Julie A Theriot, Jennifer Lippincott-Schwartz, Erika L F Holzbaur.
      Symmetric cell division requires the even partitioning of genetic information and cytoplasmic contents between daughter cells. Whereas the mechanisms coordinating the segregation of the genome are well known, the processes that ensure organelle segregation between daughter cells remain less well understood1. Here we identify multiple actin assemblies with distinct but complementary roles in mitochondrial organization and inheritance in mitosis. First, we find a dense meshwork of subcortical actin cables assembled throughout the mitotic cytoplasm. This network scaffolds the endoplasmic reticulum and organizes three-dimensional mitochondrial positioning to ensure the equal segregation of mitochondrial mass at cytokinesis. Second, we identify a dynamic wave of actin filaments reversibly assembling on the surface of mitochondria during mitosis. Mitochondria sampled by this wave are enveloped within actin clouds that can spontaneously break symmetry to form elongated comet tails. Mitochondrial comet tails promote randomly directed bursts of movement that shuffle mitochondrial position within the mother cell to randomize inheritance of healthy and damaged mitochondria between daughter cells. Thus, parallel mechanisms mediated by the actin cytoskeleton ensure both equal and random inheritance of mitochondria in symmetrically dividing cells.
    DOI:  https://doi.org/10.1038/s41586-021-03309-5
  2. Nat Commun. 2021 Mar 05. 12(1): 1460
    Mitochondrial arginase-2 is essential for IL-10 metabolic reprogramming of inflammatory macrophages.
    Jennifer K Dowling, Remsha Afzal, Linden J Gearing, Mariana P Cervantes-Silva, Stephanie Annett, Gavin M Davis, Chiara De Santi, Nadine Assmann, Katja Dettmer, Daniel J Gough, Glenn R Bantug, Fidinny I Hamid, Frances K Nally, Conor P Duffy, Aoife L Gorman, Alex M Liddicoat, Ed C Lavelle, Christoph Hess, Peter J Oefner, David K Finlay, Gavin P Davey, Tracy Robson, Annie M Curtis, Paul J Hertzog, Bryan R G Williams, Claire E McCoy.
      Mitochondria are important regulators of macrophage polarisation. Here, we show that arginase-2 (Arg2) is a microRNA-155 (miR-155) and interleukin-10 (IL-10) regulated protein localized at the mitochondria in inflammatory macrophages, and is critical for IL-10-induced modulation of mitochondrial dynamics and oxidative respiration. Mechanistically, the catalytic activity and presence of Arg2 at the mitochondria is crucial for oxidative phosphorylation. We further show that Arg2 mediates this process by increasing the activity of complex II (succinate dehydrogenase). Moreover, Arg2 is essential for IL-10-mediated downregulation of the inflammatory mediators succinate, hypoxia inducible factor 1α (HIF-1α) and IL-1β in vitro. Accordingly, HIF-1α and IL-1β are highly expressed in an LPS-induced in vivo model of acute inflammation using Arg2-/- mice. These findings shed light on a new arm of IL-10-mediated metabolic regulation, working to resolve the inflammatory status of the cell.
    DOI:  https://doi.org/10.1038/s41467-021-21617-2
  3. Cell Death Differ. 2021 Mar 01.
    Deletion of the mitochondria-shaping protein Opa1 during early thymocyte maturation impacts mature memory T cell metabolism.
    Mauro Corrado, Dijana Samardžić, Marta Giacomello, Nisha Rana, Erika L Pearce, Luca Scorrano.
      Optic atrophy 1 (OPA1), a mitochondria-shaping protein controlling cristae biogenesis and respiration, is required for memory T cell function, but whether it affects intrathymic T cell development is unknown. Here we show that OPA1 is necessary for thymocyte maturation at the double negative (DN)3 stage when rearrangement of the T cell receptor β (Tcrβ) locus occurs. By profiling mitochondrial function at different stages of thymocyte maturation, we find that DN3 cells rely on oxidative phosphorylation. Consistently, Opa1 deletion during early T cell development impairs respiration of DN3 cells and reduces their number. Opa1-deficient DN3 cells indeed display stronger TCR signaling and are more prone to cell death. The surviving Opa1-/- thymocytes that reach the periphery as mature T cells display an effector memory phenotype even in the absence of antigenic stimulation but are unable to generate metabolically fit long-term memory T cells. Thus, mitochondrial defects early during T cell development affect mature T cell function.
    DOI:  https://doi.org/10.1038/s41418-021-00747-6
  4. PLoS Pathog. 2021 Mar 02. 17(3): e1009301
    Complexome profile of Toxoplasma gondii mitochondria identifies divergent subunits of respiratory chain complexes including new subunits of cytochrome bc1 complex.
    Andrew E Maclean, Hannah R Bridges, Mariana F Silva, Shujing Ding, Jana Ovciarikova, Judy Hirst, Lilach Sheiner.
      The mitochondrial electron transport chain (mETC) and F1Fo-ATP synthase are of central importance for energy and metabolism in eukaryotic cells. The Apicomplexa, important pathogens of humans causing diseases such as toxoplasmosis and malaria, depend on their mETC in every known stage of their complicated life cycles. Here, using a complexome profiling proteomic approach, we have characterised the Toxoplasma mETC complexes and F1Fo-ATP synthase. We identified and assigned 60 proteins to complexes II, IV and F1Fo-ATP synthase of Toxoplasma, of which 16 have not been identified previously. Notably, our complexome profile elucidates the composition of the Toxoplasma complex III, the target of clinically used drugs such as atovaquone. We identified two new homologous subunits and two new parasite-specific subunits, one of which is broadly conserved in myzozoans. We demonstrate all four proteins are essential for complex III stability and parasite growth, and show their depletion leads to decreased mitochondrial potential, supporting their assignment as complex III subunits. Our study highlights the divergent subunit composition of the apicomplexan mETC and F1Fo-ATP synthase complexes and sets the stage for future structural and drug discovery studies.
    DOI:  https://doi.org/10.1371/journal.ppat.1009301
  5. iScience. 2021 Feb 19. 24(2): 102119
    Protease OMA1 modulates mitochondrial bioenergetics and ultrastructure through dynamic association with MICOS complex.
    Martonio Ponte Viana, Roman M Levytskyy, Ruchika Anand, Andreas S Reichert, Oleh Khalimonchuk.
      Remodeling of mitochondrial ultrastructure is a process that is critical for organelle physiology and apoptosis. Although the key players in this process-mitochondrial contact site and cristae junction organizing system (MICOS) and Optic Atrophy 1 (OPA1)-have been characterized, the mechanisms behind its regulation remain incompletely defined. Here, we found that in addition to its role in mitochondrial division, metallopeptidase OMA1 is required for the maintenance of intermembrane connectivity through dynamic association with MICOS. This association is independent of OPA1, mediated via the MICOS subunit MIC60, and is important for stability of MICOS and the intermembrane contacts. The OMA1-MICOS relay is required for optimal bioenergetic output and apoptosis. Loss of OMA1 affects these activities; remarkably it can be alleviated by MICOS-emulating intermembrane bridge. Thus, OMA1-dependent ultrastructure support is required for mitochondrial architecture and bioenergetics under basal and stress conditions, suggesting a previously unrecognized role for OMA1 in mitochondrial physiology.
    Keywords:  Cell Biology; Molecular Biology; Organizational Aspects of Cell Biology
    DOI:  https://doi.org/10.1016/j.isci.2021.102119
  6. EMBO J. 2021 Mar 05. e106283
    ATAD3B is a mitophagy receptor mediating clearance of oxidative stress-induced damaged mitochondrial DNA.
    Li Shu, Chao Hu, Meng Xu, Jianglong Yu, He He, Jie Lin, Hongying Sha, Bin Lu, Simone Engelender, Minxin Guan, Zhiyin Song.
      Mitochondrial DNA (mtDNA) encodes several key components of respiratory chain complexes that produce cellular energy through oxidative phosphorylation. mtDNA is vulnerable to damage under various physiological stresses, especially oxidative stress. mtDNA damage leads to mitochondrial dysfunction, and dysfunctional mitochondria can be removed by mitophagy, an essential process in cellular homeostasis. However, how damaged mtDNA is selectively cleared from the cell, and how damaged mtDNA triggers mitophagy, remain mostly unknown. Here, we identified a novel mitophagy receptor, ATAD3B, which is specifically expressed in primates. ATAD3B contains a LIR motif that binds to LC3 and promotes oxidative stress-induced mitophagy in a PINK1-independent manner, thus promoting the clearance of damaged mtDNA induced by oxidative stress. Under normal conditions, ATAD3B hetero-oligomerizes with ATAD3A, thus promoting the targeting of the C-terminal region of ATAD3B to the mitochondrial intermembrane space. Oxidative stress-induced mtDNA damage or mtDNA depletion reduces ATAD3B-ATAD3A hetero-oligomerization and leads to exposure of the ATAD3B C-terminus at the mitochondrial outer membrane and subsequent recruitment of LC3 for initiating mitophagy. Furthermore, ATAD3B is little expressed in m.3243A > G mutated cells and MELAS patient fibroblasts showing endogenous oxidative stress, and ATAD3B re-expression promotes the clearance of m.3243A > G mutated mtDNA. Our findings uncover a new pathway to selectively remove damaged mtDNA and reveal that increasing ATAD3B activity is a potential therapeutic approach for mitochondrial diseases.
    Keywords:  ATAD3B; mitochondrial DNA; mitophagy; oxidative stress
    DOI:  https://doi.org/10.15252/embj.2020106283
  7. EMBO Rep. 2021 Mar 03. e51606
    OXPHOS deficiency activates global adaptation pathways to maintain mitochondrial membrane potential.
    Siqi Liu, Shanshan Liu, Baiyu He, Lanlan Li, Lin Li, Jiawen Wang, Tao Cai, She Chen, Hui Jiang.
      Reduction of mitochondrial membrane potential (Δψm ) is a hallmark of mitochondrial dysfunction. It activates adaptive responses in organisms from yeast to human to rewire metabolism, remove depolarized mitochondria, and degrade unimported precursor proteins. It remains unclear how cells maintain Δψm , which is critical for maintaining iron-sulfur cluster (ISC) synthesis, an indispensable function of mitochondria. Here, we show that yeast oxidative phosphorylation mutants deficient in complex III, IV, V, and mtDNA, respectively, exhibit activated stress responses and progressive reduction of Δψm . Extensive omics analyses of these mutants show that these mutants progressively activate adaptive responses, including transcriptional downregulation of ATP synthase inhibitor Inh1 and OXPHOS subunits, Puf3-mediated upregulation of import receptor Mia40 and global mitochondrial biogenesis, Snf1/AMPK-mediated upregulation of glycolysis and repression of ribosome biogenesis, and transcriptional upregulation of cytoplasmic chaperones. These adaptations disinhibit mitochondrial ATP hydrolysis, remodel mitochondrial proteome, and optimize ATP supply to mitochondria to convergently maintain Δψm , ISC biosynthesis, and cell proliferation.
    Keywords:  mitochondrial membrane potential; mitochondrial stress responses; oxidative phosphorylation
    DOI:  https://doi.org/10.15252/embr.202051606
  8. Development. 2021 Mar 05. pii: dev.196295. [Epub ahead of print]
    MFN2 interacts with Nuage-associated proteins and is essential for male germ cell development by controlling mRNA fate during spermatogenesis.
    Xiaoli Wang, Yujiao Wen, Jin Zhang, Grace Swanson, Shuangshuang Guo, Congcong Cao, Stephen A Krawetz, Zhibing Zhang, Shuiqiao Yuan.
      Mitochondria play a critical role in spermatogenesis and are regulated by several mitochondrial fusion proteins. However, their functional importance associated with their structure formation and mRNA fate regulation during spermatogenesis remains unclear. Here, we show that Mitofusin 2 (MFN2), a mitochondrial fusion protein, interacts with Nuage-associated proteins (including MIWI, DDX4, TDRKH, and GASZ). Conditional mutation of Mfn2 in postnatal germ cells results in male sterility due to germ cell developmental defects. Moreover, MFN2 interacts with MFN1, another mitochondrial fusion protein with a high-sequence similarity to MFN2, in testes to facilitate spermatogenesis. Simultaneous mutation of Mfn1 and Mfn2 in testes causes very severe infertile phenotypes. Importantly, we show that MFN2 is enriched in polysome fractions of testes and interacts with MSY2, a germ cell-specific DNA/RNA-binding protein to control gamete-specific mRNA (such as Spata19) translational activity during spermatogenesis. Collectively, our findings demonstrate that MFN2 interacts with Nuage-associated proteins and MSY2 to regulate male germ cell development by controlling several gamete-specific mRNA fates.
    Keywords:  MSY2; Mice; Mitofusins; Nuage proteins; Spermatogenesis
    DOI:  https://doi.org/10.1242/dev.196295
  9. PLoS Biol. 2021 Mar 03. 19(3): e3001139
    MITOL-dependent ubiquitylation negatively regulates the entry of PolγA into mitochondria.
    Mansoor Hussain, Aftab Mohammed, Shabnam Saifi, Aamir Khan, Ekjot Kaur, Swati Priya, Himanshi Agarwal, Sagar Sengupta.
      Mutations in mitochondrial replicative polymerase PolγA lead to progressive external ophthalmoplegia (PEO). While PolγA is the known central player in mitochondrial DNA (mtDNA) replication, it is unknown whether a regulatory process exists on the mitochondrial outer membrane which controlled its entry into the mitochondria. We now demonstrate that PolγA is ubiquitylated by mitochondrial E3 ligase, MITOL (or MARCH5, RNF153). Ubiquitylation in wild-type (WT) PolγA occurs at Lysine 1060 residue via K6 linkage. Ubiquitylation of PolγA negatively regulates its binding to Tom20 and thereby its mitochondrial entry. While screening different PEO patients for mitochondrial entry, we found that a subset of the PolγA mutants is hyperubiquitylated by MITOL and interact less with Tom20. These PolγA variants cannot enter into mitochondria, instead becomes enriched in the insoluble fraction and undergo enhanced degradation. Hence, mtDNA replication, as observed via BrdU incorporation into the mtDNA, was compromised in these PEO mutants. However, by manipulating their ubiquitylation status by 2 independent techniques, these PEO mutants were reactivated, which allowed the incorporation of BrdU into mtDNA. Thus, regulated entry of non-ubiquitylated PolγA may have beneficial consequences for certain PEO patients.
    DOI:  https://doi.org/10.1371/journal.pbio.3001139
  10. Cell Stem Cell. 2021 Mar 04. pii: S1934-5909(21)00061-8. [Epub ahead of print]28(3): 394-408
    Mitochondria as Signaling Organelles Control Mammalian Stem Cell Fate.
    Ram Prosad Chakrabarty, Navdeep S Chandel.
      Recent evidence supports the notion that mitochondrial metabolism is necessary for the determination of stem cell fate. Historically, mitochondrial metabolism is linked to the production of ATP and tricarboxylic acid (TCA) cycle metabolites to support stem cell survival and growth, respectively. However, it is now clear that beyond these canonical roles, mitochondria as signaling organelles dictate stem cell fate and function. In this review, we focus on key conceptual ideas on how mitochondria control mammalian stem cell fate and function through reactive oxygen species (ROS) generation, TCA cycle metabolite production, NAD+/NADH ratio regulation, pyruvate metabolism, and mitochondrial dynamics.
    Keywords:  L-2-HG; ROS; TCA cycle; acetyl-CoA; epigenetics; mitochondrial dynamics; pyruvate
    DOI:  https://doi.org/10.1016/j.stem.2021.02.011
  11. Dev Cell. 2021 Feb 24. pii: S1534-5807(21)00120-9. [Epub ahead of print]
    Quality control of the mitochondrion.
    Matthew Yoke Wui Ng, Timothy Wai, Anne Simonsen.
      Mitochondria are essential organelles that execute and coordinate various metabolic processes in the cell. Mitochondrial dysfunction severely affects cell fitness and contributes to disease. Proper organellar function depends on the biogenesis and maintenance of mitochondria and its >1,000 proteins. As a result, the cell has evolved mechanisms to coordinate protein and organellar quality control, such as the turnover of proteins via mitochondria-associated degradation, the ubiquitin-proteasome system, and mitoproteases, as well as the elimination of mitochondria through mitophagy. Specific quality control mechanisms are engaged depending upon the nature and severity of mitochondrial dysfunction, which can also feed back to elicit transcriptional or proteomic remodeling by the cell. Here, we will discuss the current understanding of how these different quality control mechanisms are integrated and overlap to maintain protein and organellar quality and how they may be relevant for cellular and organismal health.
    Keywords:  ISR; MDVs; UPRmt; UPS; mitochondria; mitochondrial dynamics; mitophagy; mitoproteases
    DOI:  https://doi.org/10.1016/j.devcel.2021.02.009
  12. J Biol Chem. 2021 Feb 25. pii: S0021-9258(21)00248-9. [Epub ahead of print] 100474
    A conserved arginine residue is critical for stabilizing the N2 FeS cluster in mitochondrial complex I.
    Mikhail A Hameedi, Daniel N Grba, Katherine H Richardson, Andrew J Y Jones, Wei Song, Maxie M Roessler, John J Wright, Judy Hirst.
      Respiratory complex I (NADH:ubiquinone oxidoreductase), the first enzyme of the electron-transport chain, captures the free energy released by NADH oxidation and ubiquinone reduction to translocate protons across an energy-transducing membrane and drive ATP synthesis during oxidative phosphorylation. The cofactor that transfers the electrons directly to ubiquinone is an iron-sulfur cluster (N2) located in the NDUFS2/NUCM subunit. A nearby arginine residue (R121), which forms part of the second coordination sphere of the N2 cluster, is known to be post-translationally dimethylated but its functional and structural significance are not known. Here, we show that mutations of this arginine residue (R121M/K) abolish the quinone-reductase activity, concomitant with disappearance of the N2 signature from the electron paramagnetic resonance (EPR) spectrum. Analysis of the cryo-EM structure of NDUFS2-R121M complex I at 3.7 Å resolution identified the absence of the cubane N2 cluster as the cause of the dysfunction, within an otherwise intact enzyme. The mutation further induced localised disorder in nearby elements of the quinone-binding site, consistent with the close connections between the cluster and substrate-binding regions. Our results demonstrate that R121 is required for the formation and/or stability of the N2 cluster, and highlight the importance of structural analyses for mechanistic interpretation of biochemical and spectroscopic data on complex I variants.
    Keywords:  Complex I; NADH:ubiquinone oxidoreductase; Yarrowia lipolytica; cryo‐electron microscopy; dimethyl-arginine; electron paramagnetic resonance (EPR); iron‐sulfur cluster
    DOI:  https://doi.org/10.1016/j.jbc.2021.100474
  13. J Biol Chem. 2021 Feb 24. pii: S0021-9258(21)00242-8. [Epub ahead of print] 100469
    Mitochondrial fission is a critical modulator of mutant APP-induced neural toxicity.
    Lauren Y Shields, Huihui Li, Kevin Nguyen, Hwajin Kim, Zak Doric, Joseph H Garcia, T Michael Gill, Dominik Haddad, Keith Vossel, Meredith Calvert, Ken Nakamura.
      Alterations in mitochondrial fission may contribute to the pathophysiology of several neurodegenerative diseases, including Alzheimer's disease (AD). However, we understand very little about the normal functions of fission, or how fission disruption may interact with AD-associated proteins to modulate pathogenesis. Here we show that loss of the central mitochondrial fission protein dynamin-related 1 (Drp1) in CA1 and other forebrain neurons markedly worsens the learning and memory of mice expressing mutant human amyloid-precursor protein (hAPP) in neurons. In cultured neurons, Drp1KO and hAPP converge to produce mitochondrial Ca2+ (mitoCa2+) overload, despite decreasing mitochondria-associated ER membranes (MAMs) and cytosolic Ca2+. This mitoCa2+ overload occurs independently of ATP levels. These findings reveal a potential mechanism by which mitochondrial fission protects against hAPP-driven pathology.
    Keywords:  Alzheimer’s disease; Drp1; amyloid precursor protein (APP); mitochondria; mitochondrial calcium; mitochondrial fission; neurodegeneration; neurodegenerative disease
    DOI:  https://doi.org/10.1016/j.jbc.2021.100469
  14. Sci Rep. 2021 Mar 04. 11(1): 5133
    Machine learning-based classification of mitochondrial morphology in primary neurons and brain.
    Garrett M Fogo, Anthony R Anzell, Kathleen J Maheras, Sarita Raghunayakula, Joseph M Wider, Katlynn J Emaus, Timothy D Bryson, Melissa J Bukowski, Robert W Neumar, Karin Przyklenk, Thomas H Sanderson.
      The mitochondrial network continually undergoes events of fission and fusion. Under physiologic conditions, the network is in equilibrium and is characterized by the presence of both elongated and punctate mitochondria. However, this balanced, homeostatic mitochondrial profile can change morphologic distribution in response to various stressors. Therefore, it is imperative to develop a method that robustly measures mitochondrial morphology with high accuracy. Here, we developed a semi-automated image analysis pipeline for the quantitation of mitochondrial morphology for both in vitro and in vivo applications. The image analysis pipeline was generated and validated utilizing images of primary cortical neurons from transgenic mice, allowing genetic ablation of key components of mitochondrial dynamics. This analysis pipeline was further extended to evaluate mitochondrial morphology in vivo through immunolabeling of brain sections as well as serial block-face scanning electron microscopy. These data demonstrate a highly specific and sensitive method that accurately classifies distinct physiological and pathological mitochondrial morphologies. Furthermore, this workflow employs the use of readily available, free open-source software designed for high throughput image processing, segmentation, and analysis that is customizable to various biological models.
    DOI:  https://doi.org/10.1038/s41598-021-84528-8
  15. IUBMB Life. 2021 Mar 05.
    IUBMB focused meeting/FEBS workshop: Crosstalk between nucleus and mitochondria in human disease (CrossMitoNus).
    Irene Díaz-Moreno, Miguel A De la Rosa.
      The IUBMB Focused Meeting/FEBS Workshop titled 'Crosstalk between Nucleus and Mitochondria in Human Disease'(CrossMitoNus) will take place on September 7-10, 2021 in Seville (Spain), with the support of both the International Union of Biochemistry and Molecular Biology (IUBMB) and the Federation of European Biochemical Societies (FEBS). Mitochondria are key organelles that act as a hub for vital metabolic processes, for example, energy transduction by oxidative phosphorylation, intermediary metabolism, redox signaling, calcium and iron homeostasis, heme and steroid biosynthesis, metal homeostasis, programmed cell death, and innate immunity. Consequently, a wide assortment of diseases-including neurodegenerative disorders, diabetes, cancer, rare syndromes, and many others-relate to mitochondrial dysfunction. The high relevance of mitochondria in metabolism centers on the core of cell signaling pathways, including those involved in cell-fate decisions. Critical metabolites synthesized in mitochondria are, for instance, key modulators of the sirtuin, AMPK, mTOR, and Hypoxia-inducible Factor 1A pathways. Mitochondria are indeed the major source of reactive oxygen species, which in turn mediate several regulatory routes. Interestingly, multiple nuclear-encoded factors control essential processes in mitochondrial dynamics, namely fusion (for instance, OPA1), fission (DNM1L), transport (RHOT1), and mitophagy (PINK1). The release of mitochondrial factors like cytochrome c to the cytoplasm is indeed key for the rapid onset of the intrinsic apoptotic pathway. The CrossMitoNus meeting aims to join efforts from diverse disciplines to unveil the mitochondrial and nuclear factors that are emerging as essential elements in mitochondria-nucleus communication. Needless to say, the mechanisms regulating mitochondrial protein trafficking into and out of the nucleus and the role of these proteins in the nucleus remain to be elucidated.
    Keywords:  FEBS workshop; IUBMB focused meeting; cell network; crosstalk; mitochondria; nucleus
    DOI:  https://doi.org/10.1002/iub.2459
  16. Cell Metab. 2021 Mar 02. pii: S1550-4131(21)00060-7. [Epub ahead of print]33(3): 468-470
    Keep your macrophages fit for healthy aging.
    Jan Van den Bossche, Pieter J M Leenen.
      As age is the greatest risk factor for the development of most prevalent chronic diseases, there is an enormous interest in understanding the process of aging, with the hope of delaying or preventing age-related comorbidities. Along these lines, a recent study by Minhas et al. (2021) describes how aged macrophages downregulate glycolysis and mitochondrial oxidative phosphorylation (OXPHOS), inducing an energy-deficient state that compromises macrophage function and supports maladaptive inflammation that together cause brain dysfunction.
    DOI:  https://doi.org/10.1016/j.cmet.2021.02.004
  17. EBioMedicine. 2021 Feb 26. pii: S2352-3964(21)00037-2. [Epub ahead of print]65 103244
    Pharmacological advances in mitochondrial therapy.
    Aarti Singh, Danilo Faccenda, Michelangelo Campanella.
      Mitochondria play a vital role in cellular metabolism and are central mediator of intracellular signalling, cell differentiation, morphogenesis and demise. An increasingly higher number of pathologies is linked with mitochondrial dysfunction, which can arise from either genetic defects affecting core mitochondrial components or malfunctioning pathways impairing mitochondrial homeostasis. As such, mitochondria are considered an important target in several pathologies spanning from neoplastic to neurodegenerative diseases as well as metabolic syndromes. In this review we provide an overview of the state-of-the-art in mitochondrial pharmacology, focusing on the novel compounds that have been generated in the bid to correct mitochondrial aberrations. Our work aims to serve the scientific community working on translational medical science by highlighting the most promising pharmacological approaches to target mitochondrial dysfunction in disease.
    Keywords:  Mitochondria-targeted and untargeted agents; Mitochondrial diseases; Mitochondrial dysfunction in pathology
    DOI:  https://doi.org/10.1016/j.ebiom.2021.103244
  18. Mol Psychiatry. 2021 Mar 04.
    The translocator protein (TSPO) is prodromal to mitophagy loss in neurotoxicity.
    Michele Frison, Danilo Faccenda, Rosella Abeti, Manuel Rigon, Daniela Strobbe, Britannie S England-Rendon, Diana Cash, Katy Barnes, Mona Sadeghian, Marija Sajic, Lisa A Wells, Dong Xia, Paola Giunti, Kenneth Smith, Heather Mortiboys, Federico E Turkheimer, Michelangelo Campanella.
      Dysfunctional mitochondria characterise Parkinson's Disease (PD). Uncovering etiological molecules, which harm the homeostasis of mitochondria in response to pathological cues, is therefore pivotal to inform early diagnosis and therapy in the condition, especially in its idiopathic forms. This study proposes the 18 kDa Translocator Protein (TSPO) to be one of those. Both in vitro and in vivo data show that neurotoxins, which phenotypically mimic PD, increase TSPO to enhance cellular redox-stress, susceptibility to dopamine-induced cell death, and repression of ubiquitin-dependent mitophagy. TSPO amplifies the extracellular signal-regulated protein kinase 1 and 2 (ERK1/2) signalling, forming positive feedback, which represses the transcription factor EB (TFEB) and the controlled production of lysosomes. Finally, genetic variances in the transcriptome confirm that TSPO is required to alter the autophagy-lysosomal pathway during neurotoxicity.
    DOI:  https://doi.org/10.1038/s41380-021-01050-z
  19. Cell Stem Cell. 2021 Mar 04. pii: S1934-5909(21)00066-7. [Epub ahead of print]28(3): 409-423
    Challenges in Studying Stem Cell Metabolism.
    Cesar A Perez-Ramirez, Heather R Christofk.
      The expanding field of stem cell metabolism has been supported by technical advances in metabolite profiling and novel functional analyses. While use of these methodologies has been fruitful, many challenges are posed by the intricacies of culturing stem cells in vitro, along with the distinctive scarcity of adult tissue stem cells and the complexities of their niches in vivo. This review provides an examination of the methodologies used to characterize stem cell metabolism, highlighting their utility while placing a sharper focus on their limitations and hurdles the field needs to overcome for the optimal study of stem cell metabolic networks.
    DOI:  https://doi.org/10.1016/j.stem.2021.02.016
  20. Bio Protoc. 2019 Dec 05. 9(23): e3446
    Mitochondrial Respiratory Measurements in Patient-derived Fibroblasts.
    Prashant Mishra, Ting Zhang, Ming Guo, David Chan.
      Mitochondrial dysfunction is associated with a number of human diseases. As an example, we recently established in vivo Drosophila models of IBMPFD (Inclusion body myopathy, Paget disease, and frontotemporal dementia), and uncovered that human disease mutations of the p97/VCP (Valosin Containing Protein) gene behave as hyperactive alleles associated with mitochondrial defects. Pharmacologic inhibition of VCP strongly suppressed disease and mitochondrial pathology in these animal models. In this protocol, we describe a method to evaluate mitochondrial respiratory function in IBMPFD patient-derived fibroblasts, as well as investigate the role of pharmacologic treatments. These experiments complement work done in animal models by investigating mitochondrial biology and the pharmacologic response in a human cell-based model of the disease. In principle, this technique can be used to investigate mitochondrial respiratory function for any disease in which patient-derived fibroblasts are available.
    Keywords:  Inclusion body myopathy; Mitochondrial respiration; Paget disease and frontotemporal dementia (IBMPFD); Patient-derived fibroblasts; Seahorse XF assay; VCP/p97
    DOI:  https://doi.org/10.21769/BioProtoc.3446
  21. Bio Protoc. 2020 Feb 05. 10(3): e3504
    Live Mitochondrial or Cytosolic Calcium Imaging Using Genetically-encoded Cameleon Indicator in Mammalian Cells.
    Elisa Greotti, Tullio Pozzan.
      Calcium (Ca2+) imaging aims at investigating the dynamic changes in live cells of its concentration ([Ca2+]) in different pathophysiological conditions. Ca2+ is an ubiquitous and versatile intracellular signal that modulates a large variety of cellular functions thanks to a cell type-specific toolkit and a complex subcellular compartmentalization. Many Ca2+ sensors are presently available (chemical and genetically encoded) that can be specifically targeted to different cellular compartments. Using these probes, it is now possible to monitor Ca2+ dynamics of living cells not only in the cytosol but also within specific organelles. The choice of a specific sensor depends on the experimental design and the spatial and temporal resolution required. Here we describe the use of novel Förster resonance energy transfer (FRET)-based fluorescent Ca2+ probes to dynamically and quantitatively monitor the changes in cytosolic and mitochondrial [Ca2+] in a variety of cell types and experimental conditions. FRET-based sensors have the enormous advantage of being ratiometric, a feature that makes them particularly suitable for quantitative and in vivo applications.
    Keywords:   Cytosolic Ca2+ imaging ; IP3 Receptor ; mitochondrial Ca2+ imaging ; Cameleon; Endoplasmic Reticulum; FRET; Genetically-Encoded Calcium Indicators; Mitochondria; Ryanodine Receptor.; SOCE
    DOI:  https://doi.org/10.21769/BioProtoc.3504
  22. Bio Protoc. 2019 Jul 05. 9(13): e3288
    Oxygen Consumption Measurements in Caenorhabditis elegans Using the Seahorse XF24.
    Suraiya Haroon, Marc Vermulst.
      Mitochondria generate 90% of the energy required to sustain life. As a result, loss of mitochondrial function compromises almost every facet of human physiology. Accordingly, most mitochondrial diseases tend to present themselves as complex, multi-systemic disorders that can be difficult to diagnose. Depending on the severity of the mitochondrial dysfunction, the pathology can range from mild discomfort to severe epilepsy, blindness and paralysis. To develop therapies to these diseases, it will be important to optimize experimental techniques that can reliably quantify mitochondrial function, particularly in live cells or intact organisms. Here, we describe how a Seahorse XF24 Analyzer can be used to measure both basal and maximal respiration in the nematode Caenorhabditis elegans, and how this data can be interpreted to evaluate mitochondrial function.
    Keywords:  C. elegans; FCCP; Maximal respiration capacity; Mitochondria; Oxygen consumption; Seahorse XF24
    DOI:  https://doi.org/10.21769/BioProtoc.3288
  23. Bio Protoc. 2019 Dec 05. 9(23): e3450
    Quantification of Mitochondrial Dynamics in Fission Yeast.
    Leeba Ann Chacko, Vaishnavi Ananthanarayanan.
      Mitochondria are double-membraned organelles responsible for several functions in the cell including energy production, calcium signaling, and cellular metabolism. An equilibrium between fission and fusion events of mitochondria is required for their proper functioning. Mitochondrial morphologies have been quantified in yeast using image processing modules such as MitoGraph and MitoLoc. However, the dynamics of mitochondrial fission and fusion have not been analyzed in these methods. Here, we present a method for measuring mitochondrial morphologies, as well as estimation of fission and fusion frequencies of mitochondria in individual fission yeast cells whose mitochondria are fluorescently-tagged or stained. The latter relies on counting of individual mitochondria upon signal filtering in each frame of a time-lapse. Taken together, we present a simple protocol for analyzing mitochondrial dynamics, which can easily be adopted to other model systems.
    Keywords:  Cell biology; Fluorescence microscopy; Live-cell imaging; Mitochondria; Mitochondrial dynamics; Mitochondrial fission; Mitochondrial fusion; Schizosaccharomyces pombe
    DOI:  https://doi.org/10.21769/BioProtoc.3450
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