bims-mitmed 2022-03-20 papers

bims-mitmed

Biomed News

on Mitochondrial medicine

Issue of 2022–03–20
29 papers selected by
Dario Brunetti, Fondazione IRCCS Istituto Neurologico

Mitochondrial Dynamics, Mitophagy, and Mitochondria-Endoplasmic Reticulum Contact Sites Crosstalk Under Hypoxia.
SPOTting stress at the mitochondrial outer membrane.
POLG mutations lead to abnormal mitochondrial remodeling during neural differentiation of human pluripotent stem cells via SIRT3/AMPK pathway inhibition.
Applying Sodium Carbonate Extraction Mass Spectrometry to Investigate Defects in the Mitochondrial Respiratory Chain.
Case Report: Thymidine Kinase 2 (TK2) Deficiency: A Novel Mutation Associated With Childhood-Onset Mitochondrial Myopathy and Atypical Progression.
Generation of four iPSC lines from four patients with Leigh syndrome carrying homoplasmic mutations m.8993T > G or m.8993T > C in the mitochondrial gene MT-ATP6.
Muscle MRI characteristic pattern for late-onset TK2 deficiency diagnosis.
Mitochondrial transport and metabolism of the vitamin B-derived cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ , and related diseases: A review.
Multimodal retinal imaging of m.3243A>G associated retinopathy.
Sirt3 ameliorates mitochondrial dysfunction and oxidative stress through regulating mitochondrial biogenesis and dynamics in cardiomyoblast.
Key features of inhibitor binding to the human mitochondrial pyruvate carrier hetero-dimer.
The Unfolded Protein Responses in Health, Aging, and Neurodegeneration: Recent Advances and Future Considerations.
Disruption of Mitochondrial Quality Control Genes Promotes Caspase-Resistant Cell Survival Following Apoptotic Stimuli.
Placental structure, function and mitochondrial phenotype relate to fetal size in each fetal sex in mice.
CEST-2.2 overexpression alters lipid metabolism and extends longevity of mitochondrial mutants.
Mitochondrial Membrane Potential Assay.
Mitochondrial depolarization after acute ethanol treatment drives mitophagy in living mice.
The effect of gestational age on mitochondrial properties of the mouse placenta.
PGC-1α affects skeletal muscle and adipose tissue development by regulating mitochondrial biogenesis.
Piezo1 regulates the regenerative capacity of skeletal muscles via orchestration of stem cell morphological states.
Autosomal Recessive Cerebellar Atrophy and Spastic Ataxia in Patients With Pathogenic Biallelic Variants in GEMIN5.
Mitochondrial DNA variants segregate during human preimplantation development into genetically different cell lineages that are maintained postnatally.
A role for cell polarity in lifespan and mitochondrial quality control in the budding yeast Saccharomyces cerevisiae.
Myostatin is involved in skeletal muscle dysfunction in chronic obstructive pulmonary disease via Drp-1 mediated abnormal mitochondrial division.
DNA replication in cell fate reprogramming.
Lysosomal Ca2+-mediated TFEB activation modulates mitophagy and functional adaptation of pancreatic β-cells to metabolic stress.
Mitochondrial uncoupling attenuates sarcopenic obesity by enhancing skeletal muscle mitophagy and quality control.
Abnormal mitochondria in Down syndrome iPSC-derived GABAergic interneurons and organoids.
Copper induces cell death by targeting lipoylated TCA cycle proteins.

Front Cell Dev Biol. 2022 ;10 848214

Mitochondrial Dynamics, Mitophagy, and Mitochondria-Endoplasmic Reticulum Contact Sites Crosstalk Under Hypoxia.

Shuying Wang, Jin Tan, Yuyang Miao, Qiang Zhang.

  Mitochondria are double membrane organelles within eukaryotic cells, which act as cellular power houses, depending on the continuous availability of oxygen. Nevertheless, under hypoxia, metabolic disorders disturb the steady-state of mitochondrial network, which leads to dysfunction of mitochondria, producing a large amount of reactive oxygen species that cause further damage to cells. Compelling evidence suggests that the dysfunction of mitochondria under hypoxia is linked to a wide spectrum of human diseases, including obstructive sleep apnea, diabetes, cancer and cardiovascular disorders. The functional dichotomy of mitochondria instructs the necessity of a quality-control mechanism to ensure a requisite number of functional mitochondria that are present to fit cell needs. Mitochondrial dynamics plays a central role in monitoring the condition of mitochondrial quality. The fission-fusion cycle is regulated to attain a dynamic equilibrium under normal conditions, however, it is disrupted under hypoxia, resulting in mitochondrial fission and selective removal of impaired mitochondria by mitophagy. Current researches suggest that the molecular machinery underlying these well-orchestrated processes are coordinated at mitochondria-endoplasmic reticulum contact sites. Here, we establish a holistic understanding of how mitochondrial dynamics and mitophagy are regulated at mitochondria-endoplasmic reticulum contact sites under hypoxia.

Keywords:  hypoxia; mitochondria; mitochondria-endoplasmic reticulum contact sites; mitochondrial dynamics; mitophagy

DOI:  https://doi.org/10.3389/fcell.2022.848214
Mol Cell. 2022 Mar 17. pii: S1097-2765(22)00168-X. [Epub ahead of print]82(6): 1086-1088

SPOTting stress at the mitochondrial outer membrane.

Max-Hinderk Schuler, Adam L Hughes.

Li et al. (2022) discover that Toxoplasma infection triggers remodeling of the mitochondrial outer membrane through generation of a mitochondrial subdomain termed "structure positive for outer mitochondrial membrane" (SPOT).

DOI: https://doi.org/10.1016/j.molcel.2022.02.030
Cell Cycle. 2022 Mar 17. 1-16

POLG mutations lead to abnormal mitochondrial remodeling during neural differentiation of human pluripotent stem cells via SIRT3/AMPK pathway inhibition.

Anbin Chen, Cecilie Katrin Kristiansen, Lena Elise Høyland, Mathias Ziegler, Jian Wang, Gareth John Sullivan, Xingang Li, Laurence A Bindoff, Kristina Xiao Liang.

  We showed previously that POLG mutations cause major changes in mitochondrial function, including loss of mitochondrial respiratory chain (MRC) complex I, mitochondrial DNA (mtDNA) depletion and an abnormal NAD+/NADH ratio in both neural stem cells (NSCs) and astrocytes differentiated from induced pluripotent stem cells (iPSCs). In the current study, we looked at mitochondrial remodeling as stem cells transit pluripotency and during differentiation from NSCs to both dopaminergic (DA) neurons and astrocytes comparing the process in POLG-mutated and control stem cells. We saw that mitochondrial membrane potential (MMP), mitochondrial volume, ATP production and reactive oxygen species (ROS) changed in similar ways in POLG and control NSCs, but mtDNA replication, MRC complex I and NAD+ metabolism failed to remodel normally. In DA neurons differentiated from NSCs, we saw that POLG mutations caused failure to increase MMP and ATP production and blunted the increase in mtDNA and complex I. Interestingly, mitochondrial remodeling during astrocyte differentiation from NSCs was similar in both POLG-mutated and control NSCs. Further, we showed downregulation of the SIRT3/AMPK pathways in POLG-mutated cells, suggesting that POLG mutations lead to abnormal mitochondrial remodeling in early neural development due to the downregulation of these pathways. [Figure: see text].

Keywords:  DA neurons; Mitochondrial remodeling; NSCs; POLG; astrocytes; iPSCs

DOI:  https://doi.org/10.1080/15384101.2022.2044136
Front Cell Dev Biol. 2022 ;10 786268

Applying Sodium Carbonate Extraction Mass Spectrometry to Investigate Defects in the Mitochondrial Respiratory Chain.

David R L Robinson, Daniella H Hock, Linden Muellner-Wong, Roopasingam Kugapreethan, Boris Reljic, Elliot E Surgenor, Carlos H M Rodrigues, Nikeisha J Caruana, David A Stroud.

  Mitochondria are complex organelles containing 13 proteins encoded by mitochondrial DNA and over 1,000 proteins encoded on nuclear DNA. Many mitochondrial proteins are associated with the inner or outer mitochondrial membranes, either peripherally or as integral membrane proteins, while others reside in either of the two soluble mitochondrial compartments, the mitochondrial matrix and the intermembrane space. The biogenesis of the five complexes of the oxidative phosphorylation system are exemplars of this complexity. These large multi-subunit complexes are comprised of more than 80 proteins with both membrane integral and peripheral associations and require soluble, membrane integral and peripherally associated assembly factor proteins for their biogenesis. Mutations causing human mitochondrial disease can lead to defective complex assembly due to the loss or altered function of the affected protein and subsequent destabilization of its interactors. Here we couple sodium carbonate extraction with quantitative mass spectrometry (SCE-MS) to track changes in the membrane association of the mitochondrial proteome across multiple human knockout cell lines. In addition to identifying the membrane association status of over 840 human mitochondrial proteins, we show how SCE-MS can be used to understand the impacts of defective complex assembly on protein solubility, giving insights into how specific subunits and sub-complexes become destabilized.

Keywords:  OXPHOS (oxidative phosphorylation); carbonate extraction; membrane protein; mitochondria; proteomic analyses; respiratory chain assembly

DOI:  https://doi.org/10.3389/fcell.2022.786268
Front Neurol. 2022 ;13 857279

Case Report: Thymidine Kinase 2 (TK2) Deficiency: A Novel Mutation Associated With Childhood-Onset Mitochondrial Myopathy and Atypical Progression.

Arianna Manini, Megi Meneri, Carmelo Rodolico, Stefania Corti, Antonio Toscano, Giacomo Pietro Comi, Olimpia Musumeci, Dario Ronchi.

  The nuclear gene TK2 encodes the mitochondrial thymidine kinase, an enzyme involved in the phosphorylation of deoxycytidine and deoxythymidine nucleosides. Biallelic TK2 mutations are associated with a spectrum of clinical presentations mainly affecting skeletal muscle and featuring muscle mitochondrial DNA (mtDNA) instability. Current classification includes infantile- ( ≤ 1 year), childhood- (1-12 years), and late-onset (≥12 years) forms. In addition to age at onset, these forms differ for progression, life expectancy, and signs of mtDNA instability (mtDNA depletion vs. accumulation of multiple mtDNA deletions). Childhood-onset TK2 deficiency typically causes a rapidly progressive proximal myopathy, which leads to wheelchair-bound status within 10 years of disease onset, and severe respiratory impairment. Muscle biopsy usually reveals a combination of mitochondrial myopathy and dystrophic features with reduced mtDNA content. Here we report the case of an Italian patient presenting childhood-onset, slowly progressive mitochondrial myopathy, ptosis, hypoacusis, dysphonia, and dysphagia, harboring the TK2 variants c.278A>G and c.543del, the latter unreported so far. Compared to other childhood-onset TK2-patients, our case displays atypical features, including slowly progressive muscle weakness and absence of respiratory failure, which are usually observed in late-onset forms. This report extends the genetic background of TK2-related myopathy, highlighting the clinical overlap among different forms.

Keywords:  TK2; deoxynucleosides; mitochondrial DNA; mtDNA maintenance defects; myopathy; thymidine kinase 2

DOI:  https://doi.org/10.3389/fneur.2022.857279
Stem Cell Res. 2022 Mar 08. pii: S1873-5061(22)00091-5. [Epub ahead of print]61 102742

Generation of four iPSC lines from four patients with Leigh syndrome carrying homoplasmic mutations m.8993T > G or m.8993T > C in the mitochondrial gene MT-ATP6.

Carmen Lorenz, Annika Zink, Marie-Therese Henke, Selma Staege, Barbara Mlody, Miriam Bünning, Erich Wanker, Sebastian Diecke, Markus Schuelke, Alessandro Prigione.

We report the generation of four human iPSC lines (8993-A12, 8993-B12, 8993-C11, and 8993-D7) from fibroblasts of four patients affected by maternally inherited Leigh syndrome (MILS) carrying homoplasmic mutations m.8993T > G or m.8993T > C in the mitochondrial gene MT-ATP6. We used Sendai viruses to deliver reprogramming factors OCT4, SOX2, KLF4, and c-MYC. The established iPSC lines expressed pluripotency markers, exhibited a normal karyotype, were capable to form cells of the three germ layers in vitro, and retained the MT-ATP6 mutations at the same homoplasmic level of the parental fibroblasts.

DOI: https://doi.org/10.1016/j.scr.2022.102742
J Neurol. 2022 Mar 14.

Muscle MRI characteristic pattern for late-onset TK2 deficiency diagnosis.

Cristina Domínguez-González, Roberto Fernández-Torrón, Ursula Moore, Carlos Pablo de Fuenmayor-Fernández de la Hoz, Beatriz Vélez-Gómez, Juan Antonio Cabezas, Jorge Alonso-Pérez, Laura González-Mera, Montse Olivé, Jorge García-García, Germán Moris, Juan Carlos León Hernández, Nuria Muelas, Emilia Servian-Morilla, Miguel A Martin, Jordi Díaz-Manera, Carmen Paradas.

   BACKGROUND AND OBJECTIVE: TK2 deficiency (TK2d) is a rare mitochondrial disorder that manifests predominantly as a progressive myopathy with a broad spectrum of severity and age of onset. The rate of progression is variable, and the prognosis is poor due to early and severe respiratory involvement. Early and accurate diagnosis is particularly important since a specific treatment is under development. This study aims to evaluate the diagnostic value of lower limb muscle MRI in adult patients with TK2d.
METHODS: We studied a cohort of 45 genetically confirmed patients with mitochondrial myopathy (16 with mutations in TK2, 9 with mutations in other nuclear genes involved in mitochondrial DNA [mtDNA] synthesis or maintenance, 10 with single mtDNA deletions, and 10 with point mtDNA mutations) to analyze the imaging pattern of fat replacement in lower limb muscles. We compared the identified pattern in patients with TK2d with the MRI pattern of other non-mitochondrial genetic myopathies that share similar clinical characteristics.
RESULTS: We found a consistent lower limb muscle MRI pattern in patients with TK2d characterized by involvement of the gluteus maximus, gastrocnemius medialis, and sartorius muscles. The identified pattern in TK2 patients differs from the known radiological involvement of other resembling muscle dystrophies that share clinical features.
CONCLUSIONS: By analyzing the largest cohort of muscle MRI from patients with mitochondrial myopathies studied to date, we identified a characteristic and specific radiological pattern of muscle involvement in patients with TK2d that could be useful to speed up its diagnosis.

Keywords:  MRI; Mitochondrial myopathy; TK2

DOI:  https://doi.org/10.1007/s00415-021-10957-0
IUBMB Life. 2022 Mar 18.

Mitochondrial transport and metabolism of the vitamin B-derived cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ , and related diseases: A review.

Ferdinando Palmieri, Magnus Monné, Giuseppe Fiermonte, Luigi Palmieri.

  Multiple mitochondrial matrix enzymes playing key roles in metabolism require cofactors for their action. Due to the high impermeability of the mitochondrial inner membrane, these cofactors need to be synthesized within the mitochondria or be imported, themselves or one of their precursors, into the organelles. Transporters belonging to the protein family of mitochondrial carriers have been identified to transport the coenzymes: thiamine pyrophosphate, coenzyme A, FAD and NAD+ , which are all structurally similar to nucleotides and derived from different B-vitamins. These mitochondrial cofactors bind more or less tightly to their enzymes and, after having been involved in a specific reaction step, are regenerated, spontaneously or by other enzymes, to return to their active form, ready for the next catalysis round. Disease-causing mutations in the mitochondrial cofactor carrier genes compromise not only the transport reaction but also the activity of all mitochondrial enzymes using that particular cofactor and the metabolic pathways in which the cofactor-dependent enzymes are involved. The mitochondrial transport, metabolism and diseases of the cofactors thiamine pyrophosphate, coenzyme A, FAD and NAD+ are the focus of this review.

Keywords:  coenzyme; coenzyme A; flavin adenine dinucleotide; mitochondria; mitochondrial carrier family SLC25; nicotinamide adenine dinucleotide; thiamine pyrophosphate

DOI:  https://doi.org/10.1002/iub.2612
Am J Ophthalmol Case Rep. 2022 Jun;26 101411

Multimodal retinal imaging of m.3243A>G associated retinopathy.

Francesco Romano, Mariano Cozzi, Giovanni Staurenghi, Anna Paola Salvetti.

  Retro-mode illumination imaging can provide good visualization of chorio-retinal atrophy and of the retinal pigment epithelial alterations occurring in m.3243A > G associated retinopathy.

Keywords:  Chorio-retinal atrophy; Encephalopathy; Lactic acidosis and stroke-like episodes syndrome; MELAS; MELAS, mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes; MTTL1 gene; Mitochondrial myopathy; Mitochondrial retinopathy; Multimodal imaging; NIR-AF, near-infrared autofluorescence; OCT, optical coherence tomography; RPE, retinal pigment epithelium; Retro-mode illumination; m.3243A>G

DOI:  https://doi.org/10.1016/j.ajoc.2022.101411
Cell Signal. 2022 Mar 15. pii: S0898-6568(22)00070-5. [Epub ahead of print] 110309

Sirt3 ameliorates mitochondrial dysfunction and oxidative stress through regulating mitochondrial biogenesis and dynamics in cardiomyoblast.

Paramesha Bugga, Md Jahangir Alam, Roshan Kumar, Subhashis Pal, Naibedya Chattopadyay, Sanjay Kumar Banerjee.

  Sirtuins are the endogenously present anti-aging protein deacetylases that regulate the mitochondrial biogenesis and function. Especially Sirt3, a mitochondrial sirtuin, is well known for maintaining mitochondrial function and health. In the present study, we have explored the novel role of Sirt3 in mitochondrial biogenesis and shown the role of Sirt3 in mito-nuclear communication through AMPK-α in Sirt3 knockdown and Sirt3 overexpressed H9c2 cells. The study found that impaired mitochondrial function in Sirt3-knockdown H9c2 cells was associated with decreased expression of mitochondrial DNA encoded genes, reduced SOD2 expression and activity. The study also revealed that Sirt3 knockdown affects mitochondrial biogenesis and dynamics. To further confirm the role of Sirt3 on mitochondrial biogenesis and health, we did Sirt3 overexpression in H9c2 cells. Sirt3 overexpression enhanced the expression of mitochondrial DNA encoded genes, increased SOD2 activity and altered mitochondrial dynamics. Sirt3 overexpression also caused an increase in mitochondrial biogenesis gene and protein (PGC-1α and TFAM) expression. All these changes were confirmed with mitochondrial functional parameters like basal respiration, maximal respiratory capacity, spare respiratory capacity and ATP production. We found decreased mitochondrial function in Sirt3-knockdown H9c2 cells when compared to control H9c2 cells. Together our data conclude that Sirt3 regulates cardiac mitochondrial health and function through the Sirt3-AMPKα-PGC-1α axis.

Keywords:  AMPK; Cardiomyoblast; Mitochondrial biogenesis; Mitochondrial dynamics; SOD2; Sirt3

DOI:  https://doi.org/10.1016/j.cellsig.2022.110309
Mol Metab. 2022 Mar 09. pii: S2212-8778(22)00038-2. [Epub ahead of print] 101469

Key features of inhibitor binding to the human mitochondrial pyruvate carrier hetero-dimer.

Sotiria Tavoulari, Tom J J Schirris, Vasiliki Mavridou, Chancievan Thangaratnarajah, Martin S King, Daniel T D Jones, Shujing Ding, Ian M Fearnley, Edmund R S Kunji.

OBJECTIVE: The mitochondrial pyruvate carrier (MPC) has emerged as a promising drug target for metabolic disorders, including non-alcoholic steatohepatitis and diabetes, metabolically dependent cancers and neurodegenerative diseases. A range of structurally diverse small molecule inhibitors have been proposed but the nature of their interaction with MPC is not understood. Moreover, the composition of the functional human MPC is still debated. The goal of this study was to characterize the human MPC protein in vitro, to understand the chemical features that determine binding of structurally diverse inhibitors and to develop novel higher affinity ones.
METHODS: We have recombinantly expressed and purified human MPC hetero-complexes and have studied the composition, transport and inhibitor binding properties by establishing in vitro transport assays, high throughput thermostability shift assays and pharmacophore modeling.
RESULTS: We have determined that the functional unit of human MPC is a hetero-dimer. We have compared all different classes of MPC inhibitors to find that three closely arranged hydrogen bond acceptors followed by an aromatic ring are shared characteristics of all inhibitors and represent the minimal requirement for high potency. We also demonstrate that high affinity binding is not attributed to covalent bond formation with MPC cysteines, as previously proposed. Following the basic pharmacophore properties, we identify 14 new inhibitors of MPC, one outperforming compound UK5099 by tenfold. Two of them are the commonly prescribed drugs entacapone and nitrofurantoin, suggesting an off-target mechanism associated with their adverse effects.
CONCLUSION: This work defines the composition of human MPC and the essential MPC inhibitor characteristics. In combination with the functional assays we describe, this new understanding will accelerate the development of clinically relevant MPC modulators.

DOI: https://doi.org/10.1016/j.molmet.2022.101469
Front Mol Neurosci. 2022 ;15 831116

The Unfolded Protein Responses in Health, Aging, and Neurodegeneration: Recent Advances and Future Considerations.

Andrew P K Wodrich, Andrew W Scott, Arvind Kumar Shukla, Brent T Harris, Edward Giniger.

  Aging and age-related neurodegeneration are both associated with the accumulation of unfolded and abnormally folded proteins, highlighting the importance of protein homeostasis (termed proteostasis) in maintaining organismal health. To this end, two cellular compartments with essential protein folding functions, the endoplasmic reticulum (ER) and the mitochondria, are equipped with unique protein stress responses, known as the ER unfolded protein response (UPR ER ) and the mitochondrial UPR (UPR mt ), respectively. These organellar UPRs play roles in shaping the cellular responses to proteostatic stress that occurs in aging and age-related neurodegeneration. The loss of adaptive UPR ER and UPR mt signaling potency with age contributes to a feed-forward cycle of increasing protein stress and cellular dysfunction. Likewise, UPR ER and UPR mt signaling is often altered in age-related neurodegenerative diseases; however, whether these changes counteract or contribute to the disease pathology appears to be context dependent. Intriguingly, altering organellar UPR signaling in animal models can reduce the pathological consequences of aging and neurodegeneration which has prompted clinical investigations of UPR signaling modulators as therapeutics. Here, we review the physiology of both the UPR ER and the UPR mt , discuss how UPR ER and UPR mt signaling changes in the context of aging and neurodegeneration, and highlight therapeutic strategies targeting the UPR ER and UPR mt that may improve human health.

Keywords:  aging; endoplasmic reticulum unfolded protein response; mitochondrial unfolded protein response (UPRmt); neurodegeneration; unfolded protein response (UPR)

DOI:  https://doi.org/10.3389/fnmol.2022.831116
J Biol Chem. 2022 Mar 15. pii: S0021-9258(22)00275-7. [Epub ahead of print] 101835

Disruption of Mitochondrial Quality Control Genes Promotes Caspase-Resistant Cell Survival Following Apoptotic Stimuli.

Yulia Kushnareva, Vivian Moraes, Julian Suess, Bjoern Peters, Donald D Newmeyer, Tomomi Kuwana.

  In cells undergoing cell-intrinsic apoptosis, mitochondrial outer membrane permeabilization (MOMP) typically marks an irreversible step in the cell death process. However, in some cases a subpopulation of treated cells can exhibit a sublethal response, termed "minority MOMP". In this phenomenon, the affected cells survive, despite a low level of caspase activation and subsequent limited activation of the endonuclease CAD (DFFB). Consequently, these cells can experience DNA damage, increasing the probability of oncogenesis. However, little is known about the minority MOMP response. To discover genes that affect the MOMP response in individual cells, we conducted an imaging-based phenotypic siRNA screen. We identified multiple candidate genes whose downregulation increased the heterogeneity of MOMP within single cells, among which were genes related to mitochondrial dynamics and mitophagy that participate in the mitochondrial quality control (MQC) system. Furthermore, to test the hypothesis that functional MQC is important for reducing the frequency of minority MOMP, we developed an assay to measure the clonogenic survival of caspase-engaged cells. We found that cells deficient in various MQC genes were indeed prone to aberrant post-MOMP survival. Our data highlight the important role of proteins involved in mitochondrial dynamics and mitophagy in preventing apoptotic dysregulation and oncogenesis.

Keywords:  apoptosis; mitochondrial dynamics; mitochondrial heterogeneity; mitochondrial outer membrane permeabilization; mitochondrial quality control; mitophagy; oncogenesis; siRNA screen

DOI:  https://doi.org/10.1016/j.jbc.2022.101835
Biol Reprod. 2022 Mar 16. pii: ioac056. [Epub ahead of print]

Placental structure, function and mitochondrial phenotype relate to fetal size in each fetal sex in mice.

Esteban Salazar-Petres, Daniela Pereira Carvalho, Jorge Lopez-Tello, Amanda Nancy Sferruzzi-Perri.

  Fetal growth depends on placental function, which requires energy from mitochondria. Here we investigated whether mitochondrial function in the placenta relates to growth of the lightest and heaviest fetuses of each sex within the litter of mice. Placentas from the lightest and heaviest fetuses were taken to evaluate placenta morphology (stereology), mitochondrial energetics (high-resolution respirometry), and mitochondrial regulators, nutrient transporters, hormone handling and signalling pathways (qPCR and western blotting). We found that mitochondrial complex I and II oxygen consumption rate was greater for placentas supporting the lightest female fetuses, although placental complex I abundance of the lightest females and complexes III and V of the lightest males were decreased compared to their heaviest counterparts. Expression of mitochondrial biogenesis (Nrf1) and fission (Drp1 and Fis1) genes was lower in the placenta from the lightest females, whilst biogenesis-related gene Tfam was greater in the placenta of the lightest male fetuses. Additionally, placental morphology and steroidogenic gene (Cyp17a1 and Cyp11a1) expression was aberrant for the lightest females, but glucose transporter (Glut1) expression was lower in only the lightest males versus their heaviest counterparts. Differences in intra-litter placental phenotype were related to changes in the expression of hormone responsive (androgen receptor) and metabolic signalling (AMPK, AKT, PPARγ) pathways. Thus, in normal mouse pregnancy, placental structure, function and mitochondrial phenotype are differentially responsive to growth of the female and the male fetus. This study may inform the design of sex-specific therapies for placental insufficiency and fetal growth abnormalities with life-long benefits for the offspring.

Keywords:  Placenta; fetus; hormones; mitochondria; sex; transport

DOI:  https://doi.org/10.1093/biolre/ioac056
EMBO Rep. 2022 Mar 17. e52606

CEST-2.2 overexpression alters lipid metabolism and extends longevity of mitochondrial mutants.

Antonia Piazzesi, Yiru Wang, Joshua Jackson, Lena Wischhof, Viktoria Zeisler-Diehl, Enzo Scifo, Ina Oganezova, Thorben Hoffmann, Pablo Gómez Martín, Fabio Bertan, Chester J J Wrobel, Frank C Schroeder, Dan Ehninger, Kristian Händler, Joachim L Schultze, Lukas Schreiber, Gerhild van Echten-Deckert, Pierluigi Nicotera, Daniele Bano.

  Mitochondrial dysfunction can either extend or decrease Caenorhabditis elegans lifespan, depending on whether transcriptionally regulated responses can elicit durable stress adaptation to otherwise detrimental lesions. Here, we test the hypothesis that enhanced metabolic flexibility is sufficient to circumvent bioenergetic abnormalities associated with the phenotypic threshold effect, thereby transforming short-lived mitochondrial mutants into long-lived ones. We find that CEST-2.2, a carboxylesterase mainly localizes in the intestine, may stimulate the survival of mitochondrial deficient animals. We report that genetic manipulation of cest-2.2 expression has a minor lifespan impact on wild-type nematodes, whereas its overexpression markedly extends the lifespan of complex I-deficient gas-1(fc21) mutants. We profile the transcriptome and lipidome of cest-2.2 overexpressing animals and show that CEST-2.2 stimulates lipid metabolism and fatty acid beta-oxidation, thereby enhancing mitochondrial respiratory capacity through complex II and LET-721/ETFDH, despite the inherited genetic lesion of complex I. Together, our findings unveil a metabolic pathway that, through the tissue-specific mobilization of lipid deposits, may influence the longevity of mitochondrial mutant C. elegans.

Keywords:   Caenorhabditis elegans ; carboxylesterase CEST-2.2; epigenetics; lipid metabolism; mitochondria

DOI:  https://doi.org/10.15252/embr.202152606
Methods Mol Biol. 2022 ;2474 11-19

Mitochondrial Membrane Potential Assay.

Srilatha Sakamuru, Jinghua Zhao, Matias S Attene-Ramos, Menghang Xia.

  Mitochondrial function, a key indicator of cell health, can be assessed through monitoring changes in mitochondrial membrane potential (MMP). Cationic fluorescent dyes are commonly used tools to assess MMP. We used a water-soluble mitochondrial membrane potential indicator (m-MPI) to detect changes in MMP in various types of cells, such as HepG2, HepaRG, and AC16 cells. A homogenous cell-based MMP assay has been optimized and performed in a 1536-well plate format, which can be used to screen several compound libraries for mitochondrial toxicity by evaluating the effects of chemical compounds on MMP.

Keywords:  1536-well plate; Mesoxalonitrile 4-trifluoromethoxyphenylhydrazone (FCCP); Mitochondrial membrane potential (MMP); Mitochondrial membrane potential indicator (m-MPI); Mitochondrial toxicity

DOI:  https://doi.org/10.1007/978-1-0716-2213-1_2
Autophagy. 2022 Mar 16. 1-15

Mitochondrial depolarization after acute ethanol treatment drives mitophagy in living mice.

Devadoss J Samuvel, Li Li, Yasodha Krishnasamy, Monika Gooz, Kenji Takemoto, Patrick M Woster, John J Lemasters, Zhi Zhong.

  Ethanol increases hepatic mitophagy driven by unknown mechanisms. Type 1 mitophagy sequesters polarized mitochondria for nutrient recovery and cytoplasmic remodeling. In Type 2, mitochondrial depolarization (mtDepo) initiates mitophagy to remove the damaged organelles. Previously, we showed that acute ethanol administration produces reversible hepatic mtDepo. Here, we tested the hypothesis that ethanol-induced mtDepo initiates Type 2 mitophagy. GFP-LC3 transgenic mice were gavaged with ethanol (2-6 g/kg) with and without pre-treatment with agents that decrease or increase mtDepo-Alda-1, tacrolimus, or disulfiram. Without ethanol, virtually all hepatocytes contained polarized mitochondria with infrequent autophagic GFP-LC3 puncta visualized by intravital microscopy. At ~4 h after ethanol treatment, mtDepo occurred in an all-or-none fashion within individual hepatocytes, which increased dose dependently. GFP-LC3 puncta increased in parallel, predominantly in hepatocytes with mtDepo. Mitochondrial PINK1 and PRKN/parkin also increased. After covalent labeling of mitochondria with MitoTracker Red (MTR), GFP-LC3 puncta encircled MTR-labeled mitochondria after ethanol treatment, directly demonstrating mitophagy. GFP-LC3 puncta did not associate with fat droplets visualized with BODIPY558/568, indicating that increased autophagy was not due to lipophagy. Before ethanol administration, rhodamine-dextran (RhDex)-labeled lysosomes showed little association with GFP-LC3. After ethanol treatment, TFEB (transcription factor EB) translocated to nuclei, and lysosomal mass increased. Many GFP-LC3 puncta merged with RhDex-labeled lysosomes, showing autophagosomal processing into lysosomes. After ethanol treatment, disulfiram increased, whereas Alda-1 and tacrolimus decreased mtDepo, and mitophagy changed proportionately. In conclusion, mtDepo after acute ethanol treatment induces mitophagic sequestration and subsequent lysosomal processing.Abbreviations : AcAld, acetaldehyde; ADH, alcohol dehydrogenase; ALDH, aldehyde dehydrogenase; ALD, alcoholic liver disease; Alda-1, N-(1,3-benzodioxol-5-ylmethyl)-2,6-dichlorobenzamide; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFP, green fluorescent protein; LAMP1, lysosomal-associated membrane protein 1; LMNB1, lamin B1; MAA, malondialdehyde-acetaldehyde adducts; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MPT, mitochondrial permeability transition; mtDAMPS, mitochondrial damage-associated molecular patterns; mtDepo, mitochondrial depolarization; mtDNA, mitochondrial DNA; MTR, MitoTracker Red; PI, propidium iodide; PINK1, PTEN induced putative kinase 1; PRKN, parkin; RhDex, rhodamine dextran; TFEB, transcription factor EB; Tg, transgenic; TMRM, tetramethylrhodamine methylester; TOMM20, translocase of outer mitochondrial membrane 20; VDAC, voltage-dependent anion channel.

Keywords:  Acetaldehyde; Alda-1; alcoholic liver disease; mitochondrial depolarization; mitophagy; tacrolimus

DOI:  https://doi.org/10.1080/15548627.2022.2046457
Reprod Fertil. 2022 Jan 01. 3(1): 19-29

The effect of gestational age on mitochondrial properties of the mouse placenta.

Lucy A Bartho, Joshua J Fisher, Sarah L Walton, Anthony V Perkins, James S M Cuffe.

  Mitochondria are organelles within the cell that generate energy, which is essential to the developing placenta. As the placenta approaches term, organelles such as mitochondria and the endoplasmic reticulum adapt to cellular stressors (e.g. oxidative stress and fluctuations in oxygen concentration) which are likely to result in the progressive decline of tissue function, known as placental ageing. This ageing phenotype may induce cellular senescence, a process whereby the cell is no longer proliferating, yet remains metabolically active. Mitochondria, endoplasmic reticulum and senescent processes are still poorly understood in the developing placenta. Therefore, a rodent ontogeny model was used to measure genes and proteins involved in mitochondrial biogenesis, antioxidant function, electron transport chain, mitophagy, dynamics and unfolded protein response in the placenta. CD-1 mouse placental samples were collected at embryonic day (E)12.5, E14.5, E16.5 and E18.5 of pregnancy for gene and protein analysis via qPCR, protein assays and Western blotting. Mitochondrial content, SDHB (complex II) and MFN2 (mitochondrial fusion) proteins were all increased throughout pregnancy, while citrate synthase activity/mitochondrial content, Tfam, Sirt3, Mfn1, TOMM20 (mitochondrial biogenesis and dynamics); Tp53(senescence); Eif2ak3, Eif4g1(endoplasmic reticulum stress);NDUFB8, UQCRC2, ATP5A (electron transport chain sub-complexes) were decreased at E18.5, compared to E12.5. Overall, mitochondria undergo changes in response to gestational progression and pathways associated with cellular ageing to facilitate adaptions in a healthy pregnancy. This data holds great promise that mitochondrial markers across pregnancy may help to establish when a placenta is ageing inappropriately.
Lay summary: Human pregnancy lasts approximately 266 days. If a baby is born early, organs may be poorly formed but if pregnancy continues past this time, stillbirth risk is increased. Gestational duration is regulated by the placenta. As the placenta approaches the end of pregnancy, it displays properties similar to tissues from aged individuals. However, it is unknown how this placental ageing contributes to pregnancy duration. This study characterised normal placental ageing by measuring properties of mitochondria in healthy placentas collected at four different gestational ages ranging from 7 days before birth to 1 day before birth of the 19-day mouse pregnancy. We found that mitochondrial number increased per cell but that a marker of mitochondrial function was reduced. Proteins that control mitochondrial number, morphology and function also changed over time. This work lays the platform to understand how placental ageing contributes to adverse pregnancy outcomes related to altered pregnancy duration.

Keywords:  ageing; endoplasmic reticulum; mitochondria; placenta; senescence

DOI:  https://doi.org/10.1530/RAF-21-0064
Mol Genet Genomics. 2022 Mar 15.

PGC-1α affects skeletal muscle and adipose tissue development by regulating mitochondrial biogenesis.

Shaofen Kong, Bolin Cai, Qinghua Nie.

  The discovery and interpretation of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) protein in mitochondrial biogenesis, skeletal muscle and adipose tissue development has broad research prospects, so it is important to review the related studies of PGC-1α in detail and comprehensively. PGC-1α is a protein composed of 798 amino acids (aa) with a molecular weight of about 91 kDa. PGC-1α is involved in the operation of the respiratory chain by combining with deacetylase and phosphorylase to bind some nuclear receptors. In addition, PGC-1α affects skeletal muscle and adipose metabolism by regulating mitochondrial oxidative phosphorylation. Recently, new data suggest that regulating mitochondrial metabolism in adipose tissue may be an effective adjunct to the treatment of obesity. In addition, dietary resveratrol, which has an effective anti-obesity effect, has been shown to promote mitochondrial biosynthesis by activating AMPK/PGC-1α axis, as well as to regenerate muscle damaged by obesity. In this review, we combined previous studies to explore the latest studies, showing that PGC-1α can regulate mitochondrial biogenesis and is regulated by AMPK and SIRT1. Furthermore, PGC-1α is a favored protein, which not only regulates muscle fiber type, inhibits muscle atrophy, but also participates in browning of white adipose tissue (WAT) and regulates body heat production. So, we concluded that PGC-1α is a key gene in mitochondrial biogenesis and plays an important role in the regulation and regulation of mitochondrial biogenesis along with other genes involved in the process. Meanwhile, PGC-1α acts as a core metabolic regulator in adipose tissue and skeletal muscle. This review comprehensively summarizes a large number of research findings. First, the role of PGC-1α in mitochondrial biogenesis was clarified, and then the key role of PGC-1α in the development of skeletal muscle and adipose tissue was reevaluated. Furthermore, the role of PGC-1α in some human diseases was discussed. Finally, the role of PGC-1α as a major gene in poultry was pointed out, and the future research direction was proposed.

Keywords:  Adipose tissue; Mitochondria; Mitochondrial biogenesis; PGC-1α; Skeletal muscle

DOI:  https://doi.org/10.1007/s00438-022-01878-2
Sci Adv. 2022 Mar 18. 8(11): eabn0485

Piezo1 regulates the regenerative capacity of skeletal muscles via orchestration of stem cell morphological states.

Nuoying Ma, Delia Chen, Ji-Hyung Lee, Paola Kuri, Edward Blake Hernandez, Jacob Kocan, Hamd Mahmood, Elisia D Tichy, Panteleimon Rompolas, Foteini Mourkioti.

Muscle stem cells (MuSCs) are essential for tissue homeostasis and regeneration, but the potential contribution of MuSC morphology to in vivo function remains unknown. Here, we demonstrate that quiescent MuSCs are morphologically heterogeneous and exhibit different patterns of cellular protrusions. We classified quiescent MuSCs into three functionally distinct stem cell states: responsive, intermediate, and sensory. We demonstrate that the shift between different stem cell states promotes regeneration and is regulated by the sensing protein Piezo1. Pharmacological activation of Piezo1 is sufficient to prime MuSCs toward more responsive cells. Piezo1 deletion in MuSCs shifts the distribution toward less responsive cells, mimicking the disease phenotype we find in dystrophic muscles. We further demonstrate that Piezo1 reactivation ameliorates the MuSC morphological and regenerative defects of dystrophic muscles. These findings advance our fundamental understanding of how stem cells respond to injury and identify Piezo1 as a key regulator for adjusting stem cell states essential for regeneration.

DOI: https://doi.org/10.1126/sciadv.abn0485
Front Cell Dev Biol. 2022 ;10 783762

Autosomal Recessive Cerebellar Atrophy and Spastic Ataxia in Patients With Pathogenic Biallelic Variants in GEMIN5.

Deepa S Rajan, Sukhleen Kour, Tyler R Fortuna, Margot A Cousin, Sarah S Barnett, Zhiyv Niu, Dusica Babovic-Vuksanovic, Eric W Klee, Brian Kirmse, Micheil Innes, Siri Lynne Rydning, Kaja K Selmer, Magnus Dehli Vigeland, Anne Kjersti Erichsen, Andrea H Nemeth, Francisca Millan, Catherine DeVile, Katherine Fawcett, Adrien Legendre, David Sims, Ricardo Parolin Schnekenberg, Lydie Burglen, Sandra Mercier, Somayeh Bakhtiari, Encarnacion Martinez-Salas, Kristen Wigby, Jerica Lenberg, Jennifer R Friedman, Michael C Kruer, Udai Bhan Pandey.

  The hereditary ataxias are a heterogenous group of disorders with an increasing number of causative genes being described. Due to the clinical and genetic heterogeneity seen in these conditions, the majority of such individuals endure a diagnostic odyssey or remain undiagnosed. Defining the molecular etiology can bring insights into the responsible molecular pathways and eventually the identification of therapeutic targets. Here, we describe the identification of biallelic variants in the GEMIN5 gene among seven unrelated families with nine affected individuals presenting with spastic ataxia and cerebellar atrophy. GEMIN5, an RNA-binding protein, has been shown to regulate transcription and translation machinery. GEMIN5 is a component of small nuclear ribonucleoprotein (snRNP) complexes and helps in the assembly of the spliceosome complexes. We found that biallelic GEMIN5 variants cause structural abnormalities in the encoded protein and reduce expression of snRNP complex proteins in patient cells compared with unaffected controls. Finally, knocking out endogenous Gemin5 in mice caused early embryonic lethality, suggesting that Gemin5 expression is crucial for normal development. Our work further expands on the phenotypic spectrum associated with GEMIN5-related disease and implicates the role of GEMIN5 among patients with spastic ataxia, cerebellar atrophy, and motor predominant developmental delay.

Keywords:  Gemin5; ataxia; cell death; cerebellar atrophy; development; developmental delay; neurodegeneration

DOI:  https://doi.org/10.3389/fcell.2022.783762
Hum Mol Genet. 2022 Mar 14. pii: ddac059. [Epub ahead of print]

Mitochondrial DNA variants segregate during human preimplantation development into genetically different cell lineages that are maintained postnatally.

Joke Mertens, Marius Regin, Neelke De Munck, Edouard Couvreu Deckersberg, Florence Belva, Karen Sermon, Herman Tournaye, Christophe Blockeel, Hilde Van de Velde, Claudia Spits.

Humans present remarkable diversity in their mitochondrial DNA (mtDNA) in terms of variants across individuals as well as across tissues and even cells within one person. We have investigated the timing of the first appearance of this variant-driven mosaicism. For this, we deep-sequenced the mtDNA of 254 oocytes from 85 donors, 158 single blastomeres of 25 day-3 embryos, 17 inner cell mass and trophectoderm samples of 7 day-5 blastocysts, 142 bulk DNA and 68 single cells of different adult tissues. We found that day-3 embryos present blastomeres that carry variants only detected in that cell, showing that mtDNA mosaicism arises very early in human development. We classified the mtDNA variants based on their recurrence or uniqueness across different samples. Recurring variants had higher heteroplasmic loads and more frequently resulted in synonymous changes or were located in non-coding regions than variants unique to one oocyte or single embryonic cell. These differences were maintained through development, suggesting that the mtDNA mosaicism arising in the embryo is maintained into adulthood. We observed a decline in potentially pathogenic variants between day-3 and day-5 of development, suggesting early selection. We propose a model in which closely clustered mitochondria carrying specific mtDNA variants in the ooplasm are asymmetrically distributed throughout the cell divisions of the preimplantation embryo, resulting in the earliest form of mtDNA mosaicism in human development.

DOI: https://doi.org/10.1093/hmg/ddac059
iScience. 2022 Mar 18. 25(3): 103957

A role for cell polarity in lifespan and mitochondrial quality control in the budding yeast Saccharomyces cerevisiae.

Emily J Yang, Wolfgang M Pernice, Liza A Pon.

  Babies are born young, largely independent of the age of their mothers. Mother-daughter age asymmetry in yeast is achieved, in part, by inheritance of higher-functioning mitochondria by buds and retention of some high-functioning mitochondria in mother cells. The mitochondrial F box protein, Mfb1p, tethers mitochondria at both poles in a cell cycle-regulated manner: it localizes to and anchors mitochondria at the mother cell tip throughout the cell cycle and at the bud tip before cytokinesis. Here, we report that cell polarity and polarized localization of Mfb1p decline with age in Saccharomyces cerevisiae. Moreover, deletion of genes (BUD1, BUD2, and BUD5) that mediate symmetry breaking during establishment of cell polarity and asymmetric yeast cell division cause depolarized Mfb1p localization and defects in mitochondrial distribution and quality control. Our results support a role for the polarity machinery in lifespan through modulating Mfb1 function in asymmetric inheritance of mitochondria during yeast cell division.

Keywords:  Biological sciences; Cell biology; Genetics; Molecular biology

DOI:  https://doi.org/10.1016/j.isci.2022.103957
Ann Transl Med. 2022 Feb;10(4): 162

Myostatin is involved in skeletal muscle dysfunction in chronic obstructive pulmonary disease via Drp-1 mediated abnormal mitochondrial division.

Zhidan Tan, Manzhi Zhao, Jing Li, Siqi Li, Su Zhu, Xiaoxuan Yao, Xinglin Gao, Shifang Yang.

   Background: Skeletal muscle dysfunction (SMD) is one of the most prominent extrapulmonary effects of chronic obstructive pulmonary disease (COPD). Myostatin negatively regulates the growth of skeletal muscle. We confirmed that myostatin expression is significantly increased in the quadriceps femoris muscle tissue of rats with COPD and is involved in the development of SMD in COPD, but the mechanism by which this occurs has yet to be uncovered. Dynamin-related protein 1 (Drp-1) has been shown to promote apoptosis and affect cellular energy metabolism by mediating enhanced mitochondrial division. Preliminary findings from our group illustrated that mitochondrial division and Drp-1 expression were increased in COPD quadriceps femoris cells. However, it is not yet clear whether mitochondrial dynamics are affected by myostatin in COPD quadriceps myocytes.
Methods: The study sought to explore the effects and potential mechanisms of myostatin on skeletal muscle atrophy, mitochondrial dynamics, apoptosis, and the links between related processes in COPD.
Results: Our findings showed that cigarette smoke exposure stimulated an increase in myostatin, increased superoxide production, decreased mitochondrial membrane potential, significantly promoted Drp-1-mediated mitochondrial fission, and promoted apoptosis.
Conclusions: In summary, our study demonstrated that cigarette smoke led to increased Drp-1 expression and enhanced mitochondrial division by upregulating myostatin, which in turn promoted apoptosis and affected cellular energy metabolism, leading to the development of SMD in COPD. This study extends understandings of skeletal muscle function in COPD and provides a basis for the use of myostatin and Drp-1 as novel therapeutic targets for SMD in COPD.

Keywords:  Chronic obstructive pulmonary disease (COPD); dynamin-related protein 1 (Drp-1); mitochondrial fission; myostatin; skeletal muscle dysfunction (SMD)

DOI:  https://doi.org/10.21037/atm-22-377
Nat Rev Genet. 2022 Mar 17.

DNA replication in cell fate reprogramming.

Linda Koch.

DOI: https://doi.org/10.1038/s41576-022-00474-9
Nat Commun. 2022 Mar 14. 13(1): 1300

Lysosomal Ca2+-mediated TFEB activation modulates mitophagy and functional adaptation of pancreatic β-cells to metabolic stress.

Kihyoun Park, Hyejin Lim, Jinyoung Kim, Yeseong Hwang, Yu Seol Lee, Soo Han Bae, Hyeongseok Kim, Hail Kim, Shin-Wook Kang, Joo Young Kim, Myung-Shik Lee.

Although autophagy is critical for pancreatic β-cell function, the role and mechanism of mitophagy in β-cells are unclear. We studied the role of lysosomal Ca2+ in TFEB activation by mitochondrial or metabolic stress and that of TFEB-mediated mitophagy in β-cell function. Mitochondrial or metabolic stress induced mitophagy through lysosomal Ca2+ release, increased cytosolic Ca2+ and TFEB activation. Lysosomal Ca2+ replenishment by ER- > lysosome Ca2+ refilling was essential for mitophagy. β-cell-specific Tfeb knockout (TfebΔβ-cell) abrogated high-fat diet (HFD)-induced mitophagy, accompanied by increased ROS and reduced mitochondrial cytochrome c oxidase activity or O2 consumption. TfebΔβ-cell mice showed aggravation of HFD-induced glucose intolerance and impaired insulin release. Metabolic or mitochondrial stress induced TFEB-dependent expression of mitophagy receptors including Ndp52 and Optn, contributing to the increased mitophagy. These results suggest crucial roles of lysosomal Ca2+ release coupled with ER- > lysosome Ca2+ refilling and TFEB activation in mitophagy and maintenance of pancreatic β-cell function during metabolic stress.

DOI: https://doi.org/10.1038/s41467-022-28874-9
J Cachexia Sarcopenia Muscle. 2022 Mar 19.

Mitochondrial uncoupling attenuates sarcopenic obesity by enhancing skeletal muscle mitophagy and quality control.

Wagner S Dantas, Elizabeth R M Zunica, Elizabeth C Heintz, Bolormaa Vandanmagsar, Z Elizabeth Floyd, Yongmei Yu, Hisashi Fujioka, Charles L Hoppel, Kathryn P Belmont, Christopher L Axelrod, John P Kirwan.

   BACKGROUND: Sarcopenic obesity is a highly prevalent disease with poor survival and ineffective medical interventions. Mitochondrial dysfunction is purported to be central in the pathogenesis of sarcopenic obesity by impairing both organelle biogenesis and quality control. We have previously identified that a mitochondrial-targeted furazano[3,4-b]pyrazine named BAM15 is orally available and selectively lowers respiratory coupling efficiency and protects against diet-induced obesity in mice. Here, we tested the hypothesis that mitochondrial uncoupling simultaneously attenuates loss of muscle function and weight gain in a mouse model of sarcopenic obesity.
METHODS: Eighty-week-old male C57BL/6J mice with obesity were randomized to 10 weeks of high fat diet (CTRL) or BAM15 (BAM15; 0.1% w/w in high fat diet) treatment. Body weight and food intake were measured weekly. Body composition, muscle function, energy expenditure, locomotor activity, and glucose tolerance were determined after treatment. Skeletal muscle was harvested and evaluated for histology, gene expression, protein signalling, and mitochondrial structure and function.
RESULTS: BAM15 decreased body weight (54.0 ± 2.0 vs. 42.3 ± 1.3 g, P < 0.001) which was attributable to increased energy expenditure (10.1 ± 0.1 vs. 11.3 ± 0.4 kcal/day, P < 0.001). BAM15 increased muscle mass (52.7 ± 0.4 vs. 59.4 ± 1.0%, P < 0.001), strength (91.1 ± 1.3 vs. 124.9 ± 1.2 g, P < 0.0001), and locomotor activity (347.0 ± 14.4 vs. 432.7 ± 32.0 m, P < 0.001). Improvements in physical function were mediated in part by reductions in skeletal muscle inflammation (interleukin 6 and gp130, both P < 0.05), enhanced mitochondrial function, and improved endoplasmic reticulum homeostasis. Specifically, BAM15 activated mitochondrial quality control (PINK1-ubiquitin binding and LC3II, P < 0.01), increased mitochondrial activity (citrate synthase and complex II activity, all P < 0.05), restricted endoplasmic reticulum (ER) misfolding (decreased oligomer A11 insoluble/soluble ratio, P < 0.0001) while limiting ER stress (decreased PERK signalling, P < 0.0001), apoptotic signalling (decreased cytochrome C release and Caspase-3/9 activation, all P < 0.001), and muscle protein degradation (decreased 14-kDa actin fragment insoluble/soluble ratio, P < 0.001).
CONCLUSIONS: Mitochondrial uncoupling by agents such as BAM15 may mitigate age-related decline in muscle mass and function by molecular and cellular bioenergetic adaptations that confer protection against sarcopenic obesity.

Keywords:  Ageing; BAM15; Bioenergetics; Mitochondrial uncoupling; Obesity; Sarcopenia

DOI:  https://doi.org/10.1002/jcsm.12982
Biochim Biophys Acta Mol Basis Dis. 2022 Mar 14. pii: S0925-4439(22)00051-5. [Epub ahead of print] 166388

Abnormal mitochondria in Down syndrome iPSC-derived GABAergic interneurons and organoids.

Lei Xu, Hai-Qin Huo, Kai-Qin Lu, Xiao-Yan Tang, Yuan Hong, Xiao Han, Zi-Xing Fu, Kai-Heng Fang, Min Xu, Xing Guo, Yan Liu.

  Down syndrome (DS) is caused by trisomy 21, and it is characterized by developmental brain disorders and neurological dysfunction. Clinical studies and basic research have revealed that defects in mitochondrial function contribute to the pathogenesis of DS. However, the underlying mechanisms of mitochondrial dysfunction in DS remain unclear. In this study, we first generated GABAergic interneurons and medial ganglionic eminence (MGE) organoids from DS patients and control induced pluripotent stem cells. The mitochondria were abnormally clustered in the perinuclear region of GABA neurons and cell in MGE organoids from DS patients, which exhibited impaired mitochondrial function as assessed by seahorse oxidative phosphorylation assay. Inhibition of the DSCAM-PAK1 pathway by gene editing or treatment with a small molecule corrected mitochondrial perinuclear aggregation in cells from DS patients. Therefore, our study provides insight into the potential mechanism of mitochondrial dysfunction in DS.

Keywords:  Down syndrome; GABAergic interneurons; MGE organoids; Mitochondria; iPSC

DOI:  https://doi.org/10.1016/j.bbadis.2022.166388
Science. 2022 Mar 18. 375(6586): 1254-1261

Copper induces cell death by targeting lipoylated TCA cycle proteins.

Peter Tsvetkov, Shannon Coy, Boryana Petrova, Margaret Dreishpoon, Ana Verma, Mai Abdusamad, Jordan Rossen, Lena Joesch-Cohen, Ranad Humeidi, Ryan D Spangler, John K Eaton, Evgeni Frenkel, Mustafa Kocak, Steven M Corsello, Svetlana Lutsenko, Naama Kanarek, Sandro Santagata, Todd R Golub.

Copper is an essential cofactor for all organisms, and yet it becomes toxic if concentrations exceed a threshold maintained by evolutionarily conserved homeostatic mechanisms. How excess copper induces cell death, however, is unknown. Here, we show in human cells that copper-dependent, regulated cell death is distinct from known death mechanisms and is dependent on mitochondrial respiration. We show that copper-dependent death occurs by means of direct binding of copper to lipoylated components of the tricarboxylic acid (TCA) cycle. This results in lipoylated protein aggregation and subsequent iron-sulfur cluster protein loss, which leads to proteotoxic stress and ultimately cell death. These findings may explain the need for ancient copper homeostatic mechanisms.

DOI: https://doi.org/10.1126/science.abf0529