bims-minimp 2022-03-27 papers

on Mitochondria, innate immunity, proteostasis

Issue of 2022–03–27
twenty papers selected by
Hanna Salmonowicz, International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

Reduced expression of mitochondrial complex I subunit Ndufs2 does not impact healthspan in mice.
Hypoxic preconditioning averts sporadic Alzheimer's disease-like phenotype in rats: a focus on mitochondria.
Localized glucose import, glycolytic processing, and mitochondria generate a focused ATP burst to power basement-membrane invasion.
Dusp26 phosphatase regulates mitochondrial respiration and oxidative stress and protects neuronal cell death.
Loss of Sam50 in hepatocytes induces cardiolipin-dependent mitochondrial membrane remodeling to trigger mtDNA release and liver injury.
GATD3A, a mitochondrial deglycase with evolutionary origins from gammaproteobacteria, restricts the formation of advanced glycation end products.
Clueless/CLUH regulates mitochondrial fission by promoting recruitment of Drp1 to mitochondria.
Sideroflexin 4 is a complex I assembly factor that interacts with the MCIA complex and is required for the assembly of the ND2 module.
Dysfunctional telomeres through mitostress-induced cGAS/STING activation to aggravate immune senescence and viral pneumonia.
Mitochondrial ATP Synthase Inhibitory Factor 1 Interacts with the p53-Cyclophilin D Complex and Promotes Opening of the Permeability Transition Pore.
Prevention and regression of megamitochondria and steatosis by blocking mitochondrial fusion in the liver.
The war against Alzheimer, the mitochondrion strikes back!
Ejection of damaged mitochondria and their removal by macrophages ensure efficient thermogenesis in brown adipose tissue.
Three-dimensional structured illumination microscopy data of mitochondria and lysosomes in cardiomyoblasts under normal and galactose-adapted conditions.
Nicotinamide riboside promotes Mfn2-mediated mitochondrial fusion in diabetic hearts through the SIRT1-PGC1α-PPARα pathway.
Live cell microscopy of mitochondria-lysosome contact site formation and tethering dynamics.
Mitochondrial ATP synthase c-subunit leak channel triggers cell death upon loss of its F1 subcomplex.
Quality control of protein complex composition.
Targeting proteostasis maintenance and autophagy in senescence.
Human clinical mutations in mitochondrially encoded subunits of Complex I can be successfully modeled in E. coli.

Sci Rep. 2022 Mar 25. 12(1): 5196

Reduced expression of mitochondrial complex I subunit Ndufs2 does not impact healthspan in mice.

Gregory S McElroy, Ram P Chakrabarty, Karis B D'Alessandro, Karthik Vasan, Jerica Tan, Joshua S Stoolman, Samuel E Weinberg, Elizabeth M Steinert, Paul A Reyfman, Benjamin D Singer, Warren C Ladiges, Lin Gao, José Lopéz-Barneo, G R Scott Budinger, Navdeep S Chandel.

Aging in mammals leads to reduction in genes encoding the 45-subunit mitochondrial electron transport chain complex I. It has been hypothesized that normal aging and age-related diseases such as Parkinson's disease are in part due to modest decrease in expression of mitochondrial complex I subunits. By contrast, diminishing expression of mitochondrial complex I genes in lower organisms increases lifespan. Furthermore, metformin, a putative complex I inhibitor, increases healthspan in mice and humans. In the present study, we investigated whether loss of one allele of Ndufs2, the catalytic subunit of mitochondrial complex I, impacts healthspan and lifespan in mice. Our results indicate that Ndufs2 hemizygous mice (Ndufs2+/-) show no overt impairment in aging-related motor function, learning, tissue histology, organismal metabolism, or sensitivity to metformin in a C57BL6/J background. Despite a significant reduction of Ndufs2 mRNA, the mice do not demonstrate a significant decrease in complex I function. However, there are detectable transcriptomic changes in individual cell types and tissues due to loss of one allele of Ndufs2. Our data indicate that a 50% decline in mRNA of the core mitochondrial complex I subunit Ndufs2 is neither beneficial nor detrimental to healthspan.

DOI: https://doi.org/10.1038/s41598-022-09074-3
Antioxid Redox Signal. 2022 Mar 22.

Hypoxic preconditioning averts sporadic Alzheimer's disease-like phenotype in rats: a focus on mitochondria.

Sónia C Correia, Marco G Alves, Pedro F Oliveira, Gemma Casadesus, Joseph LaManna, George Perry, Paula I Moreira.

AIMS: Brief episodes of sublethal hypoxia reprogram brain response to face possible subsequent lethal stimuli by triggering adaptive and pro-survival events - a phenomenon denominated hypoxic preconditioning (HP). To date, the potential therapeutic implications of HP to forestall sporadic Alzheimer's disease (sAD) pathology remain unexplored. Using a well-established protocol of HP and focusing on hippocampus as a first brain region affected in AD, the present study was undertaken to investigate the potential protective effects of HP in a sAD rat model induced by the intracerebroventricular (icv) administration of streptozotocin (STZ) and to uncover the mitochondrial adaptations underlying this non-pharmacological strategy.
RESULTS: HP prevented memory and learning deficits as well as tau pathology in the icvSTZ rat model. HP also attenuated icvSTZ-related reactive astrogliosis, as noted by increased glial fibrillary acidic protein immunoreactivity and myo-inositol levels. Notably, HP abrogated the icvSTZ-related impaired energy metabolism and oxidative damage. Particularly, HP averted increased lactate, glutamate and succinate levels and decreased mitochondrial respiratory chain function and mitochondrial DNA content. Concerning mitochondrial adaptations underlying HP-triggered tolerance to icvSTZ, preconditioned hippocampal mitochondria displayed an enhanced complex II-energized mitochondrial respiration, which resulted from a coordinated interaction between mitochondrial biogenesis and fusion-fission events. Mitochondrial biogenesis was stimulated immediately after HP, whereas in a latter phase mitochondrial fusion-fission events are modulated favoring the generation of elongated mitochondria.
INNOVATION AND CONCLUSION: Overall, these results demonstrate for the first time that HP prevents the sAD-like phenotype, in part by targeting mitochondria, emerging as potential preventive strategy in the context of AD.

DOI: https://doi.org/10.1089/ars.2019.8007
Dev Cell. 2022 Mar 14. pii: S1534-5807(22)00121-6. [Epub ahead of print]

Localized glucose import, glycolytic processing, and mitochondria generate a focused ATP burst to power basement-membrane invasion.

Aastha Garde, Isabel W Kenny, Laura C Kelley, Qiuyi Chi, Ayse Sena Mutlu, Meng C Wang, David R Sherwood.

  Invasive cells use transient, energy-consuming protrusions to breach basement membrane (BM) barriers. Using the ATP sensor PercevalHR during anchor cell (AC) invasion in Caenorhabditis elegans, we show that BM invasion is accompanied by an ATP burst from mitochondria at the invasive front. RNAi screening and visualization of a glucose biosensor identified two glucose transporters, FGT-1 and FGT-2, which bathe invasive front mitochondria with glucose and facilitate the ATP burst to form protrusions. FGT-1 localizes at high levels along the invasive membrane, while FGT-2 is adaptive, enriching most strongly during BM breaching and when FGT-1 is absent. Cytosolic glycolytic enzymes that process glucose for mitochondrial ATP production cluster with invasive front mitochondria and promote higher mitochondrial membrane potential and ATP levels. Finally, we show that UNC-6 (netrin), which polarizes invasive protrusions, also orients FGT-1. These studies reveal a robust and integrated energy acquisition, processing, and delivery network that powers BM breaching.

Keywords:  ATP; basement membrane; biosensor; cell invasion; glucose transporters; glycolytic enzyme clustering; invasive protrusions; live imaging; mitochondria

DOI:  https://doi.org/10.1016/j.devcel.2022.02.019
Cell Mol Life Sci. 2022 Mar 21. 79(4): 198

Dusp26 phosphatase regulates mitochondrial respiration and oxidative stress and protects neuronal cell death.

Binnur Eroglu, Xiongjie Jin, Sadiki Deane, Bahadır Öztürk, Owen A Ross, Demetrius Moskophidis, Nahid F Mivechi.

  The dual specificity protein phosphatases (Dusps) control dephosphorylation of mitogen-activated protein kinases (MAPKs) as well as other substrates. Here, we report that Dusp26, which is highly expressed in neuroblastoma cells and primary neurons is targeted to the mitochondrial outer membrane via its NH2-terminal mitochondrial targeting sequence. Loss of Dusp26 has a significant impact on mitochondrial function that is associated with increased levels of reactive oxygen species (ROS), reduction in ATP generation, reduction in mitochondria motility and release of mitochondrial HtrA2 protease into the cytoplasm. The mitochondrial dysregulation in dusp26-deficient neuroblastoma cells leads to the inhibition of cell proliferation and cell death. In vivo, Dusp26 is highly expressed in neurons in different brain regions, including cortex and midbrain (MB). Ablation of Dusp26 in mouse model leads to dopaminergic (DA) neuronal cell loss in the substantia nigra par compacta (SNpc), inflammatory response in MB and striatum, and phenotypes that are normally associated with Neurodegenerative diseases. Consistent with the data from our mouse model, Dusp26 expressing cells are significantly reduced in the SNpc of Parkinson's Disease patients. The underlying mechanism of DA neuronal death is that loss of Dusp26 in neurons increases mitochondrial ROS and concurrent activation of MAPK/p38 signaling pathway and inflammatory response. Our results suggest that regulation of mitochondrial-associated protein phosphorylation is essential for the maintenance of mitochondrial homeostasis and dysregulation of this process may contribute to the initiation and development of neurodegenerative diseases.

Keywords:  Dopaminergic neurons; Dusp26; LRRK2; Mouse model; Neurodegeneration; p38

DOI:  https://doi.org/10.1007/s00018-022-04162-z
Hepatology. 2022 Mar 21.

Loss of Sam50 in hepatocytes induces cardiolipin-dependent mitochondrial membrane remodeling to trigger mtDNA release and liver injury.

Li Chen, Jun Dong, Siyang Liao, Siyou Wang, Zhida Wu, Meiling Zuo, Bing Liu, Chaojun Yan, Yong Chen, He He, Qingtao Meng, Zhiyin Song.

  Sam50, a key component of the sorting and assembly machinery (SAM) complex, is also involved in bridging mitochondrial outer- and inner-membrane contacts. However, the physiological and pathological functions of Sam50 remain largely unknown. Here, we show that Sam50 interacts with MICOS and ATAD3 to form the Sam50-MICOS-ATAD3-mtDNA axis, which maintains mtDNA stability. Loss of Sam50 causes mtDNA aggregation. Furthermore, Sam50 cooperates with Mic60 to bind to cardiolipin, maintaining the integrity of mitochondrial membranes. Sam50 depletion leads to cardiolipin externalization, which causes mitochondrial outer- and inner-membrane (including crista membrane) remodeling, triggering Bax mitochondrial recruitment, mtDNA aggregation and release. Physiologically, acetaminophen (APAP, an effective antipyretic and analgesic)-caused Sam50 reduction or Sam50 liver-specific knockout induces mtDNA release, leading to activation of the cGAS-STING pathway and liver inflammation in mice. Moreover, exogenous expression of Sam50 remarkably attenuates APAP-induced liver hepatoxicity. Thus, our findings uncover the critical role of Sam50 in maintaining mitochondrial membrane integrity and mtDNA stability in hepatocytes, and reveal that Sam50 depletion-induced cardiolipin externalization is a new signal of mtDNA release and controls mtDNA-dependent innate immunity.

Keywords:  Sam50; acetaminophen; cGAS-STING; cardiolipin; mtDNA release

DOI:  https://doi.org/10.1002/hep.32471
BMC Biol. 2022 Mar 21. 20(1): 68

GATD3A, a mitochondrial deglycase with evolutionary origins from gammaproteobacteria, restricts the formation of advanced glycation end products.

Andrew J Smith, Jayshree Advani, Daniel C Brock, Jacob Nellissery, Jessica Gumerson, Lijin Dong, L Aravind, Breandán Kennedy, Anand Swaroop.

   BACKGROUND: Functional complexity of the eukaryotic mitochondrial proteome is augmented by independent gene acquisition from bacteria since its endosymbiotic origins. Mammalian homologs of many ancestral mitochondrial proteins have uncharacterized catalytic activities. Recent forward genetic approaches attributed functions to proteins in established metabolic pathways, thereby limiting the possibility of identifying novel biology relevant to human disease. We undertook a bottom-up biochemistry approach to discern evolutionarily conserved mitochondrial proteins with catalytic potential.
RESULTS: Here, we identify a Parkinson-associated DJ-1/PARK7-like protein-glutamine amidotransferase-like class 1 domain-containing 3A (GATD3A), with bacterial evolutionary affinities although not from alphaproteobacteria. We demonstrate that GATD3A localizes to the mitochondrial matrix and functions as a deglycase. Through its amidolysis domain, GATD3A removes non-enzymatic chemical modifications produced during the Maillard reaction between dicarbonyls and amines of nucleotides and amino acids. GATD3A interacts with factors involved in mitochondrial mRNA processing and translation, suggestive of a role in maintaining integrity of important biomolecules through its deglycase activity. The loss of GATD3A in mice is associated with accumulation of advanced glycation end products (AGEs) and altered mitochondrial dynamics.
CONCLUSIONS: An evolutionary perspective helped us prioritize a previously uncharacterized but predicted mitochondrial protein GATD3A, which mediates the removal of early glycation intermediates. GATD3A restricts the formation of AGEs in mitochondria and is a relevant target for diseases where AGE deposition is a pathological hallmark.

Keywords:  Advanced glycation end product; Aging; DJ-1; Deglycase; Glutamine amidotransferase; Mitochondria; Molecular evolution; PARK7

DOI:  https://doi.org/10.1186/s12915-022-01267-6
Nat Commun. 2022 Mar 24. 13(1): 1582

Clueless/CLUH regulates mitochondrial fission by promoting recruitment of Drp1 to mitochondria.

Huan Yang, Caroline Sibilla, Raymond Liu, Jina Yun, Bruce A Hay, Craig Blackstone, David C Chan, Robert J Harvey, Ming Guo.

Mitochondrial fission is critically important for controlling mitochondrial morphology, function, quality and transport. Drp1 is the master regulator driving mitochondrial fission, but exactly how Drp1 is regulated remains unclear. Here, we identified Drosophila Clueless and its mammalian orthologue CLUH as key regulators of Drp1. As with loss of drp1, depletion of clueless or CLUH results in mitochondrial elongation, while as with drp1 overexpression, clueless or CLUH overexpression leads to mitochondrial fragmentation. Importantly, drp1 overexpression rescues adult lethality, tissue disintegration and mitochondrial defects of clueless null mutants in Drosophila. Mechanistically, Clueless and CLUH promote recruitment of Drp1 to mitochondria from the cytosol. This involves CLUH binding to mRNAs encoding Drp1 receptors MiD49 and Mff, and regulation of their translation. Our findings identify a crucial role of Clueless and CLUH in controlling mitochondrial fission through regulation of Drp1.

DOI: https://doi.org/10.1038/s41467-022-29071-4
Proc Natl Acad Sci U S A. 2022 Mar 29. 119(13): e2115566119

Sideroflexin 4 is a complex I assembly factor that interacts with the MCIA complex and is required for the assembly of the ND2 module.

Thomas D Jackson, Jordan J Crameri, Linden Muellner-Wong, Ann E Frazier, Catherine S Palmer, Luke E Formosa, Daniella H Hock, Kenji M Fujihara, Tegan Stait, Alice J Sharpe, David R Thorburn, Michael T Ryan, David A Stroud, Diana Stojanovski.

  SignificanceMitochondria are double-membraned eukaryotic organelles that house the proteins required for generation of ATP, the energy currency of cells. ATP generation within mitochondria is performed by five multisubunit complexes (complexes I to V), the assembly of which is an intricate process. Mutations in subunits of these complexes, or the suite of proteins that help them assemble, lead to a severe multisystem condition called mitochondrial disease. We show that SFXN4, a protein that causes mitochondrial disease when mutated, assists with the assembly of complex I. This finding explains why mutations in SFXN4 cause mitochondrial disease and is surprising because SFXN4 belongs to a family of amino acid transporter proteins, suggesting that it has undergone a dramatic shift in function through evolution.

Keywords:  complex assembly; mitochondria; respiratory chain; sideroflexins

DOI:  https://doi.org/10.1073/pnas.2115566119
Aging Cell. 2022 Mar 21. e13594

Dysfunctional telomeres through mitostress-induced cGAS/STING activation to aggravate immune senescence and viral pneumonia.

Nianyin Lv, Yufang Zhao, Xiaoyi Liu, Lusha Ye, Zihao Liang, Yanhua Kang, Yeping Dong, Wei Wang, Narasaiah Kolliputi, Liyun Shi.

  Disproportionately high incidence and mortality of respiratory infection such as influenza A virus (IAV) and SARS-CoV-2 have been evidenced in the elderly, but the role and the mechanism of age-associated immune deregulation in disease exacerbation are not well defined. Using a late generation of mice deficient in telomerase RNA (Terc-/- ), we herein demonstrated that aged mice were exquisitely susceptible to respiratory viral infection, with excessive inflammation and increased mortality. Furthermore, we identified the cGAS/STING pathway, which was essentially induced by the leaked mitochondrial DNA, as a biologically relevant mechanism contributing to exaggerated inflammation in Terc-/- mice following viral infection. Innate immune cells, mainly, macrophages with shortened telomeres, exhibited hallmarks of cellular senescence, mitochondrial distress, and aberrant activation of STING and NLRP3 inflammasome pathways, which predisposed mice to severe viral pneumonia during commonly mild infections. Application of STING inhibitor and, more importantly, senolytic agent, reduced the burden of stressed macrophages, improved mitochondrial integrity, and suppressed STING activation, thereby conferring the protection for Terc-/- mice against respiratory infection. Together, the findings expand our understanding of innate immune senescence and reveal the potential of the senolytics as a promising treatment to alleviate the symptom of viral pneumonia, particularly for the older population.

Keywords:  STING; macrophage; respiratory virus infection; senescence; telomere

DOI:  https://doi.org/10.1111/acel.13594
J Biol Chem. 2022 Mar 22. pii: S0021-9258(22)00298-8. [Epub ahead of print] 101858

Mitochondrial ATP Synthase Inhibitory Factor 1 Interacts with the p53-Cyclophilin D Complex and Promotes Opening of the Permeability Transition Pore.

Lishu Guo.

  The mitochondrial permeability transition pore (PTP) is a Ca2+-dependent megachannel that plays an important role in mitochondrial physiology and cell fate. Cyclophilin D (CyPD) is a well-characterized PTP regulator, and its binding to the PTP favors pore opening. It has previously been shown that p53 physically interacts with CyPD and opens the PTP during necrosis. Accumulating studies also suggest that the F-ATP synthase contributes to the regulation and formation of the PTP. F-ATP synthase inhibitory factor 1 (IF1) is a natural inhibitor of F-ATP synthase activity; however, whether IF1 participates in the modulation of PTP opening is basically unknown. Here, we demonstrate using calcium retention capacity assay that IF1 overexpression promotes mitochondrial permeability transition via opening of the PTP. Intriguingly, we show that IF1 can interact with the p53-CyPD complex and facilitate cell death. We also demonstrate that the presence of IF1 is necessary for the formation of p53-CyPD complex. Therefore, we suggest that IF1 regulates the PTP via interaction with the p53-CyPD complex, and that IF1 is necessary for the inducing effect of p53-CyPD complex on PTP opening.

Keywords:  F-ATP synthase inhibitory factor 1; cyclophilin D; mitochondria; mitochondrial permeability transition; p53

DOI:  https://doi.org/10.1016/j.jbc.2022.101858
iScience. 2022 Apr 15. 25(4): 103996

Prevention and regression of megamitochondria and steatosis by blocking mitochondrial fusion in the liver.

Tatsuya Yamada, Daisuke Murata, David E Kleiner, Robert Anders, Avi Z Rosenberg, Jeffrey Kaplan, James P Hamilton, Mariam Aghajan, Moshe Levi, Nae-Yuh Wang, Ted M Dawson, Toru Yanagawa, Andrew F Powers, Miho Iijima, Hiromi Sesaki.

  Non-alcoholic steatohepatitis (NASH) is a most common chronic liver disease that is manifested by steatosis, inflammation, fibrosis, and tissue damage. Hepatocytes produce giant mitochondria termed megamitochondria in patients with NASH. It has been shown that gene knockout of OPA1, a mitochondrial dynamin-related GTPase that mediates mitochondrial fusion, prevents megamitochondria formation and liver damage in a NASH mouse model induced by a methionine-choline-deficient (MCD) diet. However, it is unknown whether blocking mitochondrial fusion mitigates NASH pathologies. Here, we acutely depleted OPA1 using antisense oligonucleotides in the NASH mouse model before or after megamitochondria formation. When OPA1 ASOs were applied at the disease onset, they effectively prevented megamitochondria formation and liver pathologies in the MCD model. Notably, even when applied after mice robustly developed NASH pathologies, OPA1 targeting effectively regressed megamitochondria and the disease phenotypes. Thus, our data show the efficacy of mitochondrial dynamics as a unique therapy for megamitochondria-associated liver disease.

Keywords:  Cell biology; Hepatology

DOI:  https://doi.org/10.1016/j.isci.2022.103996
Mitochondrion. 2022 Mar 22. pii: S1567-7249(22)00023-X. [Epub ahead of print]

The war against Alzheimer, the mitochondrion strikes back!

Kevin Zambrano, Diego Barba, Karina Castillo, Paola Robayo, Dariana Argueta-Zamora, Serena Sanon, Eduardo Arizaga, Andres Caicedo, Antonio W D Gavilanes.

  Alzheimer's disease (AD) is a leading neurodegenerative pathology associated with aging worldwide. It is estimated that AD prevalence will increase from 5.8 million people today to 13.8 million by 2050 in the United States alone. AD effects in the brain are well known; however, there is still a lack of knowledge about the cellular mechanisms behind the origin of AD. It is known that AD induces cellular stress affecting the energy metabolism in brain cells. During the pathophysiological advancement of AD, damaged mitochondria enter a vicious cycle, producing reactive oxygen species (ROS), harming mitochondrial DNA and proteins, leading to more ROS and cellular death. Additionally, mitochondria are interconnected with the plaques formed by amyloid-β in AD and have underlying roles in the progression of the disease and severity. For years, the biomedical field struggled to develop new therapeutic options for AD without a significant advancement. However, mitochondria are striking back existing outside cells in a new mechanism of intercellular communication. Extracellular mitochondria are exchanged from healthy to damaged cells to rescue those with a perturbed metabolism in a process that could be applied as a new therapeutic option to repair those brain cells affected by AD. In this review we highlight key aspects of mitochondria's role in CNS' physiology and neurodegenerative disorders, focusing on AD. We also suggest how mitochondria strikes back as a therapeutic target and as a potential agent to be transplanted to repair neurons affected by AD.

Keywords:  Alzheimer’s Disease; Extracellular mitochondria; Mitochondrial therapy; Neurodegenerative disease; mtDNA

DOI:  https://doi.org/10.1016/j.mito.2022.03.003
Cell Metab. 2022 Mar 15. pii: S1550-4131(22)00088-2. [Epub ahead of print]

Ejection of damaged mitochondria and their removal by macrophages ensure efficient thermogenesis in brown adipose tissue.

Marco Rosina, Veronica Ceci, Riccardo Turchi, Li Chuan, Nicholas Borcherding, Francesca Sciarretta, María Sánchez-Díaz, Flavia Tortolici, Keaton Karlinsey, Valerio Chiurchiù, Claudia Fuoco, Rocky Giwa, Rachael L Field, Matteo Audano, Simona Arena, Alessandro Palma, Federica Riccio, Farnaz Shamsi, Giovanni Renzone, Martina Verri, Anna Crescenzi, Salvatore Rizza, Fiorella Faienza, Giuseppe Filomeni, Sander Kooijman, Stefano Rufini, Antoine A F de Vries, Andrea Scaloni, Nico Mitro, Yu-Hua Tseng, Andrés Hidalgo, Beiyan Zhou, Jonathan R Brestoff, Katia Aquilano, Daniele Lettieri-Barbato.

  Recent findings have demonstrated that mitochondria can be transferred between cells to control metabolic homeostasis. Although the mitochondria of brown adipocytes comprise a large component of the cell volume and undergo reorganization to sustain thermogenesis, it remains unclear whether an intercellular mitochondrial transfer occurs in brown adipose tissue (BAT) and regulates adaptive thermogenesis. Herein, we demonstrated that thermogenically stressed brown adipocytes release extracellular vesicles (EVs) that contain oxidatively damaged mitochondrial parts to avoid failure of the thermogenic program. When re-uptaken by parental brown adipocytes, mitochondria-derived EVs reduced peroxisome proliferator-activated receptor-γ signaling and the levels of mitochondrial proteins, including UCP1. Their removal via the phagocytic activity of BAT-resident macrophages is instrumental in preserving BAT physiology. Depletion of macrophages in vivo causes the abnormal accumulation of extracellular mitochondrial vesicles in BAT, impairing the thermogenic response to cold exposure. These findings reveal a homeostatic role of tissue-resident macrophages in the mitochondrial quality control of BAT.

Keywords:  adipose tissue; brown adipocytes; extracellular vesicles; homeostasis; immunometabolism; macrophages; mitochondria; mitochondrial quality control; thermogenesis

DOI:  https://doi.org/10.1016/j.cmet.2022.02.016
Sci Data. 2022 Mar 23. 9(1): 98

Three-dimensional structured illumination microscopy data of mitochondria and lysosomes in cardiomyoblasts under normal and galactose-adapted conditions.

Ida S Opstad, Gustav Godtliebsen, Florian Ströhl, Truls Myrmel, Balpreet Singh Ahluwalia, Krishna Agarwal, Åsa Birna Birgisdottir.

This three-dimensional structured illumination microscopy (3DSIM) dataset was generated to highlight the suitability of 3DSIM to investigate mitochondria-derived vesicles (MDVs) in H9c2 cardiomyoblasts in living or fixed cells. MDVs act as a mitochondria quality control mechanism. The cells were stably expressing the tandem-tag eGFP-mCherry-OMP25-TM (outer mitochondrial membrane) which can be used as a sensor for acidity. A part of the dataset is showing correlative imaging of lysosomes labeled using LysoTracker in fixed and living cells. The cells were cultivated in either normal or glucose-deprived medium containing galactose. The resulting 3DSIM data were of high quality and can be used to undertake a variety of studies. Interestingly, many dynamic tubules derived from mitochondria are visible in the 3DSIM videos under both glucose and galactose-adapted growth conditions. As the raw 3DSIM data, optical parameters, and reconstructed 3DSIM images are provided, the data is especially suitable for use in the development of SIM reconstruction algorithms, bioimage analysis methods, and for biological studies of mitochondria.

DOI: https://doi.org/10.1038/s41597-022-01207-7
Free Radic Biol Med. 2022 Mar 19. pii: S0891-5849(22)00107-1. [Epub ahead of print]183 75-88

Nicotinamide riboside promotes Mfn2-mediated mitochondrial fusion in diabetic hearts through the SIRT1-PGC1α-PPARα pathway.

Lang Hu, Yanjie Guo, Liqiang Song, He Wen, Nan Sun, Ying Wang, Bingchao Qi, Qi Liang, Jing Geng, Xuteng Liu, Feng Fu, Yan Li.

  Myocardial dysfunction is associated with an imbalance in mitochondrial fusion/fission dynamics in patients with diabetes. However, effective strategies to regulate mitochondrial dynamics in the diabetic heart are still lacking. Nicotinamide riboside (NR) supplementation ameliorated mitochondrial dysfunction and oxidative stress in both cardiovascular and aging-related diseases. This study investigated whether NR protects against diabetes-induced cardiac dysfunction by regulating mitochondrial fusion/fission and further explored the underlying mechanisms. Here, we showed an evident decrease in NAD+ (nicotinamide adenine dinucleotide) levels and mitochondrial fragmentation in the hearts of leptin receptor-deficient diabetic (db/db) mouse models. NR supplementation significantly increased NAD+ content in the diabetic hearts and promoted mitochondrial fusion by elevating Mfn2 level. Furthermore, NR-induced mitochondrial fusion suppressed mitochondrial H2O2 and O2•- production and reduced cardiomyocyte apoptosis in both db/db mice hearts and neonatal primary cardiomyocytes. Mechanistically, chromatin immunoprecipitation (ChIP) and luciferase reporter assay analyses revealed that PGC1α and PPARα interdependently regulated Mfn2 transcription by binding to its promoter region. NR treatment elevated NAD+ levels and activated SIRT1, resulting in the deacetylation of PGC1α and promoting the transcription of Mfn2. These findings suggested the promotion of mitochondrial fusion via oral supplementation of NR as a potential strategy for delaying cardiac complications in patients with diabetes.

Keywords:  Diabetic cardiomyopathy; Mfn2; Mitochondrial dynamics; Nicotinamide riboside; Oxidative stress

DOI:  https://doi.org/10.1016/j.freeradbiomed.2022.03.012
STAR Protoc. 2022 Jun 17. 3(2): 101262

Live cell microscopy of mitochondria-lysosome contact site formation and tethering dynamics.

Tayler B Belton, Eric D Leisten, Jasmine Cisneros, Yvette C Wong.

  Mitochondria-lysosome contact sites are critical for maintaining cellular homeostasis by regulating mitochondrial and lysosomal network dynamics and mediating metabolite exchange. Here, we present a protocol to quantitatively analyze the formation and tethering duration of mitochondria-lysosome contact sites by using time-lapse live confocal microscopy of LAMP1 and TOMM20. Although this protocol focuses on mammalian HeLa cells, it can be applied to other cell types for further studies on mitochondria-lysosome contact regulation and function, and elucidation of their role in human disorders. For complete details on the use and execution of this protocol, please refer to Wong et al. (2018) and Wong et al. (2019b).

Keywords:  Cell Biology; Cell culture; Microscopy

DOI:  https://doi.org/10.1016/j.xpro.2022.101262
Cell Death Differ. 2022 Mar 23.

Mitochondrial ATP synthase c-subunit leak channel triggers cell death upon loss of its F1 subcomplex.

Nelli Mnatsakanyan, Han-A Park, Jing Wu, Xiang He, Marc C Llaguno, Maria Latta, Paige Miranda, Besnik Murtishi, Morven Graham, Joachim Weber, Richard J Levy, Evgeny V Pavlov, Elizabeth A Jonas.

Mitochondrial ATP synthase is vital not only for cellular energy production but also for energy dissipation and cell death. ATP synthase c-ring was suggested to house the leak channel of mitochondrial permeability transition (mPT), which activates during excitotoxic ischemic insult. In this present study, we purified human c-ring from both eukaryotic and prokaryotic hosts to biophysically characterize its channel activity. We show that purified c-ring forms a large multi-conductance, voltage-gated ion channel that is inhibited by the addition of ATP synthase F1 subcomplex. In contrast, dissociation of F1 from FO occurs during excitotoxic neuronal death suggesting that the F1 constitutes the gate of the channel. mPT is known to dissipate the osmotic gradient across the inner membrane during cell death. We show that ATP synthase c-subunit knock down (KD) prevents the osmotic change in response to high calcium and eliminates large conductance, Ca2+ and CsA sensitive channel activity of mPT. These findings elucidate the gating mechanism of the ATP synthase c-subunit leak channel (ACLC) and suggest how ACLC opening is regulated by cell stress in a CypD-dependent manner.

DOI: https://doi.org/10.1038/s41418-022-00972-7
Mol Cell. 2022 Mar 11. pii: S1097-2765(22)00167-8. [Epub ahead of print]

Quality control of protein complex composition.

Chris Padovani, Predrag Jevtić, Michael Rapé.

  Eukaryotic cells possess hundreds of protein complexes that contain multiple subunits and must be formed at the correct time and place during development. Despite specific assembly pathways, cells frequently encounter complexes with missing or aberrant subunits that can disrupt important signaling events. Cells, therefore, employ several ubiquitin-dependent quality control pathways that can prevent, correct, or degrade flawed complexes. In this review, we will discuss our emerging understanding of such quality control of protein complex composition.

Keywords:  aneuploidy; dimerization quality control; orphan quality control; proteasome; quality control; ubiquitin; ubiquitylation

DOI:  https://doi.org/10.1016/j.molcel.2022.02.029
Aging (Albany NY). 2022 Mar 07. 14(5): 2016-2017

Targeting proteostasis maintenance and autophagy in senescence.

Valentin L'Hôte, Carl Mann, Jean-Yves Thuret.



Keywords:  BRAF-V600E; cellular senescence; proteostasis; selective autophagy; senolytics

DOI:  https://doi.org/10.18632/aging.203941
Mitochondrion. 2022 Mar 17. pii: S1567-7249(22)00022-8. [Epub ahead of print]64 59-72

Human clinical mutations in mitochondrially encoded subunits of Complex I can be successfully modeled in E. coli.

Fang Zhang, Quynh-Chi L Dang, Steven B Vik.

  Respiratory Complex I is the site of a large fraction of the mutations that appear to cause mitochondrial disease. Seven of its subunits are mitochondrially encoded, and therefore, such mutants are particularly difficult to construct in cell-culture model systems. We have selected 13 human clinical mutations found in ND2, ND3, ND4, ND4L, ND5 and ND6 that are generally found at subunit interfaces, and not in critical residues. These mutations have been modeled in E. coli subunits of Complex I, nuoN, nuoA, nuoM, nuoK, nuoL, and nuoJ, respectively. All mutants were expressed from a plasmid encoding the entire nuo operon, and membrane vesicles were analyzed for deamino-NADH oxidase activity, and proton translocation activity. ND5 mutants were also analyzed using a time-delayed expression system, recently described by this lab. Other mutants were analyzed for the ability to associate in subcomplexes, after expression of subsets of the genes. For most mutants there was a positive correlation between those that were previously determined to be pathogenic, or likely to be pathogenic, and those that we found with compromised Complex I activity or subunit interactions in E. coli. In conclusion, this approach provides another way to explore the deleterious effects of human mitochondrial mutations, and it can contribute to molecular understanding of such mutations.

Keywords:  Bioenergetics; Complex I; LHON; Mitochondria; Mutations; NADH dehydrogenase

DOI:  https://doi.org/10.1016/j.mito.2022.03.001