bims-minimp 2022-02-20 papers

on Mitochondria, innate immunity, proteostasis

Issue of 2022–02–20
27 papers selected by
Hanna Salmonowicz, International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

Metabolic determination of cell fate through selective inheritance of mitochondria.
Assessing Mitochondrial DNA Release into the Cytosol and Subsequent Activation of Innate Immune-related Pathways in Mammalian Cells.
Mitochondria Fusion upon SERCA Inhibition Prevents Activation of the NLRP3 Inflammasome in Human Monocytes.
LONP-1 and ATFS-1 sustain deleterious heteroplasmy by promoting mtDNA replication in dysfunctional mitochondria.
Positive Selection Drives the Adaptive Evolution of Mitochondrial Antiviral Signaling (MAVS) Proteins-Mediating Innate Immunity in Mammals.
Extracellular Release of Mitochondrial DNA: Triggered by Cigarette Smoke and Detected in COPD.
Disuse-associated loss of the protease LONP1 in muscle impairs mitochondrial function and causes reduced skeletal muscle mass and strength.
Insight into the mitochondrial unfolded protein response and cancer: opportunities and challenges.
Mitochondrial efficiency directs cell fate.
Enhanced Expression of TRAP1 Protects Mitochondrial Function in Motor Neurons under Conditions of Oxidative Stress.
Role of eIF5A in Mitochondrial Function.
Metabolic control of adult neural stem cell self-renewal by the mitochondrial protease YME1L.
Inhibition of mitochondrial LonP1 protease by allosteric blockade of ATP -binding and -hydrolysis via CDDO and its derivatives.
Uncoupling Proteins and Regulated Proton Leak in Mitochondria.
A late-stage assembly checkpoint of the human mitochondrial ribosome large subunit.
CHCHD2 and CHCHD10 regulate mitochondrial dynamics and integrated stress response.
Loss of miR-34 in Drosophila dysregulates protein translation and protein turnover in the aging brain.
Voltage Dependent Anion Channel 3 (VDAC3) protects mitochondria from oxidative stress.
TFAM-Dependent Mitochondrial Metabolism Is Required for Alveolar Macrophage Maintenance and Homeostasis.
Changes of Gut Microbiota by Natural mtDNA Variant Differences Augment Susceptibility to Metabolic Disease and Ageing.
The ins and outs of the flavin mononucleotide cofactor of respiratory complex I.
Unresolved stalled ribosome complexes restrict cell-cycle progression after genotoxic stress.
RNA sensing via the RIG-I-like receptor LGP2 is essential for the induction of a type I IFN response in ADAR1 deficiency.
Hijacking of host mitochondria by Toxoplasma gondii and SARS-CoV-2.
Ghost mitochondria drive metastasis through adaptive GCN2/Akt therapeutic vulnerability.
Emerging Roles of COX7RP and Mitochondrial Oxidative Phosphorylation in Breast Cancer.
Adipose mitochondrial complex I deficiency modulates inflammation and glucose homeostasis in a sex-dependent manner.

Nat Cell Biol. 2022 Feb;24(2): 148-154

Metabolic determination of cell fate through selective inheritance of mitochondria.

Julia Döhla, Emilia Kuuluvainen, Nadja Gebert, Ana Amaral, Johanna I Englund, Swetha Gopalakrishnan, Svetlana Konovalova, Anni I Nieminen, Ella S Salminen, Rubén Torregrosa Muñumer, Kati Ahlqvist, Yang Yang, Hien Bui, Timo Otonkoski, Reijo Käkelä, Ville Hietakangas, Henna Tyynismaa, Alessandro Ori, Pekka Katajisto.

Metabolic characteristics of adult stem cells are distinct from their differentiated progeny, and cellular metabolism is emerging as a potential driver of cell fate conversions1-4. How these metabolic features are established remains unclear. Here we identified inherited metabolism imposed by functionally distinct mitochondrial age-classes as a fate determinant in asymmetric division of epithelial stem-like cells. While chronologically old mitochondria support oxidative respiration, the electron transport chain of new organelles is proteomically immature and they respire less. After cell division, selectively segregated mitochondrial age-classes elicit a metabolic bias in progeny cells, with oxidative energy metabolism promoting differentiation in cells that inherit old mitochondria. Cells that inherit newly synthesized mitochondria with low levels of Rieske iron-sulfur polypeptide 1 have a higher pentose phosphate pathway activity, which promotes de novo purine biosynthesis and redox balance, and is required to maintain stemness during early fate determination after division. Our results demonstrate that fate decisions are susceptible to intrinsic metabolic bias imposed by selectively inherited mitochondria.

DOI: https://doi.org/10.1038/s41556-021-00837-0
Curr Protoc. 2022 Feb;2(2): e372

Assessing Mitochondrial DNA Release into the Cytosol and Subsequent Activation of Innate Immune-related Pathways in Mammalian Cells.

Joshua D Bryant, Yuanjiu Lei, Jordyn J VanPortfliet, Ashley D Winters, A Phillip West.

  Mitochondria have emerged as key drivers of mammalian innate immune responses, functioning as signaling hubs to trigger inflammation and orchestrating metabolic switches required for phagocyte activation. Mitochondria also contain damage-associated molecular patterns (DAMPs), molecules that share similarity with pathogen-associated molecular patterns (PAMPs) and can engage innate immune sensors to drive inflammation. The aberrant release of mitochondrial DAMPs during cellular stress and injury is an increasingly recognized trigger of inflammatory responses in human diseases. Mitochondrial DNA (mtDNA) is a particularly potent DAMP that engages multiple innate immune sensors, although mounting evidence suggests that cytosolic mtDNA is primarily detected via the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. cGAS and STING are widely expressed in mammalian cells and serve as key regulators of type I interferon and cytokine expression in both infectious and inflammatory diseases. Despite growing roles for the mtDNA-cGAS-STING axis in human disease, assays to quantify mtDNA release into the cytosol and approaches to link mtDNA to cGAS-STING signaling are not standardized, which increases the possibility for experimental artifacts and misinterpretation of data. Here, we present a series of protocols for assaying the release of mtDNA into the cytosol and subsequent activation of innate immune signaling in mammalian cells. We highlight genetic and pharmacological approaches to induce and inhibit mtDNA release from mitochondria. We also describe immunofluorescence microscopy and cellular fractionation assays to visualize morphological changes in mtDNA and quantify mtDNA accumulation in the cytosol. Finally, we include protocols to examine mtDNA-dependent cGAS-STING activation by RT-qPCR and western blotting. These methods can be performed with standard laboratory equipment and are highly adaptable to a wide range of mammalian cell types. They will permit researchers working across the spectrum of biological and biomedical sciences to accurately and reproducibly measure cytosolic mtDNA release and resulting innate immune responses. © 2022 Wiley Periodicals LLC. Basic Protocol 1: siRNA-mediated knockdown of TFAM to induce mtDNA instability, cytosolic release, and activation of the cGAS-STING pathway Alternate Protocol: Pharmacological induction of mtDNA release and cGAS-STING activation using ABT-737 and Q-VD-OPH Basic Protocol 2: Isolation and quantitation of DNA from cytosolic, mitochondrial, and nuclear fractions Basic Protocol 3: Pharmacological inhibition of mtDNA replication and release.

Keywords:  STING; cGAS; innate immunity; mitochondria; mitochondrial DNA

DOI:  https://doi.org/10.1002/cpz1.372
Cells. 2022 Jan 27. pii: 433. [Epub ahead of print]11(3):

Mitochondria Fusion upon SERCA Inhibition Prevents Activation of the NLRP3 Inflammasome in Human Monocytes.

Ana Catarina Pereira, Nuno Madeira, Sofia Morais, António Macedo, Maria Teresa Cruz, Cláudia M F Pereira.

  Sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) is a crucial component of the cellular machinery responsible for Ca2+ homeostasis. The selective inhibition of SERCA by thapsigargin (TG) leads to perturbations in Ca2+ signaling, which can trigger endoplasmic reticulum (ER) stress. The unfolded protein response (UPR) pathway is activated in response to ER stress and induces an adaptive response to preserve cell survival or committee cells to programmed death, depending on stress duration and/or level. Early stages of ER stress stimulate mitochondrial metabolism to preserve survival but under chronic ER stress conditions, mitochondrial dysfunction is induced, which, in turn, can enhance inflammation through NLRP3 inflammasome activation. This study was aimed at investigating the role of SERCA inhibition on NLRP3 inflammasome activation in human monocytes, which was evaluated in primary monocytes isolated from healthy individuals and in the THP-1 human monocytic cell line. Findings obtained in both THP-1 and primary monocytes demonstrate that SERCA inhibition triggered by TG does not activate the NLRP3 inflammasome in these innate immune cells since IL-1β secretion was not affected. Results from THP-1 monocytes showing that SERCA inhibition increases mitochondrial Ca2+ content and fusion, in the absence of changes in ROS levels and membrane potential, support the view that human monocytes counteract ER stress that arises from inhibition of SERCA through modulation of mitochondrial morphology towards mitochondria fusion, thus preventing NLRP3 inflammasome activation. Overall, this work contributes to a better understanding of the molecular mechanisms that modulate the activity of the NLRP3 inflammasome leading to sterile inflammation, which are still poorly understood.

Keywords:  calcium homeostasis; endoplasmic reticulum (ER) stress; immune system; mitochondria dynamics; sterile inflammation

DOI:  https://doi.org/10.3390/cells11030433
Nat Cell Biol. 2022 Feb;24(2): 181-193

LONP-1 and ATFS-1 sustain deleterious heteroplasmy by promoting mtDNA replication in dysfunctional mitochondria.

Qiyuan Yang, Pengpeng Liu, Nadine S Anderson, Tomer Shpilka, YunGuang Du, Nandhitha Uma Naresh, Rui Li, Lihua Julie Zhu, Kevin Luk, Josh Lavelle, Rilee D Zeinert, Peter Chien, Scot A Wolfe, Cole M Haynes.

The accumulation of deleterious mitochondrial DNA (∆mtDNA) causes inherited mitochondrial diseases and ageing-associated decline in mitochondrial functions such as oxidative phosphorylation. Following mitochondrial perturbations, the bZIP protein ATFS-1 induces a transcriptional programme to restore mitochondrial function. Paradoxically, ATFS-1 is also required to maintain ∆mtDNAs in heteroplasmic worms. The mechanism by which ATFS-1 promotes ∆mtDNA accumulation relative to wild-type mtDNAs is unclear. Here we show that ATFS-1 accumulates in dysfunctional mitochondria. ATFS-1 is absent in healthy mitochondria owing to degradation by the mtDNA-bound protease LONP-1, which results in the nearly exclusive association between ATFS-1 and ∆mtDNAs in heteroplasmic worms. Moreover, we demonstrate that mitochondrial ATFS-1 promotes the binding of the mtDNA replicative polymerase (POLG) to ∆mtDNAs. Interestingly, inhibition of the mtDNA-bound protease LONP-1 increased ATFS-1 and POLG binding to wild-type mtDNAs. LONP-1 inhibition in Caenorhabditis elegans and human cybrid cells improved the heteroplasmy ratio and restored oxidative phosphorylation. Our findings suggest that ATFS-1 promotes mtDNA replication in dysfunctional mitochondria by promoting POLG-mtDNA binding, which is antagonized by LONP-1.

DOI: https://doi.org/10.1038/s41556-021-00840-5
Front Vet Sci. 2021 ;8 814765

Positive Selection Drives the Adaptive Evolution of Mitochondrial Antiviral Signaling (MAVS) Proteins-Mediating Innate Immunity in Mammals.

Hafiz Ishfaq Ahmad, Gulnaz Afzal, Muhammad Nouman Iqbal, Muhammad Arslan Iqbal, Borhan Shokrollahi, Muhammad Khalid Mansoor, Jinping Chen.

  The regulated production of filamentous protein complexes is essential in many biological processes and provides a new paradigm in signal transmission. The mitochondrial antiviral signaling protein (MAVS) is a critical signaling hub in innate immunity that is activated when a receptor induces a shift in the globular caspase activation and recruitment domain of MAVS into helical superstructures (filaments). It is of interest whether adaptive evolution affects the proteins involved in innate immunity. Here, we explore and confer the role of selection and diversification on mitochondrial antiviral signaling protein in mammalian species. We obtined the MAVS proteins of mammalian species and examined their differences in evolutionary patterns. We discovered evidence for these proteins being subjected to substantial positive selection. We demonstrate that immune system proteins, particularly those encoding recognition proteins, develop under positive selection using codon-based probability methods. Positively chosen regions within recognition proteins cluster in domains involved in microorganism recognition, implying that molecular interactions between hosts and pathogens may promote adaptive evolution in the mammalian immune systems. These significant variations in MAVS development in mammalian species highlights the involvement of MAVS in innate immunity. Our findings highlight the significance of accounting for how non-synonymous alterations affect structure and function when employing sequence-level studies to determine and quantify positive selection.

Keywords:  MAVS; adaptive evolution; innate immunity; mammals; mitochondria; positive selection

DOI:  https://doi.org/10.3389/fvets.2021.814765
Cells. 2022 Jan 22. pii: 369. [Epub ahead of print]11(3):

Extracellular Release of Mitochondrial DNA: Triggered by Cigarette Smoke and Detected in COPD.

Luca Giordano, Alyssa D Gregory, Mireia Pérez Verdaguer, Sarah A Ware, Hayley Harvey, Evan DeVallance, Tomasz Brzoska, Prithu Sundd, Yingze Zhang, Frank C Sciurba, Steven D Shapiro, Brett A Kaufman.

  Cigarette smoke (CS) is the most common risk factor for chronic obstructive pulmonary disease (COPD). The present study aimed to elucidate whether mtDNA is released upon CS exposure and is detected in the plasma of former smokers affected by COPD as a possible consequence of airway damage. We measured cell-free mtDNA (cf-mtDNA) and nuclear DNA (cf-nDNA) in COPD patient plasma and mouse serum with CS-induced emphysema. The plasma of patients with COPD and serum of mice with CS-induced emphysema showed increased cf-mtDNA levels. In cell culture, exposure to a sublethal dose of CSE decreased mitochondrial membrane potential, increased oxidative stress, dysregulated mitochondrial dynamics, and triggered mtDNA release in extracellular vesicles (EVs). Mitochondrial DNA release into EVs occurred concomitantly with increased expression of markers that associate with DNA damage responses, including DNase III, DNA-sensing receptors (cGAS and NLRP3), proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-18, and CXCL2), and markers of senescence (p16 and p21); the majority of the responses are also triggered by cytosolic DNA delivery in vitro. Exposure to a lethal CSE dose preferentially induced mtDNA and nDNA release in the cell debris. Collectively, the results of this study associate markers of mitochondrial stress, inflammation, and senescence with mtDNA release induced by CSE exposure. Because high cf-mtDNA is detected in the plasma of COPD patients and serum of mice with emphysema, our findings support the future study of cf-mtDNA as a marker of mitochondrial stress in response to CS exposure and COPD pathology.

Keywords:  COPD; cell-free DNA; cigarette smoke; extracellular vesicles; mitochondria; necroptosis; oxidative stress; senescence

DOI:  https://doi.org/10.3390/cells11030369
Nat Commun. 2022 Feb 16. 13(1): 894

Disuse-associated loss of the protease LONP1 in muscle impairs mitochondrial function and causes reduced skeletal muscle mass and strength.

Zhisheng Xu, Tingting Fu, Qiqi Guo, Danxia Zhou, Wanping Sun, Zheng Zhou, Xinyi Chen, Jingzi Zhang, Lin Liu, Liwei Xiao, Yujing Yin, Yuhuan Jia, Erkai Pang, Yuncong Chen, Xin Pan, Lei Fang, Min-Sheng Zhu, Wenyong Fei, Bin Lu, Zhenji Gan.

Mitochondrial proteolysis is an evolutionarily conserved quality-control mechanism to maintain proper mitochondrial integrity and function. However, the physiological relevance of stress-induced impaired mitochondrial protein quality remains unclear. Here, we demonstrate that LONP1, a major mitochondrial protease resides in the matrix, plays a role in controlling mitochondrial function as well as skeletal muscle mass and strength in response to muscle disuse. In humans and mice, disuse-related muscle loss is associated with decreased mitochondrial LONP1 protein. Skeletal muscle-specific ablation of LONP1 in mice resulted in impaired mitochondrial protein turnover, leading to mitochondrial dysfunction. This caused reduced muscle fiber size and strength. Mechanistically, aberrant accumulation of mitochondrial-retained protein in muscle upon loss of LONP1 induces the activation of autophagy-lysosome degradation program of muscle loss. Overexpressing a mitochondrial-retained mutant ornithine transcarbamylase (ΔOTC), a known protein degraded by LONP1, in skeletal muscle induces mitochondrial dysfunction, autophagy activation, and cause muscle loss and weakness. Thus, these findings reveal a role of LONP1-dependent mitochondrial protein quality-control in safeguarding mitochondrial function and preserving skeletal muscle mass and strength, and unravel a link between mitochondrial protein quality and muscle mass maintenance during muscle disuse.

DOI: https://doi.org/10.1038/s41467-022-28557-5
Cell Biosci. 2022 Feb 18. 12(1): 18

Insight into the mitochondrial unfolded protein response and cancer: opportunities and challenges.

Ge Wang, Yumei Fan, Pengxiu Cao, Ke Tan.

  The mitochondrial unfolded protein response (UPRmt) is an evolutionarily conserved protective transcriptional response that maintains mitochondrial proteostasis by inducing the expression of mitochondrial chaperones and proteases in response to various stresses. The UPRmt-mediated transcriptional program requires the participation of various upstream signaling pathways and molecules. The factors regulating the UPRmt in Caenorhabditis elegans (C. elegans) and mammals are both similar and different. Cancer cells, as malignant cells with uncontrolled proliferation, are exposed to various challenges from endogenous and exogenous stresses. Therefore, in cancer cells, the UPRmt is hijacked and exploited for the repair of mitochondria and the promotion of tumor growth, invasion and metastasis. In this review, we systematically introduce the inducers of UPRmt, the biological processes in which UPRmt participates, the mechanisms regulating the UPRmt in C. elegans and mammals, cross-tissue signal transduction of the UPRmt and the roles of the UPRmt in promoting cancer initiation and progression. Disrupting proteostasis in cancer cells by targeting UPRmt constitutes a novel anticancer therapeutic strategy.

Keywords:  Cancer; Mitochondrial heat shock protein; Mitochondrial protease; Mitochondrial unfolded protein response; Proteostasis

DOI:  https://doi.org/10.1186/s13578-022-00747-0
Nat Cell Biol. 2022 Feb;24(2): 125-126

Mitochondrial efficiency directs cell fate.

Jessica Brooke Spinelli, Elma Zaganjor.

DOI: https://doi.org/10.1038/s41556-021-00834-3
Int J Mol Sci. 2022 Feb 04. pii: 1789. [Epub ahead of print]23(3):

Enhanced Expression of TRAP1 Protects Mitochondrial Function in Motor Neurons under Conditions of Oxidative Stress.

Benjamin E Clarke, Bernadett Kalmar, Linda Greensmith.

  TNF-receptor associated protein (TRAP1) is a cytoprotective mitochondrial-specific member of the Hsp90 heat shock protein family of protein chaperones that has been shown to antagonise mitochondrial apoptosis and oxidative stress, regulate the mitochondrial permeability transition pore and control protein folding in mitochondria. Here we show that overexpression of TRAP1 protects motor neurons from mitochondrial dysfunction and death induced by exposure to oxidative stress conditions modelling amyotrophic lateral sclerosis (ALS). ALS is a fatal neurodegenerative disease in which motor neurons degenerate, leading to muscle weakness and atrophy and death, typically within 3 years of diagnosis. In primary murine motor neurons, shRNA-mediated knockdown of TRAP1 expression results in mitochondrial dysfunction but does not further exacerbate damage induced by oxidative stress alone. Together, these results show that TRAP1 may be a potential therapeutic target for neurodegenerative diseases such as ALS, where mitochondrial dysfunction has been shown to be an early marker of pathogenesis.

Keywords:  TRAP1; mitochondria; motor neuron; oxidative stress

DOI:  https://doi.org/10.3390/ijms23031789
Int J Mol Sci. 2022 Jan 24. pii: 1284. [Epub ahead of print]23(3):

Role of eIF5A in Mitochondrial Function.

Marina Barba-Aliaga, Paula Alepuz.

  The eukaryotic translation initiation factor 5A (eIF5A) is an evolutionarily conserved protein that binds ribosomes to facilitate the translation of peptide motifs with consecutive prolines or combinations of prolines with glycine and charged amino acids. It has also been linked to other molecular functions and cellular processes, such as nuclear mRNA export and mRNA decay, proliferation, differentiation, autophagy, and apoptosis. The growing interest in eIF5A relates to its association with the pathogenesis of several diseases, including cancer, viral infection, and diabetes. It has also been proposed as an anti-aging factor: its levels decay in aged cells, whereas increasing levels of active eIF5A result in the rejuvenation of the immune and vascular systems and improved brain cognition. Recent data have linked the role of eIF5A in some pathologies with its function in maintaining healthy mitochondria. The eukaryotic translation initiation factor 5A is upregulated under respiratory metabolism and its deficiency reduces oxygen consumption, ATP production, and the levels of several mitochondrial metabolic enzymes, as well as altering mitochondria dynamics. However, although all the accumulated data strongly link eIF5A to mitochondrial function, the precise molecular role and mechanisms involved are still unknown. In this review, we discuss the findings linking eIF5A and mitochondria, speculate about its role in regulating mitochondrial homeostasis, and highlight its potential as a target in diseases related to energy metabolism.

Keywords:  OXPHOS; TCA; eIF5A; mitochondria; mitochondrial respiration; spermidine; translation

DOI:  https://doi.org/10.3390/ijms23031284
Cell Rep. 2022 02 15. pii: S2211-1247(22)00091-2. [Epub ahead of print]38(7): 110370

Metabolic control of adult neural stem cell self-renewal by the mitochondrial protease YME1L.

Gulzar A Wani, Hans-Georg Sprenger, Kristiano Ndoci, Srikanth Chandragiri, Richard James Acton, Désirée Schatton, Sandra M V Kochan, Vignesh Sakthivelu, Milica Jevtic, Jens M Seeger, Stefan Müller, Patrick Giavalisco, Elena I Rugarli, Elisa Motori, Thomas Langer, Matteo Bergami.

  The transition between quiescence and activation in neural stem and progenitor cells (NSPCs) is coupled with reversible changes in energy metabolism with key implications for lifelong NSPC self-renewal and neurogenesis. How this metabolic plasticity is ensured between NSPC activity states is unclear. We find that a state-specific rewiring of the mitochondrial proteome by the i-AAA peptidase YME1L is required to preserve NSPC self-renewal. YME1L controls the abundance of numerous mitochondrial substrates in quiescent NSPCs, and its deletion activates a differentiation program characterized by broad metabolic changes causing the irreversible shift away from a fatty-acid-oxidation-dependent state. Conditional Yme1l deletion in adult NSPCs in vivo results in defective self-renewal and premature differentiation, ultimately leading to NSPC pool depletion. Our results disclose an important role for YME1L in coordinating the switch between metabolic states of NSPCs and suggest that NSPC fate is regulated by compartmentalized changes in protein network dynamics.

Keywords:  OMA1; YME1L; adult neurogenesis; metabolic rewiring; mitochondria; mitochondrial dynamics; mitochondrial proteome; neural stem cells; proliferation; self-renewal

DOI:  https://doi.org/10.1016/j.celrep.2022.110370
J Biol Chem. 2022 Feb 10. pii: S0021-9258(22)00159-4. [Epub ahead of print] 101719

Inhibition of mitochondrial LonP1 protease by allosteric blockade of ATP -binding and -hydrolysis via CDDO and its derivatives.

Jae Lee, Ashutosh K Pandey, Sundararajan Venkatesh, Jayapalraja Thilagavathi, Tadashi Honda, Kamal Singh, Carolyn K Suzuki.

  The mitochondrial protein LonP1 is an ATP-dependent protease that mitigates cell stress and calibrates mitochondrial metabolism and energetics. Bi-allelic mutations in the LONP1 gene are known to cause a broad spectrum of diseases, and LonP1 dysregulation is also implicated in cancer and age-related disorders. Despite the importance of LonP1 in health and disease, specific inhibitors of this protease are unknown. Here, we demonstrate that 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) and its -methyl and -imidazole derivatives reversibly inhibit LonP1 by a non-competitive mechanism, blocking ATP-hydrolysis and thus proteolysis. By contrast, we found that CDDO-anhydride inhibits the LonP1 ATPase competitively. Docking of CDDO derivatives in the cryo-EM structure of LonP1 shows these compounds bind a hydrophobic pocket adjacent to the ATP-binding site. The binding site of CDDO derivatives was validated by amino acid substitutions that increased LonP1 inhibition, and also by a pathogenic mutation that causes cerebral, ocular, dental, auricular and skeletal (CODAS) syndrome, which ablated inhibition. CDDO failed to inhibit the ATPase activity of the purified 26S proteasome, which like LonP1 belongs to the AAA+ superfamily of ATPases Associated with diverse cellular Activities, suggesting that CDDO shows selectivity within this family of ATPases. Furthermore, we show that non-cytotoxic concentrations of CDDO derivatives in cultured cells inhibited LonP1, but not the 26S proteasome. Taken together, these findings provide insights for future development of LonP1-specific inhibitors with chemotherapeutic potential.

Keywords:  ATP-dependent protease; CDDO; LonP1; allosteric inhibition; mitochondria; mitochondrial metabolism; protein quality control; proteostasis

DOI:  https://doi.org/10.1016/j.jbc.2022.101719
Int J Mol Sci. 2022 Jan 28. pii: 1528. [Epub ahead of print]23(3):

Uncoupling Proteins and Regulated Proton Leak in Mitochondria.

Afshan Ardalan, Matthew D Smith, Masoud Jelokhani-Niaraki.

  Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field.

Keywords:  ADP/ATP carrier; ATP synthesis; alternating access mechanism; biphasic proton transport model; membrane protein oligomerization; membrane protein structure and function; mitochondrial carriers; reactive oxygen species control; regulation and mechanism of proton transport; uncoupling proteins

DOI:  https://doi.org/10.3390/ijms23031528
Nat Commun. 2022 Feb 17. 13(1): 929

A late-stage assembly checkpoint of the human mitochondrial ribosome large subunit.

Pedro Rebelo-Guiomar, Simone Pellegrino, Kyle C Dent, Aldema Sas-Chen, Leonor Miller-Fleming, Caterina Garone, Lindsey Van Haute, Jack F Rogan, Adam Dinan, Andrew E Firth, Byron Andrews, Alexander J Whitworth, Schraga Schwartz, Alan J Warren, Michal Minczuk.

Many cellular processes, including ribosome biogenesis, are regulated through post-transcriptional RNA modifications. Here, a genome-wide analysis of the human mitochondrial transcriptome shows that 2'-O-methylation is limited to residues of the mitoribosomal large subunit (mtLSU) 16S mt-rRNA, introduced by MRM1, MRM2 and MRM3, with the modifications installed by the latter two proteins being interdependent. MRM2 controls mitochondrial respiration by regulating mitoribosome biogenesis. In its absence, mtLSU particles (visualized by cryo-EM at the resolution of 2.6 Å) present disordered RNA domains, partial occupancy of bL36m and bound MALSU1:L0R8F8:mtACP anti-association module, allowing five mtLSU biogenesis intermediates with different intersubunit interface configurations to be placed along the assembly pathway. However, mitoribosome biogenesis does not depend on the methyltransferase activity of MRM2. Disruption of the MRM2 Drosophila melanogaster orthologue leads to mitochondria-related developmental arrest. This work identifies a key checkpoint during mtLSU assembly, essential to maintain mitochondrial homeostasis.

DOI: https://doi.org/10.1038/s41467-022-28503-5
Cell Death Dis. 2022 02 16. 13(2): 156

CHCHD2 and CHCHD10 regulate mitochondrial dynamics and integrated stress response.

Yu Ruan, Jiaqiao Hu, Yaping Che, Yanyan Liu, Zhenhuan Luo, Jin Cheng, Qi Han, He He, Qinghua Zhou.

Mitochondrial dysfunction is becoming one of the main pathology factors involved in the etiology of neurological disorders. Recently, mutations of the coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) and 10 (CHCHD10) which encode two homologous proteins that belong to the mitochondrial CHCH domain protein family, are linked to Parkinson's disease and amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD), respectively. However, the physiological and pathological roles of these twin proteins have not been well elaborated. Here, we show that, in physiological conditions, CHCHD2 and CHCHD10 interact with OMA1 and suppress its enzyme activity, which not only restrains the initiation of the mitochondrial integrated response stress (mtISR), but also suppresses the processing of OPA1 for mitochondrial fusion. Further, during mitochondria stress-induced by carbonyl cyanide m-chlorophenylhydrazone (CCCP) treatment, CHCHD2 and CHCHD10 translocate to the cytosol and interacte with eIF2a, which attenuates mtISR overactivation by suppressing eIF2a phosphorylation and its downstream response. As such, knockdown of CHCHD2 and CHCHD10 triggers mitochondrial ISR, and such cellular response is enhanced by CCCP treatment. Therefore, our findings demonstrate the first "mtISR suppressor" localized in mitochondria for regulating stress responses in mammalian cells, which has a profound pathological impact on the CHCH2/CHCH10-linked neurodegenerative disorder.

DOI: https://doi.org/10.1038/s41419-022-04602-5
Aging Cell. 2022 Feb 15. e13559

Loss of miR-34 in Drosophila dysregulates protein translation and protein turnover in the aging brain.

Ananth R Srinivasan, Tracy T Tran, Nancy M Bonini.

  Aging is a risk factor for neurodegenerative disease, but precise mechanisms that influence this relationship are still under investigation. Work in Drosophila melanogaster identified the microRNA miR-34 as a modifier of aging and neurodegeneration in the brain. MiR-34 mutants present aspects of early aging, including reduced lifespan, neurodegeneration, and a buildup of the repressive histone mark H3K27me3. To better understand how miR-34 regulated pathways contribute to age-associated phenotypes in the brain, here we transcriptionally profiled the miR-34 mutant brain. This identified that genes associated with translation are dysregulated in the miR-34 mutant. The brains of these animals show increased translation activity, accumulation of protein aggregation markers, and altered autophagy activity. To determine if altered H3K27me3 was responsible for this proteostasis dysregulation, we studied the effects of increased H3K27me3 by mutating the histone demethylase Utx. Reduced Utx activity enhanced neurodegeneration and mimicked the protein accumulation seen in miR-34 mutant brains. However, unlike the miR-34 mutant, Utx mutant brains did not show similar altered autophagy or translation activity, suggesting that additional miR-34-targeted pathways are involved. Transcriptional analysis of predicted miR-34 targets identified Lst8, a subunit of Tor Complex 1 (TORC1), as a potential target. We confirmed that miR-34 regulates the 3' UTR of Lst8 and identified several additional predicted miR-34 targets that may be critical for maintaining proteostasis and brain health. Together, these results present novel understanding of the brain and the role of the conserved miRNA miR-34 in impacting proteostasis in the brain with age.

Keywords:   miR-34 ; aging; autophagy; neurodegeneration; proteostasis; translation

DOI:  https://doi.org/10.1111/acel.13559
Redox Biol. 2022 Feb 12. pii: S2213-2317(22)00036-2. [Epub ahead of print]51 102264

Voltage Dependent Anion Channel 3 (VDAC3) protects mitochondria from oxidative stress.

Simona Reina, Stefano Conti Nibali, Marianna Flora Tomasello, Andrea Magrì, Angela Messina, Vito De Pinto.

  Unraveling the role of VDAC3 within living cells is challenging and still requires a definitive answer. Unlike VDAC1 and VDAC2, the outer mitochondrial membrane porin 3 exhibits unique biophysical features that suggest unknown cellular functions. Electrophysiological studies on VDAC3 carrying selective cysteine mutations and mass spectrometry data about the redox state of such sulfur containing amino acids are consistent with a putative involvement of isoform 3 in mitochondrial ROS homeostasis. Here, we thoroughly examined this issue and provided for the first time direct evidence of the role of VDAC3 in cellular response to oxidative stress. Depletion of isoform 3 but not isoform 1 significantly exacerbated the cytotoxicity of redox cyclers such as menadione and paraquat, and respiratory complex I inhibitors like rotenone, promoting uncontrolled accumulation of mitochondrial free radicals. High-resolution respirometry of transiently transfected HAP1-ΔVDAC3 cells expressing the wild type or the cysteine-null mutant VDAC3 protein, unequivocally confirmed that VDAC3 cysteines are indispensable for protein ability to counteract ROS-induced oxidative stress.

Keywords:  Complex I; Cysteine; High-resolution respirometry; Mitochondria; ROS; VDAC3

DOI:  https://doi.org/10.1016/j.redox.2022.102264
J Immunol. 2022 Feb 14. pii: ji2100741. [Epub ahead of print]

TFAM-Dependent Mitochondrial Metabolism Is Required for Alveolar Macrophage Maintenance and Homeostasis.

Xiaochen Gao, Bibo Zhu, Yue Wu, Chaofan Li, Xian Zhou, Jinyi Tang, Jie Sun.

Alveolar macrophages (AMs) are major lung tissue-resident macrophages capable of proliferating and self-renewal in situ. AMs are vital in pulmonary antimicrobial immunity and surfactant clearance. The mechanisms regulating AM compartment formation and maintenance remain to be fully elucidated currently. In this study, we have explored the roles of mitochondrial transcription factor A (TFAM)-mediated mitochondrial fitness and metabolism in regulating AM formation and function. We found that TFAM deficiency in mice resulted in significantly reduced AM numbers and impaired AM maturation in vivo. TFAM deficiency was not required for the generation of AM precursors nor the differentiation of AM precursors into AMs, but was critical for the maintenance of AM compartment. Mechanistically, TFAM deficiency diminished gene programs associated with AM proliferation and self-renewal and promoted the expression of inflammatory genes in AMs. We further showed that TFAM-mediated AM compartment impairment resulted in defective clearance of cellular debris and surfactant in the lung and increased the host susceptibility to severe influenza virus infection. Finally, we found that influenza virus infection in AMs led to impaired TFAM expression and diminished mitochondrial fitness and metabolism. Thus, our data have established the critical function of TFAM-mediated mitochondrial metabolism in AM maintenance and function.

DOI: https://doi.org/10.4049/jimmunol.2100741
Int J Mol Sci. 2022 Jan 19. pii: 1056. [Epub ahead of print]23(3):

Changes of Gut Microbiota by Natural mtDNA Variant Differences Augment Susceptibility to Metabolic Disease and Ageing.

Axel Künstner, Paul Schilf, Hauke Busch, Saleh M Ibrahim, Misa Hirose.

  We recently reported on two mouse strains carrying different single nucleotide variations in the mitochondrial complex I gene, i.e., B6-mtBPL mice carrying m.11902T>C and B6-mtALR carrying m.4738C>A. B6-mtBPL mice exhibited a longer lifespan and a lower metabolic disease susceptibility despite mild mitochondrial functional differences in steady-state. As natural polymorphisms in the mitochondrial DNA (mtDNA) are known to be associated with distinct patterns of gut microbial composition, we further investigated the gut microbiota composition in these mice strains. In line with mouse phenotypes, we found a significantly lower abundance of Proteobacteria, which is positively associated with pathological conditions, in B6-mtBPL compared to B6-mtALR mice. A prediction of functional profile of significantly differential bacterial genera between these strains revealed an involvement of glucose metabolism pathways. Whole transcriptome analysis of liver samples from B6-mtBPL and B6-mtALR mice confirmed these findings. Thus, both host gene expression and gut microbial changes caused by the mtDNA variant differences may contribute to the ageing and metabolic phenotypes observed in these mice strains. Since gut microbiota are easier to modulate, compared with mtDNA variants, identification of such mtDNA variants, specific gut bacterial species and bacterial metabolites may be a potential intervention to modulate common diseases, which are differentially susceptible to individuals with different mtDNA variants.

Keywords:  ageing; complex I; glucose metabolism; gut microbiota; mitochondrial DNA polymorphisms; natural variants; proteobacteria

DOI:  https://doi.org/10.3390/ijms23031056
IUBMB Life. 2022 Feb 14.

The ins and outs of the flavin mononucleotide cofactor of respiratory complex I.

Andrea Curtabbi, José Antonio Enríquez.

  The flavin mononucleotide (FMN) cofactor of respiratory complex I occupies a key position in the electron transport chain. Here, the electrons coming from NADH start the sequence of oxidoreduction reactions, which drives the generation of the proton-motive force necessary for ATP synthesis. The overall architecture and the general catalytic proprieties of the FMN site are mostly well established. However, several aspects regarding the complex I flavin cofactor are still unknown. For example, the flavin binding to the N-module, the NADH-oxidizing portion of complex I, lacks a molecular description. The dissociation of FMN from the enzyme is beginning to emerge as an important regulatory mechanism of complex I activity and ROS production. Finally, how mitochondria import and metabolize FMN is still uncertain. This review summarizes the current knowledge on complex I flavin cofactor and discusses the open questions for future research.

Keywords:  FMN; N-module; ROS; complex I; mitochondria; respiratory chain; riboflavin

DOI:  https://doi.org/10.1002/iub.2600
Mol Cell. 2022 Feb 14. pii: S1097-2765(22)00084-3. [Epub ahead of print]

Unresolved stalled ribosome complexes restrict cell-cycle progression after genotoxic stress.

Mark Stoneley, Robert F Harvey, Thomas E Mulroney, Ryan Mordue, Rebekah Jukes-Jones, Kelvin Cain, Kathryn S Lilley, Ritwick Sawarkar, Anne E Willis.

  During the translation surveillance mechanism known as ribosome-associated quality control, the ASC-1 complex (ASCC) disassembles ribosomes stalled on the mRNA. Here, we show that there are two distinct classes of stalled ribosome. Ribosomes stalled by translation elongation inhibitors or methylated mRNA are short lived in human cells because they are split by the ASCC. In contrast, although ultraviolet light and 4-nitroquinoline 1-oxide induce ribosome stalling by damaging mRNA, and the ASCC is recruited to these stalled ribosomes, we found that they are refractory to the ASCC. Consequently, unresolved UV- and 4NQO-stalled ribosomes persist in human cells. We show that ribosome stalling activates cell-cycle arrest, partly through ZAK-p38MAPK signaling, and that this cell-cycle delay is prolonged when the ASCC cannot resolve stalled ribosomes. Thus, we propose that the sensitivity of stalled ribosomes to the ASCC influences the kinetics of stall resolution, which in turn controls the adaptive stress response.

Keywords:  ASC-1 complex; RNA damage; RNA-binding protein; cell-cycle arrest; ribosome stalling; ribosome-associated quality control; ultraviolet light

DOI:  https://doi.org/10.1016/j.molcel.2022.01.019
EMBO J. 2022 Feb 14. e109760

RNA sensing via the RIG-I-like receptor LGP2 is essential for the induction of a type I IFN response in ADAR1 deficiency.

Jorn E Stok, Timo Oosenbrug, Laurens R Ter Haar, Dennis Gravekamp, Christian P Bromley, Santiago Zelenay, Caetano Reis E Sousa, Annemarthe G van der Veen.

  RNA editing by the adenosine deaminase ADAR1 prevents innate immune responses to endogenous RNAs. In ADAR1-deficient cells, unedited self RNAs form base-paired structures that resemble viral RNAs and inadvertently activate the cytosolic RIG-I-like receptor (RLR) MDA5, leading to an antiviral type I interferon (IFN) response. Mutations in ADAR1 cause Aicardi-Goutières Syndrome (AGS), an autoinflammatory syndrome characterized by chronic type I IFN production. Conversely, ADAR1 loss and the consequent type I IFN production restricts tumor growth and potentiates the activity of some chemotherapeutics. Here, we show that another RIG-I-like receptor, LGP2, also has an essential role in the induction of a type I IFN response in ADAR1-deficient human cells. This requires the canonical function of LGP2 as an RNA sensor and facilitator of MDA5-dependent signaling. Furthermore, we show that the sensitivity of tumor cells to ADAR1 loss requires LGP2 expression. Finally, type I IFN induction in tumor cells depleted of ADAR1 and treated with some chemotherapeutics fully depends on LGP2 expression. These findings highlight a central role for LGP2 in self RNA sensing with important clinical implications.

Keywords:  RIG-I-like receptor family; RNA editing; autoinflammation; innate immunity; type I interferon

DOI:  https://doi.org/10.15252/embj.2021109760
Trends Parasitol. 2022 Feb 08. pii: S1471-4922(22)00032-0. [Epub ahead of print]

Hijacking of host mitochondria by Toxoplasma gondii and SARS-CoV-2.

Ruize Zhang, Jian Chen, Daowen Wang, Zheng Qing Fu.

  Mitochondria regulate energy production, cell cycle, and immune signaling. Li et al. recently reported that Toxoplasma gondii induces the shedding of mitochondrial outer membrane to promote its growth. Intriguingly, the hijacking of host mitochondria has been shown to play an essential role in the pathogenesis of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Keywords:  COVID-19; SARS-CoV-2; SPOTs; TOM70; TgMAF1; Toxoplasma gondii

DOI:  https://doi.org/10.1016/j.pt.2022.02.002
Proc Natl Acad Sci U S A. 2022 Feb 22. pii: e2115624119. [Epub ahead of print]119(8):

Ghost mitochondria drive metastasis through adaptive GCN2/Akt therapeutic vulnerability.

Jagadish C Ghosh, Michela Perego, Ekta Agarwal, Irene Bertolini, Yuan Wang, Aaron R Goldman, Hsin-Yao Tang, Andrew V Kossenkov, Catherine J Libby, Lucia R Languino, Edward F Plow, Annamaria Morotti, Luisa Ottobrini, Marco Locatelli, David W Speicher, M Cecilia Caino, Joel Cassel, Joseph M Salvino, Marie E Robert, Valentina Vaira, Dario C Altieri.

  Cancer metabolism, including in mitochondria, is a disease hallmark and therapeutic target, but its regulation is poorly understood. Here, we show that many human tumors have heterogeneous and often reduced levels of Mic60, or Mitofilin, an essential scaffold of mitochondrial structure. Despite a catastrophic collapse of mitochondrial integrity, loss of bioenergetics, and oxidative damage, tumors with Mic60 depletion slow down cell proliferation, evade cell death, and activate a nuclear gene expression program of innate immunity and cytokine/chemokine signaling. In turn, this induces epithelial-mesenchymal transition (EMT), activates tumor cell movements through exaggerated mitochondrial dynamics, and promotes metastatic dissemination in vivo. In a small-molecule drug screen, compensatory activation of stress response (GCN2) and survival (Akt) signaling maintains the viability of Mic60-low tumors and provides a selective therapeutic vulnerability. These data demonstrate that acutely damaged, "ghost" mitochondria drive tumor progression and expose an actionable therapeutic target in metastasis-prone cancers.

Keywords:  cell motility; metastasis; mitochondria

DOI:  https://doi.org/10.1073/pnas.2115624119
Front Cell Dev Biol. 2022 ;10 717881

Emerging Roles of COX7RP and Mitochondrial Oxidative Phosphorylation in Breast Cancer.

Shuhei Kamada, Toshihiko Takeiwa, Kazuhiro Ikeda, Kuniko Horie, Satoshi Inoue.

  Metabolic alterations are critical events in cancers, which often contribute to tumor pathophysiology. While aerobic glycolysis is a known characteristic of cancer-related metabolism, recent studies have shed light on mitochondria-related metabolic pathways in cancer biology, including oxidative phosphorylation (OXPHOS), amino acid and lipid metabolism, nucleic acid metabolism, and redox regulation. Breast cancer is the most common cancer in women; thus, elucidation of breast cancer-related metabolic alteration will help to develop cancer drugs for many patients. We here aim to define the contribution of mitochondrial metabolism to breast cancer biology. The relevance of OXPHOS in breast cancer has been recently defined by the discovery of COX7RP, which promotes mitochondrial respiratory supercomplex assembly and glutamine metabolism: the latter is also shown to promote nucleic acid and fatty acid biosynthesis as well as ROS defense regulation. In this context, the estrogen-related receptor (ERR) family nuclear receptors and collaborating coactivators peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) are essential transcriptional regulators for both energy production and cancer-related metabolism. Summarizing recent findings of mitochondrial metabolism in breast cancer, this review will aim to provide a clue for the development of alternative clinical management by modulating the activities of responsible molecules involved in disease-specific metabolic alterations.

Keywords:  ERR; OxPhos; breast cancer; metabolism; mitochondria

DOI:  https://doi.org/10.3389/fcell.2022.717881
Endocrinology. 2022 Feb 16. pii: bqac018. [Epub ahead of print]

Adipose mitochondrial complex I deficiency modulates inflammation and glucose homeostasis in a sex-dependent manner.

Kyung-Mi Choi, Karen K Ryan, John C Yoon.

  Mitochondrial dysfunction in adipose tissue has been associated with type 2 diabetes, but it is unclear whether it is a cause or the consequence. Mitochondrial complex I is a major site of reactive oxygen species generation and a therapeutic target. Here we report that genetic deletion of the complex I subunit Ndufs4 specifically in adipose tissue results in an increased propensity to develop diet-induced weight gain, glucose intolerance, and elevated levels of fat inflammatory genes. This outcome is apparent in young males but not in young females, suggesting that females are relatively protected from the adverse consequences of adipose mitochondrial dysfunction for metabolic health. Mutant mice of both sexes exhibit defects in brown adipose tissue thermogenesis. Fibroblast growth factor 21 (FGF21) signaling in adipose tissue is selectively blunted in male mutant mice relative to wild-type littermates, consistent with sex-dependent regulation of its autocrine/paracrine action in adipocytes. Together, these findings support that adipocyte-specific mitochondrial dysfunction is sufficient to induce tissue inflammation and can cause systemic glucose abnormalities in male mice.

Keywords:  FGF21; Ndufs4; impaired glucose tolerance; inflammation; mitochondria

DOI:  https://doi.org/10.1210/endocr/bqac018