bims-minimp 2021-10-03 papers

on Mitochondria, innate immunity, proteostasis

Issue of 2021–10–03
24 papers selected by
Hanna Salmonowicz, International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

The modified mitochondrial outer membrane carrier MTCH2 links mitochondrial fusion to lipogenesis.
Activation of mitochondrial unfolded protein response protects against multiple exogenous stressors.
Mitochondrial dysfunction in adult midbrain dopamine neurons triggers an early immune response.
MicroRNAs as Factors in Bidirectional Crosstalk Between Mitochondria and the Nucleus During Cellular Senescence.
Mapping protein interactions in the active TOM-TIM23 supercomplex.
Preprint Highlight: ER-lysosome lipid transfer protein VPS13C/PARK23 prevents aberrant mtDNA- dependent STING signaling.
The fasting-feeding metabolic transition regulates mitochondrial dynamics.
The multifaceted regulation of mitophagy by endogenous metabolites.
Mitochondria and Mitochondrial DNA: Key Elements in the Pathogenesis and Exacerbation of the Inflammatory State Caused by COVID-19.
Higher DNA repair in mitochondria of long-lived species.
Mitochondrial F1 FO ATP synthase determines the local proton motive force at cristae rims.
Mitochondrial Dysfunction in Diseases, Longevity, and Treatment Resistance: Tuning Mitochondria Function as a Therapeutic Strategy.
Perspectives on Mitochondria-ER and Mitochondria-Lipid Droplet Contact in Hepatocytes and Hepatic Lipid Metabolism.
TASK-1 regulates mitochondrial function under hypoxia.
MAVS: A Two-Sided CARD Mediating Antiviral Innate Immune Signaling and Regulating Immune Homeostasis.
The Mitochondrial Prohibitin (PHB) Complex in C. elegans Metabolism and Ageing Regulation.
DNA repair inhibition leads to active export of repetitive sequences to the cytoplasm triggering an inflammatory response.
Senescent immune cells promote skeletal ageing.
Nonstructural Protein NS1 of Influenza Virus Disrupts Mitochondrial Dynamics and Enhances Mitophagy via ULK1 and BNIP3.
Quantitative proteomics identifies the universally conserved ATPase Ola1p as a positive regulator of heat shock response in Saccharomyces cerevisiae.
DJ-1 attenuates the glycation of mitochondrial complex I and complex III in the post-ischemic heart.
Vitamin B12 impacts amyloid beta-induced proteotoxicity by regulating the methionine/S-adenosylmethionine cycle.
CAMKK2 regulates mitochondrial function by controlling succinate dehydrogenase expression, post-translational modification, megacomplex assembly, and activity in a cell-type-specific manner.
Identification of a small molecule SR9009 that activates NRF2 to counteract cellular senescence.

J Cell Biol. 2021 Nov 01. pii: e202103122. [Epub ahead of print]220(11):

The modified mitochondrial outer membrane carrier MTCH2 links mitochondrial fusion to lipogenesis.

Katherine Labbé, Shona Mookerjee, Maxence Le Vasseur, Eddy Gibbs, Chad Lerner, Jodi Nunnari.

Mitochondrial function is integrated with cellular status through the regulation of opposing mitochondrial fusion and division events. Here we uncover a link between mitochondrial dynamics and lipid metabolism by examining the cellular role of mitochondrial carrier homologue 2 (MTCH2). MTCH2 is a modified outer mitochondrial membrane carrier protein implicated in intrinsic cell death and in the in vivo regulation of fatty acid metabolism. Our data indicate that MTCH2 is a selective effector of starvation-induced mitochondrial hyperfusion, a cytoprotective response to nutrient deprivation. We find that MTCH2 stimulates mitochondrial fusion in a manner dependent on the bioactive lipogenesis intermediate lysophosphatidic acid. We propose that MTCH2 monitors flux through the lipogenesis pathway and transmits this information to the mitochondrial fusion machinery to promote mitochondrial elongation, enhanced energy production, and cellular survival under homeostatic and starvation conditions. These findings will help resolve the roles of MTCH2 and mitochondria in tissue-specific lipid metabolism in animals.

DOI: https://doi.org/10.1083/jcb.202103122
Life Sci Alliance. 2021 Dec;pii: e202101182. [Epub ahead of print]4(12):

Activation of mitochondrial unfolded protein response protects against multiple exogenous stressors.

Sonja K Soo, Annika Traa, Paige D Rudich, Meeta Mistry, Jeremy M Van Raamsdonk.

The mitochondrial unfolded protein response (mitoUPR) is an evolutionarily conserved pathway that responds to mitochondria insults through transcriptional changes, mediated by the transcription factor ATFS-1/ATF-5, which acts to restore mitochondrial homeostasis. In this work, we characterized the role of ATFS-1 in responding to organismal stress. We found that activation of ATFS-1 is sufficient to cause up-regulation of genes involved in multiple stress response pathways including the DAF-16-mediated stress response pathway, the cytosolic unfolded protein response, the endoplasmic reticulum unfolded protein response, the SKN-1-mediated oxidative stress response pathway, the HIF-1-mediated hypoxia response pathway, the p38-mediated innate immune response pathway, and antioxidant genes. Constitutive activation of ATFS-1 increases resistance to multiple acute exogenous stressors, whereas disruption of atfs-1 decreases stress resistance. Although ATFS-1-dependent genes are up-regulated in multiple long-lived mutants, constitutive activation of ATFS-1 decreases lifespan in wild-type animals. Overall, our work demonstrates that ATFS-1 serves a vital role in organismal survival of acute stressors through its ability to activate multiple stress response pathways but that chronic ATFS-1 activation is detrimental for longevity.

DOI: https://doi.org/10.26508/lsa.202101182
PLoS Genet. 2021 Sep 27. 17(9): e1009822

Mitochondrial dysfunction in adult midbrain dopamine neurons triggers an early immune response.

Roberta Filograna, Seungmin Lee, Katarina Tiklova, Mara Mennuni, Viktor Jonsson, Markus Ringnér, Linda Gillberg, Elena Sopova, Oleg Shupliakov, Camilla Koolmeister, Lars Olson, Thomas Perlmann, Nils-Göran Larsson.

Dopamine (DA) neurons of the midbrain are at risk to become affected by mitochondrial damage over time and mitochondrial defects have been frequently reported in Parkinson's disease (PD) patients. However, the causal contribution of adult-onset mitochondrial dysfunction to PD remains uncertain. Here, we developed a mouse model lacking Mitofusin 2 (MFN2), a key regulator of mitochondrial network homeostasis, in adult midbrain DA neurons. The knockout mice develop severe and progressive DA neuron-specific mitochondrial dysfunction resulting in neurodegeneration and parkinsonism. To gain further insights into pathophysiological events, we performed transcriptomic analyses of isolated DA neurons and found that mitochondrial dysfunction triggers an early onset immune response, which precedes mitochondrial swelling, mtDNA depletion, respiratory chain deficiency and cell death. Our experiments show that the immune response is an early pathological event when mitochondrial dysfunction is induced in adult midbrain DA neurons and that neuronal death may be promoted non-cell autonomously by the cross-talk and activation of surrounding glial cells.

DOI: https://doi.org/10.1371/journal.pgen.1009822
Front Physiol. 2021 ;12 734976

MicroRNAs as Factors in Bidirectional Crosstalk Between Mitochondria and the Nucleus During Cellular Senescence.

Chiara Giordani, Andrea Silvestrini, Angelica Giuliani, Fabiola Olivieri, Maria Rita Rippo.

  Mitochondria are essential organelles that generate most of the chemical energy to power the cell through ATP production, thus regulating cell homeostasis. Although mitochondria have their own independent genome, most of the mitochondrial proteins are encoded by nuclear genes. An extensive bidirectional communication network between mitochondria and the nucleus has been discovered, thus making them semi-autonomous organelles. The nucleus-to-mitochondria signaling pathway, called Anterograde Signaling Pathway can be deduced, since the majority of mitochondrial proteins are encoded in the nucleus, less is known about the opposite pathway, the so-called mitochondria-to-nucleus retrograde signaling pathway. Several studies have demonstrated that non-coding RNAs are essential "messengers" of this communication between the nucleus and the mitochondria and that they might have a central role in the coordination of important mitochondrial biological processes. In particular, the finding of numerous miRNAs in mitochondria, also known as mitomiRs, enabled insights into their role in mitochondrial gene transcription. MitomiRs could act as important mediators of this complex crosstalk between the nucleus and the mitochondria. Mitochondrial homeostasis is critical for the physiological processes of the cell. Disruption at any stage in their metabolism, dynamics and bioenergetics could lead to the production of considerable amounts of reactive oxygen species and increased mitochondrial permeability, which are among the hallmarks of cellular senescence. Extensive changes in mitomiR expression and distribution have been demonstrated in senescent cells, those could possibly lead to an alteration in mitochondrial homeostasis. Here, we discuss the emerging putative roles of mitomiRs in the bidirectional communication pathways between mitochondria and the nucleus, with a focus on the senescence-associated mitomiRs.

Keywords:  microRNA; mitochondria; mitomiRs; mitonuclear communication; senescence

DOI:  https://doi.org/10.3389/fphys.2021.734976
Nat Commun. 2021 Sep 29. 12(1): 5715

Mapping protein interactions in the active TOM-TIM23 supercomplex.

Ridhima Gomkale, Andreas Linden, Piotr Neumann, Alexander Benjamin Schendzielorz, Stefan Stoldt, Olexandr Dybkov, Markus Kilisch, Christian Schulz, Luis Daniel Cruz-Zaragoza, Blanche Schwappach, Ralf Ficner, Stefan Jakobs, Henning Urlaub, Peter Rehling.

Nuclear-encoded mitochondrial proteins destined for the matrix have to be transported across two membranes. The TOM and TIM23 complexes facilitate the transport of precursor proteins with N-terminal targeting signals into the matrix. During transport, precursors are recognized by the TIM23 complex in the inner membrane for handover from the TOM complex. However, we have little knowledge on the organization of the TOM-TIM23 transition zone and on how precursor transfer between the translocases occurs. Here, we have designed a precursor protein that is stalled during matrix transport in a TOM-TIM23-spanning manner and enables purification of the translocation intermediate. Combining chemical cross-linking with mass spectrometric analyses and structural modeling allows us to map the molecular environment of the intermembrane space interface of TOM and TIM23 as well as the import motor interactions with amino acid resolution. Our analyses provide a framework for understanding presequence handover and translocation during matrix protein transport.

DOI: https://doi.org/10.1038/s41467-021-26016-1
Mol Biol Cell. 2021 Oct 01. 32(20): 1110

Preprint Highlight: ER-lysosome lipid transfer protein VPS13C/PARK23 prevents aberrant mtDNA- dependent STING signaling.

Luis Bonet-Ponce.

Loss-of-function mutations in VPS13C cause familial Parkinson's disease (PD) and increase the risk to develop the sporadic form of the disease. However, the underlying disease mechanisms remain unclear. It has been previously established that VPS13C tethers lysosomes with the endoplasmic reticulum (ER) and promotes lipid interchange between both organelles. This study provides a cellular role of VPS13C, specifically regulating the cGAS/STING pathway and contributing to the innate immune response. The authors generate VPS13C knockout HeLa cells and use confocal microscopy and biochemical approaches to show loss of VPS13C leads to altered lysosome lipid composition and mitochondrial DNA leakage. Understanding how VPS13C preserves cellular homeostasis is an exciting discovery for scientists working on neurodegeneration and for cell biologists interested in lysosome-to-mitochondria cross-talk.

DOI: https://doi.org/10.1091/mbc.E21-10-0125p
FASEB J. 2021 Oct;35(10): e21891

The fasting-feeding metabolic transition regulates mitochondrial dynamics.

Mauricio Castro-Sepúlveda, Béatrice Morio, Mauro Tuñón-Suárez, Sebastian Jannas-Vela, Francisco Díaz-Castro, Jennifer Rieusset, Hermann Zbinden-Foncea.

  In humans, insulin resistance has been linked to an impaired metabolic transition from fasting to feeding (metabolic flexibility; MetFlex). Previous studies suggest that mitochondrial dynamics response is a putative determinant of MetFlex; however, this has not been studied in humans. Thus, the aim of this study was to investigate the mitochondrial dynamics response in the metabolic transition from fasting to feeding in human peripheral blood mononuclear cells (PBMCs). Six male subjects fasted for 16 h (fasting), immediately after which they consumed a 75-g oral glucose load (glucose). In both fasting and glucose conditions, blood samples were taken to obtain PBMCs. Mitochondrial dynamics were assessed by electron microscopy images. We exposed in vitro acetoacetate-treated PBMCs to the specific IP3R inhibitor Xestospongin B (XeB) to reduce IP3R-mediated mitochondrial Ca2+ accumulation. This allowed us to evaluate the role of ER-mitochondria Ca2+ exchange in the mitochondrial dynamic response to substrate availability. To determine whether PBMCs could be used in obesity context (low MetFlex), we measured mitochondrial dynamics in mouse spleen-derived lymphocytes from WT and ob/ob mice. We demonstrated that the transition from fasting to feeding reduces mitochondria-ER interactions, induces mitochondrial fission and reduces mitochondrial cristae density in human PBMCs. In addition, we demonstrated that IP3R activity is key in the mitochondrial dynamics response when PBMCs are treated with a fasting-substrate in vitro. In murine mononuclear-cells, we confirmed that mitochondria-ER interactions are regulated in the fasted-fed transition and we further highlight mitochondria-ER miscommunication in PBMCs of diabetic mice. In conclusion, our results demonstrate that the fasting/feeding transition reduces mitochondria-ER interactions, induces mitochondrial fission and reduces mitochondrial cristae density in human PBMCs, and that IP3R activity may potentially play a central role.

Keywords:  fasting; mitochondria-ER interaction; mitochondrial cristae; mitochondrial fusion; mitochondrial morphology; obesity

DOI:  https://doi.org/10.1096/fj.202100929R
Autophagy. 2021 Sep 29. 1-24

The multifaceted regulation of mitophagy by endogenous metabolites.

Ting Zhang, Qian Liu, Weihua Gao, Sheikh Arslan Sehgal, Hao Wu.

  Owing to the dominant functions of mitochondria in multiple cellular metabolisms and distinct types of regulated cell death, maintaining a functional mitochondrial network is fundamental for the cellular homeostasis and body fitness in response to physiological adaptations and stressed conditions. The process of mitophagy, in which the dysfunctional or superfluous mitochondria are selectively engulfed by autophagosome and subsequently degraded in lysosome, has been well formulated as one of the major mechanisms for mitochondrial quality control. To date, the PINK1-PRKN-dependent and receptors (including proteins and lipids)-dependent pathways have been characterized to determine the mitophagy in mammalian cells. The mitophagy is highly responsive to the dynamics of endogenous metabolites, including iron-, calcium-, glycolysis-TCA-, NAD+-, amino acids-, fatty acids-, and cAMP-associated metabolites. Herein, we summarize the recent advances toward the molecular details of mitophagy regulation in mammalian cells. We also highlight the key regulations of mammalian mitophagy by endogenous metabolites, shed new light on the bidirectional interplay between mitophagy and cellular metabolisms, with attempting to provide a perspective insight into the nutritional intervention of metabolic disorders with mitophagy deficit.Abbreviations: acetyl-CoA: acetyl-coenzyme A; ACO1: aconitase 1; ADCYs: adenylate cyclases; AMPK: AMP-activated protein kinase; ATM: ATM serine/threonine kinase; BCL2L1: BCL2 like 1; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; Ca2+: calcium ion; CALCOCO2: calcium binding and coiled-coil domain 2; CANX: calnexin; CO: carbon monoxide; CYCS: cytochrome c, somatic; DFP: deferiprone; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; FKBP8: FKBP prolyl isomerase 8; FOXO3: forkhead box O3; FTMT: ferritin mitochondrial; FUNDC1: FUN14 domain containing 1; GABA: γ-aminobutyric acid; GSH: glutathione; HIF1A: hypoxia inducible factor 1 subunit alpha; IMMT: inner membrane mitochondrial protein; IRP1: iron regulatory protein 1; ISC: iron-sulfur cluster; ITPR2: inositol 1,4,5-trisphosphate type 2 receptor; KMO: kynurenine 3-monooxygenase; LIR: LC3 interacting region; MAM: mitochondria-associated membrane; MAP1LC3: microtubule associated protein 1 light chain 3; MFNs: mitofusins; mitophagy: mitochondrial autophagy; mPTP: mitochondrial permeability transition pore; MTOR: mechanistic target of rapamycin kinase; NAD+: nicotinamide adenine dinucleotide; NAM: nicotinamide; NMN: nicotinamide mononucleotide; NO: nitric oxide; NPA: Niemann-Pick type A; NR: nicotinamide riboside; NR4A1: nuclear receptor subfamily 4 group A member 1; NRF1: nuclear respiratory factor 1; OPA1: OPA1 mitochondrial dynamin like GTPase; OPTN: optineurin; PARL: presenilin associated rhomboid like; PARPs: poly(ADP-ribose) polymerases; PC: phosphatidylcholine; PHB2: prohibitin 2; PINK1: PTEN induced kinase 1; PPARG: peroxisome proliferator activated receptor gamma; PPARGC1A: PPARG coactivator 1 alpha; PRKA: protein kinase AMP-activated; PRKDC: protein kinase, DNA-activated, catalytic subunit; PRKN: parkin RBR E3 ubiquitin protein ligase; RHOT: ras homolog family member T; ROS: reactive oxygen species; SIRTs: sirtuins; STK11: serine/threonine kinase 11; TCA: tricarboxylic acid; TP53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VDAC1: voltage dependent anion channel 1.

Keywords:  Cell metabolism; metabolite; mitochondria; mitophagy; mitophagy receptor

DOI:  https://doi.org/10.1080/15548627.2021.1975914
Medicina (Kaunas). 2021 Sep 03. pii: 928. [Epub ahead of print]57(9):

Mitochondria and Mitochondrial DNA: Key Elements in the Pathogenesis and Exacerbation of the Inflammatory State Caused by COVID-19.

José J Valdés-Aguayo, Idalia Garza-Veloz, José I Badillo-Almaráz, Sofia Bernal-Silva, Maria C Martínez-Vázquez, Vladimir Juárez-Alcalá, José R Vargas-Rodríguez, María L Gaeta-Velasco, Carolina González-Fuentes, Lorena Ávila-Carrasco, Margarita L Martinez-Fierro.

  Background and Objectives. The importance of mitochondria in inflammatory pathologies, besides providing energy, is associated with the release of mitochondrial damage products, such as mitochondrial DNA (mt-DNA), which may perpetuate inflammation. In this review, we aimed to show the importance of mitochondria, as organelles that produce energy and intervene in multiple pathologies, focusing mainly in COVID-19 and using multiple molecular mechanisms that allow for the replication and maintenance of the viral genome, leading to the exacerbation and spread of the inflammatory response. The evidence suggests that mitochondria are implicated in the replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which forms double-membrane vesicles and evades detection by the cell defense system. These mitochondrion-hijacking vesicles damage the integrity of the mitochondrion's membrane, releasing mt-DNA into circulation and triggering the activation of innate immunity, which may contribute to an exacerbation of the pro-inflammatory state. Conclusions. While mitochondrial dysfunction in COVID-19 continues to be studied, the use of mt-DNA as an indicator of prognosis and severity is a potential area yet to be explored.

Keywords:  COVID-19; SARS-CoV-2; mitochondrial DNA; mitochondrial dysfunction

DOI:  https://doi.org/10.3390/medicina57090928
Aging (Albany NY). 2021 Sep 27. undefined(undefined):

Higher DNA repair in mitochondria of long-lived species.

Gustavo Barja.



Keywords:  DNA repair; aging rate; base excision repair; longevity; mitochondria

DOI:  https://doi.org/10.18632/aging.203595
EMBO Rep. 2021 Sep 30. e52727

Mitochondrial F1 FO ATP synthase determines the local proton motive force at cristae rims.

Bettina Rieger, Tasnim Arroum, Marie-Theres Borowski, Jimmy Villalta, Karin B Busch.

  The classical view of oxidative phosphorylation is that a proton motive force (PMF) generated by the respiratory chain complexes fuels ATP synthesis via ATP synthase. Yet, under glycolytic conditions, ATP synthase in its reverse mode also can contribute to the PMF. Here, we dissected these two functions of ATP synthase and the role of its inhibitory factor 1 (IF1) under different metabolic conditions. pH profiles of mitochondrial sub-compartments were recorded with high spatial resolution in live mammalian cells by positioning a pH sensor directly at ATP synthase's F1 and FO subunits, complex IV and in the matrix. Our results clearly show that ATP synthase activity substantially controls the PMF and that IF1 is essential under OXPHOS conditions to prevent reverse ATP synthase activity due to an almost negligible ΔpH. In addition, we show how this changes lateral, transmembrane, and radial pH gradients in glycolytic and respiratory cells.

Keywords:  IF1; Mitochondrial F1FO ATP synthase; local pH measurements; proton motive force; ΔpH

DOI:  https://doi.org/10.15252/embr.202152727
Genes (Basel). 2021 Aug 29. pii: 1348. [Epub ahead of print]12(9):

Mitochondrial Dysfunction in Diseases, Longevity, and Treatment Resistance: Tuning Mitochondria Function as a Therapeutic Strategy.

Kazuo Tomita, Yoshikazu Kuwahara, Kento Igarashi, Mehryar Habibi Roudkenar, Amaneh Mohammadi Roushandeh, Akihiro Kurimasa, Tomoaki Sato.

  Mitochondria are very important intracellular organelles because they have various functions. They produce ATP, are involved in cell signaling and cell death, and are a major source of reactive oxygen species (ROS). Mitochondria have their own DNA (mtDNA) and mutation of mtDNA or change the mtDNA copy numbers leads to disease, cancer chemo/radioresistance and aging including longevity. In this review, we discuss the mtDNA mutation, mitochondrial disease, longevity, and importance of mitochondrial dysfunction in cancer first. In the later part, we particularly focus on the role in cancer resistance and the mitochondrial condition such as mtDNA copy number, mitochondrial membrane potential, ROS levels, and ATP production. We suggest a therapeutic strategy employing mitochondrial transplantation (mtTP) for treatment-resistant cancer.

Keywords:  cancer radioresistance; clinically relevant radioresistant (CRR) cells; mitochondria; mitochondrial DNA

DOI:  https://doi.org/10.3390/genes12091348
Cells. 2021 Sep 01. pii: 2273. [Epub ahead of print]10(9):

Perspectives on Mitochondria-ER and Mitochondria-Lipid Droplet Contact in Hepatocytes and Hepatic Lipid Metabolism.

Xiaowen Ma, Hui Qian, Allen Chen, Hong-Min Ni, Wen-Xing Ding.

  Emerging evidence suggests that mitochondrion-endoplasmic reticulum (ER) and mitochondrion-lipid droplet (LD) contact sites are critical in regulating lipid metabolism in cells. It is well established that intracellular organelles communicate with each other continuously through membrane contact sites to maintain organelle function and cellular homeostasis. The accumulation of LDs in hepatocytes is an early indicator of non-alcoholic fatty liver disease (NAFLD) and alcohol-related liver disease (ALD), which may indicate a breakdown in proper inter-organelle communication. In this review, we discuss previous findings in mitochondrion-ER and mitochondrion-LD contact, focusing on their roles in lipid metabolism in hepatocytes. We also present evidence of a unique mitochondrion-LD contact structure in hepatocytes under various physiological and pathological conditions and propose a working hypothesis to speculate about the role of these structures in regulating the functions of mitochondria and LDs and their implications in NAFLD and ALD.

Keywords:  NAFLD; alcohol; autophagy; lipophagy; lipotoxicity; starvation; steatosis

DOI:  https://doi.org/10.3390/cells10092273
Biochem Biophys Res Commun. 2021 Sep 21. pii: S0006-291X(21)01326-7. [Epub ahead of print]578 163-169

TASK-1 regulates mitochondrial function under hypoxia.

Yang Yu, Harrison He, Chen Kang, Keli Hu.

  TASK-1, TWIK-related acid-sensitive potassium channel 1, is a member of the two-pore- domain potassium channel family. It is constitutively active at resting potentials and strongly expressed in the heart. However, little is known about the role of TASK-1 channels in hypoxia. A cellular model of hypoxia and reoxygenation from rat heart-derived H9c2 cells or TASK-1 deficient HEK293T cells was employed to explore the role of TASK-1 channels in cytoprotection against hypoxia. The cell viability assay revealed that TASK-1 expression increased the number of viable cells subjected to 2 h of hypoxia followed by 2 h of reoxygenation (H/R). To dissect the protective role of TASK-1 on mitochondrial function, mitochondrial membrane potential (MMP) was assessed by tetramethylrhodamine fluorescence. It was demonstrated that MMP was significantly decreased by H/R, but it was maintained by TASK-1 expression or pretreatment with cyclosporin A, an inhibitor of mitochondrial permeability transition pore (mPTP). The effect of cyclosporin A on MMP was not further altered by TASK-1 expression. Moreover, TASK-1 expression significantly blocked cytochrome c release induced by H/R. While a small fraction of endogenous TASK-1 was found to colocalize with the mitochondrial marker MitoTracker in H9c2 cells, H/R did not alter the extent of colocalization of TASK-1 with MitoTracker. The total TASK-1 protein level was not significantly affected by H/R. In summary, we provided the evidence that TASK-1 channels confer cytoprotection against hypoxia-reoxygenation injury, possibly by their capacity of maintaining the mitochondrial membrane potential via inhibiting MPTP opening.

Keywords:  Cytochrome c; Hypoxia; Mitochondria; Mitochondrial membrane potential; TASK-1

DOI:  https://doi.org/10.1016/j.bbrc.2021.09.032
Front Microbiol. 2021 ;12 744348

MAVS: A Two-Sided CARD Mediating Antiviral Innate Immune Signaling and Regulating Immune Homeostasis.

Yunqiang Chen, Yuheng Shi, Jing Wu, Nan Qi.

  Mitochondrial antiviral signaling protein (MAVS) functions as a "switch" in the immune signal transduction against most RNA viruses. Upon viral infection, MAVS forms prion-like aggregates by receiving the cytosolic RNA sensor retinoic acid-inducible gene I-activated signaling and further activates/switches on the type I interferon signaling. While under resting state, MAVS is prevented from spontaneously aggregating to switch off the signal transduction and maintain immune homeostasis. Due to the dual role in antiviral signal transduction and immune homeostasis, MAVS has emerged as the central regulation target by both viruses and hosts. Recently, researchers show increasing interest in viral evasion strategies and immune homeostasis regulations targeting MAVS, especially focusing on the post-translational modifications of MAVS, such as ubiquitination and phosphorylation. This review summarizes the regulations of MAVS in antiviral innate immune signaling transduction and immune homeostasis maintenance.

Keywords:  antiviral signal transduction; immune homeostasis; mitochondrial antiviral signaling protein; post-translational modification; viral evasion

DOI:  https://doi.org/10.3389/fmicb.2021.744348
Metabolites. 2021 Sep 17. pii: 636. [Epub ahead of print]11(9):

The Mitochondrial Prohibitin (PHB) Complex in C. elegans Metabolism and Ageing Regulation.

Artur B Lourenço, Marta Artal-Sanz.

  The mitochondrial prohibitin (PHB) complex, composed of PHB-1 and PHB-2, is an evolutionarily conserved context-dependent modulator of longevity. This extremely intriguing phenotype has been linked to alterations in mitochondrial function and lipid metabolism. The true biochemical function of the mitochondrial PHB complex remains elusive, but it has been shown to affect membrane lipid composition. Recent work, using large-scale biochemical approaches, has highlighted a broad effect of PHB on the C. elegans metabolic network. Collectively, the biochemical data support the notion that PHB modulates, at least partially, worm longevity through the moderation of fat utilisation and energy production via the mitochondrial respiratory chain. Herein, we review, in a systematic manner, recent biochemical insights into the impact of PHB on the C. elegans metabolome.

Keywords:  ageing; metabolism; mitochondrial prohibitin complex

DOI:  https://doi.org/10.3390/metabo11090636
J Neurosci. 2021 Sep 28. pii: JN-RM-0845-21. [Epub ahead of print]

DNA repair inhibition leads to active export of repetitive sequences to the cytoplasm triggering an inflammatory response.

Xuan Song, Jacqueline T M Aw, Fulin Ma, Ming Fung Cheung, Danny Leung, Karl Herrup.

Adult-onset neurodegenerative diseases are often accompanied by evidence of a chronic inflammation that includes activation of microglial cells and altered levels of brain cytokines. Aspects of this response are likely secondary reactions to neurodegeneration, but for many illnesses the inflammation may itself be an early and even causative disease event. In such cases, the inflammation is referred to as "sterile" as it occurs in the absence of an actual bacterial or viral pathogen. A potent trigger of sterile inflammation in CNS microglia has been shown to be the presence of DNA in the cytoplasm (cytoDNA) induced either by direct DNA damage or by inhibited DNA repair. We have shown that cytoDNA comes from the cell nucleus as a result of insufficient DNA damage repair. Using wild type and Atm-/- mouse microglia, we extend these observations here by showing that its genomic origins are not random, but rather are heavily biased towards transcriptionally inactive, intergenic regions, in particular repetitive elements and AT-rich sequences. Once released from the genome, in both males and females, we show that cytoDNA is actively exported to the cytoplasm by a CRM1-dependent mechanism. In the cytoplasm, it is degraded either by a cytosolic exonuclease, Trex1, or an autophagy pathway that ends with degradation in the lysosome. Blocking the accumulation of cytoDNA prevents the emergence of the sterile inflammation reaction. These findings offer new insights into the emergence of sterile inflammation and offer novel approaches that may be of use in combatting a wide range of neurodegenerative conditions.Significance:Sterile inflammation describes a state where the defenses of the immune system are activated in the absence of a true pathogen. A potent trigger of this unorthodox response is the presence of DNA in the cytoplasm, which immune cells interpret as an invading virus or pathogen. We show that when DNA damage increases fragments of the cell's own genome are actively exported to the cytoplasm where they are normally degraded. If this degradation is incomplete an immune reaction is triggered. Both age and stress increase DNA damage, and as age-related neurodegenerative diseases are frequently accompanied by a chronic low-level inflammation, strategies that reduce the induction of cytoplasmic DNA or speed its clearance become attractive therapeutic targets.

DOI: https://doi.org/10.1523/JNEUROSCI.0845-21.2021
Nat Rev Endocrinol. 2021 Oct 01.

Senescent immune cells promote skeletal ageing.

Shimona Starling.

DOI: https://doi.org/10.1038/s41574-021-00578-y
Viruses. 2021 Sep 15. pii: 1845. [Epub ahead of print]13(9):

Nonstructural Protein NS1 of Influenza Virus Disrupts Mitochondrial Dynamics and Enhances Mitophagy via ULK1 and BNIP3.

Jae-Hwan Lee, Soo-Jin Oh, Jeanho Yun, Ok Sarah Shin.

  Nonstructural protein 1 (NS1) of influenza virus (IFV) is essential for evading interferon (IFN)-mediated antiviral responses, thereby contributing to the pathogenesis of influenza. Mitophagy is a type of autophagy that selectively removes damaged mitochondria. The role of NS1 in IFV-mediated mitophagy is currently unknown. Herein, we showed that overexpression of NS1 protein led to enhancement of mitophagy. Mitophagy induction via carbonyl cyanide 3-chlorophenylhydrazone treatment in IFV-infected A549 cells led to increased viral replication efficiency, whereas the knockdown of PTEN-induced kinase 1 (PINK1) led to the opposite effect on viral replication. Overexpression of NS1 protein led to changes in mitochondrial dynamics, including depolarization of mitochondrial membrane potential. In contrast, infection with NS1-deficient virus resulted in impaired mitochondrial fragmentation, subsequent mitolysosomal formation, and mitophagy induction, suggesting an important role of NS1 in mitophagy. Meanwhile, NS1 protein increased the phosphorylation of Unc-51-like autophagy activating kinase 1 (ULK1) and the mitochondrial expression of BCL2- interacting protein 3 (BNIP3), both of which were found to be important for IFV-mediated mitophagy. Overall, these data highlight the importance of IFV NS1, ULK1, and BNIP3 during mitophagy activation.

Keywords:  BNIP3; NS1; antiviral immune responses; influenza a virus; mitophagy

DOI:  https://doi.org/10.3390/v13091845
J Biol Chem. 2021 Sep 24. pii: S0021-9258(21)00852-8. [Epub ahead of print] 101050

Quantitative proteomics identifies the universally conserved ATPase Ola1p as a positive regulator of heat shock response in Saccharomyces cerevisiae.

Stefan Dannenmaier, Christine Desroches Altamirano, Lisa Schüler, Ying Zhang, Johannes Hummel, Martin Milanov, Silke Oeljeklaus, Hans-Georg Koch, Sabine Rospert, Simon Alberti, Bettina Warscheid.

  The universally conserved P-loop ATPase Ola1 is implicated in various cellular stress response pathways, as well as in cancer and tumor progression. However, Ola1p functions are divergent between species and the involved mechanisms are only poorly understood. Here, we studied the role of Ola1p in the heat shock response of the yeast Saccharomyces cerevisiae using a combination of quantitative and pulse labeling-based proteomics approaches, in vitro studies and cell-based assays. Our data show that when heat stress is applied to cells lacking Ola1p, the expression of stress-protective proteins is enhanced. During heat stress Ola1p associates with detergent-resistant protein aggregates and rapidly forms assemblies that localize to stress granules. The assembly of Ola1p was also observed in vitro using purified protein and conditions, which resembled those in living cells. We show that loss of Ola1p results in increased protein ubiquitination of detergent-insoluble aggregates recovered from heat-shocked cells. When cells lacking Ola1p were subsequently relieved from heat stress, reinitiation of translation was delayed, whereas, at the same time, de novo synthesis of central factors required for protein refolding and the clearance of aggregates was enhanced when compared to wildtype cells. The combined data suggest that upon acute heat stress, Ola1p is involved in the stabilization of misfolded proteins, which become sequestered in cytoplasmic stress granules. This function of Ola1p enables cells to resume translation in a timely manner as soon as heat stress is relieved.

Keywords:  Heat shock factor protein 1; heat shock protein; protein aggregation; protein misfolding; protein self-assembly; protein synthesis; proteomics; stress granule; translation initiation

DOI:  https://doi.org/10.1016/j.jbc.2021.101050
Sci Rep. 2021 Sep 30. 11(1): 19408

DJ-1 attenuates the glycation of mitochondrial complex I and complex III in the post-ischemic heart.

Yvanna Pantner, Rohini Polavarapu, Lih-Shen Chin, Lian Li, Yuuki Shimizu, John W Calvert.

DJ-1 is a ubiquitously expressed protein that protects cells from stress through its conversion into an active protease. Recent work found that the active form of DJ-1 was induced in the ischemic heart as an endogenous mechanism to attenuate glycative stress-the non-enzymatic glycosylation of proteins. However, specific proteins protected from glycative stress by DJ-1 are not known. Given that mitochondrial electron transport proteins have a propensity for being targets of glycative stress, we investigated if DJ-1 regulates the glycation of Complex I and Complex III after myocardial ischemia-reperfusion (I/R) injury. Initial studies found that DJ-1 localized to the mitochondria and increased its interaction with Complex I and Complex III 3 days after the onset of myocardial I/R injury. Next, we investigated the role DJ-1 plays in modulating glycative stress in the mitochondria. Analysis revealed that compared to wild-type control mice, mitochondria from DJ-1 deficient (DJ-1 KO) hearts showed increased levels of glycative stress following I/R. Additionally, Complex I and Complex III glycation were found to be at higher levels in DJ-1 KO hearts. This corresponded with reduced complex activities, as well as reduced mitochondrial oxygen consumption ant ATP synthesis in the presence of pyruvate and malate. To further determine if DJ-1 influenced the glycation of the complexes, an adenoviral approach was used to over-express the active form of DJ-1(AAV9-DJ1ΔC). Under I/R conditions, the glycation of Complex I and Complex III were attenuated in hearts treated with AAV9-DJ1ΔC. This was accompanied by improvements in complex activities, oxygen consumption, and ATP production. Together, this data suggests that cardiac DJ-1 maintains Complex I and Complex III efficiency and mitochondrial function during the recovery from I/R injury. In elucidating a specific mechanism for DJ-1's role in the post-ischemic heart, these data break new ground for potential therapeutic strategies using DJ-1 as a target.

DOI: https://doi.org/10.1038/s41598-021-98722-1
Cell Rep. 2021 Sep 28. pii: S2211-1247(21)01207-9. [Epub ahead of print]36(13): 109753

Vitamin B12 impacts amyloid beta-induced proteotoxicity by regulating the methionine/S-adenosylmethionine cycle.

Andy B Lam, Kirsten Kervin, Jessica E Tanis.

  Alzheimer's disease (AD) is a devastating neurodegenerative disorder with no effective treatment. Diet, as a modifiable risk factor for AD, could potentially be targeted to slow disease onset and progression. However, complexity of the human diet and indirect effects of the microbiome make it challenging to identify protective nutrients. Multiple factors contribute to AD pathogenesis, including amyloid beta (Aβ) deposition, energy crisis, and oxidative stress. Here, we use Caenorhabditis elegans to define the impact of diet on Aβ proteotoxicity. We discover that dietary vitamin B12 alleviates mitochondrial fragmentation, bioenergetic defects, and oxidative stress, delaying Aβ-induced paralysis without affecting Aβ accumulation. Vitamin B12 has this protective effect by acting as a cofactor for methionine synthase, impacting the methionine/S-adenosylmethionine (SAMe) cycle. Vitamin B12 supplementation of B12-deficient adult Aβ animals is beneficial, demonstrating potential for vitamin B12 as a therapy to target pathogenic features of AD triggered by proteotoxic stress.

Keywords:  ATP; Alzheimer’s disease; C. elegans; S-adenosylmethionine; amyloid beta; choline; diet; methionine; vitamin B(12)

DOI:  https://doi.org/10.1016/j.celrep.2021.109753
Cell Commun Signal. 2021 Sep 25. 19(1): 98

CAMKK2 regulates mitochondrial function by controlling succinate dehydrogenase expression, post-translational modification, megacomplex assembly, and activity in a cell-type-specific manner.

Mohammad Golam Sabbir, Carla G Taylor, Peter Zahradka.

   BACKGROUND: The calcium (Ca2+)/calmodulin (CAM)-activated kinase kinase 2 (CAMKK2)-signaling regulates several physiological processes, for example, glucose metabolism and energy homeostasis, underlying the pathogenesis of metabolic diseases. CAMKK2 exerts its biological function through several downstream kinases, therefore, it is expected that depending on the cell-type-specific kinome profile, the metabolic effects of CAMKK2 and its underlying mechanism may differ. Identification of the cell-type-specific differences in CAMKK2-mediated glucose metabolism will lead to unravelling the organ/tissue-specific role of CAMKK2 in energy metabolism. Therefore, the objective of this study was to understand the cell-type-specific regulation of glucose metabolism, specifically, respiration under CAMKK2 deleted conditions in transformed human embryonic kidney-derived HEK293 and hepatoma-derived HepG2 cells.
METHODS: Cellular respiration was measured in terms of oxygen consumption rate (OCR). OCR and succinate dehydrogenase (SDH) enzyme activity were measured following the addition of substrates. In addition, transcription and proteomic and analyses of the electron transport system (ETS)-associated proteins, including mitochondrial SDH protein complex (complex-II: CII) subunits, specifically SDH subunit B (SDHB), were performed using standard molecular biology techniques. The metabolic effect of the altered SDHB protein content in the mitochondria was further evaluated by cell-type-specific knockdown or overexpression of SDHB.
RESULTS: CAMKK2 deletion suppressed cellular respiration in both cell types, shifting metabolic phenotype to aerobic glycolysis causing the Warburg effect. However, isolated mitochondria exhibited a cell-type-specific enhancement or dampening of the respiratory kinetics under CAMKK2 deletion conditions. This was mediated in part by the cell-type-specific effect of CAMKK2 loss-of-function on transcription, translation, post-translational modification (PTM), and megacomplex assembly of nuclear-encoded mitochondrial SDH enzyme complex subunits, specifically SDHB. The cell-type-specific increase or decrease in SDHs protein levels, specifically SDHB, under CAMKK2 deletion condition resulted in an increased or decreased enzymatic activity and CII-mediated respiration. This metabolic phenotype was reversed by cell-type-specific knockdown or overexpression of SDHB in respective CAMKK2 deleted cell types. CAMKK2 loss-of-function also affected the overall assembly of mitochondrial supercomplex involving ETS-associated proteins in a cell-type-specific manner, which correlated with differences in mitochondrial bioenergetics.
CONCLUSION: This study provided novel insight into CAMKK2-mediated cell-type-specific differential regulation of mitochondrial function, facilitated by the differential expression, PTMs, and assembly of SDHs into megacomplex structures. Video Abstract.

Keywords:  CAMKK2; Oxidative phosphorylation; Respiration; Respiratory supercomplex; Succinate dehydrogenase

DOI:  https://doi.org/10.1186/s12964-021-00778-z
Aging Cell. 2021 Sep 29. e13483

Identification of a small molecule SR9009 that activates NRF2 to counteract cellular senescence.

Li-Bin Gao, Ya-Hong Wang, Zhi-Hua Liu, Yu Sun, Peng Cai, Qing Jing.

  The senescence-associated secretory phenotype (SASP) is a striking characteristic of senescence. Accumulation of SASP factors causes a pro-inflammatory response linked to chronic disease. Suppressing senescence and SASP represents a strategy to prevent or control senescence-associated diseases. Here, we identified a small molecule SR9009 as a potent SASP suppressor in therapy-induced senescence (TIS) and oncogene-induced senescence (OIS). The mechanism studies revealed that SR9009 inhibits the SASP and full DNA damage response (DDR) activation through the activation of the NRF2 pathway, thereby decreasing the ROS level by regulating the expression of antioxidant enzymes. We further identified that SR9009 effectively prevents cellular senescence and suppresses the SASP in the livers of both radiation-induced and oncogene-induced senescence mouse models, leading to alleviation of immune cell infiltration. Taken together, our findings suggested that SR9009 prevents cellular senescence via the NRF2 pathway in vitro and in vivo, and activation of NRF2 may be a novel therapeutic strategy for preventing cellular senescence.

Keywords:  DNA damage; NRF2; ROS; SASP; SR9009; cellular senescence

DOI:  https://doi.org/10.1111/acel.13483