bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2021‒10‒24
23 papers selected by
Avinash N. Mukkala
University of Toronto

  1. Front Cardiovasc Med. 2021 ;8 720085
      Heart function maintenance requires a large amount of energy, which is supplied by the mitochondria. In addition to providing energy to cardiomyocytes, mitochondria also play an important role in maintaining cell function and homeostasis. Although adult cardiomyocyte mitochondria appear as independent, low-static organelles, morphological changes have been observed in cardiomyocyte mitochondria under stress or pathological conditions. Indeed, cardiac mitochondrial fission and fusion are involved in the occurrence and development of heart diseases. As mitochondrial fission and fusion are primarily regulated by mitochondrial dynamins in a GTPase-dependent manner, GTPase-dependent mitochondrial fusion (MFN1, MFN2, and OPA1) and fission (DRP1) proteins, which are abundant in the adult heart, can also be regulated in heart diseases. In fact, these dynamic proteins have been shown to play important roles in specific diseases, including ischemia-reperfusion injury, heart failure, and metabolic cardiomyopathy. This article reviews the role of GTPase-dependent mitochondrial fusion and fission protein-mediated mitochondrial dynamics in the occurrence and development of heart diseases.
    Keywords:  DRP1; MFN2; OPA1; heart disease; mfn1
  2. Biology (Basel). 2021 Oct 15. pii: 1050. [Epub ahead of print]10(10):
      Human mitochondria are highly dynamic organelles, fusing and budding to maintain reticular networks throughout many cell types. Although extending to the extremities of the cell, the majority of the network is concentrated around the nucleus in most of the commonly cultured cell lines. This organelle harbours its own genome, mtDNA, with a different gene content to the nucleus, but the expression of which is critical for maintaining oxidative phosphorylation. Recent advances in click chemistry have allowed us to visualise sites of mitochondrial protein synthesis in intact cultured cells. We show that the majority of translation occurs in the peri-nuclear region of the network. Further analysis reveals that whilst there is a slight peri-nuclear enrichment in the levels of mitoribosomal protein and mitochondrial rRNA, it is not sufficient to explain this substantial heterogeneity in the distribution of translation. Finally, we also show that in contrast, a mitochondrial mRNA does not show such a distinct gradient in distribution. These data suggest that the relative lack of translation in the peripheral mitochondrial network is not due to an absence of mitoribosomes or an insufficient supply of the mt-mRNA transcripts.
    Keywords:  co-localisation; heterogeneity; mammalian; mitochondria; peri-nuclear; peripheral; protein synthesis
  3. Exp Cell Res. 2021 Oct 13. pii: S0014-4827(21)00420-1. [Epub ahead of print] 112866
      The occurrence of liver diseases is attributed to mitochondrial damage. Mitophagy selectively removes dysfunctional mitochondria, thereby preserving mitochondrial function. Augmenter of liver regeneration (ALR) protects the mitochondria from injury. However, whether ALR protection is associated with mitophagy remains unclear. In this study, mitochondrial damage was induced by carbonyl cyanide 3-chlorophenylhydrazone (CCCP), and long form ALR (lfRNA) -mediated protection against this damage was investigated. Treatment of HepG2 cells with CCCP elevated the level of intracellular ROS, inhibited ATP production, and increased the mitochondrial membrane potential and cell apoptotic rate. However, in lfALR-transfected cells, CCCP-induced cell injury was clearly alleviated, the apoptosis and ROS levels clearly declined, and the ATP production was significantly enhanced as compared with that in vector-Tx cells. Furthermore, lfALR overexpression promoted autophagy and mitophagy via a PINK1/Parkin-dependent pathway, whereas knockdown of ALR suppressed mitophagy. In lfALR-transfected cells, the phosphorylation of AKT was decreased, thus, downregulating the phosphorylation of the transcription factor FOXO3a at Ser315. In contrast, the phosphorylation of AMPK was enhanced, thereby upregulating the phosphorylation of FOXO3a at Ser413. Consequently, FOXO3a's nuclear translocation and binding to the promoter region of PINK1 was enhanced, and the accumulation of PINK1/Parkin in mitochondria increased. Meanwhile, short form ALR (sfALR) also increased PINK1 expression through FOXO3a with the similar pathway to lfALR. In conclusion, our data suggest a novel mechanism through which both lfALR and sfALR protect mitochondria by promoting PINK1/Parkin-dependent mitophagy through FOXO3a activation.
    Keywords:  Augmenter of liver regeneration; FOXO3a; Mitophagy; PINK1/Parkin
  4. Cell Rep. 2021 Oct 19. pii: S2211-1247(21)01310-3. [Epub ahead of print]37(3): 109846
      Optical methods for measuring intracellular ions including Ca2+ revolutionized our understanding of signal transduction. However, these methods are not extensively applied to intact organs due to issues including inner filter effects, motion, and available probes. Mitochondrial Ca2+ is postulated to regulate cell energetics and death pathways that are best studied in an intact organ. Here, we develop a method to optically measure mitochondrial Ca2+ and demonstrate its validity for mitochondrial Ca2+ and metabolism using hearts from wild-type mice and mice with germline knockout of the mitochondria calcium uniporter (MCU-KO). We previously reported that germline MCU-KO hearts do not show an impaired response to adrenergic stimulation. We find that these MCU-KO hearts do not take up Ca2+, consistent with no alternative Ca2+ uptake mechanisms in the absence of MCU. This approach can address the role of mitochondrial Ca2+ to the myriad of functions attributed to alterations in mitochondrial Ca2+.
    Keywords:  calcium; heart; isoproterenol; mitochondria; spectroscopy
  5. Int J Mol Sci. 2021 Oct 15. pii: 11125. [Epub ahead of print]22(20):
      Mitochondria regulate a myriad of cellular functions. Dysregulation of mitochondrial control within airway epithelial cells has been implicated in the pro-inflammatory response to allergens in asthma patients. Because of their multifaceted nature, mitochondrial structure must be tightly regulated through fission and fusion. Dynamin Related Protein 1 (DRP1) is a key driver of mitochondrial fission. During allergic asthma, airway epithelial mitochondria appear smaller and structurally altered. The role of DRP1-mediated mitochondrial fission, however, has not been fully elucidated in epithelial response to allergens. We used a Human Bronchial Epithelial Cell line (HBECs), primary Mouse Tracheal Epithelial Cells (MTECs), and conditional DRP1 ablation in lung epithelial cells to investigate the impact of mitochondrial fission on the pro-inflammatory response to house dust mite (HDM) in vitro and in vivo. Our data suggest that, following HDM challenge, mitochondrial fission is rapidly upregulated in airway epithelial cells and precedes production of pro-inflammatory cytokines and chemokines. Further, deletion of Drp1 in lung epithelial cells leads to decreased fission and enhanced pro-inflammatory signaling in response to HDM in vitro, as well as enhanced airway hyper-responsiveness (AHR), inflammation, differential mucin transcription, and epithelial cell death in vivo. Mitochondrial fission, therefore, regulates the lung epithelial pro-inflammatory response to HDM.
    Keywords:  DRP1; HDM; allergic airway disease; epithelial cell; mitochondrial fission
  6. Trends Microbiol. 2021 Oct 13. pii: S0966-842X(21)00237-7. [Epub ahead of print]
      Mitochondria control various processes that are integral to cellular and organismal homeostasis, including Ca2+ fluxes, bioenergetic metabolism, and cell death. Perhaps not surprisingly, multiple pathogenic bacteria have evolved strategies to subvert mitochondrial functions in support of their survival and dissemination. Here, we discuss nonimmunological pathogenic mechanisms that converge on the ability of bacteria to control the mitochondrial compartment of host cells.
    Keywords:  Listeria monocytogenes; Mycobacterium tuberculosis; autophagy; mitochondria-associated ER membranes; oxidative phosphorylation; regulated cell death
  7. J Cell Sci. 2021 Oct 22. pii: jcs.258653. [Epub ahead of print]
      Diverse genes associated with familial Parkinson's disease (familial Parkinsonism) have been implicated in mitochondrial quality control. One such gene, PARK7 encodes the protein DJ-1, pathogenic mutations of which trigger its translocation from the cytosol to the mitochondrial matrix. The translocation of steady-state cytosolic proteins like DJ-1 to the mitochondrial matrix by missense mutations is rare and the underlying mechanism remains to be elucidated. Here, we show that the protein unfolding associated with various DJ-1 mutations drives its import into the mitochondrial matrix. Increasing the structural stability of these DJ-1 mutants restores cytosolic localization. Mechanistically, we show that a reduction in the structural stability of DJ-1 exposes a cryptic N-terminal mitochondrial targeting signal (MTS) including Leu10 that promotes DJ-1 import into the mitochondrial matrix for subsequent degradation. Our work describes a novel cellular mechanism for targeting a destabilized cytosolic protein to the mitochondria for degradation.
    Keywords:  DJ-1; Import; Mitochondria; Parkinson's disease
  8. BMC Biol. 2021 Oct 21. 19(1): 229
      BACKGROUND: Mitochondrial dynamics is the result of a dynamic balance between fusion and fission events, which are driven via a set of mitochondria-shaping proteins. These proteins are generally considered to be binary components of either the fission or fusion machinery, but potential crosstalk between the fission and fusion machineries remains less explored. In the present work, we analyzed the roles of mitochondrial elongation factors 1 and 2 (MIEF1/2), core components of the fission machinery in mammals.RESULTS: We show that MIEFs (MIEF1/2), besides their action in the fission machinery, regulate mitochondrial fusion through direct interaction with the fusion proteins Mfn1 and Mfn2, suggesting that MIEFs participate in not only fission but also fusion. Elevated levels of MIEFs enhance mitochondrial fusion in an Mfn1/2- and OPA1-dependent but Drp1-independent manner. Moreover, mitochondrial localization and self-association of MIEFs are crucial for their fusion-promoting ability. In addition, we show that MIEF1/2 can competitively decrease the interaction of hFis1 with Mfn1 and Mfn2, alleviating hFis1-induced mitochondrial fragmentation and contributing to mitochondrial fusion.
    CONCLUSIONS: Our study suggests that MIEFs serve as a central hub that interacts with and regulates both the fission and fusion machineries, which uncovers a novel mechanism for balancing these opposing forces of mitochondrial dynamics in mammals.
    Keywords:  Drp1; MIEF1/2; Mfn1/2; Mitochondrial dynamics; Mitochondrial fission; Mitochondrial fusion; hFis1
  9. Cell. 2021 Oct 11. pii: S0092-8674(21)01116-8. [Epub ahead of print]
      The human mitochondrial genome encodes thirteen core subunits of the oxidative phosphorylation system, and defects in mitochondrial gene expression lead to severe neuromuscular disorders. However, the mechanisms of mitochondrial gene expression remain poorly understood due to a lack of experimental approaches to analyze these processes. Here, we present an in vitro system to silence translation in purified mitochondria. In vitro import of chemically synthesized precursor-morpholino hybrids allows us to target translation of individual mitochondrial mRNAs. By applying this approach, we conclude that the bicistronic, overlapping ATP8/ATP6 transcript is translated through a single ribosome/mRNA engagement. We show that recruitment of COX1 assembly factors to translating ribosomes depends on nascent chain formation. By defining mRNA-specific interactomes for COX1 and COX2, we reveal an unexpected function of the cytosolic oncofetal IGF2BP1, an RNA-binding protein, in mitochondrial translation. Our data provide insight into mitochondrial translation and innovative strategies to investigate mitochondrial gene expression.
    Keywords:  IGF2BP1; antisense; mitochondria; mitochondrial ribosome; morpholino; oxidative phosphorylation; translation
  10. Cells. 2021 Oct 17. pii: 2781. [Epub ahead of print]10(10):
      Regulation of mitochondrial morphology and motility is critical for neurons, but the exact mechanisms are unclear. Here, we demonstrate that these mechanisms may involve collapsin response mediator protein 2 (CRMP2). CRMP2 is attached to neuronal mitochondria and binds to dynamin-related protein 1 (Drp1), Miro 2, and Kinesin 1 light chain (KLC1). Treating neurons with okadaic acid (OA), an inhibitor of phosphatases PP1 and PP2A, resulted in increased CRMP2 phosphorylation at Thr509/514, Ser522, and Thr555, and augmented Drp1 phosphorylation at Ser616. The CRMP2-binding small molecule (S)-lacosamide ((S)-LCM) prevented an OA-induced increase in CRMP2 phosphorylation at Thr509/514 and Ser522 but not at Thr555, and also failed to alleviate Drp1 phosphorylation. The increased CRMP2 phosphorylation correlated with decreased CRMP2 binding to Drp1, Miro 2, and KLC1. (S)-LCM rescued CRMP2 binding to Drp1 and Miro 2 but not to KLC1. In parallel with CRMP2 hyperphosphorylation, OA increased mitochondrial fission and suppressed mitochondrial traffic. (S)-LCM prevented OA-induced alterations in mitochondrial morphology and motility. Deletion of CRMP2 with a small interfering RNA (siRNA) resulted in increased mitochondrial fission and diminished mitochondrial traffic. Overall, our data suggest that the CRMP2 expression level and phosphorylation state are involved in regulating mitochondrial morphology and motility in neurons.
    Keywords:  CRMP2; mitochondria; morphology; motility; neuron
  11. Pharmaceuticals (Basel). 2021 Oct 14. pii: 1045. [Epub ahead of print]14(10):
      Pioglitazone (PIO) is an insulin-sensitizing antidiabetic drug, which normalizes glucose and lipid metabolism but may provoke heart and liver failure and chronic kidney diseases. Both therapeutic and adverse effects of PIO can be accomplished through mitochondrial targets. Here, we explored the capability of PIO to modulate the mitochondrial membrane potential (ΔΨm) and the permeability transition pore (mPTP) opening in different models in vitro. ΔΨm was measured using tetraphenylphosphonium and the fluorescent dye rhodamine 123. The coupling of oxidative phosphorylation was estimated polarographically. The transport of ions and solutes across membranes was registered by potentiometric and spectral techniques. We found that PIO decreased ΔΨm in isolated mitochondria and intact thymocytes and the efficiency of ADP phosphorylation, particularly after the addition of Ca2+. The presence of the cytosolic fraction mitigated mitochondrial depolarization but made it sustained. Carboxyatractyloside diminished the PIO-dependent depolarization. PIO activated proton transport in deenergized mitochondria but not in artificial phospholipid vesicles. PIO had no effect on K+ and Ca2+ inward transport but drastically decreased the mitochondrial Ca2+-retention capacity and protective effects of adenine nucleotides against mPTP opening. Thus, PIO is a mild, partly ATP/ADP-translocase-dependent, uncoupler and a modulator of ATP production and mPTP sensitivity to Ca2+ and adenine nucleotides. These properties contribute to both therapeutic and adverse effects of PIO.
    Keywords:  ATP production; adenine nucleotide translocase; permeability transition pore; uncoupling protein; unilamellar vesicles
  12. BMB Rep. 2021 Oct 22. pii: 5426. [Epub ahead of print]
      Parkinson's disease (PD) is one of the most common neurodegenerative diseases in the elderly population and is caused by the loss of dopaminergic neurons. PD has been predominantly attributed to mitochondrial dysfunction. The structural alteration of α-synuclein triggers toxic oligomer formation in the neurons, which greatly contributes to PD. In this article, we discuss the role of several familial PD-related proteins, such as α-synuclein, DJ-1, LRRK2, PINK1, and parkin in mitophagy, which entails a selective degradation of mitochondria via autophagy. Defective changes in mitochondrial dynamics and their biochemical and functional interaction induce the formation of toxic α-synuclein-containing protein aggregates in PD. In addition, these gene products play an essential role in ubiquitin proteasome system (UPS)-mediated proteolysis as well as mitophagy. Interestingly, a few deubiquitinating enzymes (DUBs) additionally modulate these two pathways negatively or positively. Based on these findings, we summarize the close relationship between several DUBs and the precise modulation of mitophagy. For example, the USP8, USP10, and USP15, among many DUBs are reported to specifically regulate the K48- or K63-linked de-ubiquitination reactions of several target proteins associated with the mitophagic process, in turn upregulating the mitophagy and protecting neuronal cells from α-synuclein-derived toxicity. In contrast, USP30 inhibits mitophagy by opposing parkin-mediated ubiquitination of target proteins. Furthermore, the association between these changes and PD pathogenesis will be discussed. Taken together, although the functional roles of several PD-related genes have yet to be fully understood, they are substantially associated with mitochondrial quality control as well as UPS. Therefore, a better understanding of their relationship provides valuable therapeutic clues for appropriate management strategies.
  13. Free Radic Biol Med. 2021 Oct 16. pii: S0891-5849(21)00762-0. [Epub ahead of print]
      As hypoxia is a major driver for the pathophysiology of COVID-19, it is crucial to characterize the hypoxic response at the cellular and molecular levels. In order to augment drug repurposing with the identification of appropriate molecular targets, investigations on therapeutics preventing hypoxic cell damage is required. In this work, we propose a hypoxia model based on alveolar lung epithelial cells line using chemical inducer, CoCl2 that can be used for testing calcium channel blockers (CCBs). Since recent studies suggested that CCBs may reduce the infectivity of SARS-Cov-2, we specifically select FDA approved calcium channel blocker, nifedipine for the study. First, we examined hypoxia-induced cell morphology and found a significant increase in cytosolic calcium levels, mitochondrial calcium overload as well as ROS production in hypoxic A549 cells. Secondly, we demonstrate the protective behaviour of nifedipine for cells that are already subjected to hypoxia through measurement of cell viability as well as 4D imaging of cellular morphology and nuclear condensation. Thirdly, we show that the protective effect of nifedipine is achieved through the reduction of cytosolic calcium, mitochondrial calcium, and ROS generation. Overall, we outline a framework for quantitative analysis of mitochondrial calcium and ROS using 3D imaging in laser scanning confocal microscopy and the open-source image analysis platform ImageJ. The proposed pipeline was used to visualize mitochondrial calcium and ROS level in individual cells that provide an understanding of molecular targets. Our findings suggest that the therapeutic value of nifedipine may potentially be evaluated in the context of COVID-19 therapeutic trials.
    Keywords:  Calcium channel blocker; Hypoxia; Mitochondrial calcium; Nifedipine; Reactive oxygen species (ROS); SARS-Cov-2
  14. Life Sci. 2021 Oct 16. pii: S0024-3205(21)01038-9. [Epub ahead of print]286 120051
      AIMS: To overcome radioresistant cancer cells, clinically relevant radioresistant (CRR) cells were established. To maintain their radioresistance, CRR cells were exposed 2 Gy/day of X-rays daily (maintenance irradiation: MI). To understand whether the radioresistance induced by X-rays was reversible or irreversible, the difference between CRR cells and those without MI for a year (CRR-NoIR cells) was investigated by the mitochondrial function as an index.MAIN METHODS: Radiation sensitivity was determined by modified high density survival assay. Mitochondrial membrane potential (Δψm) was determined by 5,5',6,6'-tetrachloro-1,1', tetraethylbenzimidazolocarbo-cyanine iodide (JC-1) staining. Rapid Glucose-Galactose assay was performed to determine the shift in their energy metabolism from aerobic glycolysis to oxidative phosphorylation in CRR cells. Involvement of prohibitin-1 (PHB1) in Δψm was evaluated by knockdown of PHB1 gene followed by real-time PCR.
    KEY FINDINGS: CRR cells that exhibited resistant to 2 Gy/day X-ray lost their radioresistance after more than one year of culture without MI for a year. In addition, CRR cells lost their radioresistance when the mitochondria were activated by galactose. Furthermore, Δψm were increased and PHB1 expression was down-regulated, in the process of losing their radioresistance.
    SIGNIFICANCE: Our finding reveled that tune regulation of mitochondrial function is implicated in radioresistance phenotype of cancer cells. Moreover, as our findings indicate, though further studies are required to clarify the precise mechanisms underlying cancer cell radioresistance, radioresistant cells induced by irradiation and cancer stem cells that are originally radioresistant should be considered separately, the radioresistance of CRR cells is reversible.
    Keywords:  Glycolysis; Hydrogen peroxide; Membrane potential; Mitochondria; Prohibitin; Radioresistance
  15. Cell Death Dis. 2021 Oct 16. 12(11): 953
      Many cell death pathways, including apoptosis, regulated necrosis, and ferroptosis, are relevant for neuronal cell death and share common mechanisms such as the formation of reactive oxygen species (ROS) and mitochondrial damage. Here, we present the role of the actin-regulating protein cofilin1 in regulating mitochondrial pathways in oxidative neuronal death. Cofilin1 deletion in neuronal HT22 cells exerted increased mitochondrial resilience, assessed by quantification of mitochondrial ROS production, mitochondrial membrane potential, and ATP levels. Further, cofilin1-deficient cells met their energy demand through enhanced glycolysis, whereas control cells were metabolically impaired when challenged by ferroptosis. Further, cofilin1 was confirmed as a key player in glutamate-mediated excitotoxicity and associated mitochondrial damage in primary cortical neurons. Using isolated mitochondria and recombinant cofilin1, we provide a further link to toxicity-related mitochondrial impairment mediated by oxidized cofilin1. Our data revealed that the detrimental impact of cofilin1 on mitochondria depends on the oxidation of cysteine residues at positions 139 and 147. Overall, our findings show that cofilin1 acts as a redox sensor in oxidative cell death pathways of ferroptosis, and also promotes glutamate excitotoxicity. Protective effects by cofilin1 inhibition are particularly attributed to preserved mitochondrial integrity and function. Thus, interfering with the oxidation and pathological activation of cofilin1 may offer an effective therapeutic strategy in neurodegenerative diseases.
  16. J Cell Sci. 2021 Oct 21. pii: jcs.259091. [Epub ahead of print]
      Hepatic lipid homeostasis depends on intracellular pathways that respire fatty acid (FA) in peroxisomes and mitochondria and on systemic pathways that secrete FA into the bloodstream, either free or condensed in very-low-density lipoprotein (VLDL) triglycerides. These systemic and intracellular pathways are interdependent, but it is unclear whether and how they integrate into a single cellular circuit. Here, we report that mouse liver wrappER, a distinct ER compartment with apparent FA- and VLDL-secretion functions, connects peroxisomes and mitochondria. Correlative light electron microscopy, quantitative serial section electron tomography, and 3D organelle reconstruction analysis show that the number of peroxisome-wrappER-mitochondria complexes changes throughout fasting-to-feeding transitions and doubles when VLDL synthesis stops following acute genetic ablation of Mttp in the liver. Quantitative proteomic analysis of peroxisome-wrappER-mitochondria complex-enriched fractions indicates that the loss of Mttp upregulates global FA β-oxidation, thereby integrating the dynamics of this three-organelle association into hepatic FA flux responses. Therefore, liver lipid homeostasis occurs through the convergence of systemic and intracellular FA-elimination pathways in the peroxisome-wrappER-mitochondria complex.
    Keywords:  Fatty acid; Inter-organelle contacts; Liver lipid homeostasis; Mitochondria; Peroxisome; WrappER
  17. Biomolecules. 2021 Oct 14. pii: 1511. [Epub ahead of print]11(10):
      Parkin plays an important role in ensuring efficient mitochondrial function and calcium homeostasis. Parkin-mutant human fibroblasts, with defective oxidative phosphorylation activity, showed high basal cAMP level likely ascribed to increased activity/expression of soluble adenylyl cyclase and/or low expression/activity of the phosphodiesterase isoform 4 and to a higher Ca2+ level. Overall, these findings support the existence, in parkin-mutant fibroblasts, of an abnormal Ca2+ and cAMP homeostasis in mitochondria. In our previous studies resveratrol treatment of parkin-mutant fibroblasts induced a partial rescue of mitochondrial functions associated with stimulation of the AMPK/SIRT1/PGC-1α pathway. In this study we provide additional evidence of the potential beneficial effects of resveratrol inducing an increase in the pre-existing high Ca2+ level and remodulation of the cAMP homeostasis in parkin-mutant fibroblasts. Consistently, we report in these fibroblasts higher expression of proteins implicated in the tethering of ER and mitochondrial contact sites along with their renormalization after resveratrol treatment. On this basis we hypothesize that resveratrol-mediated enhancement of the Ca2+ level, fine-tuned by the ER-mitochondria Ca2+ crosstalk, might modulate the pAMPK/AMPK pathway in parkin-mutant fibroblasts.
    Keywords:  cAMP; calcium (Ca2+); endoplasmic reticulum (ER); mitochondria; parkin; resveratrol
  18. Front Physiol. 2021 ;12 713564
      It has been convincingly demonstrated that remote ischemic preconditioning (RIPC) can make the myocardium resistant to the subsequent ischemia reperfusion injury (IRI), which causes severe damages by mainly generating cell death. However, the cardioprotective effects of the hepatic RIPC, which is the largest metabolic organ against I/R, have not been fully studied. The aim of our research is whether remote liver RIPC may provide cardioprotective effects against the I/R-induced injury. Here, we generated an I/R mice model in four groups to analyze the effect. The control group is the isolated hearts with 140-min perfusion. I/R group added ischemia in 30 min following 90-min reperfusion. The third group (sham) was subjected to the same procedure as the latter group. The animals in the fourth group selected as the treatment group, underwent a hepatic RIPC by three cycles of 5-min occlusion of the portal triad and then followed by induction of I/R in the isolated heart. The level of myocardial infarction and the preventive effects of RIPC were assessed by pathological characteristics, namely, infarct, enzyme releases, pressure, and cardiac mechanical activity. Subjected to I/R, the hepatic RIPC minimized the infarct size (17.7 ± 4.96 vs. 50.06 ± 5, p < 0.001) and improved the left ventricular-developed pressure (from 47.42 ± 6.27 to 91.62 ± 5.22 mmHg) and the mechanical activity. Release of phosphocreatine kinase-myocardial band (73.86 ± 1.95 vs. 25.93 ± 0.66 IUL-1) and lactate dehydrogenase (299.01 ± 10.7 vs. 152.3 ± 16.7 IUL-1) was also decreased in the RIPC-treated group. These results demonstrate the cardioprotective effects of the hepatic remote preconditioning against the injury caused by I/R in the isolated perfused hearts.
    Keywords:  heart damage; hepatic; ischemia reperfusion injury; left ventricular developed pressure; remote ischemic preconditioning
  19. EMBO J. 2021 Oct 18. e108428
      Mitochondrial cristae are extraordinarily crowded with proteins, which puts stress on the bilayer organization of lipids. We tested the hypothesis that the high concentration of proteins drives the tafazzin-catalyzed remodeling of fatty acids in cardiolipin, thereby reducing bilayer stress in the membrane. Specifically, we tested whether protein crowding induces cardiolipin remodeling and whether the lack of cardiolipin remodeling prevents the membrane from accumulating proteins. In vitro, the incorporation of large amounts of proteins into liposomes altered the outcome of the remodeling reaction. In yeast, the concentration of proteins involved in oxidative phosphorylation (OXPHOS) correlated with the cardiolipin composition. Genetic ablation of either remodeling or biosynthesis of cardiolipin caused a substantial drop in the surface density of OXPHOS proteins in the inner membrane of the mouse heart and Drosophila flight muscle mitochondria. Our data suggest that OXPHOS protein crowding induces cardiolipin remodelling and that remodeled cardiolipin supports the high concentration of these proteins in the inner mitochondrial membrane.
    Keywords:  Barth syndrome; lipid-protein interaction; macromolecular crowding; mitochondria; oxidative phosphorylation
  20. Cells. 2021 Oct 16. pii: 2775. [Epub ahead of print]10(10):
      Mitochondria are ubiquitous organelles of eukaryotic organisms with a number of essential functions, including synthesis of iron-sulfur clusters, amino acids, lipids, and adenosine triphosphate (ATP). During aging of the fungal aging model Podospora anserina, the inner mitochondrial membrane (IMM) undergoes prominent morphological alterations, ultimately resulting in functional impairments. Since phospholipids (PLs) are key components of biological membranes, maintenance of membrane plasticity and integrity via regulation of PL biosynthesis is indispensable. Here, we report results from a lipidomic analysis of isolated mitochondria from P. anserina that revealed an age-related reorganization of the mitochondrial PL profile and the involvement of the i-AAA protease PaIAP in proteolytic regulation of PL metabolism. The absence of PaIAP enhances biosynthesis of characteristic mitochondrial PLs, leads to significant alterations in the acyl composition of the mitochondrial signature PL cardiolipin (CL), and induces mitophagy. These alterations presumably cause the lifespan increase of the PaIap deletion mutant under standard growth conditions. However, PaIAP is required at elevated temperatures and for degradation of superfluous CL synthase PaCRD1 during glycolytic growth. Overall, our study uncovers a prominent role of PaIAP in the regulation of PL homeostasis in order to adapt membrane plasticity to fluctuating environmental conditions as they occur in nature.
    Keywords:  P. anserina; PaCRD1; PaIAP; aging; lipid metabolism; mitochondria
  21. Mol Cell. 2021 Oct 21. pii: S1097-2765(21)00798-X. [Epub ahead of print]81(20): 4191-4208.e8
      To survive, mammalian cells must adapt to environmental challenges. While the cellular response to mild stress has been widely studied, how cells respond to severe stress remains unclear. We show here that under severe hyperosmotic stress, cells enter a transient hibernation-like state in anticipation of recovery. We demonstrate this adaptive pausing response (APR) is a coordinated cellular response that limits ATP supply and consumption through mitochondrial fragmentation and widespread pausing of mRNA translation. This pausing is accomplished by ribosome stalling at translation initiation codons, which keeps mRNAs poised to resume translation upon recovery. We further show that recovery from severe stress involves ISR (integrated stress response) signaling that permits cell cycle progression, resumption of growth, and reversal of mitochondria fragmentation. Our findings indicate that cells can respond to severe stress via a hibernation-like mechanism that preserves vital elements of cellular function under harsh environmental conditions.
    Keywords:  ATF4; ISR; hypertonic; mTOR; mitochondria; neMito mRNAs; ribosome stalling; stress; translation
  22. Circulation. 2021 Oct 21.
      Background: The catalytic subunit of telomerase, Telomerase Reverse Transcriptase (TERT) has protective functions in the cardiovascular system. TERT is not only present in the nucleus, but also in mitochondria. However, it is unclear whether nuclear or mitochondrial TERT is responsible for the observed protection and appropriate tools are missing to dissect this. Methods: We generated new mouse models containing TERT exclusively in the mitochondria (mitoTERT mice) or the nucleus (nucTERT mice) to finally distinguish between the functions of nuclear and mitochondrial TERT. Outcome after ischemia/reperfusion, mitochondrial respiration in the heart as well as cellular functions of cardiomyocytes, fibroblasts, and endothelial cells were determined. Results: All mice were phenotypically normal. While respiration was reduced in cardiac mitochondria from TERT-deficient and nucTERT mice, it was increased in mitoTERT animals. The latter also had smaller infarcts than wildtype mice, whereas nucTERT animals had larger infarcts. The decrease in ejection fraction after one, two and four weeks of reperfusion was attenuated in mitoTERT mice. Scar size was also reduced and vascularization increased. Mitochondrial TERT protected a cardiomyocyte cell line from apoptosis. Myofibroblast differentiation, which depends on complex I activity, was abrogated in TERT-deficient and nucTERT cardiac fibroblasts and completely restored in mitoTERT cells. In endothelial cells, mitochondrial TERT enhanced migratory capacity and activation of endothelial NO synthase. Mechanistically, mitochondrial TERT improved the ratio between complex I matrix arm and membrane subunits explaining the enhanced complex I activity. In human right atrial appendages, TERT was localized in mitochondria and there increased by remote ischemic preconditioning. The Telomerase activator, TA-65 evoked a similar effect in endothelial cells, thereby increasing their migratory capacity, and enhanced myofibroblast differentiation. Conclusions: Mitochondrial, but not nuclear TERT, is critical for mitochondrial respiration and during ischemia/reperfusion injury. Mitochondrial TERT improves complex I subunit composition. TERT is present in human heart mitochondria, and remote ischemic preconditioning increases its level in those organelles. TA-65 has comparable effects ex vivo and improves migratory capacity of endothelial cells and myofibroblast differentiation. We conclude that mitochondrial TERT is responsible for cardioprotection and its increase could serve as a therapeutic strategy.
  23. Biomedicines. 2021 Sep 30. pii: 1362. [Epub ahead of print]9(10):
      This study tested whether extracorporeal shock wave (ECSW) supported-exogenous mitochondria (Mito) into adipose-derived mesenchymal stem cells (ADMSCs) would preserve left-ventricular-ejection-fraction (LVEF) in doxorubicin/12 mg/kg-induced dilated cardiomyopathy (DCM) rat. Adult-male-SD rats were equally categorized into group 1 (sham-control), group 2 (DCM), group 3 (DCM + ECSW/1.5 mJ/mm2 for 140 shots/week × 3 times/since day 14 after DCM induction), group 4 (DCM + ECSW/1.5 mJ/mm2/100 shots-assisted mito delivery (500 μg) into ADMSCs/1.2 × 106 cells, then implanted into LV myocardium day 14 after DCM induction) and group 5 (DCM + ECSW-assisted mito delivery into ADMSCs/1.2 × 106 cells, then implanted into LV, followed by ECSW/1.5 mJ/mm2 for 140 shots/week × 3 times/since day 14 after DCM induction) and euthanized by day 49. Microscopic findings showed mitochondria were abundantly enhanced by ECSW into H9C2 cells. The q-PCR showed a significant increase in relative number of mitDNA in mitochondrial-transferred H9C2 cells than in control group (p < 0.01). The angiogenesis/angiogenesis factors (VEGF/SDF-1α/IG-F1) in HUVECs were significantly progressively increased by a stepwise-increased amount of ECSW energy (0.1/0.25/0.35 mJ/mm2) (all p < 0.001). The 49-day LVEF was highest in group 1 and significantly progressively increased from groups 2 to 5 (all p < 0.0001). Cardiomyocyte size/fibrosis exhibited an opposite pattern of LVEF, whereas cellular/protein levels of angiogenesis factors (VEGF/SDF-1α) in myocardium were significantly progressively increased from groups 1 to 5 (all p < 0.0001). The protein expressions of apoptotic/mitochondrial (cleaved-caspase-3/cleaved-PARP/mitochondrial-Bax/cytosolic-cytochrome-C), fibrotic (p-Smad3/TGF-ß), oxidative-stress (NOX-1/NOX-2) and pressure-overload/heart failure (BNP/ß-MHC) biomarkers exhibited an opposite pattern of LVEF among the five groups (all p < 0.0001). ECSW-assisted mitochondrial-delivery into ADMSCs plus ECSW offered an additional benefit for preserving LVEF in DCM rat.
    Keywords:  angiogenesis; dilated cardiomyopathy; exogenous mitochondria delivery; extracorporeal shock wave; left ventricular ejection fraction