bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2020‒10‒11
twelve papers selected by
Avinash N. Mukkala
University of Toronto

  1. Brain Res Bull. 2020 Oct 01. pii: S0361-9230(20)30640-7. [Epub ahead of print]165 70-80
      Acute ischemia stroke (AIS) is one of the leading causes of mortality and disability worldwide, and its neurological impacts are devastating and permanent. There is no efficient and real treatment for acute ischemia stroke so far. Therefore, development of efficient therapeutic strategies is under focus of investigations by basic and clinical scientists. Brain is one of the organs with high energy consumption and metabolism. Hence, its functionality is highly dependent on mitochondrial activity and integrity. Therefore, mitochondria play a vital homeostatic role in neurons physiology and mitochondrial dysfunction implications have been reported in a variety of nervous system diseases including acute ischemia stroke. In an attempt to investigate and introduce a novel potential therapeutic strategy for AIS, we isolated healthy mitochondria from human umbilical cord derived mesenchymal stem cells (hUC-MSCs) followed by their intracerebroventricular transplantation in a rat model of ischemia, i.e. middle cerebral artery occlusion (MCAO). Here we report that the mitochondrial transplantation ameliorated the reperfusion/ischemia-induced damages as reflected by declined blood creatine phosphokinase level, abolished apoptosis, decreased astroglyosis and microglia activation, reduced infarct size, and improved motor function. Although further preclinical and clinical studies are required, our findings strongly suggest that transplantation of MSCs-derived mitochondria is a suitable, potential and efficient therapeutic option for acute ischemia stroke.
    Keywords:  Apoptosis; Brain stroke; Mesenchymal stems cells; Mitochondrial transplantation
  2. Sci Rep. 2020 Oct 09. 10(1): 16886
      Mitochondrial quality control is essential for the long-term survival of postmitotic neurons. The E3 ubiquitin ligase Parkin promotes the degradation of damaged mitochondria via mitophagy and mutations in Parkin are a major cause of early-onset Parkinson's disease (PD). Surprisingly however, mice deleted for Parkin alone are rather asymptomatic for PD-related pathology, suggesting that other complementary or redundant mitochondrial quality control pathways may exist in neurons. Mitochondrial damage is often accompanied by the release of toxic proteins such as cytochrome c. We have reported that once in the cytosol, cytochrome c is targeted for degradation by the E3 ligase CUL9 in neurons. Here we examined whether CUL9 and Parkin cooperate to promote optimal neuronal survival in vivo. We generated mice deficient for both Cul9 and Parkin and examined them for PD-related phenotypes. Specifically, we conducted assays to examine behavioural deficits (locomotor, sensory, memory and learning) and loss of dopaminergic neurons in both males and females. Our results show that the loss of Cul9 and Parkin together did not enhance the effect of Parkin deficiency alone. These results indicate that while both Parkin and CUL9 participate in mitochondrial quality control, neurons likely have multiple redundant mechanisms to ensure their long-term survival.
  3. Annu Rev Cell Dev Biol. 2020 Oct 06. 36 265-289
      Maintaining mitochondrial health is essential for the survival and function of eukaryotic organisms. Misfunctioning mitochondria activate stress-responsive pathways to restore mitochondrial network homeostasis, remove damaged or toxic proteins, and eliminate damaged organelles via selective autophagy of mitochondria, a process termed mitophagy. Failure of these quality control pathways is implicated in the pathogenesis of Parkinson's disease and other neurodegenerative diseases. Impairment of mitochondrial quality control has been demonstrated to activate innate immune pathways, including inflammasome-mediated signaling and the antiviral cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING)-regulated interferon response. Immune system malfunction is a common hallmark in many neurodegenerative diseases; however, whether inflammation suppresses or exacerbates disease pathology is still unclear. The goal of this review is to provide a historical overview of the field, describe mechanisms of mitochondrial quality control, and highlight recent advances on the emerging role of mitochondria in innate immunity and inflammation.
    Keywords:  immunity; inflammation; mitochondria; mitophagy; neurodegeneration
  4. Biol Chem. 2020 Oct 09. pii: /j/bchm.ahead-of-print/hsz-2020-0231/hsz-2020-0231.xml. [Epub ahead of print]
      Mitochondria are key players of cellular metabolism, Ca2+ homeostasis, and apoptosis. The functionality of mitochondria is tightly regulated, and dysfunctional mitochondria are removed via mitophagy, a specialized form of autophagy that is compromised in hereditary forms of Parkinson's disease. Through mitophagy, cells are able to cope with mitochondrial stress until the damage becomes too great, which leads to the activation of pro-apoptotic BCL-2 family proteins located on the outer mitochondrial membrane. Active pro-apoptotic BCL-2 proteins facilitate the release of cytochrome c from the mitochondrial intermembrane space (IMS) into the cytosol, committing the cell to apoptosis by activating a cascade of cysteinyl-aspartate specific proteases (caspases). We are only beginning to understand how the choice between mitophagy and the activation of caspases is determined on the mitochondrial surface. Intriguingly in neurons, caspase activation also plays a non-apoptotic role in synaptic plasticity. Here we review the current knowledge on the interplay between mitophagy and caspase activation with a special focus on the central nervous system.
    Keywords:  BCL-2 family; PINK1; Parkin; Parkinson’s disease; caspase-3; synaptic plasticity
  5. Free Radic Biol Med. 2020 Oct 02. pii: S0891-5849(20)31271-5. [Epub ahead of print]161 60-70
      Most anti-cancer agents and radiotherapy exert their therapeutic effects via the production of free radicals. Ferroptosis is a recently described cell death process that is accompanied by iron-dependent lipid peroxidation. Hydrogen peroxide (H2O2) has been reported to induce cell death. However, it remains controversial whether H2O2-induced cell death is ferroptosis. In the present study, we aimed to elucidate the involvement of mitochondria in H2O2-induced ferroptosis and examined the molecules that regulate ferroptosis. We found that one mechanism underlying H2O2-induced cell death is ferroptosis, which occurs soon after H2O2 treatment (within 3 h after H2O2 treatment). We also investigated the involvement of mitochondria in H2O2-induced ferroptosis using mitochondrial DNA-depleted ρ0 cells because ρ0 cells produce more lipid peroxidation, hydroxyl radicals (•OH), and are more sensitive to H2O2 treatment. We found that ρ0 cells contain high Fe2+ levels that lead to •OH production by H2O2. Further, we observed that aquaporin (AQP) 3, 5, and 8 bind nicotinamide-adenine dinucleotide phosphate oxidase 2 and regulate the permeability of extracellular H2O2, thereby contributing to ferroptosis. Additionally, the role of mitochondria in ferroptosis was investigated using mitochondrial transfer in ρ0 cells. When mitochondria were transferred into ρ0 cells, the cells exhibited no sensitivity to H2O2-induced cytotoxicity because of decreased Fe2+ levels. Moreover, mitochondrial transfer upregulated the mitochondrial quality control protein prohibitin 2 (PHB2), which contributes to reduced AQP expression. Our findings also revealed the involvement of AQP and PHB2 in ferroptosis. Our results indicate that H2O2 treatment enhances AQP expression, Fe2+ level, and lipid peroxidation, and decrease mitochondrial function by downregulating PHB2, and thus, is a promising modality for effective cancer treatment.
    Keywords:  Aquaporin; Fe(2+); Ferroptosis; Hydrogen peroxide; Mitochondria
  6. Front Pharmacol. 2020 ;11 565160
      Aims: Several recent reports have shown irisin protects the heart against ischemia/reperfusion injury. However, the effect of irisin on I/R injury in diabetic mice has not been described. The present study was designed to investigate the role of irisin in myocardial ischemia-reperfusion (MI/R) injury in diabetic mice.Methods: A mouse model of diabetes was established by feeding wild type or gene-manipulated adult male mice with a high-fat diet. All the mice received intraperitoneal injection of irisin or PBS. Thirty minutes after injection, mice were subjected to 30 min of myocardial ischemia followed by 3h (for cell apoptosis and protein determination), 24 h (for infarct size and cardiac function).
    Results: Knock-out of gene FNDC5 augmented MI/R injury in diabetic mice, while irisin treatment attenuated MI/R injury, improved cardiac function, cellular ATP biogenetics, mitochondria potential, and impaired mitochondrion-related cell death. More severely impaired AMPK pathway was observed in diabetic FNDC5-/- mice received MI/R. Knock-out of gene AMPK blocks the beneficial effects of irisin on MI/R injury, cardiac function, cellular ATP biogenetics, mitochondria potential, and mitochondrion-related cell death.
    Conclusions: Our present study demonstrated that irisin improves the mitochondria function and attenuates MI/R injury in diabetic mice through AMPK pathway.
    Keywords:  AMPK; diabetes; irisin; ischemia/reperfusion; mitochondria
  7. PLoS One. 2020 ;15(10): e0240562
      Glutamate dehydrogenase (GLDH) is a liver-specific biomarker of hepatocellular damage currently undergoing qualification as a drug development tool. Since GLDH is located within the mitochondrial matrix, it has been hypothesized that it might also be useful in assessing mitotoxicity as an initiating event during drug-induced liver injury. According to this hypothesis, hepatocyte death that does not involve primary mitochondrial injury would result in release of intact mitochondria into circulation that could be removed by high speed centrifugation and result in lower GLDH activity measured in spun serum vs un-spun serum. A single prior study in mice has provided some support for this hypothesis. We sought to repeat and extend the findings of this study. Accordingly, mice were treated with the known mitochondrial toxicant, acetaminophen (APAP), or with furosemide (FS), a toxicant believed to cause hepatocyte death through mechanisms not involving mitotoxicity as initiating event. We measured GLDH levels in fresh plasma before and after high speed centrifugation to remove intact mitochondria. We found that both APAP and FS treatments caused substantial hepatocellular necrosis that correlated with plasma alanine aminotransferase (ALT) and GLDH elevations. The plasma GLDH activity in both the APAP- and FS- treated mice was not affected by high-speed centrifugation. Interestingly, the ratio of GLDH:ALT was 5-fold lower during FS compared to APAP hepatotoxicity. Electron microscopy confirmed that both APAP- and FS-treatments had resulted in mitochondrial injury. Mitochondria within vesicles were only observed in the FS-treated mice raising the possibility that mitophagy might account for reduced release of GLDH in the FS-treated mice. Although our results show that plasma GLDH is not clinically useful for evaluating mitotoxicity, the GLDH:ALT ratio as a measure of mitophagy needs to be further studied.
  8. Redox Biol. 2020 Sep 29. pii: S2213-2317(20)30942-3. [Epub ahead of print]37 101737
      Peroxiredoxin 6 (PRDX6) has been associated with tumor progression and cancer metastasis. Its acting on phospholipid hydroperoxides and its phospholipase-A2 activity are unique among the peroxiredoxin family and add complexity to its action mechanisms. As a first step towards the study of PRDX6 involvement in cancer, we have constructed a human hepatocarcinoma HepG2PRDX6-/- cell line using the CRISPR/Cas9 technique and have characterized the cellular response to lack of PRDX6. Applying quantitative global and redox proteomics, flow cytometry, in vivo extracellular flow analysis, Western blot and electron microscopy, we have detected diminished respiratory capacity, downregulation of mitochondrial proteins and altered mitochondrial morphology. Autophagic vesicles were abundant while the unfolded protein response (UPR), HIF1A and NRF2 transcription factors were not activated, despite increased levels of p62/SQSTM1 and reactive oxygen species (ROS). Insulin receptor (INSR), 3-phosphoinositide-dependent protein kinase 1 (PDPK1), uptake of glucose and hexokinase-2 (HK2) decreased markedly while nucleotide biosynthesis, lipogenesis and synthesis of long chain polyunsaturated fatty acids (LC-PUFA) increased. 254 Cys-peptides belonging to 202 proteins underwent significant redox changes. PRDX6 knockout had an antiproliferative effect due to cell cycle arrest at G2/M transition, without signs of apoptosis. Loss of PLA2 may affect the levels of specific lipids altering lipid signaling pathways, while loss of peroxidase activity could induce redox changes at critical sensitive cysteine residues in key proteins. Oxidation of specific cysteines in Proliferating Cell Nuclear Antigen (PCNA) could interfere with entry into mitosis. The GSH/Glutaredoxin system was downregulated likely contributing to these redox changes. Altogether the data demonstrate that loss of PRDX6 slows down cell division and alters metabolism and mitochondrial function, so that cell survival depends on glycolysis to lactate for ATP production and on AMPK-independent autophagy to obtain building blocks for biosynthesis. PRDX6 is an important link in the chain of elements connecting redox homeostasis and proliferation.
    Keywords:  CRISPR-Cas9; Carbohydrate metabolism; Cell cycle; Glucose metabolism; Lipokines; Mitochondria; NRF2; PCNA; Peroxiredoxin 6; Proteomics; Redox proteome
  9. Redox Biol. 2020 Sep 24. pii: S2213-2317(20)30941-1. [Epub ahead of print]37 101736
      The apoptotic nuclease EndoG is involved in mitochondrial DNA replication. Previous results suggested that, in addition to regulate cardiomyocyte hypertrophy, EndoG could be involved in cell proliferation. Here, by using in vivo and cell culture models, we investigated the role of EndoG in cell proliferation. Genetic deletion of Endog both in vivo and in cultured cells or Endog silencing in vitro induced a defect in rodent and human cell proliferation with a tendency of cells to accumulate in the G1 phase of cell cycle and increased reactive oxygen species (ROS) production. The defect in cell proliferation occurred with a decrease in the activity of the AKT/PKB-GSK-3β-Cyclin D axis and was reversed by addition of ROS scavengers. EndoG deficiency did not affect the expression of ROS detoxifying enzymes, nor the expression of the electron transport chain complexes and oxygen consumption rate. Addition of the micropeptide Humanin to EndoG-deficient cells restored AKT phosphorylation and proliferation without lowering ROS levels. Thus, our results show that EndoG is important for cell proliferation through the control of ROS and that Humanin can restore cell division in EndoG-deficient cells and counteracts the effects of ROS on AKT phosphorylation.
    Keywords:  Cell proliferation; Cell signaling; EndoG; Humanin; Mitochondria; Reactive oxygen species; Romo1
  10. Front Cell Dev Biol. 2020 ;8 819
      Background: In animal models of ventilation-induced lung injury, mitophagy triggers mitochondria damage and the release of mitochondrial (mt) DNA, which activates inflammation. However, the mechanism of this process is unclear.Methods: A model of cyclic stretching (CS)-induced lung epithelial cell injury was established. The genetic intervention of phosphatase and tensin homolog-induced kinase 1 (PINK1) expression via lentivirus transfection was used to identify the relationship between PINK1-mediated mitophagy and mtDNA release in stretching-induced inflammatory response and injury. Pharmacological inhabitation of Toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88) expression was performed via their related inhibitors, while pre-treatment of exogenous mtDNA was used to verify the role of mtDNA in stretching-induced inflammatory response and injury.
    Results: Using a cell culture model of CS, we found that knocking down PINK1 in lung epithelial cells reduced mitophagy activation and mtDNA release, leading to milder inflammatory response and injury; conversely, up-regulating PINK1 exacerbated stretching-induced inflammation and injury, and similar effects were observed by upregulating TLR9 to induce expression of MyD88 and nuclear factor-κB (NF-κB)/p65. Down-regulating MyD88 protected lung epithelial cells from stretching injury and decreased NF-κB/p65 expression.
    Conclusion: These findings suggest that PINK1-dependent mitophagy and associated TLR9 activation is indeed a major factor in stretch-induced cell injury via a mechanism in which released mtDNA activates TLR9 and thereby the MyD88/NF-κB pathway. Inhibiting this process may be a therapeutic approach to prevent inflammation and cell injury in patients on mechanical ventilation.
    Keywords:  Toll-like receptor 9; lung injury; mechanical stretching; mitochondrial DNA; mitophagy
  11. Sci Rep. 2020 Oct 05. 10(1): 16489
      Redox status influences the course of the inflammatory, metabolic, and proliferative liver diseases. Oxidative stress is thought to play a crucial and sustained role in the pathological progression of early steatosis to severe hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Oxidative stress induced by reactive oxygen species which are generated in the mitochondria can lead to chronic organelle damage in hepatocytes. Currently, the diagnosis of liver disease requires liver biopsy, which is invasive and associated with complications. The present report describes the development of a novel molecular probe, EDA-PROXYL, with higher reactivity and mitochondrial selectivity than standard carboxyl-PROXYL and carbamoyl-PROXYL probes. The membrane permeability of our probe improved in aqueous environments which led to increased accumulation in the liver and interaction of EDA-PROXYL with the carnitine transporter via the amine (NH3+) group further increased accumulation. This increased mitochondrial sensitivity and enhanced accumulation highlight the potential of EDA-PROXYL as a molecular probe for determining metabolic reactions of the mitochondria. Thus, this novel probe could be a tool for the evaluation of redox status of the mitochondria to assess the degree of liver injury and, ultimately, the response to pharmacological therapy.
  12. Mitochondrion. 2020 Oct 06. pii: S1567-7249(20)30196-3. [Epub ahead of print]
      We report on validating a mitochondrial gene therapeutic strategy using fibroblasts derived from patients with an A1555G point mutation in mitochondrial DNA coding 12S ribosomal RNA (rRNA (12S)).Wild-type rRNA (12S) as a therapeutic RNA was encapsulated in a mitochondrial targeting liposome, a MITO-Porter (rRNA-MITO-Porter), and an attempt was made to deliver the MITO-Porter to mitochondria of the diseased cells. It was confirmed that the rRNA-MITO-Porter treatment significantly decreased the ratio of the mutant rRNA content. Moreover, it was shown that the mitochondrial respiratory activities of the diseased cells were improved as the result of the mitochondrial transfection of the rRNA-MITO-Porter.
    Keywords:  A1555G mutation; MITO-Porter; Mitochondrial delivery; mitochondrial gene therapy; mitochondrial ribosomal RNA