bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2021‒06‒27
sixteen papers selected by
Avinash N. Mukkala
University of Toronto

  1. Dev Cell. 2021 Jun 24. pii: S1534-5807(21)00481-0. [Epub ahead of print]
      Mitochondria are critical metabolic and signaling hubs, and dysregulated mitochondrial homeostasis is implicated in many diseases. Degradation of damaged mitochondria by selective GABARAP/LC3-dependent macro-autophagy (mitophagy) is critical for maintaining mitochondrial homeostasis. To identify alternate forms of mitochondrial quality control that functionally compensate if mitophagy is inactive, we selected for autophagy-dependent cancer cells that survived loss of LC3-dependent autophagosome formation caused by inactivation of ATG7 or RB1CC1/FIP200. We discovered rare surviving autophagy-deficient clones that adapted to maintain mitochondrial homeostasis after gene inactivation and identified two enhanced mechanisms affecting mitochondria including mitochondrial dynamics and mitochondrial-derived vesicles (MDVs). To further understand these mechanisms, we quantified MDVs via flow cytometry and confirmed an SNX9-mediated mechanism necessary for flux of MDVs to lysosomes. We show that the autophagy-dependent cells acquire unique dependencies on these processes, indicating that these alternate forms of mitochondrial homeostasis compensate for loss of autophagy to maintain mitochondrial health.
    Keywords:  ATG7; FIP200; SNX9; autophagy; cancer; late endosomes; mitochondria; mitochondrial dynamics; mitochondrial-derived vesicles; mitophagy
  2. J Cell Mol Med. 2021 Jun 23.
      Mitochondria are important organelles in eukaryotic cells. Normal mitochondrial homeostasis is subject to a strict mitochondrial quality control system, including the strict regulation of mitochondrial production, fission/fusion and mitophagy. The strict and accurate modulation of the mitochondrial quality control system, comprising the mitochondrial fission/fusion, mitophagy and other processes, can ameliorate the myocardial injury of myocardial ischaemia and ischaemia-reperfusion after myocardial infarction, which plays an important role in myocardial protection after myocardial infarction. Further research into the mechanism will help identify new therapeutic targets and drugs for the treatment of myocardial infarction. This article aims to summarize the recent research regarding the mitochondrial quality control system and its molecular mechanism involved in myocardial infarction, as well as the potential therapeutic targets in the future.
    Keywords:  ischemia-reperfusion; mitochondrial apoptosis; mitochondrial fission; mitochondrial fusion; mitochondrial quality control; myocardial infarction
  3. EMBO J. 2021 Jun 21. e100715
      Clearance of mitochondria following damage is critical for neuronal homeostasis. Here, we investigate the role of Miro proteins in mitochondrial turnover by the PINK1/Parkin mitochondrial quality control system in vitro and in vivo. We find that upon mitochondrial damage, Miro is promiscuously ubiquitinated on multiple lysine residues. Genetic deletion of Miro or block of Miro1 ubiquitination and subsequent degradation lead to delayed translocation of the E3 ubiquitin ligase Parkin onto damaged mitochondria and reduced mitochondrial clearance in both fibroblasts and cultured neurons. Disrupted mitophagy in vivo, upon post-natal knockout of Miro1 in hippocampus and cortex, leads to a dramatic increase in mitofusin levels, the appearance of enlarged and hyperfused mitochondria and hyperactivation of the integrated stress response (ISR). Altogether, our results provide new insights into the central role of Miro1 in the regulation of mitochondrial homeostasis and further implicate Miro1 dysfunction in the pathogenesis of human neurodegenerative disease.
    Keywords:  Parkinson’s disease; Rhot1; Rhot2; eIF2α; megamitochondria
  4. Dis Model Mech. 2021 Jun 01. pii: dmm048912. [Epub ahead of print]14(6):
      Mitochondria are organelles with vital functions in almost all eukaryotic cells. Often described as the cellular 'powerhouses' due to their essential role in aerobic oxidative phosphorylation, mitochondria perform many other essential functions beyond energy production. As signaling organelles, mitochondria communicate with the nucleus and other organelles to help maintain cellular homeostasis, allow cellular adaptation to diverse stresses, and help steer cell fate decisions during development. Mitochondria have taken center stage in the research of normal and pathological processes, including normal tissue homeostasis and metabolism, neurodegeneration, immunity and infectious diseases. The central role that mitochondria assume within cells is evidenced by the broad impact of mitochondrial diseases, caused by defects in either mitochondrial or nuclear genes encoding for mitochondrial proteins, on different organ systems. In this Review, we will provide the reader with a foundation of the mitochondrial 'hardware', the mitochondrion itself, with its specific dynamics, quality control mechanisms and cross-organelle communication, including its roles as a driver of an innate immune response, all with a focus on development, disease and aging. We will further discuss how mitochondrial DNA is inherited, how its mutation affects cell and organismal fitness, and current therapeutic approaches for mitochondrial diseases in both model organisms and humans.
    Keywords:  Mitochondrial diseases; Mitochondrial fusion and fission; Mitochondrial unfolded protein response; Mitophagy; mtDNA heteroplasmy and inheritance; mtDNA-mediated innate immune response
  5. Cell Death Dis. 2021 Jun 19. 12(7): 632
      Dysregulation of the PINK1/Parkin-mediated mitophagy is essential to Parkinson's disease. Although important progress has been made in previous researches, the biochemical reagents that induce global and significant mitochondrial damage may still hinder deeper insights into the mechanisms of mitophagy. The origin of PINK1/Parkin pathway activation in mitophagy remains elusive. In this study, we develop an optical method, ultra-precise laser stimulation (UPLaS) that delivers a precise and noninvasive stimulation onto a submicron region in a single mitochondrial tubular structure. UPLaS excites localized mitochondrial Ca2+ (mitoCa2+) oscillations with tiny perturbation to mitochondrial membrane potential (MMP) or mitochondrial reactive oxygen species. The UPLaS-induced mitoCa2+ oscillations can directly induce PINK1 accumulation and Parkin recruitment on mitochondria. The Parkin recruitment by UPLaS requires PINK1. Our results provide a precise and noninvasive technology for research on mitophagy, which stimulates target mitochondria with little damage, and reveal mitoCa2+ oscillation directly initiates the PINK1-Parkin pathway for mitophagy without MMP depolarization.
  6. Anal Chem. 2021 Jun 21.
      Mitophagy plays a critical role in regulating and maintaining cellular functions, particularly regulating the quantity and quality of mitochondria. In this research, a multifunctional two-photon fluorescent probe Mito-PV with improved mitochondria-anchored ability was designed. The proposed probe can track the fluctuation of polarity and viscosity in mitochondria simultaneously with two well-distinguished emissions. It can also precisely visualize the change in mitochondrial morphology (including mitochondrial form factor and length). The real-time and accurate monitoring of mitophagy under two-photon excitation was successfully achieved by utilizing probe Mito-PV through supervising the alterations of diverse mitophagy-related parameters (including colocalization coefficient, polarity, viscosity, and mitochondrial morphology). In addition, probe Mito-PV can be applied to evaluate drug bpV(phen) as an effective mitophagy inhibitor. Therefore, our work may provide a more efficient and reliable method for precisely monitoring mitophagy from multiple evaluations.
  7. Mitochondrion. 2021 Jun 19. pii: S1567-7249(21)00083-0. [Epub ahead of print]
      There is growing scientific interest to develop scalable biological measures that capture mitochondrial (dys)function. Mitochondria have their own genome, the mitochondrial DNA (mtDNA), and it has been proposed that the number of mtDNA copies per cell (mtDNA copy number; mtDNAcn) reflects mitochondrial health. The common availability of stored DNA material or existing DNA sequencing data, especially from blood and other easy-to-collect samples, has made its quantification a popular approach in clinical and epidemiological studies. However, the interpretation of mtDNAcn is not univocal, and either a reduction or elevation in mtDNAcn can indicate dysfunction. The major determinants of blood-derived mtDNAcn are the heterogeneous cell type composition of leukocytes and platelet abundance, which can change with time of day, aging, and with disease. Hematopoiesis as a likely driver of blood mtDNAcn. Here we discuss the rationale and available methods to quantify mtDNAcn, the influence of blood cell type variations, and consider important gaps in knowledge that need to be resolved to maximize the scientific output around the investigation of blood mtDNAcn in humans.
    Keywords:  White blood cells; biomarker; count; leukocytes; mitochondrial function; mitochondrial genome; mitochondrion
  8. Eur J Pharmacol. 2021 Jun 17. pii: S0014-2999(21)00415-5. [Epub ahead of print]907 174262
      Parkinson's disease (PD) is the prevalent neurodegenerative disorder characterized by the degeneration of the nigrostriatal neurons. Dynamin-related protein 1 (Drp1) is a key regulator mediating mitochondrial fission and affecting mitophagy in neurons. It has been reported that the inhibition of Drp1 may be beneficial to PD. However, the role of Drp1 and mitophagy in PD remains elusive. Therefore, in this research, we investigated the role of Drp1 and the underlying mechanisms in the mice model of PD. We used the dynasore, a GTPase inhibitor, to inhibit the expression of Drp1. We found that inhibition of Drp1 could ameliorate the motor deficits and the expression of tyrosine hydroxylase in the mice of the PD model. But Drp1 inhibition did not affect mitochondria number and morphological parameters. Moreover, suppression of Drp1 up-regulated the mitochondrial expressions of PINK1 and Parkin while not affected the expressions of NIX and BNIP3. Conclusively, our findings suggest that the inhibition of Drp1 ameliorated the mitochondrial ultrastructure at least via regulating PINK1 and Parkin in the mice of the PD model. This study also implicates that inhibition of Drp1 might impact mitophagy and recover mitochondrial homeostasis in PD.
    Keywords:  Dynamin-related protein 1; Dynasore; Mitochondria; Mitophagy; Parkinson's disease
  9. Cell Chem Biol. 2021 Jun 08. pii: S2451-9456(21)00260-9. [Epub ahead of print]
      Mitochondria, the powerhouse of the cell, are dynamic organelles that undergo constant morphological changes. Increasing evidence indicates that mitochondria morphologies and functions can be modulated by mechanical cues. However, the mechano-sensing and -responding properties of mitochondria and the relation between mitochondrial morphologies and functions are unclear due to the lack of methods to precisely exert mechano-stimulation on and deform mitochondria inside live cells. Here, we present an optogenetic approach that uses light to induce deformation of mitochondria by recruiting molecular motors to the outer mitochondrial membrane via light-activated protein-protein hetero-dimerization. Mechanical forces generated by motor proteins distort the outer membrane, during which the inner mitochondrial membrane can also be deformed. Moreover, this optical method can achieve subcellular spatial precision and be combined with different optical dimerizers and molecular motors. This method presents a mitochondria-specific mechano-stimulator for studying mitochondria mechanobiology and the interplay between mitochondria shapes and functions.
    Keywords:  cryptochrome 2; light-gated hetero-dimerization; mitochondria; mitochondrial morphology; molecular motor; optical dimerizer; optogenetics; organelle mechanobiology
  10. J Biol Chem. 2021 Jun 19. pii: S0021-9258(21)00704-3. [Epub ahead of print] 100904
      Mitochondria are critical for regulation of the activation, differentiation, and survival of macrophages and other immune cells. In response to various extracellular signals, such as microbial or viral infection, changes to mitochondrial metabolism and physiology could underlie the corresponding state of macrophage activation. These changes include alterations of oxidative metabolism, mitochondrial membrane potential, and tricarboxylic acid (TCA) cycling, as well as the release of mitochondrial reactive oxygen species (mtROS) and mitochondrial DNA (mtDNA) and transformation of the mitochondrial ultrastructure. Here, we provide an updated review of how changes in mitochondrial metabolism and various metabolites such as fumarate, succinate, and itaconate coordinate to guide macrophage activation to distinct cellular states, thus clarifying the vital link between mitochondria metabolism and immunity. We also discuss how in disease settings, mitochondrial dysfunction and oxidative stress contribute to dysregulation of the inflammatory response. Therefore, mitochondria are a vital source of dynamic signals that regulate macrophage biology to fine-tune immune responses.
    Keywords:  macrophage activation; macrophage biology; mitochondrial dysfunction; mitochondrial metabolism; oxidative stress
  11. Mitochondrion. 2021 Jun 19. pii: S1567-7249(21)00082-9. [Epub ahead of print]
      The dynamin-related protein 1 (Drp1) and its homologs in various eukaryotes are essential to maintain mitochondrial morphology and regulate mitochondrial division. Several mutations in different domains of Drp1 have been reported, which result in debilitating conditions. Four such disease-causing mutations of the middle domain of Drp1 were mimicked in the yeast dynamin-related GTPase (Dnm1) and were characterized in this study. Mitochondrial morphology and protein function were observed to be altered to a variable extent in cells expressing the mutated variants of Dnm1. Several aspects related to the protein such as punctate formation, localization to mitochondria, dynamic behavior and structure were analyzed by microscopy, biochemical studies and molecular dynamics simulations. Significant effects on the protein structure and function were observed in cells expressing A430D and G397D mutations. Overall, our data provide insight into the molecular and cellular alterations resulting from middle domain mutations in Dnm1.
    Keywords:  Dnm1; Drp1; dynamin-like GTPase; mitochondria; neurodegenerative diseases; yeast
  12. Cell Rep. 2021 Jun 22. pii: S2211-1247(21)00642-2. [Epub ahead of print]35(12): 109275
      The mitochondrial calcium uniporter (MCU), the highly selective channel responsible for mitochondrial Ca2+ entry, plays important roles in physiology and pathology. However, only few pharmacological compounds directly and selectively modulate its activity. Here, we perform high-throughput screening on a US Food and Drug Administration (FDA)-approved drug library comprising 1,600 compounds to identify molecules modulating mitochondrial Ca2+ uptake. We find amorolfine and benzethonium to be positive and negative MCU modulators, respectively. In agreement with the positive effect of MCU in muscle trophism, amorolfine increases muscle size, and MCU silencing is sufficient to blunt amorolfine-induced hypertrophy. Conversely, in the triple-negative breast cancer cell line MDA-MB-231, benzethonium delays cell growth and migration in an MCU-dependent manner and protects from ceramide-induced apoptosis, in line with the role of mitochondrial Ca2+ uptake in cancer progression. Overall, we identify amorolfine and benzethonium as effective MCU-targeting drugs applicable to a wide array of experimental and disease conditions.
    Keywords:  FDA-approved drugs; MCU; amorolfine; benzethonium; high-throughput screening; mitochondrial Ca(2+) uptake; mitochondrial calcium uniporter; skeletal muscle hypertrophy; triple-negative breast cancer
  13. JCI Insight. 2021 Jun 22. pii: 143540. [Epub ahead of print]
      Estrogen-related receptor gamma (Esrrg) is a murine lupus susceptibility gene associated with T cell activation. Here, we report that Esrrg controls regulatory T cells (Treg) through mitochondria homeostasis. Esrrg deficiency impaired the maintenance and function of Treg cells, leading to global T cell activation and autoimmunity in aged mice. Further, Esrrg-deficient Treg cells presented an impaired differentiation into follicular Treg (Tfr) cells that enhanced follicular helper T cells (Tfh) responses. Mechanistically, Esrrg-deficient Treg cells presented with dysregulated mitochondria with decreased oxygen consumption as well as ATP and NAD+ production. In addition, Esrrg-deficient Treg cells exhibited decreased phosphatidylinositol and TGF-β signaling pathways and increased mTORC1 activation. We found that the expression of human ESRRG, which is high in Treg cells, was lower in CD4+ T cells from lupus patients than in healthy controls. Finally, knocking down ESRRG in Jurkat T cells decreased their metabolism. Together, our results reveal a critical role of Esrrg in the maintenance and metabolism of Treg cells, which may provide a genetic link between lupus pathogenesis and mitochondrial dysfunction in T cells.
    Keywords:  Autoimmunity; Lupus; Mitochondria; T cells
  14. Redox Biol. 2021 Jun 16. pii: S2213-2317(21)00203-2. [Epub ahead of print]45 102044
      The chief ROS formed by mitochondria are superoxide (O2·-) and hydrogen peroxide (H2O2). Superoxide is converted rapidly to H2O2 and therefore the latter is the chief ROS emitted by mitochondria into the cell. Once considered an unavoidable by-product of aerobic respiration, H2O2 is now regarded as a central mitokine used in mitochondrial redox signaling. However, it has been postulated that O2·- can also serve as a signal in mammalian cells. Progress in understanding the role of mitochondrial H2O2 in signaling is due to significant advances in the development of methods and technologies for its detection. Unfortunately, the development of techniques to selectively measure basal O2·- changes has been met with more significant hurdles due to its short half-life and the lack of specific probes. The development of sensitive techniques for the selective and real time measure of O2·- and H2O2 has come on two fronts: development of genetically encoded fluorescent proteins and small molecule reporters. In 2015, I published a detailed comprehensive review on the state of knowledge for mitochondrial ROS production and how it is controlled, which included an in-depth discussion of the up-to-date methods utilized for the detection of both superoxide (O2·-) and H2O2. In the article, I presented the challenges associated with utilizing these probes and their significance in advancing our collective understanding of ROS signaling. Since then, many other authors in the field of Redox Biology have published articles on the challenges and developments detecting O2·- and H2O2 in various organisms [1-3]. There has been significant advances in this state of knowledge, including the development of novel genetically encoded fluorescent H2O2 probes, several O2·- sensors, and the establishment of a toolkit of inhibitors and substrates for the interrogation of mitochondrial H2O2 production and the antioxidant defenses utilized to maintain the cellular H2O2 steady-state. Here, I provide an update on these methods and their implementation in furthering our understanding of how mitochondria serve as cell ROS stabilizing devices for H2O2 signaling.
    Keywords:  Methods for measuring ROS; Mitochondria; Peroxide detectors; Reactive oxygen species; Superoxide probes
  15. Redox Biol. 2021 Jun 08. pii: S2213-2317(21)00196-8. [Epub ahead of print]45 102037
      Parkinson's Disease (PD) is a neurodegenerative disorder affecting more than 10 million people worldwide. Currently, PD has no cure and no early diagnostics methods exist. Mitochondrial dysfunction is presented in the early stages of PD, and it is considered an important pathophysiology component. We have previously developed mitochondria-targeted hydroxycinnamic acid derivatives, presenting antioxidant and iron-chelating properties, and preventing oxidative stress in several biological models of disease. We have also demonstrated that skin fibroblasts from male sporadic PD patients (sPD) presented cellular and mitochondrial alterations, including increased oxidative stress, hyperpolarized and elongated mitochondria and decreased respiration and ATP levels. We also showed that forcing mitochondrial oxidative phosphorylation (OXPHOS) in sPD fibroblasts uncovers metabolic defects that were otherwise hidden. In this work, we tested the hypothesis that a lead mitochondria-targeted hydroxycinnamic acid derivative would revert the phenotype found in skin fibroblasts from sPD patients. Our results demonstrated that treating human skin fibroblasts from sPD patients with non-toxic concentrations of AntiOxCIN4 restored mitochondrial membrane potential and mitochondrial fission, decreased autophagic flux, and enhanced cellular responses to stress by improving the cellular redox state and decreasing reactive oxygen species (ROS) levels. Besides, fibroblasts from sPD patients treated with AntiOxCIN4 showed increased maximal respiration and metabolic activity, converting sPD fibroblasts physiologically more similar to their sex- and age-matched healthy controls. The positive compound effect was reinforced using a supervised machine learning model, confirming that AntiOxCIN4 treatment converted treated fibroblasts from sPD patients closer to the phenotype of control fibroblasts. Our data points out a possible mechanism of AntiOxCIN4 action contributing to a deeper understanding of how the use of mitochondria-targeted antioxidants based on a polyphenol scaffold can be used as potential drug candidates for delaying PD progression, validating the use of fibroblasts from sPD patients with more active OXPHOS as platforms for mitochondria-based drug development.
    Keywords:  Human skin fibroblasts; Metabolism; Mitochondria; Mitochondriotropic antioxidant; Sporadic Parkinson's disease
  16. Proc Natl Acad Sci U S A. 2021 Jun 22. pii: e2023647118. [Epub ahead of print]118(25):
      Mitogen-activated protein kinase kinase kinase 7 (MAP3K7), known as TAK1, is an intracellular signaling intermediate of inflammatory responses. However, a series of mouse Tak1 gene deletion analyses have revealed that ablation of TAK1 does not prevent but rather elicits inflammation, which is accompanied by elevation of reactive oxygen species (ROS). This has been considered a consequence of impaired TAK1-dependent maintenance of tissue integrity. Contrary to this view, here we propose that TAK1 inhibition-induced ROS are an active cellular process that targets intracellular bacteria. Intracellular bacterial effector proteins such as Yersinia's outer membrane protein YopJ are known to inhibit TAK1 to circumvent the inflammatory host responses. We found that such TAK1 inhibition induces mitochondrial-derived ROS, which effectively destroys intracellular bacteria. Two cell death-signaling molecules, caspase 8 and RIPK3, cooperatively participate in TAK1 inhibition-induced ROS and blockade of intracellular bacterial growth. Our results reveal a previously unrecognized host defense mechanism, which is initiated by host recognition of pathogen-induced impairment in a host protein, TAK1, but not directly of pathogens.
    Keywords:  ROS; TAK1; intracellular bacteria; mitochondria