bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2021‒06‒13
eighteen papers selected by
Avinash N. Mukkala
University of Toronto

  1. Redox Biol. 2021 Jun 01. pii: S2213-2317(21)00179-8. [Epub ahead of print]45 102021
      Ferroptosis is a programmed iron-dependent cell death associated with peroxidation of lipids particularly, phospholipids. Several studies suggested a possible contribution of mitochondria to ferroptosis although the mechanisms underlying mitochondria-mediated ferroptotic pathways remain elusive. Reduced glutathione (GSH) is a central player in ferroptosis that is required for glutathione peroxidase 4 to eliminate oxidized phospholipids. Mitochondria do not produce GSH, and although the transport of GSH to mitochondria is not fully understood, two carrier proteins, the dicarboxylate carrier (DIC, SLC25A10) and the oxoglutarate carrier (OGC, SLC25A11) have been suggested to participate in GSH transport. Here, we elucidated the role of DIC and OGC as well as mitochondrial bioenergetics in ferroptosis in H9c2 cardioblasts. Results showed that mitochondria are highly sensitive to ferroptotic stimuli displaying fragmentation, and lipid peroxidation shortly after the onset of ferroptotic stimulus. Inhibition of electron transport chain complexes and oxidative phosphorylation worsened RSL3-induced ferroptosis. LC-MS/MS analysis revealed a dramatic increase in the levels of pro-ferroptotic oxygenated phosphatidylethanolamine species in mitochondria in response to RSL3 (ferroptosis inducer) and cardiac ischemia-reperfusion. Inhibition of DIC and OGC aggravated ferroptosis and increased mitochondrial ROS, membrane depolarization, and GSH depletion. Dihydrolipoic acid, an essential cofactor for several mitochondrial multienzyme complexes, attenuated ferroptosis and induced direct reduction of pro-ferroptotic peroxidized phospholipids to hydroxy-phospholipids in vitro. In conclusion, we suggest that ferroptotic stimuli diminishes mitochondrial bioenergetics and stimulates GSH depletion and glutathione peroxidase 4 inactivation leading to ferroptosis.
    Keywords:  Ferroptosis; Glutathione; Heart; Ischemia-reperfusion; Mitochondria; Oxidized phosphatidylethanolamine
  2. Cell Transplant. 2021 Jan-Dec;30:30 9636897211024210
      Mitochondrial transplantation emerges as a novel therapeutic solution for ischemia/reperfusion injury (IRI) in various tissues. Platelets have recently been used in mitochondrial transplantation as readily-available donors of small-size platelet mitochondria (plt-mito). Interestingly, FUN14 Domain Containing 2 (FUNDC2), a protein highly-expressed in the outer membrane (OMM) of plt-mito, has been identified to maintain platelet survival under hypoxic condition. The current study determined whether and how FUNDC2 contributed to the therapeutic effect of plt-mito transplantation for hypoxia/reoxygenation (HR) injury. The results showed that incorporation of human plt-mito into SH-SY5Y cells rescued HR-induced mitochondrial malfunction and mitochondrial apoptotic pathway. Mechanistically, plt-mito transplantation led to an increased expression of FUNDC2 in the recipient cells. This protein induced mitochondrial translocation of phosphatidylinositol-3,4,5-trisphosphate (PIP3) via its N-term, resulting in the stimulation of the protein kinase B (Akt)/forkhead box O3a (FOXO3a) pathway, which inhibited HR-induced mitochondrial accumulation of a mitochondrial target of FOXO3a, Bim, also known as a pro-apoptotic protein. Therefore, the FUNDC2/PIP3/Akt/FOXO3a axis may facilitate the incorporated plt-mito to restore mitochondrial function and cell viability of the recipient cells, and platelets may serve as readily-available sources of donor mitochondria that afford therapeutic benefits against IRI.
    Keywords:  FUN14 Domain Containing 2; hypoxia/reoxygenation; mitochondrial transplantation; neuronal apoptosis; platelet mitochondria
  3. Sci Rep. 2021 Jun 11. 11(1): 12387
      Metabolic and bioenergetic plasticity of immune cells is essential for optimal responses to bacterial infections. AMPK and Parkin ubiquitin ligase are known to regulate mitochondrial quality control mitophagy that prevents unwanted inflammatory responses. However, it is not known if this evolutionarily conserved mechanism has been coopted by the host immune defense to eradicate bacterial pathogens and influence post-sepsis immunosuppression. Parkin, AMPK levels, and the effects of AMPK activators were investigated in human leukocytes from sepsis survivors as well as wild type and Park2-/- murine macrophages. In vivo, the impact of AMPK and Parkin was determined in mice subjected to polymicrobial intra-abdominal sepsis and secondary lung bacterial infections. Mice were treated with metformin during established immunosuppression. We showed that bacteria and mitochondria share mechanisms of autophagic killing/clearance triggered by sentinel events that involve depolarization of mitochondria and recruitment of Parkin in macrophages. Parkin-deficient mice/macrophages fail to form phagolysosomes and kill bacteria. This impairment of host defense is seen in the context of sepsis-induced immunosuppression with decreased levels of Parkin. AMPK activators, including metformin, stimulate Parkin-independent autophagy and bacterial killing in leukocytes from post-shock patients and in lungs of sepsis-immunosuppressed mice. Our results support a dual role of Parkin and AMPK in the clearance of dysfunctional mitochondria and killing of pathogenic bacteria, and explain the immunosuppressive phenotype associated Parkin and AMPK deficiency. AMPK activation appeared to be a crucial therapeutic target for the macrophage immunosuppressive phenotype and to reduce severity of secondary bacterial lung infections and respiratory failure.
  4. Methods Mol Biol. 2021 ;2310 113-159
      Mitochondria are dynamic organelles that participate in a broad array of molecular functions within the cell. They are responsible for maintaining the appropriate energetic levels and control the cellular homeostasis throughout the generation of intermediary metabolites. Preserving a healthy and functional mitochondrial population is of fundamental importance throughout the life of the cells under pathophysiological conditions. Hence, cells have evolved fine-tuned mechanisms of quality control that help to preserve the right amount of functional mitochondria to meet the demand of the cell. The specific recycling of mitochondria by autophagy, termed mitophagy, represents the primary contributor to mitochondrial quality control. During this process, damaged or unnecessary mitochondria are recognized and selectively degraded. In the past few years, the knowledge in mitophagy has seen rapid progress, and a growing body of evidence confirms that mitophagy holds a central role in controlling cellular functions and the progression of various human diseases.In this chapter, we will discuss the pathophysiological roles of mitophagy and provide a general overview of the current methods used to monitor and quantify mitophagy. We will also outline the main established approaches to investigate the mitochondrial function, metabolism, morphology, and protein damage.
    Keywords:  Cardiovascular diseases (CVD); Homeostasis; Metabolism; Mitochondrial morphology; Mitochondrial quality control; Pathology
  5. Methods Mol Biol. 2021 ;2310 287-299
      The dynamism of mitochondria, considered as complex and motile organelles, is brought about by mitochondria ability to undergo cycles of fission and fusion events, whose fine balance determines their morphology in a specific physiological context. A huge body of evidence makes it possible to associate mitochondrial organization to regulation of an increasing number of key cellular processes, such as biosynthetic pathways, oxidative phosphorylation and ATP production, calcium buffering, mtDNA homeostasis, autophagy, and cell death. Here, we review the recently developed imaging methods for studying mitochondrial dynamics, including live-cell imaging, by using mitochondrial-targeted fluorescent proteins. In more details, we focus our attention on two different protocols in the T cell model, an example of nonadherent cells, which present some particularities and difficulties in the analysis of mitochondrial shape. Also, we discuss some examples of mouse models carrying mitochondria-targeted fluorescent proteins, which allow to investigate the mitochondrial morphology in vivo.
    Keywords:  Dynamic network; Fission; Fusion; Imaging; Mitochondria; Morphology
  6. Methods Mol Biol. 2021 ;2275 415-432
      The cross talk between mitochondrial dynamic structure, determined primarily by mitochondrial fission and fusion events, and mitochondrial function of energetics, primarily ATP and ROS production, is widely appreciated. Understanding the mechanistic details of such cross talk between mitochondrial structure and function needs integrated quantitative analyses between mitochondrial dynamics and energetics. Here we describe our recently designed approach of mito-SinCe2 that involves high resolution confocal microscopy of genetically expressed ratiometric fluorescent probes targeted to mitochondria, and its quantitative analyses. Mito-SinCe2 analyses allows for quantitative analyses of mitochondrial structure-function relationship in single cells toward understanding the role of mitochondria and their heterogeneity in various physiological and pathological conditions.
    Keywords:  ATP; Confocal Microscopy; Fission; Fusion; Mitochondrial Dynamics; Mitochondrial Energetics; Quantitative analyses; Ratiometric Probes; Redox State; Single Cell; Structure–Function Relationships
  7. PLoS Comput Biol. 2021 Jun 09. 17(6): e1009073
      Neurons rely on localized mitochondria to fulfill spatially heterogeneous metabolic demands. Mitochondrial aging occurs on timescales shorter than the neuronal lifespan, necessitating transport of fresh material from the soma. Maintaining an optimal distribution of healthy mitochondria requires an interplay between a stationary pool localized to sites of high metabolic demand and a motile pool capable of delivering new material. Interchange between these pools can occur via transient fusion / fission events or by halting and restarting entire mitochondria. Our quantitative model of neuronal mitostasis identifies key parameters that govern steady-state mitochondrial health at discrete locations. Very infrequent exchange between stationary and motile pools optimizes this system. Exchange via transient fusion allows for robust maintenance, which can be further improved by selective recycling through mitophagy. These results provide a framework for quantifying how perturbations in organelle transport and interactions affect mitochondrial homeostasis in neurons, a key aspect underlying many neurodegenerative disorders.
  8. Oxid Med Cell Longev. 2021 ;2021 6617256
      Mitochondria are multifaceted organelles that serve to power critical cellular functions, including act as power generators of the cell, buffer cytosolic calcium overload, production of reactive oxygen species, and modulating cell survival. The structure and the cellular location of mitochondria are critical for their function and depend on highly regulated activities such as mitochondrial quality control (MQC) mechanisms. The MQC is regulated by several sets of processes: mitochondrial biogenesis, mitochondrial fusion and fission, mitophagy, and other mitochondrial proteostasis mechanisms such as mitochondrial unfolded protein response (mtUPR) or mitochondrial-derived vesicles (MDVs). These processes are important for the maintenance of mitochondrial homeostasis, and alterations in the mitochondrial function and signaling are known to contribute to the dysregulation of cell death pathways. Recent studies have uncovered regulatory mechanisms that control the activity of the key components for mitophagy. In this review, we discuss how mitophagy is controlled and how mitophagy impinges on health and disease through regulating cell death.
  9. Proc Natl Acad Sci U S A. 2021 Jun 15. pii: e2020078118. [Epub ahead of print]118(24):
      Multiple sclerosis (MS) is a neuroinflammatory and neurodegenerative disease characterized by myelin damage followed by axonal and ultimately neuronal loss. The etiology and physiopathology of MS are still elusive, and no fully effective therapy is yet available. We investigated the role in MS of autophagy (physiologically, a controlled intracellular pathway regulating the degradation of cellular components) and of mitophagy (a specific form of autophagy that removes dysfunctional mitochondria). We found that the levels of autophagy and mitophagy markers are significantly increased in the biofluids of MS patients during the active phase of the disease, indicating activation of these processes. In keeping with this idea, in vitro and in vivo MS models (induced by proinflammatory cytokines, lysolecithin, and cuprizone) are associated with strongly impaired mitochondrial activity, inducing a lactic acid metabolism and prompting an increase in the autophagic flux and in mitophagy. Multiple structurally and mechanistically unrelated inhibitors of autophagy improved myelin production and normalized axonal myelination, and two such inhibitors, the widely used antipsychotic drugs haloperidol and clozapine, also significantly improved cuprizone-induced motor impairment. These data suggest that autophagy has a causal role in MS; its inhibition strongly attenuates behavioral signs in an experimental model of the disease. Therefore, haloperidol and clozapine may represent additional therapeutic tools against MS.
    Keywords:  antipsychotic drugs; autophagy; mitochondria; multiple sclerosis; remyelination
  10. Mitochondrion. 2021 Jun 05. pii: S1567-7249(21)00078-7. [Epub ahead of print]
      The variety of available mitochondrial quantification tools makes it difficult to select the most reliable and accurate quantification tool. Here, we performed elaborate analyses on five open source ImageJ tools. Excessive clustering of mitochondrial structures was observed in four tools, caused by the global thresholding applied by these tools. The Mitochondrial Analyzer, which uses adaptive thresholding, outperformed the other examined tools, with accurate structural segregation and identification. Additionally, we showed that the Mitochondrial Analyzer successfully identifies mitochondrial morphology differences. Based on the observed performance, we consider the Mitochondrial Analyzer the best open source tool for mitochondrial network morphology quantification.
    Keywords:  Image analysis; ImageJ; Mitochondria; Mitochondrial Dynamics; Mitochondrial quantification
  11. Methods Mol Biol. 2021 ;2310 79-89
      Mitochondria are the organelles where the most fundamental processes of energy transformation within the cell are located. They are also involved in several processes like apoptosis and autophagy, reactive oxygen species formation, and calcium signaling, which are crucial for proper cell functioning. In addition, mitochondrial genome hosts genes encoding important proteins incorporated in respiratory chain complexes and indispensable for the oxidative phosphorylation. Studying isolated mitochondria is, therefore, crucial for better understanding of cell physiology. The presented protocol describes a relatively simple and handy method for crude mitochondrial fraction isolation from different mammalian cell lines. It includes mechanical cells disruption (homogenization) and differential centrifugation. In addition, this chapter presents two basic ways to assess mitochondrial functionality: by measuring mitochondrial inner membrane potential and coupled respiration.
    Keywords:  Cell cultures; Mitochondria isolation; Mitochondrial membrane potential; Oxidative phosphorylation; Oxygen consumption
  12. J Cell Sci. 2021 Jun 10. pii: jcs.253443. [Epub ahead of print]
      The mitochondria-ER contacts (MERCs) plays an essential role in multiple cell physiological process. While Mfn2 was the first protein implicated in the formation of MERCs, it is debated whether it acts as a tether or antagonizer, largely based on in vitro studies. To understand the role of Mfn2 in MERCs in vivo, we characterized ultrastructural and biochemical changes of MERCs in pyramidal neurons of hippocampus in Mfn2 conditional knockout (KO) mice and in Mfn2 overexpression (OE) mice and found Mfn2 ablation caused reduced close contacts while Mfn2 OE caused increased close contacts between ER and mitochondria in vivo. Functional studies on SH-SY5Y cells with Mfn2 KO or overexpression demonstrating similar biochemical changes found that mitochondrial calcium uptake along with IP3R3-Grp75 interaction was decreased in Mfn2 KO cells but increased in the Mfn2 OE cells. Lastly, we found Mfn2 KO decreased and Mfn2 OE increased the interaction between the ER-mitochondria tethering pair of VAPB-PTPIP51. In conclusion, our study supports the notion that Mfn2 plays a critical role in ER-mitochondrial tethering and the formation of close contacts in neuronal cells in vivo.
    Keywords:  ER-mitochondria tethering; Mfn2; Mitochondria-ER contact; Mitochondria-associated membrane; Mitochondrial calcium uptake; VAPB
  13. Aging Cell. 2021 Jun 07. e13408
      Changes in the rate and fidelity of mitochondrial protein synthesis impact the metabolic and physiological roles of mitochondria. Here we explored how environmental stress in the form of a high-fat diet modulates mitochondrial translation and affects lifespan in mutant mice with error-prone (Mrps12ep / ep ) or hyper-accurate (Mrps12ha / ha ) mitochondrial ribosomes. Intriguingly, although both mutations are metabolically beneficial in reducing body weight, decreasing circulating insulin and increasing glucose tolerance during a high-fat diet, they manifest divergent (either deleterious or beneficial) outcomes in a tissue-specific manner. In two distinct organs that are commonly affected by the metabolic disease, the heart and the liver, Mrps12ep / ep mice were protected against heart defects but sensitive towards lipid accumulation in the liver, activating genes involved in steroid and amino acid metabolism. In contrast, enhanced translational accuracy in Mrps12ha / ha mice protected the liver from a high-fat diet through activation of liver proliferation programs, but enhanced the development of severe hypertrophic cardiomyopathy and led to reduced lifespan. These findings reflect the complex transcriptional and cell signalling responses that differ between post-mitotic (heart) and highly proliferative (liver) tissues. We show trade-offs between the rate and fidelity of mitochondrial protein synthesis dictate tissue-specific outcomes due to commonly encountered stressful environmental conditions or aging.
    Keywords:  ageing; metabolism; mitochondria; protein synthesis
  14. Metabolism. 2021 Jun 03. pii: S0026-0495(21)00103-7. [Epub ahead of print] 154803
      BACKGROUND AND AIMS: A diminution in skeletal muscle mitochondrial function due to ectopic lipid accumulation and excess nutrient intake is thought to contribute to insulin resistance and the development of type 2 diabetes. However, the functional integrity of mitochondria in insulin-resistant skeletal muscle remains highly controversial.METHODS: 19 healthy adults (age:28.4 ± 1.7 years; BMI:22.7 ± 0.3 kg/m2) received an overnight intravenous infusion of lipid (20% Intralipid) or saline followed by a hyperinsulinemic-euglycemic clamp to assess insulin sensitivity using a randomized crossover design. Skeletal muscle biopsies were obtained after the overnight lipid infusion to evaluate activation of mitochondrial dynamics proteins, ex-vivo mitochondrial membrane potential, ex-vivo oxidative phosphorylation and electron transfer capacity, and mitochondrial ultrastructure.
    RESULTS: Overnight lipid infusion increased dynamin related protein 1 (DRP1) phosphorylation at serine 616 and PTEN-induced kinase 1 (PINK1) expression (P = 0.003 and P = 0.008, respectively) in skeletal muscle while reducing mitochondrial membrane potential (P = 0.042). The lipid infusion also increased mitochondrial-associated lipid droplet formation (P = 0.011), the number of dilated cristae, and the presence of autophagic vesicles without altering mitochondrial number or respiratory capacity. Additionally, lipid infusion suppressed peripheral glucose disposal (P = 0.004) and hepatic insulin sensitivity (P = 0.014).
    CONCLUSIONS: These findings indicate that activation of mitochondrial fission and quality control occur early in the onset of insulin resistance in human skeletal muscle. Targeting mitochondrial dynamics and quality control represents a promising new pharmacological approach for treating insulin resistance and type 2 diabetes.
  15. Methods Mol Biol. 2021 ;2310 271-285
      NAD+ is a redox cofactor essential to the proper functioning of a variety of important metabolic pathways, including key steps in mitochondrial energy metabolism. In addition, it serves as a signaling substrate for enzymes such as sirtuins and the poly-ADP ribosyl-polymerase family of enzymes. Sirtuins, which are NAD+-dependent protein deacylases, harness changes in cellular NAD+ concentrations to produce changes in protein acylation status, thereby affecting downstream functions including energy metabolism, stress resistance, and cell survival. Thus, the availability of NAD+ in cells, or in specific organelles such as the mitochondrion, regulates downstream signaling and key biological processes. This concept has driven a need for researchers to easily and precisely measure NAD+ concentrations in biological samples. We herein describe several protocols for the measurement of NAD+ and NADH concentrations in tissues, cells, or subcellular compartments such as mitochondria. These protocols include a cycling assay that can quickly measure NAD+ or NADH levels using a plate reader equipped with fluorescence measurement capabilities. This plate assay relies only upon commercially available materials in addition to the biological samples of interest. In addition, we describe a protocol employing stable isotope-labeled NAD+ as an internal standard to determine biological NAD+ content by isotope-dilution methods. This method requires mass spectrometry to ratio endogenous NAD+ with exogenous isotope-labeled NAD+ to obtain quantification using HPLC and mass spectrometry.
    Keywords:  18O-NAD+; Diaphorase; HPLC; Isotopes; LC-MS; Lactate; Lactate dehydrogenase (LDH); Mitochondria isolation; NAD+; NAD+/NADH cycling assay; Resazurin; Resorufin
  16. Analyst. 2021 Jun 09.
      BACKGROUND: Because of the interplay between mitochondrial respiration and cellular metabolism, the simultaneous monitoring of both cellular processes provides important insights for the understanding of biological processes. NMR flow systems provide a unique window into the metabolome of cultured cells. Simplified bioreactor construction based on commercially available flow systems increase the practicability and reproducibility of bioreactor studies using standard NMR spectrometers. We therefore aim at establishing a reproducible NMR bioreactor system for metabolic 1H-NMR investigations of small molecules and concurrent oxygenation determination by 19F-NMR, with in depth description and validation by accompanying measures.METHODS: We demonstrate a detailed and standardized workflow for the preparation and transfer of collagen based 3D cell culture of high cell density for perfused investigation in a 5 mm NMR tube. Self-constructed gas mixing station enables 5% CO2 atmosphere for physiological pH in carbon based medium and is perfused by HPLC pump.
    RESULTS & DISCUSSION: Implemented perfused bioreactor allows detection of perfusion rate dependent metabolite content. We show interleaved dynamic profiling of 26 metabolites and mitochondrial respiration. During constant perfusion, sequential injection of rotenone/oligomycin and 2-deoxy-glucose indicated immediate activation and deactivation of glycolytic rate and full inhibition of oxygen consumption. We show sensitivity to detect substrate degradation rates of major mitochondrial fuel pathways and were able to simultaneously measure cellular oxygen consumption.
  17. Oxid Med Cell Longev. 2021 ;2021 6677955
      Peroxisome proliferator-activated receptors (PPARs) α and γ have been shown to be protective in hepatic ischemia/reperfusion (I/R) injury. However, the precise role of PPARγ coactivator-1α (PGC-1α), which can coactivate both of these receptors, in hepatic I/R injury, remains largely unknown. This study was designed to test our hypothesis that PGC-1α is protective during hepatic I/R injury in vitro and in vivo. Our results show that endogenous PGC-1α is basally expressed in normal livers and is moderately increased by I/R. Ectopic PGC-1α protects against hepatic I/R and hepatocyte anoxia/reoxygenation (A/R) injuries, whereas knockdown of endogenous PGC-1α aggravates such injuries, as evidenced by assessment of the levels of serum aminotransferases and inflammatory cytokines, necrosis, apoptosis, cell viability, and histological examination. The EMSA assay shows that the activation of PPARα and PPARγ is increased or decreased by the overexpression or knockdown of PGC-1α, respectively, during hepatic I/R and hepatocyte A/R injuries. In addition, the administration of specific antagonists of either PPARα (MK886) or PPARγ (GW9662) can effectively decrease the protective effect of PGC-1α against hepatic I/R and hepatocyte A/R injuries. We also demonstrate an important regulatory role of PGC-1α in reactive oxygen species (ROS) metabolism during hepatic I/R, which is correlated with the induction of ROS-detoxifying enzymes and is also dependent on the activations of PPARα and PPARγ. These data demonstrate that PGC-1α protects against hepatic I/R injury, mainly by regulating the activation of PPARα and PPARγ. Thus, PGC-1α may be a promising therapeutic target for the protection of the liver against I/R injury.
  18. World J Biol Psychiatry. 2021 Jun 07. 1-38
      OBJECTIVES: Circulating cell-free mitochondrial DNA (ccf-mtDNA) are detectable fragments of mtDNA released from the cell as a result of mitochondrial dysfunction or apoptosis. The brain is one of the most energy demanding organs in the human body, and many neuropsychiatric and non-psychiatric neurological diseases have mitochondrial dysfunction associated with disease pathophysiology. Thus, we aimed to assess ccf-mtDNA as a potential biomarker for brain diseases. Methods: We conducted a systematic review and meta-analyses of studies that examined peripheral and/or cerebrospinal fluid (CSF) ccf-mtDNA relevant to neuropsychiatric, which we define as disorders of affect, behaviour and mood, and non-psychiatric neurological diseases, which consist of neurological diseases not related to psychiatry including neurodegenerative diseases. Results: The results of the sensitivity analysis investigating the levels of peripheral ccf-mtDNA in neuropsychiatric studies showed no significant difference between cases and controls (Z = 1.57; p = 0.12), whereas the results of the sensitivity analysis investigating the levels of CSF ccf-mtDNA in non-psychiatric neurological diseases showed a decreasing trend in cases compared with controls (Z = 2.32; p = 0.02). Interestingly, the results indicate an overall mitochondrial stress associated mainly with non-psychiatric neurological diseases. Conclusions: Our study supports the involvement of mitochondrial stress, here defined as ccf-mtDNA, in brain diseases and encourage further investigation of ccf-mtDNA among patients with brain diseases.
    Keywords:  circulating cell-free mitochondrial DNA; mitochondria; neurodegeneration; neuropsychiatry