bims-mikwok Biomed News
on Mitochondrial quality control
Issue of 2020‒08‒30
twelve papers selected by
Avinash N. Mukkala
University of Toronto

  1. Int J Mol Sci. 2020 Aug 25. pii: E6130. [Epub ahead of print]21(17):
    Kim H, Jeon BT, Kim IM, Bennett SJ, Lorch CM, Viana MP, Myers JF, Trupp CJ, Whipps ZT, Kundu M, Chung S, Sun X, Khalimonchuk O, Lee J, Ro SH.
      Selective autolysosomal degradation of damaged mitochondria, also called mitophagy, is an indispensable process for maintaining integrity and homeostasis of mitochondria. One well-established mechanism mediating selective removal of mitochondria under relatively mild mitochondria-depolarizing stress is PINK1-Parkin-mediated or ubiquitin-dependent mitophagy. However, additional mechanisms such as LC3-mediated or ubiquitin-independent mitophagy induction by heavy environmental stress exist and remain poorly understood. The present study unravels a novel role of stress-inducible protein Sestrin2 in degradation of mitochondria damaged by transition metal stress. By utilizing proteomic methods and studies in cell culture and rodent models, we identify autophagy kinase ULK1-mediated phosphorylation sites of Sestrin2 and demonstrate Sestrin2 association with mitochondria adaptor proteins in HEK293 cells. We show that Ser-73 and Ser-254 residues of Sestrin2 are phosphorylated by ULK1, and a pool of Sestrin2 is strongly associated with mitochondrial ATP5A in response to Cu-induced oxidative stress. Subsequently, this interaction promotes association with LC3-coated autolysosomes to induce degradation of mitochondria damaged by Cu-induced ROS. Treatment of cells with antioxidants or a Cu chelator significantly reduces Sestrin2 association with mitochondria. These results highlight the ULK1-Sestrin2 pathway as a novel stress-sensing mechanism that can rapidly induce autophagic degradation of mitochondria under severe heavy metal stress.
    Keywords:  ATP5A; Sestrin2; ULK1; autophagy; mitochondria; phosphorylation
  2. EMBO Rep. 2020 Aug 27. e50964
    Lightowlers RN, Chrzanowska-Lightowlers ZM, Russell OM.
      Transplantation of functional mitochondria directly into defective cells is a novel approach that has recently caught the attention of scientists and the general public alike. Could this be too good to be true?
  3. Transplantation. 2020 Aug 24.
    Dai SH, Chen LJ, Qi WH, Ye CL, Zou GW, Liu WC, Yu BT, Tang J.
      BACKGROUND: MicroRNA-145 (miR-145) has been shown to play a critical role in ischemia/reperfusion (I/R) injury; however, the expression and function of miR-145 in lung I/R injury have not been reported yet. This study aimed to elucidate the potential effects of miR-145 in lung I/R injury.METHODS: Lung I/R mice models and hypoxia/reoxygenation (H/R) pulmonary microvascular endothelial cell (PMVEC) models were established. The expression of miR-145 and sirtuin 1 (SIRT1) was measured with RT-qPCR and Western blot analysis in mouse lung tissue and cells. Artificial modulation of miR-145 and SIRT1 (down-regulation) was done in I/R mice and H/R cells. Additionally, PaO2/FiO2 ratio, wet weight-to-dry weight (W/D) ratio, and cell apoptosis in mouse lung tissues were determined by blood gas analyzer, electronic balance, and TUNEL assay, respectively. Autophagy marker Beclin 1 and LC3 expression, NF-κB acetylation levels, and autophagy bodies were detected in cell H/R and mouse I/R models by Western blot analysis. PMVEC apoptosis was detected with flow cytometry.
    RESULTS: miR-145 was abundantly expressed in the lung tissue of mice and PMVECs following I/R injury. In addition, miR-145 directly targeted SIRT1, which led to significantly decreased PaO2/FiO2 ratio and increased W/D ratio, elevated acetylation levels and transcriptional activity of NF-κB, up-regulated expressions of TNF-α, IL-6 and Beclin 1, autophagy bodies, cell apoptosis, as well as LC3-II/LC3I ratio.
    CONCLUSIONS: In summary, miR-145 enhances autophagy and aggravates lung I/R injury by promoting NF-κB transcriptional activity via SIRT1 expression.
  4. Front Cell Neurosci. 2020 ;14 175
    Quintanilla RA, Tapia-Monsalves C, Vergara EH, Pérez MJ, Aranguiz A.
      Mitochondria are highly specialized organelles essential for the synapse, and their impairment contributes to the neurodegeneration in Alzheimer's disease (AD). Previously, we studied the role of caspase-3-cleaved tau in mitochondrial dysfunction in AD. In neurons, the presence of this AD-relevant tau form induced mitochondrial fragmentation with a concomitant reduction in the expression of Opa1, a mitochondrial fission regulator. More importantly, we showed that caspase-cleaved tau affects mitochondrial transport, decreasing the number of moving mitochondria in the neuronal processes without affecting their velocity rate. However, the molecular mechanisms involved in these events are unknown. We studied the possible role of motor proteins (kinesin 1 and dynein) and mitochondrial protein adaptors (RhoT1/T2, syntaphilin, and TRAK2) in the mitochondrial transport failure induced by caspase-cleaved tau. We expressed green fluorescent protein (GFP), GFP-full-length, and GPF-caspase-3-cleaved tau proteins in rat hippocampal neurons and immortalized cortical neurons (CN 1.4) and analyzed the expression and localization of these proteins involved in mitochondrial transport regulation. We observed that hippocampal neurons expressing caspase-cleaved tau showed a significant accumulation of a mitochondrial population in the soma. These changes were accompanied by evident mitochondrial bioenergetic deficits, including depolarization, oxidative stress, and a significant reduction in ATP production. More critically, caspase-cleaved tau significantly decreased the expression of TRAK2 in immortalized and primary hippocampal neurons without affecting RhoT1/T2 and syntaphilin levels. Also, when we analyzed the expression of motor proteins-Kinesin 1 (KIF5) and Dynein-we did not detect changes in their expression, localization, and binding to the mitochondria. Interestingly, the expression of truncated tau significantly increases the association of TRAK2 with mitochondria compared with neuronal cells expressing full-length tau. Altogether these results indicate that caspase-cleaved tau may affect mitochondrial transport through the increase of TRAK2-mitochondria binding and reduction of ATP production available for the process of movement of these organelles. These observations are novel and represent a set of exciting findings whereby tau pathology could affect mitochondrial distribution in neurons, an event that may contribute to synaptic failure observed in AD.
    Keywords:  TRAK2/Milton; kinesin; mitochondria; tau; transport; truncated tau
  5. Curr Opin Physiol. 2019 Aug;10 96-101
    Drake JC, Yan Z.
      The profound energetic demand of prolonged exercise imposed upon skeletal muscle and the heart is met by oxidation of substrate within mitochondria. As such, several coordinated events are initiated in order to maintain mitochondria, collectively known as mitochondrial quality control. In this review, we discuss how mitochondrial quality control functions to maintain the integrity of the reticulum and energy production in response to prolonged exercise, as well as the relevant signaling events that dictate these responses. Based upon the prevailing data in the field, we propose a model where exercise-mediated quality control may be chiefly regulated through local mechanisms, thus allowing for the remarkable precision in mitochondrial quality control events.
    Keywords:  exercise; mitochondria; mitophagy; muscle; myofiber; quality control
  6. Front Cell Neurosci. 2020 ;14 194
    Liao Y, Dong Y, Cheng J.
      Membrane tethering is an important communication method for membrane-packaged organelles. Mitochondria are organelles with a bilayer membrane, and the membrane contact between mitochondria and other organelles is indispensable for maintaining cellular homeostasis. Increased levels of molecular determinants that mediate the membrane contact between mitochondria and other organelles, and their functions, have been revealed in recent years. In this review article, we aim to summarize the findings on the tethering between mitochondria and other organelles in physiological or pathological conditions, and discuss their roles in cellular homeostasis, neural activity, and neurodegenerative diseases.
    Keywords:  determinant; membrane contact; mitochondria; neurological diseases; pathological condition; physiological condition
  7. Cell Rep. 2020 Aug 25. pii: S2211-1247(20)31064-0. [Epub ahead of print]32(8): 108079
    Tur J, Pereira-Lopes S, Vico T, Marín EA, Muñoz JP, Hernández-Alvarez M, Cardona PJ, Zorzano A, Lloberas J, Celada A.
      Mitofusin 2 (Mfn2) plays a major role in mitochondrial fusion and in the maintenance of mitochondria-endoplasmic reticulum contact sites. Given that macrophages play a major role in inflammation, we studied the contribution of Mfn2 to the activity of these cells. Pro-inflammatory stimuli such as lipopolysaccharide (LPS) induced Mfn2 expression. The use of the Mfn2 and Mfn1 myeloid-conditional knockout (KO) mouse models reveals that Mfn2 but not Mfn1 is required for the adaptation of mitochondrial respiration to stress conditions and for the production of reactive oxygen species (ROS) upon pro-inflammatory activation. Mfn2 deficiency specifically impairs the production of pro-inflammatory cytokines and nitric oxide. In addition, the lack of Mfn2 but not Mfn1 is associated with dysfunctional autophagy, apoptosis, phagocytosis, and antigen processing. Mfn2floxed;CreLysM mice fail to be protected from Listeria, Mycobacterium tuberculosis, or LPS endotoxemia. These results reveal an unexpected contribution of Mfn2 to ROS production and inflammation in macrophages.
    Keywords:  apoptotic bodies; inflammation; lipopolysaccharide (LPS); macrophages; mitochondria; mitofusin; phagocytosis; protein degradation; reactive oxygen species (ROS); septic shock
  8. Methods Mol Biol. 2021 ;2202 33-42
    Angelova PR, Dinkova-Kostova AT, Abramov AY.
      Production of reactive oxygen species (ROS) in the mitochondria plays multiple roles in physiology, and excessive production of ROS leads to the development of various pathologies. ROS in the mitochondria are generated by various enzymes, mainly in the electron transporvt chain, and it is important to identify not only the trigger but also the source of free radical production. It is important to measure mitochondrial ROS in live, intact cells, because activation of ROS production could be initiated by changes in extramitochondrial processes which could be overseen when using isolated mitochondria. Here we describe the approaches, which allow to measure production of ROS in the matrix of mitochondria in live cells. We also demonstrate how to measure kinetic changes in lipid peroxidation in mitochondria of live cells. These methods could be used for understanding the mechanisms of pathology in a variety of disease models and also for testing neuro- or cardioprotective chemicals.
    Keywords:  Lipid peroxidation; Live cell imaging; Mitochondria; ROS production
  9. Front Physiol. 2020 ;11 897
    Tian Y, Song H, Qin W, Ding Z, Zhang Y, Shan W, Jin D.
      In this study, we analyzed the role of mammalian STE20-like protein kinase 2 (Mst2), a serine-threonine protein kinase, in Lipopolysaccharides (LPS)-mediated inflammation and apoptosis in the H9C2 cardiomyocytes. Mst2 mRNA and protein levels were significantly upregulated in the LPS-treated H9C2 cardiomyocytes. LPS treatment induced expression of IL-2, IL-8, and MMP9 mRNA and proteins in the H9C2 cardiomyocytes, and this was accompanied by increased caspase-3/9 mediating H9C2 cardiomyocyte apoptosis. LPS treatment also increased mitochondrial reactive oxygen species (ROS) and the levels of antioxidant enzymes, such as GSH, SOD, and GPX, in the H9C2 cardiomyocytes. The LPS-treated H9C2 cardiomyocytes showed lower cellular ATP levels and mitochondrial state-3/4 respiration but increased mitochondrial fragmentation, including upregulation of the mitochondrial fission genes Drp1, Mff, and Fis1. LPS-induced inflammation, mitochondrial ROS, mitochondrial fission, and apoptosis were all significantly suppressed by pre-treating the H9C2 cardiomyocytes with the Mst2 inhibitor, XMU-MP1. However, the beneficial effects of Mst2 inhibition by XMU-MP1 were abolished by carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP), a potent activator of mitochondrial fission. These findings demonstrate that Mst2 mediates LPS-induced cardiomyocyte inflammation and apoptosis by increasing mitochondrial fission.
    Keywords:  FCCP; Mst2; cardiomyocyte; inflammation; mitochondrial fission
  10. Redox Biol. 2020 Aug 07. pii: S2213-2317(20)30876-4. [Epub ahead of print]36 101671
    Fu ZJ, Wang ZY, Xu L, Chen XH, Li XX, Liao WT, Ma HK, Jiang MD, Xu TT, Xu J, Shen Y, Song B, Gao PJ, Han WQ, Zhang W.
      In the present study, we hypothesized that hypoxia-inducible factor 1α (HIF-1α)-mediated mitophagy plays a protective role in ischemia/reperfusion (I/R)-induced acute kidney injury (AKI). Mitophagy was evaluated by measuring the changes of mitophagy flux, mitochondria DNA copy number, and the changes of mitophagy-related proteins including translocase of outer mitochondrial membrane 20 (TOMM20), cytochrome c oxidase IV (COX IV), microtubule-associated protein 1 light chain 3B (LC3B), and mitochondria adaptor nucleoporin p62 in HK2 cells, a human tubular cell line. Results show that HIF-1α knockout significantly attenuated hypoxia/reoxygenation (H/R)-induced mitophagy, aggravated H/R-induced apoptosis, and increased the production of reactive oxygen species (ROS). Similarly, H/R induced significantly increase in Bcl-2 19-kDa interacting protein 3 (BNIP3), a downstream regulator of HIF-1α. Notably, BNIP3 overexpression reversed the inhibitory effect of HIF-1α knockout on H/R-induced mitophagy, and prevented the enhancing effect of HIF-1α knockout on H/R-induced apoptosis and ROS production. For in vivo study, we established HIF-1αflox/flox; cadherin-16-cre mice in which tubular HIF-1α was specifically knockout. It was found that tubular HIF-1α knockout significantly inhibited I/R-induced mitophagy, and aggravated I/R-induced tubular apoptosis and kidney damage. In contrast, adenovirus-mediated BNIP3 overexpression significantly reversed the decreased mitophagy, and prevented enhanced kidney damage in tubular HIF-1α knockout mice with I/R injury. In summary, our study demonstrated that HIF-1α-BNIP3-mediated mitophagy in tubular cells plays a protective role through inhibition of apoptosis and ROS production in acute kidney damage.
    Keywords:  Acute kidney injury; Bcl-2 19-kDa interacting protein 3; Hypoxia-inducible factor 1α; Mitophagy; Tubular cells
  11. J Cell Biol. 2020 Sep 07. pii: e202008031. [Epub ahead of print]219(9):
    Ikeda F.
      Mitophagy has a critical role in maintaining cellular homeostasis by removing damaged mitochondria. In this issue, Yamano et al. (2020. J. Cell Biol. uncover that a novel complex of the autophagy adaptor optineurin and the membrane protein ATG9A specifically regulate ubiquitin-induced mitophagy.
  12. Chin Med J (Engl). 2020 Aug 26.
    Wang R, Maimaitijuma T, Ma YY, Jiao Y, Cao YP.
      BACKGROUND: Previous studies have reported that mitochondrial dysfunction participates in the pathological process of osteoarthritis (OA). However, studies that improve mitochondrial function are rare in OA. Mitochondrial transfer from mesenchymal stem cells (MSCs) to OA chondrocytes might be a cell-based therapy for the improvement of mitochondrial function to prevent cartilage degeneration. This study aimed to determine whether MSCs can donate mitochondria and protect the mitochondrial function and therefore reduce cartilage degeneration.METHODS: Bone-marrow-derived mesenchymal stromal cells (BM-MSCs) were harvested from the marrow cavities of femurs and tibia in young rats. OA chondrocytes were gathered from the femoral and tibial plateau in old OA model rats. BM-MSCs and OA chondrocytes were co-cultured and mitochondrial transfer from BM-MSCs to chondrocytes was identified. Chondrocytes with mitochondria transferred from BM-MSCs were selected by fluorescence-activated cell sorting. Mitochondrial function of these cells, including mitochondrial membrane potential (Δψm), the activity of mitochondrial respiratory chain (MRC) enzymes, and adenosine triphosphate (ATP) content were quantified and compared to OA chondrocytes without mitochondrial transfer. Chondrocytes proliferation, apoptosis, and secretion ability were also analyzed between the two groups.
    RESULTS: Mitochondrial transfer was found from BM-MSCs to OA chondrocytes. Chondrocytes with mitochondrial from MSCs (MSCs + OA group) showed increased mitochondrial membrane potential compared with OA chondrocytes without mitochondria transfer (OA group) (1.79 ± 0.19 vs. 0.71 ± 0.12, t = 10.42, P < 0.0001). The activity of MRC enzymes, including MRC complex I, II, III, and citrate synthase was also improved (P < 0.05). The content of ATP in MSCs + OA group was significantly higher than that in OA group (161.90 ± 13.49 vs. 87.62 ± 11.07 nmol/mg, t = 8.515, P < 0.0001). Meanwhile, we observed decreased cell apoptosis (7.09% ± 0.68% vs.15.89% ± 1.30%, t = 13.39, P < 0.0001) and increased relative secretion of type II collagen (2.01 ± 0.14 vs.1.06 ± 0.11, t = 9.141, P = 0.0008) and proteoglycan protein (2.08 ± 0.20 vs. 0.97 ± 0.12, t = 8.227, P = 0.0012) in MSCs + OA group, contrasted with OA group.
    CONCLUSIONS: Mitochondrial transfer from BM-MSCs provided protection for OA chondrocytes against mitochondrial dysfunction and degeneration through improving mitochondrial function, cell proliferation, and inhibiting apoptosis in chondrocytes. This finding may offer a new therapeutic direction for OA.