1
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Kotrys AV, Durham TJ, Guo XA, Vantaku VR, Parangi S, Mootha VK. Single-cell analysis reveals context-dependent, cell-level selection of mtDNA. Nature 2024; 629:458-466. [PMID: 38658765 PMCID: PMC11078733 DOI: 10.1038/s41586-024-07332-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2023] [Accepted: 03/18/2024] [Indexed: 04/26/2024]
Abstract
Heteroplasmy occurs when wild-type and mutant mitochondrial DNA (mtDNA) molecules co-exist in single cells1. Heteroplasmy levels change dynamically in development, disease and ageing2,3, but it is unclear whether these shifts are caused by selection or drift, and whether they occur at the level of cells or intracellularly. Here we investigate heteroplasmy dynamics in dividing cells by combining precise mtDNA base editing (DdCBE)4 with a new method, SCI-LITE (single-cell combinatorial indexing leveraged to interrogate targeted expression), which tracks single-cell heteroplasmy with ultra-high throughput. We engineered cells to have synonymous or nonsynonymous complex I mtDNA mutations and found that cell populations in standard culture conditions purge nonsynonymous mtDNA variants, whereas synonymous variants are maintained. This suggests that selection dominates over simple drift in shaping population heteroplasmy. We simultaneously tracked single-cell mtDNA heteroplasmy and ancestry, and found that, although the population heteroplasmy shifts, the heteroplasmy of individual cell lineages remains stable, arguing that selection acts at the level of cell fitness in dividing cells. Using these insights, we show that we can force cells to accumulate high levels of truncating complex I mtDNA heteroplasmy by placing them in environments where loss of biochemical complex I activity has been reported to benefit cell fitness. We conclude that in dividing cells, a given nonsynonymous mtDNA heteroplasmy can be harmful, neutral or even beneficial to cell fitness, but that the 'sign' of the effect is wholly dependent on the environment.
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Affiliation(s)
- Anna V Kotrys
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Timothy J Durham
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Xiaoyan A Guo
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Venkata R Vantaku
- Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - Sareh Parangi
- Department of Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
- Cancer Center, Massachusetts General Hospital, Boston, MA, USA
| | - Vamsi K Mootha
- Howard Hughes Medical Institute and Department of Molecular Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
- Broad Institute of MIT and Harvard, Cambridge, MA, USA.
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2
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Heo J, Park YJ, Kim Y, Lee HS, Kim J, Kwon SH, Kang MG, Rhee HW, Sun W, Lee JH, Cho H. Mitochondrial E3 ligase MARCH5 is a safeguard against DNA-PKcs-mediated immune signaling in mitochondria-damaged cells. Cell Death Dis 2023; 14:788. [PMID: 38040710 PMCID: PMC10692114 DOI: 10.1038/s41419-023-06315-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 11/10/2023] [Accepted: 11/15/2023] [Indexed: 12/03/2023]
Abstract
Mitochondrial dysfunction is important in various chronic degenerative disorders, and aberrant immune responses elicited by cytoplasmic mitochondrial DNA (mtDNA) may be related. Here, we developed mtDNA-targeted MTERF1-FokI and TFAM-FokI endonuclease systems to induce mitochondrial DNA double-strand breaks (mtDSBs). In these cells, the mtDNA copy number was significantly reduced upon mtDSB induction. Interestingly, in cGAS knockout cells, synthesis of interferon β1 and interferon-stimulated gene was increased upon mtDSB induction. We found that mtDSBs activated DNA-PKcs and HSPA8 in a VDAC1-dependent manner. Importantly, the mitochondrial E3 ligase MARCH5 bound active DNA-PKcs in cells with mtDSBs and reduced the type І interferon response through the degradation of DNA-PKcs. Likewise, mitochondrial damage caused by LPS treatment in RAW264.7 macrophage cells increased phospho-HSPA8 levels and the synthesis of mIFNB1 mRNA in a DNA-PKcs-dependent manner. Accordingly, in March5 knockout macrophages, phospho-HSPA8 levels and the synthesis of mIFNB1 mRNA were prolonged after LPS stimulation. Together, cytoplasmic mtDNA elicits a cellular immune response through DNA-PKcs, and mitochondrial MARCH5 may be a safeguard to prevent persistent inflammatory reactions.
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Affiliation(s)
- June Heo
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea
- Department of Biomedical Sciences, Graduate School of Ajou University, Suwon, South Korea
| | - Yeon-Ji Park
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea
| | - Yonghyeon Kim
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea
- Department of Biomedical Sciences, Graduate School of Ajou University, Suwon, South Korea
| | - Ho-Soo Lee
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea
| | - Jeongah Kim
- Department of Anatomy, College of medicine, Korea University, Seoul, South Korea
| | - Soon-Hwan Kwon
- Department of Infectious Diseases, Research Center of Infectious and Environmental Diseases, Armed Forces Medical Research Institute, Daejeon, South Korea
| | - Myeong-Gyun Kang
- Department of Chemistry, Seoul National University, Seoul, South Korea
| | - Hyun-Woo Rhee
- Department of Chemistry, Seoul National University, Seoul, South Korea
| | - Woong Sun
- Department of Anatomy, College of medicine, Korea University, Seoul, South Korea
| | - Jae-Ho Lee
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea.
- Department of Biomedical Sciences, Graduate School of Ajou University, Suwon, South Korea.
| | - Hyeseong Cho
- Department of Biochemistry and Molecular Biology, Ajou University School of Medicine, Suwon, South Korea.
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3
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Potter A, Cabrera-Orefice A, Spelbrink JN. Let's make it clear: systematic exploration of mitochondrial DNA- and RNA-protein complexes by complexome profiling. Nucleic Acids Res 2023; 51:10619-10641. [PMID: 37615582 PMCID: PMC10602928 DOI: 10.1093/nar/gkad697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2023] [Revised: 07/18/2023] [Accepted: 08/11/2023] [Indexed: 08/25/2023] Open
Abstract
Complexome profiling (CP) is a powerful tool for systematic investigation of protein interactors that has been primarily applied to study the composition and dynamics of mitochondrial protein complexes. Here, we further optimized this method to extend its application to survey mitochondrial DNA- and RNA-interacting protein complexes. We established that high-resolution clear native gel electrophoresis (hrCNE) is a better alternative to preserve DNA- and RNA-protein interactions that are otherwise disrupted when samples are separated by the widely used blue native gel electrophoresis (BNE). In combination with enzymatic digestion of DNA, our CP approach improved the identification of a wide range of protein interactors of the mitochondrial gene expression system without compromising the detection of other multiprotein complexes. The utility of this approach was particularly demonstrated by analysing the complexome changes in human mitochondria with impaired gene expression after transient, chemically induced mitochondrial DNA depletion. Effects of RNase on mitochondrial protein complexes were also evaluated and discussed. Overall, our adaptations significantly improved the identification of mitochondrial DNA- and RNA-protein interactions by CP, thereby unlocking the comprehensive analysis of a near-complete mitochondrial complexome in a single experiment.
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Affiliation(s)
- Alisa Potter
- Department of Pediatrics, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, The Netherlands
- Radboud Center for Mitochondrial Medicine (RCMM), Radboud University Medical Center, Nijmegen, The Netherlands
| | - Alfredo Cabrera-Orefice
- Radboud Center for Mitochondrial Medicine (RCMM), Radboud University Medical Center, Nijmegen, The Netherlands
- Department of Medical BioSciences, Radboud University Medical Center, Nijmegen, The Netherlands
- Functional Proteomics, Institute for Cardiovascular Physiology, Goethe University, Frankfurt am Main, Germany
| | - Johannes N Spelbrink
- Department of Pediatrics, Amalia Children's Hospital, Radboud University Medical Center, Nijmegen, The Netherlands
- Radboud Center for Mitochondrial Medicine (RCMM), Radboud University Medical Center, Nijmegen, The Netherlands
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4
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Zhang Q, Song Q, Liu S, Xu Y, Gao D, Lu P, Liu Y, Zhao G, Wu L, Zhao C, Yang J. Integrated transcriptomic and metabolomic analysis reveals the metabolic programming of GM-CSF- and M-CSF- differentiated mouse macrophages. Front Immunol 2023; 14:1230772. [PMID: 37818352 PMCID: PMC10560851 DOI: 10.3389/fimmu.2023.1230772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Accepted: 09/11/2023] [Indexed: 10/12/2023] Open
Abstract
Macrophages play a critical role in the inflammatory response and tumor development. Macrophages are primarily divided into pro-inflammatory M1-like and anti-inflammatory M2-like macrophages based on their activation status and functions. In vitro macrophage models could be derived from mouse bone marrow cells stimulated with two types of differentiation factors: GM-CSF (GM-BMDMs) and M-CSF (M-BMDMs), to represent M1- and M2-like macrophages, respectively. Since macrophage differentiation requires coordinated metabolic reprogramming and transcriptional rewiring in order to fulfill their distinct roles, we combined both transcriptome and metabolome analysis, coupled with experimental validation, to gain insight into the metabolic status of GM- and M-BMDMs. The data revealed higher levels of the tricarboxylic acid cycle (TCA cycle), oxidative phosphorylation (OXPHOS), fatty acid oxidation (FAO), and urea and ornithine production from arginine in GM-BMDMs, and a preference for glycolysis, fatty acid storage, bile acid metabolism, and citrulline and nitric oxide (NO) production from arginine in M-BMDMs. Correlation analysis with the proteomic data showed high consistency in the mRNA and protein levels of metabolic genes. Similar results were also obtained when compared to RNA-seq data of human monocyte derived macrophages from the GEO database. Furthermore, canonical macrophage functions such as inflammatory response and phagocytosis were tightly associated with the representative metabolic pathways. In the current study, we identified the core metabolites, metabolic genes, and functional terms of the two distinct mouse macrophage populations. We also distinguished the metabolic influences of the differentiation factors GM-CSF and M-CSF, and wish to provide valuable information for in vitro macrophage studies.
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Affiliation(s)
- Qianyue Zhang
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
| | - Qiaoling Song
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
- Innovation Platform of Marine Drug Screening and Evaluation, Qingdao Marine Science and Technology Center, Qingdao, China
| | - Shan Liu
- Innovation Platform of Marine Drug Screening and Evaluation, Qingdao Marine Science and Technology Center, Qingdao, China
| | - Yuting Xu
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
| | - Danling Gao
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
| | - Peizhe Lu
- Department of Neuroscience, University of Michigan, Ann Arbor, MI, United States
| | - Yuantao Liu
- Department of Endocrinology, Qilu Hospital (Qingdao), Cheeloo College of Medicine, Shandong University, Qingdao, China
| | - Guanghui Zhao
- Medical Laboratory Center, Qilu Hospital (Qingdao), Cheeloo College of Medicine, Shandong University, Qingdao, China
- Oncology Laboratory, Qilu Hospital (Qingdao), Cheeloo College of Medicine, Shandong University, Qingdao, China
| | - Lihong Wu
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
| | - Chenyang Zhao
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
| | - Jinbo Yang
- Key Laboratory of Marine Drugs, Ministry of Education of China, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China
- Innovation Platform of Marine Drug Screening and Evaluation, Qingdao Marine Science and Technology Center, Qingdao, China
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5
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Kristiansen CK, Furriol J, Chen A, Sullivan GJ, Bindoff LA, Liang KX. Deoxyribonucleoside treatment rescues EtBr-induced mtDNA depletion in iPSC-derived neural stem cells with POLG mutations. FASEB J 2023; 37:e23139. [PMID: 37584631 DOI: 10.1096/fj.202300650rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 07/26/2023] [Accepted: 07/31/2023] [Indexed: 08/17/2023]
Abstract
Mutations in POLG, the gene encoding the catalytic subunit of the mitochondrial DNA (mtDNA) polymerase gamma (Pol-γ), lead to diseases driven by defective mtDNA maintenance. Despite being the most prevalent cause of mitochondrial disease, treatments for POLG-related disorders remain elusive. In this study, we used POLG patient-induced pluripotent stem cell (iPSC)-derived neural stem cells (iNSCs), one homozygous for the POLG mutation c.2243G>C and one compound heterozygous with c.2243G>C and c.1399G>A, and treated these iNSCs with ethidium bromide (EtBr) to study the rate of depletion and repopulation of mtDNA. In addition, we investigated the effect of deoxyribonucleoside (dNs) supplementation on mtDNA maintenance during EtBr treatment and post-treatment repopulation in the same cells. EtBr-induced mtDNA depletion occurred at a similar rate in both patient and control iNSCs, however, restoration of mtDNA levels was significantly delayed in iNSCs carrying the compound heterozygous POLG mutations. In contrast, iNSC with the homozygous POLG mutation recovered their mtDNA at a rate similar to controls. When we treated cells with dNs, we found that this reduced EtBr-induced mtDNA depletion and significantly increased repopulation rates in both patient iNSCs. These observations are consistent with the hypothesis that mutations in POLG impair mtDNA repopulation also within intact neural lineage cells and suggest that those with compound heterozygous mutation have a more severe defect of mtDNA synthesis. Our findings further highlight the potential for dNs to improve mtDNA replication in the presence of POLG mutations, suggesting that this may offer a new therapeutic modality for mitochondrial diseases caused by disturbed mtDNA homeostasis.
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Affiliation(s)
- Cecilie Katrin Kristiansen
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
- Neuro-SysMed, Center of Excellence for Clinical Research in Neurological Diseases, Haukeland University Hospital, Bergen, Norway
| | - Jessica Furriol
- Department of Medicine, Haukeland University Hospital, Bergen, Norway
| | - Anbin Chen
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
- Department of Neurosurgery, Xinhua Hospital Affiliated with Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Gareth John Sullivan
- Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway
- Institute of Immunology, Oslo University Hospital, Oslo, Norway
- Department of Pediatric Research, Oslo University Hospital, Oslo, Norway
| | - Laurence A Bindoff
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
- Department of Neurology, Haukeland University Hospital, Bergen, Norway
- National Advisory Unit for Congenital Metabolic Diseases, Oslo University Hospital, Oslo, Norway
| | - Kristina Xiao Liang
- Department of Clinical Medicine, University of Bergen, Bergen, Norway
- Neuro-SysMed, Center of Excellence for Clinical Research in Neurological Diseases, Haukeland University Hospital, Bergen, Norway
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6
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Kozhukhar N, Alexeyev MF. 35 Years of TFAM Research: Old Protein, New Puzzles. BIOLOGY 2023; 12:823. [PMID: 37372108 DOI: 10.3390/biology12060823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 05/29/2023] [Accepted: 06/03/2023] [Indexed: 06/29/2023]
Abstract
Transcription Factor A Mitochondrial (TFAM), through its contributions to mtDNA maintenance and expression, is essential for cellular bioenergetics and, therefore, for the very survival of cells. Thirty-five years of research on TFAM structure and function generated a considerable body of experimental evidence, some of which remains to be fully reconciled. Recent advancements allowed an unprecedented glimpse into the structure of TFAM complexed with promoter DNA and TFAM within the open promoter complexes. These novel insights, however, raise new questions about the function of this remarkable protein. In our review, we compile the available literature on TFAM structure and function and provide some critical analysis of the available data.
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Affiliation(s)
- Natalya Kozhukhar
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, AL 36688, USA
| | - Mikhail F Alexeyev
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, AL 36688, USA
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7
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Abstract
In the course of its short history, mitochondrial DNA (mtDNA) has made a long journey from obscurity to the forefront of research on major biological processes. mtDNA alterations have been found in all major disease groups, and their significance remains the subject of intense research. Despite remarkable progress, our understanding of the major aspects of mtDNA biology, such as its replication, damage, repair, transcription, maintenance, etc., is frustratingly limited. The path to better understanding mtDNA and its role in cells, however, remains torturous and not without errors, which sometimes leave a long trail of controversy behind them. This review aims to provide a brief summary of our current knowledge of mtDNA and highlight some of the controversies that require attention from the mitochondrial research community.
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Affiliation(s)
- Inna Shokolenko
- Department of Biomedical Sciences, Pat Capps Covey College of Allied Health Professions, University of South Alabama, Mobile, AL 36688, USA
| | - Mikhail Alexeyev
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, AL 36688, USA
- Correspondence:
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8
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Bryant JD, Lei Y, VanPortfliet JJ, Winters AD, West AP. Assessing Mitochondrial DNA Release into the Cytosol and Subsequent Activation of Innate Immune-related Pathways in Mammalian Cells. Curr Protoc 2022; 2:e372. [PMID: 35175686 PMCID: PMC8986093 DOI: 10.1002/cpz1.372] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Mitochondria have emerged as key drivers of mammalian innate immune responses, functioning as signaling hubs to trigger inflammation and orchestrating metabolic switches required for phagocyte activation. Mitochondria also contain damage-associated molecular patterns (DAMPs), molecules that share similarity with pathogen-associated molecular patterns (PAMPs) and can engage innate immune sensors to drive inflammation. The aberrant release of mitochondrial DAMPs during cellular stress and injury is an increasingly recognized trigger of inflammatory responses in human diseases. Mitochondrial DNA (mtDNA) is a particularly potent DAMP that engages multiple innate immune sensors, although mounting evidence suggests that cytosolic mtDNA is primarily detected via the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. cGAS and STING are widely expressed in mammalian cells and serve as key regulators of type I interferon and cytokine expression in both infectious and inflammatory diseases. Despite growing roles for the mtDNA-cGAS-STING axis in human disease, assays to quantify mtDNA release into the cytosol and approaches to link mtDNA to cGAS-STING signaling are not standardized, which increases the possibility for experimental artifacts and misinterpretation of data. Here, we present a series of protocols for assaying the release of mtDNA into the cytosol and subsequent activation of innate immune signaling in mammalian cells. We highlight genetic and pharmacological approaches to induce and inhibit mtDNA release from mitochondria. We also describe immunofluorescence microscopy and cellular fractionation assays to visualize morphological changes in mtDNA and quantify mtDNA accumulation in the cytosol. Finally, we include protocols to examine mtDNA-dependent cGAS-STING activation by RT-qPCR and western blotting. These methods can be performed with standard laboratory equipment and are highly adaptable to a wide range of mammalian cell types. They will permit researchers working across the spectrum of biological and biomedical sciences to accurately and reproducibly measure cytosolic mtDNA release and resulting innate immune responses. © 2022 Wiley Periodicals LLC. Basic Protocol 1: siRNA-mediated knockdown of TFAM to induce mtDNA instability, cytosolic release, and activation of the cGAS-STING pathway Alternate Protocol: Pharmacological induction of mtDNA release and cGAS-STING activation using ABT-737 and Q-VD-OPH Basic Protocol 2: Isolation and quantitation of DNA from cytosolic, mitochondrial, and nuclear fractions Basic Protocol 3: Pharmacological inhibition of mtDNA replication and release.
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Affiliation(s)
- Joshua D. Bryant
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX,These authors contributed equally
| | - Yuanjiu Lei
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX,These authors contributed equally
| | - Jordyn J. VanPortfliet
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX
| | - Ashley D. Winters
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX
| | - A. Phillip West
- Department of Microbial Pathogenesis and Immunology, College of Medicine, Texas A&M University, Bryan, TX,Corresponding author:
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9
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Inatomi T, Matsuda S, Ishiuchi T, Do Y, Nakayama M, Abe S, Kasho K, Wanrooij S, Nakada K, Ichiyanagi K, Sasaki H, Yasukawa T, Kang D. TFB2M and POLRMT are essential for mammalian mitochondrial DNA replication. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2021; 1869:119167. [PMID: 34744028 DOI: 10.1016/j.bbamcr.2021.119167] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 10/13/2021] [Accepted: 10/13/2021] [Indexed: 12/24/2022]
Abstract
Two classes of replication intermediates have been observed from mitochondrial DNA (mtDNA) in many mammalian tissue and cells with two-dimensional agarose gel electrophoresis. One is assigned to leading-strand synthesis in the absence of synchronous lagging-strand synthesis (strand-asynchronous replication), and the other has properties of coupled leading- and lagging-strand synthesis (strand-coupled replication). While strand-asynchronous replication is primed by long noncoding RNA synthesized from a defined transcription initiation site, little is known about the commencement of strand-coupled replication. To investigate it, we attempted to abolish strand-asynchronous replication in cultured human cybrid cells by knocking out the components of the transcription initiation complexes, mitochondrial transcription factor B2 (TFB2M/mtTFB2) and mitochondrial RNA polymerase (POLRMT/mtRNAP). Unexpectedly, removal of either protein resulted in complete mtDNA loss, demonstrating for the first time that TFB2M and POLRMT are indispensable for the maintenance of human mtDNA. Moreover, a lack of TFB2M could not be compensated for by mitochondrial transcription factor B1 (TFB1M/mtTFB1). These findings indicate that TFB2M and POLRMT are crucial for the priming of not only strand-asynchronous but also strand-coupled replication, providing deeper insights into the molecular basis of mtDNA replication initiation.
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Affiliation(s)
- Teppei Inatomi
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Shigeru Matsuda
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan; Department of Modomics Biology and Medicine, Institute of Development, Aging and Cancer, Tohoku University, 4-1 Seiryocho, Aoba-ku, Sendai-shi, Miyagi 980-8575, Japan
| | - Takashi Ishiuchi
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Yura Do
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Masunari Nakayama
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Shusaku Abe
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Kazutoshi Kasho
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Sjoerd Wanrooij
- Department of Medical Biochemistry and Biophysics, Umeå University, Umeå, Sweden
| | - Kazuto Nakada
- Faculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba-shi, Ibaraki 305-8572, Japan
| | - Kenji Ichiyanagi
- Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi 464-8601, Japan
| | - Hiroyuki Sasaki
- Division of Epigenomics and Development, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
| | - Takehiro Yasukawa
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan; Department of Pathology and Oncology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
| | - Dongchon Kang
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka-shi, Fukuoka 812-8582, Japan
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10
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Neueder A, Orth M. Mitochondrial biology and the identification of biomarkers of Huntington's disease. Neurodegener Dis Manag 2020; 10:243-255. [PMID: 32746707 DOI: 10.2217/nmt-2019-0033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Apart from finding novel compounds for treating Huntington's disease (HD) an important challenge at present consists in finding reliable read-outs or biomarkers that reflect key biological processes involved in HD pathogenesis. The core elements of HD biology, for example, HTT RNA levels or protein species can serve as biomarker, as could measures from biological systems or pathways in which Huntingtin plays an important role. Here we review the evidence for the involvement of mitochondrial biology in HD. The most consistent findings pertain to mitochondrial quality control, for example, fission/fusion. However, a convincing mitochondrial signature with biomarker potential is yet to emerge. This requires more research including in peripheral sources of human material, such as blood, or skeletal muscle.
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Affiliation(s)
| | - Michael Orth
- Department of Neurology, Ulm University, Ulm, Germany.,SwissHuntington's Disease Centre, Neurozentrum Siloah, Worbstr. 312, 3073 Gümligenbei Bern, Switzerland
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11
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de Oliveira VC, Gomes Mariano Junior C, Belizário JE, Krieger JE, Fernandes Bressan F, Roballo KCS, Fantinato-Neto P, Meirelles FV, Chiaratti MR, Concordet JP, Ambrósio CE. Characterization of post-edited cells modified in the TFAM gene by CRISPR/Cas9 technology in the bovine model. PLoS One 2020; 15:e0235856. [PMID: 32649732 PMCID: PMC7351154 DOI: 10.1371/journal.pone.0235856] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Accepted: 06/23/2020] [Indexed: 12/21/2022] Open
Abstract
Gene editing in large animal models for future applications in translational medicine and food production must be deeply investigated for an increase of knowledge. The mitochondrial transcription factor A (TFAM) is a member of the HMGB subfamily that binds to mtDNA promoters. This gene maintains mtDNA, and it is essential for the initiation of mtDNA transcription. Lately, we generated a new cell line through the disruption of the TFAM gene in bovine fibroblast cells by CRISPR/Cas 9 technology. We showed that the CRISPR/Cas9 design was efficient through the generation of heterozygous mutant clones. In this context, once this gene regulates the mtDNA replication specificity, the study aimed to determine if the post-edited cells are capable of in vitro maintenance and assess if they present changes in mtDNA copies and mitochondrial membrane potential after successive passages in culture. The post-edited cells were expanded in culture, and we performed a growth curve, doubling time, cell viability, mitochondrial DNA copy number, and mitochondrial membrane potential assays. The editing process did not make cell culture unfeasible, even though cell growth rate and viability were decreased compared to control since we observed the cells grow well when cultured in a medium supplemented with uridine and pyruvate. They also exhibited a classical fibroblastoid appearance. The RT-qPCR to determine the mtDNA copy number showed a decrease in the edited clones compared to the non-edited ones (control) in different cell passages. Cell staining with Mitotracker Green and red suggests a reduction in red fluorescence in the edited cells compared to the non-edited cells. Thus, through characterization, we demonstrated that the TFAM gene is critical to mitochondrial maintenance due to its interference in the stability of the mitochondrial DNA copy number in different cell passages and membrane potential confirming the decrease in mitochondrial activity in cells edited in heterozygosis.
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Affiliation(s)
- Vanessa Cristina de Oliveira
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
- * E-mail: ,
| | - Clésio Gomes Mariano Junior
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
| | - José Ernesto Belizário
- Department of Pharmacology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - José Eduardo Krieger
- Laboratory of Genetics and Molecular Cardiology, Heart Institute, University of São Paulo Medical School, São Paulo, Brazil
| | - Fabiana Fernandes Bressan
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
| | - Kelly Cristine Santos Roballo
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
- School of Pharmacy at College of Health Sciences, University of Wyoming, Laramie, WY, United States of America
| | - Paulo Fantinato-Neto
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
| | - Flávio Vieira Meirelles
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
| | | | - Jean-Paul Concordet
- Laboratoire Structure et Instabilité des Génomes, Museum National d’Histoire Naturelle, INSERM U1154, CNRS UMR7196, Paris, France
| | - Carlos Eduardo Ambrósio
- Department of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, São Paulo, Brazil
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12
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Mitochondria as target to inhibit proliferation and induce apoptosis of cancer cells: the effects of doxycycline and gemcitabine. Sci Rep 2020; 10:4363. [PMID: 32152409 PMCID: PMC7063048 DOI: 10.1038/s41598-020-61381-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Accepted: 02/25/2020] [Indexed: 01/09/2023] Open
Abstract
Doxycycline has anti-tumour effects in a range of tumour systems. The aims of this study were to define the role mitochondria play in this process and examine the potential of doxycycline in combination with gemcitabine. We studied the adenocarcinoma cell line A549, its mitochondrial DNA-less derivative A549 ρ° and cultured fibroblasts. Treatment with doxycycline for 5 days resulted in a decrease of mitochondrial-encoded proteins, respiration and membrane potential, and an increase of reactive oxygen species in A549 cells and fibroblasts, but fibroblasts were less affected. Doxycycline slowed proliferation of A549 cells by 35%. Cellular ATP levels did not change. Doxycycline alone had no effect on apoptosis; however, in combination with gemcitabine given during the last 2 days of treatment, doxycycline increased caspase 9 and 3/7 activities, resulting in a further decrease of surviving A549 cells by 59% and of fibroblasts by 24% compared to gemcitabine treatment alone. A549 ρ° cells were not affected by doxycycline. Key effects of doxycycline observed in A549 cells, such as the decrease of mitochondrial-encoded proteins and surviving cells were also seen in the cancer cell lines COLO357 and HT29. Our results suggest that doxycycline suppresses cancer cell proliferation and primes cells for apoptosis by gemcitabine.
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13
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Kotrys AV, Cysewski D, Czarnomska SD, Pietras Z, Borowski LS, Dziembowski A, Szczesny RJ. Quantitative proteomics revealed C6orf203/MTRES1 as a factor preventing stress-induced transcription deficiency in human mitochondria. Nucleic Acids Res 2019; 47:7502-7517. [PMID: 31226201 PMCID: PMC6698753 DOI: 10.1093/nar/gkz542] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 06/05/2019] [Accepted: 06/13/2019] [Indexed: 12/18/2022] Open
Abstract
Maintenance of mitochondrial gene expression is crucial for cellular homeostasis. Stress conditions may lead to a temporary reduction of mitochondrial genome copy number, raising the risk of insufficient expression of mitochondrial encoded genes. Little is known how compensatory mechanisms operate to maintain proper mitochondrial transcripts levels upon disturbed transcription and which proteins are involved in them. Here we performed a quantitative proteomic screen to search for proteins that sustain expression of mtDNA under stress conditions. Analysis of stress-induced changes of the human mitochondrial proteome led to the identification of several proteins with poorly defined functions among which we focused on C6orf203, which we named MTRES1 (Mitochondrial Transcription Rescue Factor 1). We found that the level of MTRES1 is elevated in cells under stress and we show that this upregulation of MTRES1 prevents mitochondrial transcript loss under perturbed mitochondrial gene expression. This protective effect depends on the RNA binding activity of MTRES1. Functional analysis revealed that MTRES1 associates with mitochondrial RNA polymerase POLRMT and acts by increasing mitochondrial transcription, without changing the stability of mitochondrial RNAs. We propose that MTRES1 is an example of a protein that protects the cell from mitochondrial RNA loss during stress.
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Affiliation(s)
- Anna V Kotrys
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Dominik Cysewski
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Sylwia D Czarnomska
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland
| | - Zbigniew Pietras
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland.,Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Lukasz S Borowski
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland.,Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Warsaw 02-106, Poland
| | - Andrzej Dziembowski
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland.,Faculty of Biology, Institute of Genetics and Biotechnology, University of Warsaw, Warsaw 02-106, Poland
| | - Roman J Szczesny
- Institute of Biochemistry and Biophysics Polish Academy of Sciences, Warsaw 02-106, Poland
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14
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Kozhukhar N, Alexeyev MF. Limited predictive value of TFAM in mitochondrial biogenesis. Mitochondrion 2019; 49:156-165. [PMID: 31419493 DOI: 10.1016/j.mito.2019.08.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Revised: 06/23/2019] [Accepted: 08/12/2019] [Indexed: 12/16/2022]
Abstract
Mitochondrial transcription factor A (TFAM) plays an important role in mitochondrial DNA (mtDNA) transcription and replication. In some experimental settings, TFAM expression parallels parameters of mitochondrial biogenesis, which led to a widespread acceptance of TFAM as marker of mitochondrial biogenesis. We modulated TFAM expression in several experimental systems and observed that it fails to consistently parallel mtDNA copy number and expression of mtDNA-encoded polypeptides. We suggest that the use of TFAM as a marker of mitochondrial biogenesis should be avoided outside of systems in which its performance has been carefully validated.
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Affiliation(s)
- Natalya Kozhukhar
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, AL 36688, USA.
| | - Mikhail F Alexeyev
- Department of Physiology and Cell Biology, University of South Alabama, Mobile, AL 36688, USA.
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15
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The effects of rooibos (Aspalathus linearis) on 3T3-L1 preadipocytes after the induction of mitochondrial dysfunction. J Funct Foods 2019. [DOI: 10.1016/j.jff.2019.02.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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16
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RAD51C/XRCC3 Facilitates Mitochondrial DNA Replication and Maintains Integrity of the Mitochondrial Genome. Mol Cell Biol 2018; 38:MCB.00489-17. [PMID: 29158291 DOI: 10.1128/mcb.00489-17] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 11/10/2017] [Indexed: 12/12/2022] Open
Abstract
Mechanisms underlying mitochondrial genome maintenance have recently gained wide attention, as mutations in mitochondrial DNA (mtDNA) lead to inherited muscular and neurological diseases, which are linked to aging and cancer. It was previously reported that human RAD51, RAD51C, and XRCC3 localize to mitochondria upon oxidative stress and are required for the maintenance of mtDNA stability. Since RAD51 and RAD51 paralogs are spontaneously imported into mitochondria, their precise role in mtDNA maintenance under unperturbed conditions remains elusive. Here, we show that RAD51C/XRCC3 is an additional component of the mitochondrial nucleoid having nucleus-independent roles in mtDNA maintenance. RAD51C/XRCC3 localizes to the mtDNA regulatory regions in the D-loop along with the mitochondrial polymerase POLG, and this recruitment is dependent upon Twinkle helicase. Moreover, upon replication stress, RAD51C and XRCC3 are further enriched at the mtDNA mutation hot spot region D310. Notably, the absence of RAD51C/XRCC3 affects the stability of POLG on mtDNA. As a consequence, RAD51C/XRCC3-deficient cells exhibit reduced mtDNA synthesis and increased lesions in the mitochondrial genome, leading to overall unhealthy mitochondria. Together, these findings lead to the proposal of a mechanism for a direct role of RAD51C/XRCC3 in maintaining mtDNA integrity under replication stress conditions.
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17
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Qiao L, Ru G, Mao Z, Wang C, Nie Z, Li Q, Huang-Yang Y, Zhu L, Liang X, Yu J, Jiang P. Mitochondrial DNA depletion, mitochondrial mutations and high TFAM expression in hepatocellular carcinoma. Oncotarget 2017; 8:84373-84383. [PMID: 29137431 PMCID: PMC5663603 DOI: 10.18632/oncotarget.21033] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Accepted: 08/17/2017] [Indexed: 12/16/2022] Open
Abstract
We investigated the role of mitochondrial genetic alterations in hepatocellular carcinoma by directly comparing the mitochondrial genomes of 86 matched pairs of HCC and non-tumor liver samples. Substitutions in 637 mtDNA sites were detected, comprising 89.80% transitions and 6.60% transversions. Forty-six somatic variants, including 15 novel mutations, were identified in 40.70% of tumor tissues. Of those, 21 were located in the non-coding region and 25 in the protein-coding region. Twenty-two somatic nonsynonymous changes were identified as putative pathogenic variants, including 4 truncating mutations produced by three frameshifts (MT-ATP6 8628 insC; MT-ND5 13475 T-del, and MT-CYB 14984 insA) and 1 nonsense mutation in MT-CO3 9253 G>A. Among the somatic variants, only m.13676 A>G (MT-ND5), found in only 1 tumor, was heteroplasmic. Both inherited and somatic variants were predominately located in the D-loop region and the MT-ND5 gene. Tumor/non-tumor paired analysis showed that 69% of HCC samples contained significantly reduced mtDNA, compared with 49.0% of non-tumor counterparts. In 81.40% of HCC samples, mitochondrial transcription factor A (TFAM) was enriched in tumor cells but not in adjacent non-tumor cells. Neither mtDNA depletion nor TFAM overexpression correlated with the degree of cell differentiation, though TFAM expression correlated with tumor size.
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Affiliation(s)
- Lihua Qiao
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Guoqing Ru
- Department of Pathology, The Zhejiang Provincial People's Hospital, Hangzhou, China
| | - Zhuochao Mao
- Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.,Department of Surgical Oncology, First Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, China
| | - Chenghui Wang
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Zhipeng Nie
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Qiang Li
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Yiyi Huang-Yang
- Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Ling Zhu
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Xiaoyang Liang
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
| | - Jialing Yu
- Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.,School of Public Health, Zhejiang University, Hangzhou, China
| | - Pingping Jiang
- Division of Medical Genetics and Genomics, The Children's Hospital, Zhejiang University School of Medicine, Hangzhou, China.,Institute of Genetics, Zhejiang University and Department of Genetics, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China
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18
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Tetramethylpyrazine blocks TFAM degradation and up-regulates mitochondrial DNA copy number by interacting with TFAM. Biosci Rep 2017; 37:BSR20170319. [PMID: 28465355 PMCID: PMC5434891 DOI: 10.1042/bsr20170319] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Revised: 04/25/2017] [Accepted: 05/02/2017] [Indexed: 01/26/2023] Open
Abstract
The natural small molecule compound: 2,3,5,6-tetramethylpyrazine (TMP), is a major component of the Chinese medicine Chuanxiong, which has wide clinical applications in dilating blood vessels, inhibiting platelet aggregation and treating thrombosis. Recent work suggests that TMP is also an antitumour agent. Despite its chemotherapeutic potential, the mechanism(s) underlying TMP action are unknown. Herein, we demonstrate that TMP binds to mitochondrial transcription factor A (TFAM) and blocks its degradation by the mitochondrial Lon protease. TFAM is a key regulator of mtDNA replication, transcription and transmission. Our previous work showed that when TFAM is not bound to DNA, it is rapidly degraded by the ATP-dependent Lon protease, which is essential for mitochondrial proteostasis. In cultured cells, TMP specifically blocks Lon-mediated degradation of TFAM, leading to TFAM accumulation and subsequent up-regulation of mtDNA content in cells with substantially low levels of mtDNA. In vitro protease assays show that TMP does not directly inhibit mitochondrial Lon, rather interacts with TFAM and blocks degradation. Pull-down assays show that biotinylated TMP interacts with TFAM. These findings suggest a novel mechanism whereby TMP stabilizes TFAM and confers resistance to Lon-mediated degradation, thereby promoting mtDNA up-regulation in cells with low mtDNA content.
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19
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Alán L, Špaček T, Pajuelo Reguera D, Jabůrek M, Ježek P. Mitochondrial nucleoid clusters protect newly synthesized mtDNA during Doxorubicin- and Ethidium Bromide-induced mitochondrial stress. Toxicol Appl Pharmacol 2016; 302:31-40. [PMID: 27102948 DOI: 10.1016/j.taap.2016.04.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 03/31/2016] [Accepted: 04/14/2016] [Indexed: 10/21/2022]
Abstract
Mitochondrial DNA (mtDNA) is compacted in ribonucleoprotein complexes called nucleoids, which can divide or move within the mitochondrial network. Mitochondrial nucleoids are able to aggregate into clusters upon reaction with intercalators such as the mtDNA depletion agent Ethidium Bromide (EB) or anticancer drug Doxorobicin (DXR). However, the exact mechanism of nucleoid clusters formation remains unknown. Resolving these processes may help to elucidate the mechanisms of DXR-induced cardiotoxicity. Therefore, we addressed the role of two key nucleoid proteins; mitochondrial transcription factor A (TFAM) and mitochondrial single-stranded binding protein (mtSSB); in the formation of mitochondrial nucleoid clusters during the action of intercalators. We found that both intercalators cause numerous aberrations due to perturbing their native status. By blocking mtDNA replication, both agents also prevented mtDNA association with TFAM, consequently causing nucleoid aggregation into large nucleoid clusters enriched with TFAM, co-existing with the normal nucleoid population. In the later stages of intercalation (>48h), TFAM levels were reduced to 25%. In contrast, mtSSB was released from mtDNA and freely distributed within the mitochondrial network. Nucleoid clusters mostly contained nucleoids with newly replicated mtDNA, however the nucleoid population which was not in replication mode remained outside the clusters. Moreover, the nucleoid clusters were enriched with p53, an anti-oncogenic gatekeeper. We suggest that mitochondrial nucleoid clustering is a mechanism for protecting nucleoids with newly replicated DNA against intercalators mediating genotoxic stress. These results provide new insight into the common mitochondrial response to mtDNA stress and can be implied also on DXR-induced mitochondrial cytotoxicity.
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Affiliation(s)
- Lukáš Alán
- Dept. 75, Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i, Czech Republic.
| | - Tomáš Špaček
- Dept. 75, Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i, Czech Republic
| | - David Pajuelo Reguera
- Dept. 75, Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i, Czech Republic
| | - Martin Jabůrek
- Dept. 75, Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i, Czech Republic
| | - Petr Ježek
- Dept. 75, Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i, Czech Republic
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20
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Reznik E, Miller ML, Şenbabaoğlu Y, Riaz N, Sarungbam J, Tickoo SK, Al-Ahmadie HA, Lee W, Seshan VE, Hakimi AA, Sander C. Mitochondrial DNA copy number variation across human cancers. eLife 2016; 5:e10769. [PMID: 26901439 PMCID: PMC4775221 DOI: 10.7554/elife.10769] [Citation(s) in RCA: 341] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 01/08/2016] [Indexed: 12/18/2022] Open
Abstract
Mutations, deletions, and changes in copy number of mitochondrial DNA (mtDNA), are observed throughout cancers. Here, we survey mtDNA copy number variation across 22 tumor types profiled by The Cancer Genome Atlas project. We observe a tendency for some cancers, especially of the bladder, breast, and kidney, to be depleted of mtDNA, relative to matched normal tissue. Analysis of genetic context reveals an association between incidence of several somatic alterations, including IDH1 mutations in gliomas, and mtDNA content. In some but not all cancer types, mtDNA content is correlated with the expression of respiratory genes, and anti-correlated to the expression of immune response and cell-cycle genes. In tandem with immunohistochemical evidence, we find that some tumors may compensate for mtDNA depletion to sustain levels of respiratory proteins. Our results highlight the extent of mtDNA copy number variation in tumors and point to related therapeutic opportunities.
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Affiliation(s)
- Ed Reznik
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Martin L Miller
- Cancer Research UK, Cambridge Institute, Cambridge, United Kingdom
| | - Yasin Şenbabaoğlu
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Nadeem Riaz
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Judy Sarungbam
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Satish K Tickoo
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Hikmat A Al-Ahmadie
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, United States
| | - William Lee
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
- Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Venkatraman E Seshan
- Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, United States
| | - A Ari Hakimi
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
- Urology Service, Department of Surgery, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Chris Sander
- Computational Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
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21
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Nouws J, Goswami AV, Bestwick M, McCann BJ, Surovtseva YV, Shadel GS. Mitochondrial Ribosomal Protein L12 Is Required for POLRMT Stability and Exists as Two Forms Generated by Alternative Proteolysis during Import. J Biol Chem 2015; 291:989-97. [PMID: 26586915 DOI: 10.1074/jbc.m115.689299] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Indexed: 01/21/2023] Open
Abstract
To translate the 13 mtDNA-encoded mRNAs involved in oxidative phosphorylation (OXPHOS), mammalian mitochondria contain a dedicated set of ribosomes comprising rRNAs encoded by the mitochondrial genome and mitochondrial ribosomal proteins (MRPs) that are encoded by nuclear genes and imported into the matrix. In addition to their role in the ribosome, several MRPs have auxiliary functions or have been implicated in other cellular processes like cell cycle regulation and apoptosis. For example, we have shown that human MRPL12 binds and activates mitochondrial RNA polymerase (POLRMT), and hence has distinct functions in the ribosome and mtDNA transcription. Here we provide concrete evidence that there are two mature forms of mammalian MRPL12 that are generated by a two-step cleavage during import, involving efficient cleavage by mitochondrial processing protease and a second inefficient or regulated cleavage by mitochondrial intermediate protease. We also show that knock-down of MRPL12 by RNAi results in instability of POLRMT, but not other primary mitochondrial transcription components, and a corresponding decrease in mitochondrial transcription rates. Knock-down of MRPL10, the binding partner of MRPL12 in the ribosome, results in selective degradation of the mature long form of MRPL12, but has no effect on POLRMT. We propose that the two forms of MRPL12 are involved in homeostatic regulation of mitochondrial transcription and ribosome biogenesis that likely contribute to cell cycle, growth regulation, and longevity pathways to which MRPL12 has been linked.
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Affiliation(s)
| | | | - Megan Bestwick
- From the Departments of Pathology and the Department of Chemistry, Linfield College, McMinnville, Oregon 97128, and
| | - Beverly Jo McCann
- From the Departments of Pathology and the Department of Biology, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | | | - Gerald S Shadel
- From the Departments of Pathology and Genetics, Yale School of Medicine, New Haven, Connecticut 06520-8023,
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22
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Huang WC, Tseng TY, Chen YT, Chang CC, Wang ZF, Wang CL, Hsu TN, Li PT, Chen CT, Lin JJ, Lou PJ, Chang TC. Direct evidence of mitochondrial G-quadruplex DNA by using fluorescent anti-cancer agents. Nucleic Acids Res 2015; 43:10102-13. [PMID: 26487635 PMCID: PMC4666356 DOI: 10.1093/nar/gkv1061] [Citation(s) in RCA: 57] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 09/30/2015] [Indexed: 11/26/2022] Open
Abstract
G-quadruplex (G4) is a promising target for anti-cancer treatment. In this paper, we provide the first evidence supporting the presence of G4 in the mitochondrial DNA (mtDNA) of live cells. The molecular engineering of a fluorescent G4 ligand, 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC), can change its major cellular localization from the nucleus to the mitochondria in cancer cells, while remaining primarily in the cytoplasm of normal cells. A number of BMVC derivatives with sufficient mitochondrial uptake can induce cancer cell death without damaging normal cells. Fluorescence studies of these anti-cancer agents in live cells and in isolated mitochondria from HeLa cells have demonstrated that their major target is mtDNA. In this study, we use fluorescence lifetime imaging microscopy to verify the existence of mtDNA G4s in live cells. Bioactivity studies indicate that interactions between these anti-cancer agents and mtDNA G4 can suppress mitochondrial gene expression. This work underlines the importance of fluorescence in the monitoring of drug-target interactions in cells and illustrates the emerging development of drugs in which mtDNA G4 is the primary target.
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Affiliation(s)
- Wei-Chun Huang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Ting-Yuan Tseng
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Ying-Ting Chen
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Cheng-Chung Chang
- Institute of Biomedical Engineering, National Chung-Hsing University, Taichung 40227, Taiwan
| | - Zi-Fu Wang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Chiung-Lin Wang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
| | - Tsu-Ning Hsu
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | - Pei-Tzu Li
- Department of Biochemical Science and Technology, National Taiwan University, Taipei 10617, Taiwan
| | - Chin-Tin Chen
- Department of Biochemical Science and Technology, National Taiwan University, Taipei 10617, Taiwan
| | - Jing-Jer Lin
- Institute of Biochemistry and Molecular Biology, National Taiwan University College of Medicine, Taipei 10051, Taiwan
| | - Pei-Jen Lou
- Department of Otolaryngology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei 10051, Taiwan
| | - Ta-Chau Chang
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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23
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Sayas E, García-López F, Serrano R. Toxicity, mutagenicity and transport inSaccharomyces cerevisiaeof three popular DNA intercalating fluorescent dyes. Yeast 2015; 32:595-606. [DOI: 10.1002/yea.3081] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 06/11/2015] [Accepted: 06/16/2015] [Indexed: 11/10/2022] Open
Affiliation(s)
- Enric Sayas
- Instituto de Biología Molecular y Celular de Plantas; Universidad Politécnica de Valencia-CSIC; Valencia Spain
| | - Federico García-López
- Instituto de Biología Molecular y Celular de Plantas; Universidad Politécnica de Valencia-CSIC; Valencia Spain
| | - Ramón Serrano
- Instituto de Biología Molecular y Celular de Plantas; Universidad Politécnica de Valencia-CSIC; Valencia Spain
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24
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Zhang F, Qi Y, Zhou K, Zhang G, Linask K, Xu H. The cAMP phosphodiesterase Prune localizes to the mitochondrial matrix and promotes mtDNA replication by stabilizing TFAM. EMBO Rep 2015; 16:520-7. [PMID: 25648146 PMCID: PMC4388618 DOI: 10.15252/embr.201439636] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 01/06/2015] [Accepted: 01/08/2015] [Indexed: 12/21/2022] Open
Abstract
Compartmentalized cAMP signaling regulates mitochondrial dynamics, morphology, and oxidative phosphorylation. However, regulators of the mitochondrial cAMP pathway, and its broad impact on organelle function, remain to be explored. Here, we report that Drosophila Prune is a cyclic nucleotide phosphodiesterase that localizes to the mitochondrial matrix. Knocking down prune in cultured cells reduces mitochondrial transcription factor A (TFAM) and mitochondrial DNA (mtDNA) levels. Our data suggest that Prune stabilizes TFAM and promotes mitochondrial DNA (mtDNA) replication through downregulation of mitochondrial cAMP signaling. In addition, our work demonstrates the prevalence of mitochondrial cAMP signaling in metazoan and its new role in mitochondrial biogenesis.
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Affiliation(s)
- Fan Zhang
- Laboratory of Molecular Genetics, National Heart, Lung and Blood Institute, Bethesda, MD, USA
| | - Yun Qi
- Laboratory of Molecular Genetics, National Heart, Lung and Blood Institute, Bethesda, MD, USA
| | - Kiet Zhou
- Laboratory of Molecular Genetics, National Heart, Lung and Blood Institute, Bethesda, MD, USA
| | - Guofeng Zhang
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA
| | - Kaari Linask
- Laboratory of Molecular Genetics, National Heart, Lung and Blood Institute, Bethesda, MD, USA
| | - Hong Xu
- Laboratory of Molecular Genetics, National Heart, Lung and Blood Institute, Bethesda, MD, USA
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25
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Hering T, Birth N, Taanman JW, Orth M. Selective striatal mtDNA depletion in end-stage Huntington's disease R6/2 mice. Exp Neurol 2015; 266:22-9. [PMID: 25682918 DOI: 10.1016/j.expneurol.2015.02.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2014] [Revised: 01/20/2015] [Accepted: 02/05/2015] [Indexed: 12/21/2022]
Abstract
In Huntington's disease (HD) the striatum and cortex seem particularly vulnerable. Mitochondrial dysfunction can also cause neurodegeneration with prominent striatal involvement very similar to HD. We first examined if mitochondrial biogenesis, mitochondrial DNA (mtDNA) transcription, and the implications for mitochondrial respiratory chain (MRC) assembly and function differ between the striatum and cortex compared with the whole brain average in the healthy mouse brain. We then examined the effects of the mutant huntingtin transgene in end-stage R6/2 mice. In wild-type mice, mitochondrial mass (citrate synthase levels, mtDNA copy number) was higher in the striatum than in the cortex or whole brain average. PGC-1α and TFAM mRNA levels were also higher in the striatum than the whole brain average and cortex. mRNA reserve for MRC Complex proteins was higher in the striatum and cortex. In addition, in the cortex a greater part of mitochondrial mass was dedicated to the generation of ATP by oxidative phosphorylation than in the striatum or on average in the brain. In the HD transgenic striatum there was selective mtDNA depletion without evidence that this translated to abnormalities of steady-state MRC function. Our data indicate that in mice the striatum differs from the cortex, or whole brain average, in potentially important aspects of mitochondrial biology. This may contribute to the increased vulnerability of the striatum to insults such as the HD mutation, causing selective striatal mtDNA depletion in end-stage R6/2 mice.
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Affiliation(s)
- Tanja Hering
- Department of Neurology, Ulm University, Germany
| | | | - Jan-Willem Taanman
- Department of Clinical Neurosciences, Institute of Neurology, University College London, London, UK
| | - Michael Orth
- Department of Neurology, Ulm University, Germany
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26
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Michel S, Canonne M, Arnould T, Renard P. Inhibition of mitochondrial genome expression triggers the activation of CHOP-10 by a cell signaling dependent on the integrated stress response but not the mitochondrial unfolded protein response. Mitochondrion 2015; 21:58-68. [PMID: 25643991 DOI: 10.1016/j.mito.2015.01.005] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 01/10/2015] [Accepted: 01/20/2015] [Indexed: 12/29/2022]
Abstract
Mitochondria-to-nucleus communication, known as retrograde signaling, is important to adjust the nuclear gene expression in response to organelle dysfunction. Among the transcription factors described to respond to mitochondrial stress, CHOP-10 is activated by respiratory chain inhibition, mitochondrial accumulation of unfolded proteins and mtDNA mutations. In this study, we show that altered/impaired expression of mtDNA induces CHOP-10 expression in a signaling pathway that depends on the eIF2α/ATF4 axis of the integrated stress response rather than on the mitochondrial unfolded protein response.
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Affiliation(s)
- Sebastien Michel
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences (NARILIS), University of Namur (UNamur), 61 rue de Bruxelles, 5000 Namur, Belgium
| | - Morgane Canonne
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences (NARILIS), University of Namur (UNamur), 61 rue de Bruxelles, 5000 Namur, Belgium
| | - Thierry Arnould
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences (NARILIS), University of Namur (UNamur), 61 rue de Bruxelles, 5000 Namur, Belgium
| | - Patricia Renard
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences (NARILIS), University of Namur (UNamur), 61 rue de Bruxelles, 5000 Namur, Belgium.
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27
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Wang G, Yang E, Mandhan I, Brinkmeyer-Langford CL, Cai JJ. Population-level expression variability of mitochondrial DNA-encoded genes in humans. Eur J Hum Genet 2014; 22:1093-9. [PMID: 24398800 DOI: 10.1038/ejhg.2013.293] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 10/22/2013] [Accepted: 11/09/2013] [Indexed: 12/28/2022] Open
Abstract
Human mitochondria contain multiple copies of a circular genome made up of double-stranded DNA (mtDNA) that encodes proteins involved in cellular respiration. Transcript abundance of mtDNA-encoded genes varies between human individuals, yet the level of variation in the general population has not been systematically assessed. In the present study, we revisited large-scale RNA sequencing data generated from lymphoblastoid cell lines of HapMap samples of European and African ancestry to estimate transcript abundance and quantify expression variation for mtDNA-encoded genes. In both populations, we detected up to over 100-fold difference in mtDNA gene expression between individuals. The marked variation was not due to differences in mtDNA copy number between individuals, but was shaped by the transcription of hundreds of nuclear genes. Many of these nuclear genes were co-expressed with one another, resulting in a module-enriched co-expression network. Significant correlations in expression between genes of the mtDNA and nuclear genomes were used to identify factors involved with the regulation of mitochondrial functions. In conclusion, we determined the baseline amount of variability in mtDNA gene expression in general human populations and cataloged a complete set of nuclear genes whose expression levels are correlated with those of mtDNA-encoded genes. Our findings will enable the integration of information from both mtDNA and nuclear genetic systems, and facilitate the discovery of novel regulatory pathways involving mitochondrial functions.
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Affiliation(s)
- Gang Wang
- Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA
| | - Ence Yang
- Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA
| | - Ishita Mandhan
- Electrical and Computer Engineering, Texas A&M University, College Station, TX, USA
| | | | - James J Cai
- 1] Veterinary Integrative Biosciences, Texas A&M University, College Station, TX, USA [2] Interdisciplinary Program in Genetics, Texas A&M University, College Station, TX, USA
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28
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Nacarelli T, Azar A, Sell C. Inhibition of mTOR Prevents ROS Production Initiated by Ethidium Bromide-Induced Mitochondrial DNA Depletion. Front Endocrinol (Lausanne) 2014; 5:122. [PMID: 25104948 PMCID: PMC4109433 DOI: 10.3389/fendo.2014.00122] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Accepted: 07/11/2014] [Indexed: 11/30/2022] Open
Abstract
The regulation of mitochondrial mass and DNA content involves a complex interaction between mitochondrial DNA replication machinery, functional components of the electron transport chain, selective clearance of mitochondria, and nuclear gene expression. In order to gain insight into cellular responses to mitochondrial stress, we treated human diploid fibroblasts with ethidium bromide at concentrations that induced loss of mitochondrial DNA over a period of 7 days. The decrease in mitochondrial DNA was accompanied by a reduction in steady state levels of the mitochondrial DNA binding protein, TFAM, a reduction in several electron transport chain protein levels, increased mitochondrial and total cellular ROS, and activation of p38 MAPK. However, there was an increase in mitochondrial mass and voltage dependent anion channel levels. In addition, mechanistic target of rapamycin (mTOR) activity, as judged by p70S6K targets, was decreased while steady state levels of p62/SQSTM1 and Parkin were increased. Treatment of cells with rapamycin created a situation in which cells were better able to adapt to the mitochondrial dysfunction, resulting in decreased ROS and increased cell viability but did not prevent the reduction in mitochondrial DNA. These effects may be due to a more efficient flux through the electron transport chain, increased autophagy, or enhanced AKT signaling, coupled with a reduced growth rate. Together, the results suggest that mTOR activity is affected by mitochondrial stress, which may be part of the retrograde signal system required for normal mitochondrial homeostasis.
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Affiliation(s)
- Timothy Nacarelli
- Department of Pathology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Ashley Azar
- Department of Pathology, Drexel University College of Medicine, Philadelphia, PA, USA
| | - Christian Sell
- Department of Pathology, Drexel University College of Medicine, Philadelphia, PA, USA
- *Correspondence: Christian Sell, Department of Pathology, Drexel University College of Medicine, 245 N 15th Street, Philadelphia, PA 19102, USA e-mail:
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29
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Chatre L, Ricchetti M. Large heterogeneity of mitochondrial DNA transcription and initiation of replication exposed by single-cell imaging. J Cell Sci 2012; 126:914-26. [PMID: 23239030 DOI: 10.1242/jcs.114322] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Mitochondrial DNA (mtDNA) replication and transcription are crucial for cell function, but these processes are poorly understood at the single-cell level. We describe a novel fluorescence in situ hybridization protocol, called mTRIP (mitochondrial transcription and replication imaging protocol), that reveals simultaneously mtDNA and RNA, and that can also be coupled to immunofluorescence for in situ protein examination. mTRIP reveals mitochondrial structures engaged in initiation of DNA replication by identification of a specific sequence in the regulatory D-loop, as well as unique transcription profiles in single human cells. We observe and quantify at least three classes of mitochondrial structures: (i) replication initiation active and transcript-positive (Ia-Tp); (ii) replication initiation silent and transcript-positive (Is-Tp); and (iii) replication initiation silent and transcript-negative (Is-Tn). Thus, individual mitochondria are dramatically heterogeneous within the same cell. Moreover, mTRIP exposes a mosaic of distinct nucleic acid patterns in the D-loop, including H-strand versus L-strand transcripts, and uncoupled rRNA transcription and mtDNA initiation of replication, which might have functional consequences in the regulation of the mtDNA. Finally, mTRIP identifies altered mtDNA processing in cells with unbalanced mtDNA content and function, including in human mitochondrial disorders. Thus, mTRIP reveals qualitative and quantitative alterations that provide additional tools for elucidating the dynamics of mtDNA processing in single cells and mitochondrial dysfunction in diseases.
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Affiliation(s)
- Laurent Chatre
- Institut Pasteur, Unité de Génétique Moléculaire des Levures, CNRS UMR 3525, 25 rue du Dr. Roux, 75724 Paris, France
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30
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Lu B, Lee J, Nie X, Li M, Morozov YI, Venkatesh S, Bogenhagen DF, Temiakov D, Suzuki CK. Phosphorylation of human TFAM in mitochondria impairs DNA binding and promotes degradation by the AAA+ Lon protease. Mol Cell 2012. [PMID: 23201127 DOI: 10.1016/j.molcel.2012.10.023] [Citation(s) in RCA: 226] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Human mitochondrial transcription factor A (TFAM) is a high-mobility group (HMG) protein at the nexus of mitochondrial DNA (mtDNA) replication, transcription, and inheritance. Little is known about the mechanisms underlying its posttranslational regulation. Here, we demonstrate that TFAM is phosphorylated within its HMG box 1 (HMG1) by cAMP-dependent protein kinase in mitochondria. HMG1 phosphorylation impairs the ability of TFAM to bind DNA and to activate transcription. We show that only DNA-free TFAM is degraded by the Lon protease, which is inhibited by the anticancer drug bortezomib. In cells with normal mtDNA levels, HMG1-phosphorylated TFAM is degraded by Lon. However, in cells with severe mtDNA deficits, nonphosphorylated TFAM is also degraded, as it is DNA free. Depleting Lon in these cells increases levels of TFAM and upregulates mtDNA content, albeit transiently. Phosphorylation and proteolysis thus provide mechanisms for rapid fine-tuning of TFAM function and abundance in mitochondria, which are crucial for maintaining and expressing mtDNA.
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Affiliation(s)
- Bin Lu
- Department of Biochemistry and Molecular Biology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, NJ 07103, USA
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31
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Campbell CT, Kolesar JE, Kaufman BA. Mitochondrial transcription factor A regulates mitochondrial transcription initiation, DNA packaging, and genome copy number. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1819:921-9. [DOI: 10.1016/j.bbagrm.2012.03.002] [Citation(s) in RCA: 236] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 03/08/2012] [Accepted: 03/15/2012] [Indexed: 10/28/2022]
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32
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Mitochondrial DNA damage and its consequences for mitochondrial gene expression. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1819:979-91. [PMID: 22728831 DOI: 10.1016/j.bbagrm.2012.06.002] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2012] [Revised: 06/06/2012] [Accepted: 06/14/2012] [Indexed: 12/11/2022]
Abstract
How mitochondria process DNA damage and whether a change in the steady-state level of mitochondrial DNA damage (mtDNA) contributes to mitochondrial dysfunction are questions that fuel burgeoning areas of research into aging and disease pathogenesis. Over the past decade, researchers have identified and measured various forms of endogenous and environmental mtDNA damage and have elucidated mtDNA repair pathways. Interestingly, mitochondria do not appear to contain the full range of DNA repair mechanisms that operate in the nucleus, although mtDNA contains types of damage that are targets of each nuclear DNA repair pathway. The reduced repair capacity may, in part, explain the high mutation frequency of the mitochondrial chromosome. Since mtDNA replication is dependent on transcription, mtDNA damage may alter mitochondrial gene expression at three levels: by causing DNA polymerase γ nucleotide incorporation errors leading to mutations, by interfering with the priming of mtDNA replication by the mitochondrial RNA polymerase, or by inducing transcriptional mutagenesis or premature transcript termination. This review summarizes our current knowledge of mtDNA damage, its repair, and its effects on mtDNA integrity and gene expression. This article is part of a special issue entitled: Mitochondrial Gene Expression.
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33
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Furukawa R, Yamada Y, Matsushima Y, Goto YI, Harashima H. The manner in which DNA is packaged with TFAM has an impact on transcription activation and inhibition. FEBS Open Bio 2012; 2:145-50. [PMID: 23650593 PMCID: PMC3642137 DOI: 10.1016/j.fob.2012.06.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Revised: 06/07/2012] [Accepted: 06/07/2012] [Indexed: 12/12/2022] Open
Abstract
For successful mitochondrial transgene expression, an optimal packaging exogenous DNA is an important issue. We report herein on the effects of DNA packaged with mitochondrial transcription factor A (TFAM), which packages mitochondrial DNA (mtDNA), on the transcription process. Our initial findings indicated that the transcription of the TFAM/DNA complex was activated, when the complex was formed at an optimal ratio. We also found that TFAM has a significant advantage over protamine, a nuclear DNA packaging protein, from the viewpoint of transcription efficiency. This result indicates that TFAM can be useful packaging protein for exogenous DNA to achieve mitochondrial transgene expression.
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Affiliation(s)
- Ryo Furukawa
- Laboratory for Molecular Design of Pharmaceutics, Faculty of Pharmaceutical Sciences, Hokkaido University, Kita-12, Nishi-6, Kita-ku, Sapporo 060-0812, Japan
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34
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Huang SXL, Partridge MA, Ghandhi SA, Davidson MM, Amundson SA, Hei TK. Mitochondria-derived reactive intermediate species mediate asbestos-induced genotoxicity and oxidative stress-responsive signaling pathways. ENVIRONMENTAL HEALTH PERSPECTIVES 2012; 120:840-847. [PMID: 22398240 PMCID: PMC3385428 DOI: 10.1289/ehp.1104287] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Accepted: 03/07/2012] [Indexed: 05/26/2023]
Abstract
BACKGROUND The incidence of asbestos-induced human cancers is increasing worldwide, and considerable evidence suggests that reactive oxygen species (ROS) are important mediators of these diseases. Our previous studies suggested that mitochondria might be involved in the initiation of oxidative stress in asbestos-exposed mammalian cells. OBJECTIVE We investigated whether mitochondria are a potential cytoplasmic target of asbestos using a mitochondrial DNA-depleted (ρ(0)) human small airway epithelial (SAE) cell model: ρ(0) SAE cells lack the capacity to produce mitochondrial ROS. METHODS We examined nuclear DNA damage, micronuclei (MN), intracellular ROS production, and the expression of inflammation-related nuclear genes in both parental and ρ(0) SAE cells in response to asbestos treatment. RESULTS Asbestos induced a dose-dependent increase in nuclear DNA oxidative damage and MN in SAE cells. Furthermore, there was a significant increase in intracellular oxidant production and activation of genes involved in nuclear factor κB and proinflammatory signaling pathways in SAE cells. In contrast, the effects of asbestos were minimal in ρ(0) SAE cells. CONCLUSIONS Mitochondria are a major cytoplasmic target of asbestos. Asbestos may initiate mitochondria-associated ROS, which mediate asbestos-induced nuclear mutagenic events and inflammatory signaling pathways in exposed cells. These data provide new insights into the molecular mechanisms of asbestos-induced genotoxicity.
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Affiliation(s)
- Sarah X L Huang
- Department of Environmental Health Sciences, Mailman School of Public Health, Columbia University, New York, New York 10032, USA
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35
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The mitochondrial ATP-dependent Lon protease: a novel target in lymphoma death mediated by the synthetic triterpenoid CDDO and its derivatives. Blood 2012; 119:3321-9. [PMID: 22323447 DOI: 10.1182/blood-2011-02-340075] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Synthetic triterpenoids are multitarget compounds exhibiting promise as preventative and therapeutic agents for cancer. Their proposed mechanism of action is by forming Michael adducts with reactive nucleophilic groups on target proteins. Our previous work demonstrates that the 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and its derivatives promote B-lymphoid cell apoptosis through a mitochondria-mediated pathway linked to mitochondrial protein aggregation. As one function of the Lon protease is to eliminate abnormal mitochondrial proteins, we hypothesized that CDDO-induced protein aggregation and lymphoma apoptosis occur by inactivating this enzyme. Here, we show that CDDO and its derivatives directly and selectively inhibit Lon. CDDO blocks Lon-mediated proteolysis in biochemical and cellular assays, but does not inhibit the 20S proteasome. Furthermore, a biotinylated-CDDO conjugate modifies mitochondrial Lon. A striking common phenotype of CDDO-treated lymphoma cells and Lon-knockdown cells is the accumulation of electron-dense aggregates within mitochondria. We also show that Lon protein levels are substantially elevated in malignant lymphoma cells, compared with resting or activated B cells. Finally, we demonstrate that Lon knockdown leads to lymphoma cell death. Together, these findings suggest that Lon inhibition plays a contributory role in CDDO-induced lymphoma cell death, and support the concept that mitochondrial Lon is a novel anticancer drug target.
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36
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Matsushima Y, Kaguni LS. Matrix proteases in mitochondrial DNA function. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:1080-7. [PMID: 22172992 DOI: 10.1016/j.bbagrm.2011.11.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2011] [Revised: 11/22/2011] [Accepted: 11/23/2011] [Indexed: 10/14/2022]
Abstract
Lon, ClpXP and m-AAA are the three major ATP-dependent proteases in the mitochondrial matrix. All three are involved in general quality control by degrading damaged or abnormal proteins. In addition to this role, they are proposed to serve roles in mitochondrial DNA functions including packaging and stability, replication, transcription and translation. In particular, Lon has been implicated in mtDNA metabolism in yeast, fly and humans. Here, we review the role of Lon protease in mitochondrial DNA functions, and discuss a putative physiological role for mitochondrial transcription factor A (TFAM) degradation by Lon protease. We also discuss the possible roles of m-AAA and ClpXP in mitochondrial DNA functions, and the putative candidate substrates for the three matrix proteases. This article is part of a Special Issue entitled: Mitochondrial Gene Expression.
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Affiliation(s)
- Yuichi Matsushima
- Department of Mental Retardation & Birth Defect Research, National Institute of Neuroscience, National Center of Neurology & Psychiatry, Tokyo 187-8502, Japan
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37
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The role of microglial mtDNA damage in age-dependent prolonged LPS-induced sickness behavior. ACTA ACUST UNITED AC 2011; 7:17-23. [PMID: 22032249 DOI: 10.1017/s1740925x1100010x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Microglia are the main cellular source of oxidation products and inflammatory molecules in the brain during aging. The accumulation of mitochondrial DNA (mtDNA) oxidative damage in microglia during aging results in the increased production of reactive oxygen species (ROS). The increased intracellular ROS, in turn, activates a redox-sensitive nuclear factor-κB (NF-κB) to provoke excessive neuroinflammation, resulting in memory deficits and the prolonged behavioral consequence of infection. Besides its role in regulating the gene copy number, mitochondrial transcription factor A (TFAM) is closely associated with the stabilization of mtDNA structures. Lipopolysaccharide (LPS) induces the generation of ROS from the actively respirating mitochondria as well as NADPH oxidase, and leads to the subsequent activation of the NF-κB-dependent inflammatory pathway in aging microglia. The overexpression of human TFAM improves the age-dependent prolonged LPS-induced sickness behaviors by ameliorating the mtDNA damage and reducing the resultant redox-regulated inflammatory responses. Therefore, 'microglia-aging' plays important roles in the age-dependent enhanced behavioral consequences of infection.
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38
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Arduini A, Serviddio G, Escobar J, Tormos AM, Bellanti F, Viña J, Monsalve M, Sastre J. Mitochondrial biogenesis fails in secondary biliary cirrhosis in rats leading to mitochondrial DNA depletion and deletions. Am J Physiol Gastrointest Liver Physiol 2011; 301:G119-27. [PMID: 21415417 DOI: 10.1152/ajpgi.00253.2010] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Chronic cholestasis is characterized by mitochondrial dysfunction, associated with loss of mitochondrial membrane potential, decreased activities of respiratory chain complexes, and ATP production. Our aim was to determine the molecular mechanisms that link long-term cholestasis to mitochondrial dysfunction. We studied a model of chronic cholestasis induced by bile duct ligation in rats. Key sensors and regulators of the energetic state and mitochondrial biogenesis, mitochondrial DNA (mtDNA)-to-nuclear DNA (nDNA) ratio (mtDNA/nDNA) relative copy number, mtDNA deletions, and indexes of apoptosis (BAX, BCL-2, and cleaved caspase 3) and cell proliferation (PCNA) were evaluated. Our results show that long-term cholestasis is associated with absence of activation of key sensors of the energetic state, evidenced by decreased SIRT1 and pyruvate dehydrogenase kinase levels and lack of AMPK activation. Key mitochondrial biogenesis regulators (PGC-1α and GABP-α) decreased and NRF-1 was not transcriptionally active. Mitochondrial transcription factor A (TFAM) protein levels increased transiently in liver mitochondria at 2 wk after bile duct ligation, but they dramatically decreased at 4 wk. Reduced TFAM levels at this stage were mirrored by a marked decrease (65%) in mtDNA/nDNA relative copy number. The blockade of mitochondrial biogenesis should not be ascribed to activation of apoptosis or inhibition of cell proliferation. Impaired mitochondrial turnover and loss of the DNA stabilizing effect of TFAM are likely the causative event involved in the genetic instability evidenced by accumulation of mtDNA deletions. In conclusion, the lack of stimulation of mitochondrial biogenesis leads to mtDNA severe depletion and deletions in long-term cholestasis. Hence, long-term cholestasis should be considered a secondary mitochondrial hepatopathy.
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Lauritzen KH, Cheng C, Wiksen H, Bergersen LH, Klungland A. Mitochondrial DNA toxicity compromises mitochondrial dynamics and induces hippocampal antioxidant defenses. DNA Repair (Amst) 2011; 10:639-53. [PMID: 21550321 DOI: 10.1016/j.dnarep.2011.04.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Revised: 03/18/2011] [Accepted: 04/06/2011] [Indexed: 11/20/2022]
Abstract
Mitochondria are highly dynamic organelles that can be actively transported within the cell to satisfy local requirements. They are vital for providing cellular energy, but are also an important endogenous source of reactive oxygen species. The distribution of mitochondria is particularly important for neurons because of the morphological complexity of these cells, and because neural processing is metabolically expensive. Defects in mitochondrial distribution, observed in several neurodegenerative diseases, can result in synaptic dysfunction. We have generated transgenic mice expressing an enzyme in forebrain neurons that causes mitochondrial DNA (mtDNA) damage in the form of abasic-sites, creating mtDNA toxicity. Here, we report that mitochondrial distribution is disturbed in hippocampal neurons of these mice. Moreover, mtDNA copy number and mitochondrial transcription are reduced, and oxidative stress is increased. There is also a loss of receptors at excitatory glutamatergic synapses in the dentate gyrus, and the size of the postsynaptic density in this region is abnormal. We speculate that the loss of synaptic mitochondria caused by accumulation in the neuronal cell body contributes to the observed synaptic abnormalities, as well as the overall loss of mtDNA and diminished mitochondrial transcription. Collectively, these changes lead to mitochondria with reduced function and increased oxidative stress.
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Affiliation(s)
- Knut H Lauritzen
- Centre for Molecular Biology and Neuroscience, Institute of Medical Microbiology, Oslo University Hospital and University of Oslo, NO-0027 Oslo, Norway
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40
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Levanets O, Reinecke F, Louw R, Pretorius PJ, du Plessis LH, Nijtmans L, Smeitink JA, van der Westhuizen FH. Mitochondrial DNA replication and OXPHOS gene transcription show varied responsiveness to Rieske protein knockdown in 143B cells. Biochimie 2011; 93:758-65. [DOI: 10.1016/j.biochi.2011.01.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Accepted: 01/10/2011] [Indexed: 01/10/2023]
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41
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POLG mutations cause decreased mitochondrial DNA repopulation rates following induced depletion in human fibroblasts. Biochim Biophys Acta Mol Basis Dis 2010; 1812:321-5. [PMID: 21138766 DOI: 10.1016/j.bbadis.2010.11.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2010] [Revised: 11/09/2010] [Accepted: 11/29/2010] [Indexed: 11/22/2022]
Abstract
Disorders of mitochondrial DNA (mtDNA) maintenance have emerged as an important cause of human genetic disease, but demonstrating the functional consequences of de novo mutations remains a major challenge. We studied the rate of depletion and repopulation of mtDNA in human fibroblasts exposed to ethidium bromide in patients with heterozygous POLG mutations, POLG2 and TK2 mutations. Ethidium bromide induced mtDNA depletion occurred at the same rate in human fibroblasts from patients and healthy controls. By contrast, the restoration of mtDNA levels was markedly delayed in fibroblasts from patients with compound heterozygous POLG mutations. Specific POLG2 and TK2 mutations did not delay mtDNA repopulation rates. These observations are consistent with the hypothesis that mutations in POLG impair mtDNA repopulation within intact cells, and provide a potential method of demonstrating the functional consequences of putative pathogenic alleles causing a defect of mtDNA synthesis.
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Mitochondrial Lon protease regulates mitochondrial DNA copy number and transcription by selective degradation of mitochondrial transcription factor A (TFAM). Proc Natl Acad Sci U S A 2010; 107:18410-5. [PMID: 20930118 DOI: 10.1073/pnas.1008924107] [Citation(s) in RCA: 207] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Lon is the major protease in the mitochondrial matrix in eukaryotes, and is well conserved among species. Although a role for Lon in mitochondrial biogenesis has been proposed, the mechanistic basis is unclear. Here, we demonstrate a role for Lon in mtDNA metabolism. An RNA interference (RNAi) construct was designed that reduces Lon to less than 10% of its normal level in Drosophila Schneider cells. RNAi knockdown of Lon results in increased abundance of mitochondrial transcription factor A (TFAM) and mtDNA copy number. In a corollary manner, overexpression of Lon reduces TFAM levels and mtDNA copy number. Notably, induction of mtDNA depletion in Lon knockdown cells does not result in degradation of TFAM, thereby causing a dramatic increase in the TFAMmtDNA ratio. The increased TFAMmtDNA ratio in turn causes inhibition of mitochondrial transcription. We conclude that Lon regulates mitochondrial transcription by stabilizing the mitochondrial TFAMmtDNA ratio via selective degradation of TFAM.
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Chiaratti MR, Bressan FF, Ferreira CR, Caetano AR, Smith LC, Vercesi AE, Meirelles FV. Embryo Mitochondrial DNA Depletion Is Reversed During Early Embryogenesis in Cattle1. Biol Reprod 2010; 82:76-85. [DOI: 10.1095/biolreprod.109.077776] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
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Abstract
PURPOSE OF REVIEW To discuss novel developments related to the mechanisms of antiretroviral therapy-related mitochondrial toxicity, describe some apparent paradoxes in the current understanding of this field, and present questions that should be addressed by future research. RECENT FINDINGS The early polymerase gamma hypothesis states that nucleoside reverse transcriptase inhibitors can inhibit mitochondrial DNA replication and cause mitochondrial toxicity through mtDNA depletion. This mechanism is supported by a large body of evidence. Clinical manifestations of mitochondrial dysfunction are not always associated with mtDNA depletion. Increased mtDNA levels after nucleoside reverse transcriptase inhibitor exposure, as well as seemingly severe mtDNA depletion in individuals who show no clinical toxicity, have been reported. These and other observations suggest that additional mechanisms are involved in antiretroviral therapy toxicity, a notion supported by recent studies. Individuals given the same antiretroviral regimen can differ vastly with respect to the development of mitochondrial toxicity symptoms, reflecting interindividual variability. Some factors that may modulate this variability will be discussed. SUMMARY Mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors and their metabolic intermediates is probably mediated through many direct and indirect mechanisms. Depending on the mechanisms at play, the long-term health consequences of this toxicity may vary.
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Liu Y, Geng L, Suo Z. Differentiation Effect of Pyruvate and Uridine on Cultured U937-ρ° Cells. Ultrastruct Pathol 2009. [DOI: 10.3109/01913120902889187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Rebelo AP, Williams SL, Moraes CT. In vivo methylation of mtDNA reveals the dynamics of protein-mtDNA interactions. Nucleic Acids Res 2009; 37:6701-15. [PMID: 19740762 PMCID: PMC2777446 DOI: 10.1093/nar/gkp727] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
To characterize the organization of mtDNA–protein complexes (known as nucleoids) in vivo, we have probed the mtDNA surface exposure using site-specific DNA methyltransferases targeted to the mitochondria. We have observed that DNA methyltransferases have different accessibility to different sites on the mtDNA based on the levels of protein occupancy. We focused our studies on selected regions of mtDNA that are believed to be major regulatory regions involved in transcription and replication. The transcription termination region (TERM) within the tRNALeu(UUR) gene was consistently and strongly protected from methylation, suggesting frequent and high affinity binding of mitochondrial transcription termination factor 1 (mTERF1) to the site. Protection from methylation was also observed in other regions of the mtDNA, including the light and heavy strand promoters (LSP, HSP) and the origin of replication of the light strand (OL). Manipulations aiming at increasing or decreasing the levels of the mitochondrial transcription factor A (TFAM) led to decreased in vivo methylation, whereas manipulations that stimulated mtDNA replication led to increased methylation. We also analyzed the effect of ATAD3 and oxidative stress in mtDNA exposure. Our data provide a map of human mtDNA accessibility and demonstrate that nucleoids are dynamically associated with proteins.
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Affiliation(s)
- Adriana P Rebelo
- Department of Cell Biology and Anatomy, University of Miami School of Medicine, Miami, FL 33136, USA
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Dalla Rosa I, Goffart S, Wurm M, Wiek C, Essmann F, Sobek S, Schroeder P, Zhang H, Krutmann J, Hanenberg H, Schulze-Osthoff K, Mielke C, Pommier Y, Boege F, Christensen MO. Adaptation of topoisomerase I paralogs to nuclear and mitochondrial DNA. Nucleic Acids Res 2009; 37:6414-28. [PMID: 19720733 PMCID: PMC2770673 DOI: 10.1093/nar/gkp708] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Topoisomerase I is essential for DNA metabolism in nuclei and mitochondria. In yeast, a single topoisomerase I gene provides for both organelles. In vertebrates, topoisomerase I is divided into nuclear and mitochondrial paralogs (Top1 and Top1mt). To assess the meaning of this gene duplication, we targeted Top1 to mitochondria or Top1mt to nuclei. Overexpression in the fitting organelle served as control. Targeting of Top1 to mitochondria blocked transcription and depleted mitochondrial DNA. This was also seen with catalytically inactive Top1 mutants, but not with Top1mt overexpressed in mitochondria. Targeting of Top1mt to the nucleus revealed that it was much less able to interact with mitotic chromosomes than Top1 overexpressed in the nucleus. Similar experiments with Top1/Top1mt hybrids assigned these functional differences to structural divergences in the DNA-binding core domains. We propose that adaptation of this domain to different chromatin environments in nuclei and mitochondria has driven evolutional development and conservation of organelle-restricted topoisomerase I paralogs in vertebrates.
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Affiliation(s)
- Ilaria Dalla Rosa
- Institute of Clinical Chemistry and Laboratory Diagnostics, Heinrich-Heine-University, Medical School, D-40225 Düsseldorf, Germany
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Baughman JM, Nilsson R, Gohil VM, Arlow DH, Gauhar Z, Mootha VK. A computational screen for regulators of oxidative phosphorylation implicates SLIRP in mitochondrial RNA homeostasis. PLoS Genet 2009; 5:e1000590. [PMID: 19680543 PMCID: PMC2721412 DOI: 10.1371/journal.pgen.1000590] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Accepted: 07/09/2009] [Indexed: 11/18/2022] Open
Abstract
The human oxidative phosphorylation (OxPhos) system consists of approximately 90 proteins encoded by nuclear and mitochondrial genomes and serves as the primary cellular pathway for ATP biosynthesis. While the core protein machinery for OxPhos is well characterized, many of its assembly, maturation, and regulatory factors remain unknown. We exploited the tight transcriptional control of the genes encoding the core OxPhos machinery to identify novel regulators. We developed a computational procedure, which we call expression screening, which integrates information from thousands of microarray data sets in a principled manner to identify genes that are consistently co-expressed with a target pathway across biological contexts. We applied expression screening to predict dozens of novel regulators of OxPhos. For two candidate genes, CHCHD2 and SLIRP, we show that silencing with RNAi results in destabilization of OxPhos complexes and a marked loss of OxPhos enzymatic activity. Moreover, we show that SLIRP plays an essential role in maintaining mitochondrial-localized mRNA transcripts that encode OxPhos protein subunits. Our findings provide a catalogue of potential novel OxPhos regulators that advance our understanding of the coordination between nuclear and mitochondrial genomes for the regulation of cellular energy metabolism. Respiratory chain disorders represent the largest class of inborn errors in metabolism affecting 1 in every 5,000 individuals. Biochemically, these disorders are characterized by a breakdown in the cellular process called oxidative phosphorylation (OxPhos), which is responsible for generating most of the cell's energy in the form of ATP. Sadly, for approximately 50% of patients diagnosed, we do not know the molecular cause behind these disorders. One possible reason for our limited diagnostic capability is that these patients harbor a mutation in a gene that is not known to act in the OxPhos pathway. We therefore designed a computational strategy called expression screening that integrates publicly available genome-wide gene expression data to predict new genes that may play a role in OxPhos biology. We identified several uncharacterized genes that were strongly predicted by our procedure to function in the OxPhos pathway and experimentally validated two genes, SLIRP and CHCHD2, as being essential for OxPhos function. These genes, as well as others predicted by expression screening to regulate OxPhos, represent a valuable resource for identifying the molecular underpinnings of respiratory chain disorders.
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Affiliation(s)
- Joshua M. Baughman
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Roland Nilsson
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Vishal M. Gohil
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Daniel H. Arlow
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Zareen Gauhar
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Vamsi K. Mootha
- Center for Human Genetic Research, Massachusetts General Hospital, Boston, Massachusetts, United States of America
- Broad Institute of MIT and Harvard, Cambridge, Massachusetts, United States of America
- Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America
- * E-mail:
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Bacman SR, Williams SL, Moraes CT. Intra- and inter-molecular recombination of mitochondrial DNA after in vivo induction of multiple double-strand breaks. Nucleic Acids Res 2009; 37:4218-26. [PMID: 19435881 PMCID: PMC2715231 DOI: 10.1093/nar/gkp348] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
To investigate mtDNA recombination induced by multiple double strand breaks (DSBs) we used a mitochondria-targeted form of the ScaI restriction endonuclease to introduce DSBs in heteroplasmic mice and cells in which we were able to utilize haplotype differences to trace the origin of recombined molecules. ScaI cleaves multiple sites in each haplotype of the heteroplasmic mice (five in NZB and three in BALB mtDNA) and prolonged expression causes severe mtDNA depletion. After a short pulse of restriction enzyme expression followed by a long period of recovery, mitochondrial genomes with large deletions were detected by PCR. Curiously, we found that some ScaI sites were more commonly involved in recombined molecules than others. In intra-molecular recombination events, deletion breakpoints were close to or upstream of ScaI cleavage sites, confirming the recombinogenic character of DSBs in mtDNA. A region adjacent to the D-loop was preferentially involved in recombination of all molecules. Sequencing through NZB and BALB haplotype markers in recombined molecules enabled us to show that in addition to intra-molecular mtDNA recombination, rare inter-molecular mtDNA recombination events can also occur. This study underscores the role of DSBs in the generation of mtDNA rearrangements and supports the existence of recombination hotspots.
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Affiliation(s)
- Sandra R Bacman
- Department of Neurology, University of Miami School of Medicine, Miami, FL 33136, USA
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Reinecke F, Smeitink JAM, van der Westhuizen FH. OXPHOS gene expression and control in mitochondrial disorders. Biochim Biophys Acta Mol Basis Dis 2009; 1792:1113-21. [PMID: 19389473 DOI: 10.1016/j.bbadis.2009.04.003] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2008] [Revised: 04/08/2009] [Accepted: 04/14/2009] [Indexed: 12/20/2022]
Abstract
The cellular consequences of deficiencies of the mitochondrial OXPHOS system include a variety of direct and secondary changes in metabolite homeostasis, such as ROS, Ca(2+), ADP/ATP, and NAD/NADH. The adaptive responses to these changes include the transcriptional responses of nuclear and mitochondrial genes that are mediated by these metabolites, control of the mitochondria permeability transition pore, and a great variety of secondary signalling elements. Among the transcriptional responses reported over more than a decade using material harboring mtDNA mutations, deletions, or depletions, nuclear and mitochondrial DNA OXPHOS genes have mostly been up-regulated. However, it is evident from the limited data in a variety of disease models that expression responses are highly diverse and inconsistent. In this article, the mechanisms and controlling elements of these transcriptional responses are reviewed. In addition, the elements that need to be evaluated, in order to gain an improved perspective of the manner in which OXPHOS genes respond and impact on mitochondrial disease expression, are highlighted.
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Affiliation(s)
- Fimmie Reinecke
- Centre for Human Metabonomics, School for Physical and Chemical Sciences, North-West University, Hoffman street, Potchefstroom 2531, South Africa
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