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Volobaev VP, Kunizheva SS, Uralsky LI, Kupriyanova DA, Rogaev EI. Quantifying human genome parameters in aging. Vavilovskii Zhurnal Genet Selektsii 2023; 27:495-501. [PMID: 37808212 PMCID: PMC10551942 DOI: 10.18699/vjgb-23-60] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 02/07/2023] [Accepted: 02/07/2023] [Indexed: 10/10/2023] Open
Abstract
Healthy human longevity is a global goal of the world health system. Determining the causes and processes influencing human longevity is the primary fundamental goal facing the scientific community. Currently, the main efforts of the scientific community are aimed at identifying the qualitative characteristics of the genome that determine the trait. At the same time, when evaluating qualitative characteristics, there are many challenges that make it difficult to establish associations. Quantitative traits are burdened with such problems to a lesser extent, but they are largely overlooked in current genomic studies of aging and longevity. Although there is a wide repertoire of quantitative trait analyses based on genomic data, most opportunities are ignored by authors, which, along with the inaccessibility of published data, leads to the loss of this important information. This review focuses on describing quantitative traits important for understanding aging and necessary for analysis in further genomic studies, and recommends the inclusion of the described traits in the analysis. The review considers the relationship between quantitative characteristics of the mitochondrial genome and aging, longevity, and age-related neurodegenerative diseases, such as the frequency of extensive mitochondrial DNA (mtDNA) deletions, mtDNA half-life, the frequency of A>G replacements in the mtDNA heavy chain, the number of mtDNA copies; special attention is paid to the mtDNA methylation sign. A separate section of this review is devoted to the correlation of telomere length parameters with age, as well as the association of telomere length with the amount of mitochondrial DNA. In addition, we consider such a quantitative feature as the rate of accumulation of somatic mutations with aging in relation to the lifespan of living organisms. In general, it may be noted that there are quite serious reasons to suppose that various quantitative characteristics of the genome may be directly or indirectly associated with certain aspects of aging and longevity. At the same time, the available data are clearly insufficient for definitive conclusions and the determination of causal relationships.
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Affiliation(s)
- V P Volobaev
- Sirius University of Science and Technology, Scientific Center for Genetics and Life Sciences, Sochi, Russia
| | - S S Kunizheva
- Sirius University of Science and Technology, Scientific Center for Genetics and Life Sciences, Sochi, Russia Vavilov Institute of General Genetics, Russian Academy of Sciences, Department of Genomics and Human Genetics, Moscow, Russia Lomonosov Moscow State University, Center for Genetics and Genetic Technologies, Faculty of Biology, Moscow, Russia
| | - L I Uralsky
- Sirius University of Science and Technology, Scientific Center for Genetics and Life Sciences, Sochi, Russia Vavilov Institute of General Genetics, Russian Academy of Sciences, Department of Genomics and Human Genetics, Moscow, Russia
| | - D A Kupriyanova
- Sirius University of Science and Technology, Scientific Center for Genetics and Life Sciences, Sochi, Russia
| | - E I Rogaev
- Sirius University of Science and Technology, Scientific Center for Genetics and Life Sciences, Sochi, Russia Vavilov Institute of General Genetics, Russian Academy of Sciences, Department of Genomics and Human Genetics, Moscow, Russia Lomonosov Moscow State University, Center for Genetics and Genetic Technologies, Faculty of Biology, Moscow, Russia University of Massachusetts Chan Medical School, Department of Psychiatry, Shrewsbury, USA
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2
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Caston RA, Fortini P, Chen K, Bauer J, Dogliotti E, Yin YW, Demple B. Maintenance of Flap Endonucleases for Long-Patch Base Excision DNA Repair in Mouse Muscle and Neuronal Cells Differentiated In Vitro. Int J Mol Sci 2023; 24:12715. [PMID: 37628896 PMCID: PMC10454756 DOI: 10.3390/ijms241612715] [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: 05/17/2023] [Revised: 08/02/2023] [Accepted: 08/03/2023] [Indexed: 08/27/2023] Open
Abstract
After cellular differentiation, nuclear DNA is no longer replicated, and many of the associated proteins are downregulated accordingly. These include the structure-specific endonucleases Fen1 and DNA2, which are implicated in repairing mitochondrial DNA (mtDNA). Two more such endonucleases, named MGME1 and ExoG, have been discovered in mitochondria. This category of nuclease is required for so-called "long-patch" (multinucleotide) base excision DNA repair (BER), which is necessary to process certain oxidative lesions, prompting the question of how differentiation affects the availability and use of these enzymes in mitochondria. In this study, we demonstrate that Fen1 and DNA2 are indeed strongly downregulated after differentiation of neuronal precursors (Cath.a-differentiated cells) or mouse myotubes, while the expression levels of MGME1 and ExoG showed minimal changes. The total flap excision activity in mitochondrial extracts of these cells was moderately decreased upon differentiation, with MGME1 as the predominant flap endonuclease and ExoG playing a lesser role. Unexpectedly, both differentiated cell types appeared to accumulate less oxidative or alkylation damage in mtDNA than did their proliferating progenitors. Finally, the overall rate of mtDNA repair was not significantly different between proliferating and differentiated cells. Taken together, these results indicate that neuronal cells maintain mtDNA repair upon differentiation, evidently relying on mitochondria-specific enzymes for long-patch BER.
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Affiliation(s)
- Rachel A. Caston
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Paola Fortini
- Department of Environment and Health, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy; (P.F.)
| | - Kevin Chen
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Jack Bauer
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Eugenia Dogliotti
- Department of Environment and Health, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy; (P.F.)
| | - Y. Whitney Yin
- Department of Pharmacology and Toxicology, Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX 77555, USA
| | - Bruce Demple
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
- Department of Radiation Oncology, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
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3
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Shamanskiy V, Mikhailova AA, Tretiakov EO, Ushakova K, Mikhailova AG, Oreshkov S, Knorre DA, Ree N, Overdevest JB, Lukowski SW, Gostimskaya I, Yurov V, Liou CW, Lin TK, Kunz WS, Reymond A, Mazunin I, Bazykin GA, Fellay J, Tanaka M, Khrapko K, Gunbin K, Popadin K. Secondary structure of the human mitochondrial genome affects formation of deletions. BMC Biol 2023; 21:103. [PMID: 37158879 PMCID: PMC10166460 DOI: 10.1186/s12915-023-01606-1] [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: 06/17/2022] [Accepted: 04/19/2023] [Indexed: 05/10/2023] Open
Abstract
BACKGROUND Aging in postmitotic tissues is associated with clonal expansion of somatic mitochondrial deletions, the origin of which is not well understood. Such deletions are often flanked by direct nucleotide repeats, but this alone does not fully explain their distribution. Here, we hypothesized that the close proximity of direct repeats on single-stranded mitochondrial DNA (mtDNA) might play a role in the formation of deletions. RESULTS By analyzing human mtDNA deletions in the major arc of mtDNA, which is single-stranded during replication and is characterized by a high number of deletions, we found a non-uniform distribution with a "hot spot" where one deletion breakpoint occurred within the region of 6-9 kb and another within 13-16 kb of the mtDNA. This distribution was not explained by the presence of direct repeats, suggesting that other factors, such as the spatial proximity of these two regions, can be the cause. In silico analyses revealed that the single-stranded major arc may be organized as a large-scale hairpin-like loop with a center close to 11 kb and contacting regions between 6-9 kb and 13-16 kb, which would explain the high deletion activity in this contact zone. The direct repeats located within the contact zone, such as the well-known common repeat with a first arm at 8470-8482 bp (base pair) and a second arm at 13,447-13,459 bp, are three times more likely to cause deletions compared to direct repeats located outside of the contact zone. A comparison of age- and disease-associated deletions demonstrated that the contact zone plays a crucial role in explaining the age-associated deletions, emphasizing its importance in the rate of healthy aging. CONCLUSIONS Overall, we provide topological insights into the mechanism of age-associated deletion formation in human mtDNA, which could be used to predict somatic deletion burden and maximum lifespan in different human haplogroups and mammalian species.
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Affiliation(s)
- Victor Shamanskiy
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Alina A Mikhailova
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Evgenii O Tretiakov
- Department of Molecular Neurosciences, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| | - Kristina Ushakova
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Alina G Mikhailova
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
- Vavilov Institute of General Genetics RAS, Moscow, Russia
| | - Sergei Oreshkov
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Dmitry A Knorre
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Natalia Ree
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Jonathan B Overdevest
- Department of Otolaryngology, Columbia University Irving Medical Center, New York, USA
| | - Samuel W Lukowski
- Institute for Molecular Bioscience, University of Queensland, St Lucia, Brisbane, Australia
| | - Irina Gostimskaya
- Manchester Institute of Biotechnology, The University of Manchester, Manchester, UK
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Valerian Yurov
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
| | - Chia-Wei Liou
- Department of Neurology, Kaohsiung Chang-Gung Memorial Hospital and Chang-Gung University, Kaohsiung, Taiwan
| | - Tsu-Kung Lin
- Department of Neurology, Kaohsiung Chang-Gung Memorial Hospital and Chang-Gung University, Kaohsiung, Taiwan
| | - Wolfram S Kunz
- Division of Neurochemistry, Department of Experimental Epileptology and Cognition Research, University Bonn, Bonn, Germany
- Department of Epileptology, University Hospital of Bonn, Bonn, Germany
| | - Alexandre Reymond
- Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland
- Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Ilya Mazunin
- Center for Molecular and Cellular Biology, Skolkovo Institute of Science and Technology, Moscow, Russia
| | - Georgii A Bazykin
- Center for Molecular and Cellular Biology, Skolkovo Institute of Science and Technology, Moscow, Russia
- Laboratory of Molecular Evolution, Institute for Information Transmission Problems (Kharkevich Institute) of the Russian Academy of Sciences, Moscow, Russia
| | - Jacques Fellay
- Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
| | - Masashi Tanaka
- Department for Health and Longevity Research, National Institutes of Biomedical Innovation, Health and Nutrition, 1-23-1 Toyama, Shinjuku-Ku, Tokyo, 162-8636, Japan
- Department of Neurology, Juntendo University Graduate School of Medicine, 2-1-1 Hongo, Bunkyo-Ku, Tokyo, 113-8421, Japan
- Department of Clinical Laboratory, IMS Miyoshi General Hospital, Fujikubo, Miyoshi-Machi, Iruma, Saitama Prefecture, 974-3354-0041, Japan
| | | | - Konstantin Gunbin
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia
- Institute of Molecular and Cellular Biology SB RAS, Novosibirsk, Russia
| | - Konstantin Popadin
- Center for Mitochondrial Functional Genomics, Immanuel Kant Baltic Federal University, Kaliningrad, Russia.
- Swiss Institute of Bioinformatics, Lausanne, Switzerland.
- Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland.
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Mitochondrial transplantation in cardiac surgical patients: optimism, caveats, and outstanding questions. Curr Opin Anaesthesiol 2023; 36:5-10. [PMID: 36550601 DOI: 10.1097/aco.0000000000001202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
PURPOSE OF REVIEW Mitochondria satisfy the high metabolic demand of the heart, and also play major roles in reactive oxygen species signaling, calcium buffering, and regulation of cell death. Mitochondrial damage or dysfunction can drive diseases seen in cardiac surgical patients, including heart failure and ischemia/reperfusion injury. Exogenous transplantation of isolated mitochondria has been proposed as one way to augment mitochondrial function and mitigate a number of pathologic processes, with a heavy focus on ischemia/reperfusion injury. RECENT FINDINGS Animal models of cardiac ischemia/reperfusion injury have shown functional benefits after mitochondrial transplantation. Many of the mechanisms underlying this therapy's effect; optimal dosing, delivery, and timing; and how it will translate to cardiac surgical patients are yet unknown. SUMMARY Mitochondrial transplantation is a potential therapeutic strategy for cardiac ischemia/reperfusion injury. Effective application to selected cardiac surgical patients can be informed by further mechanistic investigations.
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5
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Khanijou JK, Yee Z, Raida M, Lee JM, Tay EZE, Gruber J, Walczyk T. Efficiency of Protein Renewal Is Limited by Feed Intake and Not by Protein Lifetime in Aging Caenorhabditis elegans. J Proteome Res 2022; 21:2664-2686. [PMID: 36181456 DOI: 10.1021/acs.jproteome.2c00383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Protein turnover maintains the proteome's functional integrity. Here, protein turnover efficiency over time in wild-type Caenorhabditis elegans was assessed using inverse [15N]-pulse labeling up to 7 days after the egg-laying phase at 20 °C. Isotopic analysis of some abundant proteins was executed favoring data quality over quantity for mathematical modeling. Surprisingly, isotopic enrichment over time reached an upper limit showing an apparent cessation of protein renewal well before death, with protein fractions inaccessible to turnover ranging from 14 to 83%. For life span modulation, worms were raised at different temperatures after egg laying. Mathematical modeling of isotopic enrichment points either to a slowdown of protein turnover or to an increasing protein fraction resistant to turnover with time. Most notably, the estimated time points of protein turnover cessation from our mathematical model were highly correlated with the observed median life span. Thrashing and pumping rates over time were linearly correlated with isotopic enrichment, therefore linking protein/tracer intake to protein turnover rate and protein life span. If confirmed, life span extension is possible by optimizing protein turnover rate through modulating protein intake in C. elegans and possibly other organisms. While proteome maintenance benefits from a high protein turnover rate, protein turnover is fundamentally energy-intensive, where oxidative stress contributes to damage that it is supposed to repair.
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Affiliation(s)
- Jasmeet Kaur Khanijou
- Department of Chemistry, National University of Singapore (NUS), Singapore 117543, Singapore.,Shared Analytics, Singapore Institute of Food and Biotechnology Innovation (SIFBI), Agency for Science, Technology and Research (A*STAR), Singapore 138673, Singapore
| | - Zhuangli Yee
- Yale-NUS College, Singapore 138527, Singapore.,Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore
| | - Manfred Raida
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore.,Singapore Lipidomics Incubator (SLING), Life Sciences Institute, National University of Singapore, Singapore 117456, Singapore
| | - Jin Meng Lee
- Department of Chemistry, National University of Singapore (NUS), Singapore 117543, Singapore
| | - Evan Zhi En Tay
- Department of Chemistry, National University of Singapore (NUS), Singapore 117543, Singapore
| | - Jan Gruber
- Yale-NUS College, Singapore 138527, Singapore.,Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore (NUS), Singapore 117597, Singapore
| | - Thomas Walczyk
- Department of Chemistry, National University of Singapore (NUS), Singapore 117543, Singapore
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6
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Holt AG, Davies AM. The Effect of Mitochondrial DNA Half-Life on Deletion Mutation Proliferation in Long Lived Cells. Acta Biotheor 2021; 69:671-695. [PMID: 34131800 DOI: 10.1007/s10441-021-09417-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 06/07/2021] [Indexed: 01/21/2023]
Abstract
The proliferation of mitochondrial DNA (mtDNA) with deletion mutations has been linked to aging and age related neurodegenerative conditions. In this study we model the effect of mtDNA half-life on mtDNA competition and selection. It has been proposed that mutation deletions ([Formula: see text]) have a replicative advantage over wild-type ([Formula: see text]) and that this is detrimental to the host cell, especially in post-mitotic cells. An individual cell can be viewed as forming a closed ecosystem containing a large population of independently replicating mtDNA. Within this enclosed environment a selfishly replicating [Formula: see text] would compete with the [Formula: see text] for space and resources to the detriment of the host cell. In this paper, we use a computer simulation to model cell survival in an environment where [Formula: see text] compete with [Formula: see text] such that the cell expires upon [Formula: see text] extinction. We focus on the survival time for long lived post-mitotic cells, such as neurons. We confirm previous observations that [Formula: see text] do have a replicative advantage over [Formula: see text]. As expected, cell survival times diminished with increased mutation probabilities, however, the relationship between survival time and mutation rate was non-linear, that is, a ten-fold increase in mutation probability only halved the survival time. The results of our model also showed that a modest increase in half-life had a profound affect on extending cell survival time, thereby, mitigating the replicative advantage of [Formula: see text]. Given the relevance of mitochondrial dysfunction to various neurodegenerative conditions, we propose that therapies to increase mtDNA half-life could significantly delay their onset.
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7
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Ghazal N, Peoples JN, Mohiuddin TA, Kwong JQ. Mitochondrial functional resilience after TFAM ablation in the adult heart. Am J Physiol Cell Physiol 2021; 320:C929-C942. [PMID: 33760663 DOI: 10.1152/ajpcell.00508.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The nuclear genome-encoded mitochondrial DNA (mtDNA) transcription factor A (TFAM) is indispensable for mitochondrial energy production in the developing and postnatal heart; a similar role for TFAM is inferred in adult heart. Here, we provide evidence that challenges this long-standing paradigm. Unexpectedly, conditional Tfam ablation in vivo in adult mouse cardiomyocytes resulted in a prolonged period of functional resilience characterized by preserved mtDNA content, mitochondrial function, and cardiac function, despite mitochondrial structural alterations and decreased transcript abundance. Remarkably, TFAM protein levels did not directly dictate mtDNA content in the adult heart, and mitochondrial translation was preserved with acute TFAM inactivation, suggesting maintenance of respiratory chain assembly/function. Long-term Tfam inactivation, however, downregulated the core mtDNA transcription and replication machinery, leading to mitochondrial dysfunction and cardiomyopathy. Collectively, in contrast to the developing heart, these data reveal a striking resilience of the differentiated adult heart to acute insults to mtDNA regulation.
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Affiliation(s)
- Nasab Ghazal
- Division of Pediatric Cardiology, Department of Pediatrics, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, Georgia
| | - Jessica N Peoples
- Division of Pediatric Cardiology, Department of Pediatrics, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, Georgia
| | | | - Jennifer Q Kwong
- Division of Pediatric Cardiology, Department of Pediatrics, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, Georgia
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8
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Lakshmanan LN, Yee Z, Halliwell B, Gruber J, Gunawan R. Thermodynamic analysis of DNA hybridization signatures near mitochondrial DNA deletion breakpoints. iScience 2021; 24:102138. [PMID: 33665557 PMCID: PMC7900216 DOI: 10.1016/j.isci.2021.102138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 01/14/2021] [Accepted: 01/29/2021] [Indexed: 11/17/2022] Open
Abstract
Broad evidence in the literature supports double-strand breaks (DSBs) as initiators of mitochondrial DNA (mtDNA) deletion mutations. While DNA misalignment during DSB repair is commonly proposed as the mechanism by which DSBs cause deletion mutations, details such as the specific DNA repair errors are still lacking. Here, we used DNA hybridization thermodynamics to infer the sequence lengths of mtDNA misalignments that are associated with mtDNA deletions. We gathered and analyzed 9,921 previously reported mtDNA deletion breakpoints in human, rhesus monkey, mouse, rat, and Caenorhabditis elegans. Our analysis shows that a large fraction of mtDNA breakpoint positions can be explained by the thermodynamics of short ≤ 5-nt misalignments. The significance of short DNA misalignments supports an important role for erroneous non-homologous and micro-homology-dependent DSB repair in mtDNA deletion formation. The consistency of the results of our analysis across species further suggests a shared mode of mtDNA deletion mutagenesis.
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Affiliation(s)
- Lakshmi Narayanan Lakshmanan
- Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore
- Institute for Chemical and Bioengineering, ETH Zurich, Zurich, Switzerland
| | - Zhuangli Yee
- Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore, Singapore
| | - Barry Halliwell
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Jan Gruber
- Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- Ageing Research Laboratory, Science Division, Yale-NUS College, Singapore, Singapore
| | - Rudiyanto Gunawan
- Department of Chemical and Biological Engineering, University at Buffalo, Buffalo, NY, USA
- Corresponding author
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9
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Wolff CA, Reid JJ, Musci RV, Linden MA, Konopka AR, Peelor FF, Miller BF, Hamilton KL, Bruns DR. Differential Effects of Rapamycin and Metformin in Combination With Rapamycin on Mechanisms of Proteostasis in Cultured Skeletal Myotubes. J Gerontol A Biol Sci Med Sci 2020; 75:32-39. [PMID: 30820523 DOI: 10.1093/gerona/glz058] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 02/23/2019] [Indexed: 12/12/2022] Open
Abstract
mTOR inhibition extends life span in multiple organisms. In mice, when metformin treatment (Met) is added to the mTOR inhibitor rapamycin (Rap), median and maximal life span is extended to a greater degree than with Rap or Met alone. Treatments that extend life span often maintain proteostasis. However, it is less clear how individual tissues, such as skeletal muscle, maintain proteostasis with life span-extending treatments. In C2C12 myotubes, we used deuterium oxide (D2O) to directly measure two primary determinants of proteostasis, protein synthesis, and degradation rates, with Rap or Met+Rap treatments. We accounted for the independent effects of cell growth and loss, and isolated the contribution of autophagy and mitochondrial fission to obtain a comprehensive assessment of protein turnover. Compared with control, both Rap and Met+Rap treatments lowered mitochondrial protein synthesis rates (p < .001) and slowed cellular proliferation (p < .01). These changes resulted in greater activation of mechanisms promoting proteostasis for Rap, but not Met+Rap. Compared with control, both Rap and Met+Rap slowed protein breakdown. Autophagy and mitochondrial fission differentially influenced the proteostatic effects of Rap and Met+Rap in C2C12 myotubes. In conclusion, we demonstrate that Met+Rap did not increase protein turnover and that these treatments do not seem to promote proteostasis through increased autophagy.
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Affiliation(s)
- Christopher A Wolff
- Department of Health and Exercise Science, Colorado State University, Fort Collins
| | - Justin J Reid
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City
| | - Robert V Musci
- Department of Health and Exercise Science, Colorado State University, Fort Collins
| | - Melissa A Linden
- Department of Health and Exercise Science, Colorado State University, Fort Collins
| | - Adam R Konopka
- Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign
| | - Frederick F Peelor
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City
| | - Benjamin F Miller
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City
| | - Karyn L Hamilton
- Department of Health and Exercise Science, Colorado State University, Fort Collins
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10
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Cosemans C, Nawrot TS, Janssen BG, Vriens A, Smeets K, Baeyens W, Bruckers L, Den Hond E, Loots I, Nelen V, Van Larebeke N, Schoeters G, Martens D, Plusquin M. Breastfeeding predicts blood mitochondrial DNA content in adolescents. Sci Rep 2020; 10:387. [PMID: 31941967 PMCID: PMC6962168 DOI: 10.1038/s41598-019-57276-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Accepted: 12/19/2019] [Indexed: 02/06/2023] Open
Abstract
Nutrition during early childhood is linked to metabolic programming. We hypothesized that breastfeeding has long-term consequences on the energy metabolism exemplified by mitochondrial DNA (mtDNA). As part of the third cycle of the Flemish Environment and Health Study (FLEHSIII) cohort, 303 adolescents aged 14–15 years were included. We associated breastfeeding and blood mtDNA content 14–15 years later while adjusting for confounding variables. Compared with non-breastfed adolescents, mtDNA content was 23.1% (95%CI: 4.4–45.2; p = 0.013) higher in breastfed adolescents. Being breastfed for 1–10 weeks, 11–20 weeks, and >20 weeks, was associated with a higher mtDNA content of respectively 16.0% (95%CI: −7.1–44.9; p = 0.191), 23.5% (95%CI: 0.8–51.3; p = 0.042), and 31.5% (95%CI: 4.3–65.7; p = 0.021). Our study showed a positive association between breastfeeding and mtDNA content in adolescents which gradually increased with longer periods of breastfeeding. Higher mtDNA content may be an underlying mechanism of the beneficial effects of breastfeeding on children’s metabolism.
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Affiliation(s)
- Charlotte Cosemans
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Tim S Nawrot
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium.,School of Public Health, Occupational & Environmental Medicine, Leuven University, Leuven, Belgium
| | - Bram G Janssen
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Annette Vriens
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Karen Smeets
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Willy Baeyens
- Department of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
| | - Liesbeth Bruckers
- Interuniversity Institute for Biostatistics and Statistical Bioinformatics, Hasselt University, Hasselt, Belgium
| | | | - Ilse Loots
- Faculty of Social Sciences and IMDO-Institute, University of Antwerp, Antwerp, Belgium
| | - Vera Nelen
- Provincial Institute for Hygiene, Antwerp, Belgium
| | - Nicolas Van Larebeke
- Department of Radiotherapy and Experimental Cancerology, Ghent University, Ghent, Belgium.,Department of Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel, Brussels, Belgium
| | - Greet Schoeters
- Environmental Risk and Health, Flemish Institute for Technological Research (VITO), Mol, Belgium
| | - Dries Martens
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Michelle Plusquin
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium.
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11
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Hübner A, Wachsmuth M, Schröder R, Li M, Eis-Hübinger AM, Madea B, Stoneking M. Sharing of heteroplasmies between human liver lobes varies across the mtDNA genome. Sci Rep 2019; 9:11219. [PMID: 31375696 PMCID: PMC6677727 DOI: 10.1038/s41598-019-47570-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 07/16/2019] [Indexed: 01/10/2023] Open
Abstract
Mitochondrial DNA (mtDNA) heteroplasmy (intra-individual variation) varies among different human tissues and increases with age, suggesting that the majority of mtDNA heteroplasmies are acquired, rather than inherited. However, the extent to which heteroplasmic sites are shared across a tissue remains an open question. We therefore investigated heteroplasmy in two liver samples (one from each primary lobe) from 83 Europeans, sampled at autopsy. Minor allele frequencies (MAF) at heteroplasmic sites were significantly correlated between the two liver samples from an individual, with significantly more sharing of heteroplasmic sites in the control region than in the non-control region. We show that this increased sharing for the control region cannot be explained by recent mutations at just a few specific heteroplasmic sites or by the possible presence of 7S DNA. Moreover, we carried out simulations to show that there is significantly more sharing than would be predicted from random genetic drift from a common progenitor cell. We also observe a significant excess of non-synonymous vs. synonymous heteroplasmies in the protein-coding region, but significantly more sharing of synonymous heteroplasmies. These contrasting patterns for the control vs. the non-control region, and for non-synonymous vs. synonymous heteroplasmies, suggest that selection plays a role in heteroplasmy sharing.
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Affiliation(s)
- Alexander Hübner
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103, Leipzig, Germany.
| | - Manja Wachsmuth
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103, Leipzig, Germany
| | - Roland Schröder
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103, Leipzig, Germany
| | - Mingkun Li
- Key Laboratory of Genomic and Precision Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, 100101, Beijing, China
| | - Anna Maria Eis-Hübinger
- Institut für Virologie, Universitätsklinikum Bonn, Sigmund-Freud-Str. 25, D-53105, Bonn, Germany
| | - Burkhard Madea
- Institut für Rechtsmedizin, Universitätsklinikum Bonn, Stiftsplatz 12, D-53111, Bonn, Germany
| | - Mark Stoneking
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, D-04103, Leipzig, Germany.
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12
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Aryaman J, Bowles C, Jones NS, Johnston IG. Mitochondrial Network State Scales mtDNA Genetic Dynamics. Genetics 2019; 212:1429-1443. [PMID: 31253641 PMCID: PMC6707450 DOI: 10.1534/genetics.119.302423] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Accepted: 06/28/2019] [Indexed: 11/18/2022] Open
Abstract
Mitochondrial DNA (mtDNA) mutations cause severe congenital diseases but may also be associated with healthy aging. mtDNA is stochastically replicated and degraded, and exists within organelles which undergo dynamic fusion and fission. The role of the resulting mitochondrial networks in the time evolution of the cellular proportion of mutated mtDNA molecules (heteroplasmy), and cell-to-cell variability in heteroplasmy (heteroplasmy variance), remains incompletely understood. Heteroplasmy variance is particularly important since it modulates the number of pathological cells in a tissue. Here, we provide the first wide-reaching theoretical framework which bridges mitochondrial network and genetic states. We show that, under a range of conditions, the (genetic) rate of increase in heteroplasmy variance and de novo mutation are proportionally modulated by the (physical) fraction of unfused mitochondria, independently of the absolute fission-fusion rate. In the context of selective fusion, we show that intermediate fusion:fission ratios are optimal for the clearance of mtDNA mutants. Our findings imply that modulating network state, mitophagy rate, and copy number to slow down heteroplasmy dynamics when mean heteroplasmy is low could have therapeutic advantages for mitochondrial disease and healthy aging.
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Affiliation(s)
- Juvid Aryaman
- Department of Mathematics, Imperial College London, SW7 2AZ, United Kingdom
- Department of Clinical Neurosciences, University of Cambridge, CB2 0QQ, United Kingdom
- Medical Research Council Mitochondrial Biology Unit, University of Cambridge, CB2 0XY, United Kingdom
| | - Charlotte Bowles
- School of Biosciences, University of Birmingham, B15 2TT, United Kingdom
| | - Nick S Jones
- Department of Mathematics, Imperial College London, SW7 2AZ, United Kingdom
- Engineering and Physical Sciences Research Council Centre for the Mathematics of Precision Healthcare, Imperial College London, SW7 2AZ, United Kingdom
| | - Iain G Johnston
- Faculty of Mathematics and Natural Sciences, University of Bergen, 5007, Norway
- Alan Turing Institute, London NW1 2DB, United Kingdom
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13
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Mitochondrial DNA Variants and Common Diseases: A Mathematical Model for the Diversity of Age-Related mtDNA Mutations. Cells 2019; 8:cells8060608. [PMID: 31216686 PMCID: PMC6627076 DOI: 10.3390/cells8060608] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Revised: 05/30/2019] [Accepted: 06/14/2019] [Indexed: 12/18/2022] Open
Abstract
The mitochondrion is the only organelle in the human cell, besides the nucleus, with its own DNA (mtDNA). Since the mitochondrion is critical to the energy metabolism of the eukaryotic cell, it should be unsurprising, then, that a primary driver of cellular aging and related diseases is mtDNA instability over the life of an individual. The mutation rate of mammalian mtDNA is significantly higher than the mutation rate observed for nuclear DNA, due to the poor fidelity of DNA polymerase and the ROS-saturated environment present within the mitochondrion. In this review, we will discuss the current literature showing that mitochondrial dysfunction can contribute to age-related common diseases such as cancer, diabetes, and other commonly occurring diseases. We will then turn our attention to the likely role that mtDNA mutation plays in aging and senescence. Finally, we will use this context to develop a mathematical formula for estimating for the accumulation of somatic mtDNA mutations with age. This resulting model shows that almost 90% of non-proliferating cells would be expected to have at least 100 mutations per cell by the age of 70, and almost no cells would have fewer than 10 mutations, suggesting that mtDNA mutations may contribute significantly to many adult onset diseases.
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14
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Vincow ES, Thomas RE, Merrihew GE, Shulman NJ, Bammler TK, MacDonald JW, MacCoss MJ, Pallanck LJ. Autophagy accounts for approximately one-third of mitochondrial protein turnover and is protein selective. Autophagy 2019; 15:1592-1605. [PMID: 30865561 DOI: 10.1080/15548627.2019.1586258] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The destruction of mitochondria through macroautophagy (autophagy) has been recognised as a major route of mitochondrial protein degradation since its discovery more than 50 years ago, but fundamental questions remain unanswered. First, how much mitochondrial protein turnover occurs through auto-phagy? Mitochondrial proteins are also degraded by nonautophagic mechanisms, and the proportion of mitochondrial protein turnover that occurs through autophagy is still unknown. Second, does auto-phagy degrade mitochondrial proteins uniformly or selectively? Autophagy was originally thought to degrade all mitochondrial proteins at the same rate, but recent work suggests that mitochondrial autophagy may be protein selective. To investigate these questions, we used a proteomics-based approach in the fruit fly Drosophila melanogaster, comparing mitochondrial protein turnover rates in autophagy-deficient Atg7 mutants and controls. We found that ~35% of mitochondrial protein turnover occurred via autophagy. Similar analyses using parkin mutants revealed that parkin-dependent mitophagy accounted for ~25% of mitochondrial protein turnover, suggesting that most mitochondrial autophagy specifically eliminates dysfunctional mitochondria. We also found that our results were incompatible with uniform autophagic turnover of mitochondrial proteins and consistent with protein-selective autophagy. In particular, the autophagic turnover rates of individual mitochondrial proteins varied widely, and only a small amount of the variation could be attributed to tissue differences in mitochondrial composition and autophagy rate. Furthermore, analyses comparing autophagy-deficient and control human fibroblasts revealed diverse autophagy-dependent turnover rates even in homogeneous cells. In summary, our work indicates that autophagy acts selectively on mitochondrial proteins, and that most mitochondrial protein turnover occurs through non-autophagic processes. Abbreviations: Atg5: Autophagy-related 5 (Drosophila); ATG5: autophagy related 5 (human); Atg7: Autophagy-related 7 (Drosophila); ATG7: autophagy related 7 (human); DNA: deoxyribonucleic acid; ER: endoplasmic reticulum; GFP: green fluorescent protein; MS: mass spectrometry; park: parkin (Drosophila); Pink1: PTEN-induced putative kinase 1 (Drosophila); PINK1: PTEN-induced kinase 1 (human); PRKN: parkin RBR E3 ubiquitin protein ligase (human); RNA: ribonucleic acid; SD: standard deviation; Ub: ubiquitin/ubiquitinated; WT: wild-type; YME1L: YME1 like ATPase (Drosophila); YME1L1: YME1 like 1 ATPase (human).
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Affiliation(s)
- Evelyn S Vincow
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
| | - Ruth E Thomas
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
| | - Gennifer E Merrihew
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
| | - Nicholas J Shulman
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
| | - Theo K Bammler
- b Department of Environmental and Occupational Health Sciences, University of Washington , Seattle , WA , USA
| | - James W MacDonald
- b Department of Environmental and Occupational Health Sciences, University of Washington , Seattle , WA , USA
| | - Michael J MacCoss
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
| | - Leo J Pallanck
- a Department of Genome Sciences, University of Washington , Seattle , WA , USA
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15
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Lakshmanan LN, Yee Z, Ng LF, Gunawan R, Halliwell B, Gruber J. Clonal expansion of mitochondrial DNA deletions is a private mechanism of aging in long-lived animals. Aging Cell 2018; 17:e12814. [PMID: 30043489 PMCID: PMC6156498 DOI: 10.1111/acel.12814] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Revised: 05/25/2018] [Accepted: 06/13/2018] [Indexed: 02/06/2023] Open
Abstract
Disruption of mitochondrial metabolism and loss of mitochondrial DNA (mtDNA) integrity are widely considered as evolutionarily conserved (public) mechanisms of aging (López-Otín et al., Cell, 153, 2013 and 1194). Human aging is associated with loss in skeletal muscle mass and function (Sarcopenia), contributing significantly to morbidity and mortality. Muscle aging is associated with loss of mtDNA integrity. In humans, clonally expanded mtDNA deletions colocalize with sites of fiber breakage and atrophy in skeletal muscle. mtDNA deletions may therefore play an important, possibly causal role in sarcopenia. The nematode Caenorhabditis elegans also exhibits age-dependent decline in mitochondrial function and a form of sarcopenia. However, it is unclear if mtDNA deletions play a role in C. elegans aging. Here, we report identification of 266 novel mtDNA deletions in aging nematodes. Analysis of the mtDNA mutation spectrum and quantification of mutation burden indicates that (a) mtDNA deletions in nematode are extremely rare, (b) there is no significant age-dependent increase in mtDNA deletions, and (c) there is little evidence for clonal expansion driving mtDNA deletion dynamics. Thus, mtDNA deletions are unlikely to drive the age-dependent functional decline commonly observed in C. elegans. Computational modeling of mtDNA dynamics in C. elegans indicates that the lifespan of short-lived animals such as C. elegans is likely too short to allow for significant clonal expansion of mtDNA deletions. Together, these findings suggest that clonal expansion of mtDNA deletions is likely a private mechanism of aging predominantly relevant in long-lived animals such as humans and rhesus monkey and possibly in rodents.
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Affiliation(s)
- Lakshmi Narayanan Lakshmanan
- Institute for Chemical and BioengineeringETH ZurichZurichSwitzerland
- Swiss Institute of Bioinformatics, Quartier Sorge – Batiment GenopodeLausanneSwitzerland
| | - Zhuangli Yee
- Department of BiochemistryYong Loo Lin School of Medicine, National University of SingaporeSingapore
| | - Li Fang Ng
- Ageing Research Laboratory, Science DivisionYale‐NUS CollegeSingaporeSingapore
| | - Rudiyanto Gunawan
- Institute for Chemical and BioengineeringETH ZurichZurichSwitzerland
- Swiss Institute of Bioinformatics, Quartier Sorge – Batiment GenopodeLausanneSwitzerland
| | - Barry Halliwell
- Department of BiochemistryYong Loo Lin School of Medicine, National University of SingaporeSingapore
| | - Jan Gruber
- Department of BiochemistryYong Loo Lin School of Medicine, National University of SingaporeSingapore
- Ageing Research Laboratory, Science DivisionYale‐NUS CollegeSingaporeSingapore
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16
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Gruber J, Chen CB, Fong S, Ng LF, Teo E, Halliwell B. Caenorhabditis elegans: What We Can and Cannot Learn from Aging Worms. Antioxid Redox Signal 2015; 23:256-79. [PMID: 25544992 DOI: 10.1089/ars.2014.6210] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
SIGNIFICANCE The nematode Caenorhabditis elegans is a widely used model organism for research into aging. However, nematodes diverged from other animals between 600 and 1300 million years ago. Beyond the intuitive impression that some aspects of aging appear to be universal, is there evidence that insights into the aging process of nematodes may be applicable to humans? RECENT ADVANCES There have been a number of results in nematodes that appear to contradict long-held beliefs about mechanisms and causes of aging. For example, ablation of several key antioxidant systems has often failed to result in lifespan shortening in C. elegans. CRITICAL ISSUES While it is clear that some central signaling pathways controlling lifespan are broadly conserved across large evolutionary distances, it is less clear to what extent downstream molecular mechanisms of aging are conserved. In this review we discuss the biology of C. elegans and mammals in the context of aging and age-dependent diseases. We consider evidence from studies that attempt to investigate basic, possibly conserved mechanisms of aging especially in the context of the free radical theory of aging. Practical points, such as the need for blinding of lifespan studies and for appropriate biomarkers, are also considered. FUTURE DIRECTIONS As data on the aging process(es) in different organisms increase, it is becoming increasingly clear that there are both conserved (public) and private aspects to aging. It is important to explore the dividing lines between these two aspects and to be aware of the large gray areas in-between.
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Affiliation(s)
- Jan Gruber
- 1 Department of Biochemistry, National University of Singapore , Singapore, Singapore .,2 Yale-NUS College , Singapore, Singapore
| | - Ce-Belle Chen
- 3 Department of Physics, National University of Singapore , Singapore, Singapore
| | - Sheng Fong
- 4 Duke-NUS Graduate Medical School , Singapore, Singapore
| | - Li Fang Ng
- 1 Department of Biochemistry, National University of Singapore , Singapore, Singapore
| | - Emelyne Teo
- 1 Department of Biochemistry, National University of Singapore , Singapore, Singapore
| | - Barry Halliwell
- 1 Department of Biochemistry, National University of Singapore , Singapore, Singapore
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17
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Context-Dependent Role of Mitochondrial Fusion-Fission in Clonal Expansion of mtDNA Mutations. PLoS Comput Biol 2015; 11:e1004183. [PMID: 25996936 PMCID: PMC4440705 DOI: 10.1371/journal.pcbi.1004183] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Accepted: 02/09/2015] [Indexed: 12/14/2022] Open
Abstract
The accumulation of mutant mitochondrial DNA (mtDNA) molecules in aged cells has been associated with mitochondrial dysfunction, age-related diseases and the ageing process itself. This accumulation has been shown to often occur clonally, where mutant mtDNA grow in number and overpopulate the wild-type mtDNA. However, the cell possesses quality control (QC) mechanisms that maintain mitochondrial function, in which dysfunctional mitochondria are isolated and removed by selective fusion and mitochondrial autophagy (mitophagy), respectively. The aim of this study is to elucidate the circumstances related to mitochondrial QC that allow the expansion of mutant mtDNA molecules. For the purpose of the study, we have developed a mathematical model of mitochondrial QC process by extending our previous validated model of mitochondrial turnover and fusion-fission. A global sensitivity analysis of the model suggested that the selectivity of mitophagy and fusion is the most critical QC parameter for clearing de novo mutant mtDNA molecules. We further simulated several scenarios involving perturbations of key QC parameters to gain a better understanding of their dynamic and synergistic interactions. Our model simulations showed that a higher frequency of mitochondrial fusion-fission can provide a faster clearance of mutant mtDNA, but only when mutant–rich mitochondria that are transiently created are efficiently prevented from re-fusing with other mitochondria and selectively removed. Otherwise, faster fusion-fission quickens the accumulation of mutant mtDNA. Finally, we used the insights gained from model simulations and analysis to propose a possible circumstance involving deterioration of mitochondrial QC that permits mutant mtDNA to expand with age. Mitochondria are responsible for most energy generation in human and animal cells. Loss or pathological alteration of mitochondrial function is a hallmark of many age-related diseases. Mitochondrial dysfunction may be a central and conserved feature of the ageing process. As part of quality control (QC), mitochondria are continually replicated and degraded. Furthermore, two mitochondria can fuse to form a single mitochondrion, and a mitochondrion can divide (fission) into two separate organelles. Despite this QC, mutant mitochondrial DNA (mtDNA) molecules have been observed to accumulate in cells with age which may lead to mitochondrial dysfunction. In this study, we created a detailed mathematical model of mitochondrial QC and performed model simulations to investigate circumstances allowing or preventing the accumulation of mutant mtDNA. We found that more frequent fusion-fission could quicken mutant mtDNA clearance, but only when mitochondria harboring a high fraction of mutant molecules were strongly prevented from fusing with other mitochondria and selectively degraded. Otherwise, faster fusion-fission would actually enhance the accumulation of mutant mtDNA. Our results suggested that the expansion of mutant mtDNA likely involves a decline in the selectivity of mitochondrial degradation and fusion. This insight might open new avenues for experiment and possible development of future therapies.
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18
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Lakshmanan LN, Gruber J, Halliwell B, Gunawan R. Are mutagenic non D-loop direct repeat motifs in mitochondrial DNA under a negative selection pressure? Nucleic Acids Res 2015; 43:4098-108. [PMID: 25855815 PMCID: PMC4417187 DOI: 10.1093/nar/gkv299] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 03/26/2015] [Indexed: 12/22/2022] Open
Abstract
Non D-loop direct repeats (DRs) in mitochondrial DNA (mtDNA) have been commonly implicated in the mutagenesis of mtDNA deletions associated with neuromuscular disease and ageing. Further, these DRs have been hypothesized to put a constraint on the lifespan of mammals and are under a negative selection pressure. Using a compendium of 294 mammalian mtDNA, we re-examined the relationship between species lifespan and the mutagenicity of such DRs. Contradicting the prevailing hypotheses, we found no significant evidence that long-lived mammals possess fewer mutagenic DRs than short-lived mammals. By comparing DR counts in human mtDNA with those in selectively randomized sequences, we also showed that the number of DRs in human mtDNA is primarily determined by global mtDNA properties, such as the bias in synonymous codon usage (SCU) and nucleotide composition. We found that SCU bias in mtDNA positively correlates with DR counts, where repeated usage of a subset of codons leads to more frequent DR occurrences. While bias in SCU and nucleotide composition has been attributed to nucleotide mutational bias, mammalian mtDNA still exhibit higher SCU bias and DR counts than expected from such mutational bias, suggesting a lack of negative selection against non D-loop DRs.
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Affiliation(s)
- Lakshmi Narayanan Lakshmanan
- Institute for Chemical and Bioengineering, ETH Zurich, Zurich 8093, Switzerland Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore 117585, Singapore
| | - Jan Gruber
- Yale-NUS College, Department of Biochemistry, Neurobiology and Ageing Program, National University of Singapore, Singapore 117599, Singapore
| | - Barry Halliwell
- Department of Biochemistry, Neurobiology and Ageing Program, Centre for Life Sciences (CeLS), National University of Singapore, Singapore 117599, Singapore
| | - Rudiyanto Gunawan
- Institute for Chemical and Bioengineering, ETH Zurich, Zurich 8093, Switzerland Swiss Institute of Bioinformatics, Quartier Sorge - Batiment Genopode, 1015 Lausanne, Switzerland
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19
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Mitochondrial function and mitochondrial DNA maintenance with advancing age. Biogerontology 2014; 15:417-38. [PMID: 25015781 DOI: 10.1007/s10522-014-9515-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Accepted: 07/01/2014] [Indexed: 12/24/2022]
Abstract
We review the impact of mitochondrial DNA (mtDNA) maintenance and mitochondrial function on the aging process. Mitochondrial function and mtDNA integrity are closely related. In order to create a protective barrier against reactive oxygen and nitrogen species (RONS) attacks and ensure mtDNA integrity, multiple cellular mtDNA copies are packaged together with various proteins in nucleoids. Regulation of antioxidant and RONS balance, DNA base excision repair, and selective degradation of damaged mtDNA copies preserves normal mtDNA quantities. Oxidative damage to mtDNA molecules does not substantially contribute to increased mtDNA mutation frequency; rather, mtDNA replication errors of DNA PolG are the main source of mtDNA mutations. Mitochondrial turnover is the major contributor to maintenance of mtDNA and functionally active mitochondria. Mitochondrial turnover involves mitochondrial biogenesis, mitochondrial dynamics, and selective autophagic removal of dysfunctional mitochondria (i.e., mitophagy). All of these processes exhibit decreased activity during aging and fall under greater nuclear genome control, possibly coincident with the emergence of nuclear genome instability. We suggest that the age-dependent accumulation of mutated mtDNA copies and dysfunctional mitochondria is associated primarily with decreased cellular autophagic and mitophagic activity.
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20
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Tam ZY, Gruber J, Ng LF, Halliwell B, Gunawan R. Effects of lithium on age-related decline in mitochondrial turnover and function in Caenorhabditis elegans. J Gerontol A Biol Sci Med Sci 2014; 69:810-20. [PMID: 24398558 DOI: 10.1093/gerona/glt210] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Aging has been associated with the accumulation of damages in molecules and organelles in cells, particularly mitochondria. The rate of damage accumulation is closely tied to the turnover of the affected cellular components. Perturbing mitochondrial turnover has been shown to significantly affect the rate of deterioration of mitochondrial function with age and to alter lifespan of model organisms. In this study, we investigated the effects of upregulating autophagy using lithium in Caenorhabditis elegans. We found that lithium treatment increased both the lifespan and healthspan of C. elegans without any significant change in the mortality rate and oxidative damages to proteins. The increase in healthspan was accompanied by improved mitochondrial energetic function. In contrast, mitochondrial DNA copy number decreased faster with age under lithium. To better understand the interactions among mitochondrial turnover, damage, and function, we created a mathematical model that described the dynamics of functional and dysfunctional mitochondria population. The combined analysis of model and experimental observations showed how preferential (selective) autophagy of dysfunctional mitochondria could lead to better mitochondrial functionality with age, despite a lower population size. However, the results of model analysis suggest that the benefit of increasing autophagy for mitochondrial function is expected to diminish at higher levels of upregulation due to a shrinking mitochondrial population.
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Affiliation(s)
- Zhi Yang Tam
- Institute for Chemical and Bioengineering, ETH Zurich, Switzerland
| | - Jan Gruber
- Department of Biochemistry, Centre for Life Sciences and Yale-NUS College, Science Division, National University of Singapore, Singapore
| | - Li Fang Ng
- Department of Biochemistry, Centre for Life Sciences and
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21
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Tam ZY, Gruber J, Halliwell B, Gunawan R. Mathematical modeling of the role of mitochondrial fusion and fission in mitochondrial DNA maintenance. PLoS One 2013; 8:e76230. [PMID: 24146842 PMCID: PMC3795767 DOI: 10.1371/journal.pone.0076230] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Accepted: 08/21/2013] [Indexed: 11/29/2022] Open
Abstract
Accumulation of mitochondrial DNA (mtDNA) mutations has been implicated in a wide range of human pathologies, including neurodegenerative diseases, sarcopenia, and the aging process itself. In cells, mtDNA molecules are constantly turned over (i.e. replicated and degraded) and are also exchanged among mitochondria during the fusion and fission of these organelles. While the expansion of a mutant mtDNA population is believed to occur by random segregation of these molecules during turnover, the role of mitochondrial fusion-fission in this context is currently not well understood. In this study, an in silico modeling approach is taken to investigate the effects of mitochondrial fusion and fission dynamics on mutant mtDNA accumulation. Here we report model simulations suggesting that when mitochondrial fusion-fission rate is low, the slow mtDNA mixing can lead to an uneven distribution of mutant mtDNA among mitochondria in between two mitochondrial autophagic events leading to more stochasticity in the outcomes from a single random autophagic event. Consequently, slower mitochondrial fusion-fission results in higher variability in the mtDNA mutation burden among cells in a tissue over time, and mtDNA mutations have a higher propensity to clonally expand due to the increased stochasticity. When these mutations affect cellular energetics, nuclear retrograde signalling can upregulate mtDNA replication, which is expected to slow clonal expansion of these mutant mtDNA. However, our simulations suggest that the protective ability of retrograde signalling depends on the efficiency of fusion-fission process. Our results thus shed light on the interplay between mitochondrial fusion-fission and mtDNA turnover and may explain the mechanism underlying the experimentally observed increase in the accumulation of mtDNA mutations when either mitochondrial fusion or fission is inhibited.
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Affiliation(s)
- Zhi Yang Tam
- Institute for Chemical and Bioengineering, ETH Zurich, Zurich, Switzerland
| | - Jan Gruber
- Department of Biochemistry, Centre for Life Sciences, National University of Singapore, Singapore, Singapore
| | - Barry Halliwell
- Department of Biochemistry, Centre for Life Sciences, National University of Singapore, Singapore, Singapore
| | - Rudiyanto Gunawan
- Institute for Chemical and Bioengineering, ETH Zurich, Zurich, Switzerland
- * E-mail:
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22
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Scotti M, Stella L, Shearer EJ, Stover PJ. Modeling cellular compartmentation in one-carbon metabolism. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2013; 5:343-65. [PMID: 23408533 DOI: 10.1002/wsbm.1209] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Folate-mediated one-carbon metabolism (FOCM) is associated with risk for numerous pathological states including birth defects, cancers, and chronic diseases. Although the enzymes that constitute the biological pathways have been well described and their interdependency through the shared use of folate cofactors appreciated, the biological mechanisms underlying disease etiologies remain elusive. The FOCM network is highly sensitive to nutritional status of several B-vitamins and numerous penetrant gene variants that alter network outputs, but current computational approaches do not fully capture the dynamics and stochastic noise of the system. Combining the stochastic approach with a rule-based representation will help model the intrinsic noise displayed by FOCM, address the limited flexibility of standard simulation methods for coarse-graining the FOCM-associated biochemical processes, and manage the combinatorial complexity emerging from reactions within FOCM that would otherwise be intractable.
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Affiliation(s)
- Marco Scotti
- The Microsoft Research-University of Trento Centre for Computational and Systems Biology (COSBI), Rovereto, Italy
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