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Shinde A, Deore G, Navsariwala KP, Tabassum H, Wani M. We are all aging, and here's why. Aging Med (Milton) 2022; 5:211-231. [PMID: 36247337 PMCID: PMC9549314 DOI: 10.1002/agm2.12223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 09/02/2022] [Accepted: 09/04/2022] [Indexed: 11/12/2022] Open
Abstract
Here, through this review, we aim to serve this purpose by first discussing the statistics and aging demographics, including the life expectancy of the world and India, along with the gender life expectancy gap observed throughout the world, followed by explaining the hallmarks and integral causes of aging, along with the role played by senescent cells in controlling inflammation and the effect of senescence associated secretory phenotype on longevity. A few of the molecular pathways which are crucial in modulating the process of aging, such as the nutrient-sensing mTOR pathway, insulin signaling, Nrf2, FOXO, PI3-Akt, Sirtuins, and AMPK, and their effects are also covered in paramount detail. A diverse number of ingenious research methodologies are used in the modern era of longevity exploration. We have attempted to cover these methods under the umbrella of three broad categories: in vitro, in vivo, and in silico techniques. The drugs developed to attenuate the aging process, such as rapamycin, metformin, resveratrol, etc. and their interactions with the above-mentioned molecular pathways along with their toxicity have also been reviewed in detail.
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Affiliation(s)
- Atharva Shinde
- Dr. D. Y. Patil Biotechnology and Bioinformatics InstituteDr. D. Y. Patil VidyapeethPuneMaharashtraIndia
| | - Gargi Deore
- Dr. D. Y. Patil Biotechnology and Bioinformatics InstituteDr. D. Y. Patil VidyapeethPuneMaharashtraIndia
| | - Kedar P. Navsariwala
- Dr. D. Y. Patil Biotechnology and Bioinformatics InstituteDr. D. Y. Patil VidyapeethPuneMaharashtraIndia
| | - Heena Tabassum
- Dr. D. Y. Patil Biotechnology and Bioinformatics InstituteDr. D. Y. Patil VidyapeethPuneMaharashtraIndia
| | - Minal Wani
- Dr. D. Y. Patil Biotechnology and Bioinformatics InstituteDr. D. Y. Patil VidyapeethPuneMaharashtraIndia
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Vijg J. From DNA damage to mutations: All roads lead to aging. Ageing Res Rev 2021; 68:101316. [PMID: 33711511 PMCID: PMC10018438 DOI: 10.1016/j.arr.2021.101316] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 02/26/2021] [Accepted: 03/03/2021] [Indexed: 12/20/2022]
Abstract
Damage to the repository of genetic information in cells has plagued life since its very beginning 3-4 billion years ago. Initially, in the absence of an ozone layer, especially damage from solar UV radiation must have been frequent, with other sources, most notably endogenous sources related to cell metabolism, gaining in importance over time. To cope with this high frequency of damage to the increasingly long DNA molecules that came to encode the growing complexity of cellular functions in cells, DNA repair evolved as one of the earliest genetic traits. Then as now, errors during the repair of DNA damage generated mutations, which provide the substrate for evolution by natural selection. With the emergence of multicellular organisms also the soma became a target of DNA damage and mutations. In somatic cells selection against the adverse effects of DNA damage is greatly diminished, especially in postmitotic cells after the age of first reproduction. Based on an abundance of evidence, DNA damage is now considered as the single most important driver of the degenerative processes that collectively cause aging. Here I will first briefly review the evidence for DNA damage as a cause of aging since the beginning of life. Then, after discussing the possible direct adverse effects of DNA damage and its cellular responses, I will provide an overview of the considerable progress that has recently been made in analyzing a major consequence of DNA damage in humans and other complex organisms: somatic mutations and the resulting genome mosaicism. Recent advances in studying somatic mutagenesis and genome mosaicism in different human and animal tissues will be discussed with a focus on the possible mechanisms through which loss of DNA sequence integrity could cause age-related functional decline and disease.
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Affiliation(s)
- Jan Vijg
- Department of Genetics, Albert Einstein College of Medicine, Bronx, NY, USA; Center for Single-Cell Omics, School of Public Health, Shanghai Jiao Tong University, School of Medicine, Shanghai, China.
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Zhawar VK, Kandpal RP, Athwal RS. Senescence of Normal Human Fibroblasts Relates to the Expression of Ionotropic Glutamate Receptor GluR6/Grik2. Cancer Genomics Proteomics 2020; 17:707-714. [PMID: 33099472 PMCID: PMC7675648 DOI: 10.21873/cgp.20225] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2020] [Revised: 09/10/2020] [Accepted: 09/11/2020] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND/AIM Glutamate receptor GRIK2, previously designated as GluR6, is best described in neuronal cells. However, its biological relevance in non-neuronal cells is not well understood. We have investigated the expression of this important protein in normal human fibroblasts as a function of cell proliferation. MATERIALS AND METHODS We introduced expression constructs of all five isoforms (A-E) of GRIK2 in normal human fibroblasts and investigated the cells for the presence and localization of GRIK2, as well as for cell proliferation and senescence over a period of 24 days. RESULTS The expression of GRIK2-A isoform led to immediate cessation of cell proliferation. However, the cell numbers increased by 1.5- to 9.0-fold in 24 days upon transfection with B, C, D and E isoforms, after which they entered a state of senescence. The decreased proliferation was reflected by incorporation of BrdU in only 2-8% of transfected cells even after culturing them for 16 days. CONCLUSION Our results are indicative of an association between GRIK2 and aging of fibroblasts.
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Affiliation(s)
- Vikramjit K Zhawar
- Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, PA, U.S.A
| | - Raj P Kandpal
- Department of Basic Medical Sciences, Western University of Health Sciences, Pomona, CA, U.S.A.
| | - Raghbir S Athwal
- Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, PA, U.S.A.
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Wattis JAD, Qi Q, Byrne HM. Mathematical modelling of telomere length dynamics. J Math Biol 2020; 80:1039-1076. [PMID: 31728621 PMCID: PMC7028829 DOI: 10.1007/s00285-019-01448-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 11/01/2019] [Indexed: 12/21/2022]
Abstract
Telomeres are repetitive DNA sequences located at the ends of chromosomes. During cell division, an incomplete copy of each chromosome's DNA is made, causing telomeres to shorten on successive generations. When a threshold length is reached replication ceases and the cell becomes 'senescent'. In this paper, we consider populations of telomeres and, from discrete models, we derive partial differential equations which describe how the distribution of telomere lengths evolves over many generations. We initially consider a population of cells each containing just a single telomere. We use continuum models to compare the effects of various mechanisms of telomere shortening and rates of cell division during normal ageing. For example, the rate (or probability) of cell replication may be fixed or it may decrease as the telomeres shorten. Furthermore, the length of telomere lost on each replication may be constant, or may decrease as the telomeres shorten. Where possible, explicit solutions for the evolution of the distribution of telomere lengths are presented. In other cases, expressions for the mean of the distribution are derived. We extend the models to describe cell populations in which each cell contains a distinct subpopulation of chromosomes. As for the simpler models, constant telomere shortening leads to a linear reduction in telomere length over time, whereas length-dependent shortening results in initially rapid telomere length reduction, slowing at later times. Our analysis also reveals that constant telomere loss leads to a Gaussian (normal) distribution of telomere lengths, whereas length-dependent loss leads to a log-normal distribution. We show that stochastic models, which include a replication probability, also lead to telomere length distributions which are skewed.
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Affiliation(s)
| | - Qi Qi
- School of Mathematical Sciences, University of Nottingham, Nottingham, NG7 2RD UK
| | - Helen M Byrne
- Mathematics Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford, OX2 6GG UK
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Sturm Á, Perczel A, Ivics Z, Vellai T. The Piwi-piRNA pathway: road to immortality. Aging Cell 2017; 16:906-911. [PMID: 28653810 PMCID: PMC5595689 DOI: 10.1111/acel.12630] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/20/2017] [Indexed: 12/20/2022] Open
Abstract
Despite its medical, social, and economic significance, understanding what primarily causes aging, that is, the mechanisms of the aging process, remains a fundamental and fascinating problem in biology. Accumulating evidence indicates that a small RNA-based gene regulatory machinery, the Piwi-piRNA pathway, represents a shared feature of nonaging (potentially immortal) biological systems, including the germline, somatic cancer stem cells, and certain 'lower' eukaryotic organisms like the planarian flatworm and freshwater hydra. The pathway primarily functions to repress the activity of mobile genetic elements, also called transposable elements (TEs) or 'jumping genes', which are capable of moving from one genomic locus to another, thereby causing insertional mutations. TEs become increasingly active and multiply in the genomes of somatic cells as the organism ages. These characteristics of TEs highlight their decisive mutagenic role in the progressive disintegration of genetic information, a molecular hallmark associated with aging. Hence, TE-mediated genomic instability may substantially contribute to the aging process.
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Affiliation(s)
- Ádám Sturm
- Department of Genetics; Eötvös Loránd University; Budapest Hungary
| | - András Perczel
- MTA-ELTE Protein Modelling Research Group; Institute of Chemistry; Eötvös Loránd University; Budapest Hungary
| | - Zoltán Ivics
- Division of Medical Biotechnology; Paul Ehrlich Institute; 63225 Langen Germany
| | - Tibor Vellai
- Department of Genetics; Eötvös Loránd University; Budapest Hungary
- MTA-ELTE Genetics Research Group; Budapest Hungary
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Mc Auley MT, Guimera AM, Hodgson D, Mcdonald N, Mooney KM, Morgan AE, Proctor CJ. Modelling the molecular mechanisms of aging. Biosci Rep 2017; 37:BSR20160177. [PMID: 28096317 PMCID: PMC5322748 DOI: 10.1042/bsr20160177] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 12/15/2016] [Accepted: 01/16/2017] [Indexed: 01/09/2023] Open
Abstract
The aging process is driven at the cellular level by random molecular damage that slowly accumulates with age. Although cells possess mechanisms to repair or remove damage, they are not 100% efficient and their efficiency declines with age. There are many molecular mechanisms involved and exogenous factors such as stress also contribute to the aging process. The complexity of the aging process has stimulated the use of computational modelling in order to increase our understanding of the system, test hypotheses and make testable predictions. As many different mechanisms are involved, a wide range of models have been developed. This paper gives an overview of the types of models that have been developed, the range of tools used, modelling standards and discusses many specific examples of models that have been grouped according to the main mechanisms that they address. We conclude by discussing the opportunities and challenges for future modelling in this field.
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Affiliation(s)
- Mark T Mc Auley
- Faculty of Science and Engineering, University of Chester, Chester, U.K
| | - Alvaro Martinez Guimera
- MRC/Arthritis Research UK Centre for Musculoskeletal Ageing (CIMA), Newcastle University, Newcastle upon Tyne, Ormskirk, U.K
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, U.K
| | - David Hodgson
- MRC/Arthritis Research UK Centre for Musculoskeletal Ageing (CIMA), Newcastle University, Newcastle upon Tyne, Ormskirk, U.K
- Musculoskeletal Research Group, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, U.K
| | - Neil Mcdonald
- MRC/Arthritis Research UK Centre for Musculoskeletal Ageing (CIMA), Newcastle University, Newcastle upon Tyne, Ormskirk, U.K
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, U.K
| | | | - Amy E Morgan
- Faculty of Science and Engineering, University of Chester, Chester, U.K
| | - Carole J Proctor
- MRC/Arthritis Research UK Centre for Musculoskeletal Ageing (CIMA), Newcastle University, Newcastle upon Tyne, Ormskirk, U.K.
- Musculoskeletal Research Group, Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, U.K
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Which Is the Most Significant Cause of Aging? Antioxidants (Basel) 2015; 4:793-810. [PMID: 26783959 PMCID: PMC4712935 DOI: 10.3390/antiox4040793] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 11/19/2015] [Accepted: 12/02/2015] [Indexed: 12/19/2022] Open
Abstract
It becomes clearer and clearer that aging is a result of a significant number of causes and it would seem that counteracting one or several of them should not make a significant difference. Taken at face value, this suggests, for example, that free radicals and reactive oxygen species do not play a significant role in aging and that the lifespan of organisms cannot be significantly extended. In this review, I point to the fact that the causes of aging synergize with each other and discuss the implications involved. One implication is that when two or more synergizing causes increase over time, the result of their action increases dramatically; I discuss a simple model demonstrating this. It is reasonable to conclude that this might explain the acceleration of aging and mortality with age. In this regard, the analysis of results and mortality patterns described in studies involving yeasts and Drosophila provides support for this view. Since the causes of aging are synergizing, it is also concluded that none of them is the major one but many including free radicals, etc. play significant roles. It follows that health/lifespan might be significantly extended if we eliminate or even attenuate the increase of a few or even just one of the causes of aging. While the synergism between the causes of aging is the main topic of this review, several related matters are briefly discussed as well.
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Sturm Á, Ivics Z, Vellai T. The mechanism of ageing: primary role of transposable elements in genome disintegration. Cell Mol Life Sci 2015; 72:1839-47. [PMID: 25837999 PMCID: PMC11113528 DOI: 10.1007/s00018-015-1896-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Revised: 03/16/2015] [Accepted: 03/25/2015] [Indexed: 01/11/2023]
Abstract
Understanding the molecular basis of ageing remains a fundamental problem in biology. In multicellular organisms, while the soma undergoes a progressive deterioration over the lifespan, the germ line is essentially immortal as it interconnects the subsequent generations. Genomic instability in somatic cells increases with age, and accumulating evidence indicates that the disintegration of somatic genomes is accompanied by the mobilisation of transposable elements (TEs) that, when mobilised, can be mutagenic by disrupting coding or regulatory sequences. In contrast, TEs are effectively silenced in the germ line by the Piwi-piRNA system. Here, we propose that TE repression transmits the persistent proliferation capacity and the non-ageing phenotype (e.g., preservation of genomic integrity) of the germ line. The Piwi-piRNA pathway also operates in tumorous cells and in somatic cells of certain organisms, including hydras, which likewise exhibit immortality. However, in somatic cells lacking the Piwi-piRNA pathway, gradual chromatin decondensation increasingly allows the mobilisation of TEs as the organism ages. This can explain why the mortality rate rises exponentially throughout the adult life in most animal species, including humans.
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Affiliation(s)
- Ádám Sturm
- Department of Genetics, Eötvös Loránd University, Pázmány Péter stny. 1/C, Budapest, Hungary
| | - Zoltán Ivics
- Division of Medical Biotechnology, Paul Ehrlich Institute, 63225 Langen, Germany
| | - Tibor Vellai
- Department of Genetics, Eötvös Loránd University, Pázmány Péter stny. 1/C, Budapest, Hungary
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9
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Abstract
A concerted balance between proliferation and apoptosis is essential to the survival of multicellular organisms. Thus, apoptosis per se, although it is a destructive process leading to the death of single cells, also serves as a pro-survival mechanism pro-survival mechanism that ensures healthy organismal development and acts as a life-prolonging or anti-aging anti-aging program. The discovery that yeast also possess a functional and, in many cases, highly conserved apoptotic machinery has made it possible to study the relationships between aging and apoptosis in depth using a well-established genetic system and the powerful tools available to yeast researchers for investigating complex physiological and cytological interactions. The aging process of yeast, be it replicative replicative or chronological chronological aging, is closely related to apoptosis, although it remains unclear whether apoptosis is a causal feature of the aging process or vice versa. Nevertheless, experimental results obtained during the past several years clearly demonstrate that yeast serve as a powerful and versatile experimental system for understanding the interconnections between these two fundamentally important cellular and physiological pathways.
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Affiliation(s)
- Peter Laun
- Division of Genetics, Department of Cell Biology, University of Salzburg, Salzburg, Austria,
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10
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Abstract
Ageing is intrinsically complex, being driven by multiple causal mechanisms. Each mechanism tends to be partially supported by data indicating that it has a role in the overall cellular and molecular pathways underlying the ageing process. However, the magnitude of this role is usually modest. The systems biology approach combines (i) data-driven modelling, often using the large volumes of data generated by functional genomics technologies, and (ii) hypothesis-driven experimental studies to investigate causal pathways and identify their parameter values in an unusually quantitative manner, which enables the contributions of individual mechanisms and their interactions to be better understood, and allows for the design of experiments explicitly to test the complex predictions arising from such models. A clear example of the success of the systems biology approach in unravelling the complexity of ageing can be seen in recent studies on cell replicative senescence, revealing interactions between mitochondrial dysfunction, telomere erosion and DNA damage. An important challenge also exists in connecting the network of (random) damage-driven proximate mechanisms of ageing with the higher level (genetically specified) signalling pathways that influence longevity. This connection is informed by actions of natural selection on the determinants of ageing and longevity.
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Affiliation(s)
- Thomas B L Kirkwood
- Institute for Ageing and Health, Newcastle University, Campus for Ageing and Vitality, Newcastle upon Tyne, NE4 5PL, UK.
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11
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Stambrook PJ, Tichy ED. Preservation of genomic integrity in mouse embryonic stem cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 695:59-75. [PMID: 21222199 DOI: 10.1007/978-1-4419-7037-4_5] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Embryonic stem (ES) cells and germ cells have the potential to give rise to an entire organism. A common requirement is that both must have very robust mechanisms to preserve the integrity of their genomes. This is particularly true since somatic cells have very high mutation frequencies approaching 10-4 in vivo that would lead to unacceptable levels of fetal lethality and congenital defects. Notably, between 70% and 80% of mutational events monitored at a heterozygous endogenous selectable marker were loss of heterozygosity due to mitotic recombination, a mechanism that affects multiple heterozygous loci between the reporter gene and the site of crossing over. This chapter examines three mechanisms by which mouse embryonic stem cells preserve their genomic integrity. The first entails suppression of mutation and recombination between chromosome homologues by two orders of magnitude when compared with isogenic mouse embryo fibroblasts which had a mutation frequency similar to that seen in adult somatic cells. The second renders mouse ES cells hypersensitive to environmental challenge and eliminates damaged cells from the self-renewing population. Mouse ES cells lack a G1 checkpoint so that cells damaged by exogenous insult such as ionizing radiation do not arrest at the G1/S phase checkpoint but progress into the S phase where the damaged DNA is replicated, the damage exacerbated and the cells driven to apoptosis. The third mechanism examines how mouse ES cells repair double strand DNA breaks. Somatic cells predominantly utilize error prone nonhomologous end joining which, from a teleological perspective, would be disadvantageous for ES cells since it would promote accumulation of mutations. When ES cells were tested for the preferred pathway of double strand DNA break repair, they predominantly utilized the high fidelity homology-mediated repair pathway, thereby minimizing the incurrence of mutations during the repair process. When mouse ES cells are induced to differentiate, the predominant repair pathway switches from homology-mediated repair to nonhomologous end joining that is characteristic of somatic cells.
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Affiliation(s)
- Peter J Stambrook
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, Ohio, 45267-0524, USA,
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Abstract
This year marks the 50th anniversary of a nearly forgotten hypothesis on aging by Leo Szilard, best known for his pioneering work in nuclear physics, his participation in the Manhattan Project during World War II, his opposition to the nuclear arms race in the postwar era, and his pioneering ideas in biology. Given a specific set of assumptions, Szilard hypothesized that the major reason for the phenomenon of aging was aging hits, e.g., by ionizing radiation, to the gene-bearing chromosomes and presented a mathematical target-hit model enabling the calculation of the average and maximum life span of a species, as well as the influence of increased exposure to DNA-damaging factors on life expectancy. While many new findings have cast doubt on the specific features of the model, this was the first serious effort to posit accumulated genetic damage as a cause of senescence. Here, we review Szilard's assumptions in the light of current knowledge on aging and reassess his mathematical model in an attempt to reach a conclusion on the relevance of Szilard's aging hypothesis today.
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Laun P, Heeren G, Rinnerthaler M, Rid R, Kössler S, Koller L, Breitenbach M. Senescence and apoptosis in yeast mother cell-specific aging and in higher cells: A short review. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:1328-34. [DOI: 10.1016/j.bbamcr.2008.02.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2008] [Revised: 02/12/2008] [Accepted: 02/13/2008] [Indexed: 01/30/2023]
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Wilson DM, Bohr VA, McKinnon PJ. DNA damage, DNA repair, ageing and age-related disease. Mech Ageing Dev 2008; 129:349-52. [PMID: 18420253 DOI: 10.1016/j.mad.2008.02.013] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Revised: 02/24/2008] [Accepted: 02/28/2008] [Indexed: 11/19/2022]
Affiliation(s)
- David M Wilson
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
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Laun P, Bruschi CV, Dickinson JR, Rinnerthaler M, Heeren G, Schwimbersky R, Rid R, Breitenbach M. Yeast mother cell-specific ageing, genetic (in)stability, and the somatic mutation theory of ageing. Nucleic Acids Res 2007; 35:7514-26. [PMID: 17986449 PMCID: PMC2190697 DOI: 10.1093/nar/gkm919] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Yeast mother cell-specific ageing is characterized by a limited capacity to produce daughter cells. The replicative lifespan is determined by the number of cell cycles a mother cell has undergone, not by calendar time, and in a population of cells its distribution follows the Gompertz law. Daughter cells reset their clock to zero and enjoy the full lifespan characteristic for the strain. This kind of replicative ageing of a cell population based on asymmetric cell divisions is investigated as a model for the ageing of a stem cell population in higher organisms. The simple fact that the daughter cells can reset their clock to zero precludes the accumulation of chromosomal mutations as the cause of ageing, because semiconservative replication would lead to the same mutations in the daughters. However, nature is more complicated than that because, (i) the very last daughters of old mothers do not reset the clock; and (ii) mutations in mitochondrial DNA could play a role in ageing due to the large copy number in the cell and a possible asymmetric distribution of damaged mitochondrial DNA between mother and daughter cell. Investigation of the loss of heterozygosity in diploid cells at the end of their mother cell-specific lifespan has shown that genomic rearrangements do occur in old mother cells. However, it is not clear if this kind of genomic instability is causative for the ageing process. Damaged material other than DNA, for instance misfolded, oxidized or otherwise damaged proteins, seem to play a major role in ageing, depending on the balance between production and removal through various repair processes, for instance several kinds of proteolysis and autophagy. We are reviewing here the evidence for genetic change and its causality in the mother cell-specific ageing process of yeast.
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Affiliation(s)
- Peter Laun
- Department of Cell Biology, Division of Genetics, University of Salzburg, Austria.
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16
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Abstract
Many physiological and cellular processes contribute to the ageing of individuals. One hypothesis argues that the genomes of somatic cells accumulate mutations, which, in turn, alter the metabolism of the cells and contribute to the ageing process. The frequency of somatic mutation approaches 10(-4) and the majority of mutagenic events at heterozygous loci is due to loss of heterozygosity as a consequence of mitotic recombination. A corollary to the argument that somatic cells accumulate mutations is that cells of the germ line and ES cells have a greater requirement for maintaining the integrity of their genomes. In the former case, a high somatic mutation frequency predicts an increase in somatic disease, which limits our lifespan. The corollary is that cells of the germline and ES cells must minimize the mutational burden to limit the frequency of congenital disease and to ensure the proper transmission of undamaged DNA to the gene pool. This report describes two mechanisms utilized by murine ES cells to minimize DNA damage within the proliferative pool. In the first case, murine ES cells display a frequency of mutation and mitotic recombination that is about 100-fold lower than that observed in somatic cells. Second, ES cells lack a G1 checkpoint following DNA damage. When subjected to ionizing radiation, the fraction of apoptotic cells increases to about 40%. Ectopic expression of Chk2 is sufficient to establish a G1 arrest and the concomitant protection from cell death.
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Affiliation(s)
- Peter J Stambrook
- Department of Cell and Cancer Biology, 3125 Eden Avenue, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA.
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Jones D, Song X, Mitnitski A, Rockwood K. Evaluation of a frailty index based on a comprehensive geriatric assessment in a population based study of elderly Canadians. Aging Clin Exp Res 2005; 17:465-71. [PMID: 16485864 DOI: 10.1007/bf03327413] [Citation(s) in RCA: 183] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND AND AIMS Objectives were to develop a frailty index (FI) based on a standard comprehensive geriatric assessment (CGA) derived from a clinical examination; to assess the validity of the FI-CGA and to compare its precision with other frailty measures. METHODS DESIGN Secondary analysis of a prospective cohort study, with five-year follow-up data. SETTING Second phase of the Canadian Study of Health and Aging (CSHA-2); clinical examinations were performed in clinics, nursing homes, and patients' homes. PARTICIPANTS People selected (as either cognitively impaired cases or unimpaired controls) to receive the CSHA-2 clinical examination (n = 2305; women = 1431). MEASUREMENTS Clinical and performance-based measures and diagnostic data were extracted to correspond to the 10 impairment domains and the single comorbidity domain of a CGA. The proportion of deficits accumulated in each domain was calculated to yield the FI-CGA. The FI-CGA was validated and its predictive ability compared with other frailty measures. RESULTS Within the seven grades of fitness/frailty identified, subjects with greater frailty were older, less educated, and more likely to be women. The FI-CGA correlated highly with a previously validated, empirically-derived frailty index (r = 0.76). Frailty was associated with higher risk of death (for each increment in frailty, the hazard ratio, adjusted for age, sex and education, was 1.23 (95% CI 1.18-1.29) and institutionalization (HR 1.20; 1.10-1.32). CONCLUSIONS In a population survey, the FI-CGA is a valid means of quantifying frailty from routinely collected data.
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Affiliation(s)
- David Jones
- Faculty of Medicine, Memorial University, St. John's, Canada
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18
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Mangel M, Munch SB. A life-history perspective on short- and long-term consequences of compensatory growth. Am Nat 2005; 166:E155-76. [PMID: 16475079 DOI: 10.1086/444439] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Accepted: 06/23/2005] [Indexed: 11/03/2022]
Abstract
Compensatory or catch-up growth (CG) is widely observed following periods of resource deprivation. Because of this commonness, it is generally assumed that compensatory growth is adaptive, but most theory to date has explicitly ignored considerations of fitness. Following a period of deprivation, when resources become plentiful again, individuals may not respond at all and continue on a "normal" trajectory from a smaller size at age, may exhibit faster-than-normal growth immediately following the end of the period, or may adopt a growth strategy that involves faster-than-normal growth at some later time. Compensating individuals may also overtake control individuals who have been growing normally throughout. We hypothesize that the key to understanding CG is that growth leads to the accumulation of damage at the cellular level that is expressed (and thus must be modeled) at the level of the organism. We show that a life-history model incorporating the mortality consequences of both size and damage provides a framework for understanding compensatory growth. We use the theory to classify physiological and life-history characteristics for which CG is predicted to be the optimal response to deprivation.
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Affiliation(s)
- Marc Mangel
- Center for Stock Assessment Research, Department of Applied Mathematics and Statistics, University of California, Santa Cruz, California 95064, USA.
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Hill KA, Halangoda A, Heinmoeller PW, Gonzalez K, Chitaphan C, Longmate J, Scaringe WA, Wang JC, Sommer SS. Tissue-specific time courses of spontaneous mutation frequency and deviations in mutation pattern are observed in middle to late adulthood in Big Blue mice. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2005; 45:442-454. [PMID: 15690342 DOI: 10.1002/em.20119] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
To better define the time course of spontaneous mutation frequency in middle to late adulthood of the mouse, measurements were made at 10, 14, 17, 23, 25, and 30 months of age in samples of adipose tissue, liver, cerebellum (90% neurons), and the male germline (95% germ cells). A total of 46 million plaque-forming units (pfus) were screened at the six time points and 1,450 circular blue plaques were harvested and sequenced. These data improve resolution and confirm the previously observed occurrence of at least two tissue-specific profiles of spontaneous mutation frequency (elevation with age in adipose tissue and liver, and constancy with age in neurons and male germ cells), a low mutation frequency in the male germline, and a mutation pattern unchanged with age within a tissue. These findings appear to extend to very old age (30 months). Additional findings include interanimal variation in spontaneous mutation frequency is larger in adipose tissues and liver compared with neurons and male germ cells, and subtle but significant differences in the mutation pattern among tissues, consistent with a minor effect of tissue-specific metabolism. The presumptive unaltered balance of DNA damage and repair with age in the male germline has evolutionary consequences. It is of particular interest given the controversy over whether or not increasing germline mutation frequency with paternal age underlies the reports associating older males with a higher incidence of some types of genetic disease. These most detailed measurements available to date regarding the time course of spontaneous mutation frequency and pattern in individual tissues help to constrain hypotheses regarding the role of mutational mechanisms in DNA repair and aging.
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Affiliation(s)
- Kathleen A Hill
- Department of Molecular Genetics, City of Hope National Medical Center, Duarte, California 91010, USA
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