The Danaid Theory of Aging

The classical evolutionary theories of aging suggest that aging evolves due to insufficient selective pressure against it. In these theories, declining selection pressure with age leads to aging through genes or resource allocations, implying that aging could potentially be stalled were genes, resource allocation, or selection pressure somewhat different. While these classical evolutionary theories are undeniably part of a description of the evolution of aging, they do not explain the diversity of aging patterns, and they do not constitute the only possible evolutionary explanation. Without denying selection pressure a role in the evolution of aging, we argue that the origin and diversity of aging should also be sought in the nature and evolution of organisms that are, from their very physiological make up, unmaintainable. Drawing on advances in developmental biology, genetics, biochemistry, and complex systems theory since the classical theories emerged, we propose a fresh evolutionary-mechanistic theory of aging, the Danaid theory. We argue that, in complex forms of life like humans, various restrictions on maintenance and repair may be inherent, and we show how such restrictions are laid out during development. We further argue that there is systematic variation in these constraints across taxa, and that this is a crucial factor determining variation in aging and lifespan across the tree of life. Accordingly, the core challenge for the field going forward is to map and understand the mosaic of constraints, trade-offs, chance events, and selective pressures that shape aging in diverse ways across diverse taxa.

Retrotransposons Down- and Up-Regulation in Aging Somatic Tissues

The transposon theory of aging hypothesizes the activation of transposable elements (TEs) in somatic tissues with age, leading to a shortening of the lifespan. It is thought that TE activation in aging produces an increase in DNA double-strand breaks, contributing to genome instability and promoting the activation of inflammatory responses. To investigate how TE regulation changes in somatic tissues during aging, we analyzed the expression of some TEs, as well as a source of small RNAs that specifically silence the analyzed TEs; the Drosophila cluster named flamenco. We found significant variations in the expression levels of all the analyzed TEs during aging, with a trend toward reduction in middle-aged adults and reactivation in older individuals that suggests dynamic regulation during the lifespan.

Protective Effects of Familial Longevity Decrease with Age and Become Negligible for Centenarians

It is known that biological relatives of long-lived individuals demonstrate lower mortality and longer lifespan compared to relatives of shorter-lived individuals, and at least part of this advantage is likely to be genetic. Less information, however, is available about effects of familial longevity on age-specific mortality trajectories. We compared mortality patterns after age 50 years for 10,045 siblings of U.S. centenarians and 12,308 siblings of shorter-lived individuals (died at age 65 years). Similar comparisons were made for sons and daughters of longer-lived parents (both parents lived 80 years and more) and shorter-lived parents (both parents lived less than 80 years) within each group of siblings. Although relatives of longer-lived individuals have lower mortality at younger ages compared to relatives of shorter lived individuals, this mortality advantage practically disappears by age 100 years. To validate this observation further, we analyzed survival of 3,408 U.S. centenarians born in 1890-97 with known information on maternal and paternal lifespan. We found using the Cox proportional hazards model that both maternal and paternal longevity (lifespan 80+ years) is not significantly associated with survival after age 100 years. The results are compatible with the predictions of reliability theory of aging suggesting higher initial levels of system redundancy (reserves) in individuals with protective familial/genetic background and hence lower initial mortality. Heterogeneity hypothesis is another possible explanation for the observed phenomena.

Lifelong Cytomegalovirus and Early-Life Irradiation Synergistically Potentiate Age-Related Defects in Response to Vaccination and Infection

ABSTRACTA popular “DNA-damage theory” of aging posits that unrepaired DNA damage leads to cellular (and organismal) senescence. Indeed, some hallmarks of immune aging are more prevalent in individuals exposed to Whole-Body Irradiation (WBI). To test this hypothesis in a model relevant to human immune aging, we examined separate and joint effects of lifelong latent Murine Cytomegalovirus (MCMV) and early-life WBI (i) over the course of the lifespan; (ii) in response to a West Nile virus (WNV) live attenuated vaccine; and (iii) following lethal WNV challenge subsequent to vaccination. We recently published that a single dose of non-lethal WBI in youth, on its own, was not sufficient to accelerate aging of the murine immune system despite causing widespread DNA damage and repopulation stress in hematopoietic cells. However, 4Gy sub-lethal WBI caused manifest reactivation of MCMV. Following vaccination and challenge with WNV in the old age, MCMV-infected animals experiencing 4Gy, but not lower, dose of sub-lethal WBI in youth had reduced survival. By contrast, old irradiated mice lacking MCMV and MCMV-infected, but not irradiated, mice were both protected to the same high level as the old non-irradiated, uninfected controls. Analysis of the quality and quantity of anti-WNV immunity showed that higher mortality in MCMV-positive WBI mice correlated with increased levels of MCMV-specific immune activation during WNV challenge. Moreover, we demonstrate that infection, including that by WNV, led to MCMV reactivation. Our data suggest that MCMV reactivation may be an important determinant of increased late-life mortality following early-life irradiation and late-life acute infection.

Driving Frequency and Well-Being in Older Adulthood

The activity theory of aging suggests that older adults age successfully when they remain active and engaged. While many older adults are still able to drive, not all are as engaged in social activities, despite having the transportation to be able to do so. As such, this study aimed to examine the association between the frequency of driving and overall well-being among older adults. The hypothesis is that older adults who drive more frequently would have higher well-being, as they are likely driving to engaging activities. A sample of 1,663 older adults who reported that they are able to drive were derived from the 2018 National Health and Aging Trends Study (NHATS). The NHATS is an annual longitudinal panel of survey of adults aged 65 and older living in the United States. Chi-square tests were used for bivariate analyses and a weighted multivariable logistic regression model was used to predict well-being based on driving frequency. Results showed that compared to those who drive every day, those who drive most days (OR=0.771, CI= [0.768-0.775]), some days (OR=0.495, CI= [0.492-0.497]), rarely (OR=0.558, CI= [0.555-0.562]) or never (OR=0.371, CI= [0.367-0.374]) were less likely to have high well-being. Interventions geared at improving well-being among older adults should therefore consider increasing awareness of social events, to ensure that older adults who are able to drive can have a good quality of life by driving to social activities.

TRANSDISCIPLINARY APPROACH IN FREE RADICAL THEORY OF AGING. CONTRIBUTION OF NIKOLAY M. EMANUEL AND HIS SCIENTIFIC SCHOOL TO GERONTOLOGY

Работа представляет собой обзор научных исследований влияния антиоксидантов-геропротекторов на старение экспериментальных животных и репликативное старение диплоидных клеток человека, выполненных в отделе кинетики химических и биологических процессов «ХИМБИО» Института химической физики АН СССР под руководством академика Николая Марковича Эмануэля в 1960- 1980- е гг. В работах Н.М. Эмануэля и сотрудников было установлено неизвестное ранее явление взаимодействия ингибиторов свободнорадикальных реакций в процессах окисления органических веществ, заключающееся в регенерации более эффективного ингибитора вследствие переноса атома водорода к его радикалу от молекулы менее эффективного ингибитора. Антиоксиданты поливалентны и могут влиять одновременно на многие процессы старения. Данные научной школы Н.М. Эмануэля по увеличению средней продолжительности жизни на 25,3 % и максимальной продолжительности мышей на 55,8 % под действием антиоксидантов, полученные в результате хорошо обоснованных экспериментальных и теоретических исследований, явились весомым аргументом в пользу свободнорадикальной теории старения. The work is aimed to review the results of scientific studies of the effect of antioxidants-geroprotectors on the aging of experimental animals and the replicative aging of human diploid cells, carried out in the Department of Kinetics of Chemical and Biological Processes «KHIMBIO» of the Institute of Chemical Physics of the USSR Academy of Sciences under the leadership of academician Nikolay Markovich Emanuel in the 1960-1980s after pioneer work by D. Harman. By N.M. Emanuel and colleagues, it was established a previously unknown phenomenon of radical interaction of inhibitors in the oxidation of organic substances, which consists in the regeneration of a more effective inhibitor due to the transfer of a hydrogen atom to its free radical from a molecule of a less effective inhibitor. Antioxidants are polyvalent and can simultaneously affect many stages of aging processes. Data from the N.M. Emanuel scientific school on the increase of the average lifespan of mice by 25,3 % and their maximum lifespan by 55,8 % using antioxidants, discovered at the Institute of Chemical Physics of the USSR Academy of Sciences as a result of well-founded experimental and theoretical studies, became a powerful argument in favor of the free radical theory of aging in 1970-ties. This was further promoted by approaches based on the theory of reliability, the damage theory, and as well as an approach based on oxidative activation of the Nrf2 signaling pathway, which maintains the «nucleophilic tone» of protective oxidoreductases.

The Evolution of the Hallmarks of Aging

The evolutionary theory of aging has set the foundations for a comprehensive understanding of aging. The biology of aging has listed and described the “hallmarks of aging,” i.e., cellular and molecular mechanisms involved in human aging. The present paper is the first to infer the order of appearance of the hallmarks of bilaterian and thereby human aging throughout evolution from their presence in progressively narrower clades. Its first result is that all organisms, even non-senescent, have to deal with at least one mechanism of aging – the progressive accumulation of misfolded or unstable proteins. Due to their cumulation, these mechanisms are called “layers of aging.” A difference should be made between the first four layers of unicellular aging, present in some unicellular organisms and in all multicellular opisthokonts, that stem and strike “from the inside” of individual cells and span from increasingly abnormal protein folding to deregulated nutrient sensing, and the last four layers of metacellular aging, progressively appearing in metazoans, that strike the cells of a multicellular organism “from the outside,” i.e., because of other cells, and span from transcriptional alterations to the disruption of intercellular communication. The evolution of metazoans and eumetazoans probably solved the problem of aging along with the problem of unicellular aging. However, metacellular aging originates in the mechanisms by which the effects of unicellular aging are kept under control – e.g., the exhaustion of stem cells that contribute to replace damaged somatic cells. In bilaterians, additional functions have taken a toll on generally useless potentially limited lifespan to increase the fitness of organisms at the price of a progressively less efficient containment of the damage of unicellular aging. In the end, this picture suggests that geroscience should be more efficient in targeting conditions of metacellular aging rather than unicellular aging itself.