Near-to-perfect homeostasis: examples of universal aging rule which germline evades

The Impact of Hormesis, Neuronal Stress Response, and Reproduction, upon Clinical Aging: A Narrative Review

INTRODUCTION

The primary objective of researchers in the biology of aging is to gain a comprehensive understanding of the aging process while developing practical solutions that can enhance the quality of life for older individuals. This involves a continuous effort to bridge the gap between fundamental biological research and its real-world applications.

PURPOSE

In this narrative review, we attempt to link research findings concerning the hormetic relationship between neurons and germ cells, and translate these findings into clinically relevant concepts.

METHODS

We conducted a literature search using PubMed, Embase, PLOS, Digital Commons Network, Google Scholar and Cochrane Library from 2000 to 2023, analyzing studies dealing with the relationship between hormetic, cognitive, and reproductive aspects of human aging.

RESULTS

The process of hormesis serves as a bridge between the biology of neuron-germ cell interactions on one hand, and the clinical relevance of these interactions on the other. Details concerning these processes are discussed here, emphasizing new research which strengthens the overall concept.

CONCLUSIONS

This review presents a scientifically and clinically relevant argument, claiming that maintaining a cognitively active lifestyle may decrease age-related degeneration, and improve overall health in aging. This is a totally novel approach which reflects current developments in several relevant aspects of our biology, technology, and society.

Role of Molecular Hydrogen in Ageing and Ageing-Related Diseases

Ageing is a physiological process of progressive decline in the organism function over time. It affects every organ in the body and is a significant risk for chronic diseases. Molecular hydrogen has therapeutic and preventive effects on various organs. It has antioxidative properties as it directly neutralizes hydroxyl radicals and reduces peroxynitrite level. It also activates Nrf2 and HO-1, which regulate many antioxidant enzymes and proteasomes. Through its antioxidative effect, hydrogen maintains genomic stability, mitigates cellular senescence, and takes part in histone modification, telomere maintenance, and proteostasis. In addition, hydrogen may prevent inflammation and regulate the nutrient-sensing mTOR system, autophagy, apoptosis, and mitochondria, which are all factors related to ageing. Hydrogen can also be used for prevention and treatment of various ageing-related diseases, such as neurodegenerative disorders, cardiovascular disease, pulmonary disease, diabetes, and cancer. This paper reviews the basic research and recent application of hydrogen in order to support hydrogen use in medicine for ageing prevention and ageing-related disease therapy.

Principles of alternative gerontology

Surveys of taxonomic groups of animals have shown that contrary to the opinion of most gerontologists aging is not a genuine trait. The process of aging is not universal and its mechanisms have not been widely conserved among species. All life forms are subject to extrinsic and intrinsic destructive forces. Destructive effects of stochastic events are visible only when allowed by the specific life program of an organism. Effective life programs of immortality and high longevity eliminate the impact of unavoidable damage. Organisms that are capable of agametic reproduction are biologically immortal. Mortality of an organism is clearly associated with terminal specialisation in sexual reproduction. The longevity phenotype that is not accompanied by symptoms of senescence has been observed in those groups of animals that continue to increase their body size after reaching sexual maturity. This is the result of enormous regeneration abilities of both of the above-mentioned groups. Senescence is observed when: (i) an organism by principle switches off the expression of existing growth and regeneration programs, as in the case of imago formation in insect development; (ii) particular programs of growth and regeneration of progenitors are irreversibly lost, either partially or in their entirety, in mammals and birds.

“We can't solve problems by using the same kind of thinking we used when we created them.” (Ascribed to Albert Einstein)

The budding yeast Saccharomyces cerevisiae as a model organism: possible implications for gerontological studies

Experimental gerontology is based on the fundamental assumption that the aging process has a universal character and that the mechanisms of aging are well-conserved among living things. The consequence of this assumption is the use of various organisms, including unicellular yeast Saccharomyces cerevisiae, as models in gerontology, and direct extrapolation of the conclusions drawn from the studies carried on these organisms to human beings. However, numerous arguments suggest that aging is not universal and its mechanisms are not conserved in a wide range of species. Instead, senescence can be treated as a side effect of the evolution of specific features for systematic group, unrelated to the passage of time. Hence, depending on the properties of the group, the senescence and proximal causes of death could have a diverse nature. We postulate that the selection of a model organism to explain the mechanism of human aging and human longevity should be preceded by the analysis of its potential to extrapolate the results to a wide group of organisms. Considering that gerontology is a human-oriented discipline and that aging involves complex, systemic changes affecting the entire organism, the object of experimental studies should be animals which are closest relatives of human beings in evolutionary terms, rather than lower organisms, which do not have sufficient complexity in terms of tissues and organ structures.

DNA Damage, DNA Repair, Aging, and Neurodegeneration

Aging in mammals is accompanied by a progressive atrophy of tissues and organs, and stochastic damage accumulation to the macromolecules DNA, RNA, proteins, and lipids. The sequence of the human genome represents our genetic blueprint, and accumulating evidence suggests that loss of genomic maintenance may causally contribute to aging. Distinct evidence for a role of imperfect DNA repair in aging is that several premature aging syndromes have underlying genetic DNA repair defects. Accumulation of DNA damage may be particularly prevalent in the central nervous system owing to the low DNA repair capacity in postmitotic brain tissue. It is generally believed that the cumulative effects of the deleterious changes that occur in aging, mostly after the reproductive phase, contribute to species-specific rates of aging. In addition to nuclear DNA damage contributions to aging, there is also abundant evidence for a causative link between mitochondrial DNA damage and the major phenotypes associated with aging. Understanding the mechanistic basis for the association of DNA damage and DNA repair with aging and age-related diseases, such as neurodegeneration, would give insight into contravening age-related diseases and promoting a healthy life span.

Hydra as a tractable, long-lived model system for senescence

Hydra represents a unique model system for the study of senescence, with the opportunity for the comparison of non-aging and induced senescence. Hydra maintains three stem cell lineages, used for continuous tissue morphogenesis and replacement. Recent work has elucidated the roles of the insulin/IGF-1 signaling target FoxO, of Myc proteins, and of PIWI proteins in Hydra stem cells. Under laboratory culture conditions, Hydra vulgaris show no signs of aging even under long-term study. In contrast, Hydra oligactis can be experimentally induced to undergo reproduction-associated senescence. This provides a powerful comparative system for future studies.

Evolution of aging and death: what insights bacteria can provide

Several unresolved issues, paradoxes, and information voids characterize the field of evolution of aging. The recent discovery of aging-like phenomenon in Escherichia coli, marked by asymmetric segregation of damaged components, particularly protein aggregates, has created a number of new possibilities that remain underexplored. Bacterial systems can potentially throw light on issues such as: whether evolution of aging and evolution of death are different phenomena; whether aging is inevitable for life or is an evolved strategy; whether there could be selection for aging or aging is a pleiotropic effect of some other selection; what are the possible mechanisms of antagonistic pleiotropy, if any; and whether there are mechanisms of aging that are conserved throughout the hierarchy of life. Bacterial aging itself is underexplored and least understood as of now, but even scratching the surface appears to reveal things that may compel us to revise some of the classical concepts about evolution of aging. This warrants more focused and innovative inquiry into aging-like processes in bacteria.

Consequences of telomere shortening during lifespan

Telomerase expression is restricted in human cells and so telomeres shorten throughout our lives, providing a tumour suppressor mechanism that limits cell proliferation. As a trade-off, continuous telomere erosion results in replicative senescence and contributes to ageing. Recently, telomerase therapies were proposed as a valid approach to rescue degenerative phenotypes caused by telomere dysfunction. However, systemic effects initiated by short telomeres may prove dominant in limiting tissue renewal in the whole organism. Most of our knowledge of telomere biology derives from mouse models that do not rely on telomere exhaustion for controlling cell proliferation and tissue homeostasis. In order to understand the impact of telomere shortening in natural ageing, we need to investigate animal models that, like humans, have evolved to have telomere length as a cell division clock.