Biogerontology: from here to where? The Lord Cohen Medal Lecture-2011

Harnessing Genetics to Extend Lifespan and Healthspan: Current Progress and Future Directions

Aging is inevitable, but the lifespan (duration of life) and healthspan (healthy aging) vary greatly among individuals and across species. Unlocking the secrets behind these differences has captivated scientific curiosity for ages. This review presents relevant recent advances in genetics and cell biology that are shedding new light by untangling how subtle changes in conserved genes, pathways, and epigenetic factors influence organismal senescence and associated declines. Biogerontology is a complex and rapidly growing field aimed at elucidating genetic modifications that extend lifespan and healthspan. This review explores gerontogenes, genes influencing lifespan and healthspan across species. Though subtle differences exist, long-lived individuals such as centenarians demonstrate extended healthspans, and numerous studies confirm the heritability of longevity/healthspan genes. Importantly, genes and gerontogenes are directly and indirectly involved in DNA repair, insulin/IGF-1 and mTOR signaling pathways, long non-coding RNAs, sirtuins, and heat shock proteins. The complex interactions between genetics and epigenetics are teased apart. While more research into optimizing healthspan is needed, conserved gerontogenes offer synergistic potential to forestall aging and age-related diseases. Understanding complex longevity genetics brings closer the goal of extending not only lifespan but quality years of life. The primary aim of human Biogerontology is to enhance lifespan and healthspan, but the question remains: are current genetic modifications effectively promoting healthy aging? This article collates the advancements in gerontogenes that enhance lifespan and improve healthspan alongside their potential challenges.

Seven knowledge gaps in modern biogerontology

About a year ago, members of the editorial board of Biogerontology were requested to respond to a query by the editor-in-chief of the journal as to what one question within their field of ageing research still needs to be asked and answered. This editorial is inspired by the wide range and variety of questions, ideas, comments and suggestions received in response to that query. The seven knowledge gaps identified in this article are arranged into three main categories: evolutionary aspects of longevity, biological survival and death aspects, and heterogeneity in the progression and phenotype of ageing. This is not an exhaustive and exclusive list, and may be modified and expanded. Implications of these knowledge gaps, especially in the context of ongoing attempts to develop effective interventions in ageing and longevity are also discussed.

Measuring healthy ageing: current and future tools

Human ageing is a complex, multifactorial process characterised by physiological damage, increased risk of age-related diseases and inevitable functional deterioration. As the population of the world grows older, placing significant strain on social and healthcare resources, there is a growing need to identify reliable and easy-to-employ markers of healthy ageing for early detection of ageing trajectories and disease risk. Such markers would allow for the targeted implementation of strategies or treatments that can lessen suffering, disability, and dependence in old age. In this review, we summarise the healthy ageing scores reported in the literature, with a focus on the past 5 years, and compare and contrast the variables employed. The use of approaches to determine biological age, molecular biomarkers, ageing trajectories, and multi-omics ageing scores are reviewed. We conclude that the ideal healthy ageing score is multisystemic and able to encompass all of the potential alterations associated with ageing. It should also be longitudinal and able to accurately predict ageing complications at an early stage in order to maximize the chances of successful early intervention.

Measuring healthy ageing: current and future tools

Human ageing is a complex, multifactorial process characterised by physiological damage, increased risk of age-related diseases and inevitable functional deterioration. As the population of the world grows older, placing significant strain on social and healthcare resources, there is a growing need to identify reliable and easy-to-employ markers of healthy ageing for early detection of ageing trajectories and disease risk. Such markers would allow for the targeted implementation of strategies or treatments that can lessen suffering, disability, and dependence in old age. In this review, we summarise the healthy ageing scores reported in the literature, with a focus on the past 5 years, and compare and contrast the variables employed. The use of approaches to determine biological age, molecular biomarkers, ageing trajectories, and multi-omics ageing scores are reviewed. We conclude that the ideal healthy ageing score is multisystemic and able to encompass all of the potential alterations associated with ageing. It should also be longitudinal and able to accurately predict ageing complications at an early stage in order to maximize the chances of successful early intervention.

Metabolism, homeostasis, and aging

We propose a two-mode (pursuit/maintenance) model of metabolism defined by usable resource availability. Pursuit, consisting of anabolism and catabolism, dominates when usable resources are plentiful and leads to the generation of metabolic waste. In turn, maintenance of a system is activated by elevated metabolic waste during resource depletion. Interaction with the environment results in pendulum-like swings between these metabolic states in thriveless attempts to maintain the least deleterious organismal state - ephemeral homeostasis. Imperfectness of biological processes during these attempts supports the accumulation of the deleteriome, driving organismal aging. We discuss how metabolic adjustment by the environment and resource stabilization may modulate healthspan and lifespan.

Longitudinal brain age prediction and cognitive function after stroke

Advanced age is associated with post-stroke cognitive decline. Machine learning based on brain scans can be used to estimate brain age of patients, and the corresponding difference from chronological age, the brain age gap (BAG), has been investigated in a range of clinical conditions, yet not thoroughly in post-stroke neurocognitive disorder (NCD). We aimed to investigate the association between BAG and post-stroke NCD over time. Lower BAG (younger appearing brain compared to chronological age) was found associated with lower risk of post-stroke NCD up to 36 months after stroke, even among those showing no evidence of impairments 3 months after hospital admission. For patients with no NCD at baseline, survival analysis suggested that higher baseline BAG was associated with higher risk of post-stroke NCD at 18 and 36 months. In conclusion, a younger appearing brain is associated with a lower risk of post-stroke NCD.

Irisin enhances longevity by boosting SIRT1, AMPK, autophagy and telomerase

Ageing is characterised by the accumulation of molecular and cellular damage through time, leading to a decline in physical and mental abilities. Currently, society has experienced a rapid increase in life expectancy, which has led to an increase in age-associated diseases. Therefore, it is crucial to study the process of ageing to guarantee the best conditions in the final stages of life. In recent years, interest has increased in a myokine known as irisin, which is secreted during physical exercise. This polypeptide hormone is produced by various organs, mainly muscle, and once it is released into the blood, it performs a wide variety of functions that are involved in metabolic control and may be relevant during some of the diseases associated with ageing. The aim of this review is to highlight the recent studies of irisin, such as its mechanism of expression, blood release, distribution, tissue target and participation in various cellular metabolic reactions and the relationship with key anti-ageing pathways such as adenosine monophosphate-activated protein kinase, silent information regulator T 1, autophagy and telomerase. In conclusion, irisin is a key player during the ageing process and it could be a novel target molecule for the therapeutic approach to boost longevity pathways. However, more research will be necessary to use this promising hormone for this gain.

An essay on the nominal vs. real definitions of aging

In the current literature, the definitions of aging range from relying on certain sets of distinctive features at the molecular, organismal, populational and/or even evolutional levels/scales to declaring it a treatable disease and, moreover, to treating aging as a mental construct rather than a natural phenomenon. One reason of such a mess may be that it is common in the natural sciences to disregard philosophy of science where several categories of definitions are recognized, among which the nominal are less, and the so-called real ones are more appropriate in scientific contexts. E.g., water is, by its nominal definition, a liquid having certain observable features and, by its real definition, a specific combination (or a product of interaction) of hydrogen and oxygen atoms. Noteworthy, the real definition is senseless for people ignorant of atoms. Likewise, the nominal definition of aging as a set of observable features should be supplemented, if not replaced, with its real definition. The latter is suggested here to imply that aging is the product of chemical interactions between the rapidly turning-over free metabolites and the slowly turning-over metabolites incorporated in macromolecules involved in metabolic control. The phenomenon defined in this way emerged concomitantly with metabolic pathways controlled by enzymes coded for by information-storing macromolecules and is inevitable wherever such conditions coincide. Aging research, thus, is concerned with the elucidation of the pathways and mechanisms that link aging defined as above to its hallmarks and manifestations, including those comprised by its nominal definitions. Esoteric as it may seem, defining aging is important for deciding whether aging is what should be declared as the target of interventions aimed at increasing human life and health spans.

Human ageing, longevity and evolution: can ageing be programmed?

Understanding the proximate and ultimate causes of ageing is one of the key challenges in current biology and medicine. These problems are so important that they are sometimes referred to as the Holy Grail of biology and the Great Conundrum in biogerontology. From an evolutionary perspective, ageing is due to a failure of selection that is caused either by declining strength of selection after the onset of sexual reproduction (Medawar’s theory and Charlesworth’s model) or pleiotropic constraints (Williams’ theory). According to the disposable soma theory, which was proposed by Kirkwood and Holliday, ageing is driven by the accumulation of damage during life and failures of defensive and repair mechanisms as the more an animal expends on sexual reproduction, the less it can expend on bodily maintenance, and vice versa. Although these standard models rule out the possibility that ageing is programmed, there is no consensus about the nature of ageing within the life history in current biogerontology. Interestingly, empirical studies show that there are molecular instructions for ageing and evolutionarily conserved mechanisms for ageing, which seems inconsistent with the idea that ageing is a matter of neglect or a consequence of a failure of selection due to pleiotropic constraints. Here, selected arguments for programmed (i.e. either determined and adaptive or prearranged but non-adaptive) and non-programmed ageing are discussed. Recent advances in biogerontology that cast new light on these problems are outlined here in the context of the idea that the pace of ageing can act as an adaptation in nature, even though ageing is non-programmed and non-adaptive.

Naive extrapolations, overhyped claims and empty promises in ageing research and interventions need avoidance

Most proclamations about another wonder breakthrough and another imminent miracle treatment of ageing are usually overhyped claims and empty promises. It is not that the experimental science behind those claims is totally wrong or fake. But it is often a case of being ahistorical and ignoring the cumulated knowledge and understanding of the evolutionary and biological principles of ageing and longevity. Furthermore, remaining stuck to the body-as-a-machine viewpoint reduces ageing and its associated health challenges to a mere problem of engineering and design. However, highly dynamic nature of the living systems with properties of interaction, interdependence, tolerance, adaptation and constant remodelling requires wholistic and interactive modes of understanding and maintaining health. The physiological relevance and significance of progressively accumulating molecular damage remains to be fully understood. As for ageing interventions, the three pillars of health-food, physical activity, and social and mental engagement-which actually show health-promoting effect, cannot simply be reduced to a single or a limited number of molecular targets with hopes of creating an exercise pill, a fasting pill, a happiness pill and so on. If we want to increase the credibility and socio-political-economic support of ageing research and interventions, we need to resist the temptation to overhype the claims or to make far-fetched promises, which undermine the theoretical and practical significance of new discoveries in biogerontology.

Human ageing as a dynamic, emergent and malleable process: from disease-oriented to health-oriented approaches

Over the decades, biogerontology has matured as a scientific discipline. Currently, a number of theoretical frameworks are available to researchers when interpreting empirical data. Despite the great progress that has been made, a comprehensive understanding of biological processes that shape ageing is lacking. Senescence is a dynamic, plastic and highly complex metaphenomenon whose aetiology remains unclear. The paucity of information notwithstanding, some researchers promote ‘anti-ageing’ drugs and formulae every now and again. The rationale behind this concept is that ageing can be reduced to a mixture of biochemical reactions. Furthermore, the distinction between ageing and disease has been questioned on the grounds that ageing is the root of age-related diseases. It has been claimed that disease-oriented approaches can help delay ageing and prevent age-related diseases. Although these methods seem incongruous from an evolutionary standpoint, they become popular amongst the public. Moreover, if ageing is classified as a disease, this situation is likely to be exacerbated. Therefore, it is important to recognise the limitations of these reductionist and disease-oriented approaches. Only holistic and evidence-based strategies might be useful in slowing down ageing and preventing age-related diseases in the future.

The protective function of non-coding DNA in DNA damage accumulation with age and its roles in age-related diseases

Aging is a progressive decline of physiological function in tissue and organ accompanying both accumulation of DNA damage and reduction of non-coding DNA. Peripheral non-coding DNA/heterochromatin has been proposed to protect the genome and centrally-located protein-coding sequences in soma and male germ cells against radiation and the invasion of exogenous nucleic acids. Therefore, this review summarizes the reduction of non-coding DNA/heterochromatin (including telomeric DNA and rDNA) and DNA damage accumulation during normal physiological aging and in various aging-related diseases. Based on analysis of data, it is found that DNA damage accumulation is roughly negatively correlated with the reduction of non-coding DNA and therefore speculated that DNA damage accumulation is likely due to the reduction of non-coding DNA protection in genome defense during aging. Therefore, it is proposed here that means to increase the total amount of non-coding DNA and/or heterochromatin prior to the onset of these diseases could potentially better protect the genome and protein-coding DNA, reduce the incidence of aging-related diseases, and thus lead to better health during aging.

Biogerontology: research status, challenges and opportunities

Biogerontology is the study of the biological basis of ageing and age-related diseases. The phenomenon and the process of ageing are well understood in evolutionary and biological terms; and a conceptual framework has been established within which general principles of ageing and longevity can be formulated. The phenotype of ageing in terms of progressive loss of physical function and fitness is best seen during the period of survival after the evolution-determined essential lifespan (ELS) of a species. However, the ageing phenotype is highly heterogenous and individualistic at all levels from the whole body to the molecular one. Most significantly, the process and the progression of ageing are not determined by any specific gerontogenes. Ageing is the result of imperfect maintenance and repair systems that allow a progressive shrinkage of the homeodynamic space of an individual. The challenge is to develop and apply wholistic approaches to the complex trait of ageing for maintaining and/or improving health. One such approach is that of mild stress-induced physiological hormesis by physical, mental and nutritional hormetins. Biogerontological research offers numerous opportunities for developing evidence-based novel biomedical technologies for maintaining and improving health, for preventing the onset of age-related diseases, and for extending the health-span.

Targeting Protein Quality Control Mechanisms by Natural Products to Promote Healthy Ageing

Organismal ageing is associated with increased chance of morbidity or mortality and it is driven by diverse molecular pathways that are affected by both environmental and genetic factors. The progression of ageing correlates with the gradual accumulation of stressors and damaged biomolecules due to the time-dependent decline of stress resistance and functional capacity, which eventually compromise cellular homeodynamics. As protein machines carry out the majority of cellular functions, proteome quality control is critical for cellular functionality and is carried out through the curating activity of the proteostasis network (PN). Key components of the PN are the two main degradation machineries, namely the ubiquitin-proteasome and autophagy-lysosome pathways along with several stress-responsive pathways, such as that of nuclear factor erythroid 2-related factor 2 (Nrf2), which mobilises cytoprotective genomic responses against oxidative and/or xenobiotic damage. Reportedly, genetic or dietary interventions that activate components of the PN delay ageing in evolutionarily diverse organisms. Natural products (extracts or pure compounds) represent an extraordinary inventory of highly diverse structural scaffolds that offer promising activities towards meeting the challenge of increasing healthspan and/or delaying ageing (e.g., spermidine, quercetin or sulforaphane). Herein, we review those natural compounds that have been found to activate proteostatic and/or anti-stress cellular responses and hence have the potential to delay cellular senescence and/or in vivo ageing.

Oxidative stress, genomic features and DNA repair in frail elderly: A systematic review

Frailty is an emerging geriatric syndrome characterized by higher vulnerability to stressors, with an increased risk of adverse health outcomes such as mortality, morbidity, disability, hospitalization, and institutionalization. Although it is generally recognized to have a biological basis, no particular biological trait has been consistently associated to frailty status so far. In this work, epidemiological studies evaluating association of frailty status with alterations at cellular level - namely oxidative stress, genomic instability and DNA damage and repair biomarkers -were revised and compared. A total of 25 studies fulfilled inclusion/exclusion criteria and, consequently, were included in the review. Variations of oxidative stress biomarkers were often associated to frailty status in older people. On the contrary, genomic instability seems not to be linked to frailty. The only study which addressed the possible relationship between DNA repair modulations and frailty status also failed in finding association. Despite the large number of cellular alterations known to be associated with frailty, studies on this issue are still very scarce and limited to some of the possible cellular targets. The established link between DNA repair, genomic instability, and age and age-related disorders, encourage deeper investigations on this line.

Skeletal stem cells and their contribution to skeletal fragility: senescence and rejuvenation

Age-related osteoporotic fractures are major health care problem worldwide and are the result of impaired bone formation, decreased bone mass and bone fragility. Bone formation is accomplished by skeletal stem cells (SSC) that are recruited to bone surfaces from bone marrow microenvironment. This review discusses targeting SSC to enhance bone formation and to abolish age-related bone fragility in the context of using stem cells for treatment of age-related disorders. Recent studies are presented that have demonstrated that SSC exhibit impaired functions during aging due to intrinsic senescence-related changes as well as the presence of senescent microenvironment. Also, a number of approaches aiming at increasing bone formation through targeting SSC and that include systemic SSC transplantation, systemic SSC targeting using aptamers or antibodies, use of therapeutic screteome and tissue engineering approaches will be presented and discussed.

Comparative Meta-Analysis of Transcriptomics Data during Cellular Senescence and In Vivo Tissue Ageing

Several studies have employed DNA microarrays to identify gene expression signatures that mark human ageing; yet the features underlying this complicated phenomenon remain elusive. We thus conducted a bioinformatics meta-analysis on transcriptomics data from human cell- and biopsy-based microarrays experiments studying cellular senescence or in vivo tissue ageing, respectively. We report that coregulated genes in the postmitotic muscle and nervous tissues are classified into pathways involved in cancer, focal adhesion, actin cytoskeleton, MAPK signalling, and metabolism regulation. Genes that are differentially regulated during cellular senescence refer to pathways involved in neurodegeneration, focal adhesion, actin cytoskeleton, proteasome, cell cycle, DNA replication, and oxidative phosphorylation. Finally, we revealed genes and pathways (referring to cancer, Huntington's disease, MAPK signalling, focal adhesion, actin cytoskeleton, oxidative phosphorylation, and metabolic signalling) that are coregulated during cellular senescence and in vivo tissue ageing. The molecular commonalities between cellular senescence and tissue ageing are also highlighted by the fact that pathways that were overrepresented exclusively in the biopsy- or cell-based datasets are modules either of the same reference pathway (e.g., metabolism) or of closely interrelated pathways (e.g., thyroid cancer and melanoma). Our reported meta-analysis has revealed novel age-related genes, setting thus the basis for more detailed future functional studies.

The amazing ubiquitin-proteasome system: structural components and implication in aging

Proteome quality control (PQC) is critical for the maintenance of cellular functionality and it is assured by the curating activity of the proteostasis network (PN). PN is constituted of several complex protein machines that under conditions of proteome instability aim to, firstly identify, and then, either rescue or degrade nonnative polypeptides. Central to the PN functionality is the ubiquitin-proteasome system (UPS) which is composed from the ubiquitin-conjugating enzymes and the proteasome; the latter is a sophisticated multi-subunit molecular machine that functions in a bimodal way as it degrades both short-lived ubiquitinated normal proteins and nonfunctional polypeptides. UPS is also involved in PQC of the nucleus, the endoplasmic reticulum and the mitochondria and it also interacts with the other main cellular degradation axis, namely the autophagy-lysosome system. UPS functionality is optimum in the young organism but it is gradually compromised during aging resulting in increasing proteotoxic stress; these effects correlate not only with aging but also with most age-related diseases. Herein, we present a synopsis of the UPS components and of their functional alterations during cellular senescence or in vivo aging. We propose that mild UPS activation in the young organism will, likely, promote antiaging effects and/or suppress age-related diseases.

Healthy ageing, but what is health?

Ageing occurs in spite of complex pathways of maintenance and repair. There is no "enemy within", which has the specific evolution-selected function to cause ageing and death. This understanding of ageing should transform our approach towards interventions from therapeutic "anti-ageing" to maintaining health. But what is health? Ideally, health is a state of complete physical and mental independence in activities of daily living. But in pragmatic terms, health is a state of adequate physical and mental independence in activities of daily living. In order to identify a set of measurable, evidence-based and demonstratable parameters of health, robustness and resilience at various levels, the concept of homeodynamic space can be a useful one. Age-related health problems for which there are no clear-cut causative agents, except the complex process of ageing, may be better tackled by focusing on health mechanisms and their maintenance, rather than disease management and treatment. Continuing the disease-oriented research approaches are economically, socially and psychologically unsustainable as compared with health-oriented and preventive strategies, such as hormesis. Supporting health-oriented research is the urgency of our time.

Aging is not a disease: implications for intervention

Aging of biological systems occurs in spite of numerous complex pathways of maintenance, repair and defense. There are no gerontogenes which have the specific evolutionary function to cause aging. Although aging is the common cause of all age-related diseases, aging in itself cannot be considered a disease. This understanding of aging as a process should transform our approach towards interventions from developing illusory anti-aging treatments to developing realistic and practical methods for maintaining health throughout the lifespan. The concept of homeodynamic space can be a useful one in order to identify a set of measurable, evidence-based and demonstratable parameters of health, robustness and resilience. Age-induced health problems, for which there are no other clear-cut causative agents, may be better tackled by focusing on health mechanisms and their maintenance, rather than only disease management and treatment. Continuing the disease-oriented research and treatment approaches, as opposed to health-oriented and preventive strategies, are economically, socially and psychologically unsustainable.

Effect of restricted feeding on nocturnality and daily leptin rhythms in OVLT in aged male Wistar rats

Circadian system has direct relevance to the problems of modern lifestyle, shift workers, jet lag etc. To understand non-photic regulation of biological clock, the effects of restricted feeding (RF) on locomotor activity and daily leptin immunoreactivity (ir) rhythms in three age groups [3, 12 and 24 months (m)] of male Wistar rats maintained in light:dark (LD) 12:12 h conditions were studied. Leptin-ir was examined in the suprachiasmatic nucleus (SCN), the medial preoptic area (MPOA) and organum vasculosum of the lamina terminalis (OVLT). Reversal of feeding time due to restricted food availability during daytime resulted in switching of the animals from nocturnality to diurnality with significant increase in day time activity and decrease in night time activity. The RF resulted in % diurnality of approximately 32, 29 and 73 from % nocturnality of 82, 92 and 89 in control rats of 3, 12 and 24 m age, respectively. The increase in such switching from nocturnality to diurnality with restricted feeding was found to be robust in 24 m rats. The OVLT region showed daily leptin-ir rhythms with leptin-ir maximum at ZT-0 in all the three age groups. However leptin-ir levels were minimum at ZT-12 in 3 and 12 m though at ZT-18 in 24 m. In addition the mean leptin-ir levels decreased with increase in food intake and body weight significantly in RF aged rats. Thus we report here differential effects of food entrained regulation in switching nocturnality to diurnality and daily leptin-ir rhythms in OVLT in aged rats.

Natural compounds with anti-ageing activity

Ageing is a complex molecular process driven by diverse molecular pathways and biochemical events that are promoted by both environmental and genetic factors. Specifically, ageing is defined as a time-dependent decline of functional capacity and stress resistance, associated with increased chance of morbidity and mortality. These effects relate to age-related gradual accumulation of stressors that result in increasingly damaged biomolecules which eventually compromise cellular homeostasis. Nevertheless, the findings that genetic or diet interventions can increase lifespan in evolutionarily diverse organisms indicate that mortality can be postponed. Natural compounds represent an extraordinary inventory of high diversity structural scaffolds that can offer promising candidate chemical entities in the major healthcare challenge of increasing health span and/or delaying ageing. Herein, those natural compounds (either pure forms or extracts) that have been found to delay cellular senescence or in vivo ageing will be critically reviewed and summarized according to affected cellular signalling pathways. Moreover, the chemical structures of the identified natural compounds along with the profile of extracts related to their bioactive components will be presented and discussed. Finally, novel potential molecular targets for screening natural compounds for anti-ageing activity, as well as the idea that anti-ageing interventions represent a systemic approach that is also effective against age-related diseases will be discussed.

Molecular effects of advanced glycation end products on cell signalling pathways, ageing and pathophysiology

Advanced glycation end-products (AGEs) are a heterogeneous group of compounds formed by the Maillard chemical process of non- enzymatic glycation of free amino groups of proteins, lipids and nucleic acids. This chemical modification of biomolecules is triggered by endogeneous hyperglycaemic or oxidative stress-related processes. Additionally, AGEs can derive from exogenous, mostly diet-related, sources. Considering that AGE accumulation in tissues correlates with ageing and is a hallmark in several age-related diseases it is not surprising that the role of AGEs in ageing and pathology has become increasingly evident. The receptor for AGEs (RAGE) is a single transmembrane protein being expressed in a wide variety of human cells. RAGE binds a broad repertoire of extracellular ligands and mediates responses to stress conditions by activating multiple signal transduction pathways being mostly responsible for acute and/or chronic inflammation. RAGE activation has been implicated in ageing as well as in a number of age-related diseases, including atherosclerosis, neurodegeneration, arthritis, stoke, diabetes and cancer. Here we present a synopsis of findings that relate to AGEs-reported implication in cell signalling pathways and ageing, as well as in pathology. Potential implications and opportunities for translational research and the development of new therapies are also discussed.

A cigarette component acrolein induces accelerated senescence in human diploid fibroblast IMR-90 cells

Cigarette smoking causes various diseases, including lung cancer and cardiovascular disease, and reduces life span, though the mechanisms are not well understood. We hypothesize that smoking may cause cellular mitochondrial dysfunction and oxidative stress, leading to aging acceleration. In the present study, we tested the effects of acrolein, a major representative smoking toxicant, on human lung fibroblast IMR-90 cells with regard to cellular senescence, oxidative stress, and mitochondrial function. The results showed that subacute treatment with low dose of acrolein induces the following events compared to the control cells: cell senescence demonstrated by increases in the activity of β-galactosidase, the higher expression of p53 and p21, decreases in DNA synthesis, Sirt1 expression, and telomere length; oxidative stress occurred as the increases in the production of reactive oxygen species, DNA damage, and protein oxidation; and mitochondrial dysfunction shown as decreases in the mitochondrial membrane potential, mitochondrial biogenesis regulator PGC-1 alpha and mitochondria complex I, II, III, and V. These results suggest that acrolein may accelerate aging through the mechanism of increasing oxidative stress and mitochondrial dysfunction.

Assessing biological aging: the origin of deficit accumulation

The health of individuals is highly heterogeneous, as is the rate at which they age. To account for such heterogeneity, we have suggested that an individual’s health status can be represented by the number of health deficits (broadly defined by biological and clinical characteristics) that they accumulate. This allows health to be expressed in a single number: the frailty index (FI) is the ratio of the deficits present in a person to the total number of deficits considered (e.g. in a given database or experimental procedure). Changes in the FI characterize the rate of individual aging. The behavior of the FI is highly characteristic: it shows an age specific, nonlinear increase, (similar to Gompertz law), higher values in females, strong associations with adverse outcomes (e.g., mortality), and a universal limit to its increase (at FI ~0.7). These features have been demonstrated in dozens of studies. Even so, little is known about the origin of deficit accumulation. Here, we apply a stochastic dynamics framework to illustrate that the average number of deficits present in an individual is the product of the average intensity of the environmental stresses and the average recovery time. The age-associated increase in recovery time results in the accumulation of deficits. This not only explains why the number of deficits can be used to estimate individual differences in aging rates, but also suggests that targeting the recovery rate (e.g. by preventive or therapeutic interventions) will decrease the number of deficits that individuals accumulate and thereby benefit life expectancy.

Differential regulation of proteasome functionality in reproductive vs. somatic tissues of Drosophila during aging or oxidative stress

Proteasome is central to proteostasis maintenance, as it degrades both normal and damaged proteins. Herein, we undertook a detailed analysis of proteasome regulation in the in vivo setting of Drosophila melanogaster. We report that a major hallmark of somatic tissues of aging flies is the gradual accumulation of ubiquitinated and carbonylated proteins; these effects correlated with a ~50% reduction of proteasome expression and catalytic activities. In contrast, gonads of aging flies were relatively free of proteome oxidative damage and maintained substantial proteasome expression levels and highly active proteasomes. Moreover, gonads of young flies were found to possess more abundant and more active proteasomes than somatic tissues. Exposure of flies to oxidants induced higher proteasome activities specifically in the gonads, which were, independently of age, more resistant than soma to oxidative challenge and, as analyses in reporter transgenic flies showed, retained functional antioxidant responses. Finally, inducible Nrf2 activation in transgenic flies promoted youthful proteasome expression levels in the aged soma, suggesting that age-dependent Nrf2 dysfunction is causative of decreasing somatic proteasome expression during aging. The higher investment in proteostasis maintenance in the gonads plausibly facilitates proteome stability across generations; it also provides evidence in support of the trade-off theories of aging.

Possible role of NF-κB in hormesis during ageing

Hormesis in ageing is probably represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Mild stress and hormetins may act on bifurcation points in the complex network of cell signaling and transcription factors, often turning homeodynamics to health or survival. Several signaling pathways activated by diverse stimuli and by stress response converge on NF-κB activation, resulting in a regulatory system characterized by high complexity. NF-κB behaves as a chaotic oscillator and it is increasingly recognized that the number of components that impinges upon phenotypic outcomes of signal transduction pathways may be higher than those taken into consideration from canonical pathway representations. NF-κB is closely related to other important upstream signaling networks, creating chaotic oscillators with other receptor-related kinases and targeting hubs for hormesis. The great bulk of natural hormetins acts on these signaling pathways, while NF-κB appears as a key regulatory factor in this context. Due to its tight relationship with main signaling system NF-κB plays a fundamental role in stress response, apoptosis and autophagy and appears to be a possible target for hormesis in ageing.

Differential regulation of proteasome functionality in reproductive vs. somatic tissues of Drosophila during aging or oxidative stress

Proteasome is central to proteostasis maintenance, as it degrades both normal and damaged proteins. Herein, we undertook a detailed analysis of proteasome regulation in the in vivo setting of Drosophila melanogaster. We report that a major hallmark of somatic tissues of aging flies is the gradual accumulation of ubiquitinated and carbonylated proteins; these effects correlated with a ~50% reduction of proteasome expression and catalytic activities. In contrast, gonads of aging flies were relatively free of proteome oxidative damage and maintained substantial proteasome expression levels and highly active proteasomes. Moreover, gonads of young flies were found to possess more abundant and more active proteasomes than somatic tissues. Exposure of flies to oxidants induced higher proteasome activities specifically in the gonads, which were, independently of age, more resistant than soma to oxidative challenge and, as analyses in reporter transgenic flies showed, retained functional antioxidant responses. Finally, inducible Nrf2 activation in transgenic flies promoted youthful proteasome expression levels in the aged soma, suggesting that age-dependent Nrf2 dysfunction is causative of decreasing somatic proteasome expression during aging. The higher investment in proteostasis maintenance in the gonads plausibly facilitates proteome stability across generations; it also provides evidence in support of the trade-off theories of aging.

Sesamin extends the mean lifespan of fruit flies

The present study investigated the anti-ageing activity of sesamin and its effect on gene expression of superoxide dismutase (SOD), catalase (CAT), methuselah (Mth) and Rpn11 in Drosophila melanogaster. Results demonstrated that 0.2 % sesamin in diet prolonged the mean lifespan of OR wild fruit flies by 12 %, accompanied by up-regulation of SOD1, SOD2, CAT and Rpn11. Sesamin at 0.2 % in diet also attenuated paraquat-induced neurodegeneration with up-regulation of SOD1, SOD2 and Rpn11 in OR wild fruit flies. Supplementation of 0.2 % sesamin in diet increased the survival time of OR wild type flies and Alzheimer flies Aβ42 33769 when they were challenged with paraquat. Furthermore, sesamin-induced increase in the activity and expression of antioxidant enzymes also suggests that the longevity promoting activity of sesamin are possibly due to its action as a hormetin by inducing oxidative stress response-mediated hormesis. It was concluded that sesamin extended the mean lifespan and alleviated the neurodegeneration in Drosophila melanogaster at least mediated by its interaction with genes SOD1, SOD2, CAT, and Rpn11, but not with gene Mth.

Hormesis and Cellular Quality Control: A Possible Explanation for the Molecular Mechanisms that Underlie the Benefits of Mild Stress

In contrast to the detrimental action of severe stress conditions, the beneficial effects of mild stress, known as hormesis, is increasingly discussed and studied. A variety of applications for hormesis in risk assessment processes, anti-ageing strategies and clinical therapies have been proposed. The molecular mechanisms underlying the phenomenon of hormesis, however, are not yet fully understood. A possible mechanism that has been proposed for hormesis, the homoeostasis overshoot hypothesis, assumes that an overshoot of repair- and self-recovery mechanisms in response to mild damage can be held responsible for the beneficial effects of hormesis. The present paper proposes 'cellular quality control' as a further explanation of the molecular mechanisms underlying the benefits observed after exposure to mild stress. The most important quality control mechanisms are outlined and their known and hypothesised actions in hormesis are discussed. As an example, different aspects of protein quality control will be described in more detail, which includes the reaction of the cell upon stress-induced protein damage and -aggregation. The regulation of Heat Shock Proteins and components from the ubiquitin proteasome system as part of cellular quality control is described in relation to its beneficial role in hormesis.

Age-related and sex-specific differences in proteasome activity in individual Drosophila flies from wild type, longevity-selected and stress resistant strains

We have measured the caspase-like proteasome activity in individual male and female Drosophila flies by using a non-denaturing lysing technique that consistently extracts total protein. The mean proteasome activity in control C1 females was more than two times higher as compared with that in C1 males. However, in longevity-selected LS1 flies the proteasome activity was significantly lower compared to C1 flies, but the sex differences were maintained to some extent. Five other stress resistant lines also had significantly reduced proteasome activity in both sexes. During ageing, there was a progressive decrease in proteasome activity in C1 females, but not in C1 males. This age-related decline in proteasome activity observed in C1 females was not observed in LS1 flies. We conclude that the proteasome activity in control male and female flies is significantly different from each other and that increased lifespan and stress resistance lead to a reduction in proteasome activity and recession of the age-related decline observed in control females.

Rationale and methods of discovering hormetins as drugs for healthy ageing

INTRODUCTION

Mild stress-induced hormesis is becoming increasingly attractive as an ageing interventional strategy and is leading to the discovery of hormesis-inducing compounds called hormetins. Almost 50 years of modern biogerontolgical research has established a clear framework regarding the biological basis of ageing and longevity, and it is now generally accepted that ageing occurs in spite of the presence of complex pathways of maintenance, repair and defense, and there is no 'enemy within.' This viewpoint makes modulation of ageing different from the treatment of one or more age-related diseases. A promising strategy to slow down ageing and prevent or delay the onset of age-related diseases is that of mild stress-induced hormesis by using hormetins.

AREAS COVERED

The article presents the rationale and a strategy for discovering novel hormetins as potential drugs for ageing intervention by elucidating multiple stress responses of normal human cells. Furthermore, it discusses the first steps in identifying prospective hormetin drugs and provides a recent example of successful product development, based on the ideas of hormesis and by following the strategy described here.

EXPERT OPINION

As a biomedical issue, the biological process of ageing underlies several major diseases, and although the optimal treatment of every disease, irrespective of age, is a social and moral necessity, preventing the onset of age-related diseases by intervening in the basic process of ageing is the best approach for achieving healthy ageing and for extending the healthspan.

Glucose metabolite glyoxal induces senescence in telomerase-immortalized human mesenchymal stem cells

BACKGROUND

Various by-products of the cellular metabolism, such as reactive carbonyl species (RCS) are potentially harmful to cells and tissues, and play a role in many physiological and pathological processes. Among various RCS is the highly reactive dicarbonyl glyoxal (GO), which is a natural physiological metabolite produced by the auto-oxidation of glucose, and can form covalent adducts known as advanced glycation endproducts (AGE). We have previously reported that GO accelerates ageing and causes premature senescence in normal human skin fibroblasts.

RESULTS

Using a bone marrow-derived telomerase-immortalised mesenchymal stem cell line hMSC-TERT we have observed that an exposure of cells to 0.75 mM and 1 mM GO induces irreversible cellular senescence within 3 days. Induction of senescence in hMSC-TERT was demonstrated by a variety of markers, including characteristic cell morphology and enlargement, vacuolisation, multinucleation, induction of senescence associated β-galactosidase, cell cycle arrest, and increased levels of a cell cycle inhibitor p16. These changes were accompanied by increased extent of DNA breaks as measured by the comet assay, and increased levels of the AGE product, carboxymethyl-lysine (CML). Furthermore, the in vitro differentiation potential of hMSC-TERT to become functional osteoblasts was highly reduced in GO-treated stem cells, as determined by alkaline phosphatase (ALP) activity and mineralized matrix (MM) formation.

CONCLUSIONS

The results of our study imply that an imbalanced glucose metabolism can reduce the functioning ability of stem cells in vivo both during ageing and during stem cell-based therapeutic interventions.

Hormesis-based anti-aging products: a case study of a novel cosmetic

Application of hormesis in aging research and interventions is becoming increasingly attractive and successful. The reason for this is the realization that mild stress-induced activation of one or more stress response (SR) pathways, and its consequent stimulation of repair mechanisms, is effective in reducing the age-related accumulation of molecular damage. For example, repeated heat stress-induced synthesis of heat shock proteins has been shown to have a variety of anti-aging effects on growth and other cellular and biochemical characteristics of normal human skin fibroblasts, keratinocytes and endothelial cells undergoing aging in vitro. Therefore, searching for potential hormetins - conditions and compounds eliciting SR-mediated hormesis - is drawing attention of not only the researchers but also the industry involved in developing healthcare products, including nutriceuticals, functional foods and cosmeceuticals. Here we present the example of a skin care cosmetic as one of the first successful product developments incorporating the ideas of hormesis. This was based on the studies to analyse the molecular effects of active ingredients extracted from the roots of the Chinese herb Sanchi (Panax notoginseng) on gene expression at the level of mRNAs and proteins in human skin cells. The results showed that the ginsenosides extracted from Sanchi induced the transcription of stress genes and increased the synthesis of stress proteins, especially the heat shock protein HSP1A1 or Hsp70, in normal human keratinocytes and dermal fibroblasts. Furthermore, this extract also has significant positive effects against facial wrinkles and other symptoms of facial skin aging as tested clinically, which may be due to its hormetic mode of action by stress-induced synthesis of chaperones involved in protein repair and removal of abnormal proteins. Acceptance of such a hormesis-based product by the wider public could be instrumental in the social recognition of the concept of hormesis as the beneficial effects of mild stress of choice, and will encourage the development of novel health care products with physical, nutritional and mental hormetins.