Positive correlation between mammalian life span and cellular resistance to stress

Chromosome-level genome provides insights into environmental adaptability and innate immunity in the common dolphin (delphinus delphis)

The common dolphin (Delphinus delphis) is widely distributed worldwide and well adapted to various habitats. Animal genomes store clues about their pasts, and can reveal the genes underlying their evolutionary success. Here, we report the first high-quality chromosome-level genome of D. delphis. The assembled genome size was 2.56 Gb with a contig N50 of 63.85 Mb. Phylogenetically, D. delphis was close to Tursiops truncatus and T. aduncus. The genome of D. delphis exhibited 428 expanded and 1,885 contracted gene families, and 120 genes were identified as positively selected. The expansion of the HSP70 gene family suggested that D. delphis has a powerful system for buffering stress, which might be associated with its broad adaptability, longevity, and detoxification capacity. The expanded IFN-α and IFN-ω gene families, as well as the positively selected genes encoding tripartite motif-containing protein 25, peptidyl-prolyl cis-trans isomerase NIMA-interacting 1, and p38 MAP kinase, were all involved in pathways for antiviral, anti-inflammatory, and antineoplastic mechanisms. The genome data also revealed dramatic fluctuations in the effective population size during the Pleistocene. Overall, the high-quality genome assembly and annotation represent significant molecular resources for ecological and evolutionary studies of Delphinus and help support their sustainable treatment and conservation.

Social life results in social stress protection: a novel concept to explain individual life-history patterns in social insects

Resistance to and avoidance of stress slow aging and confer increased longevity in numerous organisms. Honey bees and other superorganismal social insects have two main advantages over solitary species to avoid or resist stress: individuals can directly help each other by resource or information transfer, and they can cooperatively control their environment. These benefits have been recognised in the context of pathogen and parasite stress as the concept of social immunity, which has been extensively studied. However, we argue that social immunity is only a special case of a general concept that we define here as social stress protection to include group-level defences against all biotic and abiotic stressors. We reason that social stress protection may have allowed the evolution of reduced individual-level defences and individual life-history optimization, including the exceptional aging plasticity of many social insects. We describe major categories of stress and how a colonial lifestyle may protect social insects, particularly against temporary peaks of extreme stress. We use the honey bee (Apis mellifera L.) to illustrate how patterns of life expectancy may be explained by social stress protection and how modern beekeeping practices can disrupt social stress protection. We conclude that the broad concept of social stress protection requires rigorous empirical testing because it may have implications for our general understanding of social evolution and specifically for improving honey bee health.

Peto's "Paradox" and Six Degrees of Cancer Prevalence

Peto's paradox and the epidemiologic observation of the average six degrees of tumor prevalence are studied and hypothetically solved. A simple consideration, Petho's paradox challenges our intuitive understanding of cancer risk and prevalence. Our simple consideration is that the more a cell divides, the higher the chance of acquiring cancerous mutations, and so the larger or longer-lived organisms have more cells and undergo more cell divisions over their lifetime, expecting to have a higher risk of developing cancer. Paradoxically, it is not supported by the observations. The allometric scaling of species could answer the Peto paradox. Another paradoxical human epidemiology observation in six average mutations is necessary for cancer prevalence, despite the random expectations of the tumor causes. To solve this challenge, game theory could be applied. The inherited and random DNA mutations in the replication process nonlinearly drive cancer development. The statistical variance concept does not reasonably describe tumor development. Instead, the Darwinian natural selection principle is applied. The mutations in the healthy organism's cellular population can serve the species' evolutionary adaptation by the selective pressure of the circumstances. Still, some cells collect multiple uncorrected mutations, adapt to the extreme stress in the stromal environment, and develop subclinical phases of cancer in the individual. This process needs extensive subsequent DNA replications to heritage and collect additional mutations, which are only marginal alone. Still, together, they are preparing for the first stage of the precancerous condition. In the second stage, when one of the caretaker genes is accidentally mutated, the caused genetic instability prepares the cell to fight for its survival and avoid apoptosis. This can be described as a competitive game. In the third stage, the precancerous cell develops uncontrolled proliferation with the damaged gatekeeper gene and forces the new game strategy with binary cooperation with stromal cells for alimentation. In the fourth stage, the starving conditions cause a game change again, starting a cooperative game, where the malignant cells cooperate and force the cooperation of the stromal host, too. In the fifth stage, the resetting of homeostasis finishes the subclinical stage, and in the fifth stage, the clinical phase starts. The prevention of the development of mutated cells is more complex than averting exposure to mutagens from the environment throughout the organism's lifetime. Mutagenic exposure can increase the otherwise random imperfect DNA reproduction, increasing the likelihood of cancer development, but mutations exist. Toxic exposure is more challenging; it may select the tolerant cells on this particular toxic stress, so these mutations have more facility to avoid apoptosis in otherwise collected random mutational states.

Adult stem cell activity in naked mole rats for long-term tissue maintenance

The naked mole rat (NMR), Heterocephalus glaber, the longest-living rodent, provides a unique opportunity to explore how evolution has shaped adult stem cell (ASC) activity and tissue function with increasing lifespan. Using cumulative BrdU labelling and a quantitative imaging approach to track intestinal ASCs (Lgr5+) in their native in vivo state, we find an expanded pool of Lgr5+ cells in NMRs, and these cells specifically at the crypt base (Lgr5+CBC) exhibit slower division rates compared to those in short-lived mice but have a similar turnover as human LGR5+CBC cells. Instead of entering quiescence (G0), NMR Lgr5+CBC cells reduce their division rates by prolonging arrest in the G1 and/or G2 phases of the cell cycle. Moreover, we also observe a higher proportion of differentiated cells in NMRs that confer enhanced protection and function to the intestinal mucosa which is able to detect any chemical imbalance in the luminal environment efficiently, triggering a robust pro-apoptotic, anti-proliferative response within the stem/progenitor cell zone.

The Relationship between Lifespan of Marine Bivalves and Their Fatty Acids of Mitochondria Lipids

Marine bivalves belonging to the Mytilidae and Pectinidae Families were used in this research. The specific objectives of this study were: to determine the Fatty Acids (FAs) of mitochondrial gill membranes in bivalves with different lifespans, belonging to the same family, and to calculate their peroxidation index; to compare the levels of ROS generation, malondialdehyde (MDA), and protein carbonyls in the mitochondria of gills, in vitro, during the initiation of free-radical oxation; to investigate whether the FAs of mitochondria gill membranes affect the degree of their oxidative damage and the maximum lifespan of species (MLS). The qualitative membrane lipid composition was uniform in the studied marine bivalves, regardless of their MLS. In terms of the quantitative content of individual FAs, the mitochondrial lipids differed significantly. It is shown that lipid matrix membranes of the mitochondria of long-lived species are less sensitive to in vitro-initiated peroxidation compared with the medium and short-lived species. The differences in MLS are related to the peculiarities of FAs of mitochondrial membrane lipids.

Effects of Parental Dietary Restriction on Offspring Fitness in Drosophila melanogaster

Dietary restriction (DR) is a well-established strategy to increase lifespan and stress resistance in many eukaryotic species. In addition, individuals fed a restricted diet typically reduce or completely shut down reproduction compared to individuals fed a full diet. Although the parental environment can lead to changes epigenetically in offspring gene expression, little is known about the role of the parental (F₀) diet on the fitness of their offspring (F₁). This study investigated the lifespan, stress resistance, development, body weight, fecundity, and feeding rate in offspring from parental flies exposed to a full or restricted diet. The offspring flies of the parental DR showed increases in body weight, resistance to various stressors, and lifespan, but the development and fecundity were unaffected. Interestingly, parental DR reduced the feeding rate of their offspring. This study suggests that the effect of DR can extend beyond the exposed individual to their offspring, and it should be considered in both theoretical and empirical studies of senescence.

Scaling with body mass and age in glycolytic enzymes of domestic dogs

Animals produce ATP through oxidative phosphorylation using oxygen, but cellular energy can also be obtained through glycolysis when oxygen is not present at sufficient levels. Although most mammals of larger body mass have longer life spans, small dog breeds tend to outlive large breeds. Primary fibroblast cells from larger breeds of dogs have previously been shown to have increased dependency on glycolytic phenotypes across their lifespan. Different levels of activity of the glycolytic enzymes pyruvate kinase (PK), lactate dehydrogenase (LDH), and phosphoenolpyruvate carboxykinase (PEPCK) may provide insight to a mechanism that leads to the different metabolic phenotype observed in different sized breeds as they age. In this study, 1) we measured the activities of PK, LDH, and PEPCK in primary fibroblasts from dogs of different breed sizes and age classes and 2) measured the activities of PK and LDH in plasma from dogs of different breed sizes and age classes. We found that there was no significant relationship between body mass and PK, LDH and PEPCK activity in primary fibroblasts. Further, there were not significant differences with activity in these enzymes for old dogs compared to young dogs. In plasma, we found a negative correlation between PK activity and body mass and no relationship between LDH activity and body mass. There was a negative relationship between LDH activity and age in dogs. Further, while a negative correlational relationship between PK activity and age was only marginal, a best subsets regression model demonstrated a significant marginal effect of age on PK activity. PK and LDH may provide intermediates for other metabolic pathways in small breeds. However, large breed dogs may demonstrate a deficiency in metabolism at the PK level, a cellular metabolic pathway that may potentially aid in tumor progression.

Fibroblasts as an experimental model system for the study of comparative physiology

Mechanistic evaluations of processes that underlie organism-level physiology often require reductionist approaches. Dermal fibroblasts offer one such approach. These cells are easily obtained from minimally invasive skin biopsy, making them appropriate for the study of protected and/or logistically challenging species. Cell culture approaches permit extensive and fine-scale sampling regimes as well as gene manipulation techniques that are not feasible in vivo. Fibroblast isolation and culture protocols are outlined here for primary cells, and the benefits and drawbacks of immortalization are discussed. We show examples of physiological metrics that can be used to characterize primary cells (oxygen consumption, translation, proliferation) and readouts that can be informative in understanding cell-level responses to environmental stress (lactate production, heat shock protein induction). Importantly, fibroblasts may display fidelity to whole animal physiological phenotypes, facilitating their study. Fibroblasts from Antarctic Weddell seals show greater resilience to low temperatures and hypoxia exposure than fibroblasts from humans or rats. Fibroblast oxygen consumption rates are not affected by temperature stress in the heat-tolerant camel, whereas similar temperature exposures depress mitochondrial metabolism in fibroblasts from rhinoceros. Finally, dermal fibroblasts from a hibernator, the meadow jumping mouse, better resist experimental cooling than a fibroblast line from the laboratory mouse, with the hibernator demonstrating a greater maintenance of homeostatic processes such as protein translation. These results exemplify the parallels that can be drawn between fibroblast physiology and expectations in vivo, and provide evidence for the power of fibroblasts as a model system to understand comparative physiology and biomedicine.

Stress-Induced Membraneless Organelles in Eukaryotes and Prokaryotes: Bird’s-Eye View

Stress is an inevitable part of life. An organism is exposed to multiple stresses and overcomes their negative consequences throughout its entire existence. A correlation was established between life expectancy and resistance to stress, suggesting a relationship between aging and the ability to respond to external adverse effects as well as quickly restore the normal regulation of biological processes. To combat stress, cells developed multiple pro-survival mechanisms, one of them is the assembly of special stress-induced membraneless organelles (MLOs). MLOs are formations that do not possess a lipid membrane but rather form as a result of the “liquid–liquid” phase separation (LLPS) of biopolymers. Stress-responsive MLOs were found in eukaryotes and prokaryotes, they form as a reaction to the acute environmental conditions and are dismantled after its termination. These compartments function to prevent damage to the genetic and protein material of the cell during stress. In this review, we discuss the characteristics of stress-induced MLO-like structures in eukaryotic and prokaryotic cells.

Cellular aging and immunity

Science is constantly evolving and updated with current data on cell biology. The cellular aging phenomenon should be considered an evolutionary mechanism of the biological regulation of all living organisms. Factors initiating cellular aging are variable. Each cell type can respond differently to the activation factors of cellular aging. In recent decades, science has been supplemented with new data that provide a deeper understanding of cellular and molecular mechanisms of cellular aging and the formation of immune homeostasis. There is a real prospect of using effective means of its regulation. In recent years, scientists have come close to discovering the mechanisms of cellular aging. Factors and mechanisms of cell regeneration are more deeply revealed. Scientists are also better aware of the phylogeny and ontogenesis of immune processes and the role of immune factors in developing pathologies. Researchers are increasingly focusing on modern diagnostic methods and xenotherapy. However, the specific factors of immunoregulation and the interaction of microphages, macrophages, and lymphocytes with other body cells are not yet fully understood. Accordingly, this requires further in-depth study. This review reviews the current literature on cellular aging and its regulatory mechanisms. The authors also present the results of their research on the mechanisms of immune responses in reproductive pathology. They draw parallels with modern scientific theories and interpret research. We will also focus on the issues that need to be addressed in the near future for the progressive development of this field of science. Thus, the study of the mechanisms of cellular aging and the development of effective means of hay therapy today requires further painstaking work. Despite significant advances in preclinical studies, many questions remain about the practical use of the drugs. This is especially true in the medicine of oncology, neurology, and cardiology. Nevertheless, scientists will be able to use pharmacological agents to influence cell division, differentiation, and determination in the future. We also hope to have developed effective means of immunotherapy of diseases. The molecular mechanisms of cell aging and mediators involved in the mechanisms of cell aging and death are being studied in detail. The field of research contains countless fascinating studies that are sure to be discovered.

Advanced age increases frequencies of de novo mitochondrial mutations in macaque oocytes and somatic tissues

Mutations in mitochondrial DNA (mtDNA) contribute to multiple diseases. However, how new mtDNA mutations arise and accumulate with age remains understudied because of the high error rates of current sequencing technologies. Duplex sequencing reduces error rates by several orders of magnitude via independently tagging and analyzing each of the two template DNA strands. Here, using duplex sequencing, we obtained high-quality mtDNA sequences for somatic tissues (liver and skeletal muscle) and single oocytes of 30 unrelated rhesus macaques, from 1 to 23 y of age. Sequencing single oocytes minimized effects of natural selection on germline mutations. In total, we identified 17,637 tissue-specific de novo mutations. Their frequency increased ∼3.5-fold in liver and ∼2.8-fold in muscle over the ∼20 y assessed. Mutation frequency in oocytes increased ∼2.5-fold until the age of 9 y, but did not increase after that, suggesting that oocytes of older animals maintain the quality of their mtDNA. We found the light-strand origin of replication (OriL) to be a hotspot for mutation accumulation with aging in liver. Indeed, the 33-nucleotide-long OriL harbored 12 variant hotspots, 10 of which likely disrupt its hairpin structure and affect replication efficiency. Moreover, in somatic tissues, protein-coding variants were subject to positive selection (potentially mitigating toxic effects of mitochondrial activity), the strength of which increased with the number of macaques harboring variants. Our work illuminates the origins and accumulation of somatic and germline mtDNA mutations with aging in primates and has implications for delayed reproduction in modern human societies.

A new approach method for characterizing inter-species toxicodynamic variability

Inter-species differences in toxicodynamics are often a critical source of uncertainty in safety evaluations and typically dealt with using default adjustment factors. In vitro studies that use cells from different species demonstrated some success for estimating the relationships between life span and/or body weight and sensitivity to cytotoxicity; however, no apparent investigation evaluated the utility of these models for risk assessment. It was hypothesized that an in vitro model using dermal fibroblasts derived from diverse species and individuals might be utilized to inform the extent of inter-species and inter-individual variability in toxicodynamics. To test this hypothesis and characterize both inter-species and inter-individual variability in cytotoxicity, concentration-response cytotoxicity screening of 40 chemicals in primary dermal fibroblasts from 68 individuals of 54 diverse species was conducted. Chemicals examined included drugs, environmental pollutants, and food/flavor/fragrance agents; most of these were previously assessed either in vivo or in vitro for inter-species or inter-individual variation. Species included humans, the typical preclinical species and representatives from other orders of mammals and birds. Data demonstrated that both inter-species and inter-individual components of variability contribute to the observed differences in sensitivity to cell death. Further, it was found that the magnitude of the observed inter-species and inter-individual differences was chemical-dependent. This study contributes to the paradigm shift in risk assessment from reliance on in vivo toxicity testing to higher-throughput in vitro or alternative approaches, extending the strategy to replace use of default adjustment factors with experimental characterization of toxicodynamic inter-individual variability and to also address toxicodynamic inter-species variability.

Analysis of representative mutants for key DNA repair pathways on healthspan in Caenorhabditis elegans

Although the link between DNA damage and aging is well accepted, the role of different DNA repair proteins on functional/physiological aging is not well-defined. Here, using Caenorhabditis elegans, we systematically examined the effect of three DNA repair genes involved in key genome stability pathways. We assayed multiple health proxies including molecular, functional and resilience measures to define healthspan. Loss of XPF-1/ERCC-1, a protein involved in nucleotide excision repair (NER), homologous recombination (HR) and interstrand crosslink (ICL) repair, showed the highest impairment of functional and stress resilience measures along with a shortened lifespan. brc-1 mutants, with a well-defined role in HR and ICL are short-lived and highly sensitive to acute stressors, specifically oxidative stress. In contrast, ICL mutant, fcd-2 did not impact lifespan or most healthspan measures. Our efforts also uncover that DNA repair mutants show high sensitivity to oxidative stress with age, suggesting that this measure could act as a primary proxy for healthspan. Together, these data suggest that impairment of multiple DNA repair genes can drive functional/physiological aging. Further studies to examine specific DNA repair genes in a tissue specific manner will help dissect the importance and mechanistic role of these repair systems in biological aging.

New Perspectives on Avian Models for Studies of Basic Aging Processes

Avian models have the potential to elucidate basic cellular and molecular mechanisms underlying the slow aging rates and exceptional longevity typical of this group of vertebrates. To date, most studies of avian aging have focused on relatively few of the phenomena now thought to be intrinsic to the aging process, but primarily on responses to oxidative stress and telomere dynamics. But a variety of whole-animal and cell-based approaches to avian aging and stress resistance have been developed-especially the use of primary cell lines and isolated erythrocytes-which permit other processes to be investigated. In this review, we highlight newer studies using these approaches. We also discuss recent research on age-related changes in neural function in birds in the context of sensory changes relevant to homing and navigation, as well as the maintenance of song. More recently, with the advent of "-omic" methodologies, including whole-genome studies, new approaches have gained momentum for investigating the mechanistic basis of aging in birds. Overall, current research suggests that birds exhibit an enhanced resistance to the detrimental effects of oxidative damage and maintain higher than expected levels of cellular function as they age. There is also evidence that genetic signatures associated with cellular defenses, as well as metabolic and immune function, are enhanced in birds but data are still lacking relative to that available from more conventional model organisms. We are optimistic that continued development of avian models in geroscience, especially under controlled laboratory conditions, will provide novel insights into the exceptional longevity of this animal taxon.

Effects of metformin, rapamycin, and resveratrol on cellular metabolism of canine primary fibroblast cells isolated from large and small breeds as they age

Small breed dogs have longer lifespans than their large breed counterparts. Previous work demonstrated that primary fibroblast cells isolated from large breed young and old dogs have a persistent glycolytic metabolic profile compared with cells from small breed dogs. Here, we cultured primary fibroblast cells from small and large, young and old dogs and treated these cells with three commercially available drugs that show lifespan and health span benefits, and have been shown to reduce glycolytic rates: rapamycin (rapa), resveratrol (res) and metformin (met). We then measured aerobic and anaerobic cellular respiration in these cells. We found that rapa and res increased rates of non-glycolytic acidification in small and large breed puppies and basal oxygen consumption rates (OCR) in small and large breed puppies. Rapa increased proton leak and non-mitochondrial respiration in small and large breed puppies. Maximal respiration was significantly altered with rapa treatment but in opposing ways: large breed puppies showed a significant increase in maximal respiration when treated with rapa, and small old dogs demonstrated a significant decrease in maximal respiration when treated with rapa. In opposition to rapa treatments, met significantly decreased basal OCR levels in cells from small and large breed puppies. Our data suggest that rapa treatments may be metabolically beneficial to dogs when started early in life and more beneficial in larger breeds.

Melatonin to Rescue the Aged Heart: Antiarrhythmic and Antioxidant Benefits

Aging comes with gradual loss of functions that increase the vulnerability to disease, senescence, and death. The mechanisms underlying these processes are linked to a prolonged imbalance between damage and repair. Damaging mechanisms include oxidative stress, mitochondrial dysfunction, chronodisruption, inflammation, and telomere attrition, as well as genetic and epigenetic alterations. Several endogenous tissue repairing mechanisms also decrease. These alterations associated with aging affect the entire organism. The most devastating manifestations involve the cardiovascular system and may lead to lethal cardiac arrhythmias. Together with structural remodeling, electrophysiological and intercellular communication alterations during aging predispose to arrhythmic events. Despite the knowledge on repairing mechanisms in the cardiovascular system, effective antiaging strategies able to reduce the risk of arrhythmias are still missing. Melatonin is a promising therapeutic candidate due to its pleiotropic actions. This indoleamine regulates chronobiology and endocrine physiology. Of relevance, melatonin is an antiaging, antioxidant, antiapoptotic, antiarrhythmic, immunomodulatory, and antiproliferative molecule. This review focuses on the protective effects of melatonin on age-induced cardiac functional and structural alterations, potentially becoming a new fountain of youth for the heart.

On the evolution of cellular senescence

The idea that senescent cells are causally involved in aging has gained strong support from findings that the removal of such cells alleviates many age‐related diseases and extends the life span of mice. While efforts proceed to make therapeutic use of such discoveries, it is important to ask what evolutionary forces might have been behind the emergence of cellular senescence, in order better to understand the biology that we might seek to alter. Cellular senescence is often regarded as an anti‐cancer mechanism, since it limits the division potential of cells. However, many studies have shown that senescent cells often also have carcinogenic properties. This is difficult to reconcile with the simple idea of an anti‐cancer mechanism. Furthermore, other studies have shown that cellular senescence is involved in wound healing and tissue repair. Here, we bring these findings and ideas together and discuss the possibility that these functions might be the main reason for the evolution of cellular senescence. Furthermore, we discuss the idea that senescent cells might accumulate with age because the immune system had to strike a balance between false negatives (overlooking some senescent cells) and false positives (destroying healthy body cells).

Strong species differences in life history do not predict oxidative stress physiology or sensitivity to an environmental oxidant

Species typically align along a fast-slow life-history continuum, yet it is not clear to what extent oxidative stress physiology can be integrated with this continuum to form a 'pace-of-life syndrome', especially so in invertebrates. This is important, given the assumed role of oxidative stress in mediating life-history trade-offs, and the prediction that species with a faster pace should be more vulnerable to oxidative stress. We tested whether a species' life-history pace, here represented by its growth rate, can predict species-level differentiation in physiology and sensitivity to oxidative stress. Therefore, we exposed four species of Ischnura damselflies that strongly align along a fast-slow life-history continuum to different levels of ultraviolet (UV) radiation. We measured an extended set of physiological traits linked to the pace-of-life: standard metabolic rate, oxidative stress physiology (antioxidant enzymes and oxidative damage) and defence/condition traits (investment in immune function, energy storage and structural defence). Despite strong species differences in growth rate and physiology, growth rate did not predict species-level differentiation in physiology. Hence there was no support for the integration of metabolic rate, oxidative stress physiology or defence/condition traits into a species-level syndrome. Ultraviolet exposure affected nearly all traits: it reduced growth rate and increased metabolic rate, affected all oxidative stress physiology traits and increased the two defence traits (immune function, and melanin content). Nevertheless, the pace-of-life based on growth rate did not predict sensitivity to UV. Instead, the observed pattern of investment in structural UV defence (melanin) might have reduced the need for enzymatic antioxidant defence, this way potentially decoupling the covariation between the life-history pace and oxidative stress physiology. The absence of an integrated axis of life-history and physiological variation indicates no major constraints for the evolution of these traits among the studied damselfly species. Our study highlights that ecological differences between species may decouple covariation between species' life-history pace and their physiology, as well as their sensitivity to environmental stressors.

SIRT6 Is Responsible for More Efficient DNA Double-Strand Break Repair in Long-Lived Species

DNA repair has been hypothesized to be a longevity determinant, but the evidence for it is based largely on accelerated aging phenotypes of DNA repair mutants. Here, using a panel of 18 rodent species with diverse lifespans, we show that more robust DNA double-strand break (DSB) repair, but not nucleotide excision repair (NER), coevolves with longevity. Evolution of NER, unlike DSB, is shaped primarily by sunlight exposure. We further show that the capacity of the SIRT6 protein to promote DSB repair accounts for a major part of the variation in DSB repair efficacy between short- and long-lived species. We dissected the molecular differences between a weak (mouse) and a strong (beaver) SIRT6 protein and identified five amino acid residues that are fully responsible for their differential activities. Our findings demonstrate that DSB repair and SIRT6 have been optimized during the evolution of longevity, which provides new targets for anti-aging interventions.

The Ageing Process Affects the Antioxidant Defences and the Poly (ADPribosyl)ation Activity in Cistus Incanus L. Leaves

The ageing process in living organisms is characterised by the accumulation of several deleterious changes occurring in cells and tissues. The increase of reactive oxygen species with the advancement of age is responsible for the oxidative damage to proteins, lipids and DNA, enhancing the risk of diseases. The antioxidant response and the activation of the poly(ADP-ribosyl)ation process represent the first defences activated by organisms at all life stages to counteract damage to cell structures and genomic material. The regulation of poly(ADP ribosyl)ation with age is little known in plants, especially in combination with antioxidant defences modulation. In this study, the relationships between poly (ADP-ribose) polymerase (PARP) activity and enzymatic and non-enzymatic antioxidant pool have been studied together with the photosynthetic apparatus efficiency in the Mediterranean species Cistus incanus L., examining leaves at different developmental stages: young, mature and senescent. The photosynthetic performance was evaluated by chlorophyll a fluorescence measurement, the total soluble and fat-soluble antioxidant capacity, as well as the activities of enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione-S-transferase (GST), were determined by spectrophotometer, PARP activity was assessed by radioactive labelling. The highest photochemical activity was observed in young leaves, together with the highest GST activity. With the progress of the ageing process, the non-enzymatic antioxidant pool (namely ascorbic acid, α-tocopherol) declined, reaching the lowest value in senescent leaves, whereas PARP activity rose significantly. The overall results indicate that the decline of photosynthetic apparatus efficiency during senescence is due to the reduction of specific defences against oxidative damages, which increase the damages to DNA, as demonstrated by PARP activity rise.

A pro longevity role for cellular senescence

Cellular senescence is a fundamental process that may play positive or detrimental roles for the organism. It is involved in tissue development and in tumor prevention although during aging is becoming a detrimental process contributing to the decline of tissue functions. In previous investigations, we have uncovered a better capacity to detect DNA damage in cells from long-lived mammals. Here, we report that cultured cells derived from long-lived species have a higher propensity to undergo senescence when challenged with DNA damage than cells derived from short-lived species. Using a panel of cells derived from six mammals, which range in lifespan from 3-4 years up to 120 years, we examined cell cycle response, induction of apoptosis and of cellular senescence. All species exhibited a cell cycle arrest while induction of apoptosis was variable. However, a significant positive correlation was found between the relative percent of cells, within a population which entered senescence following damage, and the lifespan of the species. We suggest that cellular senescence may have a positive role during development allowing it to contribute to the evolution of longevity.

HSB-1 Inhibition and HSF-1 Overexpression Trigger Overlapping Transcriptional Changes To Promote Longevity in Caenorhabditis elegans

Heat shock factor 1 (HSF-1) is a component of the heat shock response pathway that is induced by cytoplasmic proteotoxic stress. In addition to its role in stress response, HSF-1 also acts as a key regulator of the rate of organismal aging. Overexpression of HSF-1 promotes longevity in C. elegans via mechanisms that remain less understood. Moreover, genetic ablation of a negative regulator of HSF-1, termed as heat shock factor binding protein 1 (HSB-1), results in hsf-1-dependent life span extension in animals. Here we show that in the absence of HSB-1, HSF-1 acquires increased DNA binding activity to its genomic target sequence. Using RNA-Seq to compare the gene expression profiles of the hsb-1 mutant and hsf-1 overexpression strains, we found that while more than 1,500 transcripts show ≥1.5-fold upregulation due to HSF-1 overexpression, HSB-1 inhibition alters the expression of less than 500 genes in C. elegans. Roughly half of the differentially regulated transcripts in the hsb-1 mutant have altered expression also in hsf-1 overexpressing animals, with a strongly correlated fold-expression pattern between the two strains. In addition, genes that are upregulated via both HSB-1 inhibition and HSF-1 overexpression include numerous DAF-16 targets that have known functions in longevity regulation. This study identifies how HSB-1 acts as a specific regulator of the transactivation potential of HSF-1 in non-stressed conditions, thus providing a detailed understanding of the role of HSB-1/HSF-1 signaling pathway in transcriptional regulation and longevity in C. elegans.

Incidence of Neoplasia in Pigs and Its Relevance to Clinical Organ Xenotransplantation

As clinical pig organ xenotransplantation draws closer, more attention is being paid to diseases that affect pigs and those that provide a potential risk to human recipients of pig organs. Neoplasia arising from the pig organ graft is one such concern. Various tumors and other neoplastic diseases are well known to show increased incidence in organ allotransplant recipients receiving immunosuppressive therapy. Whether this effect will prove to be the case after xenotransplantation has not yet been established. Malignant tumors in young pigs are rare, with lymphosarcoma, nephroblastoma, and melanoma being the most common. The combination of noninvasive techniques and intraoperative examination of the pig organ likely will readily confirm that a pig organ graft is tumor-free before xenotransplantation. Posttransplantion lymphoproliferative disorder (PTLD) is a concern after allotransplantation, but the incidence after solid organ allotransplantation is low when compared with hematopoietic cell allotransplantation (for example, bone marrow transplantation), unless immunosuppressive therapy is particularly intensive. Organ-source pigs used for clinical xenotransplantation will be bred and housed under designated pathogen-free conditions and will be free of the γ-herpesvirus that is a key factor in the development of PTLD in pigs. Therefore if a recipient of a pig xenograft develops PTLD, it will almost certainly be of recipient origin. The increasing availability of organs from pigs genetically-engineered to protect them from the human immune response likely will diminish the need for intensive immunosuppressive therapy. Considering the low incidence of malignant disease in young pigs, donor-derived malignancy is likely to be rare in patients who receive pig organ grafts. However, if the graft remains viable for many years, the incidence of graft malignancy may increase.

"The Same Thing That Makes You Live Can Kill You in the End": Exploring the Effects of Growth Rates and Longevity on Cellular Metabolic Rates and Oxidative Stress in Mammals and Birds

All aerobic organisms are subjected to metabolic by-products known as reactive species (RS). RS can wreak havoc on macromolecules by structurally altering proteins and inducing mutations in DNA, among other deleterious effects. To combat accumulating damage, organisms have an antioxidant system to sequester RS before they cause cellular damage. The balance between RS production, antioxidant defences, and accumulated cellular damage is termed oxidative stress. Physiological ecologists, gerontologists, and metabolic biochemists have turned their attention to whether oxidative stress is the principal, generalized mechanism that mediates and limits longevity, growth rates, and other life-history trade-offs in animals, as may be the case in mammals and birds. At the crux of this theory lies the regulation and activities of the mitochondria with respect to the organism and its metabolic rate. At the whole-animal level, evolutionary theory suggests that developmental trajectories and growth rates can shape the onset and rate of aging. Mitochondrial function is important for aging since it is the main source of energy in cells, and the main source of RS. Altering oxidative stress levels, either increase in oxidative damage or reduction in antioxidants, has proven to also decrease growth rates, which implies that oxidative stress is a cost of, as well as a constraint on, growth. Yet, in nature, many animals exhibit fast growth rates that lead to higher loads of oxidative stress, which are often linked to shorter lifespans. In this article, I summarize the latest findings on whole-animal life history trade-offs, such as growth rates and longevity, and how these can be affected by mitochondrial cellular metabolism, and oxidative stress.

Will donor-derived neoplasia be problematic after clinical pig organ or cell xenotransplantation?

There is an increased incidence of certain tumors and other neoplastic disease in organ allotransplant recipients receiving immunosuppressive therapy. Following clinical pig organ xenotransplantation, will there be a risk of the development of neoplasia in the pig graft or in other tissues transplanted with it, eg, lymph nodes? The incidence of neoplasia in young slaughterhouse pigs is very low (<0.005%), but in older pigs is largely unknown (as most pigs are killed within the first six months of life). However, lymphosarcoma, nephroblastoma, and melanoma have been reported in pigs. These tumors should be readily identified by ultrasound or direct inspection and palpation before an organ is excised for clinical xenotransplantation, and so transfer to the human recipient should be unlikely. Post-transplant lymphoproliferative disorder (PTLD) has been reported in pigs receiving intensive immunomodulatory therapy, particularly if this includes whole body irradiation, in an effort to induce mixed hematopoietic chimerism and immunological tolerance. However, the pigs used as sources of organs in xenotransplantation should be free of the porcine lymphotropic herpesvirus that is a key causative factor for PTLD in pigs, and so donor-derived PTLD should not occur. We conclude that the risk of a malignant tumor developing in a transplanted organ from a young pig is small.

Metabolic rates, climate and macroevolution: a case study using Neogene molluscs

Basal metabolic rate (BMR) is posited to be a fundamental control on the structure and dynamics of ecological networks, influencing organism resource use and rates of senescence. Differences in the maintenance energy requirements of individual species therefore potentially predict extinction likelihood. If validated, this would comprise an important link between organismic ecology and macroevolutionary dynamics. To test this hypothesis, the BMRs of organisms within fossil species were determined using body size and temperature data, and considered in the light of species' survival and extinction through time. Our analysis focused on the high-resolution record of Pliocene to recent molluscs (bivalves and gastropods) from the Western Atlantic. Species-specific BMRs were calculated by measuring the size range of specimens from museum collections, determining ocean temperature using the HadCM3 global climate model, and deriving values based on relevant equations. Intriguingly, a statistically significant difference in metabolic rate exists between those bivalve and gastropod taxa that went extinct and those that survived throughout the course of the Neogene. This indicates that there is a scaling up from organismic properties to species survival for these communities. Metabolic rate could therefore represent an important metric for predicting future extinction patterns, with changes in global climate potentially affecting the lifespan of individuals, ultimately leading to the extinction of the species they are contained within. We also find that, at the assemblage level, there are no significant differences in metabolic rates for different time intervals throughout the entire study period. This may suggest that Neogene mollusc communities have remained energetically stable, despite many extinctions.

Bacteria in the ageing gut: did the taming of fire promote a long human lifespan?

Unique among animals as they evolved towards Homo sapiens, hominins progressively cooked their food on a routine basis. Cooked products are characterized by singular chemical compounds, derived from the pervasive Maillard reaction. This same reaction is omnipresent in normal metabolism involving carbonyls and amines, and its products accumulate with age. The gut microbiota acts as a first line of defence against the toxicity of cooked Maillard compounds, that also selectively shape the microbial flora, letting specific metabolites to reach the blood stream. Positive selection of metabolic functions allowed the body of hominins who tamed fire to use and dispose of these age-related compounds. I propose here that, as a hopeful accidental consequence, this resulted in extending human lifespan far beyond that of our great ape cousins. The limited data exploring the role of taming fire on the human genetic setup and on its microbiota is discussed in relation with ageing.

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.

Cellular metabolism and oxidative stress as a possible determinant for longevity in small breed and large breed dogs

Among species, larger animals tend to live longer than smaller ones, however, the opposite seems to be true for dogs-smaller dogs tend to live significantly longer than larger dogs across all breeds. We were interested in the mechanism that may allow for small breeds to age more slowly compared with large breeds in the context of cellular metabolism and oxidative stress. Primary dermal fibroblasts from small and large breed dogs were grown in culture. We measured basal oxygen consumption (OCR), proton leak, and glycolysis using a Seahorse XF96 oxygen flux analyzer. Additionally, we measured rates of reactive species (RS) production, reduced glutathione (GSH) content, mitochondrial content, lipid peroxidation (LPO) damage and DNA (8-OHdg) damage. Our data suggests that as dogs of both size classes age, proton leak is significantly higher in older dogs, regardless of size class. We found that all aspects of glycolysis were significantly higher in larger breeds compared with smaller breeds. We found significant differences between age classes in GSH concentration, and a negative correlation between DNA damage in puppies and mean breed lifespan. Interestingly, RS production showed no differences across size and age class. Thus, large breed dogs may have higher glycolytic rates, and DNA damage, suggesting a potential mechanism for their decreased lifespan compared with small breed dogs.

Neurobiological Mechanisms of Stress Resilience and Implications for the Aged Population

BACKGROUND

Stress is a common reaction to an environmental adversity, but a dysregulation of the stress response can lead to psychiatric illnesses such as major depressive disorder (MDD), post-traumatic stress disorder (PTSD), and anxiety disorders. Yet, not all individuals exposed to stress will develop psychiatric disorders; those with enhanced stress resilience mechanisms have the ability to adapt successfully to stress without developing persistent psychopathology. Notably, the potential to enhance stress resilience in at-risk populations may prevent the onset of stress-induced psychiatric disorders. This novel idea has prompted a number of studies probing the mechanisms of stress resilience and how it can be manipulated.

METHODS

Here, we review the neurobiological factors underlying stress resilience, with particular focus on the serotoninergic (5-HT), glutamatergic, and γ-Aminobutyric acid (GABA) systems, as well as the hypothalamic-pituitary axis (HPA) in rodents and in humans. Finally, we discuss stress resiliency in the context of aging, as the likelihood of mood disorders increases in older adults.

RESULTS

Interestingly, increased resiliency has been shown to slow aging and improved overall health and quality of life. Research in the neurobiology of stress resilience, particularly throughout the aging process, is a nascent, yet, burgeoning field.

CONCLUSION

Overall, we consider the possible methods that may be used to induce resilient phenotypes, prophylactically in at-risk populations, such as in military personnel or in older MDD patients. Research in the mechanisms of stress resilience may not only elucidate novel targets for antidepressant treatments, but also provide novel insight about how to prevent these debilitating disorders from developing.

Hepatoprotective effects of capping protein gelsolin against hyperoxia-induced hepatotoxicity, oxidative stress and DNA damage in neonatal rats

Tissues and organs get exposed to high oxygen (O₂) supply in hyperoxia conditions. The goal of this research was to investigate the protective effect of actin binding protein gelsolin on hyperoxia-induced hepatotoxicity through histopathology and measurement of oxidative stress parameters and DNA damage in a neonatal Wistar albino rats. The pups were randomly separated to four equal groups such as: normoxia control group (NC), normoxia plus gelsolin group (NG, 10 ng/kg bw/day gelsolin), hyperoxia (≥85% O₂) group (HC), hyperoxia plus gelsolin group (HG, ≥85% O₂; 10 ng/kg bw/day gelsolin). Histopathological changes of pups in hyperoxia condition were revealed in the form of severe leukocyte infiltration, vascular congestion, necrosis, vacuolar degeneration, binucleated hepatocytes and hemorrhage in the liver tissue. SOD, CAT, GPx and GST activities decreased and MDA level increased in the hyperoxia-induced group in liver tissue (P < 0.05). Tail DNA%, tail length and moment indicating DNA damage statistically increased in hyperoxia treatment groups when compared to controls. Treatment of rats with hyperoxia plus gelsolin prevented hyperoxia-induced changes in tissue structure, antioxidant enzyme activities and MDA level, mean tail DNA% and length. Based on these findings, gelsolin restored these changing to near normal levels but it does not protect completely in the hyperoxia conditions.

Cutting back on the essentials: Can manipulating intake of specific amino acids modulate health and lifespan?

With few exceptions, nutritional and dietary interventions generally impact upon both old-age quality of life and longevity. The life prolonging effects, commonly observed with dietary restriction reportedly are linked to alterations in protein intake and specifically limiting the dietary intake of certain essential amino acids. There is however a paucity of data methodically evaluating the various essential amino acids on health- and lifespan and the mechanisms involved. Rodent diets containing either lower methionine content, or tryptophan, than that found in commercially available chow, appear to elicit beneficial effects. It is unclear whether all of these favorable effects associated with restricted intake of methionine and tryptophan are due to their specific unique properties or if restriction of other essential amino acids, or proteins in general, may produce similar results. Considerably more work remains to be done to elucidate the mechanisms by which limiting these vital molecules may delay the onset of age-associated diseases and improve quality of life at older ages.

Expression of cellular protective proteins SIRT1, HSP70 and SOD2 correlates with age and is significantly higher in NK cells of the oldest seniors

Background

NK cells are key effector lymphocytes of innate immunity provided with constitutive cytolytic activity, however, their role in human ageing is not entirely understood. The study aimed to analyze the expression of proteins involved in cellular stress response sirtuin 1 (SIRT1), heat shock protein 70 (HSP70) and manganese superoxide dismutase (SOD2) in non-stimulated NK cells of the oldest seniors (n = 25; aged over 85; mean age 88 years) and compare with NK cells of the old (n = 30; aged under 85; mean age 76 years) and the young (n = 32; mean age 21 years) to find potential relationships between the level of expression of these proteins in NK cells and longevity. The concentration of carbonyl groups and 8-isoprostanes in NK cell lysates reflecting the level of oxidative stress was also measured.

Results

The group of the oldest seniors differed from the other age groups by significantly higher percentage of NK cells expressing SIRT1, HSP70 and SOD2. The concentration of both carbonyl groups and 8-isoprostanes in NK cell extracts remained within the normal range in all age groups. The percentage of NK cells with the expression of, respectively, SIRT1, HSP70 and SOD2 correlated positively with age. Some correlations between expression levels of particular protective proteins SIRT1, HSP70 and SOD2 were observed in the study population.

Conclusions

The increased expression of cellular protective proteins SIRT1, HSP70 and SOD2 in NK cells of the oldest seniors seems to correspond to longevity and the observed correlations may suggest the involvement of these proteins in establishing NK cell homeostasis specific for healthy ageing process.

Reflections on the role of senescence during development and aging

New and stimulating results have challenged the concept that cellular senescence might not be synonymous with aging. It is indisputable that during aging, senescent cell accumulation has an impact on organismal health. Nevertheless, senescent cells are now known to display physiological roles during embryonic development, during wound healing repair and as a cellular response to stress. The fact that senescence has been found in cells that did not attain their maximal round of replications, nor have metabolic alterations or DNA damage, also challenges the paradigm that senescence is cellular aging, and it is in favor of the idea that cellular senescence is a phenomenon that has a function by itself. Therefore, in order to understand this phenomenon it is important to analyze the relationship between senescence and other cellular responses that have many features in common, such as apoptosis, cancer and autophagy, particularly highlighting their role during development and adulthood.

Prominent role of exopeptidase DPP III in estrogen-mediated protection against hyperoxia in vivo

A number of age-related diseases have a low incidence in females, which is attributed to a protective effect of sex hormones. For instance, the female sex hormone estrogen (E₂) has a well established cytoprotective effect against oxidative stress, which strongly contributes to ageing. However, the mechanism by which E₂ exerts its protective activity remains elusive.

In this study we address the question whether the E₂-induced protective effect against hyperoxia is mediated by the Nrf-2/Keap-1 signaling pathway. In particular, we investigate the E₂-induced expression and cellular distribution of DPP III monozinc exopeptidase, a member of the Nrf-2/Keap-1 pathway, upon hyperoxia treatment.

We find that DPP III accumulates in the nucleus in response to hyperoxia. Further, we show that combined induction of hyperoxia and E₂ administration have an additive effect on the nuclear accumulation of DPP III. The level of nuclear accumulation of DPP III is comparable to nuclear accumulation of Nrf-2 in healthy female mice exposed to hyperoxia. In ovariectomized females exposed to hyperoxia, supplementation of E₂ induced upregulation of DPP III, Ho-1, Sirt-1 and downregulation of Ppar-γ. While other cytoprotective mechanisms cannot be excluded, these findings demonstrate a prominent role of DPP III, along with Sirt-1, in the E₂-mediated protection against hyperoxia.

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DPP III accumulates in the nucleus in response to hyperoxia.

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Additive effect of hyperoxia and E₂ on nuclear accumulation of DPP III is observed.

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Protective effect of E₂ is associated with increased DPP III, Ho-1 and Sirt-1.

Comparative cellular biogerontology: Where do we stand?

Due to the extreme variation in life spans among species, using a comparative approach to address fundamental questions about the aging process has much to offer. For example, maximum life span can vary by as much as several orders of magnitude among taxa. In recent years, using primary cell lines cultured from species with disparate life spans and aging rates has gained considerable momentum as a means to dissect the mechanisms underlying the variation in aging rates among animals. In this review, we reiterate the strengths of comparative cellular biogerontology, as well as provide a survey of the current state of the field. By and large this work sprang from early studies using cell lines derived from long-lived mutant mice. Specifically, they suggested that an enhanced resistance to cellular stress was strongly associated with increased longevity of select laboratory models. Since then, we and others have shown that the degree of stress resistance and species longevity is also correlated among cell lines derived from free-living populations of both mammals and birds, and more recent studies have begun to reveal the biochemical and physiological underpinnings to these differences. The continued study of cultured cell lines from vertebrates with disparate life spans is likely to provide considerable insight toward unifying mechanisms of longevity assurance.

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

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Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

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Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

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NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

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ROS are powerful post-transcriptional and epigenetic regulators.

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Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Longevity Is Linked to Mitochondrial Mutation Rates in Rockfish: A Test Using Poisson Regression

The mitochondrial theory of ageing proposes that the cumulative effect of biochemical damage in mitochondria causes mitochondrial mutations and plays a key role in ageing. Numerous studies have applied comparative approaches to test one of the predictions of the theory: That the rate of mitochondrial mutations is negatively correlated with longevity. Comparative studies face three challenges in detecting correlates of mutation rate: Covariation of mutation rates between species due to ancestry, covariation between life-history traits, and difficulty obtaining accurate estimates of mutation rate. We address these challenges using a novel Poisson regression method to examine the link between mutation rate and lifespan in rockfish (Sebastes). This method has better performance than traditional sister-species comparisons when sister species are too recently diverged to give reliable estimates of mutation rate. Rockfish are an ideal model system: They have long life spans with indeterminate growth and little evidence of senescence, which minimizes the confounding tradeoffs between lifespan and fecundity. We show that lifespan in rockfish is negatively correlated to rate of mitochondrial mutation, but not the rate of nuclear mutation. The life history of rockfish allows us to conclude that this relationship is unlikely to be driven by the tradeoffs between longevity and fecundity, or by the frequency of DNA replications in the germline. Instead, the relationship is compatible with the hypothesis that mutation rates are reduced by selection in long-lived taxa to reduce the chance of mitochondrial damage over its lifespan, consistent with the mitochondrial theory of ageing.

Lifespan of mice and primates correlates with immunoproteasome expression

There is large variation in lifespan among different species, and there is evidence that modulation of proteasome function may contribute to longevity determination. Comparative biology provides a powerful tool for identifying genes and pathways that control the rate of aging. Here, we evaluated skin-derived fibroblasts and demonstrate that among primate species, longevity correlated with an elevation in proteasomal activity as well as immunoproteasome expression at both the mRNA and protein levels. Immunoproteasome enhancement occurred with a concurrent increase in other elements involved in MHC class I antigen presentation, including β-2 microglobulin, (TAP1), and TAP2. Fibroblasts from long-lived primates also appeared more responsive to IFN-γ than cells from short-lived primate species, and this increase in IFN-γ responsiveness correlated with elevated expression of the IFN-γ receptor protein IFNGR2. Elevation of immunoproteasome and proteasome activity was also observed in the livers of long-lived Snell dwarf mice and in mice exposed to drugs that have been shown to extend lifespan, including rapamycin, 17-α-estradiol, and nordihydroguaiaretic acid. This work suggests that augmented immunoproteasome function may contribute to lifespan differences in mice and among primate species.

Siglec receptors impact mammalian lifespan by modulating oxidative stress

Aging is a multifactorial process that includes the lifelong accumulation of molecular damage, leading to age-related frailty, disability and disease, and eventually death. In this study, we report evidence of a significant correlation between the number of genes encoding the immunomodulatory CD33-related sialic acid-binding immunoglobulin-like receptors (CD33rSiglecs) and maximum lifespan in mammals. In keeping with this, we show that mice lacking Siglec-E, the main member of the CD33rSiglec family, exhibit reduced survival. Removal of Siglec-E causes the development of exaggerated signs of aging at the molecular, structural, and cognitive level. We found that accelerated aging was related both to an unbalanced ROS metabolism, and to a secondary impairment in detoxification of reactive molecules, ultimately leading to increased damage to cellular DNA, proteins, and lipids. Taken together, our data suggest that CD33rSiglecs co-evolved in mammals to achieve a better management of oxidative stress during inflammation, which in turn reduces molecular damage and extends lifespan.

DOI:http://dx.doi.org/10.7554/eLife.06184.001

As we get older, we are more likely to become frail, be less mobile and develop heart disease, diabetes, and other age-related diseases. This is partly due to damage to tissues and organs that accumulates over the course of our lifetime. How quickly we age is controlled both by our genetics and by the environment we live in.

It is thought that damage to DNA, proteins, and other molecules in the body caused by chemically active molecules called reactive oxygen species (ROS) can influence aging. ROS are produced during respiration, immune responses, and other important processes in cells, but in excessive amounts they can be extremely harmful. To avoid damage to DNA and other important molecules, cells have several ways to control the levels of ROS.

One of the other hallmarks of aging is the development of chronic inflammation in tissues around the body, which is partly triggered by the immune system in response to cell damage. A group of genes called the CD33rSIGLEC genes are involved in controlling inflammation. The genomes of different mammal species carry different numbers of these genes, but it is not clear whether this alters the aging process in these animals.

In this study, Schwarz et al. investigated whether the CD33rSIGLEC genes influence the lifespans of mammals. Species with a higher number of CD33rSIGLEC genes generally have a longer lifespan than those with fewer of these genes. Mice that were missing one of these genes and were subjected to inflammation early in life showed signs of accelerated aging and had shortened lifespans compared with normal mice. As predicted, these mice also had higher levels of ROS, which led to a greater amount of damage to the DNA and other molecules in their bodies.

Schwarz et al.'s findings suggest that the CD33rSIGLECs co-evolved in mammals to help control the levels of ROS during inflammation, thereby reducing the damage to cells and extending the lifespan of the animals. Given that individual humans have different numbers of working CD33rSIGLEC genes, it would be interesting to see if this influences human lifespan.

DOI:http://dx.doi.org/10.7554/eLife.06184.002

Regulation of Nrf2 signaling and longevity in naturally long-lived rodents

The preternaturally long-lived naked mole-rat, like other long-lived species and experimental models of extended longevity, is resistant to both endogenous (e.g., reactive oxygen species) and environmental stressors and also resists age-related diseases such as cancer, cardiovascular disease, and neurodegeneration. The mechanisms behind the universal resilience of longer-lived organisms to stress, however, remain elusive. We hypothesize that this resilience is linked to the activity of a highly conserved transcription factor, nuclear factor erythroid 2-related factor (Nrf2). Nrf2 regulates the transcription of several hundred cytoprotective molecules, including antioxidants, detoxicants, and molecular chaperones (heat shock proteins). Nrf2 itself is tightly regulated by mechanisms that either promote its activity or increase its degradation. We used a comparative approach and examined Nrf2-signaling activity in naked mole-rats and nine other rodent species with varying maximum lifespan potential (MLSP). We found that constitutive Nrf2-signaling activity was positively correlated (P = 0.0285) with MLSP and that this activity was also manifested in high levels of downstream gene expression and activity. Surprisingly, we found that species longevity was not linked to the protein levels of Nrf2 itself, but rather showed a significant (P < 0.01) negative relationship with the regulators Kelch-like ECH-Associated Protein 1 (Keap1) and β-transducin repeat-containing protein (βTrCP), which target Nrf2 for degradation. These findings highlight the use of a comparative biology approach for the identification of evolved mechanisms that contribute to health span, aging, and longevity.

Long-lived species have improved proteostasis compared to phylogenetically-related shorter-lived species

Our previous studies have shown that the liver from Naked Mole Rats (NMRs), a long-lived rodent, has increased proteasome activity and lower levels of protein ubiquitination compared to mice. This suggests that protein quality control might play a role in assuring species longevity. To determine whether enhanced proteostasis is a common mechanism in the evolution of other long-lived species, here we evaluated the major players in protein quality control including autophagy, proteasome activity, and heat shock proteins (HSPs), using skin fibroblasts from three phylogenetically-distinct pairs of short- and long-lived mammals: rodents, marsupials, and bats. Our results indicate that in all cases, macroautophagy was significantly enhanced in the longer-lived species, both at basal level and after induction by serum starvation. Similarly, basal levels of most HSPs were elevated in all the longer-lived species. Proteasome activity was found to be increased in the long-lived rodent and marsupial but not in bats. These observations suggest that long-lived species may have superior mechanisms to ensure protein quality, and support the idea that protein homeostasis might play an important role in promoting longevity.

Uncoupling lifespan and healthspan in Caenorhabditis elegans longevity mutants

Aging research has been very successful at identifying signaling pathways and evolutionarily conserved genes that extend lifespan with the assumption that an increase in lifespan will also increase healthspan. However, it is largely unknown whether we are extending the healthy time of life or simply prolonging a period of frailty with increased incidence of age-associated diseases. Here we use Caenorhabditis elegans, one of the premiere systems for lifespan studies, to determine whether lifespan and healthspan are intrinsically correlated. We conducted multiple cellular and organismal assays on wild type as well as four long-lived mutants (insulin/insulin-like growth factor-1, dietary restriction, protein translation, mitochondrial signaling) in a longitudinal manner to determine the health of the animals as they age. We find that some long-lived mutants performed better than wild type when measured chronologically (number of days). However, all long-lived mutants increased the proportion of time spent in a frail state. Together, these data suggest that lifespan can no longer be the sole parameter of interest and reveal the importance of evaluating multiple healthspan parameters for future studies on antiaging interventions.

Fibroblasts derived from long-lived insulin receptor substrate 1 null mice are not resistant to multiple forms of stress

Reduced signalling through the insulin/insulin-like growth factor-1 signalling (IIS) pathway is a highly conserved lifespan determinant in model organisms. The precise mechanism underlying the effects of the IIS on lifespan and health is currently unclear, although cellular stress resistance may be important. We have previously demonstrated that mice globally lacking insulin receptor substrate 1 (Irs1^−/−) are long-lived and enjoy a greater period of their life free from age-related pathology compared with wild-type (WT) controls. In this study, we show that primary dermal fibroblasts and primary myoblasts derived from Irs1^−/− mice are no more resistant to a range of oxidant and nonoxidant chemical stressors than cells derived from WT mice.

Fibroblasts From Longer-Lived Species of Primates, Rodents, Bats, Carnivores, and Birds Resist Protein Damage

Species differ greatly in their rates of aging. Among mammalian species life span ranges from 2 to over 60 years. Here, we test the hypothesis that skin-derived fibroblasts from long-lived species of animals differ from those of short-lived animals in their defenses against protein damage. In parallel studies of rodents, nonhuman primates, birds, and species from the Laurasiatheria superorder (bats, carnivores, shrews, and ungulates), we find associations between species longevity and resistance of proteins to oxidative stress after exposure to H(2)O(2) or paraquat. In addition, baseline levels of protein carbonyl appear to be higher in cells from shorter-lived mammals compared with longer-lived mammals. Thus, resistance to protein oxidation is associated with species maximal life span in independent clades of mammals, suggesting that this cellular property may be required for evolution of longevity. Evaluation of the properties of primary fibroblast cell lines can provide insights into the factors that regulate the pace of aging across species of mammals.