Fibroblasts from long-lived bird species are resistant to multiple forms of stress

Fmo induction as a tool to screen for pro-longevity drugs

Dietary restriction (DR) and hypoxia (low oxygen) extend lifespan in Caenorhabditis elegans through the induction of a convergent downstream longevity gene, fmo-2. Flavin-containing monooxygenases (FMOs) are highly conserved xenobiotic-metabolizing enzymes with a clear role in promoting longevity in nematodes and a plausible similar role in mammals. This makes them an attractive potential target of small molecule drugs to stimulate the health-promoting effects of longevity pathways. Here, we utilize an fmo-2 fluorescent transcriptional reporter in C. elegans to screen a set of 80 compounds previously shown to improve stress resistance in mouse fibroblasts. Our data show that 19 compounds significantly induce fmo-2, and 10 of the compounds induce fmo-2 more than twofold. Interestingly, 9 of the 10 high fmo-2 inducers also extend lifespan in C. elegans. Two of these drugs, mitochondrial respiration chain complex inhibitors, interact with the hypoxia pathway to induce fmo-2, whereas two dopamine receptor type 2 (DRD2) antagonists interact with the DR pathway to induce fmo-2, indicating that dopamine signaling is involved in DR-mediated fmo-2 induction. Together, our data identify nine drugs that each (1) increase stress resistance in mouse fibroblasts, (2) induce fmo-2 in C. elegans, and (3) extend nematode lifespan, some through known longevity pathways. These results define fmo-2 induction as a viable approach to identifying and understanding mechanisms of putative longevity compounds.

The resistance of domestic canine skin-derived fibroblasts to oxidative and non-oxidative chemical injury: implications of breed and body size

Small-breed dogs live significantly longer lives than large-breed dogs, while having higher mass-specific metabolic rates and faster growth rates. Underlying this observed physiological difference across domestic dogs, there must also be differences at other levels of organization that could lead to elucidating what accounts for the disparity in aging rates and life span within this species. At the cellular level, a clear mechanism underlying whole animal traits has not been fully elucidated. Here, we cultured dermal fibroblasts from large and small breed dogs from both young and old age categories and examined the degree of resistance to multiple sources of cytotoxic stress. This included heat (42 °C), paraquat, cadmium, and hydrogen peroxide for increasing amounts of time (heat) or increasing concentrations (chemical stressors). We hypothesized that small breed dogs, with longer lifespans, would have greater cellular resistance to stress compared with large breed dogs. Final sample sizes include small puppies (N = 18), large puppy (N = 32), small old (N = 11), and large old (N = 23) dogs. Using a 2 (donor size) by 2 (donor age) between-subjects multivariate analysis of variance, we found that the values for the dose that killed 50% of the cells (LD50) were not significantly different based on donor size (p = 0.45) or donor age (p = 0.20). The interaction was also not significant (p = 0.47). Interestingly, we did find that the degree of resistance to cadmium toxicity was significantly correlated with the degree of resistance to both heat and hydrogen peroxide, but not paraquat (p < 0.01 for both). These data suggest that cellular stress resistance does not differ among domestic dogs as a function of size or age, pointing to other cellular pathways as the mechanistic basis for the observed differences in lifespan.

Primary Cell Culture as a Model System for Evolutionary Molecular Physiology

Primary cell culture is a powerful model system to address fundamental questions about organismal physiology at the cellular level, especially for species that are difficult, or impossible, to study under natural or semi-natural conditions. Due to their ease of use, primary fibroblast cultures are the dominant model system, but studies using both somatic and germ cells are also common. Using these models, genome evolution and phylogenetic relationships, the molecular and biochemical basis of differential longevities among species, and the physiological consequences of life history evolution have been studied in depth. With the advent of new technologies such as gene editing and the generation of induced pluripotent stem cells (iPSC), the field of molecular evolutionary physiology will continue to expand using both descriptive and experimental approaches.

Novel 3D printed polysaccharide-based materials with prebiotic activity for potential treatment of diaper rash

Diaper rash, mainly occurring as erythema and itching in the diaper area, causes considerable distress to infants and toddlers. Increasing evidence suggests that an unequal distribution of microorganisms on the skin contributes to the development of diaper dermatitis. Probiotic bacteria, like Staphylococcus epidermidis, are crucial for maintaining a healthy balance in the skin's microbiome, among others, through their fermentative metabolites, such as short-chain fatty acids. Using a defined prebiotic as a carbon source (e.g., as part of the diaper formulation) can selectively trigger the fermentation of probiotic bacteria. A proper material choice can reduce diaper rash incidence by diminishing the skin exposure to wetness and faeces. Using 3D printing, we fabricated carbon-rich materials for the top sheet layer of baby diapers that enhance the probiotic activity of S. epidermidis. The developed materials' printability, chemical composition, swelling ability, and degradation rate were analysed. In addition, microbiological tests evaluated their potential as a source of in situ short-chain fatty acid production. Finally, biocompatibility testing with skin cells evaluated their safety for potential use as part of diapers. The results demonstrate a cost-effective approach for producing novel materials that can tailor the ecological balance of the skin microflora and help treat diaper rash.

Cellular metabolic pathways of aging in dogs: could p53 and SIRT1 be at play?

Aging and cancer seem to be closely associated, such that cancer is generally considered a disease of the elderly in both humans and dogs. Additionally, cancer is a metabolic shift in itself towards aerobic glycolysis. Larger dog breeds with shorter lifespans, and increased glycolytic cellular metabolic rates, die of cancer more often than smaller breeds. The tumor suppressor p53 factor is a key suppressor oncogene, and the p53 pathway arrests cellular proliferation and prevents DNA mutations from accumulating during cellular stress. The p53 pathway is also associated with the control of cellular metabolism to prevent cellular metabolic shifts common to cancerous phenotypes. SIRT1 deacetylates the p53 tumor suppressor protein, downregulating p53 via effects on stability and activity during stress. Here, we used primary fibroblast cells from small and large puppies and old dogs. Using UV radiation to upregulate the p53 system (100 J/m2), control cells and UV-treated cells were used to measure aerobic and glycolytic metabolic rates using a Seahorse XFe96 oxygen flux analyzer. We also quantified p53 expression and SIRT1 concentration in canine primary fibroblasts before and after UV treatment. We demonstrate that, due to a higher p53 nuclear to cytoplasmic ratio in large breed dogs after UV treatment, p53 could have a more regulatory effect on large breed dogs' metabolism compared with smaller breeds. Thus, there may be a link between p53 upregulation and inhibition of glycolysis in large breed dogs during times of cellular stress compared with small breed dogs. However, SIRT1 concentrations decrease with age in domestic dogs of both size classes, suggesting a possible release of inhibition of p53 through the SIRT1 pathway with age. This may lead to increased incidences of cancer, especially due to the more pronounced upregulation of p53 with cellular stress.

Tendon-Derived Mesenchymal Stem Cells (TDSCs) as an In Vitro Model for Virological Studies in Wild Birds

The use of wild animals in research is complicated due to the capture and housing conditions, as well as to legal aspects, making it difficult to develop in vivo and in vitro models for the study of pathologies that affect these species. Here we validate an in vitro model of tendon-derived mesenchymal cells (TDSC) from Eurasian blackbird (Turdus merula) cadaveric samples. Through the expression of surface markers and the ability to differentiate into multiple lineages, the nature of the cells was confirmed. We then evaluated Mesenchymal Stem Cells (MSCs) as an infection model for the Usutu Flavivirus. To this aim, blackbird TDSCs were compared to Vero E6 cells, commonly used in Flavivirus studies. Both cells showed permissiveness to USUV infection as confirmed by immunocytochemistry. Moreover, TDSCs exhibited replication kinetics similar to, although slightly lower than, Vero E6, confirming these cells as a pertinent study model for the study of the pathogenesis of USUV. In this work, we isolated and characterized tendon-derived mesenchymal stem cells, which represent an interesting and convenient in vitro model for the study of wildlife species in laboratories.

Methionine Sources Differently Affect Production of Reactive Oxygen Species, Mitochondrial Bioenergetics, and Growth of Murine and Quail Myoblasts In Vitro

An optimal supply of L-methionine (L-Met) improves muscle growth, whereas over-supplementation exerts adverse effects. To understand the underlying mechanisms, this study aims at exploring effects on the growth, viability, ROS production, and mitochondrial bioenergetics of C2C12 (mouse) and QM7 (quail) myoblasts additionally supplemented (100 or 1000 µM) with L-Met, DL-methionine (DL-Met), or DL-2-hydroxy-4-(methylthio)butanoic acid (DL-HMTBA). In both cell lines, all the supplements stimulated cell growth. However, in contrast to DL-Met, 1000 µM of L-Met (C2C12 cells only) or DL-HMTBA started to retard growth. This negative effect was stronger with DL-HMTBA and was accompanied by significantly elevated levels of extracellular H₂O₂, an indicator for OS, in both cell types. In addition, oversupplementation with DL-HMTBA (1000 µM) induced adaptive responses in mitochondrial bioenergetics, including reductions in basal (C2C12 and QM7) and ATP-synthase-linked (C2C12) oxygen consumption, maximal respiration rate, and reserve capacity (QM7). Only QM7 cells switched to nonmitochondrial aerobic glycolysis to reduce ROS production. In conclusion, we found a general negative effect of methionine oversupplementation on cell proliferation. However, only DL-HMTBA-induced growth retardation was associated with OS and adaptive, species-specific alterations in mitochondrial functionality. OS could be better compensated by quail cells, highlighting the role of species differences in the ability to cope with methionine oversupplementation.

Revisiting glucose regulation in birds - A negative model of diabetes complications

Birds naturally have blood glucose concentrations that are nearly double levels measured for mammals of similar body size and studies have shown that birds are resistant to insulin-mediated glucose uptake into tissues. While a combination of high blood glucose and insulin resistance is associated with diabetes-related pathologies in mammals, birds do not develop such complications. Moreover, studies have shown that birds are resistant to oxidative stress and protein glycation and in fact, live longer than similar-sized mammals. This review seeks to explore how birds regulate blood glucose as well as various theories that might explain their apparent resistance to insulin-mediated glucose uptake and adaptations that enable them to thrive in a state of relative hyperglycemia.

Establishment of the Primary Avian Gonadal Somatic Cell Lines for Cytogenetic Studies

Simple Summary

We developed a simple method for primary somatic cell culture establishment from the ovaries of the great tits and testes of ten Passerine species. The ovary-derived cell cultures were cultivated until the tenth passage without any noticeable decrease in their proliferative activity, while testis-derived cell cultures demonstrated a decreased proliferation potential. However, sufficient material was available from both cell cultures originating from the ovary and testis to make excellent mitotic metaphase chromosomal preparations. We demonstrated the high efficiency of electroporation for genetic modification of the ovary-derived cell line. Thus, the established ovary-derived cell line could be efficiently used in cytogenetic and genomic studies.

Abstract

The last decade was marked by a steep rise in avian studies at genomic and cellular levels. Cell lines are important tools for in vitro studies in cell biology and cytogenetics. We developed a simple method of primary somatic cell culture establishment from the ovaries of the great tits (Parus major) and testes of ten Passerine species, characterized the cellular composition of the ovary-derived lines using RT-PCR and immunolocalization of the tissue-specific markers and tested the efficiency of two methods of genetic transformation of the ovary-derived cell line. We found that the ovary-derived cell cultures of the great tit were composed of fibroblasts mainly, but also contained interstitial and granulosa cells. They were cultivated until the 10th passage without any noticeable decrease in their proliferative activity. The testis-derived cell cultures had lower proliferative potential. However, both ovary- and testis-derived cell cultures provided enough material for high quality mitotic metaphase chromosome preparations. The efficiency of its transduction with lentivirus containing a GFP reporter was very low, while electroporation with episomal vectors expressing GFP resulted in a high yield of GFP-positive cells. The proposed method could be used for the generation of high quality material for various cytogenetic and genomic studies.

Transient early life growth hormone exposure permanently alters brain, muscle, liver, macrophage, and adipocyte status in long-lived Ames dwarf mice

The exceptional longevity of Ames dwarf (DF) mice can be abrogated by a brief course of growth hormone (GH) injections started at 2 weeks of age. This transient GH exposure also prevents the increase in cellular stress resistance and decline in hypothalamic inflammation characteristic of DF mice. Here, we show that transient early-life GH treatment leads to permanent alteration of pertinent changes in adipocytes, fat-associated macrophages, liver, muscle, and brain that are seen in DF mice. Ames DF mice, like Snell dwarf and GHRKO mice, show elevation of glycosylphosphatidylinositol specific phospholipase D1 in liver, neurogenesis in brain as indicated by BDNF and DCX proteins, muscle production of fibronectin type III domain-containing protein 5 (a precursor of irisin), uncoupling protein 1 as an index of thermogenic capacity in brown and white fat, and increase in fat-associated anti-inflammatory macrophages. In each case, transient exposure to GH early in life reverts the DF mice to the levels of each protein seen in littermate control animals, in animals evaluated at 15-18 months of age. Thus, many of the traits seen in long-lived mutant mice, pertinent to age-related changes in inflammation, neurogenesis, and metabolic control, are permanently set by early-life GH levels.

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.

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.

Elevated metallothionein expression in long-lived species mediates the influence of cadmium accumulation on aging

Cadmium (Cd) accumulates with aging and is elevated in long-lived species. Metallothioneins (MTs), small cysteine-rich proteins involved in metal homeostasis and Cd detoxification, are known to be related to longevity. However, the relationship between Cd accumulation, the role of MTs, and aging is currently unclear. Specifically, we do not know if long-lived species evolved an efficient metal stress response by upregulating their MT levels to reduce the toxic effects of environmental pollutants, such as Cd, that accumulate over their longer life span. It is also unknown if the number of MT genes, their expression, or both protect the organisms from potentially damaging effects during aging. To address these questions, we reanalyzed several cross-species studies and obtained data on MT expression and Cd accumulation in long-lived mouse models. We confirmed a relationship between species maximum life span in captive mammals and their Cd content in liver and kidney. We found that although the number of MT genes does not affect longevity, gene expression and protein amount of specific MT paralogs are strongly related to life span in mammals. MT expression rather than gene number may influence the high Cd levels and longevity of some species. In support of this, we found that overexpression of MT-1 accelerated Cd accumulation in mice and that tissue Cd was higher in long-lived mouse strains with high MT expression. We conclude that long-lived species have evolved a more efficient stress response by upregulating the expression of MT genes in presence of Cd, which contributes to elevated tissue Cd levels.

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.

Flavin-Containing Monooxygenases Are Conserved Regulators of Stress Resistance and Metabolism

Flavin-Containing Monooxygenases are conserved xenobiotic-detoxifying enzymes. Recent studies have revealed endogenous functions of FMOs in regulating longevity in Caenorhabditis elegans and in regulating aspects of metabolism in mice. To explore the cellular mechanisms of FMO's endogenous function, here we demonstrate that all five functional mammalian FMOs may play similar endogenous roles to improve resistance to a wide range of toxic stresses in both kidney and liver cells. We further find that stress-activated c-Jun N-terminal kinase activity is enhanced in FMO-overexpressing cells, which may lead to increased survival under stress. Furthermore, FMO expression modulates cellular metabolic activity as measured by mitochondrial respiration, glycolysis, and metabolomics analyses. FMO expression augments mitochondrial respiration and significantly changes central carbon metabolism, including amino acid and energy metabolism pathways. Together, our findings demonstrate an important endogenous role for the FMO family in regulation of cellular stress resistance and major cellular metabolic activities including central carbon metabolism.

Evaluating endoplasmic reticulum stress and unfolded protein response through the lens of ecology and evolution

Considerable progress has been made in understanding the physiological basis for variation in the life-history patterns of animals, particularly with regard to the roles of oxidative stress and hormonal regulation. However, an underappreciated and understudied area that could play a role in mediating inter- and intraspecific variation of life history is endoplasmic reticulum (ER) stress, and the resulting unfolded protein response (UPR^ER ). ER stress response and the UPR^ER maintain proteostasis in cells by reducing the intracellular load of secretory proteins and enhancing protein folding capacity or initiating apoptosis in cells that cannot recover. Proper modulation of the ER stress response and execution of the UPR^ER allow animals to respond to intracellular and extracellular stressors and adapt to constantly changing environments. ER stress responses are heritable and there is considerable individual variation in UPR^ER phenotype in animals, suggesting that ER stress and UPR^ER phenotype can be subjected to natural selection. The variation in UPR^ER phenotype presumably reflects the way animals respond to ER stress and environmental challenges. Most of what we know about ER stress and the UPR^ER in animals has either come from biomedical studies using cell culture or from experiments involving conventional laboratory or agriculturally important models that exhibit limited genetic diversity. Furthermore, these studies involve the assessment of experimentally induced qualitative changes in gene expression as opposed to the quantitative variations that occur in naturally existing populations. Almost all of these studies were conducted in controlled settings that are often quite different from the conditions animals experience in nature. Herein, we review studies that investigated ER stress and the UPR^ER in relation to key life-history traits including growth and development, reproduction, bioenergetics and physical performance, and ageing and senescence. We then ask if these studies can inform us about the role of ER stress and the UPR^ER in mediating the aforementioned life-history traits in free-living animals. We propose that there is a need to conduct experiments pertaining to ER stress and the UPR^ER in ecologically relevant settings, to characterize variation in ER stress and the UPR^ER in free-living animals, and to relate the observed variation to key life-history traits. We urge others to integrate multiple physiological systems and investigate how interactions between ER stress and oxidative stress shape life-history trade-offs in free-living animals.

Yeast MED2 is involved in the endoplasmic reticulum stress response and modulation of the replicative lifespan

Saccharomyces cerevisiae MED2/YDL005C is a subunit of the mediator complex (Mediator), which is responsible for tightly controlling the transcription of protein-coding genes by mediating the interaction of RNA polymerase II with gene-specific transcription factors. Although a high-throughput analysis in yeast showed that the MED2 protein exhibits altered cellular localization under hypoxic stress, no specific function of MED2 has been described to date. In this study, we first provided evidence that MED2 is involved in the endoplasmic reticulum (ER) stress response and modulation of the replicative life span. We showed that deletion of MED2 leads to sensitivity to the ER stress inducer tunicamycin (TM) as well as a shortened replicative lifespan (RLS), accompanied by increased intracellular ROS levels and hyperpolarization of mitochondria. On the other hand, overexpression of MED2 in wild-type (WT) yeast enhanced TM resistance and extended the RLS. In addition, the IRE1-HAC1 pathway was essential for the TM resistance of MED2-overexpressing cells. Moreover, we showed that MED2 deficiency enhances ER unfolded protein response (UPR) activity compared to that in WT cells. Collectively, these results suggest the novel role of MED2 as a regulator in maintaining ER homeostasis and longevity.

Adaptation of the master antioxidant response connects metabolism, lifespan and feather development pathways in birds

Birds (Aves) display high metabolic rates and oxygen consumption relative to mammals, increasing reactive oxygen species (ROS) formation. Although excess ROS reduces lifespan by causing extensive cellular dysfunction and damage, birds are remarkably long-lived. We address this paradox by identifying the constitutive activation of the NRF2 master antioxidant response in Neoaves (~95% of bird species), providing an adaptive mechanism capable of counterbalancing high ROS levels. We demonstrate that a KEAP1 mutation in the Neoavian ancestor disrupted the repression of NRF2 by KEAP1, leading to constitutive NRF2 activity and decreased oxidative stress in wild Neoaves tissues and cells. Our evidence suggests this ancient mutation induced a compensatory program in NRF2-target genes with functions beyond redox regulation-including feather development-while enabling significant metabolic rate increases that avoid trade-offs with lifespan. The strategy of NRF2 activation sought by intense clinical investigation therefore appears to have also unlocked a massively successful evolutionary trajectory.

Stress Resistance Screen in a Human Primary Cell Line Identifies Small Molecules That Affect Aging Pathways and Extend Caenorhabditis elegans' Lifespan

Increased resistance to environmental stress at the cellular level is correlated with the longevity of long-lived mutants and wild-animal species. Moreover, in experimental organisms, screens for increased stress resistance have yielded mutants that are long-lived. To find entry points for small molecules that might extend healthy longevity in humans, we screened ∼100,000 small molecules in a human primary-fibroblast cell line and identified a set that increased oxidative-stress resistance. Some of the hits fell into structurally related chemical groups, suggesting that they may act on common targets. Two small molecules increased C. elegans’ stress resistance, and at least 9 extended their lifespan by ∼10–50%. We further evaluated a chalcone that produced relatively large effects on lifespan and were able to implicate the activity of two, stress-response regulators, NRF2/skn-1 and SESN/sesn-1, in its mechanism of action. Our findings suggest that screening for increased stress resistance in human cells can enrich for compounds with promising pro-longevity effects. Further characterization of these compounds may reveal new ways to extend healthy human lifespan.

Tolerance of Novel Toxins through Generalized Mechanisms: Simulating Gradual Host Shifts of Butterflies

Organisms encounter a wide range of toxic compounds in their environments, from chemicals that serve anticonsumption or anticompetition functions to pollutants and pesticides. Although we understand many detoxification mechanisms that allow organisms to consume toxins typical of their diet, we know little about why organisms vary in their ability to tolerate entirely novel toxins. We tested whether variation in generalized stress responses, such as antioxidant pathways, may underlie variation in reactions to novel toxins and, if so, their associated costs. We used an artificial diet to present cabbage white butterfly caterpillars (Pieris rapae) with plant material containing toxins not experienced in their evolutionary history. Families that maintained high performance (e.g., high survival, fast development time, large body size) on diets containing one novel toxic plant also performed well when exposed to two other novel toxic plants, consistent with a generalized response. Variation in constitutive (but not induced) expression of genes involved in oxidative stress responses was positively related to performance on the novel diets. While we did not detect reproductive trade-offs of this generalized response, there was a tendency to have less melanin investment in the wings, consistent with the role of melanin in oxidative stress responses. Taken together, our results support the hypothesis that variation in generalized stress responses, such as genes involved in oxidative stress responses, may explain the variation in tolerance to entirely novel toxins and may facilitate colonization of novel hosts and environments.

Oxidative stress does not differ in primary dermal fibroblasts isolated from fast-growing and control-growing Japanese Quail (Coturnix japonica)

Growth rate is a key life-history trait that influences fitness and shapes the physiology of organisms. Additionally, faster growing individuals of the same species seem to be burdened with higher whole-animal metabolism and higher cellular turnover rates, which may lead to increases in oxidative stress, though this fact remains controversial within the literature. Aerobic organisms are subjected to metabolic by-products known as reactive oxygen species (ROS), which can wreak havoc on macromolecules, such as structurally altering proteins and inducing mutations in DNA, among others. To combat accumulating damage, organisms have evolved endogenous antioxidants and can consume exogenous antioxidants to sequester ROS before they cause cellular damage. We used primary fibroblast cells isolated from control-growing and fast-growing Japanese Quail (Coturnix japonica Temminck and Schlegel, 1849) as a study model for the effects of differing growth rates on oxidative stress. We measured reduced glutathione (GSH) concentration, ROS production, mitochondrial content, and lipid peroxidation (LPO) damage. We found no significant differences in the four parameters measured between control-growing and fast-growing Quail. However, we found that in fast-growing Quail, GSH correlated with LPO damage and mitochondrial content, and LPO damage positively correlated with mitochondrial content, whereas control-growing Quail only showed positive relationships between LPO damage and ROS production.

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.

Cellular energetics and mitochondrial uncoupling in canine aging

The first domesticated companion animal, the dog, is currently represented by over 190 unique breeds. Across these numerous breeds, dogs have exceptional variation in lifespan (inversely correlated with body size), presenting an opportunity to discover longevity-determining traits. We performed a genome-wide association study on 4169 canines representing 110 breeds and identified novel candidate regulators of longevity. Interestingly, known functions within the identified genes included control of coat phenotypes such as hair length, as well as mitochondrial properties, suggesting that thermoregulation and mitochondrial bioenergetics play a role in lifespan variation. Using primary dermal fibroblasts, we investigated mitochondrial properties of short-lived (large) and long-lived (small) dog breeds. We found that cells from long-lived breeds have more uncoupled mitochondria, less electron escape, greater respiration, and capacity for respiration. Moreover, our data suggest that long-lived breeds have higher rates of catabolism and β-oxidation, likely to meet elevated respiration and electron demand of their uncoupled mitochondria. Conversely, cells of short-lived (large) breeds may accumulate amino acids and fatty acid derivatives, which are likely used for biosynthesis and growth. We hypothesize that the uncoupled metabolic profile of long-lived breeds likely stems from their smaller size, reduced volume-to-surface area ratio, and therefore a greater need for thermogenesis. The uncoupled energetics of long-lived breeds lowers reactive oxygen species levels, promotes cellular stress tolerance, and may even prevent stiffening of the actin cytoskeleton. We propose that these cellular characteristics delay tissue dysfunction, disease, and death in long-lived dog breeds, contributing to canine aging diversity.

Invertebrate and vertebrate models in aging research

Therapeutic interventions that can delay age associated diseases and ensure a longer health-span is a major goal of aging research. Consequent to understanding that aging is a modifiable trait, a large number of studies are currently being undertaken to elucidate the mechanism(s) of the aging process. Research on human aging and longevity is difficult, due to longer time frame, ethical concerns and environmental variables. Most of the present day understanding about the aging process comes through studies conducted on model organisms. These provide suitable platforms for understanding underlying mechanism(s) which control aging and have led to major discoveries that emphasize the evolutionarily conserved molecular pathways as key players that respond to extra and intracellular signals. This is a review of various invertebrate and vertebrate models including yeast, Drosophila, C. elegans, rodents, naked mole rat, and birds, currently used in aging research with emphasis on how well they can mimic aging in higher animals and humans.

Varied effects of dietary carotenoid supplementation on oxidative damage in tissues of two waterfowl species

Carotenoids are regarded as a cornerstone of avian vitality and coloration. Currently, the antioxidant potential of dietary carotenoids is debated for birds. Although some studies support a protective role, others report either no effect or pro-oxidant effects. However, the majority of research on this topic has not analyzed the oxidative status of a series of tissues in animals nor considered a range of carotenoid dosages. We investigated the effects of three levels of carotenoid supplementation on plasma, liver, adipose, heart and breast muscle oxidative damage in two congeneric species of waterfowl that exhibit marked differences in carotenoid coloration. After a 6-week depletion period, captive adult northern pintail (Anas acuta) and mallard (A. platyrhynchos) ducks of both sexes were fed either a carotenoid-depleted diet (<3 μg/g xanthophylls, lutein and zeaxanthin), a carotenoid-supplemented diet (50 μg/g) within physiological range, or a carotenoid-rich diet (100 μg/g) within pharmacological range for 22 to 32 weeks. We hypothesized that these dosages of dietary carotenoids would differentially affect oxidative damage between species and sexes and among the tissues examined. We found that dietary xanthophyll supplementation had no significant effect on tissue pro-oxidation in males and females from both species. Moreover, sex or species differences in oxidative stress were only observed in two tissues (plasma and heart). Significant correlations in the levels of oxidative damage were not observed among the tissues examined. In conclusion, the current study does not support a consistent antioxidant role for dietary carotenoids in the tissues of these two waterfowl species. Instead, our results align with the notion that carotenoids play complex, tissue- and species-specific roles in oxidative status in birds.

Cause or casualty: The role of mitochondrial DNA in aging and age-associated disease

The mitochondrial genome (mtDNA) represents a tiny fraction of the whole genome, comprising just 16.6 kilobases encoding 37 genes involved in oxidative phosphorylation and the mitochondrial translation machinery. Despite its small size, much interest has developed in recent years regarding the role of mtDNA as a determinant of both aging and age-associated diseases. A number of studies have presented compelling evidence for key roles of mtDNA in age-related pathology, although many are correlative rather than demonstrating cause. In this review we will evaluate the evidence supporting and opposing a role for mtDNA in age-associated functional declines and diseases. We provide an overview of mtDNA biology, damage and repair as well as the influence of mitochondrial haplogroups, epigenetics and maternal inheritance in aging and longevity.

Longevity and life history coevolve with oxidative stress in birds

1. The mechanisms that underpin the evolution of ageing and life histories remain elusive. Oxidative stress, which results in accumulated cellular damages, is one of the mechanisms suggested to play a role. 2. In this paper, we set out to test the "oxidative stress theory of ageing" and the "oxidative stress hypothesis of life histories" using a comprehensive phylogenetic comparison based on an unprecedented dataset of oxidative physiology in 88 free-living bird species. 3. We show for the first time that bird species with longer lifespan have higher non-enzymatic antioxidant capacity and suffer less oxidative damage to their lipids. We also found that bird species featuring a faster pace-of-life either have lower non-enzymatic antioxidant capacity or are exposed to higher levels of oxidative damage, while adult annual mortality does not relate to oxidative state. 4. These results reinforce the role of oxidative stress in the evolution of lifespan and also corroborate the role of oxidative state in the evolution of life histories among free-living birds.

Dysregulation of DAF-16/FOXO3A-mediated stress responses accelerates oxidative DNA damage induced aging

DNA damage is presumed to be one type of stochastic macromolecular damage that contributes to aging, yet little is known about the precise mechanism by which DNA damage drives aging. Here, we attempt to address this gap in knowledge using DNA repair-deficient C. elegans and mice. ERCC1-XPF is a nuclear endonuclease required for genomic stability and loss of ERCC1 in humans and mice accelerates the incidence of age-related pathologies. Like mice, ercc-1 worms are UV sensitive, shorter lived, display premature functional decline and they accumulate spontaneous oxidative DNA lesions (cyclopurines) more rapidly than wild-type worms. We found that ercc-1 worms displayed early activation of DAF-16 relative to wild-type worms, which conferred resistance to multiple stressors and was important for maximal longevity of the mutant worms. However, DAF-16 activity was not maintained over the lifespan of ercc-1 animals and this decline in DAF-16 activation corresponded with a loss of stress resistance, a rise in oxidant levels and increased morbidity, all of which were cep-1/ p53 dependent. A similar early activation of FOXO3A (the mammalian homolog of DAF-16), with increased resistance to oxidative stress, followed by a decline in FOXO3A activity and an increase in oxidant abundance was observed in Ercc1^-/- primary mouse embryonic fibroblasts. Likewise, in vivo, ERCC1-deficient mice had transient activation of FOXO3A in early adulthood as did middle-aged wild-type mice, followed by a late life decline. The healthspan and mean lifespan of ERCC1 deficient mice was rescued by inactivation of p53. These data indicate that activation of DAF-16/FOXO3A is a highly conserved response to genotoxic stress that is important for suppressing consequent oxidative stress. Correspondingly, dysregulation of DAF-16/FOXO3A appears to underpin shortened healthspan and lifespan, rather than the increased DNA damage burden itself.

The rate of telomere loss is related to maximum lifespan in birds

Telomeres are highly conserved regions of DNA that protect the ends of linear chromosomes. The loss of telomeres can signal an irreversible change to a cell's state, including cellular senescence. Senescent cells no longer divide and can damage nearby healthy cells, thus potentially placing them at the crossroads of cancer and ageing. While the epidemiology, cellular and molecular biology of telomeres are well studied, a newer field exploring telomere biology in the context of ecology and evolution is just emerging. With work to date focusing on how telomere shortening relates to individual mortality, less is known about how telomeres relate to ageing rates across species. Here, we investigated telomere length in cross-sectional samples from 19 bird species to determine how rates of telomere loss relate to interspecific variation in maximum lifespan. We found that bird species with longer lifespans lose fewer telomeric repeats each year compared with species with shorter lifespans. In addition, phylogenetic analysis revealed that the rate of telomere loss is evolutionarily conserved within bird families. This suggests that the physiological causes of telomere shortening, or the ability to maintain telomeres, are features that may be responsible for, or co-evolved with, different lifespans observed across species.This article is part of the theme issue 'Understanding diversity in telomere dynamics'.

H2O2 treatment or serum deprivation induces autophagy and apoptosis in naked mole-rat skin fibroblasts by inhibiting the PI3K/Akt signaling pathway

Naked mole-rats (NMR; Heterocephalus glaber) display extreme longevity and resistance to cancer. Here, we examined whether autophagy contributes to the longevity of NMRs by assessing the effects of the PI3K/Akt pathway inhibitor LY294002 and the autophagy inhibitor chloroquine (CQ) on autophagy and apoptosis in NMR skin fibroblasts. Serum starvation, H2O2 treatment, and LY294002 treatment all increased the LC3-II/LC3-I ratio and numbers of double-membraned autophagosomes and autophagic vacuoles, and decreased levels of p70S6K, p-Akt^Ser473, and p-Akt^Thr308. By contrast, CQ treatment decreased p70S6K, Akt^Ser473, and Akt^Thr308 levels. The Bax/Bcl-2 ratio increased after 12 h of exposure to LY294002 or CQ. These data show that inhibiting the Akt pathway promotes autophagy and apoptosis in NMR skin fibroblasts. Furthermore, LY294002 or CQ treatment decreased caspase-3, p53, and HIF1-α levels, suggesting that serum starvation or H2O2 treatment increase autophagy and apoptosis in NMR skin fibroblasts by inhibiting the PI3K/Akt pathway. CQ-induced inhibition of late autophagy stages also prevented Akt activation and induced apoptosis. Finally, the HIF-1α and p53 pathways were involved in serum starvation- or H2O2-induced autophagy in NMR skin fibroblasts.

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.

Mitochondrial thioredoxin reductase 2 is elevated in long-lived primate as well as rodent species and extends fly mean lifespan

In a survey of enzymes related to protein oxidation and cellular redox state, we found activity of the redox enzyme thioredoxin reductase (TXNRD) to be elevated in cells from long‐lived species of rodents, primates, and birds. Elevated TXNRD activity in long‐lived species reflected increases in the mitochondrial form, TXNRD2, rather than the cytosolic forms TXNRD1 and TXNRD3. Analysis of published RNA‐Seq data showed elevated TXNRD2 mRNA in multiple organs of longer‐lived primates, suggesting that the phenomenon is not limited to skin‐derived fibroblasts. Elevation of TXNRD2 activity and protein levels was also noted in liver of three different long‐lived mutant mice, and in normal male mice treated with a drug that extends lifespan in males. Overexpression of mitochondrial TXNRD2 in Drosophila melanogaster extended median (but not maximum) lifespan in female flies with a small lifespan extension in males; in contrast, overexpression of the cytosolic form, TXNRD1, did not produce a lifespan extension.

Molecular pathology endpoints useful for aging studies

The first clinical trial aimed at targeting fundamental processes of aging will soon be launched (TAME: Targeting Aging with Metformin). In its wake is a robust pipeline of therapeutic interventions that have been demonstrated to extend lifespan or healthspan of preclinical models, including rapalogs, antioxidants, anti-inflammatory agents, and senolytics. This ensures that if the TAME trial is successful, numerous additional clinical trials are apt to follow. But a significant impediment to these trials remains the question of what endpoints should be measured? The design of the TAME trial very cleverly skirts around this based on the fact that there are decades of data on metformin in humans, providing unequaled clarity of what endpoints are most likely to yield a positive outcome. But for a new chemical entity, knowing what endpoints to measure remains a formidable challenge. For economy's sake, and to achieve results in a reasonable time frame, surrogate markers of lifespan and healthy aging are desperately needed. This review provides a comprehensive analysis of molecular endpoints that are currently being used as indices of age-related phenomena (e.g., morbidity, frailty, mortality) and proposes an approach for validating and prioritizing these endpoints.

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.

Oxidative stress and life histories: unresolved issues and current needs

Life‐history theory concerns the trade‐offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life‐history trade‐offs, but the details remain obscure. As life‐history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life‐history trade‐offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life‐history information is available, cannot generally be performed without compromising the aims of the studies that generated the life‐history data. There is a need therefore for novel non‐invasive measurements of multi‐tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life‐history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life‐history trade‐offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life‐history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade‐offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.

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.

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.

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.

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.

Cellular metabolic rates from primary dermal fibroblast cells isolated from birds of different body masses

The rate of metabolism is the speed at which organisms use energy, an integration of energy transformations within the body; it governs biological processes that influence rates of growth and reproduction. Progress at understanding functional linkages between whole organism metabolic rate and underlying mechanisms that influence its magnitude has been slow despite the central role this issue plays in evolutionary and physiological ecology. Previous studies that have attempted to relate how cellular processes translate into whole-organism physiology have done so over a range of body masses of subjects. However, the data still remains controversial when observing metabolic rates at the cellular level. To bridge the gap between these ideas, we examined cellular metabolic rate of primary dermal fibroblasts isolated from 49 species of birds representing a 32,000-fold range in body masses to test the hypothesis that metabolic rate of cultured cells scales with body size. We used a Seahorse XF-96 Extracellular flux analyzer to measure cellular respiration in fibroblasts. Additionally, we measured fibroblast size and mitochondrial content. We found no significant correlation between cellular metabolic rate, cell size, or mitochondrial content and body mass. Additionally, there was a significant relationship between cellular basal metabolic rate and proton leak in these cells. We conclude that metabolic rate of cells isolated in culture does not scale with body mass, but cellular metabolic rate is correlated to growth rate in birds.

Rotifers as experimental tools for investigating aging

Comparative biogerontology has much to contribute to the study of aging. A broad range of aging rates have evolved to meet environmental challenges, and understanding these adaptations can produce valuable insights into aging. The supra Phylum Lophotrochozoa is particularly understudied and has several groups that have intriguing patterns of aging. Members of the Lophotrochozoan phylum Rotifera are particularly useful for aging studies because cohort life tables can be conducted with them easily, and biochemical and genomic tools are available for examining aging mechanisms. This paper reviews a variety of caloric restriction (CR) regimens, small molecule inhibitors, and dietary supplements that extend rotifer lifespan, as well as important interactions between CR and genotype, antioxidant supplements, and TOR and jun-N-terminal kinase (JNK) pathways, and the use of RNAi to identify key genes involved in modulating the aging response. Examples of how rapamycin and JNK inhibitor exposure keeps mortality rates low during the reproductive phase of the life cycle are presented, and the ease of conducting life table experiments to screen natural products from red algae for life extending effects is illustrated. Finally, experimental evolution to produce longer-lived rotifer individuals is demonstrated, and future directions to determine the genetic basis of aging are discussed.

On the mechanism(s) of membrane permeability transition in liver mitochondria of lamprey, Lampetra fluviatilis L.: insights from cadmium

Previously we have shown that opening of the mitochondrial permeability transition pore in its low conductance state is the case in hepatocytes of the Baltic lamprey (Lampetra fluviatilis L.) during reversible metabolic depression taking place in the period of its prespawning migration when the exogenous feeding is switched off. The depression is observed in the last year of the lamprey life cycle and is conditioned by reversible mitochondrial dysfunction (mitochondrial uncoupling in winter and coupling in spring). To further elucidate the mechanism(s) of induction of the mitochondrial permeability transition pore in the lamprey liver, we used Cd(2+) and Ca(2+) plus Pi as the pore inducers. We found that Ca(2+) plus Pi induced the high-amplitude swelling of the isolated "winter" mitochondria both in isotonic sucrose and ammonium nitrate medium while both low and high Cd(2+) did not produce the mitochondrial swelling in these media. Low Cd(2+) enhanced the inhibition of basal respiration rate of the "winter" mitochondria energized by NAD-dependent substrates whereas the same concentrations of the heavy metal evoked its partial stimulation on FAD-dependent substrates. The above changes produced by Cd(2+) or Ca(2+) plus Pi in the "winter" mitochondria were only weakly (if so) sensitive to cyclosporine A (a potent pharmacological desensitizer of the nonselective pore) added alone and they were not sensitive to dithiothreitol (a dithiol reducing agent). Under monitoring of the transmembrane potential of the "spring" lamprey liver mitochondria, we revealed that Cd(2+) produced its decrease on both types of the respiratory substrates used that was strongly hampered by cyclosporine A, and the membrane potential was partially restored by dithiothreitol. The effects of different membrane permeability modulators on the lamprey liver mitochondria function and the seasonal changes in their action are discussed.

Glycerol extends lifespan of Brachionus manjavacas (Rotifera) and protects against stressors

Diet has profound effects on animal longevity and manipulation of nutrient sensing pathways is one of the primary interventions capable of lifespan extension. This often is done through caloric restriction (CR) and a variety of CR mimics have been identified that produce life extending effects without adhering to the rigorous CR dietary regimen. Glycerol is a dietary supplement capable mimicking CR by shifting metabolism away from glycolysis and towards oxidative phosphorylation. Glycerol supplementation has a number of beneficial effects, including lifespan extension, improved stress resistance, and enhanced locomotory and mitochondria activity in older age classes. Using rotifers as a model, we show that supplements of 150-300mM glycerol produced 40-50% extension of mean lifespan. This effect was produced by raising glycerol concentration only three times higher than its baseline concentration in rotifer tissues. Glycerol supplementation decreased rotifer reliance on glycolysis and reduced the pro-aging effects of glucose. Glycerol also acted as a chemical chaperone, mitigating damage by protein aggregation. Glycerol treatment improved rotifer swimming performance in older age classes and maintained more mitochondrial activity. Glycerol treatment provided increased resistance to starvation, heat, oxidation, and osmotic stress, but not UV stress. When glycerol was co-administered with the hexokinase inhibitor 2-deoxyglucose, the lifespan extending effect of glycerol was enhanced. Co-administration of glycerol with inhibitors like 2-deoxyglucose can lower their efficacious doses, thereby reducing their toxic side effects.