Correlated resistance to glucose deprivation and cytotoxic agents in fibroblast cell lines from long-lived pituitary dwarf mice

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.

Differential mitochondrial bioenergetics and cellular resilience in astrocytes, hepatocytes, and fibroblasts from aging baboons

Biological resilience, broadly defined as the ability to recover from an acute challenge and return to homeostasis, is of growing importance to the biology of aging. At the cellular level, there is variability across tissue types in resilience and these differences are likely to contribute to tissue aging rate disparities. However, there are challenges in addressing these cell-type differences at regional, tissue, and subject level. To address this question, we established primary cells from aged male and female baboons between 13.3 and 17.8 years spanning across different tissues, tissue regions, and cell types including (1) fibroblasts from skin and from the heart separated into the left ventricle (LV), right ventricle (RV), left atrium (LA), and right atrium (RA); (2) astrocytes from the prefrontal cortex and hippocampus; and (3) hepatocytes. Primary cells were characterized by their cell surface markers and their cellular respiration was assessed with Seahorse XFe96. Cellular resilience was assessed by modifying a live-cell imaging approach; we previously reported that monitors proliferation of dividing cells following response and recovery to oxidative (50 µM-H2O2), metabolic (1 mM-glucose), and proteostasis (0.1 µM-thapsigargin) stress. We noted significant differences even among similar cell types that are dependent on tissue source and the diversity in cellular response is stressor-specific. For example, astrocytes had a higher oxygen consumption rate and exhibited greater resilience to oxidative stress (OS) than both fibroblasts and hepatocytes. RV and RA fibroblasts were less resilient to OS compared with LV and LA, respectively. Skin fibroblasts were less impacted by proteostasis stress compared to astrocytes and cardiac fibroblasts. Future studies will test the functional relationship of these outcomes to the age and developmental status of donors as potential predictive markers.

Chemically induced carcinogenesis in rodent models of aging: assessing organismal resilience to genotoxic stressors in geroscience research

There is significant overlap between the cellular and molecular mechanisms of aging and pathways contributing to carcinogenesis, including the role of genome maintenance pathways. In the field of geroscience analysis of novel genetic mouse models with either a shortened, or an extended, lifespan provides a unique opportunity to evaluate the synergistic roles of longevity assurance pathways in cancer resistance and regulation of lifespan and to develop novel targets for interventions that both delay aging and prevent carcinogenesis. There is a growing need for robust assays to assess the susceptibility of cancer in these models. The present review focuses on a well-characterized method frequently used in cancer research, which can be adapted to study resilience to genotoxic stress and susceptibility to genotoxic stress-induced carcinogenesis in geroscience research namely, chemical carcinogenesis induced by treatment with 7,12-dimethylbenz(a)anthracene (DMBA). Recent progress in understanding how longer-living mice may achieve resistance to chemical carcinogenesis and how these pathways are modulated by anti-aging interventions is reviewed. Strain-specific differences in sensitivity to DMBA-induced carcinogenesis are also explored and contrasted with mouse lifespan. The clinical relevance of inhibition of DMBA-induced carcinogenesis for the pathogenesis of mammary adenocarcinomas in older human subjects is discussed. Finally, the potential role of insulin-like growth factor-1 (IGF-1) in the regulation of pathways responsible for cellular resilience to DMBA-induced mutagenesis is discussed.

The GH/IGF-1 axis in a critical period early in life determines cellular DNA repair capacity by altering transcriptional regulation of DNA repair-related genes: implications for the developmental origins of cancer

Experimental, clinical, and epidemiological findings support the concept of developmental origins of health and disease (DOHAD), suggesting that early-life hormonal influences during a sensitive period around adolescence have a powerful impact on cancer morbidity later in life. The endocrine changes that occur during puberty are highly conserved across mammalian species and include dramatic increases in circulating GH and IGF-1 levels. Importantly, patients with developmental IGF-1 deficiency due to GH insensitivity (Laron syndrome) do not develop cancer during aging. Rodents with developmental GH/IGF-1 deficiency also exhibit significantly decreased cancer incidence at old age, marked resistance to chemically induced carcinogenesis, and cellular resistance to genotoxic stressors. Early-life treatment of GH/IGF-1-deficient mice and rats with GH reverses the cancer resistance phenotype; however, the underlying molecular mechanisms remain elusive. The present study was designed to test the hypothesis that developmental GH/IGF-1 status impacts cellular DNA repair mechanisms. To achieve that goal, we assessed repair of γ-irradiation-induced DNA damage (single-cell gel electrophoresis/comet assay) and basal and post-irradiation expression of DNA repair-related genes (qPCR) in primary fibroblasts derived from control rats, Lewis dwarf rats (a model of developmental GH/IGF-1 deficiency), and GH-replete dwarf rats (GH administered beginning at 5 weeks of age, for 30 days). We found that developmental GH/IGF-1 deficiency resulted in persisting increases in cellular DNA repair capacity and upregulation of several DNA repair-related genes (e.g., Gadd45a, Bbc3). Peripubertal GH treatment reversed the radiation resistance phenotype. Fibroblasts of GH/IGF-1-deficient Snell dwarf mice also exhibited improved DNA repair capacity, showing that the persisting influence of peripubertal GH/IGF-1 status is not species-dependent. Collectively, GH/IGF-1 levels during a critical period during early life determine cellular DNA repair capacity in rodents, presumably by transcriptional control of genes involved in DNA repair. Because lifestyle factors (e.g., nutrition and childhood obesity) cause huge variation in peripubertal GH/IGF-1 levels in children, further studies are warranted to determine their persisting influence on cellular cancer resistance pathways.

Ablation of the mitochondrial complex IV assembly protein Surf1 leads to increased expression of the UPR(MT) and increased resistance to oxidative stress in primary cultures of fibroblasts

Mice deficient in the electron transport chain (ETC) complex IV assembly protein SURF1 have reduced assembly and activity of cytochrome c oxidase that is associated with an upregulation of components of the mitochondrial unfolded protein response (UPR^MT) and increased mitochondrial number. We hypothesized that the upregulation of proteins associated with the UPR^MT in response to reduced cytochrome c oxidase activity in Surf1^−/− mice might contribute to increased stress resistance. To test this hypothesis we asked whether primary cultures of fibroblasts from Surf1^−/− mice exhibit enhanced resistance to stressors compared to wild-type fibroblasts. Here we show that primary dermal fibroblasts isolated from Surf1^−/− mice have increased expression of UPR^MT components ClpP and Hsp60, and increased expression of Lon protease. Fibroblasts from Surf1^−/− mice are significantly more resistant to cell death caused by oxidative stress induced by paraquat or tert-Butyl hydroperoxide compared to cells from wild-type mice. In contrast, Surf1^−/− fibroblasts show no difference in sensitivity to hydrogen peroxide stress. The enhanced cell survival in response to paraquat or tert-Butyl hydroperoxide in Surf1^−/− fibroblasts compared to wild-type fibroblasts is associated with induced expression of Lon, ClpP, and Hsp60, increased maximal respiration, and increased reserve capacity as measured using the Seahorse Extracellular Flux Analyzer. Overall these data support a protective role for the activation of the UPR^MT in cell survival.

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Surf1^−/− mice fibroblasts exhibit upregulation of proteins involved in the UPR^MT.

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Mitochondrial specific oxidative stressors induce UPR^MT in mammalian fibroblasts.

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Surf1^−/− fibroblasts exhibit enhanced mitochondrial specific stress resistance.

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Surf1^−/− fibroblasts have increased maximal respiration and respiratory reserve.

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.

Somatotropic signaling: trade-offs between growth, reproductive development, and longevity

Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.

The mouse as a model organism in aging research: usefulness, pitfalls and possibilities

The mouse has become the favorite mammalian model. Among the many reasons for this privileged position of mice is their genetic proximity to humans, the possibilities of genetically manipulating their genomes and the availability of many tools, mutants and inbred strains. Also in the field of aging, mice have become very robust and reliable research tools. Since laboratory mice have a life expectancy of only a few years, genetic approaches and other strategies for intervening in aging can be tested by examining their effects on life span and aging parameters during the relatively short period of, for example, a PhD project. Moreover, experiments on mice with an extended life span as well as on mice demonstrating signs of (segmental) premature aging, together with genetic mapping strategies, have provided novel insights into the fundamental processes that drive aging. Finally, the results of studies on caloric restriction and pharmacological anti-aging treatments in mice have a high degree of relevance to humans. In this paper, we review a number of recent genetic mapping studies that have yielded novel insights into the aging process. We discuss the value of the mouse as a model for testing interventions in aging, such as caloric restriction, and we critically discuss mouse strains with an extended or a shortened life span as models of aging.

Fibroblasts from long-lived mutant mice exhibit increased autophagy and lower TOR activity after nutrient deprivation or oxidative stress

Previous work has shown that primary skin-derived fibroblasts from long-lived pituitary dwarf mutants resist the lethal effects of many forms of oxidative and nonoxidative stress. We hypothesized that increased autophagy may protect fibroblasts of Pit-1(dw/dw) (Snell dwarf) mice from multiple forms of stress. We found that dwarf-derived fibroblasts had higher levels of autophagy, using LC3 and p62 as markers, in response to amino acid deprivation, hydrogen peroxide, and paraquat. Fibroblasts from dwarf mice also showed diminished phosphorylation of mTOR, S6K, and 4EBP1, consistent with the higher levels of autophagy in these cells after stress. Similar results were also observed in fibroblasts from mutant mice lacking growth hormone receptor (GHRKO mice) after amino acid withdrawal. Our results suggested that increased autophagy, regulated by TOR-dependent processes, may contribute to stress resistance in fibroblasts from long-lived mutant mice.

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

Evolutionary senescence theory postulates that aging results from the declining force of natural selection with increasing chronological age. A goal of comparative studies in the biology of aging is to identify genetic and biochemical mechanism(s) driving species-specific differences in the aging process that are the end product of life history trade-offs. We hypothesized that cells from long-lived bird species are more resistant to stress agents than are cells from short-lived species, and that cells from birds are more resistant to stress than are cells from relatively short-lived mammals of similar size. We tested primary fibroblast cultures from 35 species of free-living birds for their resistance to multiple forms of cellular stress and found that cell lines from longer-lived species were resistant to death caused by cadmium (R(2)=0.27, P=0.002), paraquat (R(2)=0.13, P=0.03), hydrogen peroxide (R(2)=0.09, P=0.07) and methyl methanesulfonate (R(2)=0.13, P=0.03), as well as to the metabolic inhibition seen in low-glucose medium (R(2)=0.37, P<0.01). They did not differ in their resistance to UV radiation, or to thapsigargin or tunicamycin, inducers of the unfolded protein response. These results were largely consistent even after accounting for the influence of body mass and phylogeny. Cell lines from longer-lived bird species also proliferate more rapidly than cells from short-lived birds, although there was no relationship between proliferation and stress resistance. Finally, avian fibroblasts were significantly more resistant than rodent fibroblasts to each of the tested stressors. These results support the idea that cellular resistance to injury may be an important contributor to the evolution of slow aging and long lifespan among bird species, and may contribute to the relatively long lifespan of birds compared with rodents of the same body size.

Heightened induction of proapoptotic signals in response to endoplasmic reticulum stress in primary fibroblasts from a mouse model of longevity

Previous work from our laboratory has shown that primary fibroblasts from long-lived Snell dwarf mice display a higher sensitivity to the lethal effects of endoplasmic reticulum (ER) stressors, such as thapsigargin, than cells from normal mice. Here we show that thapsigargin induces higher expression of CHOP, enhanced cleavage of caspase-12, higher caspase-3 activity, and increased phosphorylation of c-JUN, all indicators of enhanced apoptosis, in dwarf fibroblasts. Dwarf and normal fibroblasts show no genotypic difference in up-regulating BiP, GRP94, and ERp72 proteins after exposure to thapsigargin. However, dwarf fibroblasts express lower basal levels of a number of putative XBP1 target genes including Armet, Edem1, Erdj3, p58(IPK) and Sec61a1, as well as Ire1α itself. Furthermore, when exposed to thapsigargin, dwarf fibroblasts display attenuated splicing of Xbp1, but similar phosphorylation of eIF2α, in comparison to normal fibroblasts. These data support the notion that IRE1/XBP1 signaling is set at a lower level in dwarf fibroblasts. Diminished Xbp1 splicing in dwarf-derived fibroblasts may tilt the balance between prosurvival and proapoptotic signals in favor of apoptosis, thereby leading to higher induction of proapoptotic signals in these cells and ultimately their increased sensitivity to ER stressors. These results, together with recent findings in Caenorhabditis elegans daf-2 mutants, point to a potential interplay between insulin/IGF-1 signals and unfolded protein response signaling.

Comparative cellular biogerontology: primer and prospectus

Most prior work on the biological basis of aging has focused on describing differences between young and old individuals but provided only limited insight into the mechanisms controlling the rate of aging. Natural selection has produced a goldmine of experimental material, in the form of species of differing aging rate, whose longevity can vary by 10-fold or more within mammalian orders, but these resources remain largely unexplored at the cellular level. In this review article we focus on one approach to comparative biogerontology: the strategy of evaluating the properties of cultured cells from organisms of varying lifespan and aging rate. In addition, we discuss problems associated with the analysis and interpretations of interspecific variation of cellular trait data among species with disparate longevity. Given the impressive array of 'natural experiments' in aging rate, overcoming the technical and conceptual obstacles confronting research in comparative cellular gerontology will be well worth the effort.

Free radical production, antioxidant capacity, and oxidative stress response signatures in fibroblasts from Lewis dwarf rats: effects of life span-extending peripubertal GH treatment

The discovery that in invertebrates, disruption of the insulin/insulin-like growth factor (IGF)-1 pathway extends life span and increases resistance to oxidative injury led to the hypothesis that IGF-1 signaling may play a role in regulating cellular reactive oxygen species production, oxidative stress resistance, and consequentially, organismal life span in mammals. However, previous studies testing this hypothesis in rodent models of IGF-1 deficiency yielded controversial results. The Lewis dwarf rat is a useful model of human growth hormone (GH)/IGF-1 deficiency as it mimics many of the pathophysiological alterations present in human GH/IGF-1-deficient patients as well as elderly individuals. Peripubertal treatment of Lewis dwarf rats with GH results in a significant extension of life span. The present study was designed to test the role of the GH/IGF-1 axis in regulating cellular oxidative stress and oxidative stress resistance, utilizing primary fibroblasts derived from control rats, Lewis dwarf rats and GH-replete dwarf rats. Measurements of cellular dihydroethidium and C-H(2)DCFDA fluorescence showed that cellular O(2)(·-) and peroxide production were similar in each group. Fibroblasts from control and Lewis dwarf rats exhibited similar antioxidant capacities and comparable sensitivity to H(2)O(2), rotenone, high glucose, tunicamycin, thapsigargin, paraquat, and mitomycin, which cause apoptosis through increasing oxidative stress, mitochondrial damage, ATP depletion, and/or by damaging DNA, lipids and proteins. Fibroblasts from GH-replete rats exhibited significantly increased antioxidant capacities and superior resistance to H(2)O(2), rotenone and bacterial lipopolysaccharide-induced cell death compared with cells from Lewis dwarf rats, whereas their sensitivity to the other stressors investigated was not statistically different. Thus, low circulating IGF-1 levels present in vivo in Lewis dwarf rats do not elicit long-lasting alterations in cellular reactive oxygen species generation and oxidative stress resistance, whereas life span-extending peripubertal GH treatment resulted in increased antioxidant capacity and increased resistance to cellular injury caused by some, but not all, oxidative stressors.

Early life growth hormone treatment shortens longevity and decreases cellular stress resistance in long-lived mutant mice

Hypopituitary Ames dwarf mice were injected either with growth hormone (GH) or thyroxine for a 6-wk period to see whether this intervention would reverse their long life span or the resistance of their cells to lethal stresses. Ames dwarf mice survived 987 ± 24 d (median), longer than nonmutant control mice (664 ± 48), but GH-injected dwarf mice did not differ from controls (707 ± 9). Fibroblast cells from Ames dwarf mice were more resistant to cadmium than cells from nonmutant controls (LD(50) values of 9.98 ± 1.7 and 3.9 ± 0.8, respectively), but GH injections into Ames dwarf mice restored the normal level of cadmium resistance (LD(50)=5.8 ± 0.9). Similar restoration of normal resistance was observed for fibroblasts exposed to paraquat, methyl methanesulfonate, and rotenone (P<0.05 in each case for contrast of GH-treated vs. untreated dwarf mice; P<0.05 for dwarf vs. nonmutant control mice.) T4 injections into Ames dwarf mice, in contrast, did not restore normal life span. We conclude that the remarkable life-span extension of Ames dwarf mice, and the stress resistance of cells from these mice, depends on low levels of GH exposure in juvenile and very young adult mice.

Cell resilience in species life spans: a link to inflammation?

Species differences in life span have been attributed to cellular survival during various stressors, designated here as 'cell resilience'. In primary fibroblast cultures, cell resilience during exposure to free radicals, hypoglycemia, hyperthermia, and various toxins has shown generally consistent correlations with the species characteristic life spans of birds and mammals. However, the mechanistic links of cell resilience in fibroblast cultures to different species life spans are poorly understood. We propose that certain experimental stressors are relevant to somatic damage in vivo during inflammatory responses of innate immunity, particularly, resistance to reactive oxygen species (ROS), low glucose, and hyperthermia. According to this hypothesis, somatic cell resilience determines species differences in longevity during repeated infections and traumatic injuries in the natural environment. Infections and injury expose local fibroblasts and other cells to ROS generated by macrophages and to local temperature elevations. Systemically, acute phase immune reactions cause hypoglycemia and hyperthermia. We propose that cell resilience to somatic stressors incurred in inflammation is important in the evolution of longevity and that longer-lived species are specifically more resistant to immune-related stressors. This hypothesis further specifies Kirkwood's disposable soma theory. We suggest expanding the battery of stressors and markers used for comparative studies to additional cell types and additional parameters relevant to host defense and to their ecological specificities.

Update on the oxidative stress theory of aging: does oxidative stress play a role in aging or healthy aging?

The oxidative stress theory of aging predicts that manipulations that alter oxidative stress/damage will alter aging. The gold standard for determining whether aging is altered is life span, i.e., does altering oxidative stress/damage change life span? Mice with genetic manipulations in their antioxidant defense system designed to directly address this prediction have, with few exceptions, shown no change in life span. However, when these transgenic/knockout mice are tested using models that develop various types of age-related pathology, they show alterations in progression and/or severity of pathology as predicted by the oxidative stress theory: increased oxidative stress accelerates pathology and reduced oxidative stress retards pathology. These contradictory observations might mean that (a) oxidative stress plays a very limited, if any, role in aging but a major role in health span and/or (b) the role that oxidative stress plays in aging depends on environment. In environments with minimal stress, as expected under optimal husbandry, oxidative damage plays little role in aging. However, under chronic stress, including pathological phenotypes that diminish optimal health, oxidative stress/damage plays a major role in aging. Under these conditions, enhanced antioxidant defenses exert an "antiaging" action, leading to changes in life span, age-related pathology, and physiological function as predicted by the oxidative stress theory of aging.

Nrf2 signaling, a mechanism for cellular stress resistance in long-lived mice

Transcriptional regulation of the antioxidant response element (ARE) by Nrf2 is important for the cellular adaptive response to toxic insults. New data show that primary skin-derived fibroblasts from the long-lived Snell dwarf mutant mouse, previously shown to be resistant to many toxic stresses, have elevated levels of Nrf2 and of multiple Nrf2-sensitive ARE genes. Dwarf-derived fibroblasts exhibit many of the traits associated with enhanced activity of Nrf2/ARE, including higher levels of glutathione and resistance to plasma membrane lipid peroxidation. Treatment of control cells with arsenite, an inducer of Nrf2 activity, increases their resistance to paraquat, hydrogen peroxide, cadmium, and UV light, rendering these cells as stress resistant as untreated cells from dwarf mice. Furthermore, mRNA levels for some Nrf2-sensitive genes are elevated in at least some tissues of Snell dwarf mice, suggesting that the phenotypes observed in culture may be mirrored in vivo. Augmented activity of Nrf2 and ARE-responsive genes may coordinate many of the stress resistance traits seen in cells from these long-lived mutant mice.

Fibroblasts from long-lived mutant mice show diminished ERK1/2 phosphorylation but exaggerated induction of immediate early genes

Skin-derived fibroblasts from long-lived mutant mice, including the Snell dwarf mice and mice defective in growth hormone receptor (GHRKO mice), are resistant to death induced by oxidative stress or by UV light, but the molecular mechanism for their stress resistance is unknown. This study shows that phosphorylation of the stress-activated protein kinases ERK1/2 induced by peroxide, cadmium, or paraquat is attenuated in cells from these mice. Induction of ERK phosphorylation by UV light was not altered in the Snell dwarf cells, and neither JNK nor p38 kinase showed increased phosphorylation in response to any of the stresses tested. Surprisingly, stress-induced elevation of mRNA for certain immediate early genes (Egr-1 and Fos) was higher in Snell-derived cells than in control cells, despite the evidence of lower ERK phosphorylation. Thus cells from Snell dwarf mice differ from controls in two ways: (a) lower induction of ERK1/2 phosphorylation and (b) increased expression of some ERK-dependent immediate early genes. These alterations in kinase pathways may contribute to the resistance of these cells to lethal injury.

Lack of methionine sulfoxide reductase A in mice increases sensitivity to oxidative stress but does not diminish life span

Methionine sulfoxide reductase A (MsrA) repairs oxidized methionine residues within proteins and may also function as a general antioxidant. Previous reports have suggested that modulation of MsrA in mice and mammalian cell culture can affect the accumulation of oxidized proteins and may regulate resistance to oxidative stress. Thus, under the oxidative stress theory of aging, these results would predict that MsrA regulates the aging process in mammals. We show here that MsrA(-/-) mice are more susceptible to oxidative stress induced by paraquat. Skin-derived fibroblasts do not express MsrA, but fibroblasts cultured from MsrA(-/-) mice were, nevertheless, also more susceptible to killing by various oxidative stresses. In contrast to previous reports, we find no evidence for neuromuscular dysfunction in MsrA(-/-) mice in either young adult or in older animals. Most important, we found no difference between MsrA(-/-) and control mice in either their median or maximum life span. Thus, our results show that MsrA regulates sensitivity to oxidative stress in mice but has no effect on aging, as determined by life span.

Mechanisms of stress resistance in Snell dwarf mouse fibroblasts: enhanced antioxidant and DNA base excision repair capacity, but no differences in mitochondrial metabolism

Dermal fibroblasts from long-lived Snell dwarf mice can withstand a variety of oxidative and non-oxidative stressors compared to normal littermate controls. Here, we report differences in the levels and activities of intracellular antioxidant and DNA repair enzymes between normal and Snell dwarf mice fibroblasts cultured under a variety of conditions, including: 3% and 20% ambient O(2); the presence and absence of serum; and the addition of an exogenous oxidative stress. The only significant difference between normal and dwarf cells cultured in complete medium, at 20% O(2), was an approximately 40% elevation of glutathione peroxidase (GPx) activity in the mutant cells. Serum deprivation elicited increases in GPx in both genotypes, but these activities remained higher in dwarf mouse cells. Dwarf mouse cells deprived of serum and challenged with exposure to paraquat or hydrogen peroxide showed a generally greater upregulation of catalase and DNA base excision repair enzymes. As these toxins can interact with mitochondria to increase mitochondrial ROS production, we explored whether there were differences in mitochondrial metabolism between normal and dwarf mouse cells. However, neither mitochondrial content nor the apparent mitochondrial membrane potential differed between genotypes. Overall, the results suggest that superior hydrogen peroxide metabolism and a marginally greater DNA base excision repair capacity contribute to the stress resistance phenotype of Snell dwarf mouse fibroblasts.

Endocrine regulation of heat shock protein mRNA levels in long-lived dwarf mice

Heat shock proteins (HSPs) maintain proteostasis and may protect against age-associated pathology caused by protein malfolding. In Caenorhabditis elegans, the lifespan extension and thermotolerance in mutants with impaired insulin/IGF signals depend partly on HSP elevation. Less is known about the role of HSPs in the increased lifespan of mice with defects in GH/IGF-I pathways. We measured HSP mRNAs in liver, kidney, heart, lung, muscle and cerebral cortex from long-lived Pit1(dw/dw) Snell dwarf mice. We found many significant differences in HSP mRNA levels between dwarf and control mice, but these effects were complex and organ-specific. We noted 15 instances where HSP mRNAs were lower in Pit1(dw/dw) liver, kidney, or heart tissues, and 14/15 of these were also seen in Ghr(-/-) mice, which lack GH receptor. In contrast, of 12 examples where HSP mRNAs were higher in Snell liver, kidney, or heart, none were altered in Ghr(-/-) mice. Four liver mRNAs were depressed in both Pit1(dw/dw) and Ghr(-/-) mice, and each of these was elevated by GH injection in Ames (Prop1(df/df)) dwarf mice, consistent with the hypothesis that these declines depended on GH and/or IGF-I. Contributions of chaperones to longevity in mice may be more complex than those inferred from C. elegans.

Deafness and permanently reduced potassium channel gene expression and function in hypothyroid Pit1dw mutants

The absence of thyroid hormone (TH) during late gestation and early infancy can cause irreparable deafness in both humans and rodents. A variety of rodent models have been used in an effort to identify the underlying molecular mechanism. Here, we characterize a mouse model of secondary hypothyroidism, pituitary transcription factor 1 (Pit1(dw)), which has profound, congenital deafness that is rescued by oral TH replacement. These mutants have tectorial membrane abnormalities, including a prominent Hensen's stripe, elevated beta-tectorin composition, and disrupted striated-sheet matrix. They lack distortion product otoacoustic emissions and cochlear microphonic responses, and exhibit reduced endocochlear potentials, suggesting defects in outer hair cell function and potassium recycling. Auditory system and hair cell physiology, histology, and anatomy studies reveal novel defects of hormone deficiency related to deafness: (1) permanently impaired expression of KCNJ10 in the stria vascularis of Pit1(dw) mice, which likely contributes to the reduced endocochlear potential, (2) significant outer hair cell loss in the mutants, which may result from cellular stress induced by the lower KCNQ4 expression and current levels in Pit1(dw) mutant outer hair cells, and (3) sensory and strial cell deterioration, which may have implications for thyroid hormone dysregulation in age-related hearing impairment. In summary, we suggest that these defects in outer hair cell and strial cell function are important contributors to the hearing impairment in Pit1(dw) mice.

Fibroblasts from naked mole-rats are resistant to multiple forms of cell injury, but sensitive to peroxide, ultraviolet light, and endoplasmic reticulum stress

Fibroblasts from long-lived mutant mice are resistant to many forms of lethal injury as well as to the metabolic effects of rotenone and low-glucose medium. Here we evaluated fibroblasts from young adult naked mole-rats (NMR; Heterocephalus glaber), a rodent species in which maximal longevity exceeds 28 years. Compared to mouse cells, NMR cells were resistant to cadmium, methyl methanesulfonate, paraquat, heat, and low-glucose medium, consistent with the idea that cellular resistance to stress may contribute to disease resistance and longevity. Surprisingly, NMR cells were more sensitive than mouse cells to H(2)O(2), ultraviolet (UV) light, and rotenone. NMR cells, like cells from Snell dwarf mice, were more sensitive to tunicamycin and thapsigargin, which interfere with the function of the endoplasmic reticulum (ER stress). The sensitivity of both Snell dwarf and NMR cells to ER stress suggests that alterations in the unfolded protein response might modulate cell survival and aging rate.

Cells from long-lived mutant mice exhibit enhanced repair of ultraviolet lesions

Fibroblasts isolated from long-lived hypopituitary dwarf mice are resistant to many cell stresses, including ultraviolet (UV) light and methyl methane sulfonate (MMS), which induce cell death by producing DNA damage. Here we report that cells from Snell dwarf mice recover more rapidly than controls from the inhibition of RNA synthesis induced by UV damage. Recovery of messenger RNA (mRNA) synthesis in particular is more rapid in dwarf cells, suggesting enhanced repair of the actively transcribing genes in dwarf-derived cells. At early time points, there was no difference in the repair of cyclobutane pyrimidine dimers (CPD) or 6-4 photoproducts (6-4PP) in the whole genome, nor was there any significant difference in the repair of UV lesions in specific genes. However, at later time points we found that more lesions had been removed from the genome of dwarf-derived cells. We have also found that cells from dwarf mice express higher levels of the nucleotide excision repair proteins XPC and CSA, suggesting a causal link to enhanced DNA repair. Overall, these data suggest a mechanism for the UV resistance of Snell dwarf-derived fibroblasts that could contribute to the delay of aging and neoplasia in these mice.

Low Utilization of Circulating Glucose after Food Withdrawal in Snell Dwarf Mice

Glucose metabolism is altered in long-lived people and mice. Although it is clear that there is an association between altered glucose metabolism and longevity, it is not known whether this link is causal or not. Our current hypothesis is that decreased fasting glucose utilization may increase longevity by reducing oxygen radical production, a potential cause of aging. We observed that whole body fasting glucose utilization was lower in the Snell dwarf, a long-lived mutant mouse. Whole body fasting glucose utilization may be reduced by a decrease in the production of circulating glucose. Our isotope labeling analysis indicated both gluconeogenesis and glycogenolysis were suppressed in Snell dwarfs. Elevated circulating adiponectin may contribute to the reduction of glucose production in Snell dwarfs. Adiponectin lowered the appearance of glucose in the media over hepatoma cells by suppressing gluconeogenesis and glycogenolysis. The suppression of glucose production by adiponectin in vitro depended on AMP-activated protein kinase, a cell mediator of fatty acid oxidation. Elevated fatty acid oxidation was indicated in Snell dwarfs by increased utilization of circulating oleic acid, reduced intracellular triglyceride content, and increased phosphorylation of acetyl-CoA carboxylase. Finally, protein carbonyl content, a marker of oxygen radical damage, was decreased in Snell dwarfs. The correlation between high glucose utilization and elevated oxygen radical production was also observed in vitro by altering the concentrations of glucose and fatty acids in the media or pharmacologic inhibition of glucose and fatty acid oxidation with 4-hydroxycyanocinnamic acid and etomoxir, respectively.

“The Molecular Basis of Aging”: The Boehringer Ingelheim Fonds 95th International Titisee Conference

Nearly 20 years ago, researchers discovered that lifespan can be extended by single-gene mutations in the nematode worm Caenorhabditis elegans. Further studies revealed that the mechanisms governing aging in the smallest organisms have been evolutionarily conserved and may operate in human beings. Since then, the field of biogerontology has expanded considerably, learning from - and contributing to - such disparate fields as cell signaling, metabolism, endocrinology, and a wide range of human diseases including cancer. To date, newly discovered connections and novel interdisciplinary approaches gradually unify what once seemed unrelated observations between seemingly disparate research areas. While this unification is far from complete, several overlapping themes have clearly emerged. At the 95th International Titisee Conference, devoted to "The Molecular Basis of Aging," 60 of the world's pre-eminent biogerontologists shared their most recent findings in the biology of aging, and discussed interdisciplinary connections between diverse fields.

Skin-derived fibroblasts from long-lived species are resistant to some, but not all, lethal stresses and to the mitochondrial inhibitor rotenone

Fibroblast cell lines were developed from skin biopsies of eight species of wild-trapped rodents, one species of bat, and a group of genetically heterogeneous laboratory mice. Each cell line was tested in vitro for their resistance to six varieties of lethal stress, as well as for resistance to the nonlethal metabolic effects of the mitochondrial inhibitor rotenone and of culture at very low glucose levels. Standard linear regression of species-specific lifespan against each species mean stress resistance showed that longevity was associated with resistance to death induced by cadmium and hydrogen peroxide, as well as with resistance to rotenone inhibition. A multilevel regression method supported these associations, and suggested a similar association for resistance to heat stress. Regressions for resistance to cadmium, peroxide, heat, and rotenone remained significant after various statistical adjustments for body weight. In contrast, cells from longer-lived species did not show significantly greater resistance to ultraviolet light, paraquat, or the DNA alkylating agent methylmethanesulfonate. There was a strong correlation between species longevity and resistance to the metabolic effects of low-glucose medium among the rodent cell lines, but this test did not distinguish mice and rats from the much longer-lived little brown bat. These results are consistent with the idea that evolution of long-lived species may require development of cellular resistance to several forms of lethal injury, and provide justification for evaluation of similar properties in a much wider range of mammals and bird species.