Fibroblast cell lines from young adult mice of long-lived mutant strains are resistant to multiple forms of stress

Association between anorexia nervosa and type 2 diabetes in Sweden: Etiological clue for the primary prevention of type 2 diabetes

AIM

Caloric restriction has been found to be protective against the development of type 2 diabetes mellitus (T2D) in experimental animal studies. However, studies examining this association in humans are limited. In the present study, we examined whether individuals with anorexia nervosa, one marker of severe caloric restriction in humans, have a low incidence of T2D by using several Swedish registries.

METHODS

Individuals with anorexia nervosa were identified from the Swedish Hospital Discharge Register and Outpatient Register between 1964 and 2010. Standardized incidence ratios (SIRs) for T2D were studied among individuals with anorexia nervosa compared to those without the disorder.

RESULTS

A total of 17,135 individuals were identified with anorexia nervosa in Sweden. From this tally, 34 of them developed T2D, demonstrating a reduced risk of T2D with a SIR of 0.70, compared to individuals without anorexia nervosa. Patients with severe anorexia, indicated by more frequent hospitalizations, had a statistically non-significant lower incidence of T2D than those with fewer hospitalizations. A sibling study, controlled for familial confounding, found a statistically non-significant association between anorexia nervosa and T2D.

CONCLUSION

Our study found that severe caloric restriction by using individuals with anorexia nervosa as a proxy was negatively associated with T2D, which might provide a biological basis for the primary prevention of T2D. Further studies are needed to explore whether moderate caloric restriction can effectively prevent the development of T2D in general population.

Integrated analysis of noncoding RNAs and mRNAs reveals their potential roles in the biological activities of the growth hormone receptor

Accumulating evidence has indicated that noncoding RNAs (ncRNAs) have important regulatory potential in various biological processes. The molecular mechanisms by which growth hormone receptor (GHR) deficiency protects against age-related pathologies, reduces the incidence and delays the occurrence of fatal neoplasms are unclear. The aim of this study was to investigate miRNA, lncRNA and mRNA expression profiles and the potential functional roles of these RNA molecules in GHR knockout (GHR-KO) mice. Microarray expression profiles of miRNAs, lncRNAs and mRNAs were determined in wild type control mice and in GHR-KO mice. Differential expression, pathway and gene network analyses were developed to identify the possible biological roles of functional RNA molecules. Compared to wild type control mice, 1695 lncRNAs, 914 mRNAs and 9 miRNAs were upregulated and 1747 lncRNAs, 786 mRNAs and 21 miRNAs were downregulated in female GHR-KO mice. Moreover, 1265 lncRNAs, 724 mRNAs and 41 miRNAs were upregulated and 1377 lncRNAs, 765 mRNAs and 16 miRNAs were downregulated in male GHR-KO mice compared to wild type mice. Co-expression analysis of mRNAs, lncRNAs, and miRNAs showed that mRNAs including Hemxi2, Ero1Ib, 4933434i20RIK, Pde7a and Lgals1, lncRNAs including ASMM9PARTA014848, EL605414-P1, ASMM9PARTA051724, ASMM9PARTA045378 and ASMM9PARTA049185, and miRNAs including miR-188-3p, miR-690, miR-709 and miR-710 are situated at the core position of a three-dimensional lncRNA-mRNA-miRNA regulatory network. KEGG analysis showed that the most significantly regulated pathway was steroid hormone biosynthesis. We identified a set of lncRNAs, miRNAs and mRNAs that were aberrantly expressed in GHR-KO mice. Our results provide a foundation and an expansive view of the biological activities of the GHR.

IGF-1 deficiency in a critical period early in life influences the vascular aging phenotype in mice by altering miRNA-mediated post-transcriptional gene regulation: implications for the developmental origins of health and disease hypothesis

Epidemiological findings support the concept of Developmental Origins of Health and Disease, suggesting that early-life hormonal influences during a sensitive period of development have a fundamental impact on vascular health later in life. The endocrine changes that occur during development are highly conserved across mammalian species and include dramatic increases in circulating IGF-1 levels during adolescence. The present study was designed to characterize the effect of developmental IGF-1 deficiency on the vascular aging phenotype. To achieve that goal, early-onset endocrine IGF-1 deficiency was induced in mice by knockdown of IGF-1 in the liver using Cre-lox technology (Igf1 ^f/f mice crossed with mice expressing albumin-driven Cre recombinase). This model exhibits low-circulating IGF-1 levels during the peripubertal phase of development, which is critical for the biology of aging. Due to the emergence of miRNAs as important regulators of the vascular aging phenotype, the effect of early-life IGF-1 deficiency on miRNA expression profile in the aorta was examined in animals at 27 months of age. We found that developmental IGF-1 deficiency elicits persisting late-life changes in miRNA expression in the vasculature, which significantly differed from those in mice with adult-onset IGF-1 deficiency (TBG-Cre-AAV8-mediated knockdown of IGF-1 at 5 month of age in Igf1 ^f/f mice). Using a novel computational approach, we identified miRNA target genes that are co-expressed with IGF-1 and associate with aging and vascular pathophysiology. We found that among the predicted targets, the expression of multiple extracellular matrix-related genes, including collagen-encoding genes, were downregulated in mice with developmental IGF-1 deficiency. Collectively, IGF-1 deficiency during a critical period during early in life results in persistent changes in post-transcriptional miRNA-mediated control of genes critical targets for vascular health, which likely contribute to the deleterious late-life cardiovascular effects known to occur with developmental IGF-1 deficiency.

Energetic interventions for healthspan and resiliency with aging

Several behavioral and pharmacological strategies improve longevity, which is indicative of delayed organismal aging, with the most effective interventions extending both life- and healthspan. In free living creatures, maintaining health and function into old age requires resilience against a multitude of stressors. Conversely, in experimental settings, conventional housing of rodents limits exposure to such challenges, thereby obscuring an accurate assessment of resilience. Caloric restriction (CR) and exercise, as well as pharmacologic strategies (resveratrol, rapamycin, metformin, senolytics), are well established to improve indices of health and aging, but some paradoxical effects have been observed on resilience. For instance, CR potently retards the onset of age-related diseases, and improves lifespan to a greater extent than exercise in a variety of models. However, exercise has proven more consistently beneficial to organismal resilience against a broad array of stressors, including infections, surgery, wound healing and frailty. CR can improve cellular stress defenses and protect from frailty, but also impairs the response to infections, bed rest and healing. How an intervention will impact not only longevity, health and function, but also resiliency, is critical to better understanding translational implications. Thus, organismal robustness represents a critical, albeit understudied aspect of aging, which needs more careful attention in order to better inform on how putative age-delaying strategies will impact preservation of health and function in response to stressors with aging in humans.

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.

Dietary restriction: could it be considered as speed bump on tumor progression road?

Dietary restrictions, including fasting (or long-term starvation), calorie restriction (CR), and short-term starvation (STS), are considered a strong rationale that may protect against various diseases, including age-related diseases and cancer. Among dietary approaches, STS, in which food is not consumed during designed fasting periods but is typically not restricted during designated feeding periods, seems to be more suitable, because other dietary regimens involving prolonged fasting periods could worsen the health conditions of cancer patients, being they already naturally prone to weight loss. Until now, the limited amount of available data does not point to a single gene, pathway, or molecular mechanism underlying the benefits to the different dietary approaches. It is well known that the healthy effect is mediated in part by the reduction of nutrient-related pathways. The calorie restriction and starvation (long- and short-term) also suppress the inflammatory response reducing the expression, for example, of IL-10 and TNF-α, mitigating pro-inflammatory gene expression and increasing anti-inflammatory gene expression. The dietary restriction may regulate both genes involved in cellular proliferation and factors associated to apoptosis in normal and cancer cells. Finally, dietary restriction is an important tool that may influence the response to chemotherapy in preclinical models. However, further data are needed to correlate dietary approaches with chemotherapeutic treatments in human models. The aim of this review is to discuss the effects of various dietary approaches on the cancer progression and therapy response, mainly in preclinical models, describing some signaling pathways involved in these processes.

The Ames dwarf mutation attenuates Alzheimer's disease phenotype of APP/PS1 mice

APP/PS1 double transgenic mice expressing human mutant amyloid precursor protein (APP) and presenilin-1 (PS1) demonstrate robust brain amyloid beta (Aβ) peptide containing plaque deposition, increased markers of oxidative stress, behavioral dysfunction, and proinflammatory gliosis. On the other hand, lack of growth hormone, prolactin, and thyroid-stimulating hormone due to a recessive mutation in the Prop 1 gene (Prop1df) in Ames dwarf mice results in a phenotype characterized by potentiated antioxidant mechanisms, improved learning and memory, and significantly increased longevity in homozygous mice. Based on this, we hypothesized that a similar hormone deficiency might attenuate disease changes in the brains of APP/PS1 mice. To test this idea, APP/PS1 mice were crossed to the Ames dwarf mouse line. APP/PS1, wild-type, df/+, df/df, df/+/APP/PS1, and df/df/APP/PS1 mice were compared at 6 months of age through behavioral testing and assessing amyloid burden, reactive gliosis, and brain cytokine levels. df/df mice demonstrated lower brain growth hormone and insulin-like growth factor 1 concentrations. This correlated with decreased astrogliosis and microgliosis in the df/df/APP/PS1 mice and, surprisingly, reduced Aβ plaque deposition and Aβ 1-40 and Aβ 1-42 concentrations. The df/df/APP/PS1 mice also demonstrated significantly elevated brain levels of multiple cytokines in spite of the attenuated gliosis. These data indicate that the df/df/APP/PS1 line is a unique resource in which to study aging and resistance to disease and suggest that the affected pituitary hormones may have a role in regulating disease progression.

Reduced growth hormone signaling and methionine restriction: interventions that improve metabolic health and extend life span

Interventions that improve health are often associated with longevity. Reduced growth hormone signaling has been shown to increase life span in mice by over 50%. Similarly, reductions in dietary intake of methionine, in rats and mice, result in life-span extension. Many factors affect metabolic health, mitochondrial function, and resistance to stressors, each of which influence aging and life span. This paper presents a comparison of these two interventions, as well as the results of a study combining these interventions, to understand potential mechanisms underlying their effectiveness in enhancing healthy aging.

Loss of the Ubiquitin-conjugating Enzyme UBE2W Results in Susceptibility to Early Postnatal Lethality and Defects in Skin, Immune, and Male Reproductive Systems

UBE2W ubiquitinates N termini of proteins rather than internal lysine residues, showing a preference for substrates with intrinsically disordered N termini. The in vivo functions of this intriguing E2, however, remain unknown. We generated Ube2w germ line KO mice that proved to be susceptible to early postnatal lethality without obvious developmental abnormalities. Although the basis of early death is uncertain, several organ systems manifest changes in Ube2w KO mice. Newborn Ube2w KO mice often show altered epidermal maturation with reduced expression of differentiation markers. Mirroring higher UBE2W expression levels in testis and thymus, Ube2w KO mice showed a disproportionate decrease in weight of these two organs (~50%), suggesting a functional role for UBE2W in the immune and male reproductive systems. Indeed, Ube2w KO mice displayed sustained neutrophilia accompanied by increased G-CSF signaling and testicular vacuolation associated with decreased fertility. Proteomic analysis of a vulnerable organ, presymptomatic testis, showed a preferential accumulation of disordered proteins in the absence of UBE2W, consistent with the view that UBE2W preferentially targets disordered polypeptides. These mice further allowed us to establish that UBE2W is ubiquitously expressed as a single isoform localized to the cytoplasm and that the absence of UBE2W does not alter cell viability in response to various stressors. Our results establish that UBE2W is an important, albeit not essential, protein for early postnatal survival and normal functioning of multiple organ systems.

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.

Forward Genetic Approach to Uncover Stress Resistance Genes in Mice - A High-throughput Screen in ES Cells

Phenotype-driven genetic screens in mice is a powerful technique to uncover gene functions, but are often hampered by extremely high costs, which severely limits its potential. We describe here the use of mouse embryonic stem (ES) cells as surrogate cells to screen for a phenotype of interest and subsequently introduce these cells into a host embryo to develop into a living mouse carrying the phenotype. This method provides (1) a cost effective, high-throughput platform for genetic screen in mammalian cells; (2) a rapid way to identify the mutated genes and verify causality; and (3) a short-cut to develop mouse mutants directly from these selected ES cells for whole animal studies. We demonstrated the use of paraquat (PQ) to select resistant mutants and identify mutations that confer oxidative stress resistance. Other stressors or cytotoxic compounds may also be used to screen for resistant mutants to uncover novel genetic determinants of a variety of cellular stress resistance.

Biochemical Genetic Pathways that Modulate Aging in Multiple Species

The mechanisms underlying biological aging have been extensively studied in the past 20 years with the avail of mainly four model organisms: the budding yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, the fruitfly Drosophila melanogaster, and the domestic mouse Mus musculus. Extensive research in these four model organisms has identified a few conserved genetic pathways that affect longevity as well as metabolism and development. Here, we review how the mechanistic target of rapamycin (mTOR), sirtuins, adenosine monophosphate-activated protein kinase (AMPK), growth hormone/insulin-like growth factor 1 (IGF-1), and mitochondrial stress-signaling pathways influence aging and life span in the aforementioned models and their possible implications for delaying aging in humans. We also draw some connections between these biochemical pathways and comment on what new developments aging research will likely bring in the near future.

Nrf2 Signaling and the Slowed Aging Phenotype: Evidence from Long-Lived Models

Studying long-lived animals provides novel insight into shared characteristics of aging and represents a unique model to elucidate approaches to prevent chronic disease. Oxidant stress underlies many chronic diseases and resistance to stress is a potential mechanism governing slowed aging. The transcription factor nuclear factor (erythroid-derived 2)-like 2 is the "master regulator" of cellular antioxidant defenses. Nrf2 is upregulated by some longevity promoting interventions and may play a role in regulating species longevity. However, Nrf2 expression and activity in long-lived models have not been well described. Here, we review evidence for altered Nrf2 signaling in a variety of slowed aging models that accomplish lifespan extension via pharmacological, nutritional, evolutionary, genetic, and presumably epigenetic means.

The somatotropic axis and longevity in mice

The somatotropic signaling pathway has been implicated in aging and longevity studies in mice and other species. The physiology and lifespans of a variety of mutant mice, both spontaneous and genetically engineered, have contributed to our current understanding of the role of growth hormone and insulin-like growth factor I on aging-related processes. Several other mice discovered to live longer than their wild-type control counterparts also exhibit differences in growth factor levels; however, the complex nature of the phenotypic changes in these animals may also impact lifespan. The somatotropic axis impacts several pathways that dictate insulin sensitivity, nutrient sensing, mitochondrial function, and stress resistance as well as others that are thought to be involved in lifespan regulation.

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.

Dynamic differences in oxidative stress and the regulation of metabolism with age in visceral versus subcutaneous adipose

Once thought only as storage for excess nutrients, adipose tissue has been shown to be a dynamic organ implicated in the regulation of many physiological processes. There is emerging evidence supporting differential roles for visceral and subcutaneous white adipose tissue in maintaining health, although how these roles are modulated by the aging process is not clear. However, the proposed beneficial effects of subcutaneous fat suggest that targeting maintenance of this tissue could lead to healthier aging. In this study, we tested whether alterations in adipose function with age might be associated with changes in oxidative stress. Using visceral and subcutaneous adipose from C57BL/6 mice, we discovered effects of both age and depot location on markers of lipolysis and adipogenesis. Conversely, accumulation of oxidative damage and changes in enzymatic antioxidant expression with age were largely similar between these two depots. The activation of each of the stress signaling pathways JNK and MAPK/ERK was relatively suppressed in subcutaneous adipose tissue suggesting reduced sensitivity to oxidative stress. Similarly, pre-adipocytes from subcutaneous adipose were significantly more resistant than visceral-derived cells to cell death caused by oxidative stress. Cellular respiration in visceral-derived cells was dramatically higher than in cells derived from subcutaneous adipose despite little evidence for differences in mitochondrial density. Together, our data identify molecular mechanisms by which visceral and subcutaneous adipose differ with age and suggest potential targetable means to preserve healthy adipose aging.

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Aging alters metabolism differently in C57BL/6 visceral and subcutaneous fat.

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Oxidative stress and antioxidants show little difference between these fat depots.

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Age-induced activation of JNK and ERK/MAPK is elevated in visceral fat.

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Preadipocytes from visceral fat have relatively higher metabolic rate.

Caribbean and La Réunion Chikungunya Virus Isolates Differ in Their Capacity To Induce Proinflammatory Th1 and NK Cell Responses and Acute Joint Pathology

Chikungunya virus (CHIKV) is a mosquito-borne arthralgic alphavirus that has garnered international attention as an important emerging pathogen since 2005. More recently, it invaded the Caribbean islands and the Western Hemisphere. Intriguingly, the current CHIKV outbreak in the Caribbean is caused by the Asian CHIKV genotype, which differs from the La Réunion LR2006 OPY1 isolate belonging to the Indian Ocean lineage. Here, we adopted a systematic and comparative approach against LR2006 OPY1 to characterize the pathogenicity of the Caribbean CNR20235 isolate and consequential host immune responses in mice. Ex vivo infection using primary mouse tail fibroblasts revealed a weaker replication efficiency by CNR20235 isolate. In the CHIKV mouse model, CNR20235 infection induced an enervated joint pathology characterized by moderate edema and swelling, independent of mononuclear cell infiltration. Based on systemic cytokine analysis, localized immunophenotyping, and gene expression profiles in the popliteal lymph node and inflamed joints, two pathogenic phases were defined for CHIKV infection: early acute (2 to 3 days postinfection [dpi]) and late acute (6 to 8 dpi). Reduced joint pathology during early acute phase of CNR20235 infection was associated with a weaker proinflammatory Th1 response and natural killer (NK) cell activity. The pathological role of NK cells was further demonstrated as depletion of NK cells reduced joint pathology in LR2006 OPY1. Taken together, this study provides evidence that the Caribbean CNR20235 isolate has an enfeebled replication and induces a less pathogenic response in the mammalian host.

IMPORTANCE The introduction of CHIKV in the Americas has heightened the risk of large-scale outbreaks due to the close proximity between the United States and the Caribbean. The immunopathogenicity of the circulating Caribbean CHIKV isolate was explored, where it was demonstrated to exhibit reduced infectivity resulting in a weakened joint pathology. Analysis of serum cytokine levels, localized immunophenotyping, and gene expression profiles in the organs revealed that a limited Th1 response and reduced NK cells activity could underlie the reduced pathology in the host. Interestingly, higher asymptomatic infections were observed in the Caribbean compared to the La Réunion outbreaks in 2005 and 2006. This is the first study that showed an association between key proinflammatory factors and pathology-mediating leukocytes with a less severe pathological outcome in Caribbean CHIKV infection. Given the limited information regarding the sequela of Caribbean CHIKV infection, our study is timely and will aid the understanding of this increasingly important disease.

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.

Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression

Immune system defects are at the center of aging and a range of diseases. Here, we show that prolonged fasting reduces circulating IGF-1 levels and PKA activity in various cell populations, leading to signal transduction changes in long-term hematopoietic stem cells (LT-HSCs) and niche cells that promote stress resistance, self-renewal, and lineage-balanced regeneration. Multiple cycles of fasting abated the immunosuppression and mortality caused by chemotherapy and reversed age-dependent myeloid-bias in mice, in agreement with preliminary data on the protection of lymphocytes from chemotoxicity in fasting patients. The proregenerative effects of fasting on stem cells were recapitulated by deficiencies in either IGF-1 or PKA and blunted by exogenous IGF-1. These findings link the reduced levels of IGF-1 caused by fasting to PKA signaling and establish their crucial role in regulating hematopoietic stem cell protection, self-renewal, and regeneration.

Inhibition of adenylyl cyclase type 5 increases longevity and healthful aging through oxidative stress protection

Mice with disruption of adenylyl cyclase type 5 (AC5 knockout, KO) live a third longer than littermates. The mechanism, in part, involves the MEK/ERK pathway, which in turn is related to protection against oxidative stress. The AC5 KO model also protects against diabetes, obesity, and the cardiomyopathy induced by aging, diabetes, and cardiac stress and also demonstrates improved exercise capacity. All of these salutary features are also mediated, in part, by oxidative stress protection. For example, chronic beta adrenergic receptor stimulation induced cardiomyopathy was rescued by AC5 KO. Conversely, in AC5 transgenic (Tg) mice, where AC5 is overexpressed in the heart, the cardiomyopathy was exacerbated and was rescued by enhancing oxidative stress resistance. Thus, the AC5 KO model, which resists oxidative stress, is uniquely designed for clinical translation, since it not only increases longevity and exercise, but also protects against diabetes, obesity, and cardiomyopathy. Importantly, inhibition of AC5's action to prolong longevity and enhance healthful aging, as well as its mechanism through resistance to oxidative stress, is unique among all of the nine AC isoforms.

Role of pentraxin 3 in shaping arthritogenic alphaviral disease: from enhanced viral replication to immunomodulation

The rising prevalence of arthritogenic alphavirus infections, including chikungunya virus (CHIKV) and Ross River virus (RRV), and the lack of antiviral treatments highlight the potential threat of a global alphavirus pandemic. The immune responses underlying alphavirus virulence remain enigmatic. We found that pentraxin 3 (PTX3) was highly expressed in CHIKV and RRV patients during acute disease. Overt expression of PTX3 in CHIKV patients was associated with increased viral load and disease severity. PTX3-deficient (PTX3(-/-)) mice acutely infected with RRV exhibited delayed disease progression and rapid recovery through diminished inflammatory responses and viral replication. Furthermore, binding of the N-terminal domain of PTX3 to RRV facilitated viral entry and replication. Thus, our study demonstrates the pivotal role of PTX3 in shaping alphavirus-triggered immunity and disease and provides new insights into alphavirus pathogenesis.

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.

Screening for stress-resistance mutations in the mouse

Longevity is correlated with stress resistance in many animal models. However, previous efforts through the boosting of the antioxidant defense system did not extend life span, suggesting that longevity related stress resistance is mediated by other uncharacterized pathways. We have developed a high-throughput platform for screening and rapid identification of novel genetic mutants in the mouse that are stress resistant. Selection for resistance to stressors occurs in mutagenized mouse embryonic stem (ES) cells, which are carefully treated so as to maintain pluripotency for mouse production. Initial characterization of these mutant ES cells revealed mutations in Pigl, Tiam1, and Rffl, among others. These genes are implicated in glycosylphosphatidylinositol biosynthesis, NADPH oxidase function, and inflammation. These mutants: (1) are resistant to two different oxidative stressors, paraquat and the omission of 2-mercaptoethanol, (2) have reduced levels of endogenous reactive oxygen species (ROS), (3) are capable of generating live mice, and (4) transmit the stress resistance phenotype to the mice. This strategy offers an efficient way to select for new mutants expressing a stress resistance phenotype, to rapidly identify the causative genes, and to develop mice for in vivo studies.

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.

Effects of insulin-like growth factor 1 on glutathione S-transferases and thioredoxin in growth hormone receptor knockout mice

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) have been shown to affect processes involved in cellular stress defense, aging, and longevity. This study was designed to identify possible mechanisms of a disrupted GH signaling pathway on stress resistance using growth hormone receptor knockout (GHRKO) mice. GHRKO mice are GH resistant due to the targeted disruption of the GH receptor/binding protein gene, thus preventing GH from binding and exerting its downstream effects. These mice have very low circulating IGF-1 levels and high GH levels, are obese yet insulin sensitive, and live longer than their wild-type controls. Wild-type or GHRKO mice were treated with saline or IGF-1 (WT saline, GHRKO saline, GHRKO IGF-1) two times daily for 7 days. Glutathione S-transferase (GST) activities, proteins, and gene expression were determined. Liver mitochondrial GSTA1, GSTA3, and GSTZ1 proteins were significantly higher in GHRKO when compared to those of WT mice. The 4-hydroxynonenal (4-HNE) GST activity was upregulated in GHRKO mice and was suppressed after IGF-1 administration. Interestingly, thioredoxin (Trx)1, Trx2, thioredoxin reductase (TrxR)1, and TrxR2 messenger RNA (mRNA) levels were significantly higher in the GHRKO as compared to WT mice, and IGF-1 treatment suppressed the expression of each. We also found that glutaredoxin (Grx)2 mRNA and cytosolic Grx activity were higher in GHRKO mice. These results suggest that the detoxification and stress response mechanisms in GHRKO mice are contributed in part by the circulating level of IGF-1.

P62/SQSTM1 at the interface of aging, autophagy, and disease

Advanced age is characterized by increased incidence of many chronic, noninfectious diseases that impair the quality of living of the elderly and pose a major burden on the healthcare systems of developed countries. These diseases are characterized by impaired or altered function at the tissue and cellular level, which is a hallmark of the aging process. Age-related impairments are likely due to loss of homeostasis at the cellular level, which leads to the accumulation of dysfunctional organelles and damaged macromolecules, such as proteins, lipids, and nucleic acids. Intriguingly, aging and age-related diseases can be delayed by modulating nutrient signaling pathways converging on the target of rapamycin (TOR) kinase, either by genetic or dietary intervention. TOR signaling influences aging through several potential mechanisms, such as autophagy, a degradation pathway that clears the dysfunctional organelles and damaged macromolecules that accumulate with aging. Autophagy substrates are targeted for degradation by associating with p62/SQSTM1, a multidomain protein that interacts with the autophagy machinery. p62/SQSTM1 is involved in several cellular processes, and its loss has been linked to accelerated aging and to age-related pathologies. In this review, we describe p62/SQSTM1, its role in autophagy and in signaling pathways, and its emerging role in aging and age-associated pathologies. Finally, we propose p62/SQSTM1 as a novel target for aging studies and age-extending interventions.

Reductions in serum IGF-1 during aging impair health span

In lower or simple species, such as worms and flies, disruption of the insulin-like growth factor (IGF)-1 and the insulin signaling pathways has been shown to increase lifespan. In rodents, however, growth hormone (GH) regulates IGF-1 levels in serum and tissues and can modulate lifespan via/or independent of IGF-1. Rodent models, where the GH/IGF-1 axis was ablated congenitally, show increased lifespan. However, in contrast to rodents where serum IGF-1 levels are high throughout life, in humans, serum IGF-1 peaks during puberty and declines thereafter during aging. Thus, animal models with congenital disruption of the GH/IGF-1 axis are unable to clearly distinguish between developmental and age-related effects of GH/IGF-1 on health. To overcome this caveat, we developed an inducible liver IGF-1-deficient (iLID) mouse that allows temporal control of serum IGF-1. Deletion of liver Igf -1 gene at one year of age reduced serum IGF-1 by 70% and dramatically impaired health span of the iLID mice. Reductions in serum IGF-1 were coupled with increased GH levels and increased basal STAT5B phosphorylation in livers of iLID mice. These changes were associated with increased liver weight, increased liver inflammation, increased oxidative stress in liver and muscle, and increased incidence of hepatic tumors. Lastly, despite elevations in serum GH, low levels of serum IGF-1 from 1 year of age compromised skeletal integrity and accelerated bone loss. We conclude that an intact GH/IGF-1 axis is essential to maintain health span and that elevated GH, even late in life, associates with increased pathology.

Methionine restriction activates the retrograde response and confers both stress tolerance and lifespan extension to yeast, mouse and human cells

A methionine-restricted diet robustly improves healthspan in key model organisms. For example, methionine restriction reduces age-related pathologies and extends lifespan up to 45% in rodents. However, the mechanisms underlying these benefits remain largely unknown. We tested whether the yeast chronological aging assay could model the benefits of methionine restriction, and found that this intervention extends lifespan when enforced by either dietary or genetic approaches, and furthermore, that the observed lifespan extension is due primarily to reduced acid accumulation. In addition, methionine restriction-induced lifespan extension requires the activity of the retrograde response, which regulates nuclear gene expression in response to changes in mitochondrial function. Consistent with an involvement of stress-responsive retrograde signaling, we also found that methionine-restricted yeast are more stress tolerant than control cells. Prompted by these findings in yeast, we tested the effects of genetic methionine restriction on the stress tolerance and replicative lifespans of cultured mouse and human fibroblasts. We found that such methionine-restricted mammalian cells are resistant to numerous cytotoxic stresses, and are substantially longer-lived than control cells. In addition, similar to yeast, the extended lifespan of methionine-restricted mammalian cells is associated with NFκB-mediated retrograde signaling. Overall, our data suggest that improved stress tolerance and extension of replicative lifespan may contribute to the improved healthspan observed in methionine-restricted rodents, and also support the possibility that manipulation of the pathways engaged by methionine restriction may improve healthspan in humans.

Liver-specific GH receptor gene-disrupted (LiGHRKO) mice have decreased endocrine IGF-I, increased local IGF-I, and altered body size, body composition, and adipokine profiles

GH is an important regulator of body growth and composition as well as numerous other metabolic processes. In particular, liver plays a key role in the GH/IGF-I axis, because the majority of circulating "endocrine" IGF-I results from GH-stimulated liver IGF-I production. To develop a better understanding of the role of liver in the overall function of GH, we generated a strain of mice with liver-specific GH receptor (GHR) gene knockout (LiGHRKO mice). LiGHRKO mice had a 90% decrease in circulating IGF-I levels, a 300% increase in circulating GH, and significant changes in IGF binding protein (IGFBP)-1, IGFBP-2, IGFBP-3, IGFBP-5, and IGFBP-7. LiGHRKO mice were smaller than controls, with body length and body weight being significantly decreased in both sexes. Analysis of body composition over time revealed a pattern similar to those found in GH transgenic mice; that is, LiGHRKO mice had a higher percentage of body fat at early ages followed by lower percentage of body fat in adulthood. Local IGF-I mRNA levels were significantly increased in skeletal muscle and select adipose tissue depots. Grip strength was increased in LiGHRKO mice. Finally, circulating levels of leptin, resistin, and adiponectin were increased in LiGHRKO mice. In conclusion, LiGHRKO mice are smaller despite increased local mRNA expression of IGF-I in several tissues, suggesting that liver-derived IGF-I is indeed important for normal body growth. Furthermore, our data suggest that novel GH-dependent cross talk between liver and adipose is important for regulation of adipokines in vivo.

Elevated ATF4 function in fibroblasts and liver of slow-aging mutant mice

Work in yeast has shown that longevity extension induced by nutrient deprivation, altered ribosomal function, or diminished target of rapamycin action requires the activity of GCN4. We hypothesized that increased activity of ATF4, the mammalian equivalent of yeast GCN4, might be characteristic of mutations that extend mouse life span. Fibroblasts from the skin of two such mutants (Snell dwarf and PAPP-A knockout) were found to have higher levels of ATF4 protein and expression of several ATF4 target genes in responses to amino acid withdrawal, cadmium, hydrogen peroxide, and tunicamycin. ATF4 pathways were also elevated in liver of both kinds of long-lived mutant mice. Thus, a connection between ATF4 pathways and longevity may have deep evolutionary roots, and further studies of ATF4 mechanisms may provide insights into the links between cellular stress resistance, protein translation control, and aging.

Fibroblasts from long-lived species of mammals and birds show delayed, but prolonged, phosphorylation of ERK

Fibroblasts from long-lived mutant mice show diminished phosphorylation of the stress-activated protein kinases ERK1/2 after exposure to peroxide, cadmium, or paraquat. We have now evaluated the kinetics of ERK phosphorylation in fibroblasts from long-lived and short-lived species of mammals and birds in response to stress by cadmium or hydrogen peroxide. Fibroblasts from the shorter-lived species of rodents and birds showed rapid induction of ERK phosphorylation, with a decline to basal level within 60 min. In contrast, cells from longer-lived species showed slower and more prolonged activation of ERK phosphorylation. These results suggest that fibroblasts from long-lived species may be less susceptible to the early phases of damage from cadmium or peroxide and suggest that altered kinetics of ERK activity may contribute to their stress resistance properties.

Fibroblasts from long-lived rodent species exclude cadmium

Resistance to the lethal effects of cellular stressors, including the toxic heavy metal cadmium (Cd), is characteristic of fibroblast cell lines derived from long-lived bird and rodent species, as well as cell lines from several varieties of long-lived mutant mice. To explore the mechanism of resistance to Cd, we used inductively coupled plasma mass spectroscopy to measure the rate of Cd uptake into primary fibroblasts of 15 rodent species. These data indicate that fibroblasts from long-lived rodent species have slower rates of Cd uptake from the extracellular medium than those from short-lived species. In addition, fibroblasts from short-lived species export more zinc after exposure to extracellular Cd than cells from long-lived species. Lastly, fibroblasts from long-lived rodent species have lower baseline concentrations of two redox-active metals, iron and copper. Our results suggest that evolution of longevity among rodents required adjustment of cellular properties to alter metal homeostasis and to reduce the toxic effects of heavy metals that accumulate over the course of a longer life span.

Growth hormone alters the glutathione S-transferase and mitochondrial thioredoxin systems in long-living Ames dwarf mice

Ames dwarf mice are deficient in growth hormone (GH), prolactin, and thyroid-stimulating hormone and live significantly longer than their wild-type (WT) siblings. The lack of GH is associated with stress resistance and increased longevity. However, the mechanism underlying GH's actions on cellular stress defense have yet to be elucidated. In this study, WT or Ames dwarf mice were treated with saline or GH (WT saline, Dwarf saline, and Dwarf GH) two times daily for 7 days. The body and liver weights of Ames dwarf mice were significantly increased after 7 days of GH administration. Mitochondrial protein levels of the glutathione S-transferase (GST) isozymes, K1 and M4 (GSTK1 and GSTM4), were significantly higher in dwarf mice (Dwarf saline) when compared with WT mice (WT saline). GH administration downregulated the expression of GSTK1 proteins in dwarf mice. We further investigated GST activity from liver lysates using different substrates. Substrate-specific GST activity (bromosulfophthalein, dichloronitrobenzene, and 4-hydrox-ynonenal) was significantly reduced in GH-treated dwarf mice. In addition, GH treatment attenuated the activity of thioredoxin and glutaredoxin in liver mitochondria of Ames mice. Importantly, GH treatment suppressed Trx2 and TrxR2 mRNA expression. These data indicate that GH has a role in stress resistance by altering the functional capacity of the GST system through the regulation of specific GST family members in long-living Ames dwarf mice. It also affects the regulation of thioredoxin and glutaredoxin, factors that regulate posttranslational modification of proteins and redox balance, thereby further influencing stress resistance.

Low levels of plasma IGF-1 inhibit intracortical bone remodeling during aging

Studies linking insulin-like growth factor-1 (IGF-1) to age-related bone loss in humans have been reported but remain only correlative. In this investigation, we characterized the bone phenotype of aged WT C57BL/6J male mice in comparison to that of C57BL/6J mice with reduced serum IGF-1 levels arising from an igfals gene deletion (ALS knockout (ALSKO)). During the aging process, WT mice showed an increase in fat mass and decrease lean mass while ALSKO mice had stable lean and fat mass values. Skeletal analyses of femora from WT mice revealed an expansion of the marrow area and a significant accumulation of intracortical porosity associated with increased intracortical remodeling. In contrast, ALSKO mice showed only small age-related declines in the amount of cortical bone tissue and minimal intracortical porosity, at 2 years of age. Accordingly, mechanical tests of femora from 2-year-old WT mice revealed reduced stiffness and maximal load when compared to bones from ALSKO mice. We show here that lifelong reductions in serum IGF-1 compromise skeletal size in development leading to slender bones; they are also associated with decreased intracortical bone remodeling and preservation of bone strength during aging.

Longitudinal analysis of calorie restriction on rat taste bud morphology and expression of sweet taste modulators

Calorie restriction (CR) is a lifestyle intervention employed to reduce body weight and improve metabolic functions primarily via reduction of ingested carbohydrates and fats. Taste perception is highly related to functional metabolic status and body adiposity. We have previously shown that sweet taste perception diminishes with age; however, relatively little is known about the effects of various lengths of CR upon taste cell morphology and function. We investigated the effects of CR on taste bud morphology and expression of sweet taste-related modulators in 5-, 17-, and 30-month-old rats. In ad libitum (AL) and CR rats, we consistently found the following parameters altered significantly with advancing age: reduction of taste bud size and taste cell numbers per taste bud and reduced expression of sonic hedgehog, type 1 taste receptor 3 (T1r3), α-gustducin, and glucagon-like peptide-1 (GLP-1). In the oldest rats, CR affected a significant reduction of tongue T1r3, GLP-1, and α-gustducin expression compared with age-matched AL rats. Leptin receptor immunopositive cells were elevated in 17- and 30-month-old CR rats compared with age-matched AL rats. These alterations of sweet taste-related modulators, specifically during advanced aging, suggest that sweet taste perception may be altered in response to different lengths of CR.

The key role of growth hormone-insulin-IGF-1 signaling in aging and cancer

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors in aging. GH/Insulin/insulin-like growth factor-1 (IGF-1) signaling molecules that have been linked to longevity include daf-2 and InR and their homologues in mammals, and inactivation of the corresponding genes increases lifespan in nematodes, fruit flies and mice. The life-prolonging effects of caloric restriction are likely related to decreasing IGF-1 levels. Evidence has emerged that antidiabetic drugs are promising candidates for both lifespan extension and prevention of cancer. Thus, antidiabetic drugs postpone spontaneous carcinogenesis in mice and rats, as well as chemical and radiation carcinogenesis in mice, rats and hamsters. Furthermore, metformin seems to decrease the risk for cancer in diabetic patients.

Metabolic adaptations to short-term every-other-day feeding in long-living Ames dwarf mice

Restrictive dietary interventions exert significant beneficial physiological effects in terms of aging and age-related disease in many species. Every other day feeding (EOD) has been utilized in aging research and shown to mimic many of the positive outcomes consequent with dietary restriction. This study employed long living Ames dwarf mice subjected to EOD feeding to examine the adaptations of the oxidative phosphorylation and antioxidative defense systems to this feeding regimen. Every other day feeding lowered liver glutathione (GSH) concentrations in dwarf and wild type (WT) mice but altered GSH biosynthesis and degradation in WT mice only. The activities of liver OXPHOS enzymes and corresponding proteins declined in WT mice fed EOD while in dwarf animals, the levels were maintained or increased with this feeding regimen. Antioxidative enzymes were differentially affected depending on the tissue, whether proliferative or post-mitotic. Gene expression of components of liver methionine metabolism remained elevated in dwarf mice when compared to WT mice as previously reported however, enzymes responsible for recycling homocysteine to methionine were elevated in both genotypes in response to EOD feeding. The data suggest that the differences in anabolic hormone levels likely affect the sensitivity of long living and control mice to this dietary regimen, with dwarf mice exhibiting fewer responses in comparison to WT mice. These results provide further evidence that dwarf mice may be better protected against metabolic and environmental perturbations which may in turn, contribute to their extended longevity.

Decreased levels of proapoptotic factors and increased key regulators of mitochondrial biogenesis constitute new potential beneficial features of long-lived growth hormone receptor gene-disrupted mice

Decreased somatotrophic signaling is among the most important mechanisms associated with extended longevity. Mice homozygous for the targeted disruption of the growth hormone (GH) receptor gene (GH receptor knockout; GHRKO) are obese and dwarf, are characterized by a reduced weight and body size, undetectable levels of GH receptor, high concentration of serum GH, and greatly reduced plasma levels of insulin and insulin-like growth factor-I, and are remarkably long lived. Recent results suggest new features of GHRKO mice that may positively affect longevity-decreased levels of proapoptotic factors and increased levels of key regulators of mitochondrial biogenesis. The alterations in levels of the proapoptotic factors and key regulators of mitochondrial biogenesis were not further improved by two other potential life-extending interventions-calorie restriction and visceral fat removal. This may attribute the primary role to GH resistance in the regulation of apoptosis and mitochondrial biogenesis in GHRKO mice in terms of increased life span.

Oxidative stress activates a specific p53 transcriptional response that regulates cellular senescence and aging

Oxidative stress is a determining factor of cellular senescence and aging and a potent inducer of the tumour-suppressor p53. Resistance to oxidative stress correlates with delayed aging in mammals, in the absence of accelerated tumorigenesis, suggesting inactivation of selected p53-downstream pathways. We investigated p53 regulation in mice carrying deletion of p66, a mutation that retards aging and confers cellular resistance and systemic resistance to oxidative stress. We identified a transcriptional network of ~200 genes that are repressed by p53 and encode for determinants of progression through mitosis or suppression of senescence. They are selectively down-regulated in cultured fibroblasts after oxidative stress, and, in vivo, in proliferating tissues and during physiological aging. Selectivity is imposed by p66 expression and activation of p44/p53 (also named Delta40p53), a p53 isoform that accelerates aging and prevents mitosis after protein damage. p66 deletion retards aging and increases longevity of p44/p53 transgenic mice. Thus, oxidative stress activates a specific p53 transcriptional response, mediated by p44/p53 and p66, which regulates cellular senescence and aging.

The oxidizing agent, paraquat, is more toxic to Wolbachia than to mosquito host cells

Cultured cells provide an important in vitro system for examining metabolic interactions between the intracellular bacterium, Wolbachia pipientis, and its insect hosts. To test whether Wolbachia-associated changes in antioxidant activities could provide a tool to select for infected cells, we tested the effects of paraquat (PQ) on Aedes albopictus mosquito cells. Like mammalian cells, mosquito cells tolerate PQ over a wide range of concentrations, and for considerable lengths of time, depending on cell density at the time of treatment. When mosquito cells were plated at low density and allowed to grow in the presence of PQ, we measured an LC50 of approximately 1-2 μM. Unexpectedly, cells persistently infected with Wolbachia strain wStr, from the planthopper Laodelphax striatellus, grew to higher densities in the presence of 1.5 μM PQ than in its absence. This effect of PQ was similar to the improved growth of host cells that occurs in the presence of antibiotics that suppress the Wolbachia infection. A more detailed examination of growth and metabolic sensitivity indicated that wStr is about 10-fold more sensitive to PQ than the mosquito host cells. Microscopic examination confirmed that Wolbachia levels were reduced in PQ-treated cells, and DNA estimates based on the polymerase chain reaction (PCR) indicated that Wolbachia abundance decreased by approximately 100-fold over a 10-d period. Although Wolbachia genomes encode superoxide dismutase, inspection of annotated genomes indicates that they lack several genes encoding products that ameliorate oxidative damage, including catalase, which converts the PQ byproduct, hydrogen peroxide, to molecular oxygen and water. We suggest that loss of multiple genes that participate in repair of oxidative damage accounts for increased sensitivity of Wolbachia to PQ, relative to its host cells.

The effect of low and high plasma levels of insulin-like growth factor-1 (IGF-1) on the morphology of major organs: studies of Laron dwarf and bovine growth hormone transgenic (bGHTg) mice

It is well known that somatotrophic/insulin signaling affects lifespan in experimental animals. To study the effects of insulin-like growth factor-1 (IGF-1) plasma level on the morphology of major organs, we analyzed lung, heart, liver, kidney, bone marrow, and spleen isolated from 2-year-old growth hormone receptor knockout (GHR-KO) Laron dwarf mice (with low circulating plasma levels of IGF-1) and 6-month-old bovine growth hormone transgenic (bGHTg) mice (with high circulating plasma levels of IGF-1). The ages of the two mutant strains employed in our studies were selected based on their overall ~50% survival (Laron dwarf mice live up to ~4 years and bGHTg mice up to ~1 year). Morphological analysis of the organs of long-living 2-year-old Laron dwarf mice revealed a lower biological age for their organs compared with normal littermates, with more brown adipose tissue (BAT) surrounding the main body organs, lower levels of steatosis in liver, and a lower incidence of leukocyte infiltration in different organs. By contrast, the organs of 6-month-old, short-living bGHTg mice displayed several abnormalities in liver and kidney and a reduced content of BAT around vital organs.

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.

Murine models of atrophy, cachexia, and sarcopenia in skeletal muscle

With the extension of life span over the past several decades, the age-related loss of muscle mass and strength that characterizes sarcopenia is becoming more evident and thus, has a more significant impact on society. To determine ways to intervene and delay, or even arrest the physical frailty and dependence that accompany sarcopenia, it is necessary to identify those biochemical pathways that define this process. Animal models that mimic one or more of the physiological pathways involved with this phenomenon are very beneficial in providing an understanding of the cellular processes at work in sarcopenia. The ability to influence pathways through genetic manipulation gives insight into cellular responses and their impact on the physical expression of sarcopenia. This review evaluates several murine models that have the potential to elucidate biochemical processes integral to sarcopenia. Identifying animal models that reflect sarcopenia or its component pathways will enable researchers to better understand those pathways that contribute to age-related skeletal muscle mass loss, and in turn, develop interventions that will prevent, retard, arrest, or reverse this phenomenon. This article is part of a Special Issue entitled: Animal Models of Disease.

Viperin restricts chikungunya virus replication and pathology

Chikungunya virus (CHIKV) is a mosquito-borne arthralgia arbovirus that is reemergent in sub-Saharan Africa and Southeast Asia. CHIKV infection has been shown to be self-limiting, but the molecular mechanisms of the innate immune response that control CHIKV replication remain undefined. Here, longitudinal transcriptional analyses of PBMCs from a cohort of CHIKV-infected patients revealed that type I IFNs controlled CHIKV infection via RSAD2 (which encodes viperin), an enigmatic multifunctional IFN-stimulated gene (ISG). Viperin was highly induced in monocytes, the major target cell of CHIKV in blood. Anti-CHIKV functions of viperin were dependent on its localization in the ER, and the N-terminal amphipathic α-helical domain was crucial for its antiviral activity in controlling CHIKV replication. Furthermore, mice lacking Rsad2 had higher viremia and severe joint inflammation compared with wild-type mice. Our data demonstrate that viperin is a critical antiviral host protein that controls CHIKV infection and provide a preclinical basis for the design of effective control strategies against CHIKV and other reemerging arthrogenic alphaviruses.

Resistance to genotoxic stresses in Arctica islandica, the longest living noncolonial animal: is extreme longevity associated with a multistress resistance phenotype?

Bivalve molluscs are newly discovered models of successful aging. Here, we test the hypothesis that extremely long-lived bivalves are not uniquely resistant to oxidative stressors (eg, tert-butyl hydroperoxide, as demonstrated in previous studies) but exhibit a multistress resistance phenotype. We contrasted resistance (in terms of organismal mortality) to genotoxic stresses (including topoisomerase inhibitors, agents that cross-link DNA or impair genomic integrity through DNA alkylation or methylation) and to mitochondrial oxidative stressors in three bivalve mollusc species with dramatically differing life spans: Arctica islandica (ocean quahog), Mercenaria mercenaria (northern quahog), and the Atlantic bay scallop, Argopecten irradians irradians (maximum species life spans: >500, >100, and ~2 years, respectively). With all stressors, the short-lived A i irradians were significantly less resistant than the two longer lived species. Arctica islandica were consistently more resistant than M mercenaria to mortality induced by oxidative stressors as well as DNA methylating agent nitrogen mustard and the DNA alkylating agent methyl methanesulfonate. The same trend was not observed for genotoxic agents that act through cross-linking DNA. In contrast, M mercenaria tended to be more resistant to epirubicin and genotoxic stressors, which cause DNA damage by inhibiting topoisomerases. To our knowledge, this is the first study comparing resistance to genotoxic stressors in bivalve mollusc species with disparate longevities. In line with previous studies of comparative stress resistance and longevity, our data extends, at least in part, the evidence for the hypothesis that an association exists between longevity and a general resistance to multiplex stressors, not solely oxidative stress. This work also provides justification for further investigation into the interspecies differences in stress response signatures induced by a diverse array of stressors in short-lived and long-lived bivalves, including pharmacological agents that elicit endoplasmic reticulum stress and cellular stress caused by activation of innate immunity.

Decreased thyroid follicle size in dwarf mice may suggest the role of growth hormone signaling in thyroid growth regulation

Background

Altered somatotrophic signaling is among the most important potential mechanisms of extended longevity. Ames dwarf (df/df) mice are homozygous for mutation at the Prop-1 gene, leading to a lack of growth hormone (GH), prolactin and thyroid stimulating hormone (TSH). Mice homozygous for targeted disruption of the growth hormone receptor/growth hormone binding protein gene are known as GH receptor knockout (GHRKO) mice or “Laron dwarf”. Both, df/df and GHRKO mice, are characterized by reduced body size, low plasma insulin and insulin-like growth factor-I (IGF-I), remarkably extended longevity, and severe (in df/df mice) or mild (in GHRKO mice) thyroid hypofunction. Recently, by crossing df/df and GHRKO mice, double-mutant Ames dwarf/GHRKO (df/KO) mice were created. Interestingly, these mice are smaller than Ames dwarfs or GHRKOs, and also have reduced insulin and IGF-I levels. The aim of the study was to investigate if and to what extent certain thyroid morphological parameters, such as inner follicular surface area, inner follicular perimeter, as well as the follicular epithelium thickness are changed in the examined dwarf mice.

Methods

This quantification was performed in thyroids collected from df/df, GHRKO and df/KO female mice, at approximately 5–6 months of age. We used a computerized plotting programme that combines a live microscopic image of the slide with an operator-generated overlay.

Results

Inner follicular surface area and inner follicular perimeter were decreased in all examined kinds of dwarf mice as compared to normal animals. Furthermore, decreases in these two parameters were more pronounced in df/df and df/KO than in GHRKO mice. Concerning the follicular epithelium thickness, only a tendency towards decrease of this parameter was found in all three kinds of dwarf mice.

Conclusions

Parameters characterizing thyroid follicle size are decreased in all three examined models of dwarf mice, which may explain decreased thyroid hormone levels in both basal mutants (Ames dwarfs and GHRKOs). df/df mutation seems to predominate over GHRKO genetic intervention concerning their effects on thyroid growth. Beside TSH, also GH signaling seems to constitute a crucial element in the regulation of thyroid growth and, possibly, function.

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.