Genes and gene expression modules associated with caloric restriction and aging in the laboratory mouse

Genome-scale studies of aging: challenges and opportunities

Whole-genome studies involving a phenotype of interest are increasingly prevalent, in part due to a dramatic increase in speed at which many high throughput technologies can be performed coupled to simultaneous decreases in cost. This type of genome-scale methodology has been applied to the phenotype of lifespan, as well as to whole-transcriptome changes during the aging process or in mutants affecting aging. The value of high throughput discovery-based science in this field is clearly evident, but will it yield a true systems-level understanding of the aging process? Here we review some of this work to date, focusing on recent findings and the unanswered puzzles to which they point. In this context, we also discuss recent technological advances and some of the likely future directions that they portend.

Seven sirtuins for seven deadly diseases of aging

Sirtuins are a class of NAD(+)-dependent deacetylases having beneficial health effects. This extensive review describes the numerous intracellular actions of the seven mammalian sirtuins, their protein targets, intracellular localization, the pathways they modulate, and their role in common diseases of aging. Selective pharmacological targeting of sirtuins is of current interest in helping to alleviate global disease burden. Since all sirtuins are activated by NAD(+), strategies that boost NAD(+) in cells are of interest. While most is known about SIRT1, the functions of the six other sirtuins are now emerging. Best known is the involvement of sirtuins in helping cells adapt energy output to match energy requirements. SIRT1 and some of the other sirtuins enhance fat metabolism and modulate mitochondrial respiration to optimize energy harvesting. The AMP kinase/SIRT1-PGC-1α-PPAR axis and mitochondrial sirtuins appear pivotal to maintaining mitochondrial function. Downregulation with aging explains much of the pathophysiology that accumulates with aging. Posttranslational modifications of sirtuins and their substrates affect specificity. Although SIRT1 activation seems not to affect life span, activation of some of the other sirtuins might. Since sirtuins are crucial to pathways that counter the decline in health that accompanies aging, pharmacological agents that boost sirtuin activity have clinical potential in treatment of diabetes, cardiovascular disease, dementia, osteoporosis, arthritis, and other conditions. In cancer, however, SIRT1 inhibitors could have therapeutic value. Nutraceuticals such as resveratrol have a multiplicity of actions besides sirtuin activation. Their net health benefit and relative safety may have originated from the ability of animals to survive environmental changes by utilizing these stress resistance chemicals in the diet during evolution. Each sirtuin forms a key hub to the intracellular pathways affected.

Robust shifts in S100a9 expression with aging: a novel mechanism for chronic inflammation

The S100a8 and S100a9 genes encode a pro-inflammatory protein (calgranulin) that has been implicated in multiple diseases. However, involvement of S100a8/a9 in the basic mechanisms of intrinsic aging has not been established. In this study, we show that shifts in the abundance of S100a8 and S100a9 mRNA are a robust feature of aging in mammalian tissues, involving a range of cell types including the central nervous system. To identify transcription factors that control S100a9 expression, we performed a large-scale transcriptome analysis of 62 mouse and human cell types. We identified cell type-specific trends, as well as robust associations linking S100a9 coexpression to elevated frequency of ETS family motifs, and in particular, to motifs recognized by the transcription factor SPI/PU.1. Sparse occurrence of SATB1 motifs was also a strong predictor of S100a9 coexpression. These findings offer support for a novel mechanism by which a SPI1/PU.1-S100a9 axis sustains chronic inflammation during aging.

The role of ADAM17 in metabolic inflammation

The TNF-alpha Converting Enzyme (TACE), also called ADAM17 (A Disintegrin and A Metalloproteinase 17) is a type I transmembrane metalloproteinase involved in the shedding of the extracellular domain of several transmembrane proteins such as cytokines, growth factors, receptors and adhesion molecules. Some of these proteolytic events are part of cleavage cascades known as Regulated Intramembrane Proteolysis and lead to intracellular signaling. Evidence is provided that ADAM17 plays a role in atherosclerosis, in adipose tissue metabolism, insulin resistance and diabetes. The multitude of substrates cleaved by ADAM17 makes this enzyme an attractive candidate to study its role in inflammatory disorders. This review is focused on effects of ADAM17 in major metabolic tissues.

Cognitive dysfunction with aging and the role of inflammation

As the average lifespan continues to climb because of advances in medical care, there is a greater need to understand the factors that contribute to quality of life in the elderly. The capacity to live independently is highly significant in this regard, but is compromised by cognitive dysfunction. Aging is associated with decreases in cognitive function, including impairments in episodic memory and executive functioning. The prefrontal cortex appears to be particularly vulnerable to the effects of advancing age. Although the mechanism of age-related cognitive decline is not yet known, age-related inflammatory changes are likely to play a role. New insights from preclinical and clinical research may give rise to novel therapeutics which may have efficacy in slowing or preventing cognitive decline with advancing age.

Mechanisms of granulin deficiency: lessons from cellular and animal models

The identification of causative mutations in the (pro)granulin gene (GRN) has been a major breakthrough in the research on frontotemporal dementia (FTD). So far, all FTD-associated GRN mutations are leading to neurodegeneration through a “loss-of-function” mechanism, encouraging researchers to develop a growing number of cellular and animal models for GRN deficiency. GRN is a multifunctional secreted growth factor, and loss of its function can affect different cellular processes. Besides loss-of-function (i.e., mostly premature termination codons) mutations, which cause GRN haploinsufficiency through reduction of GRN expression, FTD-associated GRN missense mutations have also been identified. Several of these missense mutations are predicted to increase the risk of developing neurodegenerative diseases through altering various key biological properties of GRN-like protein secretion, proteolytic processing, and neurite outgrowth. With the use of cellular and animal models for GRN deficiency, the portfolio of GRN functions has recently been extended to include functions in important biological processes like energy and protein homeostasis, inflammation as well as neuronal survival, neurite outgrowth, and branching. Furthermore, GRN-deficient animal models have been established and they are believed to be promising disease models as they show accelerated aging and recapitulate at least some neuropathological features of FTD. In this review, we summarize the current knowledge on the molecular mechanisms leading to GRN deficiency and the lessons we learned from the established cellular and animal models. Furthermore, we discuss how these insights might help in developing therapeutic strategies for GRN-associated FTD.

Mitochondrial dysfunction and oxidative stress activate inflammasomes: impact on the aging process and age-related diseases

Oxidative stress and low-grade inflammation are the hallmarks of the aging process and are even more enhanced in many age-related degenerative diseases. Mitochondrial dysfunction and oxidative stress can provoke and potentiate inflammatory responses, but the mechanism has remained elusive. Recent studies indicate that oxidative stress can induce the assembly of multiprotein inflammatory complexes called the inflammasomes. Nod-like receptor protein 3 (NLRP3) is the major immune sensor for cellular stress signals, e.g., reactive oxygen species, ceramides, and cathepsin B. NLRP3 activation triggers the caspase-1-mediated maturation of the precursors of IL-1β and IL-18 cytokines. During aging, the autophagic clearance of mitochondria declines and dysfunctional mitochondria provoke chronic oxidative stress, which disturbs the cellular redox balance. Moreover, increased NF-κB signaling observed during aging could potentiate the expression of NLRP3 and cytokine proforms enhancing the priming of NLRP3 inflammasomes. Recent studies have demonstrated that NLRP3 activation is associated with several age-related diseases, e.g., the metabolic syndrome. We will review here the emerging field of inflammasomes in the appearance of the proinflammatory phenotype during the aging process and in age-related diseases.

Inflammaging: disturbed interplay between autophagy and inflammasomes

Inflammaging refers to a low-grade pro-inflammatory phenotype which accompanies aging in mammals. The aging process is associated with a decline in autophagic capacity which impairs cellular housekeeping, leading to protein aggregation and accumulation of dysfunctional mitochondria which provoke reactive oxygen species (ROS) production and oxidative stress. Recent studies have clearly indicated that the ROS production induced by damaged mitochondria can stimulate intracellular danger-sensing multiprotein platforms called inflammasomes. Nod-like receptor 3 (NLRP3) can be activated by many danger signals, e.g. ROS, cathepsin B released from destabilized lysosomes and aggregated proteins, all of which evoke cellular stress and are involved in the aging process. NLRP3 activation is also enhanced in many age-related diseases, e.g. atherosclerosis, obesity and type 2 diabetes. NLRP3 activates inflammatory caspases, mostly caspase-1, which cleave the inactive precursors of IL-1β and IL-18 and stimulate their secretion. Consequently, these cytokines provoke inflammatory responses and accelerate the aging process by inhibiting autophagy. In conclusion, inhibition of autophagic capacity with aging generates the inflammaging condition via the activation of inflammasomes, in particular NLRP3. We will provide here a perspective on the current research of the ROS-dependent activation of inflammasomes triggered by the decline in autophagic cleansing of dysfunctional mitochondria.

Context-Dependent Regulation of Autophagy by IKK-NF-κB Signaling: Impact on the Aging Process

The NF-κB signaling system and the autophagic degradation pathway are crucial cellular survival mechanisms, both being well conserved during evolution. Emerging studies have indicated that the IKK/NF-κB signaling axis regulates autophagy in a context-dependent manner. IKK complex and NF-κB can enhance the expression of Beclin 1 and other autophagy-related proteins and stimulate autophagy whereas as a feedback response, autophagy can degrade IKK components. Moreover, NF-κB signaling activates the expression of autophagy inhibitors (e.g., A20 and Bcl-2/xL) and represses the activators of autophagy (BNIP3, JNK1, and ROS). Several studies have indicated that NF-κB signaling is enhanced both during aging and cellular senescence, inducing a proinflammatory phenotype. The aging process is also associated with a decline in autophagic degradation. It seems that the activity of Beclin 1 initiation complex could be impaired with aging, since the expression of Beclin 1 decreases as does the activity of type III PI3K. On the other hand, the expression of inhibitory Bcl-2/xL proteins increases with aging. We will review the recent literature on the control mechanisms of autophagy through IKK/NF-κB signaling and emphasize that NF-κB signaling could be a potent repressor of autophagy with ageing.

Senemorphism: a novel perspective on aging patterns and its implication for diet-related biology

Aging can be described as the accumulation of changes in organisms over time. Aging in organisms undergoing caloric restriction (CR) is widely considered as a slowed version of aging under ad libitum (AL) conditions. However, here we argue that aging under optimized CR is fundamentally different from aging under AL based on the following facts: (1) Comparing the two dietary groups, several age-related changes run in the opposite direction over time; (2) Switching from an AL to a CR diet clearly reverts (not only delays) several "normal" accumulated changes; (3) major causes of death are as different between both groups as they are between species. These observations support the idea that CR and AL initially modulate different metabolic and physiological programs, which exclusively over time generate two biologically different organisms. Such distinct diet-related senescence is analogous to the divergent aging processes and causes of death observed between castes of social insects, such as queens versus workers ("caste-related-senescence") and also between breeding versus non-breeding semelparous animals ("reproduction-related-senescence"). All these aging phenotypes are different not because they accumulate changes at a different rate, but because they accumulate different changes over time. Thus, the environment does not simply affect the individual aging rate through stochastic effects (e.g. U.V.) but also modulates the activation of a particular program/strategy that influences lifespan (e.g. caste, calorie intake). We refer to the environment-dependent aging patterns encoded by the genome as "senemorphism". Based on this idea we propose experimental schemes for aging, evolution and biomedical research.

Will the real aging Sirtuin please stand up?

Initial studies linking Sirtuins to longevity in yeast initiated what is now a rich vein of aging research that is full of promise and fraught with controversy. Missing was a demonstration that enhanced Sirtuin expression extends lifespan in mammals. Now Kanfi et al. provide the evidence but with an interesting plot twist - the lesser known SIRT6 is the longevity factor.

Meta-profiles of gene expression during aging: limited similarities between mouse and human and an unexpectedly decreased inflammatory signature

BACKGROUND

Skin aging is associated with intrinsic processes that compromise the structure of the extracellular matrix while promoting loss of functional and regenerative capacity. These processes are accompanied by a large-scale shift in gene expression, but underlying mechanisms are not understood and conservation of these mechanisms between humans and mice is uncertain.

RESULTS

We used genome-wide expression profiling to investigate the aging skin transcriptome. In humans, age-related shifts in gene expression were sex-specific. In females, aging increased expression of transcripts associated with T-cells, B-cells and dendritic cells, and decreased expression of genes in regions with elevated Zeb1, AP-2 and YY1 motif density. In males, however, these effects were contrasting or absent. When age-associated gene expression patterns in human skin were compared to those in tail skin from CB6F1 mice, overall human-mouse correspondence was weak. Moreover, inflammatory gene expression patterns were not induced with aging of mouse tail skin, and well-known aging biomarkers were in fact decreased (e.g., Clec7a, Lyz1 and Lyz2). These unexpected patterns and weak human-mouse correspondence may be due to decreased abundance of antigen presenting cells in mouse tail skin with age.

CONCLUSIONS

Aging is generally associated with a pro-inflammatory state, but we have identified an exception to this pattern with aging of CB6F1 mouse tail skin. Aging therefore does not uniformly heighten inflammatory status across all mouse tissues. Furthermore, we identified both intercellular and intracellular mechanisms of transcriptome aging, including those that are sex- and species-specific.

The sirtuin SIRT6 regulates lifespan in male mice

The significant increase in human lifespan during the past century confronts us with great medical challenges. To meet these challenges, the mechanisms that determine healthy ageing must be understood and controlled. Sirtuins are highly conserved deacetylases that have been shown to regulate lifespan in yeast, nematodes and fruitflies. However, the role of sirtuins in regulating worm and fly lifespan has recently become controversial. Moreover, the role of the seven mammalian sirtuins, SIRT1 to SIRT7 (homologues of the yeast sirtuin Sir2), in regulating lifespan is unclear. Here we show that male, but not female, transgenic mice overexpressing Sirt6 (ref. 4) have a significantly longer lifespan than wild-type mice. Gene expression analysis revealed significant differences between male Sirt6-transgenic mice and male wild-type mice: transgenic males displayed lower serum levels of insulin-like growth factor 1 (IGF1), higher levels of IGF-binding protein 1 and altered phosphorylation levels of major components of IGF1 signalling, a key pathway in the regulation of lifespan. This study shows the regulation of mammalian lifespan by a sirtuin family member and has important therapeutic implications for age-related diseases.

A meta-analysis of caloric restriction gene expression profiles to infer common signatures and regulatory mechanisms

Caloric restriction, a reduction in calorie intake without malnutrition, retards age-related degeneration and extends lifespan in several organisms. CR induces multiple changes, yet its underlying mechanisms remain poorly understood. In this work, we first performed a meta-analysis of microarray CR studies in mammals and identified genes and processes robustly altered due to CR. Our results reveal a complex array of CR-induced changes and we re-identified several genes and processes previously associated with CR, such as growth hormone signalling, lipid metabolism and immune response. Moreover, our results highlight novel associations with CR, such as retinol metabolism and copper ion detoxification, as well as hint of a strong effect of CR on circadian rhythms that in turn may contribute to metabolic changes. Analyses of our signatures by integrating co-expression data, information on genetic mutants, and transcription factor binding site analysis revealed candidate regulators of transcriptional modules in CR. Our results hint at a transcriptional module involved in sterol metabolism regulated by Srebf1. A putative regulatory role of Ppara was also identified. Overall, our conserved molecular signatures of CR provide a comprehensive picture of CR-induced changes and help understand its regulatory mechanisms.

Potentiation of dietary restriction-induced lifespan extension by polyphenols

Dietary restriction (DR) extends lifespan across multiple species including mouse. Antioxidant plant extracts rich in polyphenols have also been shown to increase lifespan. We hypothesized that polyphenols might potentiate DR-induced lifespan extension. Twenty week old C57BL/6 mice were placed on one of three diets: continuous feeding (control), alternate day chow (Intermittent fed, IF), or IF supplemented with polyphenol antioxidants (PAO) from blueberry, pomegranate, and green tea extracts (IF+PAO). Both IF and IF+PAO groups outlived the control group and the IF+PAO group outlived the IF group (all p<0.001). In the brain, IF induced the expression of inflammatory genes and p38 MAPK phosphorylation, while the addition of PAO reduced brain inflammatory gene expression and p38 MAPK phosphorylation. Our data indicate that while IF overall promotes longevity, some aspects of IF-induced stress may paradoxically lessen this effect. Polyphenol compounds, in turn, may potentiate IF-induced longevity by minimizing specific components of IF-induced cell stress.

R-α-lipoic acid does not reverse hepatic inflammation of aging, but lowers lipid anabolism, while accentuating circadian rhythm transcript profiles

To determine the effects of age and lipoic acid supplementation on hepatic gene expression, we fed young (3 mo) and old (24 mo) male Fischer 344 rats a diet with or without 0.2% (wt/wt) R-α-lipoic acid (LA) for 2 wk. Total RNA isolated from liver tissue was analyzed by Affymetrix microarray to examine changes in transcriptional profiles. Results showed elevated proinflammatory gene expression in the aging liver and evidence for increased immune cell activation and tissue remodeling, together representing 45% of the age-related transcriptome changes. In addition, age-related increases in transcripts of genes related to fatty acid, triglyceride, and cholesterol synthesis, including acetyl-CoA carboxylase-β (Acacb) and fatty acid synthase (Fasn), were observed. Supplementation of old animals with LA did not reverse the necroinflammatory phenotype but, intriguingly, altered the expression of genes governing circadian rhythm. Most notably, Arntl, Npas2, and Per changed in a coordinated manner with respect to rhythmic transcription. LA further caused a decrease in transcripts of several bile acid and lipid synthesis genes, including Acacb and Fasn, which are regulated by first-order clock transcription factors. Similar effects of LA supplementation on bile acid and lipid synthesis genes were observed in young animals. Transcript changes of lipid metabolism genes were corroborated by a decrease in FASN and ACC protein levels. We conclude that advanced age is associated with a necroinflammatory phenotype and increased lipid synthesis, while chronic LA supplementation influences hepatic genes associated with lipid and energy metabolism and circadian rhythm, regardless of age.

SpliceAid 2: a database of human splicing factors expression data and RNA target motifs

Splicing is the most frequently altered biological process by mutations within gene regions. Information for splicing is recognized by several factors that bind pre-mRNA sequence and, through coordinated interaction, yield mature transcripts. Some in silico methods have been developed to predict if a mutation leads to aberrant splicing patterns. We previously created SpliceAid tool that is able to minimize false positive predictions because it adopts strictly experimental RNA target motifs bound by splicing proteins in humans. In order to improve prediction accuracy and better understand the splicing outcome, the tissue specificity of each splicing regulatory factor has to be taken into account. Here, we have developed SpliceAid 2 by adding the expression data related to the splicing factors extracted from the main proteomic and transcriptomic databases, true 5' and 3' splice sites, polypyrimidine tracts, and branch point sequences. The new version collects 2,220 target sites of 62 human splicing proteins and their expression data in 320 tissues per cell. SpliceAid 2 can be useful to foresee the splicing pattern alteration, to guide the identification of the molecular effect due to the mutations and to understand the tissue-specific alternative splicing. SpliceAid 2 is freely accessible at www.introni.it/spliceaid.html.

Caloric restriction and chronic inflammatory diseases

A reduction in calorie intake [caloric restriction (CR)] appears to consistently decrease the biological rate of aging in a variety of organisms as well as protect against age-associated diseases including chronic inflammatory disorders such as cardiovascular disease and diabetes. Although the mechanisms behind this observation are not fully understood, identification of the main metabolic pathways affected by CR has generated interest in finding molecular targets that could be modulated by CR mimetics. This review describes the general concepts of CR and CR mimetics as well as discusses evidence related to their effects on inflammation and chronic inflammatory disorders. Additionally, emerging evidence related to the effects of CR on periodontal disease in non-human primates is presented. While the implementation of this type of dietary intervention appears to be challenging in our modern society where obesity is a major public health problem, CR mimetics could offer a promising alternative to control and perhaps prevent several chronic inflammatory disorders including periodontal disease.

Accelerated aging in the tumor microenvironment: connecting aging, inflammation and cancer metabolism with personalized medicine

Cancer is thought to be a disease associated with aging. Interestingly, normal aging is driven by the production of ROS and mitochondrial oxidative stress, resulting in the cumulative accumulation of DNA damage. Here, we discuss how ROS signaling, NFκB- and HIF1-activation in the tumor microenvironment induces a form of "accelerated aging," which leads to stromal inflammation and changes in cancer cell metabolism. Thus, we present a unified model where aging (ROS), inflammation (NFκB) and cancer metabolism (HIF1), act as co-conspirators to drive autophagy ("self-eating") in the tumor stroma. Then, autophagy in the tumor stroma provides high-energy "fuel" and the necessary chemical building blocks, for accelerated tumor growth and metastasis. Stromal ROS production acts as a "mutagenic motor" and allows cancer cells to buffer-at a distance-exactly how much of a mutagenic stimulus they receive, further driving tumor cell selection and evolution. Surviving cancer cells would be selected for the ability to induce ROS more effectively in stromal fibroblasts, so they could extract more nutrients from the stroma via autophagy. If lethal cancer is a disease of "accelerated host aging" in the tumor stroma, then cancer patients may benefit from therapy with powerful antioxidants. Antioxidant therapy should block the resulting DNA damage, and halt autophagy in the tumor stroma, effectively "cutting off the fuel supply" for cancer cells. These findings have important new implications for personalized cancer medicine, as they link aging, inflammation and cancer metabolism with novel strategies for more effective cancer diagnostics and therapeutics.

Genome-wide expression profiling of five mouse models identifies similarities and differences with human psoriasis

Development of a suitable mouse model would facilitate the investigation of pathomechanisms underlying human psoriasis and would also assist in development of therapeutic treatments.

However, while many psoriasis mouse models have been proposed, no single model recapitulates all features of the human disease, and standardized validation criteria for psoriasis mouse models have not been widely applied. In this study, whole-genome transcriptional profiling is used to compare gene expression patterns manifested by human psoriatic skin lesions with those that occur in five psoriasis mouse models (K5-Tie2, imiquimod, K14-AREG, K5-Stat3C and K5-TGFbeta1). While the cutaneous gene expression profiles associated with each mouse phenotype exhibited statistically significant similarity to the expression profile of psoriasis in humans, each model displayed distinctive sets of similarities and differences in comparison to human psoriasis. For all five models, correspondence to the human disease was strong with respect to genes involved in epidermal development and keratinization. Immune and inflammation-associated gene expression, in contrast, was more variable between models as compared to the human disease. These findings support the value of all five models as research tools, each with identifiable areas of convergence to and divergence from the human disease. Additionally, the approach used in this paper provides an objective and quantitative method for evaluation of proposed mouse models of psoriasis, which can be strategically applied in future studies to score strengths of mouse phenotypes relative to specific aspects of human psoriasis.

Cardiomyopathy of aging in the mammalian heart is characterized by myocardial hypertrophy, fibrosis and a predisposition towards cardiomyocyte apoptosis and autophagy

Aging is associated with an increased incidence of heart failure, but the existence of an age-related cardiomyopathy remains controversial. Differences in strain, age and technique of measuring cardiac function differ between experiments, confounding the interpretation of these studies. Additionally, the structural and genetic profile at the onset of heart failure has not been extensively studied. We therefore performed serial echocardiography, which allows repeated assessment of left ventricular (LV) function, on a cohort of the same mice every 3 months as they aged and demonstrated that LV systolic dysfunction becomes apparent at 18 months of age. These aging animals had left ventricular hypertrophy and fibrosis, but did not have inducible ventricular tachyarrhythmias. Gene expression profiling of left ventricular tissue demonstrated 40 differentially expressed probesets and 36 differentially expressed gene ontology terms, largely related to inflammation and immunity. At this early stage of cardiac dysfunction, we observed increased cardiomyocyte expression of the pro-apoptotic activated caspase-3, but no actual increase in apoptosis. The aging hearts also have higher levels of anti-apoptotic and autophagic factors, which may have rendered protection from apoptosis. In conclusion, we describe the functional, structural and genetic changes in murine hearts as they first develop cardiomyopathy of aging.

The effects of aging vs. α7 nAChR subunit deficiency on the mouse brain transcriptome: aging beats the deficiency

Aging is accompanied by expression changes in multiple genes, and the brain is one of the tissues most vulnerable to aging. Since the α7 nicotinic acetylcholine receptor (nAChR) subunit has been associated with neurodevelopmental disorders and cognitive decline during aging, we hypothesized that its absence might affect gene expression profiles in aged brains. To study whether transcriptional changes occur due to aging, α7 deficiency, or both, we analyzed whole-brain transcriptomes of young (8 weeks) and aged (2 years) α7-deficient and wild-type control mice, using Mouse Genome 430 2.0 microarray. Highly significant expression changes were detected in 47 and 1,543 genes [after Bonferroni and false discovery rate (FDR) correction] in the brains of aged mice compared to young mice, regardless of their genotype. These included genes involved in immune system function and ribosome structure, as well as genes that were previously demonstrated as differentially expressed in aging human brains. Genotype-dependent changes were detected in only three genes, Chrna7 which encodes the α7 nAChR subunit, and two closely linked genes, likely due to a "mouse background effect." Expression changes dependent on age-genotype interaction were detected in 207 genes (with a low significance threshold). Age-dependent differential expression levels were approved in all nine genes that were chosen for validation by real-time RT-PCR. Our results suggest that the robust effect of aging on brain transcription clearly overcomes the almost negligible effect of α7 nAChR subunit deletion and that germ line deficiency of this subunit has a minor effect on brain expression profile in aged mice.

Differential effects of calorie restriction and exercise on the adipose transcriptome in diet-induced obese mice

We tested the hypothesis that obesity reversal by calorie restriction (CR) versus treadmill exercise (EX) differentially modulates adipose gene expression using 48 female C57BL/6 mice administered a diet-induced obesity (DIO) regimen for 8 weeks, then randomized to receive for 8 weeks either: (1) a control (AIN-76A) diet, fed ad libitum (DIO control); (2) a 30% CR regimen; (3) a treadmill EX regimen (with AIN-76A diet fed ad libitum); or (4) continuation of the DIO diet. Relative to the DIO controls, both CR and EX reduced adiposity by 35-40% and serum leptin levels by 80%, but only CR increased adiponectin and insulin sensitivity. Gene expression microarray analysis of visceral white adipose tissue revealed 209 genes responsive to both CR and EX, relative to the DIO group. However, CR uniquely altered expression of an additional 496 genes, whereas only 20 were uniquely affected by EX. Of the genes distinctly responsive to CR, 17 related to carbohydrate metabolism and glucose transport, including glucose transporter (GLUT) 4. Chromatin immunoprecipitation assays of the Glut4 promoter revealed that, relative to the DIO controls, CR significantly increased histone 4 acetylation, suggesting epigenetic regulation may underlie some of the differential effects of CR versus EX on the adipose transcriptome.

Metallothionein and the biology of aging

Metallothionein (MT) is a low molecular weight protein with anti-apoptotic properties that has been demonstrated to scavenge free radicals in vitro. MT has not been extensively investigated within the context of aging biology. The purpose of this review, therefore, is to discuss findings on MT that are relevant to basic aging mechanisms and to draw attention to the possible role of MT in pro-longevity interventions. MT is one of just a handful of proteins that, when overexpressed, has been demonstrated to increase mouse lifespan. MT also protects against development of obesity in mice provided a high fat diet as well as diet-induced oxidative stress damage. Abundance of MT is responsive to caloric restriction (CR) and inhibition of the insulin/insulin-like signaling (IIS) pathway, and elevated MT gene expression has been observed in tissues from fasted and CR-fed mice, long-lived dwarf mice, worms maintained under CR conditions, and long-lived daf-2 mutant worms. The dysregulation of MT in these systems is likely to have tissue-specific effects on aging outcomes. Further investigation will therefore be needed to understand how MT contributes to the response of invertebrates and mice to CR and the endocrine mutations studied by aging researchers.

Modulation of white adipose tissue proteome by aging and calorie restriction

Aging is associated with an accrual of body fat, progressive development of insulin resistance and other obesity comorbidities that contribute to decrease life span. Caloric restriction (CR), which primarily affects energy stores in adipose tissue, is known to extend life span and retard the aging process in animal models. In this study, a proteomic approach combining 2-DE and MS was used to identify proteins modulated by aging and CR in rat white adipose tissue proteome. Proteomic analysis revealed 133 differentially expressed spots, 57 of which were unambiguously identified by MS. Although CR opposed part of the age-associated protein expression patterns, many effects of CR were on proteins unaltered by age, suggesting that the effects of CR on adipose tissue are only weakly related to those of aging. Particularly, CR and aging altered glucose, intermediate and lipid metabolism, with CR enhancing the expression of enzymes involved in oxalacetate and NADPH production, lipid biosynthesis and lipolysis. Consistently, insulin-β and β3-adrenergic receptors were also increased by CR, which denotes improved sensitivity to lipogenic/lipolytic stimuli. Other beneficial outcomes of CR were an improvement in oxidative stress, preventing the age-associated decrease in several antioxidant enzymes. Proteins involved in cytoskeleton, iron storage, energy metabolism and several proteins with novel or unknown functions in adipose tissue were also modulated by age and/or CR. Such orchestrated changes in expression of multiple proteins provide insights into the mechanism underlying CR effects, ultimately allowing the discovery of new markers of aging and targets for the development of CR-mimetics.

ER stress and hormetic regulation of the aging process

An ability to mount a stress resistance under pressure is a major host defence mechanism and has been a fundamental force during evolution. However, the adaptation capacity clearly declines during aging and this loss of stress resistance accelerates the aging process exposing the organism to degenerative diseases. The effect of stress on organisms seems to be a dose-dependent response, i.e. mild stress induces a stress tolerance and extends the lifespan whereas excessive stress accentuates the aging process. This paradox is known as hormesis in aging research. It is essential to distinguish the intensity of cellular stress and thus mount an appropriate host defence. The endoplasmic reticulum (ER) contains three branches of stress transducers, i.e. IRE1, PERK, and ATF6 pathways, all of which recognize stress-related disturbances in the function of ER. These transducers trigger a complex signaling network which activates an unfolded protein response (UPR). Interestingly, ER stress transducers can distinguish the intensity of ER stress and induce a dose-dependent UPR, either adaptive response to stress or apoptotic cell death. The efficiency of the stress recognition system and UPR signaling declines during aging. We will discuss the role of ER stress in hormetic regulation of aging process and longevity.

Genetic dissection of dietary restriction in mice supports the metabolic efficiency model of life extension

Dietary restriction (DR) has been used for decades to retard aging in rodents, but its mechanism of action remains an enigma. A principal roadblock has been that DR affects many different processes, making it difficult to distinguish cause and effect. To address this problem, we applied a quantitative genetics approach utilizing the ILSXISS series of mouse recombinant inbred strains. Across 42 strains, mean female lifespan ranged from 380 to 1070days on DR (fed 60% of ad libitum [AL]) and from 490 to 1020days on an AL diet. Longevity under DR and AL is under genetic control, showing 34% and 36% heritability, respectively. There was no correlation between lifespans on DR and AL; thus different genes modulate longevity under the two regimens. DR lifespans are significantly correlated with female fertility after return to an AL diet after various periods of DR (R=0.44, P=0.006). We assessed fuel efficiency (FE, ability to maintain growth and body weight independent of absolute food intake) using a multivariate approach and found it to be correlated with longevity and female fertility, suggesting possible causality. We found several quantitative trait loci responsible for these traits, mapping to chromosomes 7, 9, and 15. We present a metabolic model in which the anti-aging effects of DR are consistent with the ability to efficiently utilize dietary resources.