PPARs in Calorie Restricted and Genetically Long-Lived Mice

Programmed PPAR-α downregulation induces inflammaging by suppressing fatty acid catabolism in monocytes

Inflammaging is associated with an increased risk of chronic disease. Monocytes are the principal immune cells for the production of inflammatory cytokines and contribute to inflammaging in the elderly. However, the underlying mechanisms remain largely unknown. Here, we found that monocytes from aged individuals contained high levels of lipid droplets (LDs), and this increase was correlated with impaired fatty acid oxidation. Downregulated peroxisome proliferator-activated receptor (PPAR)-α may be responsible for the pro-inflammatory phenotype of monocytes in aged individuals, as it was positively correlated with LD accumulation and increasing TNF-α concentration. Interestingly, interventions that result in PPAR-α upregulation, such as fenofibrate treatment, TNF-α neutralization, or calorie restriction, reversed the effect of aging on monocytes. Thus the downregulation of PPAR-α and LD levels in monocytes represents a novel biomarker for inflammaging. Furthermore, PPAR-α activation in the elderly may also alleviate long-term inflammaging, preventing the development of life-limiting chronic diseases.

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Monocytes from aged individuals contained high levels of lipid droplets (LDs)

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Downregulated PPAR-α is responsible for the aged monocytes profiles

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TNF-α might accelerate monocyte aging by downregulating PPAR-α expression

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PPAR-α activation in the elderly may also alleviate long-term inflammaging

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

CR reprograms acetyl-CoA metabolism and induces long-chain acyl-CoA dehydrogenase and CrAT expression

Calorie restriction (CR), an age delaying diet, affects fat oxidation through poorly understood mechanisms. We investigated the effect of CR on fat metabolism gene expression and intermediate metabolites of fatty acid oxidation in the liver. We found that CR changed the liver acylcarnitine profile: acetylcarnitine, short‐chain acylcarnitines, and long‐chain 3‐hydroxy‐acylcarnitines increased, and several long‐chain acylcarnitines decreased. Acetyl‐CoA and short‐chain acyl‐CoAs were also increased in CR. CR did not affect the expression of CPT1 and upregulated the expression of long‐chain and very‐long‐chain Acyl‐CoA dehydrogenases (LCAD and VLCAD, respectively). The expression of downstream enzymes such as mitochondrial trifunctional protein and enzymes in medium‐ and short‐chain acyl‐CoAs oxidation was not affected in CR. CR shifted the balance of fatty acid oxidation enzymes and fatty acid metabolites in the liver. Acetyl‐CoA generated through beta‐oxidation can be used for ketogenesis or energy production. In agreement, blood ketone bodies increased under CR in a time of the day‐dependent manner. Carnitine acetyltransferase (CrAT) is a bidirectional enzyme that interconverts short‐chain acyl‐CoAs and their corresponding acylcarnitines. CrAT expression was induced in CR liver supporting the increased acetylcarnitine and short‐chain acylcarnitine production. Acetylcarnitine can freely travel between cellular sub‐compartments. Supporting this CR increased protein acetylation in the mitochondria, cytoplasm, and nucleus. We hypothesize that changes in acyl‐CoA and acylcarnitine levels help to control energy metabolism and contribute to metabolic flexibility under CR.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Shedding Light on the Effects of Calorie Restriction and its Mimetics on Skin Biology

During the aging process of an organism, the skin gradually loses its structural and functional characteristics. The skin becomes more fragile and vulnerable to damage, which may contribute to age-related diseases and even death. Skin aging is aggravated by the fact that the skin is in direct contact with extrinsic factors, such as ultraviolet irradiation. While calorie restriction (CR) is the most effective intervention to extend the lifespan of organisms and prevent age-related disorders, its effects on cutaneous aging and disorders are poorly understood. This review discusses the effects of CR and its alternative dietary intake on skin biology, with a focus on skin aging. CR structurally and functionally affects most of the skin and has been reported to rescue both age-related and photo-induced changes. The anti-inflammatory, anti-oxidative, stem cell maintenance, and metabolic activities of CR contribute to its beneficial effects on the skin. To the best of the author’s knowledge, the effects of fasting or a specific nutrient-restricted diet on skin aging have not been evaluated; these strategies offer benefits in wound healing and inflammatory skin diseases. In addition, well-known CR mimetics, including resveratrol, metformin, rapamycin, and peroxisome proliferator-activated receptor agonists, show CR-like prevention against skin aging. An overview of the role of CR in skin biology will provide valuable insights that would eventually lead to improvements in skin health.

Senoinflammation: A major mediator underlying age-related metabolic dysregulation

Chronic inflammation is a complex and unresolved inflammatory response with low-grade multivariable patterns that aggravate systemic pathophysiological conditions and the aging process. To redefine and delineate these age-related complex inflammatory phenomena at the molecular, cellular, and systemic levels, the concept of "Senoinflammation" was recently formulated. In this review, we describe the accumulated data on both the multiphase systemic inflammatory process and the cellular proinflammatory signaling pathway. We also describe the proinflammatory mechanisms underlying the metabolic molecular pathways in aging. Additionally, we review age-related lipid accumulation, the role of the inflammatory senescence-associated secretory phenotype (SASP), the involvement of cytokine/chemokine secretion, endoplasmic reticulum (ER) stress, insulin resistance, and autophagy. The last section of the review highlights the modulation of the senoinflammatory process by the anti-aging and anti-inflammatory action of calorie restriction (CR). Evidence from aging and CR research strongly suggests that SASP from senescent cells may be the major source of secreted cytokines and chemokines during aging. A better understanding of the mechanisms underpinning the senoinflammatory response and the mitigating role of CR will provide insights into the molecular mechanisms of chronic inflammation and aging for potential interventions.

Anti-aging Effects of Calorie Restriction (CR) and CR Mimetics based on the Senoinflammation Concept

Chronic inflammation, a pervasive feature of the aging process, is defined by a continuous, multifarious, low-grade inflammatory response. It is a sustained and systemic phenomenon that aggravates aging and can lead to age-related chronic diseases. In recent years, our understanding of age-related chronic inflammation has advanced through a large number of investigations on aging and calorie restriction (CR). A broader view of age-related inflammation is the concept of senoinflammation, which has an outlook beyond the traditional view, as proposed in our previous work. In this review, we discuss the effects of CR on multiple phases of proinflammatory networks and inflammatory signaling pathways to elucidate the basic mechanism underlying aging. Based on studies on senoinflammation and CR, we recognized that senescence-associated secretory phenotype (SASP), which mainly comprises cytokines and chemokines, was significantly increased during aging, whereas it was suppressed during CR. Further, we recognized that cellular metabolic pathways were also dysregulated in aging; however, CR mimetics reversed these effects. These results further support and enhance our understanding of the novel concept of senoinflammation, which is related to the metabolic changes that occur in the aging process. Furthermore, a thorough elucidation of the effect of CR on senoinflammation will reveal key insights and allow possible interventions in aging mechanisms, thus contributing to the development of new therapies focused on improving health and longevity.

Pirfenidone Is an Agonistic Ligand for PPARα and Improves NASH by Activation of SIRT1/LKB1/pAMPK

Nonalcoholic steatohepatitis (NASH) is recognized by hepatic lipid accumulation, inflammation, and fibrosis. No studies have evaluated the prolonged‐release pirfenidone (PR‐PFD) properties on NASH features. The aim of this study is to evaluate how PR‐PFD performs on metabolic functions, and provide insight on a mouse model of human NASH. Male C57BL/6J mice were fed with either normo diet or high‐fat/carbohydrate diet for 16 weeks and a subgroup also fed with PR‐PFD (300 mg/kg/day). An insulin tolerance test was performed at the end of treatment. Histological analysis, determination of serum hormones, adipocytokines measurement, and evaluation of proteins by western blot was performed. Molecular docking, in silico site‐directed mutagenesis, and in vitro experiments using HepG2 cultured cells were performed to validate PR‐PFD binding to peroxisome proliferator–activated receptor alpha (PPAR‐α), activation of PPAR‐α promoter, and sirtuin 1 (SIRT1) protein expression. Compared with the high‐fat group, the PR‐PFD‐treated mice displayed less weight gain, cholesterol, very low density lipoprotein and triglycerides, and showed a significant reduction of hepatic macrosteatosis, inflammation, hepatocyte ballooning, fibrosis, epididymal fat, and total adiposity. PR‐PFD restored levels of insulin, glucagon, adiponectin, and resistin along with improved insulin resistance. Noteworthy, SIRT1–liver kinase B1–phospho‐5′ adenosine monophosphate–activated protein kinase signaling and the PPAR‐α/carnitine O‐palmitoyltransferase 1/acyl‐CoA oxidase 1 pathway were clearly induced in high fat + PR‐PFD mice. In HepG2 cells incubated with palmitate, PR‐PFD induced activation and nuclear translocation of both PPARα and SIRT1, which correlated with increased SIRT1 phosphorylated in serine 47, suggesting a positive feedback loop between the two proteins. These results were confirmed with both synthetic PPAR‐α and SIRT1 activators and inhibitors. Finally, we found that PR‐PFD is a true agonist/ligand for PPAR‐α. Conclusions: PR‐PFD provided an anti‐steatogenic effect and protection for inflammation and fibrosis.

SIRT6 Promotes Hepatic Beta-Oxidation via Activation of PPARα

The pro-longevity enzyme SIRT6 regulates various metabolic pathways. Gene expression analyses in SIRT6 heterozygotic mice identify significant decreases in PPARα signaling, known to regulate multiple metabolic pathways. SIRT6 binds PPARα and its response element within promoter regions and activates gene transcription. Sirt6+/- results in significantly reduced PPARα-induced β-oxidation and its metabolites and reduced alanine and lactate levels, while inducing pyruvate oxidation. Reciprocally, starved SIRT6 transgenic mice show increased pyruvate, acetylcarnitine, and glycerol levels and significantly induce β-oxidation genes in a PPARα-dependent manner. Furthermore, SIRT6 mediates PPARα inhibition of SREBP-dependent cholesterol and triglyceride synthesis. Mechanistically, SIRT6 binds PPARα coactivator NCOA2 and decreases liver NCOA2 K780 acetylation, which stimulates its activation of PPARα in a SIRT6-dependent manner. These coordinated SIRT6 activities lead to regulation of whole-body respiratory exchange ratio and liver fat content, revealing the interactions whereby SIRT6 synchronizes various metabolic pathways, and suggest a mechanism by which SIRT6 maintains healthy liver.

Growth Hormone Deficiency: Health and Longevity

The important role of GH in the control of mammalian longevity was first deduced from extended longevity of mice with genetic GH deficiency (GHD) or GH resistance. Mice with isolated GHD (IGHD) due to GHRH or GHRH receptor mutations, combined deficiency of GH, prolactin, and TSH, or global deletion of GH receptors live longer than do their normal siblings. They also exhibit multiple features of delayed and/or slower aging, accompanied by extension of healthspan. The unexpected, remarkable longevity benefit of severe endocrine defects in these animals presumably represents evolutionarily conserved trade-offs among aging, growth, maturation, fecundity, and the underlying anabolic processes. Importantly, the negative association of GH signaling with longevity extends to other mammalian species, apparently including humans. Data obtained in humans with IGHD type 1B, owing to a mutation of the GHRH receptor gene, in the Itabaianinha County, Brazil, provide a unique opportunity to study the impact of severe reduction in GH signaling on age-related characteristics, health, and functionality. Individuals with IGHD are characterized by proportional short stature, doll facies, high-pitched voices, and central obesity. They have delayed puberty but are fertile and generally healthy. Moreover, these IGHD individuals are partially protected from cancer and some of the common effects of aging and can attain extreme longevity, 103 years of age in one case. We think that low, but detectable, residual GH secretion combined with life-long reduction of circulating IGF-1 and with some tissue levels of IGF-1 and/or IGF-2 preserved may account for the normal longevity and apparent extension of healthspan in these individuals.

Hepatic gene body hypermethylation is a shared epigenetic signature of murine longevity

Dietary, pharmacological and genetic interventions can extend health- and lifespan in diverse mammalian species. DNA methylation has been implicated in mediating the beneficial effects of these interventions; methylation patterns deteriorate during ageing, and this is prevented by lifespan-extending interventions. However, whether these interventions also actively shape the epigenome, and whether such epigenetic reprogramming contributes to improved health at old age, remains underexplored. We analysed published, whole-genome, BS-seq data sets from mouse liver to explore DNA methylation patterns in aged mice in response to three lifespan-extending interventions: dietary restriction (DR), reduced TOR signaling (rapamycin), and reduced growth (Ames dwarf mice). Dwarf mice show enhanced DNA hypermethylation in the body of key genes in lipid biosynthesis, cell proliferation and somatotropic signaling, which strongly correlates with the pattern of transcriptional repression. Remarkably, DR causes a similar hypermethylation in lipid biosynthesis genes, while rapamycin treatment increases methylation signatures in genes coding for growth factor and growth hormone receptors. Shared changes of DNA methylation were restricted to hypermethylated regions, and they were not merely a consequence of slowed ageing, thus suggesting an active mechanism driving their formation. By comparing the overlap in ageing-independent hypermethylated patterns between all three interventions, we identified four regions, which, independent of genetic background or gender, may serve as novel biomarkers for longevity-extending interventions. In summary, we identified gene body hypermethylation as a novel and partly conserved signature of lifespan-extending interventions in mouse, highlighting epigenetic reprogramming as a possible intervention to improve health at old age.

PPARs and Metabolic Disorders Associated with Challenged Adipose Tissue Plasticity

Peroxisome proliferator-activated receptors (PPARs) are members of a family of nuclear hormone receptors that exert their transcriptional control on genes harboring PPAR-responsive regulatory elements (PPRE) in partnership with retinoid X receptors (RXR). The activation of PPARs coordinated by specific coactivators/repressors regulate networks of genes controlling diverse homeostatic processes involving inflammation, adipogenesis, lipid metabolism, glucose homeostasis, and insulin resistance. Defects in PPARs have been linked to lipodystrophy, obesity, and insulin resistance as a result of the impairment of adipose tissue expandability and functionality. PPARs can act as lipid sensors, and when optimally activated, can rewire many of the metabolic pathways typically disrupted in obesity leading to an improvement of metabolic homeostasis. PPARs also contribute to the homeostasis of adipose tissue under challenging physiological circumstances, such as pregnancy and aging. Given their potential pathogenic role and their therapeutic potential, the benefits of PPARs activation should not only be considered relevant in the context of energy balance-associated pathologies and insulin resistance but also as potential relevant targets in the context of diabetic pregnancy and changes in body composition and metabolic stress associated with aging. Here, we review the rationale for the optimization of PPAR activation under these conditions.

Reversing age-associated arterial dysfunction: insight from preclinical models

Cardiovascular diseases (CVDs) remain the leading causes of death in the United States, and advancing age is a primary risk factor. Impaired endothelium-dependent dilation and increased stiffening of the arteries with aging are independent predictors of CVD. Increased tissue and systemic oxidative stress and inflammation underlie this age-associated arterial dysfunction. Calorie restriction (CR) is the most powerful intervention known to increase life span and improve age-related phenotypes, including arterial dysfunction. However, the translatability of long-term CR to clinical populations is limited, stimulating interest in the pursuit of pharmacological CR mimetics to reproduce the beneficial effects of CR. The energy-sensing pathways, mammalian target of rapamycin, AMPK, and sirtuin-1 have all been implicated in the beneficial effects of CR on longevity and/or physiological function and, as such, have emerged as potential targets for therapeutic intervention as CR mimetics. Although manipulation of each of these pathways has CR-like benefits on arterial function, the magnitude and/or mechanisms can be disparate from that of CR. Nevertheless, targeting these pathways in older individuals may provide some benefits against arterial dysfunction and CVD. The goal of this review is to provide a brief discussion of the mechanisms and pathways underlying age-associated dysfunction in large arteries, explain how these are impacted by CR, and to present the available evidence, suggesting that targets for energy-sensing pathways may act as vascular CR mimetics.

The Involvement of PPARs in the Selective Regulation of Brain CYP2D by Growth Hormone

Brain CYP2D is responsible for the synthesis of endogenous neurotransmitters such as dopamine and serotonin. This study is to investigate the effects of cerebral CYP2D on mouse behavior and the mechanism whereby growth hormone regulates brain CYP2D. The inhibition of cerebellar CYP2D significantly affected the spatial learning and exploratory behavior of mice. CYP2D expression was lower in the brain in GHR-/- mice than that in WT mice; however, hepatic CYP2D levels were similar. Brain PPARα expression in male GHR-/- mice were markedly higher than those in WT mice, while brain PPARγ levels were decreased or unchanged in different regions. However, both hepatic PPARα and PPARγ in male GHR-/- mice were markedly higher than those in WT mice. Pulsatile GH decreased the PPARα mRNA level and increased the mRNA levels of CYP2D6 and PPARγ in SH-SY5Y cells. A luciferase assay showed that PPARγ activated the CYP2D6 gene promoter while PPARα inhibited its function. Pulsatile GH decreased the binding of PPARα to the CYP2D6 promoter by 40% and promoted the binding of PPARγ to the CYP2D6 promoter by approximately 60%. The male GH secretory pattern altered PPAR expression and the binding of PPARs to the CYP2D promoter, leading to the elevation of brain CYP2D in a tissue-specific manner. Growth hormone may alter the learning and memory functions in patients receiving GH replacement therapy via brain CYP2D.

Deciphering the Roles of PPARγ in Adipocytes via Dynamic Change of Transcription Complex

Peroxisome proliferator-activated receptor γ (PPARγ), a ligand-dependent transcription factor highly expressed in adipocytes, is a master regulator of adipogenesis and lipid storage, a central player in thermogenesis and an active modulator of lipid metabolism and insulin sensitivity. As a nuclear receptor governing numerous target genes, its specific signaling transduction relies on elegant transcriptional and post-translational regulations. Notably, in response to different metabolic stimuli, PPARγ recruits various cofactors and forms distinct transcriptional complexes that change dynamically in components and epigenetic modification to ensure specific signal transduction. Clinically, PPARγ activation via its full agonists, thiazolidinediones, has been shown to improve insulin sensitivity and induce browning of white fat, while undesirably induce weight gain, visceral obesity and other adverse effects. Thus, deciphering the combinatorial interactions between PPARγ and its transcriptional partners and their preferential regulatory network in the processes of development, function and senescence of adipocytes would provide us the molecular basis for developing novel partial agonists that promote benefits of PPARγ signaling without detrimental side effects. In this review, we discuss the dynamic components and precise regulatory mechanisms of the PPARγ-cofactors complexes in adipocytes, as well as perspectives in treating metabolic diseases via specific PPARγ signaling.

A Long-lived Mouse Lacking Both Growth Hormone and Growth Hormone Receptor: A New Animal Model for Aging Studies

Disruption of the growth hormone (GH) signaling pathway promotes insulin sensitivity and is associated with both delayed aging and extended longevity. Two kinds of long-lived mice-Ames dwarfs (df/df) and GH receptor gene-disrupted knockouts (GHRKO) are characterized by a suppressed GH axis with a significant reduction of body size and decreased plasma insulin-like growth factor-1 (IGF-1) and insulin levels. Ames dwarf mice are deficient in GH, prolactin, and thyrotropin, whereas GHRKOs are GH resistant and are dwarf with decreased circulating IGF-1 and increased GH. Crossing Ames dwarfs and GHRKOs produced a new mouse line (df/KO), lacking both GH and GH receptor. These mice are characterized by improved glucose tolerance and increased adiponectin level, which could imply that these mice should be also characterized by additional life-span extension when comparing with GHRKOs and Ames dwarfs. Importantly, our longevity experiments showed that df/KO mice maintain extended longevity when comparing with N control mice; however, they do not live longer than GHRKO and Ames df/df mice. These important findings indicate that silencing GH signal is important to extend the life span; however, further decrease of body size in mice with already inhibited GH signal does not extend the life span regardless of improved some health-span markers.

PPAR mRNA Levels Are Modified by Dietary n-3 Fatty Acid Restriction and Energy Restriction in the Brain and Liver of Growing Rats

BACKGROUND

Without dietary sources of n-3 (ω-3) long-chain polyunsaturated fatty acids (LCPUFAs), α-linolenic acid (ALA; 18:3n-3) is the precursor for docosahexaenoic acid (DHA; 22:6n-3). It is not known how energy restriction (ER) affects ALA conversion to DHA.

OBJECTIVE

We tested the hypothesis that ER reduces n-3 LCPUFA concentrations in tissues of growing rats fed diets replete with and deficient in ALA.

METHODS

Male Sprague-Dawley rats (23 d old) were provided AIN93G diets (4 wk) made with soybean oil (SO; ALA sufficient) or corn oil (CO; ALA deficient) providing 16% of energy as fat. For each dietary oil, ER rats were individually pair-fed 75% of another rat's ad libitum (AL) intake. Fatty acid (FA) concentrations in brain regions, liver, and plasma were analyzed. Expression of peroxisome proliferator-activated receptors (PPARs), uncoupling proteins (UCPs), and mitochondrial DNA was analyzed in the brain and liver.

RESULTS

AL rats consuming CO had a 65% lower concentration of n-3 docosapentaenoic acid (22:5n-3) and a 10% lower DHA concentration in the cerebral cortex and cerebellum than did the SO-AL group. ER did not alter cerebral n-3 LCPUFA status. Liver n-3 LCPUFA concentrations were reduced in rats fed CO compared with SO. ER reduced hepatic linoleic acid (18:2n-6), ALA, and arachidonic acid (20:4n-6) regardless of oil. ER and n-3 FA deficiency had independent effects on the mRNA levels of Pparα, Pparβ/δ, and Pparγ in the liver, cerebral cortex, and cerebellum. ER reduced Ucp3 mRNA by nearly 50% in the cerebral cortex, cerebellum, and liver, and Ucp5 mRNA was 30% lower in the cerebellum of rats receiving the CO diet.

CONCLUSIONS

Small perturbations in PUFA concentration and ER modify the mRNA levels of Ppar and Ucp in the juvenile rat brain. More research is needed to identify the long-term physiologic and behavioral impacts of ER and PUFA restriction in the juvenile brain.

The role of transplanted visceral fat from the long-lived growth hormone receptor knockout mice on insulin signaling

Growth hormone receptor knockout mice (GHRKO) are characterized by high insulin sensitivity and extended lifespan. Interestingly, the secretory activity of visceral fat in GHRKO mice is altered, stimulating whole body insulin sensitivity. In this study, we transplanted normal (N) mice with visceral fat pads from GHRKO or N mice to determine the role of visceral fat on the insulin signaling. We found that the transplant of visceral fat from GHRKO mice to N mice (N-GHRKO) improved whole body insulin sensitivity when comparing with sham-operated mice (N-S) and with mice that received visceral fat from N mice (N-N). This was associated with increased hepatic insulin sensitivity as observed by the increased phosphorylated insulin receptor and increased hepatic expression of Pparα and Pparγ. In conclusion, we demonstrated that visceral fat transplant from GHRKO mice into normal mice enhanced insulin sensitivity and glucose tolerance. These results further confirm the differential physiological role played by visceral adipose tissue from GH receptor deficient mice, indicating that the increase of this fat depot can be associated with beneficial effects on insulin signaling and longevity.

Intestinal PPARγ signalling is required for sympathetic nervous system activation in response to caloric restriction

Nuclear receptor PPARγ has been proven to affect metabolism in multiple tissues, and has received considerable attention for its involvement in colon cancer and inflammatory disease. However, its role in intestinal metabolism has been largely ignored. To investigate this potential aspect of PPARγ function, we submitted intestinal epithelium-specific PPARγ knockout mice (iePPARγKO) to a two-week period of 25% caloric restriction (CR), following which iePPARγKO mice retained more fat than their wild type littermates. In attempting to explain this discrepancy, we analysed the liver, skeletal muscle, intestinal lipid trafficking, and the microbiome, none of which appeared to contribute to the adiposity phenotype. Interestingly, under conditions of CR, iePPARγKO mice failed to activate their sympathetic nervous system (SNS) and increase CR-specific locomotor activity. These KO mice also manifested a defective control of their body temperature, which was overly reduced. Furthermore, the white adipose tissue of iePPARγKO CR mice showed lower levels of both hormone-sensitive lipase, and its phosphorylated form. This would result from impaired SNS signalling and possibly cause reduced lipolysis. We conclude that intestinal epithelium PPARγ plays an essential role in increasing SNS activity under CR conditions, thereby contributing to energy mobilization during metabolically stressful episodes.

Calorie restriction regulates circadian clock gene expression through BMAL1 dependent and independent mechanisms

Feeding behavior, metabolism and circadian clocks are interlinked. Calorie restriction (CR) is a feeding paradigm known to extend longevity. We found that CR significantly affected the rhythms in the expression of circadian clock genes in mice on the mRNA and protein levels, suggesting that CR reprograms the clocks both transcriptionally and post-transcriptionally. The effect of CR on gene expression was distinct from the effects of time-restricted feeding or fasting. Furthermore, CR affected the circadian output through up- or down-regulation of the expression of several clock-controlled transcriptional factors and the longevity candidate genes. CR-dependent effects on some clock gene expression were impaired in the liver of mice deficient for BMAL1, suggesting importance of this transcriptional factor for the transcriptional reprogramming of the clock, however, BMAL1- independent mechanisms also exist. We propose that CR recruits biological clocks as a natural mechanism of metabolic optimization under conditions of limited energy resources.

Omega-3 fatty acids partially revert the metabolic gene expression profile induced by long-term calorie restriction

Calorie restriction (CR) consistently extends longevity and delays age-related diseases across several animal models. We have previously shown that different dietary fat sources can modulate life span and mitochondrial ultrastructure, function and membrane fatty acid composition in mice maintained on a 40% CR. In particular, animals consuming lard as the main fat source (CR-Lard) lived longer than CR mice consuming diets with soybean oil (CR-Soy) or fish oil (CR-Fish) as the predominant lipid source. In the present work, a transcriptomic analysis in the liver and skeletal muscle was performed in order to elucidate possible mechanisms underlying the changes in energy metabolism and longevity induced by dietary fat in CR mice. After 8 months of CR, transcription downstream of several mediators of inflammation was inhibited in liver. In contrast, proinflammatory signaling was increased in the CR-Fish versus other CR groups. Dietary fish oil induced a gene expression pattern consistent with increased transcriptional regulation by several cytokines (TNF, GM-CSF, TGF-β) and sex hormones when compared to the other CR groups. The CR-Fish also had lower expression of genes involved in fatty acid biosynthesis and increased expression of mitochondrial and peroxisomal fatty acid β-oxidation genes than the other CR diet groups. Our data suggest that a diet high in n-3 PUFA, partially reverts CR-related changes in gene expression of key processes, such as inflammation and steroid hormone signaling, and this may mitigate life span extension with CR in mice consuming diets high in fish oil.

PPARα Agonist WY-14643 Induces SIRT1 Activity in Rat Fatty Liver Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) remains a frequent complication in surgery, especially in case of steatotic livers that present decreased tolerance towards IRI. Apart from its major role in metabolism, activation of peroxisome proliferator-activated receptor α (PPARα) has been related with positive effects on IRI. In addition, the deacetylase enzyme sirtuin 1 (SIRT1) has recently emerged as a promising target for preventing IRI, through its interaction with stress-related mechanisms, such as endoplasmic reticulum stress (ERS). Taking this into account, this study aims to explore whether PPARα agonist WY-14643 could protect steatotic livers against IRI through sirtuins and ERS signaling pathway. Obese Zucker rats were pretreated or not pretreated with WY-14643 (10 mg/kg intravenously) and then submitted to partial (70%) hepatic ischemia (1 hour) followed by 24 hours of reperfusion. Liver injury (ALT levels), lipid peroxidation (MDA), SIRT1 activity, and the protein expression of SIRT1 and SIRT3 and ERS parameters (IRE1α, peIF2, caspase 12, and CHOP) were evaluated. Treatment with WY-14643 reduced liver injury in fatty livers, enhanced SIRT1 activity, and prevented ERS. Together, our results indicated that PPARα agonist WY-14643 may exert its protective effect in fatty livers, at least in part, via SIRT1 induction and ERS prevention.

Effects of MHY908, a New Synthetic PPARα/γ Dual Agonist, on Inflammatory Responses and Insulin Resistance in Aged Rats

Insulin resistance is common with aging and is associated with the inflammatory response in both humans and rodents. A number of peroxisome proliferator-activated receptor (PPAR) α/γ dual agonists have been tested for their abilities to attenuate insulin resistance and type 2 diabetes. However, there is no study on the effects of PPARα/γ dual agonists on inflammation and insulin resistance during aging. In the present study, we investigated the ability of 2-[4-(5-chlorobenzothiazothiazol-2-yl)phenoxy]-2-methyl-propionic acid (MHY908), a newly synthesized novel PPARα/γ dual agonist, to suppress the inflammatory response and attenuate insulin resistance in aged rats. Twenty-month-old rats were divided into four groups: ad libitum fed, ad libitum fed supplemented with MHY908 (1 mg and 3 mg/kg/day for 4 weeks), and 40% calorie restricted. Six-month-old ad libitum fed rats were used as an age control. The aged rats supplemented with MHY908 showed reduced serum glucose, triglyceride, and insulin levels, as well as reduced liver triglyceride levels. MHY908 brought about a reduction in endoplasmic reticulum stress and activation of the c-Jun N-terminal kinase in the livers of aged rats, which consequently improved insulin signaling. In the kidneys of aged rats, the efficacy of MHY908 as a potent anti-inflammatory agent was shown by its suppression of NF-κB activation through inhibition of the Akt/IκB kinase signaling pathway. Therefore, the major finding of this study is that MHY908 acts as a therapeutic agent against age-related inflammation associated with insulin resistance by activating PPARα and PPARγ, thus attenuating endoplasmic reticulum stress.

Men and women differ in their diurnal expression of monocyte peroxisome proliferator-activated receptor-α in the fed but not in the fasted state

Peroxisome proliferator-activated receptor-α (PPARα) plays a pivotal role in regulating metabolic response to fasting and is an inhibitor of inflammatory pathways in immune cells. It represents a therapeutic target for treatment of several diseases, mainly hyperlipidemia. To shed light on PPARα expression changes in response to fasting, young healthy male and female volunteers were fed or fasted for 24 hours. Monocytes were analyzed every 2 hours to compile both profiles of mRNA and protein expression of PPARα and its interactive partner, the circadian pacemaker brain and muscle aryl hydrocarbon receptor nuclear translocator like-1 (BMAL1). We found that women change their diurnal expression profiles of PPARα and BMAL1 when switching from the fed to the fasted state, whereas men do not. Interestingly, the PPARα and BMAL1 profiles of men and women in the fed state are different, whereas the profiles in the fasted state are virtually identical. The finding of diametrically opposite responses of male and female PPARα expression in the fed state might have practical implication in human medicine as PPARα activators like fibrates are used for the therapy of chronic lymphocytic leukemia, microvascular complications in diabetes, and kidney diseases.

Energy-regulated molecules maintain young status in the trophocytes and fat cells of old queen honeybees

Queen honeybees (Apis mellifera) have much longer lifespans than worker bees. Energy-regulated molecules in the trophocytes and fat cells of workers during aging have been determined, but are unknown in queen bees. In the present study, energy-regulated molecules were evaluated in the trophocytes and fat cells of young and old queen bees. Adenosine monophosphate-activated protein kinase α2 (AMPK-α2), phosphorylated AMPK-α2 (pAMPK-α2), and cAMP-specific phosphodiesterases activity increased with aging. The pAMPK-α2/AMPK-α2 ratio and AMPK activity; adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP) concentrations; the ADP/ATP ratio and the AMP/ATP ratio; the cyclic adenosine monophosphate concentration; forkhead box protein O expression; Silent information regulator T1 (SirT1) expression and activity; and peroxisome proliferator-activated receptor-α (PPAR-α) expression were not significantly different between young and old queen bees. These results show that energy-regulated molecules maintain a youthful status in the trophocytes and fat cells of queen bees during aging. These cells seem to have longevity-promoting mechanisms and may clarify the secret of longevity in queen bees.

Adiponectin and energy homeostasis

White adipose tissue (WAT) is the premier energy depot. Since the discovery of the hormonal properties of adipose-secreted proteins such as leptin and adiponectin, WAT has been classified as an endocrine organ. Although many regulatory effects of the adipocyte-derived hormones on various biological systems have been identified, maintaining systemic energy homeostasis is still the essential function of most adipocyte-derived hormones. Adiponectin is one adipocyte-derived hormone and well known for its effect in improving insulin sensitivity in liver and skeletal muscle. Unlike most other adipocyte-derived hormones, adiponectin gene expression and blood concentration are inversely associated with adiposity. Interestingly, recent studies have demonstrated that, in addition to its insulin sensitizing effects, adiponectin plays an important role in maintaining energy homeostasis. In this review, we summarize the progress of research about 1) the causal relationship of adiposity, energy intake, and adiponectin gene expression; and 2) the regulatory role of adiponectin in systemic energy metabolism.

The contribution of visceral fat to improved insulin signaling in Ames dwarf mice

Ames dwarf (Prop1(df), df/df) mice are characterized by growth hormone (GH), prolactin, and thyrotropin deficiency, remarkable extension of longevity and increased insulin sensitivity with low levels of fasting insulin and glucose. Plasma levels of anti-inflammatory adiponectin are increased in df/df mice, while pro-inflammatory IL-6 is decreased in plasma and epididymal fat. This represents an important shift in the balance between pro- and anti-inflammatory adipokines in adipose tissue, which was not exposed to GH signals during development or adult life. To determine the role of adipose tissue in the control of insulin signaling in these long-living mutants, we examined the effects of surgical removal of visceral (epididymal and perinephric) adipose tissue. Comparison of the results obtained in df/df mice and their normal (N) siblings indicated different effects of visceral fat removal (VFR) on insulin sensitivity and glucose tolerance. The analysis of the expression of genes related to insulin signaling indicated that VFR improved insulin action in skeletal muscle in N mice. Interestingly, this surgical intervention did not improve insulin signaling in df/df mice skeletal muscle but caused suppression of the signal in subcutaneous fat. We conclude that altered profile of adipokines secreted by visceral fat of Ames dwarf mice may act as a key contributor to increased insulin sensitivity and extended longevity of these animals.

Insulin sensitivity in long-living Ames dwarf mice

Long-living Ames dwarf mice (df/df) characterized by growth hormone (GH) deficiency are widely used in aging research because of their 40-60 % lifespan extension compared to normal (N) littermates. Importantly, these mice not only live longer but are also protected from age-related diseases including insulin resistance. Several studies demonstrate that df/df mice have enhanced insulin signaling in different insulin-sensitive tissues and suggest that this is a mechanism for extended lifespan. However, it is unknown whether the enhanced insulin signaling in df/df mice translates to improved insulin action on hepatic glucose production and tissue glucose uptake. We performed hyperinsulinemic-euglycemic clamps to assess tissue-specific insulin action in vivo for the first time in these small long-living dwarfs. Our results demonstrate that the glucose infusion rate required to maintain euglycemia was ∼2-fold higher in df/df mice compared to N controls. Insulin-mediated glucose production was completely suppressed in dwarf mice, and stimulation of gastrocnemius and vastus muscle and adipose tissue glucose uptake was also enhanced in df/df mice (100, 86, and 65 %, respectively). These findings show that improved insulin signaling in df/df mice is associated with enhanced tissue-specific insulin action in vivo. This improved functionality of insulin action and glucose homeostasis may play a key role in promoting healthy aging and longer lifespan in df/df mice.

Changes in energy-regulated molecules in the trophocytes and fat cells of young and old worker honeybees (Apis mellifera)

Trophocytes and fat cells of honeybees (Apis mellifera) have been used for cellular senescence studies, but the changes in the expression, concentration, and activity of cellular energy-regulated molecules that occur with aging in worker bees is unknown. In this study, energy-regulated molecules were evaluated in the trophocytes and fat cells of young and old workers. The results showed that (i) adenosine monophosphate-activated protein kinase-α2 (AMPK-α2) expression increased with aging, whereas phosphorylated AMPK-α2 expression, the phosphorylated AMPK/AMPK ratio, and AMPK activity decreased with aging; (ii) adenosine diphosphate and adenosine triphosphate concentrations decreased with aging, the AMP concentration was unchanged, the adenosine diphosphate/adenosine triphosphate ratio did not change with aging, and the AMP/adenosine triphosphate ratio increased with aging; (iii) the cyclic AMP concentration decreased with aging, and cyclic AMP-specific phosphodiesterases activity increased with aging; (iv) silent information regulator 2 (Sir2) expression increased with aging, whereas its activity decreased with aging; and (v) peroxisome proliferator-activated receptor-α expression decreased with aging. These results show that the trophocytes and fat cells of young workers have higher cellular energy status and express higher levels of energy-regulated molecules than those of old workers and that aging results in a decline in the energy status of trophocytes and fat cells in worker honeybees.

Site-specific antioxidative therapy for prevention of atherosclerosis and cardiovascular disease

Oxidative stress has been implicated in pathophysiology of aging and age-associated disease. Antioxidative medicine has become a practice for prevention of atherosclerosis. However, limited success in preventing cardiovascular disease (CVD) in individuals with atherosclerosis using general antioxidants has prompted us to develop a novel antioxidative strategy to prevent atherosclerosis. Reducing visceral adipose tissue by calorie restriction (CR) and regular endurance exercise represents a causative therapy for ameliorating oxidative stress. Some of the recently emerging drugs used for the treatment of CVD may be assigned as site-specific antioxidants. CR and exercise mimetic agents are the choice for individuals who are difficult to continue CR and exercise. Better understanding of molecular and cellular biology of redox signaling will pave the way for more effective antioxidative medicine for prevention of CVD and prolongation of healthy life span.

Metabolic characteristics of long-lived mice

Genetic suppression of insulin/insulin-like growth factor signaling (IIS) can extend longevity in worms, insects, and mammals. In laboratory mice, mutations with the greatest, most consistent, and best documented positive impact on lifespan are those that disrupt growth hormone (GH) release or actions. These mutations lead to major alterations in IIS but also have a variety of effects that are not directly related to the actions of insulin or insulin-like growth factor I. Long-lived GH-resistant GHR-KO mice with targeted disruption of the GH receptor gene, as well as Ames dwarf (Prop1^df) and Snell dwarf (Pit1^dw) mice lacking GH (along with prolactin and TSH), are diminutive in size and have major alterations in body composition and metabolic parameters including increased subcutaneous adiposity, increased relative brain weight, small liver, hypoinsulinemia, mild hypoglycemia, increased adiponectin levels and insulin sensitivity, and reduced serum lipids. Body temperature is reduced in Ames, Snell, and female GHR-KO mice. Indirect calorimetry revealed that both Ames dwarf and GHR-KO mice utilize more oxygen per gram (g) of body weight than sex- and age-matched normal animals from the same strain. They also have reduced respiratory quotient, implying greater reliance on fats, as opposed to carbohydrates, as an energy source. Differences in oxygen consumption (VO₂) were seen in animals fed or fasted during the measurements as well as in animals that had been exposed to 30% calorie restriction or every-other-day feeding. However, at the thermoneutral temperature of 30°C, VO₂ did not differ between GHR-KO and normal mice. Thus, the increased metabolic rate of the GHR-KO mice, at a standard animal room temperature of 23°C, is apparently related to increased energy demands for thermoregulation in these diminutive animals. We suspect that increased oxidative metabolism combined with enhanced fatty acid oxidation contribute to the extended longevity of GHR-KO mice.

Activation of genes involved in xenobiotic metabolism is a shared signature of mouse models with extended lifespan

Xenobiotic metabolism has been proposed to play a role in modulating the rate of aging. Xenobiotic metabolizing enzymes (XME) are expressed at higher levels in calorically restricted mice (CR) and in GH/IGF-I-deficient, long-lived mutant mice. In this study, we show that many phase I XME genes are similarly upregulated in additional long-lived mouse models, including "crowded litter" (CL) mice, whose lifespan has been increased by food restriction limited to the first 3 wk of life, and in mice treated with rapamycin. Induction in the CL mice lasts at least through 22 mo of age, but induction by rapamycin is transient for many of the mRNAs. Cytochrome P-450s, flavin monooxygenases, hydroxyacid oxidase, and metallothioneins were found to be significantly elevated in similar proportions in each of the models of delayed aging tested, whether these were based on mutation, diet, drug treatment, or transient early intervention. The same pattern of mRNA elevation could be induced by 2 wk of treatment with tert-butylhydroquinone, an oxidative toxin known to activate Nrf2-dependent target genes. These results suggest that elevation of phase I XMEs is a hallmark of long-lived mice and may facilitate screens for agents worth testing in intervention-based lifespan studies.

Metabolic effects of intra-abdominal fat in GHRKO mice

Mice with targeted deletion of the growth hormone receptor (GHRKO mice) are growth hormone (GH) resistant, small, obese, hypoinsulinemic, highly insulin sensitive and remarkably long-lived. To elucidate the unexpected coexistence of adiposity with improved insulin sensitivity and extended longevity, we examined effects of surgical removal of visceral (epididymal and perinephric) fat on metabolic traits related to insulin signaling and longevity. Comparison of results obtained in GHRKO mice and in normal animals from the same strain revealed disparate effects of visceral fat removal (VFR) on insulin and glucose tolerance, adiponectin levels, accumulation of ectopic fat, phosphorylation of insulin signaling intermediates, body temperature, and respiratory quotient (RQ). Overall, VFR produced the expected improvements in insulin sensitivity and reduced body temperature and RQ in normal mice and had opposite effects in GHRKO mice. Some of the examined parameters were altered by VFR in opposite directions in GHRKO and normal mice, and others were affected in only one genotype or exhibited significant genotype × treatment interactions. Functional differences between visceral fat of GHRKO and normal mice were confirmed by measurements of adipokine secretion, lipolysis, and expression of genes related to fat metabolism. We conclude that in the absence of GH signaling, the secretory activity of visceral fat is profoundly altered and unexpectedly promotes enhanced insulin sensitivity. The apparent beneficial effects of visceral fat in GHRKO mice may also explain why reducing adiposity by calorie restriction fails to improve insulin signaling or further extend longevity in these animals.

Effects of adult onset mild calorie restriction on weight of reproductive organs, plasma parameters and gene expression in male mice

Calorie restriction (CR) extends lifespan and delays onset of age-related diseases in various organisms, even when started later in life. Despite benefits for health and lifespan, CR's negative impact on reproduction is documented in some animals. Studies employing approximately 40% CR detected a delay in sexual maturation and impairment of fertility, which were combined with extension of the reproductive period. In contrast, mild CR (10-20%) is apparently not deleterious to reproduction. Hence, we hypothesized that mild CR started at 8 months of age would prolong reproductive capabilities and improve health parameters of male mice. To test this hypothesis, we assessed the effects of 10 and 20% CR on reproductive organ weights, selected plasma parameters and hepatic/testicular gene expression in normal male mice of heterogeneous genetic background. Starting at 8 months of age (adult), mice were assigned to 3 regimen groups: 10% CR (n = 8), 20% CR (n = 9) or ad libitum (AL; n = 8). Four months of CR were sufficient to reduce glycemia in a non-fasted protocol. Mild CR initiated in adulthood did not significantly impact final body weight, most of the analyzed plasma parameters or weight of androgen-dependent organs. Moreover, CR did not interfere with expression of the assessed testicular genes, or most of the hepatic genes, but it did cause an increase in the levels of peroxisome proliferator-activated receptor gamma (Pparg) and mouse sulfotransferase (mSTa); and a decrease in glucose-6-phosphatase-α (G6pc) mRNA, which might signify improvement of body condition. The important finding of our study was that a mild CR regimen, as low as 10 and 20%, was sufficient to impair glycemia in a non-fasted state, and also the levels of plasma IGF-1, corroborating the concept that mild CR has the potential for improving health and longevity, even when started later in life.

The Functions of PPARs in Aging and Longevity

Peroxisome proliferator-activated receptors (PPARs) are key regulators in various age-associated pathophysiological processes related to energy metabolism and oxidative stress. A progressive rise of oxidative stress and related inflammatory reaction appears the hallmarks of the aging process and many age-related diseases. PPARs are important redox-sensitive transcription factors and their dyregulated activations seem to be major culprits for these pathological processes. Drugs targeting PPARs activity are already in widespread clinical use; however, based on these concepts, this review highlights the understanding of the role of PPARs in aging and indicates the necessary particular attention for the potential therapeutic uses of current PPAR agonists in age-associated diseases.

Caloric restriction and heart function: is there a sensible link?

Calorie restriction (CR) is defined as a reduction in calorie intake below the usual ad libitum intake without malnutrition. Ample of clinical and experimental evidence has demonstrated that CR is capable of retarding aging process and development of cardiovascular disease. Although suppression of reactive oxygen species production and inflammation plays a central role in the favorable cardiovascular effects of CR, the health benefit of CR is believed to be ultimately mediated through a cadre of biochemical and cellular adaptations including redox homeostasis, mitochondrial function, inflammation, apoptosis and autophagy. Despite the apparent beneficial cardiovascular effects of CR, implementation of CR in the health care management is still hampered by apparent applicability issues and health concerns. Here we briefly review the cardiac consequence of CR and discuss whether CR may represent a safe and effective strategy in the management of cardiovascular health.

Thiazolidinedione treatment and constitutive-PPARgamma activation induces ectopic adipogenesis and promotes age-related thymic involution

Age-related thymic involution is characterized by reduction in T cell production together with ectopic adipocyte development within the hematopoietic and thymic niches. Peroxisome proliferator-activated receptor gamma (PPARgamma) is required for adipocyte development, glucose homeostasis and is a target for several insulin-sensitizing drugs. Our prior studies showed that age-related elevation of PPARgamma expression in thymic stromal cells is associated with thymic involution. Here, using clinically relevant pharmacological and genetic manipulations in mouse models, we provide evidence that activation of PPARgamma leads to reduction in thymopoiesis. Treatment of aged mice with antihyperglycemic PPARgamma-ligand class of thiazolidinedione drug, rosiglitazone caused robust thymic expression of classical pro-adipogenic transcripts. Rosiglitazone reduced thymic cellularity, lowered the naïve T cell number and T cell receptor excision circles (TRECs) indicative of compromised thymopoiesis. To directly investigate whether PPARgamma activation induces thymic involution, we created transgenic mice with constitutive-active PPARgamma (CA-PPARg) fusion protein in cells of adipogenic lineage. Importantly, CA-PPARgamma transgene was expressed in thymus and in fibroblast-specific protein-1/S100A4 (FSP1(+)) cells, a marker of secondary mesenchymal cells. The CAPPARgamma fusion protein mimicked the liganded PPARgamma receptor and the transgenic mice displayed increased ectopic thymic adipogenesis and reduced thymopoiesis. Furthermore, the reduction in thymopoiesis in CA-PPARgamma mice was associated with higher bone marrow adiposity and lower hematopoietic stem cell progenitor pool. Consistent with lower thymic output, CAPPARgamma transgenic mice had restricted T cell receptor repertoire diversity. Collectively, our data suggest that activation of PPARgamma accelerates thymic aging and thymus-specific PPARgamma antagonist may forestall age-related decline in T cell diversity.

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.

Effects of growth hormone and thyroxine replacement therapy on insulin signaling in Ames dwarf mice

Ames dwarf (Prop1(df), df/df) mice lack growth hormone (GH), prolactin, and thyrotropin and live remarkably longer than their normal siblings. Significance of reduced activity of the somatotropic and thyroid axes during development and adulthood on longevity are unknown. Because enhanced insulin sensitivity and reduced insulin levels are among likely mechanisms responsible for increased longevity in these mutants, we compared the effects of GH and thyroxine (T4) replacement on various parameters related to insulin signaling in young and old male df/df mice. The results suggest that altered plasma adiponectin and insulin-like growth factor-1 (IGF-1) and hepatic IGF-1, insulin receptor (IR), IR substrate-1, peroxisome proliferator-activated receptor (PPAR) gamma, and PPARgamma coactivator-1 alpha may contribute to increased insulin sensitivity in Ames dwarfs. The stimulatory effect of GH and T4 treatment on plasma insulin and inhibitory effect on expression of hepatic glucose transporter-2 were greater in old than in young dwarfs. These results indicate that GH and T4 treatment has differential impact on insulin signaling during development and adulthood.

Fasting promotes the expression of SIRT1, an NAD+ -dependent protein deacetylase, via activation of PPARalpha in mice

Calorie restriction (CR) extends lifespans in a wide variety of species. CR induces an increase in the NAD(+)/NADH ratio in cells and results in activation of SIRT1, an NAD(+)-dependent protein deacetylase that is thought to be a metabolic master switch linked to the modulation of lifespans. CR also affects the expression of peroxisome proliferator-activated receptors (PPARs). The three subtypes, PPARalpha, PPARgamma, and PPARbeta/delta, are expressed in multiple organs. They regulate different physiological functions such as energy metabolism, insulin action and inflammation, and apparently act as important regulators of longevity and aging. SIRT1 has been reported to repress the PPARgamma by docking with its co-factors and to promote fat mobilization. However, the correlation between SIRT1 and other PPARs is not fully understood. CR initially induces a fasting-like response. In this study, we investigated how SIRT1 and PPARalpha correlate in the fasting-induced anti-aging pathways. A 24-h fasting in mice increased mRNA and protein expression of both SIRT1 and PPARalpha in the livers, where the NAD(+) levels increased with increasing nicotinamide phosphoribosyltransferase (NAMPT) activity in the NAD(+) salvage pathway. Treatment of Hepa1-6 cells in a low glucose medium conditions with NAD(+) or NADH showed that the mRNA expression of both SIRT1 and PPARalpha can be enhanced by addition of NAD(+), and decreased by increasing NADH levels. The cell experiments using SIRT1 antagonists and a PPARalpha agonist suggested that PPARalpha is a key molecule located upstream from SIRT1, and has a role in regulating SIRT1 gene expression in fasting-induced anti-aging pathways.

Vitamin C restores healthy aging in a mouse model for Werner syndrome

Werner syndrome (WS) is a premature aging disorder caused by mutations in a RecQ-like DNA helicase. Mice lacking the helicase domain of the WRN homologue exhibit many phenotypic features of WS, including a prooxidant status and a shorter mean life span compared to wild-type animals. Here, we show that Wrn mutant mice also develop premature liver sinusoidal endothelial defenestration along with inflammation and metabolic syndrome. Vitamin C supplementation rescued the shorter mean life span of Wrn mutant mice and reversed several age-related abnormalities in adipose tissues and liver endothelial defenestration, genomic integrity, and inflammatory status. At the molecular level, phosphorylation of age-related stress markers like Akt kinase-specific substrates and the transcription factor NF-kappaB, as well as protein kinase Cdelta and Hif-1alpha transcription factor levels, which are increased in the liver of Wrn mutants, were normalized by vitamin C. Vitamin C also increased the transcriptional regulator of lipid metabolism PPARalpha. Finally, microarray and gene set enrichment analyses on liver tissues revealed that vitamin C decreased genes normally up-regulated in human WS fibroblasts and cancers, and it increased genes involved in tissue injury response and adipocyte dedifferentiation in obese mice. Vitamin C did not have such effect on wild-type mice. These results indicate that vitamin C supplementation could be beneficial for patients with WS.

Is altered expression of hepatic insulin-related genes in growth hormone receptor knockout mice due to GH resistance or a difference in biological life spans?

Growth hormone receptor knockout (GHRKO) mice live about 40%-55% longer than their normal (N) littermates. Previous studies of 21-month-old GHRKO and N mice showed major alterations of the hepatic expression of genes involved in insulin signaling. Differences detected at this age may have been caused by the knockout of the growth hormone receptor (GHR) or by differences in biological age between GHRKO and N mice. To address this question, we compared GHRKO and N mice at ages corresponding to the same percentage of median life span to see if the differences of gene expression persisted. Comparison of GHRKO and N mice at approximately 50% of biological life span showed significant differences in hepatic expression of all 14 analyzed genes. We conclude that these changes are due to disruption of GHR gene and the consequent suppression of growth hormone signaling rather than to differences in "biological age" between mutant and normal animals sampled at the same chronological age.

Divergent regulation of adipose tissue metabolism by calorie restriction and inhibition of growth hormone signaling

Calorie restriction (CR) and a reduced growth hormone (GH) signal affect insulin sensitivity and lifespan in mammals in a similar manner. We investigated the effects of CR and moderate inhibition of GH on glucose-stimulated activation of insulin signaling and the expression of genes related to fat metabolism in white adipose tissue (WAT) in rats. We used 10-month-old male, wild-type (W) Wistar rats, fed ad libitum (AL) or a 30% CR diet from 6weeks of age, and transgenic (Tg) rats with moderately suppressed GH signaling. Rats were killed 15min after an intraperitoneal injection of glucose or saline. In control W-AL rats, the levels of serum insulin, phosphorylated (p) insulin receptor (pY-IR), p-Akt, and the expression of glucose transporter (Glut) 4 in the membrane fraction were greater in the glucose-injected group than in the saline-injected group, indicating significant activation of insulin signaling in response to glucose loading. In the W-CR and Tg-AL rats, the serum insulin and pY-IR levels were lower than those in the W-AL rats. The Akt-Glut pathway was up-regulated even after saline-injection. Expression levels of adipogenic and lipogenic genes including PPARgamma, adiponectin, and its receptors, were higher in the W-CR rats than in the W-AL and Tg-AL rats. The present findings indicate adipose tissue metabolic profiles specific to CR.

Small molecule activators of SIRT1 replicate signaling pathways triggered by calorie restriction in vivo

Background

Calorie restriction (CR) produces a number of health benefits and ameliorates diseases of aging such as type 2 diabetes. The components of the pathways downstream of CR may provide intervention points for developing therapeutics for treating diseases of aging. The NAD⁺-dependent protein deacetylase SIRT1 has been implicated as one of the key downstream regulators of CR in yeast, rodents, and humans. Small molecule activators of SIRT1 have been identified that exhibit efficacy in animal models of diseases typically associated with aging including type 2 diabetes. To identify molecular processes induced in the liver of mice treated with two structurally distinct SIRT1 activators, SIRT501 (formulated resveratrol) and SRT1720, for three days, we utilized a systems biology approach and applied Causal Network Modeling (CNM) on gene expression data to elucidate downstream effects of SIRT1 activation.

Results

Here we demonstrate that SIRT1 activators recapitulate many of the molecular events downstream of CR in vivo, such as enhancing mitochondrial biogenesis, improving metabolic signaling pathways, and blunting pro-inflammatory pathways in mice fed a high fat, high calorie diet.

Conclusion

CNM of gene expression data from mice treated with SRT501 or SRT1720 in combination with supporting in vitro and in vivo data demonstrates that SRT501 and SRT1720 produce a signaling profile that mirrors CR, improves glucose and insulin homeostasis, and acts via SIRT1 activation in vivo. Taken together these results are encouraging regarding the use of small molecule activators of SIRT1 for therapeutic intervention into type 2 diabetes, a strategy which is currently being investigated in multiple clinical trials.

Metabolic shifts due to long-term caloric restriction revealed in nonhuman primates

The long-term health benefits of caloric restriction (CR) are well known but the associated molecular mechanisms are poorly understood despite increasing knowledge of transcriptional and related metabolic changes. We report new metabolic insights into long-term CR in nonhuman primates revealed by the holistic inspection of plasma (1)H NMR spectroscopic metabolic and lipoprotein profiles. The results revealed attenuation of aging-dependant alterations of lipoprotein and energy metabolism by CR, noted by relative increase in HDL and reduction in VLDL levels. Metabonomic analysis also revealed animals exhibiting distinct metabolic trajectories from aging that correlated with higher insulin sensitivity. The plasma profiles of insulin-sensitive animals were marked by higher levels of gluconate and acetate suggesting a CR-modulated increase in metabolic flux through the pentose-phosphate pathway. The metabonomic findings, particularly those that parallel improved insulin sensitivity, are consistent with diminished adiposity in CR monkeys despite aging. The metabolic profile and the associated pathways are compatible with our previous findings that CR-induced gene transcriptional changes in tissue suggest the critical regulation of peroxisome proliferator-activated receptors as a key mechanism. The metabolic phenotyping provided in this study can be used to define a reference molecular profile of CR-associated health benefits and longevity in symbiotic superorganisms and man.

PPARs Mediate Lipid Signaling in Inflammation and Cancer

Lipid mediators can trigger physiological responses by activating nuclear hormone receptors, such as the peroxisome proliferator-activated receptors (PPARs). PPARs, in turn, control the expression of networks of genes encoding proteins involved in all aspects of lipid metabolism. In addition, PPARs are tumor growth modifiers, via the regulation of cancer cell apoptosis, proliferation, and differentiation, and through their action on the tumor cell environment, namely, angiogenesis, inflammation, and immune cell functions. Epidemiological studies have established that tumor progression may be exacerbated by chronic inflammation. Here, we describe the production of the lipids that act as activators of PPARs, and we review the roles of these receptors in inflammation and cancer. Finally, we consider emerging strategies for therapeutic intervention.

A Bayesian calibration model for combining different pre-processing methods in Affymetrix chips

BACKGROUND

In gene expression studies a key role is played by the so called "pre-processing", a series of steps designed to extract the signal and account for the sources of variability due to the technology used rather than to biological differences between the RNA samples. At the moment there is no commonly agreed gold standard pre-processing method and each researcher has the responsibility to choose one method, incurring the risk of false positive and false negative features arising from the particular method chosen.

RESULTS

We propose a Bayesian calibration model that makes use of the information provided by several pre-processing methods and we show that this model gives a better assessment of the 'true' unknown differential expression between two conditions. We demonstrate how to estimate the posterior distribution of the differential expression values of interest from the combined information.

CONCLUSION

On simulated data and on the spike-in Latin Square dataset from Affymetrix the Bayesian calibration model proves to have more power than each pre-processing method. Its biological interest is demonstrated through an experimental example on publicly available data.

Molecular mechanism of PPAR in the regulation of age-related inflammation

Evidence from many recent studies has linked uncontrolled inflammatory processes to aging and aging-related diseases. Decreased a nuclear receptor subfamily of transcription factors, peroxisome proliferator-activated receptors (PPARs) activity is closely associated with increased levels of inflammatory mediators during the aging process. The anti-inflammatory action of PPARs is substantiated by both in vitro and in vivo studies that signify the importance of PPARs as major players in the pathogenesis of many inflammatory diseases. In this review, we highlight the molecular mechanisms and roles of PPARalpha, gamma in regulation of age-related inflammation. By understanding these current findings of PPARs, we open up the possibility of developing new therapeutic agents that modulate these nuclear receptors to control various inflammatory diseases such as atherosclerosis, vascular diseases, Alzheimer's disease, and cancer.

Transcriptional response to aging and caloric restriction in heart and adipose tissue

Sustained caloric restriction (CR) extends lifespan in animal models but the mechanism and primary tissue target(s) have not been identified. Gene expression changes with aging and CR were examined in both heart and white adipose tissue (WAT) of Fischer 344 (F344) male rats using Affymetrix RAE 230 arrays and validated by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) on 18 genes. As expected, age had a substantial effect on transcription on both tissues, although only 21% of cardiac age-associated genes were also altered in WAT. Gene set enrichment analysis revealed coordinated small magnitude changes in ribosomal, proteasomal, and mitochondrial genes with similarities in aging between heart and WAT. CR had very different effects on these two tissues at the transcriptional level. In heart, very few age-associated expression changes were affected by CR, while in WAT, CR suppressed a substantial subset of the age-associated changes. Genes unaltered by aging but altered by CR were identified in WAT but not heart. Most interestingly, we identified a gene expression signature associated with mammalian target of rapamycin (mTOR) activity that was down-regulated with age but preserved by CR in both WAT and heart. In addition, lipid metabolism genes, particularly those associated with peroxisome proliferator-activated receptor gamma (PPARgamma)-mediated adipogenesis were reduced with age but preserved with CR in WAT. These results highlight tissue-specific differences in the gene expression response to CR and support a role for CR-mediated preservation of mTOR activity and adipogenesis in aging WAT.