Dietary energy restriction modulates the activity of AMP-activated protein kinase, Akt, and mammalian target of rapamycin in mammary carcinomas, mammary gland, and liver

Effect of feeding regimens on circadian rhythms: implications for aging and longevity

Increased longevity and improved health can be achieved in mammals by two feeding regimens, caloric restriction (CR), which limits the amount of daily calorie intake, and intermittent fasting (IF), which allows the food to be available ad libitum every other day. The precise mechanisms mediating these beneficial effects are still unresolved. Resetting the circadian clock is another intervention that can lead to increased life span and well being, while clock disruption is associated with aging and morbidity. Currently, a large body of evidence links circadian rhythms with metabolism and feeding regimens. In particular, CR, and possibly also IF, can entrain the master clock located in the suprachiasmatic nuclei (SCN) of the brain hypothalamus. These findings raise the hypothesis that the beneficial effects exerted by these feeding regimens could be mediated, at least in part, through resetting of the circadian clock, thus leading to synchrony in metabolism and physiology. This hypothesis is reinforced by a transgenic mouse model showing spontaneously reduced eating alongside robust circadian rhythms and increased life span. This review will summarize recent findings concerning the relationships between feeding regimens, circadian rhythms, and metabolism with implications for ageing attenuation and life span extension.

Acyclic retinoid inhibits diethylnitrosamine-induced liver tumorigenesis in obese and diabetic C57BLKS/J- +(db)/+Lepr(db) mice

Obesity and the related metabolic abnormalities are associated with increased risk of hepatocellular carcinoma (HCC). Malfunctioning of retinoid X receptor (RXR) α due to phosphorylation by Ras/MAPK also plays a critical role in liver carcinogenesis. In the present study, we examined the effects of acyclic retinoid (ACR), which targets RXRα, on the development of diethylnitrosamine (DEN)-induced liver tumorigenesis in C57BLKS/J- +Lepr(db)/+Lepr(db) (db/db) obese mice. Male db/db mice were given tap water containing 40 ppm DEN for 2 weeks, after which they were fed a diet containing 0.03% or 0.06% of ACR throughout the experiment. In mice treated with either dose of ACR for 34 weeks, the development of liver cell adenomas was significantly inhibited as compared with basal diet-fed mice. ACR markedly inhibited the activation of Ras and phosphorylation of the ERK (extracellular signal-regulated kinase) and RXRα proteins in the livers of experimental mice. It also increased the expression of RAR β and p21(CIP1) mRNA while decreasing the expression of cyclin D1, c-Fos, and c-Jun mRNA in the liver, thereby restoring RXRα function. Administration of ACR improved liver steatosis and activated the AMPK protein. The serum levels of insulin decreased by ACR treatment, whereas the quantitative insulin sensitivity check index (QUICKI) values increased, indicating improved insulin sensitivity. The serum levels of TNF-α and the expression levels of TNF- α, IL-6, and IL-1 β mRNA in the livers of DEN-treated db/db mice were decreased by ACR treatment, suggesting attenuation of the chronic inflammation induced by excessive fatty deposits. ACR may be, therefore, useful in the chemoprevention of obesity-related HCC.

Insulin resistance, serum leptin, and adiponectin levels and outcomes of viral hepatitis C cirrhosis

BACKGROUND & AIMS

Mechanisms linking obesity and unfavourable outcomes in patients with viral hepatitis C (HCV) cirrhosis are not well understood. Obesity is associated with insulin resistance, increased leptin, and decreased adiponectin serum levels.

METHODS

We assessed the predictive value of those factors for the occurrence of hepatocellular carcinoma (HCC) and liver-related death or transplantation in a cohort of 248 patients (mean age 58 (12 years, BMI 25.4 ± 4.4 kg/m(2)) with compensated HCV cirrhosis and persistent infection prospectively followed and screened for HCC.

RESULTS

The mean baseline serum levels of adiponectin and leptin were 16.8 ± 15 mg/L and 16.8 ± 19 ng/ml, respectively. The mean homeostasis model assessment of insulin resistance (HOMA) index was 3.8 ± 3; median 2.9. After a median follow-up of 72 months, 61 patients developed HCC, 58 died of liver causes, and 17 were transplanted. The incidences (Kaplan Meier) of HCC were 7%, 18%, and 27% at 5 years (p=0.017) and of liver-related death or transplantation 15%, 15% and 29% (p=0.002) according to the lowest, middle and highest tertile of HOMA, respectively. In multivariate analysis, the HOMA index was associated with HCC occurrence (HR=1.10, [1.01-1.21] p=0.026) and was a strong predictor of liver-related death or transplantation (HR=1.13, [1.07-1.21] p<0.0001). Serum levels of adiponectin and leptin were not associated with the outcome.

CONCLUSIONS

In patients with compensated HCV cirrhosis, insulin resistance but not serum levels of adiponectin and leptin predicted the occurrence of HCC and of liver-related death or transplantation.

Branched-chain amino acid supplementation promotes survival and supports cardiac and skeletal muscle mitochondrial biogenesis in middle-aged mice

Recent evidence points to a strong relationship between increased mitochondrial biogenesis and increased survival in eukaryotes. Branched-chain amino acids (BCAAs) have been shown to extend chronological life span in yeast. However, the role of these amino acids in mitochondrial biogenesis and longevity in mammals is unknown. Here, we show that a BCAA-enriched mixture (BCAAem) increased the average life span of mice. BCAAem supplementation increased mitochondrial biogenesis and sirtuin 1 expression in primary cardiac and skeletal myocytes and in cardiac and skeletal muscle, but not in adipose tissue and liver of middle-aged mice, and this was accompanied by enhanced physical endurance. Moreover, the reactive oxygen species (ROS) defense system genes were upregulated, and ROS production was reduced by BCAAem supplementation. All of the BCAAem-mediated effects were strongly attenuated in endothelial nitric oxide synthase null mutant mice. These data reveal an important antiaging role of BCAAs mediated by mitochondrial biogenesis in mammals.

Dietary restriction and aging in rodents: a current view on its molecular mechanisms

Dietary restriction (DR) is a robust non-genetic intervention that reduces morbidity and mortality in a range of organisms. This suggests the presence of an evolutionary-conserved pathway that regulates aging and lifespan in response to reduced food or energy intake. Recent genetic analyses have shown that single gene mutations could extend the lifespan, even in mammals. Many longevity genes are clustered into nutrient-sensing and metabolic adaptation pathways, which are also thought to be involved in the effect of DR. The responses of these mutant animals to DR in terms of lifespan or other aging phenotypes suggest that proteins encoded by these genes are involved in the effects of DR. This review focuses on the roles of fork head box O (FoxO) transcription factors, AMP-activated protein kinase (AMPK), and sirtuins (particularly SIRT1) in the effects of DR in rodents. FoxO transcription factors are mammalian orthologs of DAF-16, which is required for the lifespan extending effects of reduced insulin-like signaling in nematodes. A recent study in rodents suggested that FoxO1 is involved in the anti-neoplastic effects of DR. Although aak2 in nematodes (mammalian AMPK), Sir2 in yeast and Sir2.1 in nematodes (mammalian SIRT1) were also reported to be essential for lifespan extension by DR, the findings are thought to depend on the genetic backgrounds of the organisms and/or methods used to induce DR. In rodents, AMPK and SIRT1 are implicated in the metabolic regulation by long-term DR. Genetic and molecular dissection of the mechanisms underlying the effects of DR will provide us with knowledge of the basic aging processes, as well as insights into the development of DR mimetics, to extend the healthy lifespan in humans.

Energy balance, host-related factors, and cancer progression

Obesity is associated with an increased risk and worsened prognosis for many types of cancer, but the mechanisms underlying the obesity-cancer progression link are poorly understood. Several energy balance-related host factors are known to influence tumor progression and/or treatment responsiveness after cancer develops, and these have been implicated as key contributors to the complex effects of obesity on cancer outcome. These host factors include leptin, adiponectin, steroid hormones, reactive oxygen species associated with inflammation, insulin, insulin-like growth factor-1, and sirtuins. Each of these host factors is considered in this article in the context of energy balance and cancer progression. In addition, future research directions in this field are discussed, including the importance of study designs addressing energy balance across the life course, the development and application of highly relevant animal models, potential roles of cancer stem cells in the response to energy balance modulation, and emerging pharmacologic approaches that target energy balance-related pathways.

AMPK as a metabolic tumor suppressor: control of metabolism and cell growth

AMPK is an evolutionarily conserved fuel-sensing enzyme that is activated in shortage of energy and suppressed in its surfeit. AMPK activation stimulates fatty acid oxidation, enhances insulin sensitivity, alleviates hyperglycemia and hyperlipidemia, and inhibits proinflammatory changes. Thus, AMPK is a well-received therapeutic target for metabolic syndrome and Type 2 diabetes. Recent studies indicate that AMPK plays a role in linking metabolic syndrome and cancer. AMPK is an essential mediator of the tumor suppressor LKB1 and could be suppressed in cancer cells containing loss-of-function mutations of LKB1 or containing active mutations of B-Raf, or in cancers associated with metabolic syndrome. The activation of AMPK reprograms cellular metabolism and enforces metabolic checkpoints by acting on mTORC1, p53, fatty acid synthase and other molecules for regulating cell growth and metabolism. In keeping with in vitro studies, recent epidemiological studies indicate that the incidence of cancer is reduced in Type 2 diabetes treated with metformin, an AMPK activator. Thus, AMPK is emerging as an interesting metabolic tumor suppressor and a promising target for cancer prevention and therapy.

Rapamycin extends maximal lifespan in cancer-prone mice

Aging is associated with obesity and cancer. Calorie restriction both slows down aging and delays cancer. Evidence has emerged that the nutrient-sensing mammalian target of rapamycin (mTOR) pathway is involved in cellular and organismal aging. Here we show that the mTOR inhibitor rapamycin prevents age-related weight gain, decreases rate of aging, increases lifespan, and suppresses carcinogenesis in transgenic HER-2/neu cancer-prone mice. Rapamycin dramatically delayed tumor onset as well as decreased the number of tumors per animal and tumor size. We suggest that, by slowing down organismal aging, rapamycin delays cancer.

Acute energy deprivation affects skeletal muscle protein synthesis and associated intracellular signaling proteins in physically active adults

To date, few studies have characterized the influence of energy deprivation on direct measures of skeletal muscle protein turnover. In this investigation, we characterized the effect of an acute, moderate energy deficit (10 d) on mixed muscle fractional synthetic rate (FSR) and associated intracellular signaling proteins in physically active adults. Eight men and 4 women participated in a 20-d, 2-phase diet intervention study: weight maintenance (WM) and energy deficient (ED; approximately 80% of estimated energy requirements). Dietary protein (1.5 g x kg(-1) x d(-1)) and fat (approximately 30% of total energy) were constant for WM and ED. FSR and intracellular signaling proteins were measured on d 10 of both interventions using a primed, constant infusion of [(2)H(5)]-phenylalanine and Western blotting techniques, respectively. Participants lost approximately 1 kg body weight during ED (P < 0.0001). FSR was reduced approximately 19% (P < 0.05) for ED (0.06 +/- 0.01%/h) compared with WM (0.074 +/- 0.01%/h). Protein kinase B and eukaryotic initiation factor 4E binding protein 1 phosphorylation were lower (P < 0.05) during ED compared with WM. AMP activated protein kinase phosphorylation decreased (P < 0.05) over time regardless of energy status. These findings show that FSR and associated synthetic intracellular signaling proteins are downregulated in response to an acute, moderate energy deficit in physically active adults and provide a basis for future studies assessing the impact of prolonged, and perhaps more severe, energy restriction on skeletal muscle protein turnover.

Evaluation of Short-term Myelotoxicity Study in Dietary Reduced Rats

This study attempted to prove our hypothesis that a short-term toxicity study, using a 4-day dosing regimen as an example, is suitable for evaluating myelotoxicity in rats. We compared the hematological, bone marrow cytological and histopathological results of 5-fluorouracil (5-FU) treated and pair-feeding groups after a 4-day administration period. Several experimental groups were defined for this 4-day study as well as for our previously reported 14-day study (Miyata et al., 2009); these included 5-FU treated groups receiving 12, 15 and 18 mg/kg/day (FU12, FU15 and FU18), pair-feeding groups (R12, R15 and R18 receiving the same amount of food as the FU12, FU15 and FU18 groups, respectively) and a nontreated control group. Although severe reductions in body weight gain and food consumption were reported in the 14-day study, only slight reductions were observed in the 4-day study. In the 4-day study, a decrease in blood reticulocytes and a decreasing trend of marrow erythroid cells were only observed in the FU18 group, and no effects were observed in the pair-feeding groups. The erythroblastic changes observed in this 4-day study were thought to reflect the direct influence of 5-FU administration. Since concerns regarding the influence of secondary changes related to undernutrition were minimized in the 4-day study, it was thought to clarify the direct influence of 5-FU administration on erythroblastic cells. Thus, a 4-day study protocol might be helpful for distinguishing secondary changes related to undernutrition.

Metabolic reprogramming, caloric restriction and aging

Caloric restriction (CR) without malnutrition slows the aging process and extends lifespan in diverse species by unknown mechanisms. The inverse linear relationship between calorie intake and lifespan suggests that regulators of energy metabolism are important in the actions of CR. Studies in several species reveal tissue-specific changes in energy metabolism with CR and suggest that metabolic reprogramming plays a critical role in its mechanism of aging retardation. We herein describe common signatures of CR and suggest how they can slow aging. We discuss recent advances in understanding the function of key metabolic regulators that probably coordinate the response to altered nutrient availability with CR and how the pathways they regulate can retard the aging process.

Calorie restriction and cancer prevention: metabolic and molecular mechanisms

An important discovery of recent years has been that lifestyle and environmental factors affect cancer initiation, promotion and progression, suggesting that many malignancies are preventable. Epidemiological studies strongly suggest that excessive adiposity, decreased physical activity, and unhealthy diets are key players in the pathogenesis and prognosis of many common cancers. In addition, calorie restriction (CR), without malnutrition, has been shown to be broadly effective in cancer prevention in laboratory strains of rodents. Adult-onset moderate CR also reduces cancer incidence by 50% in monkeys. Whether the antitumorigenic effects of CR will apply to humans is unknown, but CR results in a consistent reduction in circulating levels of growth factors, anabolic hormones, inflammatory cytokines and oxidative stress markers associated with various malignancies. Here, we discuss the link between nutritional interventions and cancer prevention with focus on the mechanisms that might be responsible for these effects in simple systems and mammals with a view to developing chemoprevention agents.

Energy restriction as an antitumor target of thiazolidinediones

Cancer cells gain growth advantages in the microenvironment by shifting cellular metabolism to aerobic glycolysis, the so-called Warburg effect. There is a growing interest in targeting aerobic glycolysis for cancer therapy by exploiting the differential susceptibility of malignant versus normal cells to glycolytic inhibition, of which the proof-of-concept is provided by the in vivo efficacy of dietary caloric restriction and natural product-based energy restriction-mimetic agents (ERMAs) such as resveratrol and 2-deoxyglucose in suppressing carcinogenesis in animal models. Here, we identified thiazolidinediones as a novel class of ERMAs in that they elicited hallmark cellular responses characteristic of energy restriction, including transient induction of Sirt1 (silent information regulator 1) expression, activation of the intracellular fuel sensor AMP-activated protein kinase, and endoplasmic reticulum stress, the interplay among which culminated in autophagic and apoptotic death. The translational implications of this finding are multifold. First, the novel function of troglitazone and ciglitazone in targeting energy restriction provides a mechanistic basis to account for their peroxisome proliferator-activated receptor gamma-independent effects on a broad spectrum of signaling targets. Second, we demonstrated that Sirt1-mediated up-regulation of beta-transducin repeat-containing protein-facilitated proteolysis of cell cycle- and apoptosis-regulatory proteins is an energy restriction-elicited signaling event and is critical for the antitumor effects of ERMAs. Third, it provides a molecular rationale for using thiazolidinediones as scaffolds to develop potent ERMAs, of which the proof-of-principle is demonstrated by OSU-CG12. OSU-CG12, a peroxisome proliferator-activated receptor gamma-inactive ciglitazone derivative, exhibits 1- and 3-order of magnitude higher potency in eliciting starvation-like cellular responses relative to resveratrol and 2-deoxyglucose, respectively.

Calories and carcinogenesis: lessons learned from 30 years of calorie restriction research

Calorie restriction (CR) is arguably the most potent, broadly acting dietary regimen for suppressing the carcinogenesis process, and many of the key studies in this field have been published in Carcinogenesis. Translation of the knowledge gained from CR research in animal models to cancer prevention strategies in humans is urgently needed given the worldwide obesity epidemic and the established link between obesity and increased risk of many cancers. This review synthesizes the evidence on key biological mechanisms underlying many of the beneficial effects of CR, with particular emphasis on the impact of CR on growth factor signaling pathways and inflammatory processes and on the emerging development of pharmacological mimetics of CR. These approaches will facilitate the translation of CR research into effective strategies for cancer prevention in humans.

Effect of aerobic exercise on tumor physiology in an animal model of human breast cancer

Recent epidemiologic studies report that regular exercise may be associated with substantial reductions in cancer-specific and all-cause mortality following a breast cancer diagnosis. The mechanisms underlying this relationship have not been identified. We investigated the effects of long-term voluntary wheel running on growth and progression using an animal model of human breast cancer. We also examined effects on the central features of tumor physiology, including markers of tumor blood perfusion/vascularization, hypoxia, angiogenesis, and metabolism. Athymic female mice fed a high-fat diet were orthotopically (direct into the mammary fat pad) implanted with human breast cancer cells (MDA-MB-231 at 1 x 10(6)) into the right dorsal mammary fat pad and randomly assigned (1:1) to voluntary wheel running (n = 25) or a nonintervention (sedentary) control group (n = 25). Tumor volume was measured every three days using digital calipers. All experimental animals were killed when tumor volume reached > or = 1,500 mm(3). Kaplan-Meier (KM) analysis indicated that tumor growth (survival) was comparable between the experimental groups (exercise 44 days vs. control 48 days; KM proportional hazard ratio = 1.41, 95% confidence interval, 0.77-2.58, P = 0.14). However, tumors from exercising animals had significantly improved blood perfusion/vascularization relative to the sedentary control group (P < 0.05). Histological analyses indicated that intratumoral hypoxia levels (as assessed by hypoxia-inducible factor 1) were significantly higher in the exercise group relative to sedentary control (P < 0.05). Aerobic exercise can significantly increase intratumoral vascularization, leading to "normalization" of the tissue microenvironment in human breast tumors. Such findings may have important implications for inhibiting tumor metastasis and improving the efficacy of conventional cancer therapies.

Biomarkers of dietary energy restriction in women at increased risk of breast cancer

Dietary energy restriction (DER) reduces risk of spontaneous mammary cancer in rodents. In humans, DER in premenopausal years seems to reduce risk of postmenopausal breast cancer. Markers of DER are required to develop acceptable DER regimens for breast cancer prevention. We therefore examined markers of DER in the breast, adipose tissue, and serum. Nineteen overweight or obese women at moderately increased risk of breast cancer (lifetime risk, 1 in 6 to 1 in 3) ages between 35 and 45 were randomly allocated to DER [liquid diet, 3,656 kJ/d (864 kcal/d); n = 10] or asked to continue their normal eating patterns (n = 9) for one menstrual cycle. Biopsies of the breast and abdominal fat were taken before and after the intervention. RNA was extracted from whole tissues and breast epithelium (by laser capture microdissection) and hybridized to Affymetrix GeneChips. Longitudinal plasma and urine samples were collected before and after intervention, and metabolic profiles were generated using gas chromatography-mass spectrometry. DER was associated with significant reductions in weight [-7.0 (+/-2.3) kg] and in alterations of serum biomarkers of breast cancer risk (insulin, leptin, total and low-density lipoprotein cholesterol, and triglycerides). In both abdominal and breast tissues, as well as isolated breast epithelial cells, genes involved in glycolytic and lipid synthesis pathways (including stearoyl-CoA desaturase, fatty acid desaturase, and aldolase C) were significantly down-regulated. We conclude that reduced expressions of genes in the lipid metabolism and glycolytic pathways are detectable in breast tissue following DER, and these may represent targets for DER mimetics as effective chemoprophylactic agents.

The LKB1-AMPK pathway: metabolism and growth control in tumour suppression

In the past decade, studies of the human tumour suppressor LKB1 have uncovered a novel signalling pathway that links cell metabolism to growth control and cell polarity. LKB1 encodes a serine-threonine kinase that directly phosphorylates and activates AMPK, a central metabolic sensor. AMPK regulates lipid, cholesterol and glucose metabolism in specialized metabolic tissues, such as liver, muscle and adipose tissue. This function has made AMPK a key therapeutic target in patients with diabetes. The connection of AMPK with several tumour suppressors suggests that therapeutic manipulation of this pathway using established diabetes drugs warrants further investigation in patients with cancer.

Do cancer cells care if their host is hungry?

A recent report by Kalaany and Sabatini concerning mechanisms underlying the inhibitory effect of dietary restriction on the growth of certain tumors adds to the evidence that insulin and IGF-I are hormones with relevance to oncology.

LKB1 and AMP-activated protein kinase control of mTOR signalling and growth

The AMP-activated serine/threonine protein kinase (AMPK) is a sensor of cellular energy status found in all eukaryotes that is activated under conditions of low intracellular ATP following stresses such as nutrient deprivation or hypoxia. In the past 5 years, work from a large number of laboratories has revealed that one of the major downstream signalling pathways regulated by AMPK is the mammalian target-of-rapamycin [mammalian target of rapamycin (mTOR) pathway]. Interestingly, like AMPK, the mTOR serine/threonine kinase plays key roles not only in growth control and cell proliferation but also in metabolism. Recent work has revealed that across eukaryotes mTOR orthologues are found in two biochemically distinct complexes and only one of those complexes (mTORC1 in mammals) is acutely sensitive to rapamycin and regulated by nutrients and AMPK. Many details of the molecular mechanism by which AMPK inhibits mTORC1 signalling have also been decoded in the past 5 years. AMPK directly phosphorylates at least two proteins to induce rapid suppression of mTORC1 activity, the TSC2 tumour suppressor and the critical mTORC1 binding subunit raptor. Here we explore the molecular connections between AMPK and mTOR signalling pathways and examine the physiological processes in which AMPK regulation of mTOR is critical for growth or metabolic control. The functional conservation of AMPK and TOR in all eukaryotes, and the sequence conservation around the AMPK phosphorylation sites in raptor across all eukaryotes examined suggest that this represents a fundamental cell growth module connecting nutrient status to the cell growth machinery. These findings have broad implications for the control of cell growth by nutrients in a number of cellular and organismal contexts.

AMP-activated protein kinase in the regulation of hepatic energy metabolism: from physiology to therapeutic perspectives

As the liver is central in the maintenance of glucose homeostasis and energy storage, knowledge of the physiology as well as physiopathology of hepatic energy metabolism is a prerequisite to our understanding of whole-body metabolism. Hepatic fuel metabolism changes considerably depending on physiological circumstances (fed vs. fasted state). In consequence, hepatic carbohydrate, lipid and protein synthesis/utilization are tightly regulated according to needs. Fatty liver and hepatic insulin resistance (both frequently associated with the metabolic syndrome) or increased hepatic glucose production (as observed in type 2 diabetes) resulted from alterations in substrates oxidation/storage balance in the liver. Because AMP-activated protein kinase (AMPK) is considered as a cellular energy sensor, it is important to gain understanding of the mechanism by which hepatic AMPK coordinates hepatic energy metabolism. AMPK has been implicated as a key regulator of physiological energy dynamics by limiting anabolic pathways (to prevent further ATP consumption) and by facilitating catabolic pathways (to increase ATP generation). Activation of hepatic AMPK leads to increased fatty acid oxidation and simultaneously inhibition of hepatic lipogenesis, cholesterol synthesis and glucose production. In addition to a short-term effect on specific enzymes, AMPK also modulates the transcription of genes involved in lipogenesis and mitochondrial biogenesis. The identification of AMPK targets in hepatic metabolism should be useful in developing treatments to reverse metabolic abnormalities of type 2 diabetes and the metabolic syndrome.

Short-term calorie restriction in male mice feminizes gene expression and alters key regulators of conserved aging regulatory pathways

Background

Calorie restriction (CR) is the only intervention known to extend lifespan in a wide range of organisms, including mammals. However, the mechanisms by which it regulates mammalian aging remain largely unknown, and the involvement of the TOR and sirtuin pathways (which regulate aging in simpler organisms) remain controversial. Additionally, females of most mammals appear to live longer than males within species; and, although it remains unclear whether this holds true for mice, the relationship between sex-biased and CR-induced gene expression remains largely unexplored.

Methodology/Principal Findings

We generated microarray gene expression data from livers of male mice fed high calorie or CR diets, and we find that CR significantly changes the expression of over 3,000 genes, many between 10- and 50-fold. We compare our data to the GenAge database of known aging-related genes and to prior microarray expression data of genes expressed differently between male and female mice. CR generally feminizes gene expression and many of the most significantly changed individual genes are involved in aging, hormone signaling, and p53-associated regulation of the cell cycle and apoptosis. Among the genes showing the largest and most statistically significant CR-induced expression differences are Ddit4, a key regulator of the TOR pathway, and Nnmt, a regulator of lifespan linked to the sirtuin pathway. Using western analysis we confirmed post-translational inhibition of the TOR pathway.

Conclusions

Our data show that CR induces widespread gene expression changes and acts through highly evolutionarily conserved pathways, from microorganisms to mammals, and that its life-extension effects might arise partly from a shift toward a gene expression profile more typical of females.

Energy homeostasis and cancer prevention: the AMP-activated protein kinase

Caloric restriction has long been recognized as an extremely effective cancer preventive. Current population demographics suggest that caloric excess and obesity will lead to increased cancer incidence, underscoring the need to elucidate the molecular mechanisms that couple dysregulated energy homeostasis to aberrant cell growth. The AMP-activated protein kinase (AMPK) is a critical monitor of cellular energy status, largely studied for its importance in metabolic regulation. AMPK also controls processes relevant to tumor development, including cell cycle progression, protein synthesis, cell growth, and survival. Several tumor suppressors impinge on AMPK signaling, and activation of the kinase inhibits tumor growth. However, AMPK can also promote cancer in some settings, necessitating a more complete understanding of the complexities of this signaling network. Because dysregulated energy balance is a nexus for multiple chronic diseases of aging, drugs that target these pathways may find broad utility in aging populations.

Effects of physical activity and restricted energy intake on chemically induced mammary carcinogenesis

In the field of energetics and cancer, little attention has been given to whether energy balance directed interventions designed to regulate body weight by increasing energy expenditure versus reducing energy intake have an equivalent effect on the development of breast cancer. The objective of this experiment was to determine the effects on mammary carcinogenesis of physical activity (PA), achieved via running on an activity wheel, or restricted energy intake (RE). Food intake of PA and RE rats was controlled so that both groups had the same net energy balance determined by growth rate, which was 92% of the sedentary control group (SC). A total of 135 female Sprague-Dawley rats were injected with 1-methyl-1-nitrosourea (50 mg/kg) and 7 days thereafter were randomized to either SC, PA, or RE. Mammary cancer incidence was 97.8%, 88.9%, and 84.4% and cancer multiplicity was 3.66, 3.11, and 2.64 cancers/rat in SC, RE, and PA, respectively (SC versus PA, P = 0.02 for incidence and P = 0.03 for multiplicity). Analyses of mammary carcinomas revealed that cell proliferation-associated proteins were reduced and caspase-3 activity and proapoptotic proteins were elevated by PA or RE relative to SC (P < 0.05). It was observed that these effects may be mediated, in part, by activation of AMP-activated protein kinase and down-regulation of protein kinase B and the mammalian target of rapamycin.

Insulin and insulin-like growth factor signalling in neoplasia

Insulin and insulin-like growth factors (IGFs) are well known as key regulators of energy metabolism and growth. There is now considerable evidence that these hormones and the signal transduction networks they regulate have important roles in neoplasia. Epidermiological, clinical and laboratory research methods are being used to investigate novel cancer prevention and treatment strategies related to insulin and IGF signalling. Pharmacological strategies under study include the use of novel receptor-specific antibodies, receptor kinase inhibitors and AMP-activated protein kinase activators such as metformin. There is evidence that insulin and IGF signalling may also be relevant to dietary and lifestyle factors that influence cancer risk and cancer prognosis. Recent results are encouraging and have justified the expansion of many translational research programmes.

Reducing the weight of cancer: mechanistic targets for breaking the obesity-carcinogenesis link

The prevalence of obesity, an established epidemiologic risk factor for many cancers, has risen steadily for the past several decades in the US. The increasing rates of obesity among children are especially alarming and suggest continuing increases in the rates of obesity-related cancers for many years to come. Unfortunately, the mechanisms underlying the association between obesity and cancer are not well understood. In particular, the effects on the carcinogenesis process and mechanistic targets of interventions that modulate energy balance, such as reduced-calorie diets and physical activity, have not been well characterized. The purpose of this review is to provide a strong foundation for the translation of mechanism-based research in this area by describing key animal and human studies of energy balance modulations involving diet or physical activity and by focusing on the interrelated pathways affected by alterations in energy balance. Particular attention is placed on signaling through the insulin and insulin-like growth factor-1 receptors, including components of the Akt and mammalian target of rapamycin (mTOR) signaling pathways downstream of these growth factor receptors. These pathways have emerged as potential targets for disrupting the obesity-cancer link. The ultimate goal of this work is to provide the missing mechanistic information necessary to identify targets for the prevention and control of cancers related to or caused by excess body weight.