Role of insulin, adipocyte hormones, and nutrient-sensing pathways in regulating fuel metabolism and energy homeostasis: a nutritional perspective of diabetes, obesity, and cancer

Effect of walking exercise on abdominal fat, insulin resistance and serum cytokines in obese women

PURPOSE

The purpose of the study was to investigate the effect of 12-week walking exercise on abdominal fat, insulin resistance and serum cytokines in obese women.

METHODS

Following baseline measurements, obese women (N = 20) who met obesity criterion of BMI at 25 kg/m(2) or greater were randomly assigned to the control (n = 10) or exercise groups (n = 10). Women assigned to the exercise group participated in a walking exercise (with an intensity of 50-60% of predetermined VO(2)max, a frequency of 3 days per week and duration of 50-70 minutes targeting 400 kcal of energy expenditure per session) for 12 weeks, while women assigned to the control group maintained their sedentary lifestyle. After the 12-week walking intervention, post-test measurements were conducted using the same procedure as the baseline measurement. Analyses of variance with repeated measures were used to evaluate any significant time by group interactions for the measured variables.

RESULTS

With respect to body fat parameters, significant time-by-group interactions were found in the abdominal subcutaneous (p = < 0.001) and visceral adipose tissues (p = 0.011). The exercise group had significant reductions in both subcutaneous and visceral adiposity, and the control group had no significant changes in those parameters. Similarly, there were significant time by group interactions in fasting glucose (p = 0.008), HOMA-IR (p = 0.029), serum TNF-α (p = 0.027), and IL-6 (p = 0.048) such that the exercise group had significant reductions in those parameters, with no such significant changes found in the control group. The exercise group also had a significant increase in serum adiponectin (p = 0.002), whereas the control group had no significant change in the parameter.

CONCLUSION

In summary, the current findings suggest that walking exercise can provide a safe and effective lifestyle strategy against abdominal obesity and serum insulin resistance markers in obese women.

O-GlcNAcylation regulates cancer metabolism and survival stress signaling via regulation of the HIF-1 pathway

The hexosamine biosynthetic pathway elevates posttranslational addition of O-linked β-N-acetylglucosamine (O-GlcNAc) on intracellular proteins. Cancer cells elevate total O-GlcNAcylation by increasing O-GlcNAc transferase (OGT) and/or decreasing O-GlcNAcase (OGA) levels. Reducing O-GlcNAcylation inhibits oncogenesis. Here, we demonstrate that O-GlcNAcylation regulates glycolysis in cancer cells via hypoxia-inducible factor 1 (HIF-1α) and its transcriptional target GLUT1. Reducing O-GlcNAcylation increases α-ketoglutarate, HIF-1 hydroxylation, and interaction with von Hippel-Lindau protein (pVHL), resulting in HIF-1α degradation. Reducing O-GlcNAcylation in cancer cells results in activation of endoplasmic reticulum (ER) stress and cancer cell apoptosis mediated through C/EBP homologous protein (CHOP). HIF-1α and GLUT1 are critical for OGT-mediated regulation of metabolic stress, as overexpression of stable HIF-1 or GLUT1 rescues metabolic defects. Human breast cancers with high levels of HIF-1α contain elevated OGT, and lower OGA levels correlate independently with poor patient outcome. Thus, O-GlcNAcylation regulates cancer cell metabolic reprograming and survival stress signaling via regulation of HIF-1α.

Early detection of metabolic and energy disorders by thermal time series stochastic complexity analysis

Maintenance of thermal homeostasis in rats fed a high-fat diet (HFD) is associated with changes in their thermal balance. The thermodynamic relationship between heat dissipation and energy storage is altered by the ingestion of high-energy diet content. Observation of thermal registers of core temperature behavior, in humans and rodents, permits identification of some characteristics of time series, such as autoreference and stationarity that fit adequately to a stochastic analysis. To identify this change, we used, for the first time, a stochastic autoregressive model, the concepts of which match those associated with physiological systems involved and applied in male HFD rats compared with their appropriate standard food intake age-matched male controls (n=7 per group). By analyzing a recorded temperature time series, we were able to identify when thermal homeostasis would be affected by a new diet. The autoregressive time series model (AR model) was used to predict the occurrence of thermal homeostasis, and this model proved to be very effective in distinguishing such a physiological disorder. Thus, we infer from the results of our study that maximum entropy distribution as a means for stochastic characterization of temperature time series registers may be established as an important and early tool to aid in the diagnosis and prevention of metabolic diseases due to their ability to detect small variations in thermal profile.

Increased sugar uptake promotes oncogenesis via EPAC/RAP1 and O-GlcNAc pathways

There is a considerable resurgence of interest in the role of aerobic glycolysis in cancer; however, increased glycolysis is frequently viewed as a consequence of oncogenic events that drive malignant cell growth and survival. Here we provide evidence that increased glycolytic activation itself can be an oncogenic event in a physiologically relevant 3D culture model. Overexpression of glucose transporter type 3 (GLUT3) in nonmalignant human breast cells activated known oncogenic signaling pathways, including EGFR, β1 integrin, MEK, and AKT, leading to loss of tissue polarity and increased growth. Conversely, reduction of glucose uptake in malignant cells promoted the formation of organized and growth-arrested structures with basal polarity, and suppressed oncogenic pathways. Unexpectedly and importantly, we found that unlike reported literature, in 3D the differences between "normal" and malignant phenotypes could not be explained by HIF-1α/2α, AMPK, or mTOR pathways. Loss of epithelial integrity involved activation of RAP1 via exchange protein directly activated by cAMP (EPAC), involving also O-linked N-acetylglucosamine modification downstream of the hexosamine biosynthetic pathway. The former, in turn, was mediated by pyruvate kinase M2 (PKM2) interaction with soluble adenylyl cyclase. Our findings show that increased glucose uptake activates known oncogenic pathways to induce malignant phenotype, and provide possible targets for diagnosis and therapeutics.

TRIB3 mediates glucose-induced insulin resistance via a mechanism that requires the hexosamine biosynthetic pathway

In the current study, we investigated the role of tribbles homolog 3 (TRIB3) in glucose-induced insulin resistance and whether the induction of TRIB3 by glucose is dependent on the nutrient-sensing hexosamine biosynthetic pathway (HBP) known to mediate glucose toxicity in diabetes. In diabetic rats, TRIB3 expression in skeletal muscle was increased after 10 days of hyperglycemia, and glycemia and muscle TRIB3 were both restored toward normal by insulin therapy. In L6 myocytes, the induction of TRIB3 by high glucose or glucosamine was reversible upon removal of these substrates. To assess the role of HBP in the induction of TRIB3, we demonstrated that the ability of high glucose to augment TRIB3 expression was prevented by azaserine, an inhibitor of glutamine: fructose-6-phosphate amidotransferase (GFAT), which is the rate-limiting enzyme in the HBP pathway. TRIB3 expression was also substantially stimulated by glucosamine, which bypasses GFAT, accompanied by a decrease in the insulin-stimulated glucose transport rate, and neither response was affected by azaserine. Further, knockdown of TRIB3 inhibited, and TRIB3 overexpression enhanced, the ability of both high glucose and glucosamine to induce insulin resistance. These data provide the mechanistic link between the HBP flux and insulin resistance and point to TRIB3 as a novel target for treatment of glucose-induced insulin resistance.

Metabolic and transcriptional response to a high-fat diet in Drosophila melanogaster

Obesity has dramatically increased in prevalence, making it essential to understand its accompanying metabolic changes. Modeling diet-induced obesity in Drosophila melanogaster (fruit flies), we elucidated transcriptional and metabolic changes in w¹¹¹⁸ flies on a high-fat diet (HFD). Mass spectrometry-based metabolomics revealed altered fatty acid, amino acid, and carbohydrate metabolism with HFD. Microarray analysis uncovered transcriptional changes in nitrogen metabolism, including CG9510, homolog of human argininosuccinate lyase (ASL). CG9510 knockdown in flies phenocopied traits observed with HFD, namely increased triglyceride levels and decreased cold tolerance. Restoration of CG9510 expression ameliorated observed negative consequences of HFD. Metabolomic analysis of CG9510 knockdown flies confirmed functional similarity to ASL, regulating the balance of carbon and nitrogen metabolism. In summary, we found that HFD suppresses CG9510 expression, a gene required for proper triglyceride storage and stress tolerance. These results draw an important link between regulation of amino acid metabolism and the response to diet-induced obesity.

Cranberry interacts with dietary macronutrients to promote healthy aging in Drosophila

Botanicals possess numerous bioactivities, and some promote healthy aging. Dietary macronutrients are major determinants of life span. The interaction between botanicals and macronutrients that modulates life span is not well understood. Here, we investigated the effect of a cranberry-containing botanical on life span and the influence of macronutrients on the longevity-related effect of cranberry in Drosophila. Flies were supplemented with cranberry on three dietary conditions: standard, high sugar-low protein, and low sugar-high protein diets. We found that cranberry slightly extended life span in males fed with the low sugar-high protein diet but not with other diets. Cranberry extended life span in females fed with the standard diet and more prominently the high sugar-low protein diet but not with the low sugar-high protein diet. Life-span extension was associated with increased reproduction and higher expression of oxidative stress and heat shock response genes. Moreover, cranberry improved survival of sod1 knockdown and dfoxo mutant flies but did not increase wild-type fly's resistance to acute oxidative stress. Cranberry slightly extended life span in flies fed with a high-fat diet. These findings suggest that cranberry promotes healthy aging by increasing stress responsiveness. Our study reveals an interaction of cranberry with dietary macronutrients and stresses the importance of considering diet composition in designing interventions for promoting healthy aging.

Common Beans and Their Non-Digestible Fraction: Cancer Inhibitory Activity-An Overview

The US Department of Agriculture’s MyPyramid guidelines introduced a near doubling of the dietary recommendations for vegetables including dry beans—an important food staple in many traditional diets that can improve public health and nutrition. Populations with high legume (peas, beans, lentils) consumption have a low risk of cancer and chronic degenerative diseases. Common beans (Phaseolus vulgaris L.) are known as a rich, reliable source of non-digested compounds like fiber, phenolics, peptides and phytochemicals that are associated with health benefits. Emerging evidence indicates that common bean consumption is associated with reduced cancer risk in human populations, inhibiting carcinogenesis in animal models and inducing cell cycle arrest and apoptosis in cell cultures. Fiber may reduce the risk of premature death from all causes, whereas the whole non-digestible fraction from common beans exhibits anti-proliferative activity and induces apoptosis in vitro and in vivo colon cancer. The mechanisms responsible for this apparently protective role may include gene-nutrient interactions and modulation of proteins’ expression. This review investigates the potential health benefits and bioactivity of beans on tumor inhibition, highlighting studies involving functional compounds, mainly non-digestible fractions that modulate genes and proteins, thereby, unraveling their preventive role against the development of cancer.

[New perspectives for metformin in cancer therapy]

Cancer and type II diabetes are two diseases that appear to be associated. In fact, diabetes increases the incidence of several cancers (colon, endometrium, rectum and breast). Retrospective epidemiological studies show that metformin, a drug commonly used in type II diabetes, has antitumor properties. Therefore, many experimental studies (in vivo and in vitro) have been initiated in recent years to understand the cellular and molecular mechanisms that may explain the protective effects of metformin against cancer. Two main mode of action have been proposed. The first, indirect, involves the decrease of insulinemia. The second, via a direct action on cells, results in the regulation of the activated AMPK kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway, which plays a central role in many cellular processes such as energy metabolism, protein synthesis, autophagy and apoptosis. Here, we review recent results concerning the antitumor action of metformin: epidemiological, metabolic, cellular and molecular levels. Ongoing experimental and clinical trials should help us better understand the mechanisms of action of metformin and allow us to determine whether the drug can be used in the treatment of cancer.

Reduction of dietary glycaemic load modifies the expression of microRNA potentially associated with energy balance and cancer pathways in pre-menopausal women

Energy metabolism, insulin resistance and adiposity have been implicated in breast cancer, but dietary interventions to reduce breast cancer morbidity and mortality have had limited success. MicroRNA (miRNA) are short, non-coding RNA that participate in the control of metabolic processes through the post-transcriptional modification of RNA. We investigated the effect of a low-glycaemic load dietary intervention on miRNA expression, with subsequent bioinformatics pathway analyses to explore metabolic pathways potentially affected by the diet. Total RNA, including miRNA, was isolated from the serum of fourteen otherwise healthy pre-menopausal women with a high breast cancer risk participating in a 12-month dietary intervention designed to lower glycaemic load by at least 15% from baseline. Genome-wide miRNA expression was conducted using Illumina BeadChips. In the intervention subjects, three differentially expressed miRNA were validated by real-time (RT)-PCR, and in the twenty control participants, four top differentially expressed miRNA were evaluated to confirm a diet effect. In post-intervention v. baseline serum, twenty miRNA were found to be differentially expressed, with twelve up-regulated and eight down-regulated. These differentially expressed miRNA were predicted to be potentially associated with energy balance and cancer pathways based on exploratory enrichment analysis. Quantitative RT-PCR validations in the controls confirmed that the observed miRNA differential expression was dietary intervention induced. Manipulation of dietary glycaemic load has the potential to modify the expression of multiple miRNA predicted to be involved in energy balance and cancer pathways. Further research is necessary to confirm the role of these miRNA in the control of energy metabolism and relationships with cancer-related processes.

Development of a core collection of Triticum and Aegilops species for improvement of wheat for activity against chronic diseases

Background

The objective of this study was to develop a core collection of Triticum and Aegilops species as a resource for the identification and characterization of wheat lines with preventive activity against chronic diseases. Given that cancer is the leading cause of mortality in the world and shares risk factors with obesity, type-2 diabetes, and cardiovascular disease, and given that wheat has been reported to protect against these diseases, the core collection was developed based on cancer prevalence.

Methods

The Germplasm Resources Information Network (GRIN) database was used to identify Triticum and Aegilops species grown in regions of the world that vary in cancer prevalence based on the International Agency for Cancer Research GLOBOCAN world map of cancer statistics (2008). Cancer incidence data drove variety selection with secondary consideration of ploidy, center of origin, and climate.

Results

Analysis indicated that the geographic regions from which wheat is considered to have originated have a lower incidence of cancer than other geographic regions (P <0.01), so wheat lines from countries that comprise the ‘Fertile Crescent’ were highly represented in the core collection. A total of 188 lines were selected from 62,571 accessions maintained by GRIN. The accessions identified comprised two genera and 14 taxa of 10 species within 19 groups from 82 countries. The core collection is comprised of 153 spring, 25 winter, and five facultative selections of wheat.

Conclusions

A diverse core collection of wheat germplasm has been established from a range of regions worldwide. This core collection will be used to identify wheat lines with activity against chronic diseases using anticancer activity as a screening tool.

Altered lipid homeostasis in Drosophila InsP3 receptor mutants leads to obesity and hyperphagia

Obesity is a complex metabolic disorder that often manifests with a strong genetic component in humans. However, the genetic basis for obesity and the accompanying metabolic syndrome is poorly defined. At a metabolic level, obesity arises from an imbalance between the nutritional intake and energy utilization of an organism. Mechanisms that sense the metabolic state of the individual and convey this information to satiety centers help achieve this balance. Mutations in genes that alter or modify such signaling mechanisms are likely to lead to either obese individuals, who in mammals are at high risk for diabetes and cardiovascular disease, or excessively thin individuals with accompanying health problems. Here we show that Drosophila mutants for an intracellular calcium signaling channel, the inositol 1,4,5-trisphosphate receptor (InsP₃R) store excess triglycerides in their fat bodies and become unnaturally obese on a normal diet. Although excess insulin signaling can rescue obesity in InsP₃R mutants to some extent, we show that it is not the only cause of the defect. Through mass spectrometric analysis of lipids we find that homeostasis of storage and membrane lipids are altered in InsP₃R mutants. Possibly as a compensatory mechanism, InsP₃R mutant adults also feed excessively. Thus, reduced InsP₃R function alters lipid metabolism and causes hyperphagia in adults. Together, the metabolic and behavioral changes lead to obesity. Our results implicate altered InsP₃ signaling as a previously unknown causative factor for metabolic syndrome in humans. Importantly, our studies also suggest preventive dietary interventions.

The multi-functional roles of GNMT in toxicology and cancer

Although glycine N-methyltransferase (GNMT) has been discovered for five decades, its function was not elucidated until recently. In this review, we discuss the multiple roles of GNMT in toxicology and cancer. Besides catalyzing the production of methylglycine (sarcosine) in one carbon metabolism pathway, GNMT was found to be able to bind a number of polycyclic aromatic hydrocarbons and inhibit DNA adducts formation. Moreover, GNMT exerts protective effects against the cytotoxicity and carcinogenicity of benzo(a)pyrene and aflatoxin B(1) in vitro and in vivo. Occupational study showed that workers who had genotypes with higher GNMT promoter activity may have lower content of oxidative damaged DNA products in their urine. In terms of cancer, recent studies using GNMT knockout mouse models demonstrated that GNMT deficiency has high penetrance in inducing the development of steatohepatitis and hepatocellular carcinoma. In terms of the mechanism, besides dysregulation of epigenetic modification, insights have been provided by recent identification of two novel proteins interacting with GNMT-DEPTOR and NPC2. These studies suggest that GNMT not only is involved in mTOR signaling pathway, but also plays an important role in the intracellular trafficking of cholesterol. The implication of these findings to the preventive medicine and translational research will be discussed.

Fat body dSir2 regulates muscle mitochondrial physiology and energy homeostasis nonautonomously and mimics the autonomous functions of dSir2 in muscles

Sir2 is an evolutionarily conserved NAD(+)-dependent deacetylase which has been shown to play a critical role in glucose and fat metabolism. In this study, we have perturbed Drosophila Sir2 (dSir2) expression, bidirectionally, in muscles and the fat body. We report that dSir2 plays a critical role in insulin signaling, glucose homeostasis, and mitochondrial functions. Importantly, we establish the nonautonomous functions of fat body dSir2 in regulating mitochondrial physiology and insulin signaling in muscles. We have identified a novel interplay between dSir2 and dFOXO at an organismal level, which involves Drosophila insulin-like peptide (dILP)-dependent insulin signaling. By genetic perturbations and metabolic rescue, we provide evidence to illustrate that fat body dSir2 mediates its effects on the muscles via free fatty acids (FFA) and dILPs (from the insulin-producing cells [IPCs]). In summary, we show that fat body dSir2 is a master regulator of organismal energy homeostasis and is required for maintaining the metabolic regulatory network across tissues.

Secreted frizzled-related protein 5 suppresses adipocyte mitochondrial metabolism through WNT inhibition

Preadipocytes secrete several WNT family proteins that act through autocrine/paracrine mechanisms to inhibit adipogenesis. The activity of WNT ligands is often decreased by secreted frizzled-related proteins (SFRPs). Sfrp5 is strongly induced during adipocyte differentiation and increases in adipocytes during obesity, presumably to counteract WNT signaling. We tested the hypothesis that obesity-induced Sfrp5 expression promotes the development of new adipocytes by inhibiting endogenous suppressors of adipogenesis. As predicted, mice that lack functional SFRP5 were resistant to diet-induced obesity. However, counter to our hypothesis, we found that adipose tissue of SFRP5-deficient mice had similar numbers of adipocytes, but a reduction in large adipocytes. Transplantation of adipose tissue from SFRP5-deficient mice into leptin receptor-deficient mice indicated that the effects of SFRP5 deficiency are tissue-autonomous. Mitochondrial gene expression was increased in adipose tissue and cultured adipocytes from SFRP5-deficient mice. In adipocytes, lack of SFRP5 stimulated oxidative capacity through increased mitochondrial activity, which was mediated in part by PGC1α and mitochondrial transcription factor A. WNT3a also increased oxygen consumption and the expression of mitochondrial genes. Thus, our findings support a model of adipogenesis in which SFRP5 inhibits WNT signaling to suppress oxidative metabolism and stimulate adipocyte growth during obesity.

Regulation of the proteasome by AMPK in endothelial cells: the role of O-GlcNAc transferase (OGT)

26S proteasome is a macromolecular multi-subunit complex responsible for recognizing, unfolding, and ultimately destroying proteins. It remains poorly understood how 26S proteasome activity is regulated. The present study was to investigate if AMP-activated protein kinase (AMPK) functions as a physiological suppressor of the 26S proteasome in endothelial cells. 26S proteasome assembly, activity, and O-GlcNAcylation of P700 were assayed in cultured human umbilical vein endothelial cells (HUVEC) and mouse aortas isolated from C57BL6 wild type and AMPKα2 knockout mice with or without being exposed to selective AMPK activators or inhibitors. Pharmacological and genetic activation of AMPK effectively suppresses 26S proteasomes in endothelial cells. Conversely, inactivation of AMPK either pharmacologically or genetically increases 26S proteasome activity; furthermore, the inactivation decreases the O-GlcNAcylation of PA700/S10B (the regulatory complex in 26S proteasomes) and increases the assembly of 26S proteasomes. In contrast, AMPK activation increases levels of O-GlcNAcylated PA700/S10B, likely through enhanced association of PA700 with O-GlcNAc transferase (OGT), the enzyme that catalyzes protein O-GlcNAcylation. Finally, aortas from AMPK-KO vs wild type mice exhibit elevated 26S proteasome activity in parallel with decreased PA700/S10B O-GlcNAcylation and PA700/S10B-OGT association. Taken together, we conclude that AMPK functions as a physiological suppressor of 26S proteasomes.

A two-way street: reciprocal regulation of metabolism and signalling

It is becoming increasingly clear that cellular signalling and metabolism are not just separate entities but rather are tightly linked. Although nutrient metabolism is known to be regulated by signal transduction, an emerging paradigm is that signalling and transcriptional networks can be modulated by nutrient-sensitive protein modifications, such as acetylation and glycosylation, which depend on the availability of acetyl-CoA and sugar donors such as UDP-N-acetylglucosamine (UDP-GlcNAc), respectively. The integration of metabolic and signalling cues allows cells to modulate activities such as metabolism, cell survival and proliferation according to their intracellular metabolic resources.

Roles of AMP-activated protein kinase in Alzheimer's disease

AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis and a central player in glucose and lipid metabolism, is potentially implicated in the pathogenesis of Alzheimer's disease (AD). AMPK activity decreases in AD brain, indicating decreased mitochondrial biogenesis and function. Emerging evidence demonstrates that AMPK activation is a potential target for improving perturbed brain energy metabolism that is involved in the pathogenesis of AD. The roles of AMPK in the pathogenesis of AD include β-amyloid protein (Aβ) generation and tau phosphorylation. In particular, AMPK may regulate Aβ generation through modulating neuronal cholesterol and sphingomyelin levels and through regulating APP distribution in the lipid rafts. AMPK is activated by phosphorylation of Thr-172 by LKB1 complex in response to increase in the AMP/ATP ratio and by calmodulin-dependent protein kinase kinase-beta in response to elevated Ca(2+) levels, which contributes to regulating Aβ generation. AMPK is a physiological tau kinase and can increase the phosphorylation of tau at Ser-262. AMPK can also directly phosphorylate tau at Thr-231 and Ser-396/404. Furthermore, AMPK activation decreases mTOR signaling activity to facilitate autophagy and promotes lysosomal degradation of Aβ. However, AMPK activation has non-neuroprotective property and may lead to detrimental outcomes, including Aβ generation and tau phosphorylation. Therefore, it is still unclear whether AMPK could serve a potential therapeutic target for AD, and hence, further studies will be needed to clarify the role of AMPK in AD.

TBC1D3, a hominoid-specific gene, delays IRS-1 degradation and promotes insulin signaling by modulating p70 S6 kinase activity

Insulin/IGF-1 signaling plays a pivotal role in the regulation of cellular homeostasis through its control of glucose metabolism as well as due to its effects on cell proliferation. Aberrant regulation of insulin signaling has been repeatedly implicated in uncontrolled cell growth and malignant transformations. TBC1D3 is a hominoid specific gene previously identified as an oncogene in breast and prostate cancers. Our efforts to identify the molecular mechanisms of TBC1D3-induced oncogenesis revealed the role of TBC1D3 in insulin/IGF-1 signaling pathway. We document here that TBC1D3 intensifies insulin/IGF-1-induced signal transduction through intricate, yet elegant fine-tuning of signaling mechanisms. We show that TBC1D3 expression substantially delayed ubiquitination and degradation of insulin receptor substrate-1 (IRS-1). This effect is achieved through suppression of serine phosphorylation at S636/639, S307 and S312 of IRS-1, which are key phosphorylation sites required for IRS-1 degradation. Furthermore, we report that the effect of TBC1D3 on IRS-1:S636/639 phosphorylation is mediated through TBC1D3-induced activation of protein phosphatase 2A (PP2A), followed by suppression of T389 phosphorylation on p70 S6 kinase (S6K). TBC1D3 specifically interacts with PP2A regulatory subunit B56γ, indicating that TBC1D3 and PP2A B56γ operate jointly to promote S6K:T389 dephosphorylation. These findings suggest that TBC1D3 plays an unanticipated and potentially unique role in the fine-tuning of insulin/IGF-1 signaling, while providing novel insights into the regulation of tumorigenesis by a hominoid-specific protein.

Expression of new loci associated with obesity in diet-induced obese rats: from genetics to physiology

Genome-wide association studies (GWAS) are a powerful tool for revealing genes associated with common human obesity. New loci associated with obesity have recently been reported, but their function and metabolic implications remain to be elucidated. In order to begin identifying the role of some of these obesity-related loci, the closest genes to the polymorphism of each locus were selected and their expression was compared in the hypothalamus, adipose tissue, liver, soleus muscle, and extensor digitorum longus muscle (EDL) of Long-Evans rats maintained on chow or a high-fat diet (HFD) for 6 weeks. From a total of 19 genes analyzed, seven genes (ETV5, FTO, GNPDA2, KCTD15, TMEM18, MC4R, and SH2B1) were down-regulated in the hypothalamus of HFD compared to chow-fed rats. In adipose tissue of rats fed on HFD, the mRNA levels of BCDIN3, KCTD15, and SULT1A1 were down-regulated, whereas those of MTCH2, PTER, and TUFM were up-regulated. In the liver, three genes were up-regulated (PTER, SULT1A1, and TUFM) in HFD relative to chow-fed rats, and TMEM18 was down-regulated. Finally, in soleus muscle of HFD-fed rats, BCDIN3, BDNF, and TMEM18 were down-regulated, and in the EDL muscle SH2B1 and TUFM were up-regulated. mRNA levels in the hypothalamus were compared between fed and fasted states, and only KCTD15 was down-regulated during fasting when fed a chow diet. In conclusion, novel genes found to be associated with obesity are regulated by a HFD and the mRNA levels of KCTD15 is dependent on the nutritional status. These results suggest a potential role of these genes in the regulation of energy balance.

Critical role of O-Linked β-N-acetylglucosamine transferase in prostate cancer invasion, angiogenesis, and metastasis

Cancer cells universally increase glucose and glutamine consumption, leading to the altered metabolic state known as the Warburg effect; one metabolic pathway, highly dependent on glucose and glutamine, is the hexosamine biosynthetic pathway. Increased flux through the hexosamine biosynthetic pathway leads to increases in the post-translational addition of O-linked β-N-acetylglucosamine (O-GlcNAc) to various nuclear and cytosolic proteins. A number of these target proteins are implicated in cancer, and recently, O-GlcNAcylation was shown to play a role in breast cancer; however, O-GlcNAcylation in other cancers remains poorly defined. Here, we show that O-GlcNAc transferase (OGT) is overexpressed in prostate cancer compared with normal prostate epithelium and that OGT protein and O-GlcNAc levels are elevated in prostate carcinoma cell lines. Reducing O-GlcNAcylation in PC3-ML cells was associated with reduced expression of matrix metalloproteinase (MMP)-2, MMP-9, and VEGF, resulting in inhibition of invasion and angiogenesis. OGT-mediated regulation of invasion and angiogenesis was dependent upon regulation of the oncogenic transcription factor FoxM1, a key regulator of invasion and angiogenesis, as reducing OGT expression led to increased FoxM1 protein degradation. Conversely, overexpression of a degradation-resistant FoxM1 mutant abrogated OGT RNAi-mediated effects on invasion, MMP levels, angiogenesis, and VEGF expression. Using a mouse model of metastasis, we found that reduction of OGT expression blocked bone metastasis. Altogether, these data suggest that as prostate cancer cells alter glucose and glutamine levels, O-GlcNAc modifications and OGT levels become elevated and are required for regulation of malignant properties, implicating OGT as a novel therapeutic target in the treatment of cancer.

Prevalence, risk factors and complications associated with type 2 diabetes in migrant South Asians

It is estimated that type 2 diabetes (T2D) currently affects about 246 million people worldwide, with South Asians, especially Indians, having both the largest number of cases and the fastest growing prevalence. South Asian ethnicity has been identified as a major risk factor for the development of T2D with central adiposity, insulin resistance and an unfavourable lipid profile being identified as predominant signals of alarm. Leading databases, including Web of Science, Medline, PubMed and Science Direct, were consulted and manual searches were conducted for cited references in leading diabetes-related journals. In all, 152 articles were included for the final assessment reported in this review. Genetic predisposition, central adiposity and unfavourable lifestyle, including physical inactivity and an unhealthy diet, were associated with the prevalence of T2D in migrant South Asians. 'Westernization', acculturation, socio-economic factors and lack of knowledge about the disease have also been identified as contributors to the development of T2D in this population. Higher prevalence of T2D in migrant South Asians may not be entirely attributed to genetic predisposition; hence, ethnicity and associated modifiable risk factors need further investigation. Preventive measures and appropriate interventions are currently limited by the lack of ethnic-specific cut-off points for anthropometric and biological markers, as well as by the absence of reliable methods for dietary and physical activity assessment. This article describes the prevalence rate, risk factors and complications associated with T2D in migrant South Asians living in different countries.

A lipid-droplet-targeted O-GlcNAcase isoform is a key regulator of the proteasome

Protein-O-linked N-Acetyl-β-D-glucosaminidase (O-GlcNAcase, OGA; also known as hexosaminidase C) participates in a nutrient-sensing, hexosamine signaling pathway by removing O-linked N-acetylglucosamine (O-GlcNAc) from key target proteins. Perturbations in O-GlcNAc signaling have been linked to Alzheimer's disease, diabetes and cancer. Mammalian O-GlcNAcase exists as two major spliced isoforms differing only by the presence (OGA-L) or absence (OGA-S) of a histone-acetyltransferase domain. Here we demonstrate that OGA-S accumulates on the surface of nascent lipid droplets with perilipin-2; both of these proteins are stabilized by proteasome inhibition. We show that selective downregulation of OGA-S results in global proteasome inhibition and the striking accumulation of ubiquitinylated proteins. OGA-S knockdown increased levels of perilipin-2 and perilipin-3 suggesting that O-GlcNAc-dependent regulation of proteasomes might occur on the surface of lipid droplets. By locally activating proteasomes during maturation of the nascent lipid droplet, OGA-S could participate in an O-GlcNAc-dependent feedback loop regulating lipid droplet surface remodeling. Our findings therefore suggest a mechanistic link between hexosamine signaling and lipid droplet assembly and mobilization.

Cell signaling pathways associated with a reduction in mammary cancer burden by dietary common bean (Phaseolus vulgaris L.)

Emerging evidence indicates that common bean (Phaseolus vulgaris L.) is associated with reduced cancer risk in human populations and rodent carcinogenesis models. This study sought to identify cancer-associated molecular targets that mediate the effects of bean on cancer burden in a chemically induced rat model for breast cancer. Initial experiments were conducted using a high dietary concentration of bean (60% wt/wt) where carcinoma burden in bean-fed rats was reduced 62.2% (P < 0.001) and histological and western blot analyses revealed that the dominant cellular process associated with reduced burden was induction of apoptosis. Further analysis of mammary carcinomas revealed changes in the phosphorylation states of mammalian target of rapamycin (mTOR) substrates (4E-binding protein 1 and p70S6 kinase) and mTOR regulators adenosine monophosphate-activated protein kinase and protein kinase B (Akt) (P < 0.001). Effects on mTOR signaling in carcinomas were also found at lower dietary concentrations of bean (7.5-30% wt/wt). Liquid chromatography-time of flight-mass spectrometry analysis of plasma provided evidence of altered lipid metabolism consistent with reduced mTOR network activity in the liver (P < 0.001). Plasma concentrations of insulin and insulin-like growth factor-1 were reduced by 36.3 and 38.9%, respectively, (P < 0.001), identifying a link to Akt regulation. Plasma C-reactive protein, a prognostic marker for long-term survival in breast cancer patients, was reduced by 23% (P < 0.001) in bean-fed rats. Identification of a role for the mTOR signaling network in the reduction of cancer burden by dietary bean is highly relevant given that this pathway is deregulated in the majority of human breast cancers.

Metabolic Syndrome and Breast Cancer Risk: Is There a Role for Metformin?

Obesity is one of the most important known preventable causes of cancer, accounting for up to 20% of cancer deaths in women. Obese women have increased risk of dying from breast cancer as well as an increased risk of distant metastasis. Metabolic Syndrome (MetSyn) is a group of metabolic conditions that include 1) abdominal obesity, 2) atherogenic dyslipidemia, 3) elevated blood pressure, and 4) insulin resistance. MetSyn is known to promote the development of cardiovascular disease and diabetes and may be associated with increased breast cancer risk. Emerging evidence supports an association between mammary adipocytes and their secreted adipocytokines and breast cancer initiation and progression. Metformin (1,1-dimethylbiguanide hydrochloride) is a drug used to treat type 2 diabetes and MetSyn. We review the potential association between MetSyn in promoting breast cancer and emerging evidence for the use of metformin in cancer prevention.

Glucose metabolism gene variants modulate the risk of pancreatic cancer

Long-term type 2 diabetes is a known risk factor for pancreatic cancer (PC). We hypothesized that genetic variants in glucose metabolism modify individual susceptibility to PC, especially those associated with diabetes. We retrospectively genotyped 26 single-nucleotide polymorphisms of 5 glucose metabolism genes: glucokinase (GCK), glutamine-fructose-6-phosphate transaminase 1 (GFPT1), glucose phosphate isomerase (GPI), hexokinase 2 (HK2), and O-linked N-acetylglucosamine transferase (OGT) in a case-control study of PC conducted at MD Anderson during 2004 to 2010. Initial genotyping was conducted in 706 patients with PC and 706 cancer-free controls by using the Sequenom method. A HK2 genotype (R844K) with low frequency of homozygous variant was further examined in additional 948 patients and 476 controls. In the combined set of 1,654 cases and 1,182 controls, we showed a significant association of the HK2 R844K GA/AA genotype with reduced PC risk (OR = 0.78; 95% CI, 0.64-0.94; P = 0.009) and a significant interaction with diabetes (P(interaction) < 0.001). The HK2 R844K GA/AA genotype was associated with a reduced risk of PC among nondiabetic individuals (OR = 0.68; 95% CI, 0.56-0.83) but with increased risk among diabetic patients (OR = 3.69; 95% CI, 2.34-5.82). These risk associations remained statistically significant when the analysis was restricted to whites or after exclusion of recent onset diabetes. No significant main effect of other genes or significant interaction of genotype with other risk factors was observed. The findings show a potential role of HK2 gene, alone or in interaction with diabetes, in modifying the risk of PC.

Polyphenols: planting the seeds of treatment for the metabolic syndrome

Greater understanding about the pathogenesis of metabolic syndrome and potential causes suggests that plant polyphenols might be useful as a treatment. Dietary excess energy can be stored in adipocytes, leading to the release of proinflammatory cytokines and adipose-related hormones that cause vascular injury. Plant polyphenols, organic compounds found in numerous plant species and their fruits, are being actively studied as potential treatments for components of the metabolic syndrome. Individual polyphenols that have been examined include resveratrol, quercetin, epigallocathechin-3-gallate, and curcumin. Resveratrol lowers weight, blood pressure, glucose, and insulin resistance in rodents, and a human trial is currently underway. Quercetin decreases lipid and glucose levels in obese rats, and in a human investigation of subjects with the metabolic syndrome has lowered blood pressure without significant alteration of lipids. Epigallocathechin-3-gallate-induced weight loss has attenuated glucose levels and insulin resistance in rodents and improved hemoglobin A(1c) and lipid in human studies. Plant extracts also can be used. Grape seed and chokeberry extracts have decreased blood pressure and lipid levels in small human trials. Other human investigations have shown the beneficial effects of cocoa, coffee, carob, and Momordica charantia. Thus far, most studies have involved a small number of subjects and have been of short duration. Future studies should be designed to account for a disease process in which the pathogenic factors may take place for years before disease manifestations take place, the possibly limited bioavailability of polyphenols, and the potential need to provide combinations or modifications of polyphenols.

Digestion rate of dietary starch affects the systemic circulation of lipid profiles and lipid metabolism-related gene expression in weaned pigs

The present study was conducted to investigate the effect of digestion rate of dietary starch on postprandial systemic circulating glucose, insulin and lipid profiles, and the activity and gene expression of lipid metabolism-related enzymes in weaned pigs. A total of twenty-four weaned pigs, surgically fitted with a catheter in the jugular vein, were randomly assigned to three dietary treatment groups, representing the high digestion rate starch (HDRS) group, the moderate-digestion rate starch (MDRS) group and the low-digestion rate starch (LDRS) group. The amylopectin:amylose ratios in the diets of each group were 27·6:1, 27·6:8·5 and 1:27·6, respectively. The serum concentrations of glucose, TAG, total cholesterol, LDL-cholesterol and HDL-cholesterol in the HDRS group were increased to the peak point at postprandial 1·5, 2·5, 2·5, 1·5 and 1·5 h, those in the MDRS group were at postprandial 2·5, 3·5, 3·5, 3·5 and 3·5 h and those in the LDRS group were at postprandial 2·5, 3·5, 3·5, 1·5 and 3·5 h, respectively. The serum concentration of insulin in the HDRS group was higher (P < 0·05) than those in the MDRS group, and those in the MDRS group was also higher (P < 0·05) than those in the LDRS group at postprandial 0·5, 1·5 and 2·5 h, respectively. The serum concentrations of acetate, propionate and butyrate in the HDRS group were higher (P < 0·05) than those in the MDRS group, and those in the MDRS group were higher (P < 0·05) than in the LDRS group in each feeding cycle, in turn, respectively. The activity of fatty acid synthase (FAS) in the liver and abdominal adipose tissues, that of acetyl CoA carboxylase (ACC) in the myocardium and interscapular brown adipose tissues and that of the ATP-citrate lyase (ATP-CL) in the liver and interscapular brown adipose tissues in pigs of the HDRS group were higher (P < 0·05) than that of the MDRS group. The mRNA levels of FAS in the myocardium, liver and interscapular brown adipose tissues of pigs in the HDRS group were higher (P < 0·05) than those of the MDRS group. The activities and mRNA levels of FAS, ACC and ATP-CL in the myocardium, liver, abdominal and interscapular brown adipose tissues of the HDRS group were higher than those of the LDRS group. We conclude that the digestion rate of dietary starch affected not only the postprandial systemic circulating levels of glucose and insulin but also the lipid metabolism in weaned pigs. Dietary starch with higher digestion rate produces higher blood glucose and insulin response, ameliorates the blood lipid profiles and up-regulates the activity and gene expression profile of lipid metabolism-related genes in weaned pigs.

A heuristic model for paradoxical effects of biotin starvation on carbon metabolism genes in the presence of abundant glucose

We recently showed that in biotin starvation in yeast Saccharomyces cerevisiae, nematode Caenorhabditis elegans and rat Rattus norvegicus, despite abundant glucose provision, the expression of genes for glucose utilization and lipogenesis were lowered, and for fatty acid β-oxidation and gluconeogenesis were raised, and glycolytic/fermentative flow was reduced. This work explored the mechanisms of these results. We show that they are associated with ATP deficit and activation of the energy stress sensor AMP kinase (AMPK; Snf1 in yeast). Analysis of microarray results revealed extensive changes of transcripts for signal transduction pathways and transcription factors AMPK, SREBP-1c, ChREBP, NAMPT, PGC-1α, mTORC1 in rat, and their homologs in worm. In yeast the altered factor transcripts were Adr1, Cat8, Sip4, Mig1, HXK2, and Rgt1. The insulin pathway was negatively enriched (in rat and worm), whereas the adiponectins and JAK/STAT pathways were increased (present only in the rat; they activate AMPK). Together, all these changes explain the effects of biotin starvation on glucose utilization, energy status and carbon metabolism gene expression in a coherent manner across three phylogenetically distant eukaryotes and may have clinical significance in humans, since the effects are reminiscent of insulin resistance. We propose a general model for integrating these results in regulatory circuitries, according to the biology of each species, based on impaired anaplerosis due to pyruvate carboxylase deficiency, that have a basic underlying logic. In a preliminary test in yeast, aspartate corrects all the alterations produced by biotin starvation.

Influence of gestational overfeeding on cardiac morphometry and hypertrophic protein markers in fetal sheep

Intrauterine overnutrition is associated with development of cardiovascular disease in adulthood although the underlying mechanism has not been precisely elucidated. This study evaluated the effects of maternal overnutrition on fetal cardiac morphometry and hypertrophy-related mRNA/protein expression. Multiparous ewes were fed either 150% of National Research Council (NRC) nutrient requirements (overfed group) or 100% of NRC requirements (control group) from 60 days before mating to Day 75 (D75) of gestation, when ewes were euthanized. Cardiac morphometry, histology and expression of Akt, forkhead-3a (Foxo3a), glycogen synthase kinase-3β (GSK3β), mammalian target of rapamycin (mTOR), NFATc3 and GATA4, atrial natriuretic factor (ANF), calcineurin A and caspase-8 were examined. Crown rump length, left and right ventricular free wall weights and left ventricular wall thickness were increased in D75 overnourished fetuses. Hematoxylin and eosin staining revealed irregular myofiber orientation and increased interstitial space in heart tissues from overfed group. Masson's trichrome staining displayed myofiber hypertrophy and fascicular disarray in heart tissues from overfed group. Overfeeding significantly enhanced Foxo3a phosphorylation in both ventricles, while protein expression of Akt, Foxo3a, GSK3β and caspase-8 as well as phosphorylated Akt and GSK3β in either ventricle was unaffected. Overfeeding increased left ventricular mTOR, NFATc3 (both total and phosphorylated) and calcineurin A. GATA4, pGATA4 and ANF expression were unchanged in both ventricles. Collectively, our data suggested that overfeeding during early to mid gestation (D75) leads to morphometric changes without overt pathology which may be related to elevated expression of mTOR, NFATc3, calcineurin A and phosphorylation of Foxo3a, mTOR and NFATc3.

Cellular metabolic stress: considering how cells respond to nutrient excess

Nutrient stress is generally considered from the standpoint of how cells detect and respond to an insufficient supply of nutrients to meet their bioenergetic needs. However, cells also experience stress as a result of nutrient excess, during which reactive oxygen species (ROS) production exceeds that required for normal physiological responses. This may occur as a result of oncogene activation or chronic exposure to growth factors combined with high levels of nutrients. As a result, multiple mechanisms have evolved to allow cells to detect and adapt to elevated levels of intracellular metabolites, including promotion of signaling and proliferation by ROS, amino acid-dependent mTOR activation, and regulation of signaling and transcription through metabolite-sensitive protein modifications. We discuss how each of these responses can contribute to the development and/or progression of cancer under conditions of cellular nutrient excess and their potential roles in linking chronic organismal over-nutrition (obesity) with cancer.

Structural bases of PAS domain-regulated kinase (PASK) activation in the absence of activation loop phosphorylation

Per-Arnt-Sim (PAS) domain-containing protein kinase (PASK) is an evolutionary conserved protein kinase that coordinates cellular metabolism with metabolic demand in yeast and mammals. The molecular mechanisms underlying PASK regulation, however, remain unknown. Herein, we describe a crystal structure of the kinase domain of human PASK, which provides insights into the regulatory mechanisms governing catalysis. We show that the kinase domain adopts an active conformation and has catalytic activity in vivo and in vitro in the absence of activation loop phosphorylation. Using site-directed mutagenesis and structural comparison with active and inactive kinases, we identified several key structural features in PASK that enable activation loop phosphorylation-independent activity. Finally, we used combinatorial peptide library screening to determine that PASK prefers basic residues at the P-3 and P-5 positions in substrate peptides. Our results describe the key features of the PASK structure and how those features are important for PASK activity and substrate selection.

Inhibition of O-GlcNAcase using a potent and cell-permeable inhibitor does not induce insulin resistance in 3T3-L1 adipocytes

To probe increased O-GlcNAc levels as an independent mechanism governing insulin resistance in 3T3-L1 adipocytes, a new class of O-GlcNAcase (OGA) inhibitor was studied. 6-Acetamido-6-deoxy-castanospermine (6-Ac-Cas) is a potent inhibitor of OGA. The structure of 6-Ac-Cas bound in the active site of an OGA homolog reveals structural features contributing to its potency. Treatment of 3T3-L1 adipocytes with 6-Ac-Cas increases O-GlcNAc levels in a dose-dependent manner. These increases in O-GlcNAc levels do not induce insulin resistance functionally, measured using a 2-deoxyglucose (2-DOG) uptake assay, or at the molecular level, determined by evaluating levels of phosphorylated IRS-1 and Akt. These results, and others described, provide a structural blueprint for improved inhibitors and collectively suggest that increased O-GlcNAc levels, brought about by inhibition of OGA, does not by itself cause insulin resistance in 3T3-L1 adipocytes.

Glucose metabolism gene polymorphisms and clinical outcome in pancreatic cancer

BACKGROUND

Altered glucose metabolism is the most common metabolic hallmark of malignancies. The authors tested the hypothesis that glucose metabolism gene variations affect clinical outcome in pancreatic cancer.

METHODS

The authors retrospectively genotyped 26 single nucleotide polymorphisms from 5 glucose metabolism genes in 154 patients with localized disease and validated the findings in 552 patients with different stages of pancreatic adenocarcinoma. Association between genotypes and overall survival (OS) was evaluated using multivariate Cox proportional hazard regression models with adjustment for clinical predictors.

RESULTS

Glucokinase (GCK) IVS1 + 9652C > T and hexokinase 2 (HK2) N692N homozygous variants were significantly associated with reduced OS in the training set of 154 patients (P < .001). These associations were confirmed in the validation set of 552 patients and in the combined dataset of all 706 patients (P ≤ .001). In addition, HK2 R844K variant K allele was associated with a better survival in the validation set and the combined dataset (P ≤ .001). When data were further analyzed by disease stage, glutamine-fructose-6-phosphate transaminase (GFPT1) IVS14-3094T>C, HK2 N692N and R844K in patients with localized disease and GCK IVS1 + 9652C>T in patients with advanced disease were significant independent predictors for OS (P ≤ .001). Haplotype CGG of GPI and GCTATGG of HK2 were associated with better OS, respectively, with P values of .004 and .007.

CONCLUSIONS

The authors demonstrated that glucose metabolism gene polymorphisms affect clinical outcome in pancreatic cancer. These observations support a role of abnormal glucose metabolism in pancreatic carcinogenesis.

O-GlcNAc Modification: Friend or Foe in Diabetic Cardiovascular Disease

O-Linked β-N-acetyl glucosaminylation (O-GlcNAcylation) is a dynamic post-translational modification that occurs on serine and threonine residues of cytosolic and nuclear proteins in all cell types, including those involved in the cardiovascular system. O-GlcNAcylation is thought to act in a manner analogous to protein phosphorylation. O-GlcNAcylation rapidly cycles on/off proteins in a time scale similar to that for phosphorylation/dephosphorylation of proteins. Several studies indicate that O-GlcNAc might induce nuclear localization of some transcription factors and may affect their DNA binding activities. However, at the cellular level, it has been shown that O-GlcNAc levels increase in response to stress and augmentation of this response suppresses cell survival. Increased levels of O-GlcNAc have been implicated as a pathogenic contributor to glucose toxicity and insulin resistance, which are major hallmarks of type 2 diabetes and diabetes-related cardiovascular complications. Thus, O-GlcNAc and its metabolic functions are not yet well-understood; focusing on the role of O-GlcNAc in the cardiovascular system is a viable target for biomedical investigation. In this review, we summarize our current understanding of the role of O-GlcNAc on the regulation of cell function and survival in the cardiovascular system.

Adiponectin activation of AMPK disrupts leptin-mediated hepatic fibrosis via suppressors of cytokine signaling (SOCS-3)

Adiponectin is an adipocytokine that was recently shown to be anti-fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS-3, TIMP-1, and the phosphorylated species of Stat3 and adenosine monophosphate-activated protein kinase (AMPK) were conducted. We also examined MMP-1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin-induced phosphorylation of AMPK, and subsequently suppressed leptin-mediated Stat3 phosphorylation and SOCS-3 induction. Adiponectin also blocked leptin-stimulated secretion of TIMP-1, and significantly increased MMP-1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad-/-) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post-necropsy analysis was performed to examine for inflammation, and histological changes in the Ad-/- and wild-type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl(4) enhanced hepatic fibrosis in both wild-type and Ad-/- mice, as estimated by amount of collagen in injured livers, but wild-type mice had significantly higher levels of SOCS-3 and significantly lower levels of TIMP-1 mRNA and protein than did adiponectin KO mice exposed to both CCl(4) and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak-Stat signal transduction pathway.

Mitochondrial pyrimidine nucleotide carrier (PNC1) regulates mitochondrial biogenesis and the invasive phenotype of cancer cells

The insulin-like growth factor (IGF-I) signalling pathway is essential for metabolism, cell growth and survival. It induces expression of the mitochondrial pyrimidine nucleotide carrier 1 (PNC1) in transformed cells, but the consequences of this for cell phenotype are unknown. Here we show that PNC1 is necessary to maintain mitochondrial function by controlling mitochondrial DNA replication and the ratio of transcription of mitochondrial genes relative to nuclear genes. PNC1 suppression causes reduced oxidative phosphorylation and leakage of reactive oxygen species (ROS), which activates the AMPK-PGC1alpha signalling pathway and promotes mitochondrial biogenesis. Overexpression of PNC1 suppresses mitochondrial biogenesis. Suppression of PNC1 causes a profound ROS-dependent epithelial-mesenchymal transition (EMT), whereas overexpression of PNC1 suppresses both basal EMT and induction of EMT by TGF-beta. Overall, our findings indicate that PNC1 is essential for mitochondria maintenance and suggest that its induction by IGF-I facilitates cell growth whereas protecting cells from an ROS-promoted differentiation programme that arises from mitochondrial dysfunction.

Metformin, independent of AMPK, inhibits mTORC1 in a rag GTPase-dependent manner

Dysfunctional mTORC1 signaling is associated with a number of human pathologies owing to its central role in controlling cell growth, proliferation, and metabolism. Regulation of mTORC1 is achieved by the integration of multiple inputs, including those of mitogens, nutrients, and energy. It is thought that agents that increase the cellular AMP/ATP ratio, such as the antidiabetic biguanides metformin and phenformin, inhibit mTORC1 through AMPK activation of TSC1/2-dependent or -independent mechanisms. Unexpectedly, we found that biguanides inhibit mTORC1 signaling, not only in the absence of TSC1/2 but also in the absence of AMPK. Consistent with these observations, in two distinct preclinical models of cancer and diabetes, metformin acts to suppress mTORC1 signaling in an AMPK-independent manner. We found that the ability of biguanides to inhibit mTORC1 activation and signaling is, instead, dependent on the Rag GTPases.

Dynamic O-GlcNAc cycling at promoters of Caenorhabditis elegans genes regulating longevity, stress, and immunity

Nutrient-driven O-GlcNAcylation of key components of the transcription machinery may epigenetically modulate gene expression in metazoans. The global effects of GlcNAcylation on transcription can be addressed directly in C. elegans because knockouts of the O-GlcNAc cycling enzymes are viable and fertile. Using anti-O-GlcNAc ChIP-on-chip whole-genome tiling arrays on wild-type and mutant strains, we detected over 800 promoters where O-GlcNAc cycling occurs, including microRNA loci and multigene operons. Intriguingly, O-GlcNAc-marked promoters are biased toward genes associated with PIP3 signaling, hexosamine biosynthesis, and lipid/carbohydrate metabolism. These marked genes are linked to insulin-like signaling, metabolism, aging, stress, and pathogen-response pathways in C. elegans. Whole-genome transcriptional profiling of the O-GlcNAc cycling mutants confirmed dramatic deregulation of genes in these key pathways. As predicted, the O-GlcNAc cycling mutants show altered lifespan and UV stress susceptibility phenotypes. We propose that O-GlcNAc cycling at promoters participates in a molecular program impacting nutrient-responsive pathways in C. elegans, including stress, pathogen response, and adult lifespan. The observed impact of O-GlcNAc cycling on both signaling and transcription in C. elegans has important implications for human diseases of aging, including diabetes and neurodegeneration.

Down-regulation of honey bee IRS gene biases behavior toward food rich in protein

Food choice and eating behavior affect health and longevity. Large-scale research efforts aim to understand the molecular and social/behavioral mechanisms of energy homeostasis, body weight, and food intake. Honey bees (Apis mellifera) could provide a model for these studies since individuals vary in food-related behavior and social factors can be controlled. Here, we examine a potential role of peripheral insulin receptor substrate (IRS) expression in honey bee foraging behavior. IRS is central to cellular nutrient sensing through transduction of insulin/insulin-like signals (IIS). By reducing peripheral IRS gene expression and IRS protein amount with the use of RNA interference (RNAi), we demonstrate that IRS influences foraging choice in two standard strains selected for different food-hoarding behavior. Compared with controls, IRS knockdowns bias their foraging effort toward protein (pollen) rather than toward carbohydrate (nectar) sources. Through control experiments, we establish that IRS does not influence the bees' sucrose sensory response, a modality that is generally associated with food-related behavior and specifically correlated with the foraging preference of honey bees. These results reveal a new affector pathway of honey bee social foraging, and suggest that IRS expressed in peripheral tissue can modulate an insect's foraging choice between protein and carbohydrate sources.

Loss of the actin remodeler Eps8 causes intestinal defects and improved metabolic status in mice

Background

In a variety of organisms, including mammals, caloric restriction improves metabolic status and lowers the incidence of chronic-degenerative diseases, ultimately leading to increased lifespan.

Methodology/Principal Findings

Here we show that knockout mice for Eps8, a regulator of actin dynamics, display reduced body weight, partial resistance to age- or diet-induced obesity, and overall improved metabolic status. Alteration in the liver gene expression profile, in behavior and metabolism point to a calorie restriction-like phenotype in Eps8 knockout mice. Additionally, and consistent with a calorie restricted metabolism, Eps8 knockout mice show increased lifespan. The metabolic alterations in Eps8 knockout mice correlated with a significant reduction in intestinal fat absorption presumably caused by a 25% reduction in intestinal microvilli length.

Conclusions/Significance

Our findings implicate actin dynamics as a novel variable in the determination of longevity. Additionally, our observations suggest that subtle differences in energy balance can, over time, significantly affect bodyweight and metabolic status in mice.

Nutrient sensor O-GlcNAc transferase regulates breast cancer tumorigenesis through targeting of the oncogenic transcription factor FoxM1

Cancer cells upregulate glycolysis, increasing glucose uptake to meet energy needs. A small fraction of a cell's glucose enters the hexosamine biosynthetic pathway (HBP), which regulates levels of O-linked beta-N-acetylglucosamine (O-GlcNAc), a carbohydrate posttranslational modification of diverse nuclear and cytosolic proteins. We discovered that breast cancer cells upregulate the HBP, including increased O-GlcNAcation and elevated expression of O-GlcNAc transferase (OGT), which is the enzyme catalyzing the addition of O-GlcNAc to proteins. Reduction of O-GlcNAcation through RNA interference of OGT in breast cancer cells leads to inhibition of tumor growth both in vitro and in vivo and is associated with decreased cell-cycle progression and increased expression of the cell-cycle inhibitor p27(Kip1). Elevation of p27(Kip1) was associated with decreased expression and activity of the oncogenic transcription factor FoxM1, a known regulator of p27(Kip1) stability through transcriptional control of Skp2. Reducing O-GlcNAc levels in breast cancer cells decreased levels of FoxM1 protein and caused a decrease in multiple FoxM1-specific targets, including Skp2. Moreover, reducing O-GlcNAcation decreased cancer cell invasion and was associated with the downregulation of matrix metalloproteinase-2, a known FoxM1 target. Finally, pharmacological inhibition of OGT in breast cancer cells had similar anti-growth and anti-invasion effects. These findings identify O-GlcNAc as a novel mechanism through which alterations in glucose metabolism regulate cancer growth and invasion and suggest that OGT may represent novel therapeutic targets for breast cancer.

Mammalian Tribbles homolog 3 impairs insulin action in skeletal muscle: role in glucose-induced insulin resistance

Tribbles homolog 3 (TRIB3) was found to inhibit insulin-stimulated Akt phosphorylation and modulate gluconeogenesis in rodent liver. Currently, we examined a role for TRIB3 in skeletal muscle insulin resistance. Ten insulin-sensitive, ten insulin-resistant, and ten untreated type 2 diabetic (T2DM) patients were metabolically characterized by hyperinsulinemic euglycemic glucose clamps, and biopsies of vastus lateralis were obtained. Skeletal muscle samples were also collected from rodent models including streptozotocin (STZ)-induced diabetic rats, db/db mice, and Zucker fatty rats. Finally, L6 muscle cells were used to examine regulation of TRIB3 by glucose, and stable cell lines hyperexpressing TRIB3 were generated to identify mechanisms underlying TRIB3-induced insulin resistance. We found that 1) skeletal muscle TRIB3 protein levels are significantly elevated in T2DM patients; 2) muscle TRIB3 protein content is inversely correlated with glucose disposal rates and positively correlated with fasting glucose; 3) skeletal muscle TRIB3 protein levels are increased in STZ-diabetic rats, db/db mice, and Zucker fatty rats; 4) stable TRIB3 hyperexpression in muscle cells blocks insulin-stimulated glucose transport and glucose transporter 4 (GLUT4) translocation and impairs phosphorylation of Akt, ERK, and insulin receptor substrate-1 in insulin signal transduction; and 5) TRIB3 mRNA and protein levels are increased by high glucose concentrations, as well as by glucose deprivation in muscle cells. These data identify TRIB3 induction as a novel molecular mechanism in human insulin resistance and diabetes. TRIB3 acts as a nutrient sensor and could mediate the component of insulin resistance attributable to hyperglycemia (i.e., glucose toxicity) in diabetes.

Parenteral amino acid intakes in critically ill children: a matter of convenience

BACKGROUND

Parenteral and enteral amino acid requirements for nutrition balance and function have not been defined in critically ill children or adults. In addition to playing a role in protein synthesis, amino acids trigger signaling cascades that regulate various aspects of fuel and energy metabolism and serve as precursors for important substrates. Amino acids can also be toxic. In this study, parenteral intakes of essential and nonessential amino acids (EAAs and NEAAs) supplied to critically ill children were assessed as an initial step for further studies aimed at establishing parenteral amino acid requirements.

METHODS

A retrospective review was conducted to assess intakes of parenteral amino acid for 116 critically ill children, and these intakes were compared with EAA intakes recommended by the Institute of Medicine. Because there are no recommended intakes for NEAA, NEAA intakes were compared with mixed muscle protein content in the older children and breast milk amino acid content in the infants.

RESULTS

Parenteral EAAs were provided in amounts that exceeded recommended intakes for healthy children, except for phenylalanine and methionine, which although excessive, were given in less generous amounts. NEAAs were supplied in lower or higher amounts than the content of mixed muscle proteins or breast milk. Parenteral amino acid formulas are limited in taurine, glutamine, and asparagine despite the fact that inflammatory/immune proteins are rich in these amino acids.

CONCLUSIONS

Amino acid composition of parenteral formulas is variable and lacks scientific support. Parenteral amino acid intakes should be based on measured requirements to maintain nutrition and functional balance and on knowledge of toxicity.

Phosphoinositide signalling pathways in metabolic regulation

The Insulin Receptor/PI 3-kinase (INSR/PI3K) signalling pathway is a key regulator of cell and organismal metabolism. Phosphoinositides generated by PI 3-kinases following insulin and other metabolic hormone receptor activation give rise to signalling cascades involving a multitude of effector molecules. The physiological roles of these molecules have been dissected with the use of both pharmacological and genetic tools. Furthermore, tissue-specific mutagenesis has revealed the extent to which individual insulin-target organs and signalling molecules contribute to whole-body carbohydrate and lipid homeostasis. These studies have generated important information with respect to the function of these molecules in normal physiology and their implication in the development of metabolic diseases such as type-2 diabetes and obesity.