Mice deficient in C/EBP alpha have defective development of adipose tissue, but the precise role of C/EBP alpha has not been defined. Fibroblasts from C/EBP alpha(-/-) mice undergo adipose differentiation through expression and activation of PPAR gamma, though several clear defects are apparent. C/EBP alpha-deficient adipocytes accumulates less lipid, and they do not induce endogenous PPAR gamma, indicating that cross-regulation between C/EBP alpha and PPAR gamma is important in maintaining the differentiated state. The cells also show a complete absence of insulin-stimulated glucose transport, secondary to reduced gene expression and tyrosine phosphorylation for the insulin receptor and IRS-1. These results define multiple roles for C/EBP alpha in adipogenesis and show that cross-regulation between PPAR gamma and C/EBP alpha is a key component of the transcriptional control of this cell lineage.

Oxidative stress has been implicated as a contributor to both the onset and the progression of diabetes and its associated complications. Some of the consequences of an oxidative environment are the development of insulin resistance, β-cell dysfunction, impaired glucose tolerance, and mitochondrial dysfunction, which can lead ultimately to the diabetic disease state. Experimental and clinical data suggest an inverse association between insulin sensitivity and ROS levels. Oxidative stress can arise from a number of different sources, whether disease state or lifestyle, including episodes of ketosis, sleep restriction, and excessive nutrient intake. Oxidative stress activates a series of stress pathways involving a family of serine/threonine kinases, which in turn have a negative effect on insulin signaling. More experimental evidence is needed to pinpoint the mechanisms contributing to insulin resistance in both type 1 diabetics and nondiabetic individuals. Oxidative stress can be reduced by controlling hyperglycemia and calorie intake. Overall, this review outlines various mechanisms that lead to the development of oxidative stress. Intervention and therapy that alter or disrupt these mechanisms may serve to reduce the risk of insulin resistance and the development of diabetes.

OBJECTIVE

Fibroblast growth factor 21 (FGF21) is a metabolic regulator with multiple beneficial effects on glucose homeostasis and insulin sensitivity in animal models. This study aimed to investigate the relationship between its serum levels and various cardiometabolic parameters in humans.

METHODS

A newly developed immunoassay was used to measure serum FGF21 levels in 232 Chinese subjects recruited from our previous cross-sectional studies. The mRNA expression levels of FGF21 in the liver and adipose tissues were quantified by real-time PCR.

RESULTS

Serum FGF21 levels in overweight/obese subjects were significantly higher than in lean individuals. Serum FGF21 correlated positively with adiposity, fasting insulin, and triglycerides but negatively with HDL cholesterol, after adjusting for age and BMI. Logistic regression analysis demonstrated an independent association between serum FGF21 and the metabolic syndrome. Furthermore, the increased risk of the metabolic syndrome associated with high serum FGF21 was over and above the effects of individual components of the metabolic syndrome. Our in vitro study detected a differentiation-dependent expression of FGF21 in 3T3-L1 adipocytes and human adipocytes. In db/db obese mice, FGF21 mRNA expression was markedly increased in both the liver and adipose tissue compared with that in their lean littermates. Furthermore, FGF21 expression in subcutaneous fat correlated well with its circulating concentrations in humans.

CONCLUSIONS

FGF21 is a novel adipokine associated with obesity-related metabolic complications in humans. The paradoxical increase of serum FGF21 in obese individuals, which may be explained by a compensatory response or resistance to FGF21, warrants further investigation.

We have screened a cDNA library for gene sequences that are regulated by platelet-derived growth factor (PDGF) in BALB/c-3T3 cells. Of 8000 clones screened, less than 14 independent PDGF-inducible sequences were found. Two of these (KC and JE) were studied in detail. By hybrid-selection and translation the KC and JE mRNAs encode 10,000 and 19,000 dalton polypeptides, respectively. In the absence of PDGF, the JE and KC sequences correspond to low abundance mRNAs. One hour after addition of PDGF their abundance level can be increased 10- to 20-fold. Within 4 hr, a 60-fold induction of JE can be attained. Nanogram per ml quantities of pure PDGF regulate these sequences whereas microgram/ml quantities of chemically unrelated mitogens (EGF, insulin, or platelet-poor plasma) have either a weak or an undetectable effect. Inhibitors of protein synthesis block the progression of quiescent 3T3 cells through G1 into S phase; however these drugs do not block the induction of KC and JE by PDGF. This result indicates that these sequences correspond to "early genes" which are not induced as a consequence of cell growth, but rather are directly regulated by PDGF.

The genetic analysis of life span has revealed many interesting genes and pathways; however, our understanding of aging has been limited by the lack of a way to assay the aging process itself. Here we show that the tissues of aging worms have a characteristic appearance that is easy to recognize and quantify using Nomarski optics. We have used this assay to determine whether life-span mutations affect the rate of aging, to identify animals that age more rapidly than normal, and to infer the cause of death in C. elegans. Mutations that reduce insulin/IGF-1 signaling double the life span of C. elegans, and we find that tissue decline is slowed in these mutants. Thus this endocrine system appears to influence the rate at which tissues age. This effect extends even to the germline, which is the only mitotically active tissue in the adult. We find that Nomarski microscopy also allows a ready distinction between short-lived mutants that age more rapidly than normal and those that are simply sick, and we have identified an RNAi clone that confers a dramatic rapid-aging phenotype. This clone encodes the C. elegans heat-shock factor (HSF), a transcription factor that regulates the response to heat and oxidative stress. This suggests that heat-shock proteins, many of which act as chaperones, may function in normal animals to slow the rate of aging. Finally, we have identified a cause of death of C. elegans: namely, proliferating bacteria. This suggests that increased susceptibility to bacterial infections contributes to mortality in these animals, just as it does in humans.

Although a full understanding of insulin/insulin-like growth factor (IGF) action is evolving, the discovery of insulin receptor substrate (IRS) proteins and their role to link cell surface receptors to the intracellular signaling cascades provided an important step forward. Moreover, Insulin/IGF receptors use common signaling pathways to accomplish many tasks, the IRS proteins add a unique layer of specificity and control. Importantly, the IRS-2 branch of the insulin/IGF-signaling pathway is a common element in peripheral insulin response and pancreatic beta-cell growth and function. Failure of IRS-2 signaling might explain the eventual loss of compensatory hyperinsulinemia during prolonged periods of peripheral insulin resistance. Moreover, short-term inhibition of IRS protein functions by serine phosphorylation, or sustained inhibition by ubiquitin-targeted proteosome-mediated degradation suggests a common molecular mechanism for insulin resistance during acute injury or infection, or the sensitivity of beta-cells to autoimmune destruction. The broad role of IRS-1 and IRS-2 in cell growth and survival reveals a common regulatory pathway linking development, somatic growth, fertility, neuronal proliferation, and aging to the core mechanisms used by vertebrates for nutrient sensing.

OBJECTIVE

To investigate duration of the period between diabetes onset and its clinical diagnosis.

METHODS

Two population-based groups of white patients with non-insulin-dependent diabetes (NIDDM) in the United States and Australia were studied. Prevalence of retinopathy and duration of diabetes subsequent to clinical diagnosis were determined for all subjects. Weighted linear regression was used to examine the relationship between diabetes duration and prevalence of retinopathy.

RESULTS

Prevalence of retinopathy at clinical diagnosis of diabetes was estimated to be 20.8% in the U.S. and 9.9% in Australia and increased linearly with longer duration of diabetes. By extrapolating this linear relationship to the time when retinopathy prevalence was estimated to be zero, onset of detectable retinopathy was calculated to have occurred approximately 4-7 yr before diagnosis of NIDDM. Because other data indicate that diabetes may be present for 5 yr before retinopathy becomes evident, onset of NIDDM may occur 9-12 yr before its clinical diagnosis.

CONCLUSIONS

These findings suggest that undiagnosed NIDDM is not a benign condition. Clinically significant morbidity is present at diagnosis and for years before diagnosis. During this preclinical period, treatment is not being offered for diabetes or its specific complications, despite the fact that reduction in hyperglycemia, hypertension, and cardiovascular risk factors is believed to benefit patients. Imprecise dating of diabetes onset also obscures investigations of the etiology of NIDDM and studies of the nature and importance of risk factors for diabetes complications.

Terminal differentiation of cultured 3T3-L1 fibroblasts to the adipogenic phenotype is potently stimulated by dexamethasone (DEX) and methylisobutylxanthine (MIX). Previous studies have shown that these hormones induce the expression of genes encoding two members of the CCAAT/enhancer binding protein (C/EBP) family of transcription factors. In the absence of new protein synthesis DEX activates the gene encoding C/EBP delta. Likewise, MIX is a direct inducer of C/EBP beta gene expression. Optimal conditions for differentiation entail a 2-day period wherein confluent fibroblasts are exposed to DEX and MIX, followed by removal of the hormones and subsequent culture in the presence of insulin and fetal bovine serum. During the early phase of differentiation, high levels of C/EBP delta and C/EBP beta accumulate. These transcription factors diminish during the terminal phase of differentiation and come to be replaced by a third member of the C/EBP family, C/EBP alpha. Conclusive evidence has already shown that C/EBP alpha regulates terminal adipocyte differentiation, turning on the battery of fat-specific genes required for the synthesis, uptake, and storage of long chain fatty acids. Here we provide evidence that C/EBP delta and C/EBP beta play early catalytic roles in the differentiation pathway, relaying the effects of the hormonal stimulants DEX and MIX in a cascade-like fashion, leading to the activation of the gene encoding C/EBP alpha. Conditions facilitating the precocious expression of either C/EBP delta or C/EBP beta were observed to accelerate adipogenesis and, in the case of C/EBP beta, relieve dependence on the early hormonal stimulants. Likewise, conditions that prevented the expression of functional C/EBP beta effectively blocked terminal differentiation. Finally, we have discovered that ectopic expression of C/EBP beta in multipotential NIH-3T3 cells results in their conversion into committed adipoblasts capable, upon hormonal stimulation, of synchronous and uniform differentiation into fat-laden adipocytes.

ATP-sensitive potassium channels (K-ATP channels) couple cell metabolism to electrical activity and are important in the physiology and pathophysiology of many tissues. In pancreatic beta-cells, K-ATP channels link changes in blood glucose concentration to insulin secretion. They are also the target for clinically important drugs such as sulphonylureas, which stimulate secretion, and the K+ channel opener diazoxide, which inhibits insulin release. Metabolic regulation of K-ATP channels is mediated by changes in intracellular ATP and Mg-ADP levels, which inhibit and activate the channel, respectively. The beta-cell K-ATP channel is a complex of two proteins: an inward-rectifier K+ channel subunit, Kir6.2, and the sulphonylurea receptor, SUR1. We show here that the primary site at which ATP acts to mediate K-ATP channel inhibition is located on Kir6.2, and that SUR1 is required for sensitivity to sulphonylureas and diazoxide and for activation by Mg-ADP.

Adipose tissue can undergo rapid expansion during times of excess caloric intake. Like a rapidly expanding tumor mass, obese adipose tissue becomes hypoxic due to the inability of the vasculature to keep pace with tissue growth. Consequently, during the early stages of obesity, hypoxic conditions cause an increase in the level of hypoxia-inducible factor 1alpha (HIF1alpha) expression. Using a transgenic model of overexpression of a constitutively active form of HIF1alpha, we determined that HIF1alpha fails to induce the expected proangiogenic response. In contrast, we observed that HIF1alpha initiates adipose tissue fibrosis, with an associated increase in local inflammation. "Trichrome- and picrosirius red-positive streaks," enriched in fibrillar collagens, are a hallmark of adipose tissue suffering from the early stages of hypoxia-induced fibrosis. Lysyl oxidase (LOX) is a transcriptional target of HIF1alpha and acts by cross-linking collagen I and III to form the fibrillar collagen fibers. Inhibition of LOX activity by beta-aminoproprionitrile treatment results in a significant improvement in several metabolic parameters and further reduces local adipose tissue inflammation. Collectively, our observations are consistent with a model in which adipose tissue hypoxia serves as an early upstream initiator for adipose tissue dysfunction by inducing a local state of fibrosis.

Obesity predisposes individuals to the development of insulin resistance in skeletal muscle and the liver, and researchers have recently proposed two mechanisms by which excess adiposity antagonizes insulin action in peripheral tissues. First, when adipocytes exceed their storage capacity, fat begins to accumulate in tissues not suited for lipid storage, leading to the formation of specific metabolites that inhibit insulin signal transduction. Second, obesity triggers a chronic inflammatory state, and cytokines released from either adipocytes or from macrophages infiltrating adipose tissue antagonize insulin action. The sphingolipid ceramide is a putative intermediate linking both excess nutrients (i.e. saturated fatty acids) and inflammatory cytokines (e.g. tumor necrosis factor-alpha, TNFalpha) to the induction of insulin resistance. Moreover, ceramide has been shown to be toxic in a variety of different cell types (e.g. pancreatic beta-cells, cardiomyocytes, etc.), and review of the literature reveals putative roles for the sphingolipid in the damage of cells and tissues which accompany diabetes, hypertension, cardiac failure, atherosclerosis, etc. In this review, I will evaluate the contribution of ceramides in the development of insulin resistance and the complications associated with metabolic diseases.

The adipokine resistin is suggested to be an important link between obesity and insulin resistance. In the present study, we assessed the impact of resistin as inflammatogenic cytokine in the setting of arthritis. In vitro experiments on human PBMC were performed to assess cytokine response and transcription pathways of resistin-induced inflammation. Proinflammatory properties of resistin were evaluated in animal model by intra-articular injection of resistin followed by histological evaluation of the joint. Levels of resistin were assessed by ELISA in 74 paired blood and synovial fluid samples of patients with rheumatoid arthritis. Results were compared with the control group comprised blood samples from 34 healthy individuals and 21 synovial fluids from patients with noninflammatory joint diseases. We now show that resistin displays potent proinflammatory properties by 1) strongly up-regulating IL-6 and TNF-alpha, 2) responding to TNF-alpha challenge, 3) enhancing its own activity by a positive feedback, and finally 4) inducing arthritis when injected into healthy mouse joints. Proinflammatory properties of resistin were abrogated by NF-kappaB inhibitor indicating the importance of NF-kappaB signaling pathway for resistin-induced inflammation. Resistin is also shown to specifically accumulate in the inflamed joints of patients with rheumatoid arthritis and its levels correlate with other markers of inflammation. Our results indicate that resistin is a new and important member of the cytokine family with potent regulatory functions. Importantly, the identified properties of resistin make it a novel and interesting therapeutic target in chronic inflammatory diseases such as rheumatoid arthritis.

The broad nature of insulin resistant glucose metabolism in skeletal muscle of patients with type 2 diabetes suggests a defect in the proximal part of the insulin signaling network. We sought to identify the pathways compromised in insulin resistance and to test the effect of moderate exercise on whole-body and cellular insulin action. We conducted euglycemic clamps and muscle biopsies on type 2 diabetic patients, obese nondiabetics and lean controls, with and without a single bout of exercise. Insulin stimulation of the phosphatidylinositol 3-kinase (PI 3-kinase) pathway, as measured by phosphorylation of the insulin receptor and IRS-1 and by IRS protein association with p85 and with PI 3-kinase, was dramatically reduced in obese nondiabetics and virtually absent in type 2 diabetic patients. Insulin stimulation of the MAP kinase pathway was normal in obese and diabetic subjects. Insulin stimulation of glucose-disposal correlated with association of p85 with IRS-1. Exercise 24 hours before the euglycemic clamp increased phosphorylation of insulin receptor and IRS-1 in obese and diabetic subjects but did not increase glucose uptake or PI 3-kinase association with IRS-1 upon insulin stimulation. Thus, insulin resistance differentially affects the PI 3-kinase and MAP kinase signaling pathways, and insulin-stimulated IRS-1-association with PI 3-kinase defines a key step in insulin resistance.

Forkhead transcription factors of the FOXO class are negatively regulated by PKB/c-Akt in response to insulin/IGF signalling, and are involved in regulating cell cycle progression and cell death. Here we show that, in contrast to insulin signalling, low levels of oxidative stress generated by treatment with H2O2 induce the activation of FOXO4. Upon treatment of cells with H2O2, the small GTPase Ral is activated and this results in a JNK-dependent phosphorylation of FOXO4 on threonine 447 and threonine 451. This Ral-mediated, JNK-dependent phosphorylation is involved in the nuclear translocation and transcriptional activation of FOXO4 after H2O2 treatment. In addition, we show that this signalling pathway is also employed by tumor necrosis factor alpha to activate FOXO4 transcriptional activity. FOXO members have been implicated in cellular protection against oxidative stress via the transcriptional regulation of manganese superoxide dismutase and catalase gene expression. The results reported here, therefore, outline a homeostasis mechanism for sustaining cellular reactive oxygen species that is controlled by signalling pathways that can convey both negative (PI-3K/PKB) and positive (Ras/Ral) inputs.

The metabolism of high-density lipoproteins (HDL), which are inversely related to risk of atherosclerotic cardiovascular disease, involves a complex interplay of factors regulating HDL synthesis, intravascular remodeling, and catabolism. The individual lipid and apolipoprotein components of HDL are mostly assembled after secretion, are frequently exchanged with or transferred to other lipoproteins, are actively remodeled within the plasma compartment, and are often cleared separately from one another. HDL is believed to play a key role in the process of reverse cholesterol transport (RCT), in which it promotes the efflux of excess cholesterol from peripheral tissues and returns it to the liver for biliary excretion. This review will emphasize 3 major evolving themes regarding HDL metabolism and RCT. The first theme is that HDL is a universal plasma acceptor lipoprotein for cholesterol efflux from not only peripheral tissues but also hepatocytes, which are a major source of cholesterol efflux to HDL. Furthermore, although efflux of cholesterol from macrophages represents only a tiny fraction of overall cellular cholesterol efflux, it is the most important with regard to atherosclerosis, suggesting that it be specifically termed macrophage RCT. The second theme is the critical role that intravascular remodeling of HDL by lipid transfer factors, lipases, cell surface receptors, and non-HDL lipoproteins play in determining the ultimate metabolic fate of HDL and plasma HDL-c concentrations. The third theme is the growing appreciation that insulin resistance underlies the majority of cases of low HDL-c in humans and the mechanisms by which insulin resistance influences HDL metabolism. Progress in our understanding of HDL metabolism and macrophage reverse cholesterol transport will increase the likelihood of developing novel therapies to raise plasma HDL concentrations and promote macrophage RCT and in proving that these new therapeutic interventions prevent or cause regression of atherosclerosis in humans.

OBJECTIVE

Sleep deprivation has been hypothesized to contribute toward obesity by decreasing leptin, increasing ghrelin, and compromising insulin sensitivity. This study examines cross-sectional and longitudinal data from a large United States sample to determine whether sleep duration is associated with obesity and weight gain.

METHODS

Longitudinal analyses of the 1982-1984, 1987, and 1992 NHANES I Followup Studies and cross-sectional analysis of the 1982-1984 study.

METHODS

Probability sample of the civilian noninstitutionalized population of the United States.

METHODS

Sample sizes of 9,588 for the cross-sectional analyses, 8,073 for the 1987, and 6,981 for the 1992 longitudinal analyses.

RESULTS

Measured weight in 1982-1984 and self-reported weights in 1987 and 1992. Subjects between the ages of 32 and 49 years with self-reported sleep durations at baseline less than 7 hours had higher average body mass indexes and were more likely to be obese than subjects with sleep durations of 7 hours. Sleep durations over 7 hours were not consistently associated with either an increased or decreased likelihood of obesity in the cross-sectional and longitudinal results. Each additional hour of sleep at baseline was negatively associated with change in body mass index over the follow-up period, but this association was small and statistically insignificant.

CONCLUSIONS

These findings support the hypothesis that sleep duration is associated with obesity in a large longitudinally monitored United States sample. These observations support earlier experimental sleep studies and provide a basis for future studies on weight control interventions that increase the quantity and quality of sleep.

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes, many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay type 2 diabetes, along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower type 2 diabetes risk by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. The benefits of physical training are discussed, along with recommendations for varying activities, PA-associated blood glucose management, diabetes prevention, gestational diabetes mellitus, and safe and effective practices for PA with diabetes-related complications.

The mammalian target of rapamycin (MTOR) protein kinase complex is a key component of a pathway that regulates cell growth and proliferation in response to energy levels, hypoxia, nutrients and insulin. Inhibition of MTORC1 strongly induces autophagy by regulating the activity of the ULK protein kinase complex that is required for the formation of autophagosomes. However, the participation of MTORC1 in the expression of autophagy genes has not been characterized. Here we show that MTORC1 regulates nuclear localization and activity of the transcription factor EB (TFEB), a member of the bHLH leucine-zipper family of transcription factors that drives expression of autophagy and lysosomal genes. Under normal nutrient conditions, TFEB is phosphorylated in Ser211 in an MTORC1-dependent manner. This phosphorylation promotes association of TFEB with members of the YWHA (14-3-3) family of proteins and retention of the transcription factor in the cytosol. Pharmacological or genetic inhibition of MTORC1 causes dissociation of the TFEB/YWHA complex and rapid transport of TFEB to the nucleus where it increases transcription of multiple genes implicated in autophagy and lysosomal function. Active TFEB also associates with late endosomal/lysosomal membranes through interaction with the LAMTOR/RRAG/MTORC1 complex. Our results unveil a novel role for MTORC1 in the maintenance of cellular homeostasis by regulating autophagy at the transcriptional level.

Transcription of the proto-oncogene c-fos is stimulated rapidly and transiently by serum growth factors and mitogens. Critical for this response is the serum-response element which is bound in vivo in a ternary complex containing the transcription factors p67SRF and p62TCF (ref. 2). Disruption of the ternary complex correlates with impaired induction by serum and phorbol ester. Mitogen-activated protein (MAP) kinase is a serine/threonine kinase which is activated 1-5 minutes after treatment of cells with mitogens and growth factors that induce re-entry into the cell cycle, making MAP kinase a candidate for the transmission of proliferative signals. Here we show that p62TCF is phosphorylated by MAP kinase in vitro and that phosphorylation results in enhanced ternary complex formation. Serum-starved Swiss 3T3 cells treated with epidermal growth factor, which induces MAP kinase in these cells, are induced to express c-fos and yield p62TCF active in ternary complex formation. In contrast, treatment of Swiss 3T3 cells with insulin, which does not activate MAP kinase under these conditions, does not lead to enhanced ternary complex formation nor does it induce c-fos transcription. Our results link the expression of the human c-fos proto-oncogene to signal transduction pathways known to be activated before its own induction.

BACKGROUND

Guidelines for triaging patients for cardiac catheterization recommend a risk assessment and noninvasive testing. We determined patterns of noninvasive testing and the diagnostic yield of catheterization among patients with suspected coronary artery disease in a contemporary national sample.

METHODS

From January 2004 through April 2008, at 663 hospitals in the American College of Cardiology National Cardiovascular Data Registry, we identified patients without known coronary artery disease who were undergoing elective catheterization. The patients' demographic characteristics, risk factors, and symptoms and the results of noninvasive testing were correlated with the presence of obstructive coronary artery disease, which was defined as stenosis of 50% or more of the diameter of the left main coronary artery or stenosis of 70% or more of the diameter of a major epicardial vessel.

RESULTS

A total of 398,978 patients were included in the study. The median age was 61 years; 52.7% of the patients were men, 26.0% had diabetes, and 69.6% had hypertension. Noninvasive testing was performed in 83.9% of the patients. At catheterization, 149,739 patients (37.6%) had obstructive coronary artery disease. No coronary artery disease (defined as <20% stenosis in all vessels) was reported in 39.2% of the patients. Independent predictors of obstructive coronary artery disease included male sex (odds ratio, 2.70; 95% confidence interval [CI], 2.64 to 2.76), older age (odds ratio per 5-year increment, 1.29; 95% CI, 1.28 to 1.30), presence of insulin-dependent diabetes (odds ratio, 2.14; 95% CI, 2.07 to 2.21), and presence of dyslipidemia (odds ratio, 1.62; 95% CI, 1.57 to 1.67). Patients with a positive result on a noninvasive test were moderately more likely to have obstructive coronary artery disease than those who did not undergo any testing (41.0% vs. 35.0%; P<0.001; adjusted odds ratio, 1.28; 95% CI, 1.19 to 1.37).

CONCLUSIONS

In this study, slightly more than one third of patients without known disease who underwent elective cardiac catheterization had obstructive coronary artery disease. Better strategies for risk stratification are needed to inform decisions and to increase the diagnostic yield of cardiac catheterization in routine clinical practice.

BACKGROUND

Obesity is associated with chronic inflammation, which includes increased macrophage accumulation in adipose tissue (AT) and upregulation of chemokines and cytokines. T cells also play important roles in chronic inflammatory diseases such as atherosclerosis but have not been well studied in obesity.

RESULTS

Flow cytometric analysis showed higher numbers of T cells and macrophages in AT of diet-induced obese insulin-resistant male mice than in lean mice and obese females (P<0.05). RNase protection assay, ELISA, and flow cytometry indicated gender-dependent upregulation of mRNA and protein levels of regulated on activation, normal T cell expressed and secreted (RANTES) and its receptor CCR5 in AT of obese mice. Adipocytes, stromal/vascular cells from mouse AT, and human and murine adipocytes expressed RANTES. RANTES mRNA levels were negatively correlated with adiponectin in mouse AT. Adiponectin-deficient mice fed high-fat diet showed higher RANTES mRNA levels in AT than wild-type mice. Activated T cells coincubated with preadipocytes in vitro significantly suppressed preadipocyte-to-adipocyte differentiation. Obese humans with metabolic syndrome had higher mRNA levels of RANTES and CCR5 in subcutaneous AT than lean humans. RANTES and CCR5 mRNA levels were significantly higher in visceral than subcutaneous AT of morbidly obese humans. RANTES mRNA levels were positively correlated with CD3 and CD11b in human visceral AT.

CONCLUSIONS

Obesity is associated with increased accumulation of T cells and macrophages in AT, which may play important roles in obesity-related disease by influencing preadipocyte/adipocyte functions. RANTES is an adipokine that is upregulated in AT by obesity in both mice and humans.

Apoptosis is likely to be the main form of beta-cell death in immune-mediated diabetes mellitus in rodents and possibly in humans. Clarification of the regulation of beta-cell death could indicate novel sites for therapeutic intervention in Type I (insulin-dependent) diabetes mellitus. We review the molecular effectors and signal transduction of immune-mediated beta-cell apoptosis. Data obtained on non-obese diabetic (NOD) mice suggest that macrophages and CD4+ T-cells are the main cellular effectors, whereas CD8+ T-cells are more important initiators of the immune process leading to beta-cell death. Perforin could be the effector molecule utilized by CD8+ T-cell initiation, whereas CD4+ mediated beta-cell destruction is mostly dependent on Fas/FasL and the cytokines IFNgamma and TNF-alpha. The macrophage cytokine IL-1beta in combination with IFN-gamma and TNF-alpha, plays an important role for beta-cell dysfunction and death. Signal transduction by these cytokines involves: (i) binding to specific receptors, (ii) signal transduction by cytosolic kinases (especially the so-called mitogen- and stress-activated protein kinases) and/or phosphatases, (iii) mobilization of diverse transcription factors - with nuclear factor kappaB (NF-kappaB), AP-1 and STAT-1 probably playing key roles for beta-cell apoptosis; (iv) up-regulation or down-regulation of gene transcription. Recent data obtained by microarray and proteomic analysis suggest that the process of beta-cell apoptosis depends on the parallel and/or sequential up-regulation and down-regulation of considerable numbers of genes, which can be grouped in gene modules or patterns according to their functions. A detailed characterization of these "gene modules", and of the signalling pathways and transcription factors regulating them could allow us to understand the ultimate mechanisms leading to beta-cell apoptosis.

beta cells sense glucose through its metabolism and the resulting increase in ATP, which subsequently stimulates insulin secretion. Uncoupling protein-2 (UCP2) mediates mitochondrial proton leak, decreasing ATP production. In the present study, we assessed UCP2's role in regulating insulin secretion. UCP2-deficient mice had higher islet ATP levels and increased glucose-stimulated insulin secretion, establishing that UCP2 negatively regulates insulin secretion. Of pathophysiologic significance, UCP2 was markedly upregulated in islets of ob/ob mice, a model of obesity-induced diabetes. Importantly, ob/ob mice lacking UCP2 had restored first-phase insulin secretion, increased serum insulin levels, and greatly decreased levels of glycemia. These results establish UCP2 as a key component of beta cell glucose sensing, and as a critical link between obesity, beta cell dysfunction, and type 2 diabetes.

Our aim was to critically evaluate the relations among smoking, body weight, body fat distribution, and insulin resistance as reported in the literature. In the short term, nicotine increases energy expenditure and could reduce appetite, which may explain why smokers tend to have lower body weight than do nonsmokers and why smoking cessation is frequently followed by weight gain. In contrast, heavy smokers tend to have greater body weight than do light smokers or nonsmokers, which likely reflects a clustering of risky behaviors (eg, low degree of physical activity, poor diet, and smoking) that is conducive to weight gain. Other factors, such as weight cycling, could also be involved. In addition, smoking increases insulin resistance and is associated with central fat accumulation. As a result, smoking increases the risk of metabolic syndrome and diabetes, and these factors increase risk of cardiovascular disease. In the context of the worldwide obesity epidemic and a high prevalence of smoking, the greater risk of (central) obesity and insulin resistance among smokers is a matter of major concern.