Angiotensinogen, adipocyte differentiation and fat mass enlargement

JTT-654, an 11-beta hydroxysteroid dehydrogenase type 1 inhibitor, improves hypertension and diabetic kidney injury by suppressing angiotensinogen production

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays an important role in regulating the expression of glucocorticoid actions in target tissues. Overexpression of 11β-HSD1 in mouse adipose tissue causes a metabolic syndrome-like phenotype, leading to hypertension. Although, many 11β-HSD1 inhibitors have been studied, few have shown a clear ameliorative effect against hypertension. We investigated whether JTT-654, a novel 11β-HSD1 inhibitor, ameliorated hypertension and elucidated the underlying mechanisms. JTT-654 showed inhibitory effects on angiotensinogen production in cortisone-treated 3T3-L1 adipocytes and in a rat model. JTT-654 improved hypertension not only in cortisone-treated rats and spontaneously hypertensive rats (SHR), but also in SHR/NDmcr-cp rats. In the SHR study, JTT-654 and losartan showed the same degree of antihypertensive efficacy. In addition, JTT-654 ameliorated diabetic nephropathy by suppressing renal angiotensinogen production in SHR/NDmcr-cp rats. These effects of JTT-654 were independent of its insulin-sensitizing effects, and similar effects were not observed for pioglitazone, an insulin sensitizer. Moreover, JTT-654 did not affect normotension or hypothalamus-pituitary-adrenal (HPA) axis function in normal Sprague-Dawley rats. Our results indicate that JTT-654 ameliorates hypertension and diabetic nephropathy by inhibiting 11β-HSD1 in the adipose tissue, liver, and kidney.

Renin-Angiotensin System: Updated Understanding and Role in Physiological and Pathophysiological States

The classical view of the renin-angiotensin system (RAS) is that of the circulating hormone pathway involved in salt and water homeostasis and blood pressure regulation. It is also involved in the pathogenesis of cardiac and renal disorders. This led to the creation of drugs blocking the actions of this classical pathway, which improved cardiac and renal outcomes. Our understanding of the RAS has significantly expanded with the discovery of new peptides involved in this complex pathway. Over the last two decades, a counter-regulatory or protective pathway has been discovered that opposes the effects of the classical pathway. Components of RAS are also implicated in the pathogenesis of obesity and its metabolic diseases. The continued discovery of newer molecules also provides novel therapeutic targets to improve disease outcomes. This article aims to provide an overview of an updated understanding of the RAS, its role in physiological and pathological processes, and potential novel therapeutic options from RAS for managing cardiorenal disorders, obesity, and related metabolic disorders.

Effects of treatment of non-alcoholic fatty liver disease on heart failure with preserved ejection fraction

In the past few decades, non-alcoholic fatty liver disease (NAFLD) and heart failure with preserved ejection fraction (HFpEF) have become the most common chronic liver disease and the main form of heart failure (HF), respectively. NAFLD is closely associated with HFpEF by sharing common risk factors and/or by boosting systemic inflammation, releasing other secretory factors, and having an expansion of epicardial adipose tissue (EAT). Therefore, the treatments of NAFLD may also affect the development and prognosis of HFpEF. However, no specific drugs for NAFLD have been approved by the Food and Drug Administration (FDA) and some non-specific treatments for NAFLD are applied in the clinic. Currently, the treatments of NAFLD can be divided into non-pharmacological and pharmacological treatments. Non-pharmacological treatments mainly include dietary intervention, weight loss by exercise, caloric restriction, and bariatric surgery. Pharmacological treatments mainly include administering statins, thiazolidinediones, glucagon-like peptide-1 receptor agonists, sodium-glucose cotransporter 2 inhibitors, and metformin. This review will mainly focus on analyzing how these treatments may affect the development and prognosis of HFpEF.

Coexistence of metabolic syndrome and osteopenia associated with social inequalities and unhealthy lifestyle among postmenopausal women in South Korea: the 2008 to 2011 Korea National Health and Nutritional Examination Survey (KNHANES)

OBJECTIVE

The prevalence of metabolic syndrome (MetS) and osteoporosis (OP) among postmenopausal women has been rapidly increasing. We examined the associations between socioeconomic status-related factors, unhealthy lifestyle, and the coexistence of MetS and osteopenia or OP.

METHODS

One thousand nine hundred ninety-one postmenopausal women aged 45 to 65 years were used to select a representative sample of the civilian, noninstitutionalized South Korean population from the 2008 to 2011 Korea National Health and Nutrition Examination Survey data. Women were grouped as neither MetS nor OP (normal), MetS, OP, and both MetS and OP (MetS + OP). Socioeconomic status (education, household income, place of residence, employment status), health-related behaviors (physical activity, alcohol consumption, smoking), and diet-related factors (intake of nutrients and food groups, eating habits, food insecurity) were obtained. Logistic regression models were used to examine the odds ratio (OR) and 95% confidence interval (CI).

RESULTS

The prevalence of MetS + OP was 32.5%. The average number of MetS risk factors in MetS + OP was 3.5, higher than that of normal and OP groups (P < 0.001). Bone mineral density at all sites was significantly lower in MetS + OP than normal and MetS groups (P < 0.001). Also, calcium, phosphorus, vitamin A, riboflavin, and niacin levels were lowest in the MetS + OP group compared with the three other groups (P < 0.05). After controlling for covariates, low-income and low-education women were more likely to have MetS + OP (OR 1.97, 95% CI 1.04-3.72); high-income and high-education group was 70% less likely to have MetS + OP (OR 0.30, 95% CI 0.10-0.86) compared with the middle-income and middle-education group.

CONCLUSIONS

Social inequalities might be powerful contributors in Korean postmenopausal women with coexistence of MetS and OP. Therefore, social and political perspective approaches are required in this population for prevention and treatment of MetS and OP. Future studies should explore to find controllable factors and thereby improve health status in postmenopausal women.

Nonalcoholic Fatty Liver Disease Pandemic Fuels the Upsurge in Cardiovascular Diseases

Cardiovascular diseases (CVDs) remain a leading cause of death worldwide. Among the major risk factors for CVD, obesity and diabetes mellitus have received considerable attention in terms of public policy and awareness. However, the emerging prevalence of nonalcoholic fatty liver disease (NAFLD), as the most common liver and metabolic disease and a cause of CVD, has been largely overlooked. Currently, the number of individuals with NAFLD is greater than the total number of individuals with diabetes mellitus and obesity. Epidemiological studies have established a strong correlation between NAFLD and an increased risk of CVD and CVD-associated events. Although debate continues over the causal relationship between NAFLD and CVD, many mechanistic and longitudinal studies have indicated that NAFLD is one of the major driving forces for CVD and should be recognized as an independent risk factor for CVD apart from other metabolic disorders. In this review, we summarize the clinical evidence that supports NAFLD as a risk factor for CVD epidemics and discuss major mechanistic insights regarding the acceleration of CVD in the setting of NAFLD. Finally, we address the potential treatments for NAFLD and their potential impact on CVD.

Tributyltin impacts in metabolic syndrome development through disruption of angiotensin II receptor signaling pathways in white adipose tissue from adult female rats

White adipose tissue (WAT) dysfunction and obesity are a consequence of a low-grade inflammation state. These WAT irregularities could result from abnormal metabolic renin-angiotensin system (RAS) control. Recently, tributyltin (TBT) has been found to play a critical role in these metabolic irregularities. However, TBT actions on the WAT-RAS functions are not currently well understood. In this study, we assessed whether TBT exposure resulted in metabolic syndrome (MetS) development and other metabolic complications as a result of abnormal modulation of WAT-RAS pathways. TBT (100 ng/kg/day) was administered to adult female Wistar rats, and their WAT morphophysiology and adipokine profiles were assessed. We further assessed the expression of Angiotensin-II receptor proteins (AT1R and AT2R) and proteins involved in downstream pathways mediating inflammation and adipogenesis modulation. TBT-exposed rats exhibited increases in body weight and adiposity. TBT rats present dyslipidemia and insulin resistance, suggesting MetS development. TBT promoted WAT inflammatory infiltration, AT1R protein overexpression and reduced Angiotensin-(1-7) expression. These TBT WAT abnormalities are reflected by NFκB activation, with higher adipokine levels (leptin, TNF-α and IL-6) and overexpression of AKT, ERK, P38, FAS and PPARγ protein. In vitro, TBT exposure stimulates lipid accumulation, reduces AT2R protein expression, and increases leptin, AKT and ERK protein expression in 3T3L1 cells. These findings suggest that TBT exposure participates in MetS development via the improper function of WAT-RAS metabolic control.

Early pharmacological inhibition of angiotensin-I converting enzyme activity induces obesity in adulthood

We have investigated early programming of body mass in order to understand the multifactorial etiology of obesity. Considering that the renin-angiotensin system (RAS) is expressed and functional in the white adipose tissue (WAT) and modulates its development, we reasoned whether early transitory inhibition of angiotensin-I converting enzyme activity after birth could modify late body mass development. Therefore, newborn Wistar rats were treated with enalapril (10 mg/kg of body mass) or saline, starting at the first day of life until the age of 16 days. Between days ninetieth and hundred and eightieth, a group of these animals received high fat diet (HFD). Molecular, biochemical, histological, and physiological data were collected. Enalapril treated animals presented hyperphagia, overweight, and increased serum level of triglycerides, total cholesterol and leptin, in adult life. Body composition analyses revealed higher fat mass with increased adipocyte size in these animals. Molecular analyses revealed that enalapril treatment increases neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) gene expression in hypothalamus, fatty acid synthase (FAS), and hormone-sensitive lipase (HSL) gene expression in retroperitoneal WAT, and decreases peroxixome proliferators-activated receptor (PPAR)γ, PPARα, uncoupling protein (UCP)2, and UCP3 gene expression in WAT. The results of the current study indicate that enalapril administration during early postnatal development increases body mass, adiposity and serum lipids in adulthood associated with enhanced food intake and decreased metabolic activity in WAT, predisposing to obesity in adulthood.

The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity

Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.

Angiotensinogen gene silencing reduces markers of lipid accumulation and inflammation in cultured adipocytes

Inflammatory adipokines secreted from adipose tissue are major contributors to obesity-associated inflammation and other metabolic dysfunctions. We and others have recently documented the contribution of adipose tissue renin-angiotensin system to the pathogenesis of obesity, inflammation, and insulin resistance. We hypothesized that adipocyte-derived angiotensinogen (Agt) plays a critical role in adipogenesis and/or lipogenesis as well as inflammation. This was tested using 3T3-L1 adipocytes, stably transfected with Agt-shRNA or scrambled Sc-shRNA as a control. Transfected preadipocytes were differentiated and used to investigate the role of adipose Agt through microarray and PCR analyses and adipokine profiling. As expected, Agt gene silencing significantly reduced the expression of Agt and its hormone product angiotensin II (Ang II), as well as lipid accumulation in 3T3-L1 adipocytes. Microarray studies identified several genes involved in lipid metabolism and inflammatory pathways which were down-regulated by Agt gene inactivation, such as glycerol-3-phosphate dehydrogenase 1 (Gpd1), serum amyloid A 3 (Saa3), nucleotide-binding oligomerization domain containing 1 (Nod1), and signal transducer and activator of transcription 1 (Stat1). Mouse adipogenesis PCR arrays revealed lower expression levels of adipogenic/lipogenic genes such as peroxisome proliferator activated receptor gamma (PPARγ), sterol regulatory element binding transcription factor 1 (Srebf1), adipogenin (Adig), and fatty acid binding protein 4 (Fabp4). Further, silencing of Agt gene significantly lowered expression of pro-inflammatory adipokines including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and monocyte chemotactic protein-1 (MCP-1). In conclusion, this study directly demonstrates critical effects of Agt in adipocyte metabolism and inflammation and further support a potential role for adipose Agt in the pathogenesis of obesity-associated metabolic alterations.

Increased total Renin levels but not Angiotensin-converting enzyme activity in obese patients with polycystic ovary syndrome

OBJECTIVE

To investigate the renin-angiotensin-aldosterone system and angiotensin-converting enzyme (ACE) activity in patients with polycystic ovarian syndrome (PCOS).

SUBJECTS AND METHODS

In this case-control study, 41 obese (PCOS) women and 29 healthy controls, matched for age and body mass index, were enrolled. Anthropometric, metabolic, and hormonal patterns, including plasma aldosterone, plasma renin, and ACE activity, were measured in each subject.

RESULTS

Plasma renin levels were significantly higher in PCOS patients (19.7 ± 14.5 µg/ml) compared with controls (12.9 ± 9.0 µg/ml, p < 0.05). ACE activity and aldosterone levels did not significantly differ between both groups (p = 0.15 and p = 0.18, respectively). Analysis of PCOS patients showed a significant correlation of fasting insulin levels with levels of renin (r = 0.305, p < 0.01) and free testosterone (r = 0.384, p = 0.001). Similarly, homeostasis model assessment index was positively correlated with total renin concentrations (r = 0.366, p < 0.01) and free testosterone (r = 0.352, p < 0.01).

CONCLUSION

Obese PCOS women had higher total renin levels, but not ACE activity and aldosterone levels, related to insulin resistance compared with controls.

Mechanisms of hypertension in the cardiometabolic syndrome

Arterial hypertension is often part of a constellation of anthropometric and metabolic abnormalities that occur simultaneously to a higher degree than would be expected by chance alone, supporting the existence of a discrete disorder, the so-called metabolic syndrome. It is the result of interactions among a large number of interconnected mechanisms, which eventually lead to both an increase in cardiovascular and renal risk, and the development of diabetes. Mechanisms involved in the metabolic syndrome are obesity, insulin resistance, and a constellation of independent factors, which include molecules of hepatic, vascular, and immunologic origin with pro-inflammatory properties. At each of these key points are interactions of demographics, lifestyle, genetic factors, and environmental fetal programming. Superimposing upon these are infections or chronic exposure or both to certain drugs that can also make their contribution. Skeletal muscle and the liver, not adipose tissue, are the two key insulin-response tissues involved in maintaining glucose balance, although abnormal insulin action in the adipocytes also plays a role in development of the syndrome. Factors commonly associated with and partly dependent on obesity, insulin resistance, such as overactivity of the sympathetic, stimulation of the renin-angiotensin-aldosterone systems, abnormal renal sodium handling, endothelial dysfunction, and large vessels' alterations, may play a key role in the blood pressure elevation of the syndrome.

Long term treatment with ACE inhibitor enalapril decreases body weight gain and increases life span in rats

Renin-angiotensin system is involved in homeostasis processes linked to renal and cardiovascular system and recently has been linked to metabolic syndrome. We analyzed the influence of long term angiotensin I converting enzyme (ACE) inhibitor enalapril treatment in normotensive adult Wistar rats fed with standard or palatable hyperlipidic diets. Our results show that long term enalapril treatment decreases absolute food intake, serum leptin concentration and body weight gain. Moreover, in adipose tissue, enalapril treatment led to decreased ACE activity, enhanced the expression of peroxisome proliferator activated receptor gamma, adiponectin, hormone-sensitive lipase, fatty acid synthase, catalase and superoxide dismutase resulting in prolonged life span. On the other hand, the ACE inhibitor was not able to improve the transport of leptin through the blood brain barrier or to alter the sensitivity of this hormone in the central nervous system. The effect of enalapril in decreasing body weight gain was also observed in older rats. In summary, these results extend our previous findings and corroborate data from the literature regarding the beneficial metabolic effects of enalapril and show for the first time that this ACE inhibitor prolongs life span in rats also fed with palatable hyperlipidic diet, an action probably correlated with adipose tissue metabolic modulation and body weight reduction.

De-novo identification of PPARgamma/RXR binding sites and direct targets during adipogenesis

Background

The pathophysiology of obesity and type 2 diabetes mellitus is associated with abnormalities in endocrine signaling in adipose tissue and one of the key signaling affectors operative in these disorders is the nuclear hormone transcription factor peroxisome proliferator-activated receptor-γ (PPARγ). PPARγ has pleiotropic functions affecting a wide range of fundamental biological processes including the regulation of genes that modulate insulin sensitivity, adipocyte differentiation, inflammation and atherosclerosis. To date, only a limited number of direct targets for PPARγ have been identified through research using the well established pre-adipogenic cell line, 3T3-L1. In order to obtain a genome-wide view of PPARγ binding sites, we applied the pair end-tagging technology (ChIP-PET) to map PPARγ binding sites in 3T3-L1 preadipocyte cells.

Methodology/Principal Findings

Coupling gene expression profile analysis with ChIP-PET, we identified in a genome-wide manner over 7700 DNA binding sites of the transcription factor PPARγ and its heterodimeric partner RXR during the course of adipocyte differentiation. Our validation studies prove that the identified sites are bona fide binding sites for both PPARγ and RXR and that they are functionally capable of driving PPARγ specific transcription. Our results strongly indicate that PPARγ is the predominant heterodimerization partner for RXR during late stages of adipocyte differentiation. Additionally, we find that PPARγ/RXR association is enriched within the proximity of the 5′ region of the transcription start site and this association is significantly associated with transcriptional up-regulation of genes involved in fatty acid and lipid metabolism confirming the role of PPARγ as the master transcriptional regulator of adipogenesis. Evolutionary conservation analysis of these binding sites is greater when adjacent to up-regulated genes than down-regulated genes, suggesting the primordial function of PPARγ/RXR is in the induction of genes. Our functional validations resulted in identifying novel PPARγ direct targets that have not been previously reported to promote adipogenic differentiation.

Conclusions/Significance

We have identified in a genome-wide manner the binding sites of PPARγ and RXR during the course of adipogenic differentiation in 3T3L1 cells, and provide an important resource for the study of PPARγ function in the context of adipocyte differentiation.

The secretory function of adipocytes in the physiology of white adipose tissue

White adipose tissue, previously regarded as a passive lipid storage site, is now viewed as a dynamic tissue. It has the capacity to actively communicate by sending and receiving different types of signals. An overview of these signals, the external modulators that affect adipose tissue and the secreted signaling molecules, the adipokines, is presented. The secretory function is highlighted in relation to energy metabolism, inflammation and the extracellular matrix and placed in the context of adipose tissue biology. We observe that the endocrine function of adipocytes receives much attention, while its paracrine and autocrine functions are underestimated. Also, we provide examples that species specificity should not be neglected. We conclude that adipose tissue primarily is an energy storage organ, well supported by its secretory function.

Combination of N-acetylcysteine and metformin improves histological steatosis and fibrosis in patients with non-alcoholic steatohepatitis

AIM

There is no proven medical therapy for the treatment of non-alcoholic steatohepatitis (NASH). Oxidative stress and insulin resistance are the mechanisms that seem to be mostly involved in its pathogenesis. The aim of our study was to evaluate the efficacy of N-acetylcysteine (NAC) in combination with metformin (MTF) in improving the aminotransferases and histological parameters (steatosis, inflammation, hepatocellular ballooning, and fibrosis) after 12 months of treatment.

METHODS

Twenty consecutive patients (mean age 53 +/- 2 years [36-68] and body mass index [BMI] 29 [25-35]) with biopsy-proven NASH were enrolled in the study. NAC (1.2 g/day) and MTF (850-1000 mg/day) were given orally for 12 months. All patients underwent evaluation of serum aminotransferases, fasting lipid profile and serum glucose, anthropometric parameters, and nutritional status at 0 and 12 months. A low calorie diet was prescribed for all patients.

RESULTS

Serum alanine aminotransferase, high-density lipoprotein, insulin, and glucose concentrations and thehomeostasis model assessment-insulin resistance (HOMA-IR) index were reduced significantly at the end of study (P < 0.05). The BMI declined, but without statistical significance. Aspartate aminotransferase, gamma-glutamyl transferase, alkaline phosphatase, cholesterol, and triglycerides levels were not altered with the treatment. Liver steatosis and fibrosis decreased (P < 0.05), but no improvement was noted in lobular inflammation or hepatocellular ballooning. The NASH activity score was significantly improved after treatment.

CONCLUSION

Based on the biochemical and histological evidence in this pilot study, NAC in combination with MTF appears to ameliorate several aspects of NASH, including fibrosis. Further studies of this form of combination therapy are warranted to assess its potential efficacy.

Effects of dietary calcium intake on body weight and prevalence of osteoporosis in early postmenopausal women

BACKGROUND

High calcium intakes seem to be ineffective at reducing bone loss in early postmenopausal women. However, the inverse relation between calcium intake and body weight can attenuate the negative effect of a low dietary calcium intake.

OBJECTIVE

The objective was to assess the role of dietary calcium and body mass index (BMI) on osteoporosis, defined according to World Health Organization criteria as a lumbar bone density >2.5 SD below the T score.

DESIGN

This was a cross-sectional, retrospective, observational study conducted in 1771 healthy, early postmenopausal women, who were not taking calcium supplements at the first densitometric evaluation. Weekly frequency of dairy food consumption was used to estimate the relative intake of dietary calcium. Total dairy intake was classified into 4 categories by quartile cutoffs. Multiple logistic regression analyses were used to study this sample.

RESULTS

BMI and prevalence of overweight showed significant inverse trends with increasing dairy intake. Calcium intake was not associated with osteoporosis when overweight was not considered. However, when overweight was considered in the analysis, women with the lowest calcium intake were more likely to have osteoporosis (odds ratio: 1.46; 95% CI: 1.12, 1.89; P = 0.008) than were women with the highest calcium intake.

CONCLUSIONS

In early postmenopausal women, a low dietary calcium intake may increase the risk of osteoporosis, but its negative effect can be offset by the greater BMI found in women with a low calcium intake.

Effect of angiotensin converting enzyme inhibitor enalapril on body weight and composition in young rats

Obesity is considered a worldwide public health problem showing an increased prevalence in developing countries, with urgent need for new and more efficient drugs and therapies. Enalapril, an angiotensin-I converting enzyme inhibitor (ACEi), is classically used in anti-hypertensive therapies, however, earlier publications have shown that this drug could also have significant impact on body weight in rats as well as in humans, besides reducing blood pressure. The effect of this drug in the white adipose tissue has been neglected for long time, even considering that most components of the renin-angiotensin and kallikrein-kinin system are expressed in this tissue. Furthermore, the adipose tissue is considered today as one of the most important sites for endocrine/inflammatory regulation of appetite and energy output and AngII has been linked to the metabolism in this tissue. Therefore, we analyzed the influence of chronic enalapril treatment in normotensive rats at earlier ages, evaluating body weight, energy homeostasis, lipid profile and serum levels of the hormones leptin and insulin, in the presence of a standard or a palatable hyperlipidic diet regimen for one month. Our results show that enalapril treatment is able to reduce body fat on both diets, without alteration in serum lipid profile. Furthermore, animals receiving enalapril showed reduction in food intake, leptin level and energy intake. In summary, these findings show for the first time that the ACEi enalapril reduces body fat in young normotensive rats and highlights a novel target to treat obesity and associated diseases.

Renin receptor expression in human adipose tissue

Adipose tissue synthesizes all components of the renin-angiotensin system. The renin receptor (RenR) is able, on renin binding, to increase its efficiency to generate angiotensin I from angiotensinogen. We demonstrate that RenR is specifically synthesized in the stromal portion of human adipose tissue in both isolated interadipocyte stromal cells and in stromal areas. RenR is expressed at the periphery of cells, strongly suggesting a membranal localization. RenR protein expression in primary cultures of human stromal cells decreased significantly during differentiation, whereas RenR mRNA levels did not change, demonstrating that RenR was expressed in both preadipocyte and nonpreadipocyte cells, and was regulated at a posttranscriptional level. Double-labeling immunohistochemistry of human adipose tissue sections revealed that RenR was colocalized with renin, whereas incubation of 3T3-L1, a preadipocyte cell line, with renin stimulated the phosphorylation state of the intracellular signaling pathway ERK 1/2, and short exposure of human adipose stromal cells in primary culture to renin was followed by a long-lasting dose-dependent increase of angiotensin I generation, indicating that adipose RenR is functional. We show, using a large set of human adipose tissue biopsies, that RenR expression was increased in visceral compared with subcutaneous adipose tissue of lean and obese patients. Taken together with our finding that RenR was colocalized with plasminogen activator inhibitor type 1, the main inhibitor of the fibrinolytic system in visceral adipose tissue, the above-mentioned data suggest that RenR plays a role in obesity-induced visceral adipose tissue accumulation and its accompanying cardiovascular complications.

Pathogenesis of non-alcoholic steatohepatitis: human data

Non-alcoholic fatty liver disease (NAFLD) has moved rapidly to the forefront of clinical disease, with a prevalence of 30% in the adult United States population and a definite but yet uncertain rate of progression to cirrhosis and end-stage liver disease. This disease has an impact on all areas of clinical medicine, with increasing prevalence and adversity. It is essential to understand the pathophysiologic mechanisms involved in NAFLD, so that therapeutic strategies can be developed. Although fatty liver may be caused by other factors, this review concentrates on fatty liver associated with insulin resistance, sometimes referred to as the primary form.

Role of transcription factor NFAT in glucose and insulin homeostasis

Compromised immunoregulation contributes to obesity and complications in metabolic pathogenesis. Here, we demonstrate that the nuclear factor of activated T cell (NFAT) group of transcription factors contributes to glucose and insulin homeostasis. Expression of two members of the NFAT family (NFATc2 and NFATc4) is induced upon adipogenesis and in obese mice. Mice with the Nfatc2-/- Nfatc4-/- compound disruption exhibit defects in fat accumulation and are lean. Nfatc2-/- Nfatc4-/- mice are also protected from diet-induced obesity. Ablation of NFATc2 and NFATc4 increases insulin sensitivity, in part, by sustained activation of the insulin signaling pathway. Nfatc2-/- Nfatc4-/- mice also exhibit an altered adipokine profile, with reduced resistin and leptin levels. Mechanistically, NFAT is recruited to the transcription loci and regulates resistin gene expression upon insulin stimulation. Together, these results establish a role for NFAT in glucose/insulin homeostasis and expand the repertoire of NFAT function to metabolic pathogenesis and adipokine gene transcription.

Changes in gene expression foreshadow diet-induced obesity in genetically identical mice

High phenotypic variation in diet-induced obesity in male C57BL/6J inbred mice suggests a molecular model to investigate non-genetic mechanisms of obesity. Feeding mice a high-fat diet beginning at 8 wk of age resulted in a 4-fold difference in adiposity. The phenotypes of mice characteristic of high or low gainers were evident by 6 wk of age, when mice were still on a low-fat diet; they were amplified after being switched to the high-fat diet and persisted even after the obesogenic protocol was interrupted with a calorically restricted, low-fat chow diet. Accordingly, susceptibility to diet-induced obesity in genetically identical mice is a stable phenotype that can be detected in mice shortly after weaning. Chronologically, differences in adiposity preceded those of feeding efficiency and food intake, suggesting that observed difference in leptin secretion is a factor in determining phenotypes related to food intake. Gene expression analyses of adipose tissue and hypothalamus from mice with low and high weight gain, by microarray and qRT-PCR, showed major changes in the expression of genes of Wnt signaling and tissue re-modeling in adipose tissue. In particular, elevated expression of SFRP5, an inhibitor of Wnt signaling, the imprinted gene MEST and BMP3 may be causally linked to fat mass expansion, since differences in gene expression observed in biopsies of epididymal fat at 7 wk of age (before the high-fat diet) correlated with adiposity after 8 wk on a high-fat diet. We propose that C57BL/6J mice have the phenotypic characteristics suitable for a model to investigate epigenetic mechanisms within adipose tissue that underlie diet-induced obesity.

Genetic models to explain the obesity epidemic are inadequate because the emergence of this epidemic over the past 30 y has been too rapid to allow for the appearance of new mutant genes. The authors show that diet-induced obesity among genetically identical mice is characterized by highly variable and stable phenotypes that are established in mice early in life, even before they become exposed to an obesogenic environment. Furthermore, strong associations occur between susceptibility to obesity and the expression of genes implicated in processes that regulate cellular development. Previous studies have shown that abnormal regulation of such genes by epigenetic mechanisms is linked with the development of cancer. Epigenetic mechanisms involve chemical processes that change chromatin structure and gene expression without changing the genetic code. Accordingly, epigenetic modifications of gene structure through nutritional and physiological stress provide mechanisms for inducing obesity that are independent of new mutations to the genome. Experimental models based upon genetically identical mice provide powerful tools for identifying epigenetic and environmental mechanisms causing obesity and other chronic diseases.

Adipose tissue as a secretory organ: from adipogenesis to the metabolic syndrome

Adipose tissue contains various types of cells that include preadipocytes and adipocytes. Studies have emphasized that (i) preadipocytes secrete factors involved in their own differentiation and (ii) adipocytes acquire the ability to communicate systemically with other organs (brain, liver, skeletal muscle) and locally with other cells (preadipocytes, endothelial cells and monocytes/macrophages). Adipocytes secrete proteins exhibiting either beneficial (leptin, adiponectin) or deleterious effects (angiotensinogen). Associated to the effect of secretory products from macrophages (cytokines), a disturbance in the balance between these various secreted factors leads to the development of a metabolic syndrome.

The expression of genes related to adipocyte differentiation in pigs1

The purpose of this study was to detect differential expression of genes related to adipocyte differentiation in pigs by suppression subtractive hybridization. Adipocytes and stromal vascular cells (a fraction containing preadipocytes) from pig adipose tissue were isolated for mRNA extraction. The cDNA from preadipocytes was subtracted from the cDNA from adipocytes. The subtracted gene fragments were cloned into pGEM-T Easy TA cloning vector. We selected 384 clones for gene sequence determination and for further analysis. These genes were subjected to a differential screening procedure to confirm the differential expression of genes between the 2 cell types. We found that at least 36 genes were highly expressed in the adipocytes compared with preadipocytes. Among these, 6 genes including 2 novel genes with the greatest differences were selected and confirmed by Northern analysis. We found that angiotensin I-converting enzyme (ACE), ataxia-telangiectasia mutated protein (ATM), calpain 1, and stearoyl coenzyme A desaturase 1 (SCD1) were highly expressed in adipocytes compared with preadipocytes (P < 0.05). The relative mRNA abundance of ACE, ATM, calpain 1, SCD1, and 2 novel genes discovered in the current study was increased at the later stages of adipocyte differentiation (P < 0.05). The results confirmed that the genes involved in lipid metabolism and adipocyte differentiation were highly expressed in porcine adipocytes. However, further investigation is needed to demonstrate specific functions of the novel genes discovered in the current study.

PKBα is required for adipose differentiation of mouse embryonic fibroblasts

Protein kinase Bα (PKBα) is a key regulator of metabolism, proliferation and differentiation. We have explored the role of PKBα in adipogenesis using wild-type and PKBα-knockout mouse embryonic fibroblasts (MEFs) and show that lack of PKBα prevents MEF differentiation into adipocytes. Expression of ectopic PKBα in PKBα-deficient cells restores adipogenesis. We identified 80 genes whose expression was upregulated in wild-type MEFs during adipogenesis but whose expression was significantly reduced in PKBα-deficient MEFs under the same conditions. Significantly, the regulator of adipogenesis Krüppel-like transcription factor 15 gene expression was downregulated in PKBα-deficient MEFs but could be restored by expressing an active PKBα in the deficient cells. The level of lipocalin 2, renin 1 and receptor-activity-modifying protein 3 genes expressed by adipose cells was also decreased in PKBα-deficient MEFs, and are inhibited by LY294002 treatment during early adipocyte differentiation of 3T3-L1 cells. The results underscore an essential role for PKBα in the transcriptional program required for adipogenesis.

Mineralocorticoid-stimulating activity of adipose tissue

Obesity is strongly associated with arterial hypertension. A positive correlation between obesity and plasma aldosterone levels has been observed by different investigators, suggesting that an abnormal secretion of aldosterone in obesity contributes to the development of arterial hypertension in obese subjects. The mechanisms proposed to explain this abnormal aldosterone production mainly involve the adipose renin-angiotensin system, an indirect effect of increased fatty acids, and direct adrenal stimulation by adipocyte secretory products. Indeed, adipose mineralocorticoid-stimulating activity was recently observed in isolated human adipocytes, suggesting a hitherto unknown direct involvement of adipose tissue in the regulation of blood pressure in obesity.

Insulin resistance: a metabolic pathway to chronic liver disease

Insulin resistance (IR) is the pathophysiological hallmark of nonalcoholic fatty liver disease (NAFLD), one of the most common causes of chronic liver disease in Western countries. We review the definition of IR, the methods for the quantitative assessment of insulin action, the pathophysiology of IR, and the role of IR in the pathogenesis of chronic liver disease. Increased free fatty acid flux from adipose tissue to nonadipose organs, a result of abnormal fat metabolism, leads to hepatic triglyceride accumulation and contributes to impaired glucose metabolism and insulin sensitivity in muscle and in the liver. Several factors secreted or expressed in the adipocyte contribute to the onset of a proinflammatory state, which may be limited to the liver or more extensively expressed throughout the body. IR is the common characteristic of the metabolic syndrome and its related features. It is a systemic disease affecting the nervous system, muscles, pancreas, kidney, heart, and immune system, in addition to the liver. A complex interaction between genes and the environment favors or enhances IR and the phenotypic expression of NAFLD in individual patients. Advanced fibrotic liver disease is associated with multiple features of the metabolic syndrome, and the risk of progressive liver disease should not be underestimated in individuals with metabolic disorders. Finally, the ability of insulin-sensitizing, pharmacological agents to treat NAFLD by reducing IR in the liver (metformin) and in the periphery (thiazolidinediones) are discussed.

Adipose tissue gene expression profiling reveals distinct molecular pathways that define visceral adiposity in offspring of maternal protein-restricted rats

There is increasing evidence that poor early growth confers an increased risk of type 2 diabetes, hypertension, and other features of the metabolic syndrome in later life. We hypothesized that this may result from poor nutrition during early life exerting permanent effects on the structure and function of key metabolic organ systems. To study the long-term impact of early-life undernutrition on susceptibility to visceral adiposity, we used a rat model of maternal protein restriction (MPR) in which dams were fed a low-protein diet (containing 8% instead of 20% protein in control diet) throughout pregnancy and lactation. MPR offspring were born smaller than controls (offspring of dams on control diet) and in adulthood developed visceral adiposity. We compared the pattern of gene expression in visceral adipose tissue (VAT) between MPR offspring and controls with Affymetrix rat expression arrays. Of the total number of genes and expressed sequence tags analyzed (15,923 probe sets), 9,790 (61.5%) were expressed in VAT. We identified 650 transcripts as differentially expressed > or =1.5-fold in the VAT of MPR offspring. Gene ontology analysis revealed a global upregulation of genes involved in carbohydrate, lipid, and protein metabolism. A number of genes involved in adipocyte differentiation, angiogenesis, and extracellular matrix remodeling were also upregulated. However, in marked contrast to other rodent models of obesity, the expression of a large number of genes associated with inflammation was reduced in this rat model. Thus visceral adiposity in this early-life programmed rat model is marked by dynamic changes in the transcriptional profile of VAT. Our data provide new insights into the molecular mechanisms that underlie the early-life programming of visceral adiposity.

Adipose tissue energy metabolism: altered gene expression profile of mice subjected to long-term caloric restriction

We investigated the influences of short-term and lifespan-prolonging long-term caloric restriction (LCR) on gene expression in white adipose tissue (WAT). Over 11,000 genes were examined using high-density oligonucleotide microarrays in four groups of 10- to 11-month-old male C57Bl6 mice that were either fasted for 18 h before death (F), subjected to short-term caloric restriction for 23 days (SCR), or LCR for 9 months and compared with nonfasted control (CO) mice. Only a few transcripts of F and SCR were differentially expressed compared with CO mice. In contrast, 345 transcripts of 6,266 genes found to be expressed in WAT were altered significantly by LCR. The expression of several genes encoding proteins involved in energy metabolism was increased by LCR. Further, many of the shifts in gene expression after LCR are known to occur during adipocyte differentiation. Selected LCR-associated alterations of gene expression were supported by quantitative reverse transcriptase-polymerase chain reaction, histology, and histochemical examinations. Our data provide new insights on the metabolic state associated with aging retardation by LCR.

Transgenic amplification of glucocorticoid action in adipose tissue causes high blood pressure in mice

Obesity is closely associated with the metabolic syndrome, a combination of disorders including insulin resistance, diabetes, dyslipidemia, and hypertension. A role for local glucocorticoid reamplification in obesity and the metabolic syndrome has been suggested. The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) regenerates active cortisol from inactive 11-keto forms, and aP2-HSD1 mice with relative transgenic overexpression of this enzyme in fat cells develop visceral obesity with insulin resistance and dyslipidemia. Here we report that aP2-HSD1 mice also have high arterial blood pressure (BP). The mice have increased sensitivity to dietary salt and increased plasma levels of angiotensinogen, angiotensin II, and aldosterone. This hypertension is abolished by selective angiotensin II receptor AT-1 antagonist at a low dose that does not affect BP in non-Tg littermates. These findings suggest that activation of the circulating renin-angiotensin system (RAS) develops in aP2-HSD1 mice. The long-term hypertension is further reflected by an appreciable hypertrophy and hyperplasia of the distal tubule epithelium of the nephron, resembling salt-sensitive or angiotensin II-mediated hypertension. Taken together, our findings suggest that overexpression of 11beta-HSD1 in fat is sufficient to cause salt-sensitive hypertension mediated by an activated RAS. The potential role of adipose 11beta-HSD1 in mediating critical features of the metabolic syndrome extends beyond obesity and metabolic complications to include the most central cardiovascular feature of this disorder.