Expression of peroxisome proliferator-activated receptor-gamma1 and peroxisome proliferator-activated receptor-gamma2 in visceral and subcutaneous adipose tissue of obese women

A glimpse of the connection between PPARγ and macrophage

Nuclear receptors are ligand-regulated transcription factors that regulate vast cellular activities and serve as an important class of drug targets. Among them, peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family and have been extensively studied for their roles in metabolism, differentiation, development, and cancer, among others. Recently, there has been considerable interest in understanding and defining the function of PPARs and their agonists in regulating innate and adaptive immune responses and their pharmacological potential in combating chronic inflammatory diseases. In this review, we focus on emerging evidence for the potential role of PPARγ in macrophage biology, which is the prior innate immune executive in metabolic and tissue homeostasis. We also discuss the role of PPARγ as a regulator of macrophage function in inflammatory diseases. Lastly, we discuss the possible application of PPARγ antagonists in metabolic pathologies.

Principal component analysis of adipose tissue gene expression of lipogenic and adipogenic factors in obesity

OBJECTIVE

A better understanding of mechanisms regulating lipogenesis and adipogenesis is needed to overcome the obesity pandemic. We aimed to study the relationship of the transcript levels of peroxisome proliferator activator receptor γ (PPARγ), CCAAT/enhancer-binding protein alpha (C/EBP-α), liver X receptor (LXR), sterol regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) in subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) from obese and normal-weight women with a variety of anthropometric indices, metabolic and biochemical parameters, and insulin resistance.

METHODS

Real-time PCR was done to evaluate the transcript levels of the above-mentioned genes in VAT and SAT from all participants.

RESULTS

Using principal component analysis (PCA) results, two significant principal components were identified for adipogenic and lipogenic genes in SAT (SPC1 and SPC2) and VAT (VPC1 and VPC2). SPC1 was characterized by relatively high transcript levels of SREBP1c, PPARγ, FAS, and ACC. However, the second pattern (SPC2) was associated with C/EBPα and LXR α mRNA expression. VPC1 was characterized by transcript levels of SREBP1c, FAS, and ACC. However, the VPC2 was characterized by transcript levels of C/EBPα, LXR α, and PPARγ. Pearson's correlation analysis showed that unlike SPC2, which disclosed an inverse correlation with body mass index, waist and hip circumference, waist to height ratio, visceral adiposity index, HOMA-IR, conicity index, lipid accumulation product, and weight-adjusted waist index, the VPC1 was positively correlated with above-mentioned obesity indices.

CONCLUSION

This study provided valuable data on multiple patterns for adipogenic and lipogenic genes in adipose tissues in association with a variety of anthropometric indices in obese subjects predicting adipose tissue dysfunction and lipid accumulation.

Parsing the Role of PPARs in Macrophage Processes

Cells are richly equipped with nuclear receptors, which act as ligand-regulated transcription factors. Peroxisome proliferator activated receptors (PPARs), members of the nuclear receptor family, have been extensively studied for their roles in development, differentiation, and homeostatic processes. In the recent past, there has been substantial interest in understanding and defining the functions of PPARs and their agonists in regulating innate and adaptive immune responses as well as their pharmacologic potential in combating acute and chronic inflammatory disease. In this review, we focus on emerging evidence of the potential roles of the PPAR subtypes in macrophage biology. We also discuss the roles of dual and pan PPAR agonists as modulators of immune cell function, microbial infection, and inflammatory diseases.

Pyruvate dehydrogenase kinase 1 and 2 deficiency reduces high-fat diet-induced hypertrophic obesity and inhibits the differentiation of preadipocytes into mature adipocytes

Obesity is now recognized as a disease. This study revealed a novel role for pyruvate dehydrogenase kinase (PDK) in diet-induced hypertrophic obesity. Mice with global or adipose tissue-specific PDK2 deficiency were protected against diet-induced obesity. The weight of adipose tissues and the size of adipocytes were reduced. Adipocyte-specific PDK2 deficiency slightly increased insulin sensitivity in HFD-fed mice. In studies with 3T3-L1 preadipocytes, PDK2 and PDK1 expression was strongly increased during adipogenesis. Evidence was found for epigenetic induction of both PDK1 and PDK2. Gain- and loss-of-function studies with 3T3-L1 cells revealed a critical role for PDK1/2 in adipocyte differentiation and lipid accumulation. PDK1/2 induction during differentiation was also accompanied by increased expression of hypoxia-inducible factor-1α (HIF1α) and enhanced lactate production, both of which were absent in the context of PDK1/2 deficiency. Exogenous lactate supplementation increased the stability of HIF1α and promoted adipogenesis. PDK1/2 overexpression-mediated adipogenesis was abolished by HIF1α inhibition, suggesting a role for the PDK-lactate-HIF1α axis during adipogenesis. In human adipose tissue, the expression of PDK1/2 was positively correlated with that of the adipogenic marker PPARγ and inversely correlated with obesity. Similarly, PDK1/2 expression in mouse adipose tissue was decreased by chronic high-fat diet feeding. We conclude that PDK1 and 2 are novel regulators of adipogenesis that play critical roles in obesity.

The discovery that two forms of a key enzyme appear to play a critical role in fat production triggered by overeating might lead to new approaches to prevent and treat obesity. Hyeon-Ji Kang at Kyungpook National University, Daegu, South Korea, and colleagues in South Korea and the USA examined the role of the enzymes pyruvate dehydrogenase kinase types 1 and 2 (PDK1/2). PDK enzymes regulate the activity of a multi-enzyme complex that catalyzes a key step in the use of glucose to provide energy stores for cells. Mice deficient in PDK2 were protected from diet-induced obesity, and PDK 1 and 2 activity was increased during the generation of fat cells. Studies using mice and human fat tissue confirmed that the enzymes regulate the development and growth of fat cells. Drugs inhibiting PDK enzymes might combat obesity.

Adipocytes fail to maintain cellular identity during obesity due to reduced PPARγ activity and elevated TGFβ-SMAD signaling

Objective

Obesity due to overnutrition causes adipose tissue dysfunction, which is a critical pathological step on the road to type 2 diabetes (T2D) and other metabolic disorders. In this study, we conducted an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity.

Methods

We used nuclear tagging and translating ribosome affinity purification (NuTRAP) reporter mice crossed with Adipoq-Cre mice to determine adipocyte-specific 1) transcriptional profiles (RNA-seq), 2) promoter and enhancer activity (H3K27ac ChIP-seq), 3) and PPARγ cistrome (ChIP-seq) profiles in mice fed chow or a high-fat diet (HFD) for 10 weeks. We also assessed the impact of the PPARγ agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from the HFD-fed mice. We integrated these data to determine the transcription factors underlying adipocyte responses to HFD and conducted functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes.

Results

Adipocytes from the HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes and enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARγ binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. We identified the TGFβ1 effector protein SMAD to be enriched at HFD-induced promoters and enhancers and associated with myofibroblast signature genes. TGFβ1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFβ1.

Conclusions

Our data demonstrate that adipocytes fail to maintain cellular identity after HFD feeding, acquiring characteristics of a myofibroblast-like cell type through reduced PPARγ activity and elevated TGFβ-SMAD signaling. This cellular identity crisis may be a fundamental mechanism that drives functional decline of adipose tissues during obesity.

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Adipocytes after HFD intake exhibit defects in cellular identity maintenance.

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Adipocytes develop actin filament networks in obesity.

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Altered PPARγ activity mediates defective adipocyte identity phenotypes.

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TGFβ-SMAD pathways promote HFD-induced aberrant phenotype of adipocytes.

Indomethacin promotes browning and brown adipogenesis in both murine and human fat cells

Indomethacin (Indo), a nonsteroidal antiinflammatory drug, has been shown to promote murine brown adipogenesis both in vitro and in vivo, possibly due to its peroxisome proliferator-activated receptor gamma (PPARγ)-agonist activities. However, it is unclear whether Indo induces browning of white adipocytes from both murine and human origins or induces human brown adipogenesis. To bridge the gap, this study investigated the effects of increasing concentrations of Indo on murine 3T3-L1, human primary subcutaneous white adipocytes (HPsubQ), and human brown (HBr) adipocytes. The results show that Indo dose-dependently enhanced 3T3-L1 adipocyte differentiation and upregulated both mRNA and protein expression of brown and beige adipocyte markers, while simultaneously suppressing white adipocyte-specific marker mRNA expression. mRNA and protein expression of mitochondrial biogenesis and structural genes were dose-dependently enhanced in Indo treated 3T3-L1 adipocytes. This was accompanied by augmented mitochondrial DNA, enhanced oxygen consumption, proton leak, and maximal and spare respiratory capacity. Dose-dependent transactivation of PPARγ confirmed Indo's PPARγ-agonist activity in 3T3-L1 cells. Knockdown of PPARγ significantly attenuated Indo's activities in selective browning genes, demonstrating PPARγ dependence of these effects. Moreover, Indo enhanced mRNA and protein expression of brown markers in HPsubQ adipocytes. Interestingly, Indo-induced differential effects on individual PPARγ isoforms with significant dose-dependent induction of PPARγ-2 and suppression of PPARγ-1 protein expression. Finally, Indo significantly promoted brown adipogenesis in HBr cells. Taken together, these results demonstrate Indo to be a potent thermogenic compound in both murine and human fat cells and may be explored as a therapeutic agent for obesity treatment and prevention.

Sex hormones influence expression and function of peroxisome proliferator-activated receptor γ in adipocytes: pathophysiological aspects

Abstract Adipose tissue plays important roles not only in storing fat but also in maintaining metabolic homeostasis by regulating hundreds of biological signaling events and the secretion of various cytokines. One of the central regulators of adipocyte differentiation is peroxisome proliferator-activated receptor γ (PPARγ), which promotes downstream transcriptional activities, such as adiponectin. Disruption of homeostasis leads to the onset of metabolic diseases such as type 2 diabetes and other triggers for metabolic syndrome. Males and post-menopausal females are more likely to be affected with metabolic diseases than pre-menopausal females, suggesting that sex hormones might be involved in the pathogenesis and development of metabolic diseases. Indeed, 17β-estradiol, testosterone, dihydrotestosterone, and their receptors clearly play a role in adipose regulation: they can alter fat distribution and can modify the expression and activities of PPARγ and its downstream adipocytokines. Furthermore, sex hormones affect inflammatory factors such as nitric oxygen, nitric oxygen synthase, and their surrounding components. Sex hormones are also suggested to be involved with sex differences in the efficacy of the PPARγ agonist thiazolidinediones. Therefore, thorough investigation of how sex hormone-dependent regulation of metabolic homeostasis occurs is necessary in order to develop individualized clinical therapies optimized with regard to each patient's biological condition and drug sensitivities.

Glial cell line-derived neurotrophic factor protects against high-fat diet-induced obesity

Obesity is a growing epidemic with limited effective treatments. The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) was recently shown to enhance β-cell mass and improve glucose control in rodents. Its role in obesity is, however, not well characterized. In this study, we investigated the ability of GDNF to protect against high-fat diet (HFD)-induced obesity. GDNF transgenic (Tg) mice that overexpress GDNF under the control of the glial fibrillary acidic protein promoter and wild-type (WT) littermates were maintained on a HFD or regular rodent diet for 11 wk, and weight gain, energy expenditure, and insulin sensitivity were monitored. Differentiated mouse brown adipocytes and 3T3-L1 white adipocytes were used to study the effects of GDNF in vitro. Tg mice resisted the HFD-induced weight gain, insulin resistance, dyslipidemia, hyperleptinemia, and hepatic steatosis seen in WT mice despite similar food intake and activity levels. They exhibited significantly (P<0.001) higher energy expenditure than WT mice and increased expression in skeletal muscle and brown adipose tissue of peroxisome proliferator activated receptor-α and β1- and β3-adrenergic receptor genes, which are associated with increased lipolysis and enhanced lipid β-oxidation. In vitro, GDNF enhanced β-adrenergic-mediated cAMP release in brown adipocytes and suppressed lipid accumulation in differentiated 3T3L-1 cells through a p38MAPK signaling pathway. Our studies demonstrate a novel role for GDNF in the regulation of high-fat diet-induced obesity through increased energy expenditure. They show that GDNF and its receptor agonists may be potential targets for the treatment or prevention of obesity.

Expression of obesity markers and Persistent Organic Pollutants levels in adipose tissue of obese patients: reinforcing the obesogen hypothesis?

Introduction

Persistent Organic Pollutants (POPs) accumulate in adipose tissue and some are described to possess endocrine disrupting capacities. Therefore, it is important to evaluate their effects on key endocrine pathways in adipose tissue (AT), to further evaluate their potential role in metabolic pathologies such as obesity.

Objectives

The aim is twofold: (i) evaluate gene expression levels of obesity marker genes, i.e. the adipokines leptin (LEP), adiponectin (ADIPOQ) and Tumor Necrosis Factor α (TNFα) and the nuclear receptor, Peroxisome Proliferator Activated Receptor γ (PPARγ) in paired subcutaneous (SAT) and visceral (VAT) AT of obese subjects (n = 50) and to relate these values to serum concentrations of LEP and ADIPOQ (ii) evaluate the association of expression levels of marker genes in AT and serum with POP concentrations in AT.

Results and Conclusions

Leptin and adiponectin levels in serum were positively correlated to respectively expression levels of leptin in SAT and adiponectin in VAT. Our study shows more significant correlations between gene expression of obesity marker genes and POP concentrations in VAT compared to SAT. Since VAT is more important than SAT in pathologies associated with obesity, this suggests that POPs are able to influence the association between obesity and the development of associated pathologies. Moreover, this finding reveals the importance of VAT when investigating the obesogen hypothesis. Concerning PPARγ expression in VAT, negative correlations with polychlorinated biphenyls (PCBs) concentrations were found in non T2D patients. LEP serum concentrations correlated with several PCBs in women whereas in men no correlations were found. This strengthens the potential importance of gender differences in obesity and within the obesogen hypothesis.

The effect of sex hormones on peroxisome proliferator-activated receptor gamma expression and activity in mature adipocytes

Peroxisome proliferator-activated receptor (PPAR) γ plays a major role in the regulation of lipid and carbohydrate metabolism. Pioglitazone is a PPARγ agonist that is widely used for the treatment of type 2 diabetes mellitus. However, female patients have been reported to experience stronger efficacy and adverse effects than male patients. This study evaluated the effects of sex hormones on PPARγ expression and activity in adipocytes. Mouse 3T3-L1 preadipocytes were used after being grown into matured adipocytes. The sex hormones 17β-estradiol (E2), testosterone (T), or 5α-androstan-17β-ol-3-one (dihydrotestosterone; DHT) were added to the matured adipocytes and the cells were then maintained for short (24-72 h) or long (1- or 2-weeks) periods. E2 significantly upregulated PPARγ protein expression in a concentration-dependent manner after extended exposure, whereas T and DHT did not have such an effect. When cells were co-treated with pioglitazone and E2, PPARγ protein expression significantly increased in an E2-dependent manner, whereas this expression seemed to be reduced by pioglitazone mono-treatment and co-treatment with DHT at higher concentrations. The secretion levels of adiponectin protein, a major indicator of PPARγ activity, were significantly decreased by DHT, but were not affected by E2. Finally a luciferase assay was performed using a PPAR response element-Luk reporter gene. Transcriptional activity was not changed by any of single sex hormone treatment, but was significantly downregulated by co-treatment with pioglitazone and DHT. Taken together, our results suggest that sex hormones may influence PPARγ expression and function, which may explain the observed sex-specific different effect of pioglitazone.

Changes in gene expression profile in human subcutaneous adipose tissue during significant weight loss

OBJECTIVE

To analyze the expression of peroxisome proliferator-activated receptor-γ1 and 2 (PPARγ1 and 2), 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1), and leptin in adipose tissue (AT) of obese women during weight loss following Roux-en-Y gastric bypass (RYGB) and to compare these levels with those obtained in AT of nonobese subjects.

METHODS

Gene expression was determined by real-time RT-PCR prior to surgery and at 3, 6, and 12 months after RYGB.

RESULTS

All obese patients lost weight, reaching a mean BMI of 29.3 ± 1.0 kg/m(2) at 1 year after surgery (-33.9 ± 1.5% of their initial body weight). In obese subjects leptin and 11βHSD1 were over-expressed, whereas PPARγ1 was expressed at lower levels compared to controls. After surgery, leptin and 11βHSD1 gene expression decreased, whereas PPARγ1 expression increased. At 12 months after RYGB, these 3 genes had reached levels similar to the controls. In contrast, PPARγ2 gene expression was not different between groups and types of tissue and remained unchanged during weight loss. We found a positive correlation between BMI and levels of gene expression of leptin and 11βHSD1.

CONCLUSION

Gene expression of leptin, PPARγ1, and 11βHSD1 in AT is modified in human obesity. This default is completely corrected by RYGB.

Parallel down-regulation of FOXO1, PPARγ and adiponectin mRNA expression in visceral adipose tissue of class III obese individuals

OBJECTIVE

Adipose tissue is responsible for secretion of several cytokines that mediate systemic effects on obesity and insulin resistance. Subcutaneous abdominal adipose tissue (SAT) and visceral adipose tissue (VAT) are metabolically different and have differences in their gene expression profile. Our study evaluated the expression of adiponectin, FOXO1, PPARγ, and SIRT1 in VAT and SAT of non-obese and class III obese subjects.

METHODS

The adipose tissue samples were obtained by surgery. Reverse transcripts of studied genes were determined by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Comparing the different lipid depots, adiponectin expression was lower only in VAT of obese individuals (p = 0.043); FOXO1 and PPARγ levels were decreased in VAT of both groups. When non-obese and obese were compared, only adiponectin expression was lower in SAT and in VAT of obese subjects (p = 0.004 and p = 0.002, respectively). No difference was found with regard to SIRT1 levels in VAT or SAT in both groups. FOXO1 expression in SAT of obese subjects had a negative correlation with age (r = -0.683; p = 0.029) and triglyceride serum levels (r = -0.794; p = 0.006).

CONCLUSION

The decrease mRNA expression of this genes in VAT, responsible for central adiposity, may be associated with an increased risk of obesity and co-morbidities.

Impaired expression of the inducible cAMP early repressor accounts for sustained adipose CREB activity in obesity

OBJECTIVE

Increase in adipose cAMP-responsive element binding protein (CREB) activity promotes adipocyte dysfunction and systemic insulin resistance in obese mice. This is achieved by increasing the expression of activating transcription factor 3 (ATF3). In this study, we investigated whether impaired expression of the inducible cAMP early repressor (ICER), a transcriptional antagonist of CREB, is responsible for the increased CREB activity in adipocytes of obese mice and humans.

RESEARCH DESIGN AND METHODS

Total RNA and nuclear proteins were prepared from visceral adipose tissue (VAT) of human nonobese or obese subjects and white adipose tissue (WAT) of C57Bl6-Rj mice that were fed with normal or high-fat diet for 16 weeks. The expression of genes was monitored by real-time PCR, Western blotting, and electromobility shift assays. RNA interference was used to silence the expression of Icer.

RESULTS

The expression of Icer/ICER was reduced in VAT and WAT of obese humans and mice, respectively. Diminution of Icer/ICER was restricted to adipocytes and was accompanied by a rise of Atf3/ATF3 and diminution of Adipoq/ADIPOQ and Glut4/GLUT4. Silencing the expression of Icer in 3T3-L1 adipocytes mimicked the results observed in human and mice cells and hampered glucose uptake, thus confirming the requirement of Icer for appropriate adipocyte function.

CONCLUSIONS

Impaired expression of ICER contributes to elevation in CREB target genes and, therefore, to the development of insulin resistance in obesity.

Genetics of adipose tissue biology

Adipose tissue morphology and release of free fatty acids, as well as peptide hormones, are believed to contribute to obesity and related metabolic disorders. These adipose tissue phenotypes are influenced by adiposity, but there is also a strong hereditary impact. Polymorphisms in numerous adipose-expressed genes have been evaluated for association with adipocyte and clinical phenotypes. In our opinion, some results are convincing. Thus ADRB2 and GPR74 genes are associated with adipocyte lipolysis, GPR74 also with BMI; PPARG and SREBP1, which promote adipogenesis and lipid storage, are associated with T2D and possible adiposity; ADIPOQ and ARL15 are associated with circulating levels of adiponectin, ARL15 also with coronary heart disease. We anticipate that the use of complementary approaches such as expression profiling and RNAi screening, and studies of additional levels of gene regulation, that is, miRNA and epigenetics, will be important to unravel the genetics of adipose tissue function.

Orexin A stimulates glucose uptake, lipid accumulation and adiponectin secretion from 3T3-L1 adipocytes and isolated primary rat adipocytes

AIMS/HYPOTHESIS

Orexin A (OXA) modulates body weight, food intake and energy expenditure. In vitro, OXA increases PPARγ (also known as PPARG) expression and inhibits lipolysis, suggesting direct regulation of lipid metabolism. Here, we characterise the metabolic effects and mechanisms of OXA action in adipocytes.

METHODS

Isolated rat adipocytes and differentiated murine 3T3-L1 adipocytes were exposed to OXA in the presence or absence of phosphoinositide 3-kinase (PI3K) inhibitors. Pparγ expression was silenced using small interfering RNA. Glucose uptake, GLUT4 translocation, phosphatidylinositol (3,4,5)-trisphosphate production, lipogenesis, lipolysis, and adiponectin secretion were measured. Adiponectin plasma levels were determined in rats treated with OXA for 4 weeks.

RESULTS

OXA PI3K-dependently stimulated active glucose uptake by translocating the glucose transporter GLUT4 from cytoplasm into the plasma membrane. OXA increased cellular triacylglycerol content via PI3K. Cellular triacylglycerol accumulation resulted from increased lipogenesis as well as from a decrease of lipolysis. Adiponectin levels in chow- and high-fat diet-fed rats treated chronically with OXA were increased. OXA stimulated adiponectin expression and secretion in adipocytes. Both pharmacological blockade of peroxisome proliferator-activated receptor γ (PPARγ) activity or silencing Pparγ expression prevented OXA from stimulating triacylglycerol accumulation and adiponectin production.

CONCLUSIONS/INTERPRETATION

Our study demonstrates that OXA stimulates glucose uptake in adipocytes and that the evolved energy is stored as lipids. OXA increases lipogenesis, inhibits lipolysis and stimulates the secretion of adiponectin. These effects are conferred via PI3K and PPARγ2. Overall, OXA's effects on lipids and adiponectin secretion resemble that of insulin sensitisers, suggesting a potential relevance of this peptide in metabolic disorders.

Selective effects of PPARgamma agonists and antagonists on human pre-adipocyte differentiation

AIM

The insulin sensitizer rosiglitazone (RTZ) acts by activating peroxisome proliferator and activated receptor gamma (PPAR gamma), an effect accompanied in vivo in humans by an increase in fat storage. We hypothesized that this effect concerns PPARgamma(1) and PPARgamma(2) differently and is dependant on the origin of the adipose cells (subcutaneous or visceral). To this aim, the effect of RTZ, the PPARgamma antagonist GW9662 and lentiviral vectors expressing interfering RNA were evaluated on human pre-adipocyte models.

METHODS

Two models were investigated: the human pre-adipose cell line Chub-S7 and primary pre-adipocytes derived from subcutaneous and visceral biopsies of adipose tissue (AT) obtained from obese patients. Cells were used to perform oil-red O staining, gene expression measurements and lentiviral infections.

RESULTS

In both models, RTZ was found to stimulate the differentiation of pre-adipocytes into mature cells. This was accompanied by significant increases in both the PPARgamma(1) and PPARgamma(2) gene expression, with a relatively stronger stimulation of PPARgamma(2). In contrast, RTZ failed to stimulate differentiation processes when cells were incubated in the presence of GW9662. This effect was similar to the effect observed using interfering RNA against PPARgamma(2). It was accompanied by an abrogation of the RTZ-induced PPARgamma(2) gene expression, whereas the level of PPARgamma(1) was not affected.

CONCLUSIONS

Both the GW9662 treatment and interfering RNA against PPARgamma(2) are able to abrogate RTZ-induced differentiation without a significant change of PPARgamma(1) gene expression. These results are consistent with previous results obtained in animal models and suggest that in humans PPARgamma(2) may also be the key isoform involved in fat storage.

Gene expression of PPARgamma and PGC-1alpha in human omental and subcutaneous adipose tissues is related to insulin resistance markers and mediates beneficial effects of physical training

OBJECTIVE

Obesity and type 2 diabetes (T2D) are reaching epidemic proportions in Western societies, and they contribute to substantial morbidity and mortality. The peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgamma coactivator-1alpha (PGC-1alpha) system plays an important role in the regulation of efficient energy utilization and oxidative phosphorylation, both of which are decreased in obesity and insulin resistance.

DESIGN AND METHODS

We measured the metabolic parameters and the expression of PPARgamma and PGC-1alpha mRNA using quantitative real-time PCR in omental and subcutaneous (SC) adipose tissues in an observational study of 153 individuals as well as in SC fat and skeletal muscle in an interventional study of 60 subjects (20 each with normal glucose tolerance, impaired glucose tolerance, and T2D) before and after intensive physical training for 4 weeks.

RESULTS

PPARgamma and PGC-1alpha mRNA expression in both fat depots as well as in skeletal muscle is associated with markers of insulin resistance and cardiovascular risk. PGC-1alpha mRNA expression is significantly higher in SC fat than in omental fat, whereas PPARgamma mRNA expression is not significantly different between these fat depots. Skeletal muscle and SC fat PPARgamma and PGC-1alpha mRNA expression increased significantly in response to physical training.

CONCLUSIONS

Gene expression of PPARgamma and PGC-1alpha in human adipose tissue is related to markers of insulin resistance and cardiovascular risk. Increased muscle and adipose tissue PPARgamma and PGC-1alpha expression in response to physical training may mediate the beneficial effects of exercise on insulin sensitivity.

PPARgamma2 protects against obesity by means of a mechanism that mediates insulin resistance

BACKGROUND

Many studies have focused on the physiological parameters and genetic predisposition of subjects presenting both obesity and insulin resistance (IR) and it has been suggested that the peroxisome proliferator-activated receptor gamma 2 (PPARgamma2) Pro12Ala variant may contribute to the observed variability in insulin sensitivity. We investigated whether the PPARgamma2 mRNA expression levels are associated with IR in morbid obesity in adipose and muscle tissues.

MATERIALS AND METHODS

In this study, tissue biopsies were obtained from 26 morbidly obese (MO) patients and eight controls. The MO patients were divided into two groups: those with a low homeostasis model assessment of IR (HOMA-IR < 5) (MO-nonIR) and those with a high HOMA-IR (HOMA-IR > or = 8) (MO-IR). PPARgamma1, PPARgamma2 and aP2 mRNA expression levels were measured using quantitative RT-PCR.

RESULTS

The study found that PPARgamma2 mRNA expression in visceral adipose tissue (VAT) was significantly lower in the MO patients (P = 0.002) than the controls. Moreover, the PPARgamma2 mRNA expression was lower in VAT (P < 0.05) and muscle tissue (P < 0.01), and higher in subcutaneous adipose tissue (SAT) (P < 0.01) in the MO-IR than the MO-nonIR group. By contrast, PPARgamma1 mRNA expression levels were not dependent on IR. Finally, the MO patients showed a significant negative correlation between PPARgamma2 mRNA expression and IR (r = -0.396, P = 0.020) in VAT and a positive correlation in SAT (r = 0.826, P < 0.001). The variable that best explained the IR was PPARgamma2 mRNA expression in SAT (P = 0.002).

CONCLUSIONS

These data show that PPARgamma2 mRNA is expressed differently in the two types of MO patients and is associated with IR.

Lack of association between the Pro12Ala polymorphism of the PPAR-gamma 2 gene and type 2 diabetes mellitus in the Qatari consanguineous population

Peroxisome proliferators-activated receptor gamma (PPAR gamma) is a nuclear hormone receptor that serves as a master regulator for adipocytes-specific genes contributing to adipocytes differentiation, insulin sensitivity and lipid metabolism. The substitution of proline to alanine at codon 12 of the PPAR gamma 2 gene (Pro12Ala polymorphism) is most widely studied, and the associations with diabetes, obesity, and other clinical parameters have been reported and discussed in several ethnic groups. Among native Qatar ethnicity, however, there is no report about this polymorphism. The aim of this study was to estimate the allele frequency of the Pro12Ala polymorphism of PPAR gamma 2 gene among Qatari population and investigate the association between this polymorphism and obesity or type 2 diabetes. This is a matched case-control study. It was carried out among diabetic patients and healthy subjects at the Primary Healthcare Clinics, and the survey was conducted from February 2003 to March 2006 in Qatari male and female nationals aged 35 to 60 years. The study was based on matched age, sex, and ethnicity of 400 cases (with diabetes) and 450 controls (without diabetes). Face-to-face interviews were based on a questionnaire that included variables such as age, sex, sociodemographic status, body mass index (BMI), and obesity. Their health status was assessed by medical conditions, family history, and blood pressure measurements. The allele frequency of Pro12Ala polymorphism in PPAR gamma 2 gene among Qataris is lower than that in many Caucasian ethnic groups. No association is seen between the Pro12Ala and type 2 Diabetes (0.055 vs 0.059, OR = 1.1311, P = 0.669). Nearly half of the diabetic type 2 patients (48.5%) were obese (BMI > 30) compared to nondiabetic subjects (29.8%) (P < 0.001). In this study, no association is seen between the Pro12Ala polymorphism in PPAR gamma 2 gene and the type 2 diabetes in Qatar.

Hedgehog signaling alters adipocyte maturation of human mesenchymal stem cells

Human stem cells are powerful tools by which to investigate molecular mechanisms of cell growth and differentiation under normal and pathological conditions. Hedgehog signaling, the dysregulation of which causes several pathologies, such as congenital defects and cancer, is involved in several cell differentiation processes and interferes with adipocyte differentiation of rodent cells. The present study was aimed at investigating the effect of Hedgehog pathway modulation on adipocyte phenotype using different sources of human mesenchymal cells, such as bone marrow stromal cells and human multipotent adipose-derived stem cells. We bring evidence that Hedgehog signaling decreases during human adipocyte differentiation. Inhibition of this pathway is not sufficient to trigger adipogenesis, but activation of Hedgehog pathway alters adipocyte morphology as well as insulin sensitivity. Analysis of glycerol-3-phosphate dehydrogenase activity and expression of adipocyte marker genes indicate that activation of Hedgehog signaling by purmorphamine impairs adipogenesis. In sharp contrast to reports in rodent cells, the maturation process, but not the early steps of human mesenchymal stem cell differentiation, is affected by Hedgehog activation. Hedgehog interferes with adipocyte differentiation by targeting CCAAT enhancer-binding protein alpha and peroxisome proliferator-activated receptor (PPAR) gamma2 expression, whereas PPARgamma1 level remains unaffected. Although Hedgehog pathway stimulation does not modify the total number of adipocytes, adipogenesis appears dramatically impaired, with reduced lipid accumulation, a decrease in adipocyte-specific markers, and acquisition of an insulin-resistant phenotype. This study indicates that a decrease in Hedgehog signaling is necessary but not sufficient to trigger adipocyte differentiation and unveils a striking difference in the adipocyte differentiation process between rodent and human mesenchymal stem cells.

Hypertrophy and hyperplasia of abdominal adipose tissues in women

OBJECTIVE

To examine the expression of selected transcription factors involved in adipogenesis and genes related to lipid metabolism in abdominal subcutaneous and omental fat tissue.

RESEARCH DESIGN AND METHODS

We obtained subcutaneous and omental adipose tissue samples from 40 women undergoing abdominal hysterectomies (age: 47+/-5 years; BMI 27.9+/-5.3 kg/m(2)). We measured isolated adipocyte size and metabolism, and detailed measures of body fat accumulation and body fat distribution were obtained (dual-energy X-ray absorptiometry and computed tomography, respectively).

RESULTS

Adipocyte size of both subcutaneous and omental fat were increased with higher body fat mass values, with similar regression slopes in each compartment. In contrast, with higher body fat mass values, fat accumulation was progressively higher in the subcutaneous than in the visceral fat compartment, suggesting hyperplasia in the subcutaneous fat compartment. Messenger RNA levels of CEBPalpha, PPARgamma2, SREBP1c and genes related to lipid metabolism (LPL, FABP4, DGAT1, DGAT2, PLIN and HSL) were significantly higher in subcutaneous than in omental fat tissue (P< or =0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPalpha, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P< or =0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P< or =0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P< or =0,05). Omental adipose tissue expression levels of these genes were not significantly related to adiposity measures.

CONCLUSIONS

These results show that in obese women, hyperplasia is predominant in the subcutaneous fat depot, whereas fat cell hypertrophy is observed both in the omental and subcutaneous compartments.

Obesity and polymorphisms in genes regulating human adipose tissue

Obesity is the result of an imbalance between food intake and energy expenditure resulting in the storing of energy as fat. Adipose tissue contains the largest store of energy in the body and plays important roles in regulating energy partitioning. Developments in genomics, in particular microarray-based expression profiling, have provided scientists with a number of new candidate genes whose expression in adipose tissue is regulated by obesity. Integrating expression profiles with genome-wide linkage and/or association analyses is a promising strategy to identify new genes underlying susceptibility to obesity. This article provides a comprehensive review of adipose-tissue-expressed genes implicated in predisposition to human obesity. The authors consider the following genes of particular interest: peroxisome proliferator-activated receptor gamma and, potentially, INSIG2 acting in adipogenesis; the adrenoreceptors beta 2 and 3, as well as hormone-sensitive lipase acting on lipolysis; uncoupling protein 2 acting in mitochondria energy expenditure; and among secreted molecules the cytokine tumor necrosis factor alpha and the hormone leptin. With the rapid development in genome research, we predict that additional alleles in genes regulating adipose tissue function will be established as risk factors for common obesity in the coming years. This has important implications for the prevention of obesity and may also offer new therapeutic targets.

Sex differences in PPARgamma expressions in rat adipose tissues

Clinical studies had suggested that there were sex differences in pharmacological and side effects of pioglitazone. However, there are few studies on the sex differences of peroxisome proliferator-activated receptor (PPAR) gamma expressions in rat adipose tissues. We investigated the sex differences in peroxisome proliferator-activated receptor (PPAR) gamma expressions in rat adipose tissues. Subcutaneous abdominal adipose tissues and perigonadal adipose tissues were obtained from male and female Wistar rats (12 weeks of age). Expressions of PPARgamma protein were determined by Western blot analysis with anti-PPARgamma antibody. Vaginal smear check was performed in female rats. We obtained adipose tissues from females, according to the different phases of the estrous cycle. Both PPARgamma1 and gamma2 subtypes were expressed in subcutaneous adipose tissues. Expressions of PPARgamma2 in subcutaneous adipose tissues were significantly higher in males than in females. On the other hand, expressions of PPARgamma2 in perigonadal adipose tissues were significantly higher in females than in males. Expressions of PPARgamma2 in perigonadal adipose tissues in females significantly decreased during diestrus. It can be suggested that the sex hormones might affect the expressions of PPARgamma2 in adipose tissues.

Abnormal expression of PPAR gamma isoforms in the subcutaneous adipose tissue of patients with Cushing's disease

BACKGROUND

Obesity is a clinical feature of patients with Cushing's disease. Peroxisome proliferators-activated receptor (PPAR)gamma is the master regulator of adipogenesis; however, the expression of PPARgamma isoforms in the subcutaneous adipose tissue (SAT) of patients with Cushing's disease is unknown.

AIM AND METHODS

The expression of PPARgamma1 and PPARgamma2 was evaluated by real-time reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence (PPARgamma2 only) in SAT samples of 7 patients with untreated active Cushing's disease (Cushing(UNTR)), 8 with Cushing's disease in remission (Cushing(REM)) after pituitary adenomectomy, 15 normal lean subjects (Control(LEAN)), and 15 obese patients (Control(OBE)).

RESULTS

Control(LEAN) had a higher degree of PPARgamma1 than PPARgamma2 (PPARgamma2/PPARgamma1 ratio, 0.55 +/- 0.35). PPARgamma2/PPARgamma1 ratio decreased in Cushing(UNTR) (0.10 +/- 0.043, P < 0.03 vs. Control(LEAN) and Control(OBE)), because of either increased PPARgamma1 or reduced PPARgamma2 expression. PPARgamma2/PPARgamma1 ratio was 0.48 +/- 0.07 in Cushing(REM) patients (P < 0.04 vs. Cushing(UNTR), P < 0.03 vs. Control(OBE)). PPARgamma2/PPARgamma1 ratio was higher in Control(OBE) 0.90 +/- 0.38 than in Control(LEAN) (P < 0.005 vs. Control(LEAN), P < 0.03 vs. Cushing(REM), P < 0.009 vs. Cushing(UNTR)). PPARgamma2/PPARgamma1 ratio was related to serum cortisol levels only in patients with Cushing'disease (r = 0.688, P < 0.02).

CONCLUSIONS

Cushing(UNTR) patients had an abnormal expression of PPARgamma isoforms in SAT related to serum cortisol levels. Although further studies are necessary, it is conceivable that variations in the expression of PPARgamma isoforms might have a role in the abnormal adipogenesis of patients with Cushing's disease.

Thiazolidinediones and their Fluid-Related Adverse Effects

Thiazolidinediones (TZDs) or glitazones are agents that are widely used for the treatment of type 2 diabetes mellitus. These drugs have a multitude of therapeutic effects including reduction in insulin resistance and hyperglycaemia, anti-inflammatory effects and amelioration of hypertension, microalbuminuria and hepatic steatosis. The TZD molecular target, peroxisome proliferator-activated receptor gamma (PPARgamma), a nuclear transcription factor, is expressed diffusely in humans, including many tissues comprising the cardiovascular and renal systems. This suggests a potential for TZDs to elicit perturbing effects on these systems, which are independent of their effects on glucose and lipid metabolism. One of the most common adverse effects of TZDs is fluid retention, which can result in, or exacerbate, oedema and congestive heart failure (CHF). The frequency of peripheral oedema is approximately 5% when TZDs are used in mono- or combination oral therapy, and about 15% when used with insulin. Patients with type 2 diabetes are at high risk of myriad morbid complications, including CHF. The development of CHF, particularly in the elderly, is a harbinger of premature mortality. TZD-induced oedema is largely peripheral, may have its origins in changes in haemodynamics, with some contribution from molecules, which regulate cell and tissue permeability (e.g. vascular endothelial growth factor and protein kinase Cbeta), and remains the preponderant manifestation of TZD-induced fluid retention even in those with existing heart failure. Preclinical and pilot clinical data attest to the fact that at least part of the fluid retention derives from a direct effect of TZDs on sodium reabsorption via the renal medullary collecting duct, a mechanism that is sensitive to diuretic agents that have this nephron segment as their site of action, in whole or in part (spironolactone, amiloride and hydrochlorothiazide). Our review suggests various potential clinical strategies by which TZD-induced fluid retention might be effectively monitored and addressed.

Activated human T lymphocytes express cyclooxygenase-2 and produce proadipogenic prostaglandins that drive human orbital fibroblast differentiation to adipocytes

The differentiation of preadipocyte fibroblasts to adipocytes is a crucial process to many disease states including obesity, cardiovascular, and autoimmune diseases. In Graves' disease, the orbit of the eye can become severely inflamed and infiltrated with T lymphocytes as part of the autoimmune process. The orbital fibroblasts convert to fat-like cells causing the eye to protrude, which is disfiguring and can lead to blindness. Recently, the transcription factor peroxisome proliferator activated receptor (PPAR)-gamma and its natural (15d-PGJ2) and synthetic (thiazolidinedione-type) PPAR-gamma agonists have been shown to be crucial to the in vitro differentiation of preadipocyte fibroblasts to adipocytes. We show herein several novel findings. First, that activated T lymphocytes from Graves' patients drive the differentiation of PPAR-gamma-expressing orbital fibroblasts to adipocytes. Second, this adipogenic differentiation is blocked by nonselective small molecule cyclooxygenase (Cox)-1/Cox-2 inhibitors and by Cox-2 selective inhibitors. Third, activated, but not naïve, human T cells highly express Cox-2 and synthesize prostaglandin D2 and related prostaglandins that are PPAR-gamma ligands. These provocative new findings provide evidence for how activated T lymphocytes, through production of PPAR-gamma ligands, profoundly influence human fibroblast differentiation to adipocytes. They also suggest the possibility that, in addition to the orbit, T lymphocytes influence the deposition of fat in other tissues.

Acquired obesity increases CD68 and tumor necrosis factor-alpha and decreases adiponectin gene expression in adipose tissue: a study in monozygotic twins

CONTEXT

Both acquired and genetic factors regulate adipose tissue function.

OBJECTIVE

We determined whether adipose tissue mRNA expression is regulated by obesity, independently of genetic effects, by studying monozygotic (MZ) twins.

DESIGN

Seventeen healthy pairs of MZ twins aged 24-27 yr (body mass index 20.0-33.9 kg/m(2), intrapair differences in body weight 0.1-24.7 kg), were identified from the population-based FinnTwin16 cohort. Body fat percent was determined by dual-energy x-ray absorptiometry, sc and intraabdominal fat by magnetic resonance imaging, liver fat by proton spectroscopy, and insulin sensitivity by using the euglycemic insulin clamp technique. Adipocyte cell size and expression of 10 genes (real-time PCR) were determined in sc adipose tissue biopsies. Serum levels of some of the genes were measured using ELISA.

RESULTS

Within MZ twin pairs, acquired obesity was significantly related to increased adipocyte size and increased adipose tissue mRNA expressions of leptin, TNFalpha and the macrophage marker CD68, and decreased mRNA expressions of adiponectin and peroxisome proliferator-activated receptor-gamma. Intrapair differences in liver fat correlated directly with those in leptin and CD68 expression. CD68 expression and serum TNFalpha concentrations were correlated with insulin resistance.

CONCLUSIONS

Acquired obesity independent of genetic influences is able to increase expression of macrophage and inflammatory markers and decrease adiponectin expression in adipose tissue.

Gonadotropin-releasing hormone-expressing neurons immortalized conditionally are activated by insulin: implication of the mitogen-activated protein kinase pathway

Energy balance exerts a critical influence on reproduction via changes in the circulating levels of hormones such as insulin. This modulation of the neuroendocrine reproductive axis ultimately involves variations in the activity of hypothalamic neurons expressing GnRH. Here we studied the effects of insulin in primary hypothalamic cell cultures as well as a GnRH neuronal cell line that we generated by conditional immortalization of adult hypothalamic neurons. These cells, which represent the first successful conditional immortalization of GnRH neurons, retain many of their mature phenotypic characteristics. In addition, we show that they express the insulin receptor. Consistently, their stimulation with insulin activates both the phosphatidylinositol 3-kinase and the Erk1/2 MAPK signaling pathways and stimulates a rapid increase in the expression of c-fos, demonstrating their responsiveness to this hormone. Further work performed in parallel in immortalized GnRH-expressing cells and primary neuronal cultures containing non-GnRH-expressing neurons shows that insulin induces the expression of GnRH in both models. In primary cultures, inhibition of the Erk1/2 pathway abolishes the stimulation of GnRH expression by insulin, whereas blockade of the phosphatidylinositol 3-kinase pathway has no effect. In conclusion, these data strongly suggest that GnRH neurons are directly sensitive to insulin and implicate for the first time the MAPK Erk1/2 signaling pathway in the central effects of insulin on the neuroendocrine reproductive axis.

Acute in vivo effects of insulin on gene expression in adipose tissue in insulin-resistant and insulin-sensitive subjects

AIMS/HYPOTHESIS

We determined the response of selected genes to in vivo insulin in adipose tissue in 21 non-diabetic women.

MATERIALS AND METHODS

The women were divided into insulin-sensitive and -resistant groups based on their median whole-body insulin sensitivity (8.7+/-0.4 vs 4.2+/-0.3 mg kg(-1) min(-1) for insulin-sensitive vs -resistant group). Subcutaneous adipose tissue biopsies were obtained before and after 3 and 6 h of i.v. maintained euglycaemic hyperinsulinaemia. Adipose tissue mRNA concentrations of facilitated glucose transporter, member 1 (SLC2A1, previously known as GLUT1), facilitated glucose transporter, member 4 (SLC2A4, previously known as GLUT4), peroxisome proliferator-activated receptor gamma ( PPARG), peroxisome proliferator-activated receptor gamma co-activator 1alpha (PPARGC1A), 11beta-hydroxysteroid dehydrogenase-1 (HSD11B1), TNF, adiponectin (ADIPOQ), IL6 and the macrophage marker CD68 were measured using real-time PCR.

RESULTS

Basal expression of 'insulin-sensitivity genes' SLC2A4 and ADIPOQ was lower while that of 'insulin-resistance genes', HSD11B1 and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. Insulin significantly increased expression of 'insulin-sensitivity genes' SLC2A4, PPARG, PPARGC1A and ADIPOQ in the insulin-sensitive group, while only expression of PPARG and PPARGC1A was increased in the insulin-resistant group. The expression of 'insulin-resistance genes' HSD11B1 and IL6 was increased by insulin in the insulin-resistant group, but insulin failed to increase HSD11B1 expression in the insulin-sensitive group. At 6 h, expression of HSD11B1, TNF and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. IL6 expression increased significantly more in response to insulin in the insulin-resistant than in the insulin-sensitive group. CD68 was overexpressed in the insulin-resistant as compared with the insulin-sensitive group at both 0 and 6 h.

CONCLUSIONS/INTERPRETATION

These data suggest that genes adversely affecting insulin sensitivity hyperrespond to insulin, while genes enhancing insulin sensitivity hyporespond to insulin in insulin-resistant human adipose tissue in vivo.

A possible association of Pro12Ala polymorphism in peroxisome proliferator-activated receptor gamma2 gene with obesity in native Javanese in Indonesia

BACKGROUND

Peroxisome proliferators-activated receptor gamma (PPAR gamma) is a nuclear hormone receptor that serves as a master regulator of adipocytes-specific genes contributing to adipocytes differentiation, susceptibility to obesity, and insulin sensitivity. The substitution of proline to alanine at codon 12 of the PPAR gamma2 gene (Pro12Ala polymorphism) is most frequently identified and the associations with diabetes, obesity, and other clinical parameters have been reported and discussed in several ethnic groups. Among native Javanese ethnicity, however, there is no report about this polymorphism.

AIMS AND METHODS

Aims of this study were to estimate the allele frequency of the Pro12Ala polymorphism of PPAR gamma2 gene among native Javanese in Indonesia and to investigate the relationship between this polymorphism and obesity or diabetes. This study included 540 native Javanese subjects consisting of 337 diabetic patients and 203 normal glucose tolerance subjects. Both groups included totally 160 obese subjects (body mass index > or = 25 kg/m(2)). PCR-restriction fragment length polymorphism was used for the genotype determination.

RESULTS

The allele frequency of Pro12Ala polymorphism in PPAR gamma2 gene among native Javanese is lower than that in other ethnic groups. No association is seen between the Pro12Ala and diabetes (0.01 vs 0.017%, p = 0.404), a trend of the higher BMI was observed in Pro12Ala carriers in nondiabetic subjects, although this association is limited by small numbers.

CONCLUSION

In this study, no association is seen between the Pro12Ala polymorphism in PPAR gamma2 gene and diabetes; a weak association with obesity is seen.

Noradrenaline represses PPAR (peroxisome-proliferator-activated receptor) gamma2 gene expression in brown adipocytes: intracellular signalling and effects on PPARgamma2 and PPARgamma1 protein levels

PPAR (peroxisome-proliferator-activated receptor) gamma is expressed in brown and white adipose tissues and is involved in the control of differentiation and proliferation. Noradrenaline stimulates brown pre-adipocyte proliferation and brown adipocyte differentiation. The aim of the present study was thus to investigate the influence of noradrenaline on PPARgamma gene expression in brown adipocytes. In primary cultures of brown adipocytes, PPARgamma2 mRNA levels were 20-fold higher than PPARgamma1 mRNA levels. PPARgamma expression occurred during both the proliferation and the differentiation phases, with the highest mRNA levels being found at the time of transition between the phases. PPARgamma2 mRNA levels were downregulated by noradrenaline treatment (EC50, 0.1 microM) in both proliferative and differentiating cells, with a lagtime of 1 h and lasting up to 4 h, after which expression gradually recovered. The down-regulation was beta-adrenoceptor-induced and intracellularly mediated via cAMP and protein kinase A; the signalling pathway did not involve phosphoinositide 3-kinase, Src, p38 mitogen-activated protein kinase or extracellular-signal-regulated kinases 1 and 2. Treatment of the cells with the protein synthesis inhibitor cycloheximide not only abolished the noradrenaline-induced down-regulation of PPARgamma2 mRNA, but also in itself induced PPARgamma2 hyperexpression. The down-regulation was probably the result of suppression of transcription. The down-regulation of PPARgamma2 mRNA resulted in similar down-regulation of PPARgamma2 and phosphoPPARgamma2 protein levels. Remarkably, the level of PPARgamma1 protein was similar to that of PPARgamma2 (despite almost no PPARgamma1 mRNA), and the down-regulation by noradrenaline demonstrated similar kinetics to that of PPARgamma2; thus PPARgamma1 was apparently translated from the PPARgamma2 template. It is suggested that beta-adrenergic stimulation via cAMP and protein kinase A represses PPARgamma gene expression, leading to reduction of PPARgamma2 mRNA levels, which is then reflected in down-regulated levels of PPARgamma2, phosphoPPARgamma2 and PPARgamma1.

Gonadotropin-releasing hormone secretion from hypothalamic neurons: stimulation by insulin and potentiation by leptin

Insulin and leptin are peripheral metabolic factors signaling the body needs in energy to the central nervous system. Because energy homeostasis and reproductive function are closely related phenomena, we investigated the respective roles played by insulin and leptin in the hypothalamic control of GnRH secretion. We observed that increasing circulating insulin levels, by performing hyperinsulinemic clamp studies in male mice, was associated with a significant rise in LH secretion. This effect of insulin is likely mediated at the hypothalamic level, because it was also found to stimulate the secretion and the expression of GnRH by hypothalamic neurons in culture. Leptin was found to potentiate the effect of insulin on GnRH secretion in vitro but was devoid of any effect on its own. These data represent the first evidence of direct insulin sensing by hypothalamic neurons involved in activating the neuroendocrine gonadotrope axis. They also demonstrate that these neurons can integrate different hormonal signals to modulate net hypothalamic GnRH output. We propose that such integration is an essential mechanism for the adaptation of reproductive function to changes in the metabolic status of an individual.