PGC-1α Promotes Breast Cancer Metastasis and Confers Bioenergetic Flexibility against Metabolic Drugs.

Metabolic adaptations play a key role in fueling tumor growth. However, less is known regarding the metabolic changes that promote cancer progression to metastatic disease. Herein, we reveal that breast cancer cells that preferentially metastasize to the lung or bone display relatively high expression of PGC-1α compared with those that metastasize to the liver. PGC-1α promotes breast cancer cell migration and invasion in vitro and augments lung metastasis in vivo. Pro-metastatic capabilities of PGC-1α are linked to enhanced global bioenergetic capacity, facilitating the ability to cope with bioenergetic disruptors like biguanides. Indeed, biguanides fail to mitigate the PGC-1α-dependent lung metastatic phenotype and PGC-1α confers resistance to stepwise increases in metformin concentration. Overall, our results reveal that PGC-1α stimulates bioenergetic potential, which promotes breast cancer metastasis and facilitates adaptation to metabolic drugs.

Soluble CD163 is associated with CD163 mRNA expression in adipose tissue and with insulin sensitivity in steady-state condition but not in response to calorie restriction.

CONTEXT: Soluble CD163 (sCD163) was suggested as a biomarker of insulin sensitivity and CD163 mRNA expression representing macrophage content in adipose tissue (AT). OBJECTIVE: The aim of this study was to investigate, in cross-sectional and prospective design, the relationship between sCD163 circulating levels and CD163 mRNA expression in adipose tissue and insulin sensitivity assessed by euglycemic-hyperinsulinemic clamp. DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS: Two cohorts of subjects were examined in the study. Cohort 1 included 42 women with a wide range of body mass index (17-48 kg/m(2)); cohort 2 included 27 obese women who followed a dietary intervention consisting of 1 month of a very low-calorie diet and 5 months of a weight-stabilization period. MAIN OUTCOME MEASURES: Serum levels of CD163 and mRNA expression of CD163 and CD68 in sc and visceral (visc) AT were determined, and insulin sensitivity [expressed as glucose disposal rate (GDR)] was measured in cohort 1. In cohort 2, serum levels of CD163, mRNA expressions of CD163, CD68, and CD163-shedding factors [TNF-α-converting enzyme (TACE) and tissue inhibitor of metalloproteinase (TIMP3)] in sc AT were examined and GDR was measured before and during dietary intervention. RESULTS: In cohort 1, circulating sCD163 correlated with CD163 mRNA levels in both sc and visc AT. sCD163 and CD163 mRNA expression in both fat depots correlated with GDR. In cohort 2, the diet-induced changes of sCD163 levels did not correlate with those of CD163, CD68, TACE, and TIMP3 mRNA levels. Although the pattern of the diet-induced change of sCD163 paralleled that of GDR, there was no correlation between the changes of these two variables. CONCLUSION: sCD163 correlates with CD163 mRNA expression in sc and visc AT and with whole-body insulin sensitivity in the steady-state condition. These associations are not observed with respect to the diet-induced changes during a weight-reducing hypocaloric diet.

WISP2 regulates preadipocyte commitment and PPARγ activation by BMP4.

Inability to recruit new adipose cells following weight gain leads to inappropriate enlargement of existing cells (hypertrophic obesity) associated with inflammation and a dysfunctional adipose tissue. We found increased expression of WNT1 inducible signaling pathway protein 2 (WISP2) and other markers of WNT activation in human abdominal s.c. adipose tissue characterized by hypertrophic obesity combined with increased visceral fat accumulation and insulin resistance. WISP2 activation in the s.c. adipose tissue, but not in visceral fat, identified the metabolic syndrome in equally obese individuals. WISP2 is a novel adipokine, highly expressed and secreted by adipose precursor cells. Knocking down WISP2 induced spontaneous differentiation of 3T3-L1 and human preadipocytes and allowed NIH 3T3 fibroblasts to become committed to the adipose lineage by bone morphogenetic protein 4 (BMP4). WISP2 forms a cytosolic complex with the peroxisome proliferator-activated receptor γ (PPARγ) transcriptional activator zinc finger protein 423 (Zfp423), and this complex is dissociated by BMP4 in a SMAD-dependent manner, thereby allowing Zfp423 to enter the nucleus, activate PPARγ, and commit the cells to the adipose lineage. The importance of intracellular Wisp2 protein for BMP4-induced adipogenic commitment and PPARγ activation was verified by expressing a mutant Wisp2 protein lacking the endoplasmic reticulum signal and secretion sequence. Secreted Wnt/Wisp2 also inhibits differentiation and PPARγ activation, albeit not through Zfp423 nuclear translocation. Thus adipogenic commitment and differentiation is regulated by the cross-talk between BMP4 and canonical WNT signaling and where WISP2 plays a key role. Furthermore, they link WISP2 with hypertrophic obesity and the metabolic syndrome.

Adipose tissue secretion and expression of adipocyte-produced and stromavascular fraction-produced adipokines vary during multiple phases of weight-reducing dietary intervention in obese women.

CONTEXT: Obesity is associated with altered plasma levels of adipokines involved in the development of insulin resistance and obesity-related metabolic disturbances. OBJECTIVE: The aim was to investigate diet-induced changes in adipokine production in sc abdominal adipose tissue (SAT) during a 6-month, multiphase, weight-reducing dietary intervention. DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS: Forty-eight obese women followed a dietary intervention consisting of a very low-calorie diet (VLCD) (1 month), followed by a weight-stabilization (WS) period, which consisted of a low-calorie diet (2 months), and a weight-maintenance diet (3 months). MAIN OUTCOME MEASURES: Before and at the end of the VLCD and WS, samples of plasma and SAT were obtained. In a subgroup of 26 women, secretion of adipokines was determined in SAT explants, and in a subgroup of 22 women, SAT mRNA expression was measured. RESULTS: Body weight decreased and insulin sensitivity increased during the intervention. Plasma levels, SAT mRNA expression, and secretion rates of adipocyte-produced adipokines (leptin, serum amyloid A, and haptoglobin) decreased during the VLCD and increased during the WS period. Adipokines produced mainly from stroma-vascular cells (IL-6, IL-8, IL-10, IL-1Ra, TNFα, plasminogen activator inhibitor-1, and monocyte chemoattractant protein-1) increased or remained unchanged during VLCD and decreased to levels equal to or lower than prediet levels during the WS period. The diet-induced changes in homeostasis model assessment of insulin resistance correlated with changes in leptin plasma levels during VLCD, WS, and the entire dietary intervention period. CONCLUSIONS: Diet-induced regulation of adipokine production in SAT differs according to their cellular origin (adipocytes vs. stroma-vascular cells) and diet phase (VLCD vs. WS). Insulin-sensitivity changes were associated only with those of plasma leptin.

PGC-1α promotes the growth of ErbB2/Neu-induced mammary tumors by regulating nutrient supply.

Cancer cells display an increased reliance on glycolysis despite the presence of sufficient oxygen levels to support mitochondrial functions. In this study, we asked whether ameliorating mitochondrial functions in cancer cells might limit their proliferative capacity. Specifically, we increased mitochondrial metabolism in a murine cellular model of ErbB2/Neu-induced breast cancer by ectopically expressing the transcriptional coactivator peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), a master regulator of mitochondrial metabolism. As predicted, ErbB2/Neu cells ectopically expressing PGC-1α displayed an increased level of mitochondrial metabolism and reduced proliferative capacity in vitro, compared with controls. In contrast, ErbB2/Neu cells ectopically expressing PGC-1α formed larger tumors in vivo. These tumors exhibited increased concentrations of glucose and the angiogenic factor VEGF as well as higher expression of ErbB2/Neu compared with controls. We discovered that ErbB2/Neu levels were sensitive to nutrient availability, such that reduced glucose concentrations resulted in diminished ErbB2/Neu protein levels. Therefore, our data indicate that PGC-1α prevents the nutrient-mediated downregulation of ErbB2/Neu in tumors by increasing glucose supply. Mechanistic investigations revealed that the regulation of ErbB2/Neu levels by glucose was mediated by the unfolded protein response (UPR). Incubation of ErbB2/Neu-induced breast cancer cells in limited glucose concentrations or with drugs that activate the UPR led to significant reductions in ErbB2/Neu protein levels. Also, ErbB2/Neu-induced tumors ectopically expressing PGC-1α displayed lowered UPR activation compared with controls. Together, our findings uncover an unexpected link between PGC-1α-mediated nutrient availability, UPR, and ErbB2/Neu levels.

Catecholamine and insulin control of lipolysis in subcutaneous adipose tissue during long-term diet-induced weight loss in obese women.

The aim of this study was to investigate the evolution of the adrenergic and insulin-mediated regulation of lipolysis during different phases of a 6-mo dietary intervention. Eight obese women underwent a 6-mo dietary intervention consisting of a 1-mo very low-calorie diet (VLCD) followed by a 2-mo low-calorie diet (LCD) and 3-mo weight maintenance (WM) diet. At each phase of the dietary intervention, microdialysis of subcutaneous adipose tissue (SCAT) was performed at rest and during a 3-h hyperinsulinemic euglycemic clamp. Responses of dialysate glycerol concentration (DGC) were determined at baseline and during local perfusions with adrenaline or adrenaline and phentolamine before and during the last 30 min of the clamp. Dietary intervention induced a body weight reduction and an improved insulin sensitivity. DGC progressively decreased during the clamp, and this decrease was similar during the different phases of the diet. The adrenaline-induced increase in DGC was higher at VLCD and LCD compared with baseline condition and returned to prediet levels at WM. In the probe with adrenaline and phentolamine, the increase in DGC was higher than that in the adrenaline probe at baseline and WM, but it was not different at VLCD and LCD. The results suggest that the responsiveness of SCAT to adrenaline-stimulated lipolysis increases during the calorie-restricted phases due to a reduction of the α(2)-adrenoceptor-mediated antilipolytic action of adrenaline. At WM, adrenaline-stimulated lipolysis returned to the prediet levels. Furthermore, no direct relationship between insulin sensitivity and the diet-induced changes in the regulation of lipolysis was found.

Impact of PGC-1α on the topology and rate of superoxide production by the mitochondrial electron transport chain.

Reactive oxygen species (ROS) play an important role in normal signaling events and excessive ROS are associated with many pathological conditions. The amount of ROS in cells is dependent on both the production of ROS by the mitochondrial electron transport chain and their removal by ROS-detoxifying enzymes. The peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is a master regulator of mitochondrial functions and a key regulator of the ROS-detoxifying program. However, the impact of PGC-1α on the topology and rate of superoxide production by the mitochondrial electron transport chain is not known. We report here, using mitochondria from muscle creatine kinase-PGC-1α transgenic mice, that PGC-1α does not affect the topology of ROS production, but increases the capacity of complexes I and III to generate ROS. These changes are associated with increased mitochondrial respiration and content of respiratory chain complexes. When normalizing ROS production to mitochondrial respiration, we find that PGC-1α preserves the percentage of free radical leak by the electron transport chain. Together, these data demonstrate that PGC-1α regulates the intrinsic properties of mitochondria in such a way as to preserve a tight coupling between mitochondrial respiration and ROS production.

Worsening of obesity and metabolic status yields similar molecular adaptations in human subcutaneous and visceral adipose tissue: decreased metabolism and increased immune response.

CONTEXT: It is not known whether biological differences reported between sc adipose tissue (SAT) and visceral adipose tissue (VAT) depots underlie the pathogenicity of visceral fat. OBJECTIVE: We compared SAT and VAT gene expression according to obesity, visceral fat accumulation, insulin resistance, and presence of the metabolic syndrome. DESIGN: Subjects were assigned into four groups (lean, overweight, obese, and obese with metabolic syndrome). SETTING: Subjects were recruited at a university hospital. PATIENTS: Thirty-two women were included. MAIN OUTCOME MEASURES: Anthropometric measurements, euglycemic-hyperinsulinemic clamps, blood analyses, and computed tomography scans were performed, and paired samples of SAT and VAT were obtained for DNA microarray-based gene expression profiling. RESULTS: Considering the two fat depots together, 1125 genes were more and 1025 genes were less expressed in lean compared with metabolic syndrome subjects. Functional annotation clustering showed, from lean to metabolic syndrome subjects, progressive down-regulation of metabolic pathways including branched-chain amino acid, fatty acid, carbohydrate, and mitochondrial energy metabolism and up-regulation of immune response genes involved in toll-like receptor, TNF, nuclear factor-κB, and apoptosis pathways. Metabolism and immune response genes showed an opposite correlation with fat mass, fat distribution, or insulin resistance indices. These associations were similar in SAT and VAT, although about 1000 genes showed differential expression between SAT and VAT. CONCLUSIONS: The increase in adiposity and the worsening of metabolic status are associated with a coordinated down-regulation of metabolism-related and up-regulation of immune response-related gene expression. Molecular adaptations in SAT prove as discriminating as those in VAT.

TCF7L2 rs7903146-macronutrient interaction in obese individuals' responses to a 10-wk randomized hypoenergetic diet.

BACKGROUND: Transcription factor 7-like 2 (TCF7L2) rs7903146 associates with type 2 diabetes and may operate via impaired glucagon-like peptide 1 secretion, which is stimulated more by fat than by carbohydrate ingestion. OBJECTIVE: The objective was to examine the interaction between TCF7L2 rs7903146 and dietary fat and carbohydrate [high-fat, low-carbohydrate: 40-45% of energy as fat (HF); compared with low-fat, high-carbohydrate: 20-25% of energy as fat (LF)] in obese individuals' responses to a 10-wk hypoenergetic diet (-600 kcal/d). DESIGN: European, obese participants (n = 771) were randomly assigned to receive an HF or an LF diet. Body weight, fat mass (FM), fat-free mass (FFM), waist circumference (WC), resting energy expenditure (REE), fasting fat oxidation in percentage of REE (FatOx), homeostasis model assessed insulin release (HOMA-beta), and HOMA-insulin resistance (HOMA-IR) were determined at baseline and after the intervention; 739 individuals were genotyped for rs7903146. RESULTS: Average weight loss was 6.9 kg with the LF and 6.6 kg with the HF (difference between diets, NS) diet. Among individuals who were homozygous for the T-risk allele, those in the HF diet group experienced smaller weight losses (Deltaweight) (2.6 kg; P = 0.009; n = 622), smaller DeltaFFM (1.6 kg; P = 0.027; n = 609), smaller DeltaWC (3.3 cm; P = 0.010; n = 608), and a smaller DeltaHOMA-IR (1.3 units; P = 0.004; n = 615) than did the LF diet group. For C allele carriers, there were no differences between the HF and LF diet groups. For the HF diet group, each additional T allele was associated with a reduced loss of FM (0.67 kg; P = 0.019; n = 609). TCF7L2 rs7903146 was not associated with DeltaREE, DeltaFatOx, DeltaHOMA-beta, or dropout. CONCLUSION: Our results suggest that obese individuals who are homozygous for the TCF7L2 rs7903146 T-risk allele are more sensitive to LF than to HF weight-loss diets.

Effect of hyperinsulinemia and very-low-calorie diet on interstitial cytokine levels in subcutaneous adipose tissue of obese women.

Type 2 diabetes and obesity are associated with an enhanced release of a number of adipocytokines. Hyperinsulinemia, frequently present in type 2 diabetes and obesity, might be one of the drivers of the enhanced production of adipocytokines. The aim of this study was to investigate the interstitial levels of cytokines in subcutaneous adipose tissue (SCAT) in response to hyperinsulinemia and the effect of weight-reducing hypocaloric diet on this regulation in obese subjects. Thirteen obese premenopausal women participated in the study. Concentrations of seven cytokines were measured in plasma and in AT interstitial fluid collected by microdialysis during a euglycemic-hyperinsulinemic clamp and during control infusion of physiological saline. A subgroup of six women underwent a 4-wk very-low-calorie diet (VLCD). Microdialysis during the clamp was performed before and at the end of VLCD. Hyperinsulinemia induced an increase of monocyte chemoatractant protein (MCP-1) and IL-6 SCAT interstitial and plasma levels and elevated IL-8 levels in SCAT. The relative changes of IL-6 levels in the dialysate correlated with changes of IL-8 and MCP-1. The interstitial and plasma levels of IL-1ß, IL-10, TNFα, and plasminogen activator inhibitor (PAI-1) remained unchanged in response to hyperinsulinemia. VLCD resulted in enhancement of the hyperinsulinemia-induced augmentation of MCP-1, IL-6, and IL-8 interstitial levels. In conclusion, hyperinsulinemia upregulates the interstitial levels of MCP-1, IL-6, and IL-8 in SCAT in obese women, whereas it does not affect IL-1ß, IL-10, TNFα, and PAI-1 levels. Hypocaloric diet associated with weight reduction enhances the hyperinsulinemia-induced upregulation of MCP-1, IL-6, and IL-8 in SCAT.

Macrophages and adipocytes in human obesity: adipose tissue gene expression and insulin sensitivity during calorie restriction and weight stabilization.

OBJECTIVE: We investigated the regulation of adipose tissue gene expression during different phases of a dietary weight loss program and its relation with insulin sensitivity. RESEARCH DESIGN AND METHODS: Twenty-two obese women followed a dietary intervention program composed of an energy restriction phase with a 4-week very-low-calorie diet and a weight stabilization period composed of a 2-month low-calorie diet followed by 3-4 months of a weight maintenance diet. At each time point, a euglycemic-hyperinsulinemic clamp and subcutaneous adipose tissue biopsies were performed. Adipose tissue gene expression profiling was performed using a DNA microarray in a subgroup of eight women. RT-quantitative PCR was used for determination of mRNA levels of 31 adipose tissue macrophage markers (n = 22). RESULTS: Body weight, fat mass, and C-reactive protein level decreased and glucose disposal rate increased during the dietary intervention program. Transcriptome profiling revealed two main patterns of variations. The first involved 464 mostly adipocyte genes involved in metabolism that were downregulated during energy restriction, upregulated during weight stabilization, and unchanged during the dietary intervention. The second comprised 511 mainly macrophage genes involved in inflammatory pathways that were not changed or upregulated during energy restriction and downregulated during weight stabilization and dietary intervention. Accordingly, macrophage markers were upregulated during energy restriction and downregulated during weight stabilization and dietary intervention. The increase in glucose disposal rates in each dietary phase was associated with variation in expression of sets of 80-110 genes that differed among energy restriction, weight stabilization, and dietary intervention. CONCLUSIONS: Adipose tissue macrophages and adipocytes show distinct patterns of gene regulation and association with insulin sensitivity during the various phases of a dietary weight loss program.

Secretion of adiponectin multimeric complexes from adipose tissue explants is not modified by very low calorie diet.

OBJECTIVE: Adiponectin is a protein abundantly secreted by the adipose tissue (AT). Plasma adiponectin levels are decreased in obese, insulin-resistant, and type 2 diabetic patients. Various multimeric complexes, i.e. high-, middle-, and low-molecular weight isoforms (HMW, MMW and LMW), are present in plasma. Here, we investigated the effect of weight reducing diet on the distribution of adiponectin isoforms in plasma and on their secretion in AT explants from obese subjects. DESIGN: A total of 20 obese subjects (age 37.8+/-7.3 years, body mass index 33.9+/-5.0 kg/m(2)) underwent eight weeks of very low-calorie diet (VLCD). A needle biopsy of subcutaneous abdominal AT and blood samples were taken before and after dietary intervention. AT explants were incubated in culture medium for 4 h. ELISA assay and western blot analyses were used to identify adiponectin complexes in culture media and in plasma. RESULTS: The distribution of adiponectin polymers in plasma was different from that secreted in human AT explants. Before VLCD, the relative amount of HMW isoform was 75.5+/-9.1% of total adiponectin in culture media and 52.2+/-11.2% in plasma. Despite the diet-induced weight loss and improvement of insulin sensitivity, VLCD neither induced change in total adiponectin level nor in the ratio of HMW to total adiponectin in plasma and in culture media of AT explants. CONCLUSIONS: The profile of adiponectin polymeric isoforms secreted by AT explants into culture media differs from the plasma profile. A dietary intervention leading to weight loss and improvement of insulin sensitivity was not associated with modifications of AT secretion of total or HMW adiponectin.

Contribution of energy restriction and macronutrient composition to changes in adipose tissue gene expression during dietary weight-loss programs in obese women.

CONTEXT: Hypoenergetic diets are used to reduce body fat mass and metabolic risk factors in obese subjects. The molecular changes in adipose tissue associated with weight loss and specifically related to the dietary composition are poorly understood. OBJECTIVE: We investigated adipose tissue gene expression from human obese women according to energy deficit and the fat and carbohydrate content of the diet. DESIGN AND SETTING: Obese subjects recruited among eight European clinical centers were followed up 10 wk of either a low-fat (high carbohydrate) or a moderate-fat (low carbohydrate) hypoenergetic diet. SUBJECTS: Two sets of 47 women in each dietary arm were selected among 648 subjects matched for anthropometric and biological parameters. MAIN OUTCOME MEASURE: We measured adipose tissue gene expression changes in one set using a candidate gene approach. The other set was used to survey 24,469 transcripts using DNA microarrays. Results were analyzed using dedicated statistical methods. Diet-sensitive regulations were confirmed on the other set of subjects. RESULTS: The two diets induced similar weight loss and similar changes for most of the biological variables except for components of the blood lipid profile. One thousand genes were regulated by energy restriction. We validated an effect of the fat to carbohydrate ratio for five genes (FABP4, NR3C1, SIRT3, FNTA, and GABARAPL2) with increased expression during the moderate-fat diet. CONCLUSIONS: Energy restriction had a more pronounced impact on variations in human adipose tissue gene expression than macronutrient composition. The macronutrient-sensitive regulation of a subset of genes may influence adipose tissue function and metabolic response.

Exercise-induced lipid mobilization in subcutaneous adipose tissue is mainly related to natriuretic peptides in overweight men.

Involvement of sympathetic nervous system and natriuretic peptides in the control of exercise-induced lipid mobilization was compared in overweight and lean men. Lipid mobilization was determined using local microdialysis during exercise. Subjects performed 35-min exercise bouts at 60% of their maximal oxygen consumption under placebo or after oral tertatolol [a beta-adrenergic receptor (AR) antagonist]. Under placebo, exercise increased dialysate glycerol concentration (DGC) in both groups. Phentolamine (alpha-AR antagonist) potentiated exercise-induced lipolysis in overweight but not in lean subjects; the alpha(2)-antilipolytic effect was only functional in overweight men. After tertatolol administration, the DGC increased similarly during exercise no matter which was used probe in both groups. Compared with the control probe under placebo, lipolysis was reduced in lean but not in overweight men treated with the beta-AR blocker. Tertatolol reduced plasma nonesterified fatty acids and insulin concentration in both groups at rest. Under placebo or tertatolol, the exercise-induced changes in plasma nonesterified fatty acids, glycerol, and insulin concentrations were similar in both groups. Exercise promoted a higher increase in catecholamine and ANP plasma levels after tertatolol administration. In conclusion, the major finding of our study is that in overweight men, in addition to an increased alpha(2)-antilipolytic effect, the lipid mobilization in subcutaneous adipose tissue that persists during exercise under beta-blockade is not dependent on catecholamine action. On the basis of correlation findings, it seems to be related to a concomitant exercise-induced rise in plasma ANP when exercise is performed under tertatolol intake and a decrease in plasma insulin.

The transcriptional coactivator peroxisome proliferator activated receptor (PPAR)gamma coactivator-1 alpha and the nuclear receptor PPAR alpha control the expression of glycerol kinase and metabolism genes independently of PPAR gamma activation in human white adipocytes.

OBJECTIVE: The purpose of this work was to determine the pattern of genes regulated by peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1 alpha (PGC-1 alpha) in human adipocytes and the involvement of PPARalpha and PPARgamma in PGC-1 alpha transcriptional action. RESEARCH DESIGN AND METHODS: Primary cultures of human adipocytes were transduced with a PGC-1 alpha adenovirus and treated with PPARgamma and PPARalpha agonists. Variation in gene expression was assessed using pangenomic microarrays and quantitative RT-PCR. To investigate glycerol kinase (GyK), a target of PGC-1 alpha, we measured enzymatic activity and glycerol incorporation into triglycerides. In vivo studies were performed on wild-type and PPARalpha(-/-) mice. The GyK promoter was studied using chromatin immunoprecipitation and promoter reporter gene assays. RESULTS: Among the large number of genes regulated by PGC-1 alpha independently of PPARgamma, new targets involved in metabolism included the gene encoding GyK. The induction of GyK by PGC-1 alpha was observed at the levels of mRNA, enzymatic activity, and glycerol incorporation into triglycerides. PPARalpha was also upregulated by PGC-1 alpha. Its activation led to an increase in GyK expression and activity. PPARalpha was shown to bind and activate the GyK promoter. Experiments in mice confirmed the role of PGC-1 alpha and PPARalpha in the regulation of GyK in vivo. CONCLUSIONS: This work uncovers novel pathways regulated by PGC-1 alpha and reveals that PPARalpha controls gene expression in human white adipocytes. The induction of GyK by PGC-1 alpha and PPARalpha may promote a futile cycle of triglyceride hydrolysis and fatty acid reesterification.

Profiling of adipokines secreted from human subcutaneous adipose tissue in response to PPAR agonists.

The role of PPARs in the regulation of human adipose tissue secretome has received little attention despite its potential importance in the therapeutic actions of PPAR agonists. Here, we have investigated the effect of selective PPARgamma, PPARalpha, and PPARbeta/delta agonists on the production of adipokines by human subcutaneous adipose tissue. Antibody arrays were used to measure secreted factors in media from cultured adipose tissue explants. Sixteen proteins were produced in significant amounts. Activation of PPARs regulated the production of five proteins. Treatments with the three PPAR agonists decreased the secretion of leptin and interleukin-6. PPARalpha and beta/delta agonists markedly enhanced hepatocyte growth factor secretion whereas PPARbeta/delta down-regulated angiogenin and up-regulated TIMP-1 release. Hepatocyte growth factor, interleukin-6, and TIMP-1 are chiefly expressed in cells from the stromal vascular fraction whereas angiogenin is expressed in both adipocytes and cells from the stromal vascular fraction. Our data show that PPAR agonists modulate secretion of bioactive molecules from the different cell types composing human adipose tissue.

Plasma levels and adipose tissue messenger ribonucleic acid expression of retinol-binding protein 4 are reduced during calorie restriction in obese subjects but are not related to diet-induced changes in insulin sensitivity.

CONTEXT: Retinol-binding protein 4 (RBP4) may play a role in the development of insulin resistance. OBJECTIVE: We investigated whether RBP4 adipose tissue mRNA expression and plasma level are related to insulin sensitivity during a diet-induced weight loss. DESIGN, SETTING, PATIENTS, AND INTERVENTION: Obese women followed a dietary intervention composed of a 4-wk very low-calorie diet (VLCD), a 2-month low-calorie diet, and 3-4 months of a weight maintenance (WM) phase. MAIN OUTCOME MEASURES: Clinical investigation was performed before and at the end of each phase. Insulin sensitivity was assessed with the euglycemic hyperinsulinemic clamp. Adipose tissue mRNA and plasma levels of RBP4 were determined using reverse transcription-quantitative PCR and ELISA, respectively. RESULTS: Weight and fat mass decreased during VLCD and were stabilized during WM. Glucose disposal rate increased during VLCD and remained elevated thereafter. Plasma levels of RBP4 decreased after VLCD and, although increasing at subsequent phases, remained lower than prediet values. Adipose tissue mRNA levels were diminished after VLCD, and increased during low-calorie diet and WM to reach basal values. Basal RBP4 levels or diet-induced variations of RBP4 were not different in lean women and two groups of obese women with high- and low-insulin sensitivity. CONCLUSIONS: Severe calorie restriction promotes a reduction in adipose tissue and plasma levels of RBP4. The study does not bring evidence for a role for RBP4 in the regulation of diet-induced changes in insulin sensitivity.

An increase in plasma adiponectin multimeric complexes follows hypocaloric diet-induced weight loss in obese and overweight pre-menopausal women.

Adiponectin is involved in the regulation of glucose and fatty acid metabolism, influences whole-body insulin sensitivity and protects arterial walls against the development of atherosclerosis. Plasma adiponectin is decreased in obese, insulin-resistant and Type 2 diabetic patients. Adiponectin circulates in plasma as high-, medium- and low-molecular-weight ('mass') forms (HMW, MMW and LMW respectively). The HMW form is believed to be closely associated with insulin sensitivity. The aim of the present study was to investigate whether diet-induced changes in body weight and insulin sensitivity were associated with changes in the quantity of adiponectin multimeric complexes. A total of 20 overweight or obese women (age, 39.4+/-9.5 years; body mass index, 32.2+/-6.4 kg/m(2)) underwent 12 weeks of low caloric diet (600 kcal/day less than energy requirements; where 1 kcal is approximately 4.184 kJ). Plasma samples were drawn before and after the study for biochemical analysis and Western blot detection of adiponectin multimeric complexes. The hypocaloric diet resulted in a weight reduction (89.8+/-16.4 kg compared with 83.1+/-15.6 kg; P<0.001) and an improvement in whole-body insulin sensitivity, as measured by HOMA (homoeostasis model assessment index; 1.9+/-0.8 compared with 1.5+/-0.7; P=0.013). Increases in the quantities of the HMW, MMW and LMW forms by 5.5, 8.5 and 18.1% respectively, were observed (P<0.05 for all of the forms). Total plasma adiponectin was increased by 36% with borderline significance (P=0.08). No correlations between changes in adiponectin complexes and changes in indices of insulin sensitivity were observed. In conclusion, diet-induced weight loss improved insulin sensitivity as well as increased the amount of HMW, MMW and LMW adiponectin complexes in plasma.

Effect of aerobic training on plasma levels and subcutaneous abdominal adipose tissue gene expression of adiponectin, leptin, interleukin 6, and tumor necrosis factor alpha in obese women.

Adipocytokines secreted by adipose tissue are suggested to play a role in the development of obesity-related complications. Regular aerobic exercise has been shown to reduce the risk of metabolic complications in obese subjects. The aim of this study was to investigate the effect of aerobic training on gene expression in subcutaneous abdominal adipose tissue (SCAAT) and on plasma levels of several adipocytokines in obese women. Twenty-five obese sedentary premenopausal women (body mass index, 32.18 +/- 3.17 kg/m(2)) underwent a 12-week aerobic exercise program, with a frequency of 5 d/wk and intensity corresponding to 50% of individual maximal oxygen consumption (V(.-)(O(2)max)) consisting of 2 sessions per week of supervised aerobic exercise and 3 sessions per week of home-based exercise on a bicycle ergometer. Before and after the aerobic training, (V(.-)(O(2)max)) and body composition were measured and plasma and SCAAT biopsy samples (in a subgroup of 8 subjects) were obtained for determination of plasma and messenger RNA levels of adipocytokines (leptin, adiponectin, interleukin 6, tumor necrosis factor alpha). The aerobic training resulted in an increase of subjects' V o(2)max by 12.8% (24.6 +/- 3.9 vs 27.7 +/- 4.8 mL x min(-1) x kg(-1), P < .05). Body weight and fat mass were reduced by 5.9% (88.5 +/- 8.2 vs 83.3 +/- 7.7 kg, P < .001) and 6.4% (38.8 +/- 4.2% vs 36.3 +/- 4.6%, P < .001), respectively, and the revised QUantitative Insulin sensitivity ChecK Index (QUICKI) increased (0.43 +/- 0.06 vs 0.48 +/- 0.06, P < .05) during the aerobic training. No aerobic training-induced changes in messenger RNA levels of the investigated genes in SCAAT were observed. A decrease of plasma leptin (24.3 +/- 8.7 vs 18.1 +/- 8.3 ng/mL, P < .05) was detected, whereas plasma levels of other cytokines remained unchanged. In moderately obese females, 3 months' aerobic training did not promote changes in the adipose tissue gene expression or plasma levels of the adipocytokines (except for leptin) involved in a regulation of lipid and carbohydrate metabolism.

Atrial natriuretic peptide stimulates lipid mobilization during repeated bouts of endurance exercise.

Atrial natriuretic peptide (ANP) controls lipolysis in human adipocytes. Lipid mobilization is increased during repeated bouts of exercise, but the underlying mechanisms involved in this process have not yet been delineated. The relative involvement of catecholamine- and ANP-dependent pathways in the control of lipid mobilization during repeated bouts of exercise was thus investigated in subcutaneous adipose tissue (SCAT) by microdialysis. The study was performed in healthy males. Subjects performed two 45-min exercise bouts (E1 and E2) at 50% of their maximal oxygen uptake separated by a 60-min rest period. Extracellular glycerol concentration (EGC), reflecting SCAT lipolysis, was measured in a control probe perfused with Ringer solution and in two other probes perfused with either Ringer plus phentolamine (alpha(1/2)-AR antagonist) or Ringer plus both phentolamine and propranolol (beta-AR antagonist). Plasma epinephrine, plasma glycerol, and EGC were 1.7-, 1.6-, and 1.2-fold higher in E2 than in E1, respectively. Phentolamine potentiated exercise-induced EGC increase during E2 only. Propranolol reduced the lipolytic rate during both E1 and E2 compared with the probe with phentolamine. Plasma ANP concentration increased more during E2 than during E1 and was correlated with the increase in EGC in the probe containing phentolamine plus propranolol. The results suggest that ANP is involved in the control of lipolysis during exercise and that it contributes to stimulation of lipolysis during repeated bouts of exercise.