Transcriptional regulation of adipocyte hormone-sensitive lipase by glucose

Transcriptional regulation of adipocyte lipolysis by IRF2BP2

Adipocyte lipolysis controls systemic energy levels and metabolic homeostasis. Lipolysis is regulated by posttranslational modifications of key lipolytic enzymes. However, less is known about the transcriptional mechanisms that regulate lipolysis. Here, we identify interferon regulatory factor-2 binding protein 2 (IRF2BP2) as a transcriptional repressor of adipocyte lipolysis. Deletion of IRF2BP2 in human adipocytes increases lipolysis without affecting glucose uptake, whereas IRF2BP2 overexpression decreases lipolysis. RNA sequencing, and chromatin immunoprecipitation sequencing analyses show that IRF2BP2 represses lipolysis-related genes, including LIPE, which encodes hormone sensitive lipase, the rate-limiting enzyme in lipolysis. Adipocyte-selective deletion of Irf2bp2 in mice increases Lipe expression and free fatty acid levels, resulting in adipose tissue inflammation and glucose intolerance. Together, these findings demonstrate that IRF2BP2 restrains adipocyte lipolysis and opens avenues to target lipolysis for the treatment of metabolic disease.

Transcriptional regulation of adipocyte lipolysis by IRF2BP2

Adipocyte lipolysis controls systemic energy levels and metabolic homeostasis. Lipolysis is regulated by post-translational modifications of key lipolytic enzymes. However, less is known about the transcriptional mechanisms that regulate lipolysis. Here, we identify the transcriptional factor interferon regulatory factor-2 binding protein 2 (IRF2BP2) as a repressor of adipocyte lipolysis. Deletion of IRF2BP2 in primary human adipocytes increases lipolysis without affecting glucose uptake, whereas IRF2BP2 overexpression decreases lipolysis. RNA-seq and ChIP-seq analyses reveal that IRF2BP2 directly represses several lipolysis-related genes, including LIPE ( HSL , hormone sensitive lipase), which encodes the rate-limiting enzyme in lipolysis. Adipocyte-selective deletion of Irf2bp2 in mice increases Lipe expression and free fatty acid levels, resulting in elevated adipose tissue inflammation and glucose intolerance. Altogether, these findings demonstrate that IRF2BP2 restrains adipocyte lipolysis and opens new avenues to target lipolysis for the treatment of metabolic disease.

Curcumin reduces oxidative stress and fat deposition in longissimus dorsi muscle of intrauterine growth-retarded finishing pigs

Dietary curcumin possessing multiple biological activities may be an effective way to alleviate oxidative damage and fat deposition in intrauterine growth retardation (IUGR) finishing pigs. Therefore, this study was conducted to evaluate effects of dietary curcumin on meat quality, antioxidant capacity, and fat deposition of longissimus dorsi muscle in IUGR finishing pigs. Twelve normal birth weight (NBW) and 24 IUGR female piglets at 26 days of age were divided into 3 dietary groups: NBW (basal diet), IUGR (basal diet), and IUGR + Cur (basal diet supplemented with 200 mg/kg curcumin). The trial lasted for 169 days. Results showed that IUGR increased concentrations of malondialdehyde (MDA) and protein carbonyls (PC) and fat deposition in longissimus dorsi muscle. However, curcumin decreased the intramuscular fat content and the levels of MDA and PC and improved meat quality in IUGR pigs. Furthermore, curcumin inhibited the decrease of nuclear factor erythroid 2-related factor 2 (Nrf2) protein expression and decreased peroxisome pro liferator-activated receptors γ (PPARγ) expression in IUGR pigs. These findings suggested that dietary addition of 200 mg/kg curcumin could improve meat quality, alleviate oxidative stress through activating Nrf2 signaling pathway, and reduce fat deposition via inhibiting PPARγ expression in longissimus dorsi muscle of IUGR finishing pigs.

Metabolite Changes After Metabolic Surgery - Associations to Parameters Reflecting Glucose Homeostasis and Lipid Levels

AIMS

To test the hypothesis that adipose tissue gene expression patterns would be affected by metabolic surgery and we aimed to identify genes and metabolic pathways as well as metabolites correlating with metabolic changes following metabolic surgery.

MATERIALS AND METHODS

This observational study was conducted at the Obesity Unit at the Catholic University Hospital of the Sacred Heart in Rome, Italy. Fifteen patients, of which six patients underwent Roux-en-Y gastric bypass and nine patients underwent biliopancreatic diversion, were included. The participants underwent an oral glucose tolerance test and a hyperinsulinemic euglycemic clamp. Small polar metabolites were analyzed with a two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOFMS). Gene expression analysis of genes related to metabolism of amino acids and fatty acids were analyzed in subcutaneous adipose tissue. All procedures were performed at study start and at follow-up (after 185.3 ± 72.9 days).

RESULTS

Twelve metabolites were significantly changed after metabolic surgery. Six metabolites were identified as 3-indoleacetic acid, 2-hydroxybutyric acid, valine, glutamic acid, 4-hydroxybenzeneacetic acid and alpha-tocopherol. The branched chain amino acids displayed a significant decrease together with a decrease in BCAT1 adipose tissue mRNA levels. Changes in the identified metabolites were associated to changes in lipid, insulin and glucose levels.

CONCLUSIONS

Our study has identified metabolites and metabolic pathways that are altered by metabolic surgery and may be used as biomarkers for metabolic improvement.

Hormone-sensitive lipase: sixty years later

Hormone-sensitive lipase (HSL) was initially characterized as the hormonally regulated neutral lipase activity responsible for the breakdown of triacylglycerols into fatty acids in adipose tissue. This review aims at providing up-to-date information on structural properties, regulation of expression, activity and function as well as therapeutic potential. The lipase is expressed as different isoforms produced from tissue-specific alternative promoters. All isoforms are composed of an N-terminal domain and a C-terminal catalytic domain within which a regulatory domain containing the phosphorylation sites is embedded. Some isoforms possess additional N-terminal regions. The catalytic domain shares similarities with bacteria, fungus and vascular plant proteins but not with other mammalian lipases. HSL singularity is provided by regulatory and N-terminal domains sharing no homology with other proteins. HSL has a broad substrate specificity compared to other neutral lipases. It hydrolyzes acylglycerols, cholesteryl and retinyl esters among other substrates. A novel role of HSL, independent of its enzymatic function, has recently been described in adipocytes. Clinical studies revealed dysregulations of HSL expression and activity in disorders, such as lipodystrophy, obesity, type 2 diabetes and cancer-associated cachexia. Development of specific inhibitors positions HSL as a pharmacological target for the treatment of metabolic complications.

Using blubber explants to investigate adipose function in grey seals: glycolytic, lipolytic and gene expression responses to glucose and hydrocortisone

Adipose tissue is fundamental to energy balance, which underpins fitness and survival. Knowledge of adipose regulation in animals that undergo rapid fat deposition and mobilisation aids understanding of their energetic responses to rapid environmental change. Tissue explants can be used to investigate adipose regulation in wildlife species with large fat reserves, when opportunities for organismal experimental work are limited. We investigated glucose removal, lactate, glycerol and NEFA accumulation in media, and metabolic gene expression in blubber explants from wild grey seals. Glycolysis was higher in explants incubated in 25 mM glucose (HG) for 24 h compared to controls (C: 5.5 mM glucose). Adipose-derived lactate likely contributes to high endogenous glucose production in seals. Lipolysis was not stimulated by HG or high hydrocortisone (HC: 500 nM hydrocortisone) and was lower in heavier animals. HC caused NEFA accumulation in media to decrease by ~30% relative to C in females, indicative of increased lipogenesis. Lipolysis was higher in males than females in C and HG conditions. Lower relative abundance of 11-β-hydroxysteroid dehydrogenase 1 mRNA in HG explants suggests glucose involvement in blubber cortisol sensitivity. Our findings can help predict energy balance responses to stress and nutritional state in seals, and highlight the use of explants to study fat tissue function in wildlife.

Contribution of lipase deficiency to mitochondrial dysfunction and insulin resistance in hMADS adipocytes

BACKGROUND/OBJECTIVES

Adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are key enzymes involved in intracellular lipid catabolism. We have previously shown decreased expression and activity of these lipases in adipose tissue of obese insulin resistant individuals. Here we hypothesized that lipase deficiency might impact on insulin sensitivity and metabolic homeostasis in adipocytes not just by enhancing lipid accumulation, but also by altering lipid and carbohydrate catabolism in a peroxisome proliferator-activated nuclear receptor (PPAR)-dependent manner.

METHODS

To address our hypothesis, we performed a series of in vitro experiments in a human white adipocyte model, the human multipotent adipose-derived stem (hMADS) cells, using genetic (siRNA) and pharmacological knockdown of ATGL and/or HSL.

RESULTS

We show that ATGL and HSL knockdown in hMADS adipocytes disrupted mitochondrial respiration, which was accompanied by a decreased oxidative phosphorylation (OxPhos) protein content. This lead to a reduced exogenous and endogenous palmitate oxidation following ATGL knockdown, but not in HSL deficient adipocytes. ATGL deficiency was followed by excessive triacylglycerol accumulation, and HSL deficiency further increased diacylglycerol accumulation. Both single and double lipase knockdown reduced insulin-stimulated glucose uptake, which was attributable to impaired insulin signaling. These effects were accompanied by impaired activation of the nuclear receptor PPARα, and restored on PPARα agonist treatment.

CONCLUSIONS

The present study indicates that lipase deficiency in human white adipocytes contributes to mitochondrial dysfunction and insulin resistance, in a PPARα-dependent manner. Therefore, modulation of adipose tissue lipases may provide a promising strategy to reverse insulin resistance in obese and type 2 diabetic patients.

SF-1 (NR5A1) expression is stimulated by the PKA pathway and is essential for the PKA-induced activation of LIPE expression in Y-1 cells

In the adrenal cortex, corticotropin induces the expression of several genes encoding proteins involved in the synthesis and intracellular transport of steroid hormones via the protein kinase A (PKA) signalling pathway, and this process is mediated by steroidogenic factor-1 (SF-1). This study was designed to elucidate the influence of the PKA and PKC pathways on the expression of the SF-1 gene in mouse adrenocortical cells, line Y-1. It has also been attempted to answer the question whether or not SF-1 plays a role in the PKA-induced expression of LIPE gene encoding hormone-sensitive lipase/cholesteryl esterase, which supplies cholesterol for steroid hormone synthesis. In this study, we found that stimulation of the PKA pathway caused a significant increase in SF-1 expression, and that this effect was abolished by the PKA inhibitor, H89. Decreased SF-1 gene transcript levels were seen with the simultaneous activation of PKA and PKC, suggesting a possible interaction between the PKA and PKC pathways. It was also observed that SF-1 increased the transcriptional activity of the LIPE gene by interacting with the SF-1 response element located in promoter A. Moreover, transient silencing of SF-1 expression with specific siRNAs abolished PKA-stimulated transcription of the LIPE gene, indicating that SF-1 is an important regulator of LIPE expression in Y-1 cells and thus could play a role in the regulation of the cholesterol supply for adrenal steroidogenesis.

Synthesis, characterization, and efficacy evaluation of a new anti-diabetic vanadyl(II) thiamine hydrochloride complex in streptozotocin-induced diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by hyperglycemia due to abnormalities in either insulin secretion or action. A range of vanadium complexes have been synthesized and demonstrated to be effective in lowering hyperglycemia. Thiamine administration was also reported to prevent deterioration in fasting glucose and insulin levels, and to improve glucose tolerance in hyperglycemic patients. This study has been conducted to evaluate the ionic vanadyl(II) thiamine hydrochloride complex (VC) as a new anti-diabetic candidate. The new complex was characterized by infrared spectroscopy (FT-IR), electronic spectra, magnetic susceptibility, electron spin resonance (ESR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The anti-diabetic effect of VC was investigated in comparison to vanadium sulfate in streptozotocin (STZ)-induced diabetic rats. Treatment of diabetic rats with VC versus vanadyl sulfate showed a more potent effect on reducing serum glucose and cholesterol close to normal levels. VC suppressed the diabetes-induced upregulation of hepatic glucose transporter (GLUT)-2, Phosphoenol pyruvate carboxykinase (PEPCK), and hormone-sensitive lipase (HSL) more significantly than vanadyl sulfate. Either vanadyl sulfate or VC restored hepatic sterol regulatory element-binding protein transcription factor-1c (SREBP-1c) and muscle hexokinase (HK) mRNA expression that was downregulated in diabetic group. Pyruvate kinase (PK) mRNA expression was restored more significantly in VC-treated than vanadyl sulfate-treated diabetic rats. These results indicate that the newly synthesized VC could be an effective anti-diabetic candidate as the anti-diabetic activity of the ionic vanadium was enhanced after being modified with the organic ligand, thiamin. The results also suggest that VC achieves its effect most likely through modulating the transcription of energy metabolizing enzymes.

Multiple E-boxes in the distal promoter of the rat pyruvate carboxylase gene function as a glucose-responsive element

Pyruvate carboxylase (PC) is an anaplerotic enzyme that regulates glucose-induced insulin secretion in pancreatic islets. Dysregulation of its expression is associated with type 2 diabetes. Herein we describe the molecular mechanism underlying the glucose-mediated transcriptional regulation of the PC gene. Incubation of the rat insulin cell line INS-1 832/13 with glucose resulted in a 2-fold increase in PC mRNA expression. Transient transfections of the rat PC promoter-luciferase reporter construct in the above cell line combined with mutational analysis indicated that the rat PC gene promoter contains the glucose-responsive element (GRE), comprising three canonical E-boxes (E1, E3 and E4) and one E-box-like element (E2) clustering between nucleotides –546 and –399, upstream of the transcription start site. Mutation of any of these E-boxes resulted in a marked reduction of glucose-mediated transcriptional induction of the reporter gene. Electrophoretic mobility shift assays revealed that the upstream stimulatory factors 1 and 2 (USF1 and USF2) bind to E1, the Specificity Protein-1 (Sp1) binds to E2, USF2 and the carbohydrate responsive element binding protein (ChREBP) binds to E4, while unknown factors binds to E3. High glucose promotes the recruitment of Sp1 to E2 and, USF2 and ChREBP to E4. Silencing the expression of Sp1, USF2 and ChREBP by their respective siRNAs in INS-1 832/13 cells blunted glucose-induced expression of endogenous PC. We conclude that the glucose-mediated transcriptional activation of the rat PC gene is regulated by at least these three transcription factors.

Apolipoprotein O is mitochondrial and promotes lipotoxicity in heart

Diabetic cardiomyopathy is a secondary complication of diabetes with an unclear etiology. Based on a functional genomic evaluation of obesity-associated cardiac gene expression, we previously identified and cloned the gene encoding apolipoprotein O (APOO), which is overexpressed in hearts from diabetic patients. Here, we generated APOO-Tg mice, transgenic mouse lines that expresses physiological levels of human APOO in heart tissue. APOO-Tg mice fed a high-fat diet exhibited depressed ventricular function with reduced fractional shortening and ejection fraction, and myocardial sections from APOO-Tg mice revealed mitochondrial degenerative changes. In vivo fluorescent labeling and subcellular fractionation revealed that APOO localizes with mitochondria. Furthermore, APOO enhanced mitochondrial uncoupling and respiration, both of which were reduced by deletion of the N-terminus and by targeted knockdown of APOO. Consequently, fatty acid metabolism and ROS production were enhanced, leading to increased AMPK phosphorylation and Ppara and Pgc1a expression. Finally, we demonstrated that the APOO-induced cascade of events generates a mitochondrial metabolic sink whereby accumulation of lipotoxic byproducts leads to lipoapoptosis, loss of cardiac cells, and cardiomyopathy, mimicking the diabetic heart-associated metabolic phenotypes. Our data suggest that APOO represents a link between impaired mitochondrial function and cardiomyopathy onset, and targeting APOO-dependent metabolic remodeling has potential as a strategy to adjust heart metabolism and protect the myocardium from impaired contractility.

Histone deacetylase 9 is a negative regulator of adipogenic differentiation

Differentiation of preadipocytes into mature adipocytes capable of efficiently storing lipids is an important regulatory mechanism in obesity. Here, we examined the involvement of histone deacetylases (HDACs) and histone acetyltransferases (HATs) in the regulation of adipogenesis. We find that among the various members of the HDAC and HAT families, only HDAC9 exhibited dramatic down-regulation preceding adipogenic differentiation. Preadipocytes from HDAC9 gene knock-out mice exhibited accelerated adipogenic differentiation, whereas HDAC9 overexpression in 3T3-L1 preadipocytes suppressed adipogenic differentiation, demonstrating its direct role as a negative regulator of adipogenesis. HDAC9 expression was higher in visceral as compared with subcutaneous preadipocytes, negatively correlating with their potential to undergo adipogenic differentiation in vitro. HDAC9 localized in the nucleus, and its negative regulation of adipogenesis segregates with the N-terminal nuclear targeting domain, whereas the C-terminal deacetylase domain is dispensable for this function. HDAC9 co-precipitates with USF1 and is recruited with USF1 at the E-box region of the C/EBPα gene promoter in preadipocytes. Upon induction of adipogenic differentiation, HDAC9 is down-regulated, leading to its dissociation from the USF1 complex, whereas p300 HAT is up-regulated to allow its association with USF1 and accumulation at the E-box site of the C/EBPα promoter in differentiated adipocytes. This reciprocal regulation of HDAC9 and p300 HAT in the USF1 complex is associated with increased C/EBPα expression, a master regulator of adipogenic differentiation. These findings provide new insights into mechanisms of adipogenic differentiation and document a critical regulatory role for HDAC9 in adipogenic differentiation through a deacetylase-independent mechanism.

Altered skeletal muscle lipase expression and activity contribute to insulin resistance in humans

OBJECTIVE

Insulin resistance is associated with elevated content of skeletal muscle lipids, including triacylglycerols (TAGs) and diacylglycerols (DAGs). DAGs are by-products of lipolysis consecutive to TAG hydrolysis by adipose triglyceride lipase (ATGL) and are subsequently hydrolyzed by hormone-sensitive lipase (HSL). We hypothesized that an imbalance of ATGL relative to HSL (expression or activity) may contribute to DAG accumulation and insulin resistance.

RESEARCH DESIGN AND METHODS

We first measured lipase expression in vastus lateralis biopsies of young lean (n = 9), young obese (n = 9), and obese-matched type 2 diabetic (n = 8) subjects. We next investigated in vitro in human primary myotubes the impact of altered lipase expression/activity on lipid content and insulin signaling.

RESULTS

Muscle ATGL protein was negatively associated with whole-body insulin sensitivity in our population (r = -0.55, P = 0.005), whereas muscle HSL protein was reduced in obese subjects. We next showed that adenovirus-mediated ATGL overexpression in human primary myotubes induced DAG and ceramide accumulation. ATGL overexpression reduced insulin-stimulated glycogen synthesis (-30%, P < 0.05) and disrupted insulin signaling at Ser1101 of the insulin receptor substrate-1 and downstream Akt activation at Ser473. These defects were fully rescued by nonselective protein kinase C inhibition or concomitant HSL overexpression to restore a proper lipolytic balance. We show that selective HSL inhibition induces DAG accumulation and insulin resistance.

CONCLUSIONS

Altogether, the data indicate that altered ATGL and HSL expression in skeletal muscle could promote DAG accumulation and disrupt insulin signaling and action. Targeting skeletal muscle lipases may constitute an interesting strategy to improve insulin sensitivity in obesity and type 2 diabetes.

Regulation of the promoter region of the human adiponutrin/PNPLA3 gene by glucose and insulin

The adiponutrin/PNPLA3 gene is highly expressed in adipose tissue and liver. Its expression is down-regulated by fasting and rapidly induced by refeeding a high carbohydrate diet. We aimed to determine whether the promoter region of adiponutrin is regulated by glucose and insulin. Endogenous adiponutrin mRNA was increased in mouse 3T3-L1 and human SGBS adipocytes and in human HepG2 cells cultured in 25 mM glucose compared to absence of glucose. A 3100 bp 5'-upstream region of the human adiponutrin gene was cloned into a luciferase reporter plasmid and used in transient transfection studies. Promoter activity was up-regulated by 25 mM glucose, 4.7-fold in HepG2 cells and 2-fold in CHO cells. The effect was shown in CHO cells to be concentration dependent and to depend on glucose metabolism as a non-metabolisable analogue was without effect. In CHO cells constitutively expressing human insulin receptor (CHO-IR), there was a concentration dependent increase of promoter activity by insulin in the presence of glucose. Cotransfection with an expression plasmid for upstream stimulatory factor 2 (USF2), increased promoter activity 1.6-fold in CHO-IR cells. The combined effect of insulin and USF2 (2.3-fold) was greater than the individual effects. Cotransfection of carbohydrate-response element binding protein did not elicit any induction of promoter activity. These results point to potential mechanisms for the observed in vivo nutritional regulation of adiponutrin expression and its up-regulation in fatty liver and by obesity.

Peroxisome proliferator-activated receptor-alpha control of lipid and glucose metabolism in human white adipocytes

This work aimed at characterizing the role of peroxisome proliferator-activated receptors (PPAR)alpha in human white adipocyte metabolism and at comparing PPAR alpha and PPAR gamma actions in these cells. Primary cultures of human fat cells were treated with the PPAR alpha agonist GW7647 or the PPAR gamma agonist rosiglitazone. Changes in gene expression were determined using DNA microarrays and quantitative RT-PCR. Western blot and metabolic studies were performed to identify the biological effects elicited by PPAR agonist treatments. GW7647 induced an up-regulation of beta-oxidation gene expression and increased palmitate oxidation. Unexpectedly, glycolysis was strongly reduced at transcriptional and functional levels by GW7647 leading to a decrease in pyruvate and lactate production. Glucose oxidation was decreased. Triglyceride esterification and de novo lipogenesis were inhibited by the PPAR alpha agonist. GW7647-induced alterations were abolished by a treatment with a PPAR alpha antagonist. Small interfering RNA-mediated extinction of PPAR alpha gene expression in hMADS adipocytes attenuated GW7647 induction of palmitate oxidation. Rosiglitazone had no major impact on glycolysis and beta-oxidation. Altogether these results show that PPAR alpha can selectively up-regulate beta-oxidation and decrease glucose utilization in human white adipocytes.

Lipolysis and lipid mobilization in human adipose tissue

Triacylglycerol (TAG) stored in adipose tissue (AT) can be rapidly mobilized by the hydrolytic action of the three main lipases of the adipocyte. The non-esterified fatty acids (NEFA) released are used by other tissues during times of energy deprivation. Until recently hormone-sensitive lipase (HSL) was considered to be the key rate-limiting enzyme responsible for regulating TAG mobilization. A novel lipase named adipose triglyceride lipase/desnutrin (ATGL) has been identified as playing an important role in the control of fat cell lipolysis. Additionally perilipin and other proteins of the surface of the lipid droplets protecting or exposing the TAG core of the droplets to lipases are also potent regulators of lipolysis. Considerable progress has been made in understanding the mechanisms of activation of the various lipases. Lipolysis is under tight hormonal regulation. The best understood hormonal effects on AT lipolysis concern the opposing regulation by insulin and catecholamines. Heart-derived natriuretic peptides (i.e., stored in granules in the atrial and ventricle cardiomyocytes and exerting stimulating effects on diuresis and natriuresis) and numerous autocrine/paracrine factors originating from adipocytes and other cells of the stroma-vascular fraction may also participate in the regulation of lipolysis. Endocrine and autocrine/paracrine factors cooperate and lead to a fine regulation of lipolysis in adipocytes. Age, anatomical site, sex, genotype and species differences all play a part in the regulation of lipolysis. The manipulation of lipolysis has therapeutic potential in the metabolic disorders frequently associated with obesity and probably in several inborn errors of metabolism.

Glucose increases hepatic lipase expression in HepG2 liver cells through upregulation of upstream stimulatory factors 1 and 2

AIMS/HYPOTHESIS

Elevated hepatic lipase (HL, also known as LIPC) expression is a key factor in the development of the atherogenic lipid profile in type 2 diabetes and insulin resistance. Recently, genetic screens revealed a possible association of type 2 diabetes and familial combined hyperlipidaemia with the USF1 gene. Therefore, we investigated the role of upstream stimulatory factors (USFs) in the regulation of HL.

METHODS

Levels of USF1, USF2 and HL were measured in HepG2 cells cultured in normal- or high-glucose medium (4.5 and 22.5 mmol/l, respectively) and in livers of streptozotocin-treated rats.

RESULTS

Nuclear extracts of cells cultured in high glucose contained 2.5 +/- 0.5-fold more USF1 and 1.4 +/- 0.2-fold more USF2 protein than cells cultured in normal glucose (mean +/- SD, n = 3). This coincided with higher DNA binding of nuclear proteins to the USF consensus DNA binding site. Secretion of HL (2.9 +/- 0.5-fold), abundance of HL mRNA (1.5 +/- 0.2-fold) and HL (-685/+13) promoter activity (1.8 +/- 0.3-fold) increased in parallel. In chromatin immunoprecipitation assays, the proximal HL promoter region was immunoprecipitated with anti-USF1 and anti-USF2 antibodies. Co-transfection with USF1 or USF2 cDNA stimulated HL promoter activity 6- to 16-fold. USF and glucose responsiveness were significantly reduced by removal of the -310E-box from the HL promoter. Silencing of the USF1 gene by RNA interference reduced glucose responsiveness of the HL (-685/+13) promoter region by 50%. The hyperglycaemia in streptozotocin-treated rats was associated with similar increases in USF abundance in rat liver nuclei, but not with increased binding of USF to the rat Hl promoter region.

CONCLUSIONS/INTERPRETATION

Glucose increases HL expression in HepG2 cells via elevation of USF1 and USF2. This mechanism may contribute to the development of the dyslipidaemia that is typical of type 2 diabetes.

Regulation and function of triacylglycerol lipases in cellular metabolism

The ability to store energy in the form of energy-dense TAG (triacylglycerol) and to mobilize these stores rapidly during times of low carbohydrate availability (fasting or famine) or during heightened metabolic demand (exercise or cold-stress) is a highly conserved process essential for survival. Today, in the presence of nutrient excess and sedentary lifestyles, the regulation of this pathway is viewed as an important therapeutic target for disease prevention, as elevated circulating fatty acids in obesity contribute to many aspects of the metabolic syndrome including hepatic steatosis, atherosclerosis and insulin resistance. In the present review, we discuss the metabolic regulation and function of TAG lipases with a focus on HSL (hormone-sensitive lipase), ATGL (adipose triacylglycerol lipase) and newly identified members of the lipolytic proteome.

Hormone-sensitive lipase is involved in hepatic cholesteryl ester hydrolysis

Hormone-sensitive lipase (HSL) regulates the hydrolysis of acylglycerol and cholesteryl ester (CE) in various organs, including adipose tissues. However, the hepatic expression level of HSL has been reported to be almost negligible. In the present study, we found that mice lacking both leptin and HSL (Lep(ob/ob)/HSL(-/-)) showed massive accumulation of CE in the liver compared with Lep(ob/ob)/HSL(+/+) mice, while triacylglycerol (TG) accumulation was modest. Similarly, feeding with a high-cholesterol diet induced hepatic CE accumulation in HSL(-/-) mice. Supporting these observations, we detected significant expression of protein as well as mRNA of HSL in the liver. HSL(-/-) mice showed reduced activity of CE hydrolase, but not of TG lipase, in the liver compared with wild-type mice. Furthermore, we confirmed the expression of HSL in viable parenchymal cells isolated from wild-type mice. The hepatocytes from HSL(-/-) mice showed reduced activity of CE hydrolase and contained more CE than those from HSL(+/+) mice even without the incubation with lipoproteins. Incubation with LDL further augmented the accumulation of CE in the HSL-deficient hepatocytes. From these results, we conclude that HSL is involved in the hydrolysis of CE in hepatocyes.

The transcriptional co-activator PGC-1alpha up regulates apelin in human and mouse adipocytes

By using pangenomic microarray, we identified apelin as a unique adipokine up regulated by the transcriptional co-activator peroxisome proliferator-activated receptor gamma (PPARgamma) co-activator 1alpha (PGC-1alpha) in human white adipocytes. We investigated its regulation in vitro and in vivo. Overexpression of PGC-1alpha by adenovirus in human adipocytes induces apelin expression and secretion. Pharmacological induction of cAMP, an upstream regulator of endogenous PGC-1alpha expression, up regulates apelin gene expression and also apelin secretion in human and mice adipocytes. Moreover, during cold exposure in mice, a physiological situation known to induce both cAMP and PGC-1alpha, apelin expression in adipocytes and plasma levels were increased. This is the first demonstration that PGC-1alpha is involved in the regulation of an adipokine gene expression and release.

A novel promoter polymorphism in the human gene GNAS affects binding of transcription factor upstream stimulatory factor 1, Galphas protein expression and body weight regulation

OBJECTIVES

Body weight regulation is under complex control involving the central nervous system and peripheral pathways. The beta-adrenoceptor Galphas protein system plays an important role in heart rate regulation and lipid mobilization suggesting a key role for the stimulatory G protein Galphas in body weight regulation.

METHODS

We sequenced the whole GNAS promoter to identify a functional variant which results in altered Galphas expression. We genotyped 110 participants of a randomized placebo-controlled weight loss trial who were under a low calorie diet and were additionally treated with either placebo or 15 mg sibutramine daily for 54 weeks and associated the respective alleles with regard to treatment outcome using an intention-to-treat analysis.

RESULTS

A G>A transition at position -1211 the human GNAS promoter (minor allele frequency=0.36) was identified resulting in altered upstream stimulatory factor 1 transcription factor binding, promoter activity, Galphas expression, and lipolysis. Under a low calorie diet -1211GG genotypes lost significantly more weight compared with A-allele carriers (placebo group: 1211GG, 7.5+/-0.4 versus -1211A, 4.5+/-0.3 kg, P=0.020). Sibutramine was effective only in A-allele carriers whereas GG genotypes showed no additional weight loss under sibutramine but showed the strongest increases in resting heart rate (8.5 bpm; 95% confidence interval: 2.7-14.21 bpm; P=0.005) and systolic blood pressure (9.1 mmHg, 95% confidence interval: 3.1-15.1; P=0.004) compared with placebo.

CONCLUSIONS

Determination of GNAS promoter alleles may identify obese individuals who lose weight easily under lifestyle changes alone but also those who benefit from adjunct sibutramine therapy.

Body mass index is associated with USF1 haplotype in Korean premenopausal women

The upstream stimulatory factor 1 (USF1) gene has been shown to play an essential role as the cause of familial combined hyperlipidemia, and there are several association studies on the relationship between USF1 and metabolic disorders. In this study, we analyzed two single nucleotide polymorphisms in USF1 rs2073653 (306A>G) and rs2516840 (1748C>T) between the case (dyslipidemia or obesity) group and the control group in premenopausal females, postmenopausal females, and males among 275 Korean subjects. We observed a statistically significant difference in the GC haplotype between body mass index (BMI) > or =25 kg/m2) and BMI <25 kg/m2 groups in premenopausal females ( chi2=4.23, p=0.04). It seems that the USF1 GC haplotype is associated with BMI in premenopausal Korean females.

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.

New indicators of beef sensory quality revealed by expression of specific genes

To identify new molecular markers of beef sensory quality, the transcriptomes of Longissimus thoracis muscle from 25 Charolais bull calves were analyzed using microarrays and compared between high and low meat quality groups; 215 genes were differentially expressed according to tenderness, juiciness, and/or flavor. Among these, 23 were up-regulated in the tenderest, juiciest, and tastiest meats, and 18 were highly correlated with both flavor and juiciness (e.g., PRKAG1), explaining up to 60% of their variability. Nine were down-regulated in the same meats, but only DNAJA1 [the results relating to DNAJA1 and its relationship with tenderness have been patented (Genomic marker for meat tenderness; Patent EP06300943.5, September 12, 2006)], which encodes a heat shock protein, showed a strong negative correlation with tenderness that alone explained 63% of its variability. This protein, known for its anti-apoptotic role, could be involved in meat aging. Thus, DNAJA1 could constitute a new marker of beef sensory quality.

Association analysis of adiponectin and somatostatin polymorphisms on BTA1 with growth and carcass traits in Angus cattle

This study tested positional candidate genes adiponectin (ADIPOQ) and somatostatin (SST) for effects on carcass traits in a commercially relevant cattle population. Both genes are located within a region of BTA1 previously reported to harbour quantitative trait loci (QTL) that affect marbling, quality grade, yield grade, ribeye area and weaning weight in Bos taurus x Bos indicus crosses. Except for the first intron of ADIPOQ, both genes, including over 2 kb upstream of the promoters, were sequenced in five registered Angus sires to identify polymorphisms. A variable copy duplication and three single nucleotide polymorphisms (SNPs) in ADIPOQ and one SNP in SST were genotyped and tested for association with 19 traits in a 14-generation pedigree of 1697 registered Angus artificial insemination sires representing all the major USA lineages of the breed. Linear models that parameterized predicted genetic merits in terms of allele substitution effects were fit by weighted least squares, and goodness-of-fit tests were employed to differentiate causal mutations or polymorphisms in strong linkage disequilibrium (LD) with causal mutations from markers in weak LD with QTL. We confirmed the presence of QTL affecting marbling, ribeye muscle area and fat thickness in the vicinity of SST and ADIPOQ on BTA1 in Angus; excluded SST as underlying the ribeye muscle area QTL; and excluded ADIPOQ as underlying the marbling score QTL. However, association analysis provides very limited information about QTL location and has little intrinsic value when performed in the absence of linkage or LD analysis using flanking marker data to localize the QTL effect relative to positional candidate genes.

ApoO, a novel apolipoprotein, is an original glycoprotein up-regulated by diabetes in human heart

Obesity is an independent risk factor for cardiac failure. Obesity promotes excessive deposition of fat in adipose and nonadipose tissues. Intramyocardial lipid overload is a relatively common finding in nonischemic heart failure, especially in obese and diabetic patients, and promotes lipoapoptosis that contributes to the alteration of cardiac function. Lipoprotein production has been proposed as a heart-protective mechanism through the unloading of surplus cellular lipids. We previously analyzed the heart transcriptome in a dog nutritional model of obesity, and we identified a new apolipoprotein, regulated by obesity in heart, which is the subject of this study. We detected this new protein in the following lipoproteins: high density lipoprotein, low density lipoprotein, and very low density lipoprotein. We designated it apolipoprotein O. Apolipoprotein O is a 198-amino acid protein that contains a 23-amino acidlong signal peptide. The apolipoprotein O gene is expressed in a set of human tissues. Confocal immunofluorescence microscopy colocalized apolipoprotein O and perilipins, a cellular marker of the lipid droplet. Chondroitinase ABC deglycosylation analysis or cell incubation with p-nitrophenyl-beta-d-xyloside indicated that apolipoprotein O belongs to the proteoglycan family. Naringenin or CP-346086 treatments indicated that apolipoprotein O secretion requires microsomal triglyceride transfer protein activity. Apolipoprotein O gene expression is up-regulated in the human diabetic heart. Apolipoprotein O promoted cholesterol efflux from macrophage cells. To our knowledge, apolipoprotein O is the first chondroitin sulfate chain containing apolipoprotein. Apolipoprotein O may be involved in myocardium-protective mechanisms against lipid accumulation, or it may have specific properties mediated by its unique glycosylation pattern.

Identification of peroxisome-proliferator responsive element in the mouse HSL gene

Hormone-sensitive lipase (HSL) catalyzes the rate-limiting step of lipolysis in adipose tissue. Several studies suggest that protein phosphorylation regulates the HSL enzymatic activity. On the other hand, the precise mechanism of the transcriptional regulation of the HSL gene remains to be elucidated. Here, we identified a functional peroxisome-proliferator responsive element (PPRE) in the mouse HSL promoter by reporter assay in CV-1 cells using serial deletion and point mutants of the 5'-flanking region. Chromatin immunoprecipitation (ChIP) analysis revealed that both peroxisome-proliferator activated receptor (PPARgamma) and retinoid X receptor (RXRalpha) interacted with the region. Binding of the PPARgamma/RXRalpha heterodimer to the PPRE sequence was also confirmed by electrophoretic mobility shift assay. These results indicate that the HSL gene is transcriptionally regulated by PPARgamma/RXRalpha heterodimer, and suggest that a cis-acting element regulates the HSL gene expression.

The involvement of upstream stimulatory factor 1 in Dutch patients with familial combined hyperlipidemia

Recently, the upstream stimulatory factor 1 gene (USF1) was proposed as a candidate gene for familial combined hyperlipidemia (FCH). In this study, we examined the previously identified risk haplotype of USF1 with respect to FCH and its related phenotypes in 36 Dutch FCH families. The diagnosis of FCH was based on both the traditional diagnostic criteria and a nomogram. The two polymorphisms, USF1s1 and USF1s2, were in complete linkage disequilibrium. No association was found for the individual single nucleotide polymorphisms (SNPs) with FCH defined by the nomogram (USF1s1, P = 0.53; USF1s2, P = 0.53), whereas suggestive associations were found when using the traditional diagnostic criteria for FCH (USF1s1, P = 0.08; USF1s2, P = 0.07). USF1 was associated with total cholesterol (USF1s1, P = 0.05; USF1s2, P = 0.04) and apolipoprotein B (USF1s1, P = 0.06; USF1s2, P = 0.04). Small dense LDL showed a suggestive association (USF1s1, P = 0.10; USF1s2, P = 0.09). The results from the haplotype analyses supported the results obtained for the individual SNPs. In conclusion, the previously identified risk haplotype of USF1 showed a suggestive association with FCH and contributed to the related lipid traits in our Dutch FCH families.

Upstream transcription factor 1 gene polymorphisms are associated with high antilipolytic insulin sensitivity and show gene–gene interactions

Upstream transcription factor 1 (USF1) regulates the expression of many genes involved in lipid and glucose metabolism, among them genes regulating lipolysis. USF1 specifically regulates the expression of the hormone-sensitive lipase gene (HSL) in adipocytes and the hepatic lipase gene (LIPC) in the liver, which was found to be involved in liver fat accumulation. The usf1s1 C > T and usf1s2 G > A single-nucleotide polymorphisms (SNPs) in USF1 are associated with increased in vitro catecholamine-induced lipolysis in adipocytes. We investigated first whether SNPs in USF1 affect the lipolysis-suppressing action of insulin in vivo, and second, whether they interact with the -60C > G SNP in HSL on lipolysis and the -514C > T SNP in LIPC on liver fat. The usf1s1 C > T and usf1s2 G > A SNPs, together with the SNPs in HSL and LIPC, were determined in 407 Caucasians. Lipolysis was estimated as a change in free fatty acid (FFA) levels from baseline to 2 h of a 75-g oral glucose tolerance test (OGTT). Fifty-four subjects had data from a euglycemic hyperinsulinemic clamp with calculation of antilipolytic insulin sensitivity. Subjects carrying the minor alleles (T of usf1s1 and A of usf1s2) had lower 2 h FFA (p = 0.01) and a larger decrease in FFA concentrations during the OGTT (p = 0.02). Antilipolytic insulin sensitivity was higher in these individuals (p = 0.03). No interaction of the usf1s1 C > T and usf1s2 G > A SNPs with the -60C > G SNP in HSL on antilipolytic insulin sensitivity was detected. Liver fat, measured by (1)H magnetic resonance spectroscopy, was elevated only in subjects who were both homozygous for the major alleles of usf1s1 and usf1s2 and carriers of the T allele of the -514C > T SNP in LIPC (p = 0.01). In conclusion, subjects carrying the T allele of SNP usf1s1 and the A allele of SNP usf1s2 have a higher antilipolytic insulin sensitivity. Moreover, both SNPs may interact with the -514C > T SNP in LIPC to determine liver fat.

The adipose tissue triglyceride lipase ATGL/PNPLA2 is downregulated by insulin and TNF-alpha in 3T3-L1 adipocytes and is a target for transactivation by PPARgamma

The minimal adipose phenotype of hormone-sensitive lipase (HSL)-null mice suggested that other hormonally responsive lipase(s) were present in adipocytes. Recent studies have characterized a new adipose tissue triglyceride lipase, ATGL/PNPLA2/destnutrin/iPLA2zeta/TTS2.2 (ATGL). We had previously cloned a novel adipose-enriched transcript by differential screening and recently determined its identity with murine ATGL. We report here on the regulation of ATGL by TNF-alpha and insulin in 3T3-L1 adipocytes and identify ATGL as a target for transcriptional activation by the key adipogenic transcription factor PPARgamma. Insulin at 100 nM resulted in a marked decrease in ATGL transcript that was effectively blocked by inhibitors for PI 3-kinase and p70 ribosomal protein S6 kinase. TNF-alpha treatment decreased ATGL transcript in a time-dependent manner that paralleled TNF-alpha downregulation of PPARgamma with a maximal decrease noted by 6 h. TNF-alpha effects on ATGL were attenuated by pretreatment with PD-98059, LY-294002, or rapamycin, suggesting involvement of the p44/42 MAP kinase, PI 3-kinase, and p70 ribosomal protein S6 kinase signals. To study transcriptional regulation of ATGL, we cloned 2,979 bp of the murine ATGL 5'-flanking region. Compared with promoterless pGL2-Basic, the -2979/+21 ATGL luciferase construct demonstrated 120- and 40-fold increases in activity in white and brown adipocytes, respectively. Luciferase reporter activities for a series of eight ATGL promoter deletions revealed that the -928/+21, -1738/+21, -1979/+21, and -2979/+21 constructs were transactivated by PPARgamma. Our findings identify the novel lipase ATGL to be a target gene for TNF-alpha and insulin action in adipocytes and reveal that it is subject to transcriptional control by PPARgamma-mediated signals.

Identification of USF2 as a key regulator of Runx2 expression in mouse pluripotent mesenchymal D1 cells

Runx2 is one of the most important transcription factors directing the osteogenesis of mesenchymal stem cells and osteoblastic functions. It is likely that the factors controlling Runx2 expression would trigger the early steps of osteoblast differentiation. By using a reporter gene assay for 4.5 kb Runx2 promoter, it was found that the first 305 bp of Runx2 promoter are active in D1 cells. Within this region, electromobility shift assays (EMSAs) delineated a 6 bp of CACATG bound specifically by the proteins from D1 cell nuclear extract. Antibody super-shift and DNA-coupling magnetic bead pull-down assay indicated that the protein bound to this sequence is USF2. Site-specific mutagenesis revealed that this sequence contributed to the activity of 305 bp Runx2 promoter. Thus, we suggest that USF2 might be one of the regulators for the expression of the Runx2 gene in D1 cells.

Familial combined hyperlipidemia: upstream transcription factor 1 and beyond

PURPOSE OF REVIEW

Familial combined hyperlipidemia is a common complex disease that accounts for up to 20% of premature coronary heart disease. The upstream transcription factor 1, located on 1q21, was recently shown to be linked and associated with familial combined hyperlipidemia in Finnish families. Upstream transcription factor 1 is the first gene identified by positional cloning for familial combined hyperlipidemia. Replication studies are critical to investigation of complex diseases because only they can verify the importance of the original findings. We review recent studies that examine the genetic contribution and functional consequence of upstream transcription factor 1 variants to familial combined hyperlipidemia and type 2 diabetes mellitus. Aiming beyond upstream transcription factor 1, we also evaluate novel strategies that have made it possible to globally examine the genome and the transcriptome.

RECENT FINDINGS

Three independent studies support the role of upstream transcription factor 1 in familial combined hyperlipidemia. The results for type 2 diabetes mellitus and the metabolic syndrome have been less conclusive highlight novel strategies for gene identification in familial combined hyperlipidemia.

SUMMARY

Currently, genetic and functional evidence is supportive of a role for upstream transcription factor 1 in the etiology of familial combined hyperlipidemia and its component traits, although the mechanism of causality still remains largely unknown.

Unraveling the complex genetics of familial combined hyperlipidemia

Familial combined hyperlipidemia (FCHL) constitutes a substantial risk factor for atherosclerosis since it is observed in about 20% of coronary heart disease (CHD) patients under 60 years. FCHL, characterized by elevated levels of total cholesterol (TC) and triglycerides (TGs), or both, is also one of the most common familial hyperlipidemias with a prevalence of 1%-6% in Western populations. Numerous studies have been performed to identify genes contributing to FCHL. The recent linkage and association studies and their replications are beginning to elucidate the genetic variations underlying the susceptibility to FCHL. Three chromosomal regions on 1q21-23, 11p and 16q22-24.1 have been replicated in different study samples, offering targets for gene hunting. In addition, several candidate gene studies have replicated the influence of the lipoprotein lipase (LPL) gene and apolipoprotein A1/C3/A4/A5 (APOA1/C3/A4/A5) gene cluster in FCHL. Recently, the linked region on chromosome 1q21 was successfully fine-mapped and the upstream transcription factor 1 (USF1) gene identified as the underlying gene for FCHL. This finding has now been replicated in independent FCHL samples. However, the total number of variants, the risk related to each variant and their relative contributions to the disease susceptibility are not known yet.

Cell type-dependent regulation of the hypoxia-responsive plasminogen activator inhibitor-1 gene by upstream stimulatory factor-2

Transcriptional regulation of the plasminogen activator inhibitor type-1 (PAI-1) gene is an important issue since PAI-1 plays a crucial role in various pathological conditions. The transcription factor USF-2 was shown to be a negative regulator for rat PAI-1 expression, and therefore it was the aim of this study to evaluate the role of USF-2 for human PAI-1 expression. We found in human hepatoma cells (HepG2) that USF-2 induced human PAI-1 expression via two classical E-boxes and the hypoxia-responsive element (HRE) within the promoter. Gel-shift analyses showed that E-box 4 and E-box 5 bound USFs, and although the HRE contributed to the USF-dependent effects, it did not bind them. By contrast, USF-2 inhibited PAI-1 promoter activity in primary rat hepatocytes suggesting that PAI-1 expression depends on either the promoter context or USF activity which might be cell type-specific. Cotransfection of human or rat PAI-1 promoter luciferase constructs with expression vectors for wild-type USF-2 or USF-2 mutants in human HepG2 and rat H4IIE cells as well as in primary rat hepatocytes revealed that the effects of USF on PAI-1 expression depend on the cell type rather than the promoter context and that the USF-specific region domain of USF accounts for the observed cell type-specific effects.

Upstream stimulatory factor 1 associated with familial combined hyperlipidemia, LDL cholesterol, and triglycerides

Positive evidence has been reported for linkage and association between the upstream stimulatory factor 1 gene (USF1) and familial combined hyperlipidemia (FCHL). We genotyped the two most positive single-nucleotide polymorphisms (SNPs) (usf1s1: rs3737787 and usf1s2: rs2073658) from previous studies in a large family sample. This sample included 2,195 subjects in 87 Utah pedigrees ascertained for early death due to coronary heart disease (CHD), early strokes, or early onset hypertension. There were a total of 262 relative pairs in these families with FCHL. In the full family sample, FCHL was associated with usf1s1 (P = 0.02). Triglyceride and LDL cholesterol defined qualitatively or quantitatively were also associated with usf1s1 (P = 0.02-0.05). Results were strengthened for qualitative and quantitative triglyceride and LDL cholesterol when data from males only was analyzed, revealing associations for usf1s1 (P = 0.001-0.02), usf1s2 (P = 0.02-0.05) and the haplotype of these two SNPs (P = 0.01-0.04). The strongest results were in the subset of subjects from families ascertained for premature stroke or hypertension, rather than those ascertained for premature CHD. This study replicates the involvement of USF1 in FCHL and related lipid traits in a family sample not ascertained for FCHL.

Insulin therapy in pregnancy complicated by diabetes: are insulin analogs a new tool?

It has been demonstrated that good metabolic control maintained throughout pregnancy can reduce maternal and fetal complications in diabetes. To achieve good metabolic control, before conception and throughout pregnancy, insulin therapy needs to be optimized, and, in this context, the new insulins currently on the market may help. We therefore review here what is known about the potential benefits and risks related to the use of these new insulins in pregnancy. Clinical and experimental data on insulin lispro strongly suggest that lispro does not have adverse maternal or fetal effects during pregnancy in women with preexisting diabetes, and also that its use in these women results in improved glycemic control, fewer hypoglycemic episodes, and improved patient satisfaction. In women with gestational diabetes mellitus (GDM), the use of insulin lispro is efficient in reducing postprandial hyperglycemia and some neonatal features related to hyperglycemia, thus stressing its usefulness in this condition. As for insulin aspart, clinical data on GDM patients shows the same efficacy as insulin lispro in lowering postprandial hyperglycemia, indicating that insulin aspart may be used in GDM when this condition is characterized by postprandial hyperglycemia. The results of a multicentric study now in progress on the efficacy and safety of insulin aspart in type 1 pregnant diabetic patients will definitely be useful in establishing whether this insulin is safe in pregnancy. For the moment, the use of insulin glargine during pregnancy is not recommended owing to the lack of data on maternal and fetal effects.

USF1 implicated in the aetiology of familial combined hyperlipidaemia and the metabolic syndrome

The upstream stimulatory factor (USF) proteins are ubiquitously expressed and, as such, represent unusual candidates for involvement in disorders of carbohydrate and lipid metabolism. Nonetheless, a recent study has reported an association between specific alleles of USF1 and familial combined hyperlipidaemia, a common disorder that substantially increases the risk of premature atherosclerotic cardiovascular disease. USF1 might, therefore, also contribute to the metabolic syndrome. The use of chromatin immunoprecipitation methodologies combined with promoter microarray assays will help to define the transcriptional networks that underlie whole-body glucose and lipid homeostasis.

Adipose tissue gene expression in obese subjects during low-fat and high-fat hypocaloric diets

AIMS/HYPOTHESIS

Adaptation to energy restriction is associated with changes in gene expression in adipose tissue. However, it is unknown to what extent these changes are dependent on the energy restriction as such or on the macronutrient composition of the diet.

METHODS

We determined the levels of transcripts for 38 genes that are expressed in adipose tissue and encode transcription factors, enzymes, transporters and receptors known to play critical roles in the regulation of adipogenesis, mitochondrial respiration, and lipid and carbohydrate metabolism. Two groups of 25 obese subjects following 10-week hypocaloric diet programmes with either 20-25 or 40-45% of total energy derived from fat were investigated. Levels of mRNA were measured by performing real-time RT-PCR on subcutaneous fat samples obtained from the subjects before and after the diets.

RESULTS

The two groups of subjects lost 7 kg over the duration of the diets. Ten genes were regulated by energy restriction; however, none of the genes showed a significantly different response to the diets. Levels of peroxisome proliferator-activated receptor gamma co-activator 1alpha mRNA were increased, while the expression of the genes encoding leptin, osteonectin, phosphodiesterase 3B, hormone-sensitive lipase, receptor A for natriuretic peptide, fatty acid translocase, lipoprotein lipase, uncoupling protein 2 and peroxisome proliferator-activated receptor gamma was decreased. Clustering analysis revealed new potential coregulation of genes. For example, the expression of the genes encoding the adiponectin receptors may be regulated by liver X receptor alpha.

CONCLUSIONS/INTERPRETATION

In accordance with the comparable loss of fat mass produced by the two diets, this study shows that energy restriction and/or weight loss rather than the ratio of fat: carbohydrate in a low-energy diet is of importance in modifying the expression of genes in the human adipose tissue.

Metabolism of lipids in human white adipocyte

Adipose tissue is considered as the body's largest storage organ for energy in the form of triacylglycerols, which are mobilized through lipolysis process, to provide fuel to other organs and to deliver substrates to liver for gluconeogenesis (glycerol) and lipoprotein synthesis (free fatty acids). The release of glycerol and free fatty acids from human adipose tissue is mainly dependent on hormone-sensitive lipase which is intensively regulated by hormones and agents, such as insulin (inhibition of lipolysis) and catecholamines (stimulation of lipolysis). A special attention is paid to the recently discovered perilipins which could regulate the activity of the lipase hormono-sensible. Most of the plasma triacylglycerols are provided by dietary lipids, secreted from the intestine in the form of chylomicron or from the liver in the form of VLDL. Released into circulation as non-esterified fatty acids by lipoprotein lipase, those are taken up by adipose tissue via specific plasma fatty acid transporters (CD36, FATP, FABPpm) and used for triacylglycerol synthesis. A small part of triacylglycerols is synthesized into adipocytes from carbohydrates (lipogenesis) but its regulation is still debated in human. Physiological factors such as dieting/fasting regulate all these metabolic pathways, which are also modified in pathological conditions e.g. obesity.

Hormone-sensitive lipase--new roles for an old enzyme

Although described initially as an intracellular adipocyte-specific triacylglycerol lipase, it is now clear that HSL (hormone-sensitive lipase) is expressed in multiple tissues and plays a number of roles in lipid metabolism, including that of a neutral cholesteryl ester hydrolase. The major isoform is a single polypeptide with a molecular mass of approx. 84 kDa and which comprises three major domains: a catalytic domain, a regulatory domain encoding several phosphorylation sites and an N-terminal domain involved in protein-protein and protein-lipid interactions. The activity of HSL is regulated acutely by several mechanisms, including reversible phosphorylation by a number of different protein kinases, translocation to different sites within the cell and interaction with a number of proteins, some of which may serve to direct the inhibitory products of HSL away from the protein. It is also apparent from work with HSL null mice that more than one enzyme species may be classified as a hormone-sensitive lipase. The possible presence of HSL in macrophages remains controversial, and the role of the protein in pancreatic beta-cells has yet to be fully elucidated. Altered expression of HSL in different cell types may be associated with a number of pathological states, including obesity, atherosclerosis and Type II diabetes.

Variation in USF1 shows haplotype effects, gene : gene and gene : environment associations with glucose and lipid parameters in the European Atherosclerosis Research Study II

Upstream stimulatory factor 1 (USF 1), is a transcription factor controlling expression of several genes involved in lipid and glucose homeostasis and co-localizes with familial combined hyperlipidemia (FCHL) and type 2 diabetes on chromosome 1q22-23. We sequenced USF1 in 24 UK FCHL probands, but found no rare or common cSNPs. Three common intronic single nucleotide ploymorphisms (SNP), 306A>G, 475C>T and 1748C>T, were identified and their association was examined with fasting and postprandial lipids and after an oral glucose tolerance test (OGTT) in the European Atherosclerosis Research Study II offspring study. There were no significant differences in allelic frequencies of the SNPs between cases and controls. Individually none of the SNPs showed significant associations with any parameter. In haplotype analysis, compared with other haplotypes, 475C/1748T showed significantly higher and 475T/1748T showed lower peak glucose (P=0.004 and 0.07, respectively) during the OGTT. There was significant case-control heterogeneity in the interaction of genotype with body mass index, on fasting low density lipoprotein with 306A>G and 1748C>T, and on borderline significance with fasting glucose with 475C>T (P=0.002, 0.0007 and 0.015, respectively). Furthermore, 475C>T showed interaction with both HSL-60C>G (case-control heterogeneity P=0.0002) on AUC TG and APOC3 -482C>T on plasma apoE levels (P=0.0012). Thus, in these healthy young men, variation in USF1 was the influencing feature of both glucose and lipid homeostasis showing case-control heterogeneity.

Specific preservation of biosynthetic responses to insulin in adipose tissue may contribute to hyperleptinemia in insulin-resistant obese mice

Obesity is characterized by whole-body insulin resistance, yet the expression of many insulin-stimulated genes, including leptin, is elevated in obesity. These observations suggest that insulin resistance may depend on tissue type and gene. To address this hypothesis, we examined the regulation of immediate-early gene expression in liver and adipose tissue after injection of insulin and glucose, in lean insulin-sensitive, and in A(y)/a obese insulin-sensitive and obese insulin-resistant mice. Expression of hepatic jun-B mRNA was robustly increased after insulin injection in lean insulin-sensitive a/a mice and insulin-sensitive A(y)/a mice. In contrast, induction of hepatic jun-B and c-fos gene expression by insulin was markedly attenuated in obese insulin-resistant mice. Surprisingly, induction of adipose jun-B and c-fos gene expression by insulin was markedly enhanced in obese insulin-resistant mice. Furthermore, the expressions of jun-B and leptin were also enhanced in insulin-resistant mice after injection of glucose. Leptin mRNA was positively correlated with blood glucose levels and jun-B mRNA in lean but not insulin-resistant mice. Multiple regression analysis indicated that the correlation between leptin mRNA and jun-B mRNA was significant even after removing the effect of blood glucose, but the correlation between leptin mRNA and glucose was no longer significant after removing the effect of jun-B mRNA. These data suggest that some impairments in biosynthetic responses to insulin are manifest primarily in the liver, leading to hyperinsulinemia and stimulating the expression of some adipose insulin-stimulated genes, including leptin. These studies demonstrate the utility of immediate-early gene expression in the analysis of biosynthetic mechanisms of insulin resistance.

Changes in glycemia by leptin administration or high- fat feeding in rodent models of obesity/type 2 diabetes suggest a link between resistin expression and control of glucose homeostasis

Resistin is an adipose-derived hormone that has been proposed as a link among obesity, insulin resistance, and diabetes. In agreement with a role of resistin in insulin resistance, the administration of recombinant resistin led to glucose intolerance in mice and impaired insulin action in rat liver. However, the regulation of resistin expression by physiological conditions, hormones, or agents known to modulate insulin sensitivity does not always support the association between resistin and obesity-induced insulin resistance. In the present study we investigated the effects of leptin administration on adipose resistin expression in insulin-resistant and obese ob/ob mice. We show that the expression of resistin mRNA and protein in adipose tissue is lower in ob/ob than in wild-type control mice, in agreement with the reduced adipocyte resistin mRNA level reported in several models of obesity. Leptin administration in ob/ob mice resulted in improvement of insulin sensitivity concomitant with a decrease in resistin gene expression. The lack of effect of leptin on resistin in db/db mice indicated that the leptin inhibitory action on resistin expression requires the long leptin receptor isoform. In addition, we demonstrated that the effect of leptin on resistin expression was centrally mediated. High-fat feeding in C57BL/6J wild-type mice, which is known to induce the development of obesity and insulin resistance, produced an increase in resistin expression. Interestingly, in both ob/ob and high fat-fed mice we obtained a striking positive correlation between glycemia and resistin gene expression. In conclusion, our results demonstrate that leptin decreases resistin expression and suggest that resistin may influence glucose homeostasis.

A Novel Hormone-sensitive Lipase Isoform Expressed in Pancreatic β-Cells

Hormone-sensitive lipase (HSL) is a key enzyme in fatty acid mobilization in many cell types. Two isoforms of HSL are known to date, namely HSL(adi) (84 kDa in rat) and HSL(tes) (130 kDa in rat). These are encoded by the same gene, with exons 1-9 encoding the parts that are common to both and an additional 5'-exon encoding the additional amino acids in HSL(tes). HSL of various tissues, among these the islet of Langerhans, is larger than HSL(adi), but not as large as HSL(tes), indicating that there may be other 5'-coding exons. Here we describe the molecular basis for a novel 89-kDa HSL isoform that is expressed in beta-cells, adipocytes, adrenal glands, and ovaries in the rat and that is encoded by exons 1-9 and exon A, which is spliced to exon 1 and thereby introducing an upstream start codon. The additional 5'-base pairs encode a 43-amino acid peptide, which is highly positively charged. Conglomerates of HSL molecules are in close association with the secretory granules of the beta-cell, as determined by immunoelectron microscopy with antibodies targeting two separate regions of HSL. We have also determined that the human genomic sequence upstream of exon A has promoter activity in INS-1 cells as well as glucose sensing capability, mediating an increase in expression at high glucose concentration. The minimal promoter is present within 170 bp from the transcriptional start site and maximal glucose responsiveness is conferred by sequence within 850 bp from the transcriptional start site.

Cha, a basic helix-loop-helix transcription factor involved in the regulation of upstream stimulatory factor activity

We report here the characterization of Cha, a transcription factor of the basic helix-loop-helix (bHLH) family. The basic region of Cha shares DNA-interacting amino acids with members of class C bHLH transcription factors. In addition, the HLH region of Cha presents a Myc-type dimerization domain signature required for heterodimer formation between members of this class. Cha protein and mRNA were ubiquitously expressed in many human tissues. Electrophoretic mobility shift assays showed that Cha and upstream stimulatory factor (USF)-1 formed a complex that specifically bound to E-box DNA elements. Moreover, pull-down and co-immunoprecipitation experiments showed an interaction between Cha and USF-1. Cha did not bind to E-box DNA elements and required USF-1 for protein-DNA complex formation. Moreover, Cha inhibited USF-1-stimulated transcription of CD2 (a USF-1-dependent gene) and E-box promoter reporter plasmids. Chromatin immunoprecipitation assays showed that Cha occupied the CD2 promoter in resting, but not in mitogen-stimulated, T cells. Finally, Cha mRNA and protein expression were high in resting T cells and absent in mitogen-activated T cells and inversely correlated with CD2 expression. Contrarily, overexpression of Cha in T cells significantly reduced CD2 expression. In summary, our results indicated that Cha is a new bHLH transcription factor that negatively regulates USF-dependent transcription.

Acquirement of brown fat cell features by human white adipocytes

Obesity, i.e. an excess of white adipose tissue (WAT), predisposes to the development of type 2 diabetes and cardiovascular disease. Brown adipose tissue is present in rodents but not in adult humans. It expresses uncoupling protein 1 (UCP1) that allows dissipation of energy as heat. Peroxisome proliferator-activated receptor gamma (PPAR gamma) and PPAR gamma coactivator 1 alpha (PGC-1 alpha) activate mouse UCP1 gene transcription. We show here that human PGC-1 alpha induced the activation of the human UCP1 promoter by PPAR gamma. Adenovirus-mediated expression of human PGC-1 alpha increased the expression of UCP1, respiratory chain proteins, and fatty acid oxidation enzymes in human subcutaneous white adipocytes. Changes in the expression of other genes were also consistent with brown adipocyte mRNA expression profile. PGC-1 alpha increased the palmitate oxidation rate by fat cells. Human white adipocytes can therefore acquire typical features of brown fat cells. The PPAR gamma agonist rosiglitazone potentiated the effect of PGC-1 alpha on UCP1 expression and fatty acid oxidation. Hence, PGC-1 alpha is able to direct human WAT PPAR gamma toward a transcriptional program linked to energy dissipation. However, the response of typical white adipocyte targets to rosiglitazone treatment was not altered by PGC-1 alpha. UCP1 mRNA induction was shown in vivo by injection of the PGC-1 alpha adenovirus in mouse white fat. Alteration of energy balance through an increased utilization of fat in WAT may be a conceivable strategy for the treatment of obesity.