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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Lack of leptin (ob) protein causes obesity in mice. The leptin gene product is important for normal regulation of appetite and metabolic rate and is produced exclusively by adipocytes. Leptin mRNA was induced during the adipose conversion of 3T3-L1 cells, which are useful for studying adipocyte differentiation and function under controlled conditions. We studied leptin regulation by antidiabetic thiazolidinedione compounds, which are ligands for the adipocyte-specific nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) that regulates the transcription of other adipocyte-specific genes. Remarkably, leptin gene expression was dramatically repressed within a few hours after thiazolidinedione treatment. The ED50 for inhibition of leptin expression by the thiazolidinedione BRL49653 was between 5 and 50 nM, similar to its Kd for binding to PPARgamma. The relatively weak, nonthiazolidinedione PPAR activator WY 14,643 also inhibited leptin expression, but was approximately 1000 times less potent than BRL49653. These results indicate that antidiabetic thiazolidinediones down-regulate leptin gene expression with potencies that correlate with their abilities to bind and activate PPARgamma.
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PMID:Antidiabetic thiazolidinediones inhibit leptin (ob) gene expression in 3T3-L1 adipocytes. 865 Jan 71

The identification of high-affinity ligands for PPAR gamma has revealed the role of this receptor as the molecular target for the antidiabetic activity of the thiazolidinediones. The surprising observation that agonists of an adipogenic transcription factor reverse the obesity-associated disease of diabetes highlights the power of using potent and selective ligands to study receptor-mediated biology. Similarly, the observation that PGD2 and its cyclopentenone metabolites compounds are microM PPAR ligands suggests that these receptors may have a physiological role in mediating prostaglandin signaling in the spleen.
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PMID:Discovery of ligands for the nuclear peroxisome proliferator-activated receptors. 899 50

The peroxisome proliferator activated receptor (PPAR gamma) plays a key role in adipogenesis and adipocyte gene expression and is the receptor for the thiazolidinedione class of insulin-sensitizing drugs. The tissue expression and potential for regulation of human PPAR gamma gene expression in vivo are unknown. We have cloned a partial human PPAR gamma cDNA, and established an RNase protection assay that permits simultaneous measurements of both PPAR gamma1 and PPAR gamma2 splice variants. Both gamma1 and gamma2 mRNAs were abundantly expressed in adipose tissue. PPAR gamma1 was detected at lower levels in liver and heart, whereas both gamma1 and gamma2 mRNAs were expressed at low levels in skeletal muscle. To examine the hypothesis that obesity is associated with abnormal adipose tissue expression of PPAR gamma, we quantitated PPARgamma mRNA splice variants in subcutaneous adipose tissue of 14 lean and 24 obese subjects. Adipose expression of PPARgamma 2 mRNA was increased in human obesity (14.25 attomol PPAR gamma2/18S in obese females vs 9.9 in lean, P = 0.003). This increase was observed in both male and females. In contrast, no differences were observed in PPAR gamma1/18S mRNA expression. There was a strong positive correlation (r = 0.70, P < 0.001) between the ratio of PPAR gamma2/gamma1 and the body mass index of these patients. We also observed sexually dimorphic expression with increased expression of both PPAR gamma1 and PPAR gamma2 mRNAs in the subcutaneous adipose tissue of women compared with men. To determine the effect of weight loss on PPAR gamma mRNA expression, seven additional obese subjects were fed a low calorie diet (800 Kcal) until 10% weight loss was achieved. Mean expression of adipose PPAR gamma2 mRNA fell 25% (P = 0.0250 after a 10% reduction in body weight), but then increased to pretreatment levels after 4 wk of weight maintenance. Nutritional regulation of PPAR gamma1 was not seen. In vitro experiments revealed a synergistic effect of insulin and corticosteroids to induce PPAR gamma expression in isolated human adipocytes in culture. We conclude that: (a) human PPAR gamma mRNA expression is most abundant in adipose tissue, but lower level expression of both splice variants is seen in skeletal muscle; to an extent that is unlikely to be due to adipose contamination. (b) RNA derived from adipose tissue of obese humans has increased expression of PPAR gamma 2 mRNA, as well as an increased ratio of PPAR gamma2/gamma1 splice variants that is proportional to the BMI; (c) a low calorie diet specifically down-regulates the expression of PPAR gamma2 mRNA in adipose tissue of obese humans; (d) insulin and corticosteroids synergistically induce PPAR gamma mRNA after in vitro exposure to isolated human adipocytes; and (e) the in vivo modulation of PPAR gamma2 mRNA levels is an additional level of regulation for the control of adipocyte development and function, and could provide a molecular mechanism for alterations in adipocyte number and function in obesity.
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PMID:Peroxisome proliferator-activated receptor gene expression in human tissues. Effects of obesity, weight loss, and regulation by insulin and glucocorticoids. 915 84

We determined the chromosomal localization and partial genomic structure of the coding region of the human PPAR gamma gene (hPPAR gamma), a nuclear receptor important for adipocyte differentiation and function. Sequence analysis and long PCR of human genomic DNA with primers that span putative introns revealed that intron positions and sizes of hPPAR gamma are similar to those previously determined for the mouse PPAR gamma gene[13]. Fluorescent in situ hybridization localized hPPAR gamma to chromosome 3, band 3p25. Radiation hybrid mapping with two independent primer pairs was consistent with hPPAR gamma being within 1.5 Mb of marker D3S1263 on 3p25-p24.2. These sequences of the intron/exon junctions of the 6 coding exons shared by hPPAR gamma 1 and hPPAR gamma 2 will facilitate screening for possible mutations. Furthermore, D3S1263 is a suitable polymorphic marker for linkage analysis to evaluate PPAR gamma's potential contribution to genetic susceptibility to obesity, lipoatrophy, insulin resistance, and diabetes.
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PMID:Chromosomal localization and partial genomic structure of the human peroxisome proliferator activated receptor-gamma (hPPAR gamma) gene. 916 28

The hypothalamic disorders of obesity include hyperphagia, a low central orthosympathetic tone (with reduced thermogenesis), vagal hyperinsulinism, low serotonin efficacy, a hyperactive hypothalamo-hypophyseal-adrenal axis, a hypoactive GHRH-GH-IGF axis and hypogonadism of central origin. Hyperlipogenesis, glucose intolerance and excessive gluconeogenesis are secondary features. Most frequently the hypothalamic ARC reacts poorly to the leptin hypersecreted by adipose tissue, so that the local synthesis of NPY is unchecked. Fortunately, two prostaglandins derived from dietary arachidonic acid bind fat cell PPAR gamma and hepatic PPAR alpha. Both nuclear proteins are phosphorylated through an insulin pathway, thereby inhibiting the expression of genes favoring obesity and stimulating that of genes accelerating fatty acid oxidation. The array of dietetic and pharmacologic tools considered today is analyzed.
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PMID:[Molecular endocrinology of hereditary obesity]. 949 39

Thiazolidinediones (TZDs) such as BRL 49653 are a class of antidiabetic agents that are agonists for the peroxisome proliferator-activated nuclear receptor (PPAR-gamma2). In vivo, TZDs reduce circulating levels of free fatty acids (FFAs) and ameliorate insulin resistance in individuals with obesity and NIDDM. Adipocyte production of TNF-alpha is proposed to play a role in the development of insulin resistance, and because BRL 49653 has been shown to antagonize some of the effects of TNF-alpha, we examined the effects of TNF-alpha and BRL 49653 on adipocyte lipolysis. After a 24-h incubation of TNF-alpha (10 ng/ml) with 3T3-L1 adipocytes, glycerol release increased by approximately 7-fold, and FFA release increased by approximately 44-fold. BRL 49653 (10 pmol/l) reduced TNF-alpha-induced glycerol release by approximately 50% (P < 0.001) and FFA release by approximately 90% (P < 0.001). BRL 49653 also reduced glycerol release by approximately 50% in adipocytes pretreated for 24 h with TNF-alpha. Prolonged treatment (5 days) with either BRL 49653 or another PPAR-gamma2 agonist, 15-d delta-12,14-prostaglandin J2 (15-d deltaPGJ2), blocked TNF-alpha-induced glycerol release by approximately 100%. Catecholamine (isoproterenol)-stimulated lipolysis was unaffected by BRL 49653 and 15-d deltaPGJ2. BRL 49653 partially blocked the TNF-alpha-mediated reduction in protein levels of hormone-sensitive lipase and perilipin A, two proteins involved in adipocyte lipolysis. These data suggest a novel pathway that may contribute to the ability of the TZDs to reduce serum FFA and increase insulin sensitivity.
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PMID:BRL 49653 blocks the lipolytic actions of tumor necrosis factor-alpha: a potential new insulin-sensitizing mechanism for thiazolidinediones. 956 6

Significant advances have been made recently toward understanding the molecular events that regulate adipocyte differentiation. In vitro models of adipogenesis, such as the 3T3-L1 and F-442A preadipocyte cell lines have proven to be an invaluable resource in elucidating mechanisms of adipocyte differentiation. Subject to modulation by hormonal, dietary, and genetic influences, the differentiation program now appears to be distinctly controlled through the coordinate regulation of transcription factors that predominantly include members of the C/EBP and PPAR families. Increased understanding of these critical factors and how they are regulated will provide insights into adipose tissue development as well as treatment of obesity.
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PMID:Molecular regulation of adipocyte differentiation. 1035 23

The peroxisomal 3-oxoacyl-CoA thiolase (thiolase) is the last enzyme involved in the beta-oxidation of fatty acids. The enzyme cleaves long chain fatty acyl-CoA to generate acetyl-CoA and shortened acyl-CoA. The enzyme is nuclear encoded, synthesized in the cytoplasm and transported into peroxisomes. The thiolase B gene is inducible by the peroxisome proliferator compounds, like other genes involved in beta-oxidation of fatty acids in peroxisomes. The importance of studying thiolase is that it generates acetyl-CoA which is the precursor for the synthesis of molecules like cholesterol and fatty acids. The structural and functional analysis of thiolase at molecular level may add to the knowledge of fatty acid metabolism and further the obesity phenomenon. It is known that several genes mediate lipid homeostasis in target organs like liver, adipose tissue and are regulated by peroxisome proliferator activated receptors (PPAR alpha and PPAR gamma). To elucidate the mechanism of induction of rat liver thiolase B gene, an upstream 2.8 kb fragment containing promoter element has been subcloned and partially sequenced. The sequence analysis revealed a putative PPRE (Peroxisome Proliferator Response Element) of AGACCT T TGAACC sequence at -681 to -668 [Kliever et al. (1992) Nature 358:771-774]. By transient expression of a luciferase reporter gene in HeLa cells, we conclude that the identified PPRE could be functional in induction of thiolase B gene, but other sequences of genes might be involved.
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PMID:Studies on regulation of the peroxisomal beta-oxidation at the 3-ketothiolase step. Dissection of the rat liver thiolase B gene promoter. 1070 52

The metabolic capacity of skeletal muscle plays a significant role for insulin sensitivity and the blood lipid profile. The metabolic capacity of the muscle is a function of the individual's physical activity level. This is also true for the content of type IIx muscle fibres, which is reduced and the number of capillaries, which is elevated with muscle usage. Several of these skeletal muscle features are risk factors for or linked with life style-induced diseases such as type II diabetes, hypertension, hyperlipidaemia and obesity. This central role of the skeletal muscle and its functional metabolic capacity for life style diseases highlights the importance of people maintaining daily physical activity. This article focuses on the link between the metabolic capacity of skeletal muscle and the metabolic syndrome and briefly discusses possible metabolic explanations for this relationship. An important aspect is that when skeletal muscle has a high capacity for lipid oxidation more saturated fatty acids are oxidized and more unsaturated fatty acids are built into the phospholipid fraction of the plasma membrane, giving it more fluidity and improved insulin sensitivity. Moreover, the article points at the role of these fatty acids in activating genes via the PPAR-receptor system essential for enzyme and transport proteins in the lipid metabolism.
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PMID:[Metabolic capacity of skeletal muscles and health]. 1077 58

PPARs are transcription factors belonging to the super family of hormonal receptors. Their activity is regulated by fibrates, thiazolidinediones, certain anti inflammatory drugs and fatty acid derivatives, present in food. PPAR isoforms play a central role in lipid homeostasis, regulating anabolic (PPAR gamma) and catabolic (PPAR alpha) pathways of lipid metabolism. Additionally, these receptors participate in glucose homeostasis, influence cellular proliferation and differentiation and participate in inflammatory processes. The effects of PPARs on oxidative substrate partitioning suggests that they have a relevant role in the development of obesity and insulin resistance.
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PMID:[Molecular nutrition, role of the PPAR system in lipidic metabolism and its importance in obesity and diabetes mellitus]. 1096 63


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