PPAR␥ is a member of the PPAR subfamily of nuclear receptors. In this work, the structure of the human PPAR␥ cDNA and gene was determined, and its promoters and tissue-specific expression were functionally characterized. Similar to the mouse, two PPAR isoforms, PPAR␥1 and PPAR␥2, were detected in man. The relative expression of human PPAR␥ was studied by a newly developed and sensitive reverse transcriptasecompetitive polymerase chain reaction method, which allowed us to distinguish between PPAR␥1 and ␥2 mRNA. In all tissues analyzed, PPAR␥2 was much less abundant than PPAR␥1. Adipose tissue and large intestine have the highest levels of PPAR␥ mRNA; kidney, liver, and small intestine have intermediate levels; whereas PPAR␥ is barely detectable in muscle. This high level expression of PPAR␥ in colon warrants further study in view of the well established role of fatty acid and arachidonic acid derivatives in colonic disease. Similarly as mouse PPAR␥s, the human PPAR␥s are activated by thiazolidinediones and prostaglandin J and bind with high affinity to a PPRE. The human PPAR␥ gene has nine exons and extends over more than 100 kilobases of genomic DNA. Alternate transcription start sites and alternate splicing generate the PPAR␥1 and PPAR␥2 mRNAs, which differ at their 5 -ends. PPAR␥1 is encoded by eight exons, and PPAR␥2 is encoded by seven exons. The 5 -untranslated sequence of PPAR␥1 is comprised of exons A1 and A2, whereas that of PPAR␥2 plus the additional PPAR␥2-specific N-terminal amino acids are encoded by exon B, located between exons A2 and A1. The remaining six exons, termed 1 to 6, are common to the PPAR␥1 and ␥2. Knowledge of the gene structure will allow screening for PPAR␥ mutations in humans with metabolic disorders, whereas knowledge of its expression pattern and factors regulating its expression could be of major importance in understanding its biology.White adipose tissue is composed of adipocytes, which play a central role in lipid homeostasis and the maintenance of energy balance in vertebrates. These cells store energy in the form of triglycerides during periods of nutritional affluence and release it in the form of free fatty acids at times of nutritional deprivation. Excess of white adipose tissue leads to obesity (1-3), whereas its absence is associated with lipodystrophic syndromes (4). In contrast to the development of brown adipose tissue, which mainly takes place before birth, the development of white adipose tissue is the result of a continuous differentiation/development process throughout life (2, 5). During development, cells that are pluripotent become increasingly restricted to specific differentiation pathways. Adipocyte differentiation results from coordinate changes in the expression of several proteins, which are mostly involved in lipid storage and metabolism, that give rise to the characteristic adipocyte phenotype. The changes in expression of these specialized proteins are mainly the result of alterations in the transcription rates of their genes.Several transcription fac...

Obesity is a disorder of energy balance, indicating a chronic disequilibrium between energy intake and expenditure. Recently, the mouse ob gene, and subsequently its human and rat homologues, have been cloned. The ob gene product, leptin, is expressed exclusively in adipose tissue, and appears to be a signalling factor regulating body-weight homeostasis and energy balance. Because the level of ob gene expression might indicate the size of the adipose depot, we suggest that it is regulated by factors modulating adipose tissue size. Here we show that ob gene exhibits diurnal variation, increasing during the night, after rats start eating. This variation was linked to changes in food intake, as fasting prevented the cyclic variation and decreased ob messenger RNA. Furthermore, refeeding fasted rats restored ob mRNA within 4 hours to levels of fed animals. A single insulin injection in fasted animals increased ob mRNA to levels of fed controls. Experiments to control glucose and insulin independently in animals, and studies in primary adipocytes, showed that insulin regulates ob gene expression directly in rats, regardless of its glucose-lowering effects. Whereas the ob gene product, leptin, has been shown to reduce food intake and increase energy expenditure, our data demonstrate that ob gene expression is increased after food ingestion in rats, perhaps through a direct action of insulin on the adipocyte.

TGR5, a metabotropic receptor that is G-protein-coupled to the induction of adenylate cyclase, has been recognized as the molecular link connecting bile acids to the control of energy and glucose homeostasis. With the aim of disclosing novel selective modulators of this receptor and at the same time clarifying the molecular basis of TGR5 activation, we report herein the biological screening of a collection of natural occurring bile acids, bile acid derivatives, and some steroid hormones, which has resulted in the discovery of new potent and selective TGR5 ligands. Biological results of the tested collection of compounds were used to extend the structure-activity relationships of TGR5 agonists and to develop a binary classification model of TGR5 activity. This model in particular could unveil some hidden properties shared by the molecular shape of bile acids and steroid hormones that are relevant to TGR5 activation and may hence be used to address the design of novel selective and potent TGR5 agonists.