In this study, we defined the role of peroxisome proliferator-activated receptor ␤͞␦ (PPAR␦) in metabolic homeostasis by using subtype selective agonists. Analysis of rat L6 myotubes treated with the PPAR␦ subtype-selective agonist, GW501516, by the Affymetrix oligonucleotide microarrays revealed that PPAR␦ controls fatty acid oxidation by regulating genes involved in fatty acid transport, ␤-oxidation, and mitochondrial respiration. Similar PPAR␦-mediated gene activation was observed in the skeletal muscle of GW501516-treated mice. Accordingly, GW501516 treatment induced fatty acid ␤-oxidation in L6 myotubes as well as in mouse skeletal muscles. Administration of GW501516 to mice fed a high-fat diet ameliorated diet-induced obesity and insulin resistance, an effect accompanied by enhanced metabolic rate and fatty acid ␤-oxidation, proliferation of mitochondria, and a marked reduction of lipid droplets in skeletal muscles. Despite a modest body weight change relative to vehicle-treated mice, GW501516 treatment also markedly improved diabetes as revealed by the decrease in plasma glucose and blood insulin levels in genetically obese ob͞ob mice. These data suggest that PPAR␦ is pivotal to control the program for fatty acid oxidation in the skeletal muscle, thereby ameliorating obesity and insulin resistance through its activation in obese animals.obesity ͉ insulin resistance ͉ thermogenesis ͉ pancreatic ␤-cell ͉ PGC-1␣

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. PPARα is mainly expressed in the liver, where it activates fatty acid catabolism. PPARα activators have been used to treat dyslipidemia, causing a reduction in plasma triglyceride and elevation of high-density lipoprotein cholesterol. PPARδ is expressed ubiquitously and is implicated in fatty acid oxidation and keratinocyte differentiation. PPARδ activators have been proposed for the treatment of metabolic disease. PPARγ2 is expressed exclusively in adipose tissue and plays a pivotal role in adipocyte differentiation. PPARγ is involved in glucose metabolism through the improvement of insulin sensitivity and represents a potential therapeutic target of type 2 diabetes. Thus PPARs are molecular targets for the development of drugs treating metabolic syndrome. However, PPARs also play a role in the regulation of cancer cell growth. Here, we review the function of PPARs in tumor growth.

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In the rat platelet factor 4 (PF4) promoter, Ets motifs and GATA motifs are located at positions Ϫ880, Ϫ75 and Ϫ135, Ϫ30, respectively, and their motifs are found in the promoter region of most megakaryocyte protein genes. In order to investigate how the Ets and GATA motifs affect PF4 promoter activity, we constructed Ets and/or GATA motif mutant genes. A single disruption of either Ϫ75Ets, Ϫ135GATA, or Ϫ30GATA significantly reduced PF4 promoter activity, and double disruptions involving these motifs completely abolished it. Furthermore, gel-retardation assays revealed that Ets-1 and GATA-1 proteins from HEL and MEG-01 cells bound to the Ets motifs and GATA motifs, respectively. Cotransfection experiments showed that the overexpression of Ets-1 and/or GATA-1 enhanced the expression of the PF4 promoter reporter gene. These effects of Ets-1 and GATA-1 on PF4 promoter activity are additive. When HEL cells were treated with dimethylsulfoxide in order to induce differentiation into megakaryocytes, the mRNA level of ets-1 increased 10-fold, which might be directly correlated with the significant increase in PF4 mRNA level induced by dimethylsulfoxide. All these results strongly suggest that both Ets-1 and GATA-1 play key roles in the positive regulation of PF4 gene expression.

Lipin 1 plays a crucial role in lipid metabolism in adipose tissue, skeletal muscle, and liver. Its physiological role involves two cellular functions: regulation of phosphatidate phosphatase activity and regulation of fatty acid oxidation. In this study, we have demonstrated that lipin 1 gene (LPIN1) expression is regulated by cellular sterols, which are key regulators of lipid metabolism. We have also characterized the sterol-response element and nuclear factor Y-binding sites in the human LPIN1 promoter. Using a luciferase assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay, we demonstrated that these elements are responsible for the transcription of LPIN1 gene, mediated by SREBP-1 (sterol regulatory element-binding protein 1) and nuclear factor Y. Furthermore, we investigated whether lipin 1 is involved in lipogenesis by transfection of LPIN1 small interfering RNA. We infer that sterolmediated regulation of lipin 1 gene transcription modulates triglyceride accumulation. This modulation involves changes in the activity of phosphatidate phosphatase.

Background: Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors and commonly play an important role in the regulation of lipid homeostasis. To identify human PPARs-responsive genes, we established tetracycline-regulated human hepatoblastoma cell lines that can be induced to express each human PPAR and investigated the gene expression profiles of these cells.

Antisense-mediated modulation of pre-mRNA splicing is an attractive therapeutic strategy for genetic diseases. Currently, there are few examples of modulation of pre-mRNA splicing using locked nucleic acid (LNA) antisense oligonucleotides, and, in particular, no systematic study has addressed the optimal design of LNA-based splice-switching oligonucleotides (LNA SSOs). Here, we designed a series of LNA SSOs complementary to the human dystrophin exon 58 sequence and evaluated their ability to induce exon skipping in vitro using reverse transcription-polymerase chain reaction. We demonstrated that the number of LNAs in the SSO sequence and the melting temperature of the SSOs play important roles in inducing exon skipping and seem to be key factors for designing efficient LNA SSOs. LNA SSO length was an important determinant of activity: a 13-mer with six LNA modifications had the highest efficacy, and a 7-mer was the minimal length required to induce exon skipping. Evaluation of exon skipping activity using mismatched LNA/DNA mixmers revealed that 9-mer LNA SSO allowed a better mismatch discrimination. LNA SSOs also induced exon skipping of endogenous human dystrophin in primary human skeletal muscle cells. Taken together, our findings indicate that LNA SSOs are powerful tools for modulating pre-mRNA splicing.

Liver X receptor alpha (LXRa) is a member of the nuclear receptor superfamily that is activated by oxysterols, and plays a pivotal role in regulating the metabolism, transport and uptake of cholesterol. Here, we demonstrate that LXRa also regulates the low-density lipoprotein receptor (LDLR) gene, which mediates the endocytic uptake of LDL cholesterol in the liver. An LXR agonist induced the expression of LDLR in cultured hepatoblastoma cells. Moreover, the LDLR promoter contained an LXR response element that was recognized by LXRa/ RXRa (retinoid X receptor alpha) heterodimers in hepatoblastoma cells. These results suggest a novel pathway whereby LXRa might modulate cholesterol metabolism.