The pleiotropic functions of peroxisome proliferator-activated receptor gamma

Concordant mRNA expression of UCP-3, but not UCP-2, with mitochondrial thioesterase-1 in brown adipose tissue and skeletal muscle in db/db diabetic mice

A recent hypothesis concerning the function of uncoupling protein-3 (UCP-3) depends upon a positive relationship with mitochondrial thioesterase (MTE-1) in situations where fatty acid beta-oxidation is increased. MTE-1 mRNA levels are raised in transgenic mice overexpressing UCP-3 in skeletal muscle and we sought to extend these findings by quantifying in vivo expression of endogenous MTE-1, UCP-1, UCP-2, and UCP-3 mRNA levels in white adipose tissue, interscapular brown adipose tissue, and skeletal muscle in db/db mice. In this study we show that changes in MTE-1 mRNA levels as a result of differences between db/db vs db/+ mice or following long-term treatment of db/db mice with rosiglitazone or Wy-14,643 were more closely correlated with changes in UCP-3 than either UCP-1 or UCP-2 mRNA levels in the tissues examined. The present data contribute to the argument that UCP-3 and MTE-1 are linked within the same metabolic pathway either in response to, or as regulators of, fatty acid beta-oxidation.

Identification of a novel peroxisome proliferator-activated receptor (PPAR) gamma promoter in man and transactivation by the nuclear receptor RORalpha1

PPARgamma has been extensively studied for the past decade mainly due to its central role in promoting and maintaining the adipocyte phenotype. To date, three PPARgamma isoforms have been described in man. Here we show the presence of a fourth PPARgamma promoter with its cognate mRNA initiating at exon 1, as evidenced by primer extension analysis. The presence of a putative responsive element (RORE) for RORalpha, a representative of the ROR/RZR orphan receptor superfamily, in the novel promoter was investigated. By gelshift experiments and site-directed mutagenesis we show that this RORE specifically binds the RORalpha1 isoform. We further demonstrate that overexpression of RORalpha1, but not the RORalpha2 and RORalpha3 isoforms, induced a 40-fold increase in promoter activity in transient transfection assays in various cell lines. Considering the strong transcriptional activation it is likely that RORalpha1 forms a part of the multifactorial regulatory mechanisms that control expression of the human PPARgamma gene.

Differential regulation of adipocytokine mRNAs by rosiglitazone in db/db mice

The precise mechanism by which PPARgamma activation by thiazolidinediones (TZDs) improves insulin sensitivity is still unclear. Recent studies have focused on the role of adipocytokines in metabolic control and their regulation by TZDs. In this study, we compared the chronic effects of antihyperglycemic doses of the TZD rosiglitazone, the beta3-adrenoceptor agonist BRL-35135, and the PPARalpha agonist Wy-14,643 on the mRNA expression of adipocytokines in WAT of db/db mice. Rosiglitazone treatment decreased adiponectin and resistin mRNA levels by 57 and 72%, respectively (P < 0.001), with no effect on the level of TNFalpha or RELMalpha transcripts. In comparison, Wy-14,643 reduced adiponectin transcript levels by 31% (P = 0.015) while BRL-35135 increased RELMalpha mRNA expression by 245% (P < 0.001) without effect on the other transcripts. Our results indicate that although a reduction in adiponectin and resistin mRNA levels in WAT by rosiglitazone treatment of diabetic mice may contribute to the antidiabetic effects, an alteration in TNFalpha, adiponectin, resistin, or RELMalpha mRNA expression is not absolutely required for the regulation of blood glucose concentration in the db/db mouse.