Abstract 522: Limited and Gene-Specific Down-Regulation of PPAR Delta Target Genes by Dominant-Negative PPAR Gamma in Mesenteric Artery.
PPARγ is a ligand-activated transcription factor expressed in multiple tissues including the vasculature. Individuals with a mutation in the ligand-binding domain of PPARγ (P467L) are insulin resistant and have early onset hypertension. Targeted expression of P467L PPARγ to smooth muscle of transgenic mice (S-P467L) increased blood pressure, induced aortic dysfunction, and enhanced myogenic tone in the mesenteric artery. To examine the mechanisms underlying these changes, we used the Affymetrix exon array to perform gene expression profiling of mesenteric arteries from S-P467L and non-transgenic (NT) littermates (n =3 for S-P467L, n=4 for NT). Classic PPARγ target genes, as a group, were down-regulated (p<0.001, gene set analysis), consistent with reports that P467L PPARγ acts in a dominant negative manner. We also observed a down-regulation in pyruvate dehydrogenase kinase, isozyme 4 (PDK4, fold change = 0.4, p = 0.01), a known PPARδ target gene. We confirmed that PDK4 was a PPARδ target (fold change = 2.3±0.3, n = 5, Q-PCR) by 6-hr incubation of NT mesenteric arteries with PPARδ specific agonist GW0742 (1 μM). Based on this, we hypothesized that P467L PPARγ was interfering with and down-regulating PPARδ target genes in the mesenteric artery. To examine this, we integrated our expression dataset with a published study (PLoS One. 2011:e16344) which used expression microarrays and chromatin immunoprecipitation/next-generation sequencing (ChIP-Seq) to experimentally identify PPARδ target genes and PPARδ binding sites in a genome-wide manner. Using this target gene list and limiting our analysis to genes expressed in mesenteric arteries (94 genes), we identified 2 additional PPARδ targets that were modestly but significantly down-regulated (p<0.001) in mesenteric artery from S-P467L mice (TIMP4 -40%, CPT1A -22%). Both of these genes also have a PPARγ binding site according to ChIP-Seq (GEO accession, GSE13511); suggesting the possibility of interaction between PPARγ and PPARδ in regulation of target gene expression. Thus, our data shows that dominant-negative PPARγ down-regulates only a small subset of PPARδ target genes in mesenteric artery suggesting that P467L PPARγ exhibits a relative selectivity to PPARγ targets instead of global inhibition.
- © 2012 by American Heart Association, Inc.