Dataset Information

Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) but not PPARalpha serves as a plasma free fatty acid sensor in liver.

ABSTRACT: Peroxisome proliferator-activated receptor alpha (PPARalpha) is an important transcription factor in liver that can be activated physiologically by fasting or pharmacologically by using high-affinity synthetic agonists. Here we initially set out to elucidate the similarities in gene induction between Wy14643 and fasting. Numerous genes were commonly regulated in liver between the two treatments, including many classical PPARalpha target genes, such as Aldh3a2 and Cpt2. Remarkably, several genes induced by Wy14643 were upregulated by fasting independently of PPARalpha, including Lpin2 and St3gal5, suggesting involvement of another transcription factor. Using chromatin immunoprecipitation, Lpin2 and St3gal5 were shown to be direct targets of PPARbeta/delta during fasting, whereas Aldh3a2 and Cpt2 were exclusive targets of PPARalpha. Binding of PPARbeta/delta to the Lpin2 and St3gal5 genes followed the plasma free fatty acid (FFA) concentration, consistent with activation of PPARbeta/delta by plasma FFAs. Subsequent experiments using transgenic and knockout mice for Angptl4, a potent stimulant of adipose tissue lipolysis, confirmed the stimulatory effect of plasma FFAs on Lpin2 and St3gal5 expression levels via PPARbeta/delta. In contrast, the data did not support activation of PPARalpha by plasma FFAs. The results identify Lpin2 and St3gal5 as novel PPARbeta/delta target genes and show that upregulation of gene expression by PPARbeta/delta is sensitive to plasma FFA levels. In contrast, this is not the case for PPARalpha, revealing a novel mechanism for functional differentiation between PPARs.

SUBMITTER: Sanderson LM

PROVIDER: S-EPMC2786701 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) but not PPARalpha serves as a plasma free fatty acid sensor in liver.

Sanderson Linda M LM Degenhardt Tatjana T Koppen Arjen A Kalkhoven Eric E Desvergne Beatrice B Müller Michael M Kersten Sander S

Molecular and cellular biology 20091005 23

Peroxisome proliferator-activated receptor alpha (PPARalpha) is an important transcription factor in liver that can be activated physiologically by fasting or pharmacologically by using high-affinity synthetic agonists. Here we initially set out to elucidate the similarities in gene induction between Wy14643 and fasting. Numerous genes were commonly regulated in liver between the two treatments, including many classical PPARalpha target genes, such as Aldh3a2 and Cpt2. Remarkably, several genes ...[more]

PMID: 19805517

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Project description:Peroxisome proliferator-activated receptor (PPAR) beta/delta-null mice exhibit exacerbated hepatotoxicity in response to administration of carbon tetrachloride (CCl(4)). To determine whether ligand activation of the receptor protects against chemical toxicity in the liver, wild-type and PPARbeta/delta-null mice were administered CCl(4) with or without coadministration of the highly specific PPARbeta/delta ligand GW0742. Biomarkers of liver toxicity, including serum alanine aminotransferase (ALT) and hepatic tumor necrosis factor (TNF) alpha mRNA, were significantly higher in CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. Hepatic expression of TNF-like weak inducer of apoptosis receptor (TWEAKr) and S100 calcium-binding protein A6 (S100A6/calcyclin), genes involved in nuclear factor kappa B signaling, was higher in the CCl(4)-treated PPARbeta/delta-null mice compared to wild-type mice. GW0742 treatment resulted in reduced serum ALT concentration and lower expression of CCl(4)-induced TNF-alpha, S100A6, monocyte chemoattractant protein-1 (MCP1), and TWEAKr in wild-type mice, and these effects were not observed in PPARbeta/delta-null mice. Expression of TNF-alpha was higher in PPARbeta/delta-null primary hepatocytes in response to interleukin-1beta treatment compared to wild-type hepatocytes, but GW0742 did not significantly modulate TNF-alpha expression in hepatocytes from either genotype. While PPARbeta/delta-null hepatic stellate exhibited higher rates of proliferation compared to wild-type cells, GW0742 did not affect alpha-smooth muscle actin expression in these cells. Combined, these findings demonstrate that ligand activation of PPARbeta/delta protects against chemically induced hepatotoxicity by downregulating expression of proinflammatory genes. Hepatocytes and hepatic stellate cells do not appear to directly mediate the inhibitory effects of ligand activation of PPARbeta/delta in liver, suggesting the involvement of paracrine and autocrine events mediated by hepatic cells.

Project description:Liver insufficiency and damage are major causes of death and disease worldwide and may result from exposure to environmental toxicants, specific combinations or dosages of pharmaceuticals, and microbial metabolites. The generation of reactive intermediates, in particular 4-hydroxynonenal (4-HNE), is a common event in liver damage caused by a variety of hepatotoxic drugs and solvents. The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that are involved in the transcriptional regulation of lipid metabolism as well as other biological functions. Importantly, we have observed that the PPARbeta/delta-/- mouse is more susceptible to chemically induced hepatotoxicity than its wild-type counterpart, and our objective in this study was to elucidate the mechanism(s) by which PPARbeta/delta confers protection to hepatocytes. We hypothesized that PPARbeta/delta plays a protective role by responding to toxic lipids and altering gene expression accordingly. In support, oxidized-VLDL and constituents including 13-S-hydroxyoctadecadienoic acid (13-S-HODE) and 4-HNE are PPARbeta/delta ligands. A structure-activity relationship was established where 4-HNE and 4-hydroperoxynonenal (4-HpNE) enhanced the activity of the PPARbeta/delta subtype while 4-hyroxyhexenal (4-HHE), 4-oxo-2-Nonenal (4-ONE), and trans-4,5-epoxy-2(E)-decenal did not activate this receptor. Increasing PPARbeta/delta activity with a synthetic agonist decreased sensitivity of hepatocytes to 4-HNE and other toxic agents, whereas inhibition of this receptor had the opposite result. Gene expression microarray analysis identified several important PPARbeta/delta-regulated detoxification enzymes involved in 4-HNE metabolism that are regulated at the transcript level. This research established 4-HNE as an endogenous modulator of PPARbeta/delta activity and raises the possibility that agonists of this nuclear receptor may be utilized to prevent or treat liver disease associated with oxidative damage.

Dataset Information

Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) but not PPARalpha serves as a plasma free fatty acid sensor in liver.

Publications

Peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) but not PPARalpha serves as a plasma free fatty acid sensor in liver.

Similar Datasets

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