Fenofibrate differentially regulates plasminogen activator inhibitor-1 gene expression via adenosine monophosphate-activated protein kinase-dependent induction of orphan nuclear receptor small heterodimer partner.
ABSTRACT: Plasminogen activator inhibitor type I (PAI-1) is a marker of the fibrinolytic system and serves as a possible predictor for hepatic metabolic syndromes. Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARalpha) agonist, is a drug used for treatment of hyperlipidemia. Orphan nuclear receptor small heterodimer partner (SHP) plays a key role in transcriptional repression of crucial genes involved in various metabolic pathways. In this study, we show that fenofibrate increased SHP gene expression in cultured liver cells and in the normal and diabetic mouse liver by activating the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway in a PPARalpha-independent manner. Administration of transforming growth factor beta (TGF-beta) or a methionine-deficient and choline-deficient (MCD) diet to induce the progressive fibrosing steatohepatitis model in C57BL/6 mice was significantly reversed by fenofibrate via AMPK-mediated induction of SHP gene expression with a dramatic decrease in PAI-1 messenger RNA (mRNA) and protein expression along with other fibrotic marker genes. No reversal was observed in SHP null mice treated with fenofibrate. Treatment with another PPARalpha agonist, WY14643, showed contrasting effects on these marker gene expressions in wild-type and SHP null mice, demonstrating the specificity of fenofibrate in activating AMPK signaling. Fenofibrate exhibited a differential inhibitory pattern on PAI-1 gene expression depending on the transcription factors inhibited by SHP.By demonstrating that a PPARalpha-independent fenofibrate-AMPK-SHP regulatory cascade can play a key role in PAI-1 gene down-regulation and reversal of fibrosis, our study suggests that various AMPK activators regulating SHP might provide a novel pharmacologic option in ameliorating hepatic metabolic syndromes.
Project description:Liver is a major regulator of lipid metabolism and adaptation to fasting, a process involving PPARalpha activation. We recently showed that the Vnn1 gene is a PPARalpha target gene in liver and that release of the Vanin-1 pantetheinase in serum is a biomarker of PPARalpha activation. Here we set up a screen to identify new regulators of adaptation to fasting using the serum Vanin-1 as a marker of PPARalpha activation. Mutagenized mice were screened for low serum Vanin-1 expression. Functional interactions with PPARalpha were investigated by combining transcriptomic, biochemical and metabolic approaches. We characterized a new mutant mouse in which hepatic and serum expression of Vanin-1 is depressed. This mouse carries a mutation in the HMG domain of the Sox17 transcription factor. Mutant mice display a metabolic phenotype featuring lipid abnormalities and inefficient adaptation to fasting. Upon fasting, a fraction of the PPAR?-driven transcriptional program is no longer induced and associated with impaired fatty acid oxidation. The transcriptional phenotype is partially observed in heterozygous Sox17+/- mice. In mutant mice, the fasting phenotype but not all transcriptomic signature is rescued by the administration of the PPARalpha agonist fenofibrate. These results identify a novel role for Sox17 in adult liver as a modulator of the metabolic adaptation to fasting.
Project description:Peroxisome proliferator-activated receptor alpha (PPARalpha) activation in rodents is thought to improve insulin sensitivity by decreasing ectopic lipids in non-adipose tissues. Fenofibrate, a lipid-modifying agent that acts as a PPARalpha agonist, may prevent adipocyte hypertrophy and insulin resistance by increasing intracellular lipolysis from adipose tissue. Consistent with this hypothesis, fenofibrate decreased visceral fat mass and adipocyte size in high fat diet-fed obese mice, and concomitantly increased the expression of PPARalpha target genes involved in fatty acid beta-oxidation in both epididymal adipose tissue and differentiated 3T3-L1 adipocytes. However, mRNA levels of adipose marker genes, such as leptin and TNFalpha, were decreased in epididymal adipose tissue by fenofibrate treatment. Fenofibrate not only reduced circulating levels of free fatty acids and triglycerides, but also normalized hyperinsulinemia and hyperglycemia in obese mice. Blood glucose levels of fenofibrate-treated mice were significantly reduced during intraperitoneal glucose tolerance test compared with obese controls. These results suggest that fenofibrate-induced fatty acid beta-oxidation in visceral adipose tissue may be one of the major factors leading to decreased adipocyte size and improved insulin sensitivity.
Project description:Phosphatidylcholine transfer protein (PC-TP, a.k.a. StarD2) is abundantly expressed in liver and is regulated by PPARalpha. When fed the synthetic PPARalpha ligand fenofibrate, Pctp(-/-) mice exhibited altered lipid and glucose metabolism. Microarray profiling of livers from fenofibrate fed wild type and Pctp(-/-) mice revealed differential expression of a broad array of metabolic genes, as well as their regulatory transcription factors. PC-TP expression in cell culture controlled the activities of both PPARalpha and HNF4alpha, suggesting that the mechanism by which it modulates hepatic metabolism is at least in part via activation of transcription factors that govern nutrient homeostasis.
Project description:BACKGROUND: The peroxisome proliferator-activated receptor alpha (PPARalpha) plays an important role in the metabolism of lipoproteins and fatty acids, and seems to protect against the development of atherosclerosis. To evaluate the possible protective role of PPARalpha on cardiovascular function, the effect of the PPARalpha agonist, fenofibrate was assessed with respect to ischaemia/reperfusion injury and endothelial function in mice. RESULTS: Fenofibrate treatment reduces myocardial infarction size and improves post-ischaemic contractile dysfunction. Hearts from PPARalpha null mice exhibit increased susceptibility to ischaemic damages and were refractory to protection by fenofibrate treatment suggesting that the beneficial effects of fenofibrate were mediated via PPARalpha. Furthermore, fenofibrate improves endothelium- and nitric oxide-mediated vasodilatation in aorta and mesenteric vascular bed. A decreased inhibitory effect of reactive oxygen species in the vessel wall accounts for enhanced endothelial vasodilatation. However, the latter cannot be explained by an increase in nitric oxide synthase expression nor by an increase sensitivity of the arteries to nitric oxide. CONCLUSIONS: Altogether the present data suggest that fenofibrate exerts cardioprotective effect against ischaemia and improves nitric oxide-mediated response probably by enhancing antioxidant capacity of the vessel wall. These data underscore new therapeutic perspectives for PPARalpha agonists in ischaemic myocardial injury and in cardiovascular diseases associated with endothelial dysfunction.
Project description:Angiogenesis and inflammation are central processes through which the tumor microenvironment influences tumor growth. We have demonstrated recently that peroxisome proliferator-activated receptor (PPAR)alpha deficiency in the host leads to overt inflammation that suppresses angiogenesis via excess production of thrombospondin (TSP)-1 and prevents tumor growth. Hence, we speculated that pharmacologic activation of PPARalpha would promote tumor growth. Surprisingly, the PPARalpha agonist fenofibrate potently suppressed primary tumor growth in mice. This effect was not mediated by cancer-cell-autonomous antiproliferative mechanisms but by the inhibition of angiogenesis and inflammation in the host tissue. Although PPARalpha-deficient tumors were still susceptible to fenofibrate, absence of PPARalpha in the host animal abrogated the potent antitumor effect of fenofibrate. In addition, fenofibrate suppressed endothelial cell proliferation and VEGF production, increased TSP-1 and endostatin, and inhibited corneal neovascularization. Thus, both genetic abrogation of PPARalpha as well as its activation by ligands cause tumor suppression via overlapping antiangiogenic pathways. These findings reveal the potential utility of the well tolerated PPARalpha agonists beyond their use as lipid-lowering drugs in anticancer therapy. Our results provide a mechanistic rationale for evaluating the clinical benefits of PPARalpha agonists in cancer treatment, alone and in combination with other therapies.
Project description:Mutations in the low-density lipoprotein receptor (LDLR) gene cause familial hypercholesterolaemia in humans and deletion of the LDLR induces lesion development in mice fed a high-fat diet. LDLR expression is predominantly regulated by sterol regulatory element-binding protein 2 (SREBP2). Fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARalpha) ligand, belongs to a drug class used to treat dyslipidaemic patients. We have investigated the effects of fenofibrate on hepatic LDLR expression.The effects of fenofibrate on hepatic LDLR expression (mRNA and protein) and function were evaluated by both in vitro (with AML12 cells) and in vivo experiments in mice.Fenofibrate increased LDLR expression and LDL binding in a mouse hepatoma cell line, AML12 cells. Fenofibrate restored sterol-inhibited hepatocyte LDLR expression. Mechanistic studies demonstrated that induction of LDLR expression by fenofibrate was dependent on PPARalpha and sterol regulatory elements (SRE). Specifically, fenofibrate induced LDLR expression by increasing maturation of SREBP2 and phosphorylation of protein kinase B (Akt) but had no effect on SREBP cleavage-activating protein. In vivo, a high-fat diet suppressed LDLR expression in mouse liver while elevating total and LDL cholesterol levels in plasma. However, fenofibrate restored LDLR expression inhibited by high-fat diets in the liver and reduced LDL cholesterol levels in plasma.Our data suggest that fenofibrate increased hepatic LDLR expression in mice by a mechanism involving Akt phosphorylation and LDLR gene transcription mediated by SREBP2.
Project description:BACKGROUND AND PURPOSE: Protective cardiovascular effects of peroxisome proliferator activated receptor (PPAR)alpha and PPARgamma activators have been demonstrated. If used as vasoprotective agents in high risk vascular patients rather than for their metabolic benefits, these agents could be associated with unwanted side effects. As a proof of concept to support the use of combined low doses of PPARalpha and PPARgamma as vascular protective agents in high risk vascular patients, we tested the hypothesis that combined low doses of PPARalpha (fenofibrate) and PPARgamma (rosiglitazone) activators would provide vascular protective benefits similar to full individual doses of these PPAR agonists. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats infused with Ang II (120 ng kg(-1) min(-1)) were treated with rosiglitazone (1 or 2 mg kg(-1) day(-1)) alone or concomitantly with fenofibrate (30 mg kg(-1) day(-1)) for 7 days. Thereafter, vessels was assessed on a pressurized myograph, while NAD(P)H oxidase activity was determined by lucigenin chemiluminescence. Inflammation was evaluated using ELISA for NFkappaB and Western blotting for adhesion molecules. KEY RESULTS: Ang II-induced blood pressure increase, impaired acetylcholine-induced vasorelaxation, altered vascular structure, and enhanced vascular NAD(P)H oxidase activity and inflammation were significantly reduced by low dose rosiglitazone+fenofibrate. CONCLUSIONS AND IMPLICATIONS: Combined low doses of PPARalpha and PPARgamma activators attenuated development of hypertension, corrected vascular structural abnormalities, improved endothelial function, oxidative stress, and vascular inflammation. These agents used in low-dose combination have synergistic vascular protective effects. The clinical effects of combined low-dose PPARalpha and PPARgamma activators as vascular protective therapy, potentially with reduced side-effects and drug interactions, should be assessed.
Project description:Leptin stimulates fatty acid oxidation in skeletal muscle through the activation of AMP-activated protein kinase (AMPK) and the induction of gene expression, such as that for peroxisome proliferator-activated receptor alpha (PPARalpha). We now show that leptin stimulates fatty acid oxidation and PPARalpha gene expression in the C2C12 muscle cell line through the activation of AMPK containing the alpha2 subunit (alpha2AMPK) and through changes in the subcellular localization of this enzyme. Activated alpha2AMPK containing the beta1 subunit was shown to be retained in the cytoplasm, where it phosphorylated acetyl coenzyme A carboxylase and thereby stimulated fatty acid oxidation. In contrast, alpha2AMPK containing the beta2 subunit transiently increased fatty acid oxidation but underwent rapid translocation to the nucleus, where it induced PPARalpha gene transcription. A nuclear localization signal and Thr(172) phosphorylation of alpha2 were found to be essential for nuclear translocation of alpha2AMPK, whereas the myristoylation of beta1 anchors alpha2AMPK in the cytoplasm. The prevention of alpha2AMPK activation and the change in its subcellular localization inhibited the metabolic effects of leptin. Our data thus suggest that the activation of and changes in the subcellular localization of alpha2AMPK are required for leptin-induced stimulation of fatty acid oxidation and PPARalpha gene expression in muscle cells.
Project description:Glucocorticoid receptor alpha (GRalpha) and peroxisome proliferator-activated receptor alpha (PPARalpha) are transcription factors with clinically important immune-modulating properties. Either receptor can inhibit cytokine gene expression, mainly through interference with nuclear factor kappaB (NF-kappaB)-driven gene expression. The present work aimed to investigate a functional cross-talk between PPARalpha- and GRalpha-mediated signaling pathways. Simultaneous activation of PPARalpha and GRalpha dose-dependently enhances transrepression of NF-kappaB-driven gene expression and additively represses cytokine production. In sharp contrast and quite unexpectedly, PPARalpha agonists inhibit the expression of classical glucocorticoid response element (GRE)-driven genes in a PPARalpha-dependent manner, as demonstrated by experiments using PPARalpha wild-type and knockout mice. The underlying mechanism for this transcriptional antagonism relies on a PPARalpha-mediated interference with the recruitment of GRalpha, and concomitantly of RNA polymerase II, to GRE-driven gene promoters. Finally, the biological relevance of this phenomenon is underscored by the observation that treatment with the PPARalpha agonist fenofibrate prevents glucocorticoid-induced hyperinsulinemia of mice fed a high-fat diet. Taken together, PPARalpha negatively interferes with GRE-mediated GRalpha activity while potentiating its antiinflammatory effects, thus providing a rationale for combination therapy in chronic inflammatory disorders.
Project description:A growing body of evidence indicates that peroxisome proliferator-activated receptor alpha (PPARalpha) not merely serves as a transcriptional regulator of fatty acid catabolism but also exerts a much broader role in hepatic lipid metabolism. We determined adaptations in hepatic lipid metabolism and related aspects of carbohydrate metabolism upon treatment of C57Bl/6 mice with the PPARalpha agonist fenofibrate. Stable isotope procedures were applied to assess hepatic fatty acid synthesis, fatty acid elongation, and carbohydrate metabolism. Fenofibrate treatment strongly induced hepatic de novo lipogenesis and chain elongation (+/-300, 150, and 600% for C16:0, C18:0, and C18:1 synthesis, respectively) in parallel with an increased expression of lipogenic genes. The lipogenic induction in fenofibrate-treated mice was found to depend on sterol regulatory element-binding protein 1c (SREBP-1c) but not carbohydrate response element-binding protein (ChREBP). Fenofibrate treatment resulted in a reduced contribution of glycolysis to acetyl-CoA production, whereas the cycling of glucose 6-phosphate through the pentose phosphate pathway presumably was enhanced. Altogether, our data indicate that beta-oxidation and lipogenesis are induced simultaneously upon fenofibrate treatment. These observations may reflect a physiological mechanism by which PPARalpha and SREBP-1c collectively ensure proper handling of fatty acids to protect the liver against cytotoxic damage.