Effect Of PPARα Activation Research Articles

YAP-TEAD mediates PPAR α-induced hepatomegaly and liver regeneration in mice.

Peroxisome proliferator-activated receptor α (PPARα, NR1C1) is a ligand-activated nuclear receptor involved in the regulation of lipid catabolism and energy homeostasis. PPARα activation induces hepatomegaly and plays an important role in liver regeneration, but the underlying mechanisms remain unclear. In this study, the effect of PPARα activation on liver enlargement and regeneration was investigated in several strains of genetically modified mice. PPARα activation by the specific agonist WY-14643 significantly induced hepatomegaly and accelerated liver regeneration after 70% partial hepatectomy (PHx) in wild-type mice and Pparafl/fl mice, while these effects were abolished in hepatocyte-specific Ppara-deficient (PparaΔHep ) mice. Moreover, PPARα activation promoted hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. Mechanistically, PPARα activation regulated expression of yes-associated protein (YAP) and its downstream targets (connective tissue growth factor, cysteine-rich angiogenic inducer 61, and ankyrin repeat domain 1) as well as proliferation-related proteins (cyclins A1, D1, and E1). Binding of YAP with the PPARα E domain was critical for the interaction between YAP and PPARα. PPARα activation further induced nuclear translocation of YAP. Disruption of the YAP-transcriptional enhancer factor domain family member (TEAD) association significantly suppressed PPARα-induced hepatomegaly and hepatocyte enlargement and proliferation. In addition, PPARα failed to induce hepatomegaly in adeno-associated virus-Yap short hairpin RNA-treated mice and liver-specific Yap-deficient mice. Blockade of YAP signaling abolished PPARα-induced hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. This study revealed a function of PPARα in regulating liver size and liver regeneration through activation of the YAP-TEAD signaling pathway. These findings have implications for understanding the physiological functions of PPARα and suggest its potential for manipulation of liver size and liver regeneration.

YAP‐TEAD mediates peroxisome proliferator‐activated receptor α‐ induced hepatomegaly and liver regeneration in mice

Peroxisome proliferator-activated receptor a (PPARα, NR1C1) is a ligand-activated nuclear receptor involved in the regulation of lipid catabolism and energy homeostasis. PPARα activation induces hepatomegaly and plays an important role in liver regeneration, but the underlying mechanisms remain unclear. In this study, the effect of PPARα activation on liver enlargement and regeneration was investigated in several strains of genetically-modified mice. PPARα activation by the specific agonist WY-14643 significantly induced hepatomegaly in wild-type mice and Pparafl/fl mice, while this effect was abolished in hepatocyte-specific PPARα-deficient (PparaΔHep) mice. Furthermore, PPARα agonist accelerated liver regeneration after 70% partial hepatectomy (PHx). PPARα activation promoted hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area in wild-type, Pparafl/fl and PHx mice. Mechanistically, PPARα activation regulated expressions of yes-associated protein (YAP) and its downstream targets (CTGF, CYR61 and ANKRD1) as well as proliferation-related proteins (CCNA1, CCND1 and CCNE1). PPARα potentially interacted with YAP and PPARα activation induced nuclear translocation of YAP. In addition, PPARα failed to induce hepatomegaly in liver-specific YAP-deficient (Yap-/-) mice and AAV-Yap shRNA-treated mice. Blockade of YAP abolished PPARα-induced hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. Additionally, disruption of YAP-transcriptional enhancer factor domain family member (TEAD) association significantly suppressed PPARα-induced hepatomegaly, as well as hepatocyte enlargement and proliferation. This study revealed a novel function of PPARα in regulating liver size and liver regeneration via activation of the YAP-TEAD signaling pathway. These findings have implications for understanding the physiological functions of PPARα and suggest its potential for manipulation of liver size and liver regeneration.

Pharmacological and Toxicological Advances in PPAR-Related Medicines

Pharmacological and Toxicological Advances in PPAR-Related Medicines

Abstract B7: Activation of PPARα suppresses HIF-1α signaling in human cancer cells.

Abstract Background: Hypoxia inducible factor-1α (HIF-1α) is a therapeutic target in solid tumors because it activates transcription of the genes associated with tumor growth, angiogenesis and chemo/radio-resistance. Activation of PPARα has been demonstrated to inhibit tumor growth and angiogenesis, yet the mechanisms behind these actions remain obscure. The present study examined the effects of PPARα activation on HIF-1α mediated signaling in human cancer cells. Methods: The human cancer lines MCF-7 (breast) and A2780 (ovarian), and human endothelial line, EA.hy926 were used as model systems for this study. Hypoxia was achieved via a hypoxia chamber. The HRE-luciferase reporter gene and Western blot were applied to analyze HIF-1α expression and activity. RT-PCR and co-immunoprecipitation were performed to understand the molecular mechanisms of PPARα-mediated suppression of HIF-1α signaling. The level of vascular endothelial growth factor (VEGF) in cultured medium was determined using an ELISA, and in vitro angiogenesis was evaluated using the tube formation assay. Results: Incubation of cancer cells with 1 % oxygen for 16 hours significantly induced HIF-1α expression and activity. Treatment of the cells with PPARα agonists, but not a PPARγ agonist, prior to hypoxia diminished hypoxia-induced HIF-1α expression and activity. Consistently, a PPARα antagonist attenuated PPARα agonist-induced suppression of HIF-1α signaling. Over-expression of an HA-tagged HIF-1α and HIF-1α-P402/P564A mutant protein demonstrated that activation of PPARα promotes HIF-1 α degradation in our model system. This was further confirmed by the use of MG-132, a proteasome inhibitor, which reversed PPARα-mediated suppression of the HIF-1α signaling, and by RT-PCR analysis of HIF-1α mRNA, which was unchanged by PPARα activation. Using the co-immunoprecipitation technique, we found that activation of PPARα enhances the binding of hydroxylated HIF-1α to the Von Hippel-Lindau tumor suppressor, a protein known to mediate HIF-1α degradation through the ubiquitin-proteasome pathway. Consequential to the PPARα-mediated suppression of HIF-1α signaling, vascular endothelial growth factor secretion from cancer cells was found to be significantly reduced, and the tube formation by EA.hy926 cells was dramatically impaired. Summary: Activation of PPARα suppresses HIF-1α expression and activity by promoting HIF-1α degradation in cancer cells. PPARα agonists are potential anticancer agents that inhibit tumor angiogenesis via the suppression of HIF-1α signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B7.

Interactions of peroxisome proliferator‐activated receptor alpha (PPARá) and adenosine receptors (AR) in angiogenesis

Hypoxia (HYP) stimulates angiogenesis (ANG) by promoting expression of many pro‐angiogenic genes, including AR. The role of PPARα in ANG is controversial. A2BR‐induced activation is known to reduce PPARα‐mediated activity but the effect of PPARα activation on A2BR is unknown. Here, we tested that PPARα attenuates adenosine(AD)‐mediated HYP –induced ANG. Using zebrafish embryo, ANG was measured by counting intersegmental vessel (ISV) and dorsal longitudinal anastomotic vessels (DLAV). Under normoxic condition, WY‐14643 (WY, 10 μM), a PPARα agonist, increased ISV (P<0.01) at 28 hpf but NECA (10 μM), a non selective AR agonist showed no effect. Combined exposure of WY 10 or 100 μM or NECA (10μM) decreased ISV at 28 hpf (p<0.01). However, WY (10 μM) +NECA increased DLAV (P<0.001), whereas, WY (100 μM)+NECA decreased DLAV (P<0.05) at 48 hpf. HYP alone increased ANG (72±19%) at 48 hpf. WY(10 μM) showed no effect on ISV but increased DLAV (P<0.05). At 28 hpf WY (10 μM)+NECA decreased ISV (P<0.001). Our data show that activation of PPARα and AR individually promote HYP‐induced ANG, but combined activation inhibits AD‐mediated HYP‐induced ANG.

CXCL9 and CXCL11 Chemokines Modulation by Peroxisome Proliferator-Activated Receptor-α Agonists Secretion in Graves’ and Normal Thyrocytes

ABSTRACT Context Peroxisome proliferator-activated receptor (PPAR)-α has been shown to exert immunomodulatory effects in autoimmune disorders. However, until now, no data were present in the literature about the effect of PPARα activation on CXCL9 and CXCL11 chemokines in general or on secretion of these chemokines in thyroid cells. Objective and Design The presence of PPARα and PPARγ has been evaluated by RT-PCR in Graves’ disease (GD) and control cells in primary culture. Furthermore, we have tested the role of PPARα and PPARγ activation on CXCL9 and CXCL11 secretion in GD and control cells after stimulation of these chemokines secretion with IFNγ and TNFα. Results This study shows the presence of PPARα and PPARγ in GD and control cells. A potent dose-dependent inhibition by PPARα-agonists was observed on the cytokines-stimulated secretion of CXCL9 and CXCL11 in GD and control cells. The potency of the PPARα agonists used was maximum on the secretion of CXCL9, reaching about 90% of inhibition by fenofibrate and 85% by ciprofibrate. The relative potency of the compounds was different with each chemokine; for example, gemfibrozil exerted a 55% inhibition on CXCL11, whereas it had a weaker activity on CXCL9 (40% inhibition). PPARα agonists were stronger (ANOVA, P < 0.001) inhibitors of CXCL9 and CXCL11 secretion in thyrocytes than PPARγ agonists. Conclusions Our study shows the presence of PPARα in GD and control thyrocytes. PPARα activators are potent inhibitors of the secretion of CXCL9 and CXCL11, suggesting that PPARα may be involved in the modulation of the immune response in the thyroid.

CXCL9 and CXCL11 Chemokines Modulation by Peroxisome Proliferator-Activated Receptor-α Agonists Secretion in Graves’ and Normal Thyrocytes

Peroxisome proliferator-activated receptor (PPAR)-α has been shown to exert immunomodulatory effects in autoimmune disorders. However, until now, no data were present in the literature about the effect of PPARα activation on CXCL9 and CXCL11 chemokines in general or on secretion of these chemokines in thyroid cells. The presence of PPARα and PPARγ has been evaluated by real-time-PCR in Graves' disease (GD) and control cells in primary culture. Furthermore, we have tested the role of PPARα and PPARγ activation on CXCL9 and CXCL11 secretion in GD and control cells after stimulation of these chemokines secretion with IFNγ and TNFα. This study shows the presence of PPARα and PPARγ in GD and control cells. A potent dose-dependent inhibition by PPARα-agonists was observed on the cytokines-stimulated secretion of CXCL9 and CXCL11 in GD and control cells. The potency of the PPARα agonists used was maximum on the secretion of CXCL9, reaching about 90% of inhibition by fenofibrate and 85% by ciprofibrate. The relative potency of the compounds was different with each chemokine; for example, gemfibrozil exerted a 55% inhibition on CXCL11, whereas it had a weaker activity on CXCL9 (40% inhibition). PPARα agonists were stronger (ANOVA, P<0.001) inhibitors of CXCL9 and CXCL11 secretion in thyrocytes than PPARγ agonists. Our study shows the presence of PPARα in GD and control thyrocytes. PPARα activators are potent inhibitors of the secretion of CXCL9 and CXCL11, suggesting that PPARα may be involved in the modulation of the immune response in the thyroid.

Different skeletal effects of the peroxisome proliferator activated receptor (PPAR)α agonist fenofibrate and the PPARγ agonist pioglitazone

BackgroundAll the peroxisome proliferator activated receptors (PPARs) are found to be expressed in bone cells. The PPARγ agonist rosiglitazone has been shown to decrease bone mass in mice and thiazolidinediones (TZDs) have recently been found to increase bone loss and fracture risk in humans treated for type 2 diabetes mellitus. The aim of the study was to examine the effect of the PPARα agonist fenofibrate (FENO) and the PPARγ agonist pioglitazone (PIO) on bone in intact female rats.MethodsRats were given methylcellulose (vehicle), fenofibrate or pioglitazone (35 mg/kg body weight/day) by gavage for 4 months. BMC, BMD, and body composition were measured by DXA. Histomorphometry and biomechanical testing of excised femurs were performed. Effects of the compounds on bone cells were studied.ResultsThe FENO group had higher femoral BMD and smaller medullary area at the distal femur; while trabecular bone volume was similar to controls. Whole body BMD, BMC, and trabecular bone volume were lower, while medullary area was increased in PIO rats compared to controls. Ultimate bending moment and energy absorption of the femoral shafts were reduced in the PIO group, while similar to controls in the FENO group. Plasma osteocalcin was higher in the FENO group than in the other groups. FENO stimulated proliferation and differentiation of, and OPG release from, the preosteoblast cell line MC3T3-E1.ConclusionWe show opposite skeletal effects of PPARα and γ agonists in intact female rats. FENO resulted in significantly higher femoral BMD and lower medullary area, while PIO induced bone loss and impairment of the mechanical strength. This represents a novel effect of PPARα activation.

The PPAR-α activator fenofibrate fails to provide myocardial protection in ischemia and reperfusion in pigs

Rodent studies suggest that peroxisome proliferator-activated receptor-alpha (PPAR-alpha) activation reduces myocardial ischemia-reperfusion (I/R) injury and infarct size; however, effects of PPAR-alpha activation in large animal models of myocardial I/R are unknown. We determined whether chronic treatment with the PPAR-alpha activator fenofibrate affects myocardial I/R injury in pigs. Domestic farm pigs were assigned to treatment with fenofibrate 50 mg.kg(-1).day(-1) orally or no drug treatment, and either a low-fat (4% by weight) or a high-fat (20% by weight) diet. After 4 wk, 66 pigs underwent 90 min low-flow regional myocardial ischemia and 120 min reperfusion under anesthetized open-chest conditions, resulting in myocardial stunning. The high-fat group received an infusion of triglyceride emulsion and heparin during this terminal experiment to maintain elevated arterial free fatty acid (FFA) levels. An additional 21 pigs underwent 60 min no-flow ischemia and 180 min reperfusion, resulting in myocardial infarction. Plasma concentration of fenofibric acid was similar to the EC50 for activation of PPAR-alpha in vitro and to maximal concentrations achieved in clinical use. Myocardial expression of PPAR-alpha mRNA was prominent but unaffected by fenofibrate treatment. Fenofibrate increased expression of carnitine palmitoyltransferase (CPT)-I mRNA in liver and decreased arterial FFA and lactate concentrations (each P < 0.01). However, fenofibrate did not affect myocardial CPT-I expression, substrate uptake, lipid accumulation, or contractile function during low-flow I/R in either the low- or high-fat group, nor did it affect myocardial infarct size. Despite expression of PPAR-alpha in porcine myocardium and effects of fenofibrate on systemic metabolism, treatment with this PPAR-alpha activator does not alter myocardial metabolic or contractile responses to I/R in pigs.

Investigation of potential mechanisms regulating protein expression of hepatic pyruvate dehydrogenase kinase isoforms 2 and 4 by fatty acids and thyroid hormone.

Liver contains two pyruvate dehydrogenase kinases (PDKs), namely PDK2 and PDK4, which regulate glucose oxidation through inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Starvation increases hepatic PDK2 and PDK4 protein expression, the latter occurring, in part, via a mechanism involving peroxisome proliferator-activated receptor-alpha (PPARalpha). High-fat feeding and hyperthyroidism, which increase circulating lipid supply, enhance hepatic PDK2 protein expression, but these increases are insufficient to account for observed increases in hepatic PDK activity. Enhanced expression of PDK4, but not PDK2, occurs in part via a mechanism involving PPAR-alpha. Heterodimerization partners for retinoid X receptors (RXRs) include PPARalpha and thyroid-hormone receptors (TRs). We therefore investigated the responses of hepatic PDK protein expression to high-fat feeding and hyperthyroidism in relation to hepatic lipid delivery and disposal. High-fat feeding increased hepatic PDK2, but not PDK4, protein expression whereas hyperthyroidism increased both hepatic PDK2 and PDK4 protein expression. Both manipulations decreased the sensitivity of hepatic carnitine palmitoyltransferase I (CPT I) to suppression by malonyl-CoA, but only hyperthyrodism elevated plasma fatty acid and ketone-body concentrations and CPT I maximal activity. Administration of the selective PPAR-alpha activator WY14,643 significantly increased PDK4 protein to a similar extent in both control and high-fat-fed rats, but WY14,643 treatment and hyperthyroidism did not have additive effects on hepatic PDK4 protein expression. PPARalpha activation did not influence hepatic PDK2 protein expression in euthyroid rats, suggesting that up-regulation of PDK2 by hyperthyroidism does not involve PPARalpha, but attenuated the effect of hyperthyroidism to increase hepatic PDK2 expression. The results indicate that hepatic PDK4 up-regulation can be achieved by heterodimerization of either PPARalpha or TR with the RXR receptor and that effects of PPARalpha activation on hepatic PDK2 and PDK4 expression favour a switch towards preferential expression of PDK4.

A role for peroxisome proliferator-activated receptor alpha (PPARalpha ) in the control of cardiac malonyl-CoA levels: reduced fatty acid oxidation rates and increased glucose oxidation rates in the hearts of mice lacking PPARalpha are associated with higher concentrations of malonyl-CoA and reduced expression of malonyl-CoA decarboxylase.

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a nuclear receptor transcription factor that has an important role in controlling cardiac metabolic gene expression. We determined whether mice lacking PPARalpha (PPARalpha (-/-) mice) have alterations in cardiac energy metabolism. Rates of palmitate oxidation were significantly decreased in isolated working hearts from PPARalpha (-/-) hearts compared with hearts from age-matched wild type mice (PPARalpha (+/+) mice), (62 +/- 12 versus 154 +/- 65 nmol/g dry weight/min, respectively, p < 0.05). This was compensated for by significant increases in the rates of glucose oxidation and glycolysis. The decreased fatty acid oxidation in PPARalpha (-/-) hearts was associated with increased levels of cardiac malonyl-CoA compared with PPARalpha (+/+) hearts (15.15 +/- 1.63 versus 7.37 +/- 1.31 nmol/g, dry weight, respectively, p < 0.05). Since malonyl-CoA is an important regulator of cardiac fatty acid oxidation, we also determined if the enzymes that control malonyl-CoA levels in the heart are under transcriptional control of PPARalpha. Expression of both mRNA and protein as well as the activity of malonyl-CoA decarboxylase, which degrades malonyl-CoA, were significantly decreased in the PPARalpha (-/-) hearts. In contrast, the expression and activity of acetyl-CoA carboxylase, which synthesizes malonyl-CoA and 5'-AMP-activated protein kinase, which regulates acetyl-CoA carboxylase, were not altered. Glucose transporter expression (GLUT1 and GLUT4) was not different between PPARalpha (-/-) and PPARalpha (+/+) hearts, suggesting that the increase in glycolysis and glucose oxidation in the PPARalpha null mice was not due to direct effects on glucose uptake but rather was occurring secondary to the decrease in fatty acid oxidation. This study demonstrates that PPARalpha is an important regulator of fatty acid oxidation in the heart and that this regulation of fatty acid oxidation may in part occur due to the transcriptional control of malonyl-CoA decarboxylase.