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We have shown previously that endocannabinoids promote sebaceous lipogenesis, and sebocytes are involved in the metabolism of the endocannabinoid-like substance oleoylethanolamide (OEA). OEA is an endogenous activator of GPR119, a recently deorphanized receptor, which currently is being investigated as a promising antidiabetic drug target. In this study, we investigated the effects of OEA as well as the expression and role of GPR119 in human sebocytes. We found that OEA promoted differentiation of human SZ95 sebocytes (elevated lipogenesis, enhanced granulation, and the induction of early apoptotic events), and it switched the cells to a proinflammatory phenotype (increased expression and release of several proinflammatory cytokines). Moreover, we could also demonstrate that GPR119 was expressed in human sebocytes, and its small interfering RNA-mediated gene silencing suppressed OEA-induced sebaceous lipogenesis, which was mediated via c-Jun N-terminal kinase, extracellular signal-regulated kinase 1/2, protein kinase B, and CRE-binding protein activation. Finally, our pilot data demonstrated that GPR119 was downregulated in the sebaceous glands of patients with acne, arguing that GPR119 signaling may indeed be disturbed in acne. Collectively, our findings introduce the OEA/GPR119 signaling as a positive regulator of sebocyte differentiation and highlight the possibility that dysregulation of this pathway may contribute to the development of seborrhea and acne., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: The endocannabinoid and neurosteroid systems regulate emotions and stress responses. Activation of peroxisome proliferator-activated receptor (PPAR)-α by the endocannabinoid congener N-palmitoylethanolamine (PEA) regulates pathophysiological systems (e.g., inflammation, oxidative stress) and induces peripheral biosynthesis of allopregnanolone, a gamma-aminobutyric acidergic neurosteroid implicated in mood disorders. However, effects of PPAR-α on emotional behavior are poorly understood., Methods: We studied the impact of PPAR-α activation on emotional behavior in a mouse model of posttraumatic stress disorder. Neurosteroid levels before and after PEA treatment were measured by gas chromatography-mass spectrometry in relevant brain regions of socially isolated versus group-housed mice exposed to the contextual fear conditioning test, elevated plus maze test, forced swim test, and tail suspension test. Neurosteroidogenic enzyme levels were quantified in hippocampus by Western blot., Results: PEA administered in a model of conditioned contextual fear reconsolidation blockade facilitated fear extinction and fear extinction retention and induced marked antidepressive- and anxiolytic-like effects in socially isolated mice with reduced brain allopregnanolone levels. These effects were mimicked by the PPAR-α synthetic agonists, fenofibrate and GW7647, and were prevented by PPAR-α deletion, PPAR-α antagonists, and neurosteroid-enzyme inhibitors. Behavioral improvements correlated with PEA-induced upregulation of PPAR-α, neurosteroidogenic enzyme expression, and normalization of corticolimbic allopregnanolone levels., Conclusions: This evidence supports a previously unknown role for PPAR-α in behavior regulation and suggests new strategies for the treatment of neuropsychopathologies characterized by deficient neurosteroidogenesis, including posttraumatic stress disorder and major depressive disorder., (Copyright © 2019 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Although the role of inflammation to combat infection is known, the contribution of metabolic changes in response to sepsis is poorly understood. Sepsis induces the release of lipid mediators, many of which activate nuclear receptors such as the peroxisome proliferator-activated receptor (PPAR)α, which controls both lipid metabolism and inflammation. We aimed to elucidate the previously unknown role of hepatic PPARα in the response to sepsis., Methods: Sepsis was induced by intraperitoneal injection of Escherichia coli in different models of cell-specific Ppara-deficiency and their controls. The systemic and hepatic metabolic response was analyzed using biochemical, transcriptomic and functional assays. PPARα expression was analyzed in livers from elective surgery and critically ill patients and correlated with hepatic gene expression and blood parameters., Results: Both whole body and non-hematopoietic Ppara-deficiency in mice decreased survival upon bacterial infection. Livers of septic Ppara-deficient mice displayed an impaired metabolic shift from glucose to lipid utilization resulting in more severe hypoglycemia, impaired induction of hyperketonemia and increased steatosis due to lower expression of genes involved in fatty acid catabolism and ketogenesis. Hepatocyte-specific deletion of PPARα impaired the metabolic response to sepsis and was sufficient to decrease survival upon bacterial infection. Hepatic PPARA expression was lower in critically ill patients and correlated positively with expression of lipid metabolism genes, but not with systemic inflammatory markers., Conclusion: During sepsis, Ppara-deficiency in hepatocytes is deleterious as it impairs the adaptive metabolic shift from glucose to FA utilization. Metabolic control by PPARα in hepatocytes plays a key role in the host defense against infection., Lay Summary: As the main cause of death in critically ill patients, sepsis remains a major health issue lacking efficacious therapies. While current clinical literature suggests an important role for inflammation, metabolic aspects of sepsis have mostly been overlooked. Here, we show that mice with an impaired metabolic response, due to deficiency of the nuclear receptor PPARα in the liver, exhibit enhanced mortality upon bacterial infection despite a similar inflammatory response, suggesting that metabolic interventions may be a viable strategy for improving sepsis outcomes., (Copyright © 2019 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Background & Aims: Cytochrome P450 2A5 (CYP2A5) is induced by ethanol, and the ethanol induction of CYP2A5 is regulated by nuclear factor-erythroid 2-related factor 2 (NRF2). Cyp2a5 knockout (Cyp2a5 -/- ) mice develop more severe alcoholic fatty liver than Cyp2a5 +/+ mice. Fibroblast growth factor 21 (FGF21), a PPARα-regulated liver hormone, is involved in hepatic lipid metabolism. Alcoholic and non-alcoholic fatty liver are enhanced in Pparα knockout (Pparα -/- ) mice. This study investigates the relationship between the PPARα-FGF21 axis and the enhanced alcoholic fatty liver in Cyp2a5 -/- mice., Methods: Mice were fed the Lieber-Decarli ethanol diet to induce alcoholic fatty liver., Results: More severe alcoholic fatty liver disease was developed in Cyp2a5 -/- mice than in Cyp2a5 +/+ mice. Basal FGF21 levels were higher in Cyp2a5 -/- mice than in Cyp2a5 +/+ mice, but ethanol did not further increase the elevated FGF21 levels in Cyp2a5 -/- mice while FGF21 was induced by ethanol in Cyp2a5 +/+ mice. Basal levels of serum FGF21 were lower in Pparα -/- mice than in Pparα +/+ mice; ethanol induced FGF21 in Pparα +/+ mice but not in Pparα -/- mice, whereas ethanol induced hypertriglyceridemia in Pparα -/- mice but not in Pparα +/+ mice. Administration of recombinant FGF21 normalized serum FGF21 and triglyceride in Pparα -/- mice. Alcoholic fatty liver was enhanced in liver-specific Fgf21 knockout mice. Pparα and Cyp2a5 double knockout (Pparα -/- /Cyp2a5 -/- ) mice developed more severe alcoholic fatty liver than Pparα +/+ /Cyp2a5 -/- mice., Conclusions: These results suggest that CYP2A5 protects against the development of alcoholic fatty liver disease, and the PPARα-FGF21 axis contributes to the protective effects of CYP2A5 on alcoholic fatty liver disease., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Perfluorinated compounds (PFCs) have been recognized as an important class of environmental contaminants commonly detected in blood samples of both wildlife and humans. These compounds have been in use for more than 60 years as surface treatment chemicals, polymerization aids, and surfactants. They possess a strong carbon-fluorine bond, which leads to their environmental persistence. There is evidence from both epidemiology and laboratory studies that PFCs may be immunotoxic, affecting both cell-mediated and humoral immunity. Reported effects of PFCs include decreased spleen and thymus weights and cellularity, reduced specific antibody production, reduced survival after influenza infection, and altered cytokine production. Immunosuppression is a critical effect associated with exposure to PFCs, as it has been reported to reduce antibody responses to vaccination in children. Mounting evidence suggests that immunotoxicity in experimental animals can occur at serum concentrations below, within, or just above the reported range for highly exposed humans and wildlife. Considering bioaccumulation and exposure to multiple PFCs, the risk of immunotoxicity for humans and wildlife cannot be discounted. This review will discuss current and recently published work exploring the immunomodulatory effects of PFCs in experimental animals and humans., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

Transient receptor potential vanilloid type-1 (TRPV1) channels expressed in primary afferent neurons play a critical role in nociception triggered by endogenous and exogenous compounds. In the present study, the functional and biochemical interaction between TRPV1 channels and type-α peroxisome proliferator-activated receptors (PPARα) has been investigated. In TRPV1-expressing CHO cells, patch-clamp studies revealed that acute application of the PPARα agonists clofibrate (CLO; 0.1-100 μM), WY14643 (1-300 μM), or GW7647 (0.1-100 nM) activated TRPV1 currents in a concentration-dependent manner, with EC50s of 5.3 ± 0.8 μM, 13.0 ± 1.2 μM, and 12.7 ± 0.3 nM, respectively. The role of PPARα in these pharmacological responses was confirmed by the ability of the PPARα antagonist GW6471 (10 μM) to block CLO-, WY14643- and GW7647-induced TRPV1 activation, and by the observation that modulation of PPARα levels via siRNA-mediated suppression or PPARα over-expression affected TRPV1 channel activation by PPARα agonists accordingly. In cells cotransfected with PPARα and TRPV1, PPARα receptors were detected in TRPV1-immunoprecipitated fractions. When compared to capsaicin (CAP), TRPV1 currents activated by PPARα agonists showed a higher degree of acute desensitization and tachyphylaxis; moreover, GW7647, when pre-incubated at a concentration (1nM) unable to activate TRPV1 currents per se, desensitized CAP-induced TRPV1 currents. Finally, a sub-effective concentration of each PPARα agonist inhibited TRPV1-dependent bradykinin-induced [Ca(2+)]i transients in sensory neurons. Collectively, these results provide evidence for a PPARα-mediated pathway triggering TRPV1 channel activation and desensitization, and highlight a novel mechanism which might contribute to the analgesic effects shown by PPARα agonists in vivo., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Background & Aims: Peroxisome proliferator-activated receptor alpha (PPARα) is a key regulator of hepatic fat oxidation that serves as an energy source during starvation. Vanin-1 has been described as a putative PPARα target gene in liver, but its function in hepatic lipid metabolism is unknown., Methods: We investigated the regulation of vanin-1, and total vanin activity, by PPARα in mice and humans. Furthermore, the function of vanin-1 in the development of hepatic steatosis in response to starvation was examined in Vnn1 deficient mice, and in rats treated with an inhibitor of vanin activity., Results: Liver microarray analyses reveals that Vnn1 is the most prominently regulated gene after modulation of PPARα activity. In addition, activation of mouse PPARα regulates hepatic- and plasma vanin activity. In humans, consistent with regulation by PPARα, plasma vanin activity increases in all subjects after prolonged fasting, as well as after treatment with the PPARα agonist fenofibrate. In mice, absence of vanin-1 exacerbates the fasting-induced increase in hepatic triglyceride levels. Similarly, inhibition of vanin activity in rats induces accumulation of hepatic triglycerides upon fasting. Microarray analysis reveal that the absence of vanin-1 associates with gene sets involved in liver steatosis, and reduces pathways involved in oxidative stress and inflammation., Conclusions: We show that hepatic vanin-1 is under extremely sensitive regulation by PPARα and that plasma vanin activity could serve as a readout of changes in PPARα activity in human subjects. In addition, our data propose a role for vanin-1 in regulation of hepatic TG levels during fasting., (Copyright © 2014 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Background & Aims: Hepatocellular steatosis is the most frequent liver disease in the western world and may develop further to steatohepatitis, liver cirrhosis and hepatocellular carcinoma. We have previously shown that lipid droplet (LD)-associated proteins of the perilipin/PAT-family are differentially expressed in hepatocyte steatosis and that perilipin is expressed de novo. The aim of this study was to determine the conditions for the temporal regulation of de novo synthesis of perilipin in vitro and in vivo., Methods: Immunohistochemical PAT-analysis was performed with over 120 liver biopsies of different etiology and duration of steatosis. Steatosis was induced in cultured hepatocytic cells with combinations of lipids, steatogenic substances and DMSO for up to 40 days under conditions of stable down-regulation of adipophilin and/or TIP47., Results: Whereas perilipin and adipophilin were expressed in human chronic liver disease irrespective of the underlying etiology, in acute/microvesicular steatosis TIP47, and MLDP were recruited from the cytoplasm to LDs, adipophilin was strongly increased, but perilipin was virtually absent. In long-term steatosis models in vitro, TIP47, MLDP, adipophilin, and finally perilipin were gradually induced. Perilipin and associated formation of LDs were intricately regulated on the transcriptional (PPARs, C/EBPs, SREBP), post-transcriptional, and post-translational level (TAG-amount, LD-fusion, phosphorylation-dependent lipolysis). In long-term steatosis models under stable down-regulation of adipophilin and/or TIP47, MLDP substituted for TIP47, and perilipin for adipophilin., Conclusions: LD-maturation in hepatocytes in vivo and in vitro involves sequential expression of TIP47, MLDP, adipophilin and finally perilipin. Thus, perilipin might be used for the differential diagnosis of chronic vs. acute steatosis., (Copyright © 2013 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Aims: In liver cirrhosis, inflammation triggers portal hypertension. Kupffer cells (KC) produce vasoconstrictors upon activation by bacterial constituents. Here, we hypothesize that the anti-inflammatory action of the cannabinoid receptor 2 (CB2) agonists JWH-133 and GP 1a attenuate portal hypertension., Main Methods: In vivo measurements of portal pressures and non-recirculating liver perfusions were performed in rats 4weeks after bile duct ligation (BDL). Zymosan (150μg/ml, isolated liver perfusion) or LPS (4mg/kgb.w., in vivo) was infused to activate the KC in the absence or presence of JWH-133 (10mg/kgb.w.), GP 1a (2.5mg/kgb.w.) or ZnPP IX (1μM). Isolated KC were treated with Zymosan (0.5mg/ml) in addition to JWH-133 (5μM). The thromboxane (TX) B2 levels in the perfusate and KC media were determined by ELISA. Heme oxygenase-1 (HO-1) and CB2 were analyzed by Western blot or confocal microscopy., Key Findings: JWH-133 or GP 1a pre-treatment attenuated portal pressures following KC activation in all experimental settings. In parallel, HO-1 expression increased with JWH-133 pre-treatment. However, the inhibition of HO-1 enhanced portal hypertension, indicating the functional role of this novel pathway. In isolated KC, the expression of CB2 and HO-1 increased with Zymosan, LPS and JWH-133 treatment while TXB2 production following KC activation was attenuated by JWH-133 pre-treatment., Significance: JWH-133 or GP 1a treatment attenuates portal hypertension. HO-1 induction by JWH-133 plays a functional role. Therefore, the administration of JWH-133 or GP 1a represents a promising new treatment option for portal hypertension triggered by microbiological products., (© 2013.)

Peroxisome proliferator-activated receptors (PPARs) are transcription factors that belong to the superfamily of nuclear hormone receptors and regulate the expression of several genes involved in metabolic processes that are potentially linked to the development of some diseases such as hyperlipidemia, diabetes, and obesity. One type of PPAR, PPAR-α, is a transcription factor that regulates the metabolism of lipids, carbohydrates, and amino acids and is activated by ligands such as polyunsaturated fatty acids and drugs used to treat dyslipidemias. There is evidence that genetic variants within the PPARα gene have been associated with a risk of the development of dyslipidemia and cardiovascular disease by influencing fasting and postprandial lipid concentrations; the gene variants have also been associated with an acceleration of the progression of type 2 diabetes. The interactions between genetic PPARα variants and the response to dietary factors will help to identify individuals or populations who can benefit from specific dietary recommendations. Interestingly, certain nutritional conditions, such as the prolonged consumption of a protein-restricted diet, can produce long-lasting effects on PPARα gene expression through modifications in the methylation of a specific locus surrounding the PPARα gene. Thus, this review underlines our current knowledge about the important role of PPAR-α as a mediator of the metabolic response to nutritional and environmental factors.

Background & Aims: Dysregulated glucose homeostasis and lipid accumulation characterize non-alcoholic fatty liver disease (NAFLD), but underlying mechanisms are obscure. We report here that Krüppel-like factor 6 (KLF6), a ubiquitous transcription factor that promotes adipocyte differentiation, also provokes the metabolic abnormalities of NAFLD by post-transcriptionally activating PPARα-signaling., Methods: Mice with either hepatocyte-specific depletion of KLF6 ('ΔHepKlf6') or global KLF6 heterozygosity (Klf6+/-) were fed a high fat diet (HFD) or chow for 8 or 16 weeks. Glucose and insulin tolerance tests were performed to assess insulin sensitivity. Overexpression and knockdown of KLF6 in cultured cells enabled the elucidation of underlying mechanisms. In liver samples from a cohort of 28 NAFLD patients, the expression of KLF6-related target genes was quantified., Results: Mice with global- or hepatocyte-depletion of KLF6 have reduced body fat content and improved glucose and insulin tolerance, and are protected from HFD-induced steatosis. In hepatocytes, KLF6 deficiency reduces PPARα-regulated genes (Trb3, Pepck) with diminished PPARα protein but no change in Pparα mRNA, which is explained by the discovery that KLF6 represses miRNA 10b, which leads to induction of PPARα. In NAFLD patients with advanced disease and inflammation, the expression of miRNA 10b is significantly downregulated, while PEPCK mRNA is upregulated; KLF6 mRNA expression also correlates with TRB3 as well as PEPCK gene expression., Conclusions: KLF6 increases PPARα activity, whereas KLF6 loss leads to PPARα repression and attenuation of lipid and glucose abnormalities associated with a high fat diet. The findings establish KLF6 as a novel regulator of hepatic glucose and lipid metabolism in fatty liver., (Copyright © 2013 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Fenofibrate is a peroxisome proliferator activated receptor alpha agonist that contains both pro and anti-inflammatory properties, and has been used in the treatment of dyslipidemia and diabetes for decades. Its receptors are expressed in the liver, skeletal muscle, cardiac, enteric, and renal cells, which allow it to provide systemic regulation of lipoprotein metabolism, fatty acid oxidation, and fatty acid transport. Hyperglycemia is a common complication found in the burn population because hepatic glucose production and catecholamine-mediated hepatic glycogenolysis are augmented. Insulin resistance occurs often in these patients and is associated with poor outcomes. In the pediatric burn population, fenofibrate has been found to ameliorate or decrease the number of hypoglycemic episodes when compared to management with insulin alone. Its mechanism of action is thought to involve an improvement in insulin signaling in skeletal muscle, as well as improvements in mitochondrial function, glucose oxidation, and insulin sensitivity. The long term use of fenofibrate in severely burned patients may improve hyperglycemia and insulin resistance, as well as improve wound healing, and reduce apoptosis, and oxidative stress., (Copyright © 2011 Elsevier Ltd and ISBI. All rights reserved.)

Background & Aims: Peroxisome proliferator-activated receptor α (PPARα) is a transcription factor activated by ligands that regulates genes related to vascular tone, oxidative stress, and fibrogenesis, pathways implicated in the development of cirrhosis and portal hypertension. This study aims at evaluating the effects of PPARα activation with fenofibrate on hepatic and systemic hemodynamics, hepatic endothelial dysfunction, and hepatic fibrosis in CCl(4)-cirrhotic rats., Methods: Mean arterial pressure (MAP), portal pressure (PP), and portal blood flow (PBF) were measured in cirrhotic rats treated with oral fenofibrate (25mg/kg/day, n=10) or its vehicle (n=12) for 7 days. The liver was then perfused and dose-relaxation curves to acetylcholine (Ach) were performed. We also evaluated Sirius Red staining of liver sections, collagen-I mRNA expression, and smooth muscle actin (α-SMA) protein expression, cyclo-oxygenase-1 (COX-1) protein expression, and cGMP levels in liver homogenates, and TXB(2) production in perfusates. Nitric oxide (NO) bioavailability and eNOS activation were measured in hepatic endothelial cells (HEC) isolated from cirrhotic rat livers., Results: CCl(4) cirrhotic rats treated with fenofibrate had a significantly lower PP (-29%) and higher MAP than those treated with vehicle. These effects were associated with a significant reduction in hepatic fibrosis and improved vasodilatory response to acetylcholine. Moreover, a reduction in COX-1 expression and TXB(2) production in rats receiving fenofibrate and a significant increase in NO bioavailability in HEC with fenofibrate were observed., Conclusions: PPARα activation markedly reduced PP and liver fibrosis and improved hepatic endothelial dysfunction in cirrhotic rats, suggesting it may represent a new therapeutic strategy for portal hypertension in cirrhosis., (Copyright © 2012 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Endocannabinoids (anandamide and 2-AG) are relevant modulators of appetite and energy expenditure through their action on cannabinoid CB(1) receptors. The actions of anandamide on feeding behavior are dependent both, on the anatomical location of CB(1) receptors (central nervous system versus peripheral tissues) and the feeding status. Anandamide uptake into cells, prior to its degradation by specific enzymatic systems, is a necessary step for the regulation of its extracellular levels. The present study explores the route and feeding stimulus dependency of the effects of the anandamide uptake blocker AM404. Peripherally, AM404 reduced feeding in partially satiated animals through a PPARα-independent mechanism, but not in food deprived ones. When AM404 was injected into the cerebral ventricles of food deprived rats, it resulted in hyperphagia that was antagonized by the cannabinoid receptor inverse agonist SR141716A. These results support the multimodal action of endocannabinoid signaling in feeding regulation, which depends on the anatomical site and the feeding status of the animal., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Emerging evidence suggests that the lack of PPARα enhances hepatic steatosis and inflammation in Ppara-null mice when fed a high-fat diet (HFD). Thus, the aim of this study was to determine whether Ppara-null mice are more susceptible to nonalcoholic steatohepatitis (NASH) than their wild-type (WT) counterparts following short-term feeding with a HFD. Age-matched male WT and Ppara-null mice were randomly assigned to consume ad libitum a standard Lieber-DeCarli liquid diet (STD) (35% energy from fat) or a HFD (71% energy from fat) for 3 wk. Liver histology, plasma transaminase levels, and indicators of oxidative/nitrosative stress and inflammatory cytokines were evaluated in all groups. Levels of lobular inflammation and the NASH activity score were greater in HFD-exposed Ppara-null mice than in the other 3 groups. Biochemical analysis revealed elevated levels of ethanol-inducible cytochrome P450 2E1 and TNFα accompanied by increased levels of malondialdehyde as well as oxidized and nitrated proteins in Ppara-null mice. Elevated oxidative stress and inflammation were associated with activation of c-Jun-N-terminal kinase and p38 kinase, resulting in increased hepatocyte apoptosis in Ppara-null mice fed a HFD. These results, with increased steatosis, oxidative stress, and inflammation observed in Ppara-null mice fed a HFD, demonstrate that inhibition of PPARα functions may increase susceptibility to high fat-induced NASH.

Background & Aims: Fibroblast growth factor 21 (FGF21), a hormone primarily secreted by the liver in response to peroxisome proliferator-activated receptor-α (PPARα) activation, has recently been shown to possess beneficial effects on lipid metabolism and hepatic steatosis in animal models. This study investigated the association of FGF21 with nonalcoholic fatty liver disease (NAFLD) in Chinese patients., Methods: Serum FGF21 levels were determined by enzyme-linked immunosorbent assay (ELISA) in 224 NAFLD and 124 control subjects, and their association with parameters of adiposity, glucose, and lipid profiles and levels of liver injury markers was studied. Besides serum concentrations, the mRNA expression of FGF21 in the liver tissue was also quantified by real-time PCR in 17 subjects with different degrees of steatosis, and was correlated with the levels of intrahepatic lipid. The protein levels of FGF21 were determined by quantitative ELISA., Results: Serum FGF21 levels in patients with NAFLD (402.38 pg/ml [242.03, 618.25]) were significantly higher than those in control subjects (198.62 pg/ml [134.96, 412.62]) (p<0.01). In human liver tissues, FGF21 mRNA expression increased with the degree of steatosis. Both FGF21 mRNA expression and serum FGF21 concentrations were positively correlated with intrahepatic triglyceride (TG) having r = 0.692 and r = 0.662, respectively, at p<0.01. Furthermore, the increased expression of FGF21 was accompanied by elevated protein levels in liver tissues., Conclusions: These results support the role of FGF21 as a key regulator of hepatic lipid metabolism in humans, and suggest that serum FGF21 can be potentially used as a biomarker for NAFLD., (Copyright © 2010 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Palmitoylethanolamde (PEA) is an endogenous lipid neuromodulator that mediates a broad spectrum of pharmacological effects by activation of peroxisome proliferator-activated receptor alpha (PPAR-alpha). Detectable or high levels of PEA in the CNS have been found, but the specific function of this lipid remains to be clarified. Here we report evidence that PEA, activating PPAR-alpha receptor and involving neurosteroids de novo synthesis, modulates pentobarbital-evoked hypnotic effect. A single i.c.v. administration of PEA (1-5microg) increases pentobarbital induced loss of righting reflex (LORR) duration in mice. This effect is mimicked by GW7647 (3microg), a synthetic PPAR-alpha agonist, and disappears in PPAR-alpha knockout mice. Antagonism experiments strongly support the engaging of neurosteroidogenic pathway in the increase of LORR duration induced by PEA. This effect disappeared using two inhibitors blocking the key steps of neurosteroids synthesis, aminogluthetimide and finasteride. Moreover, we demonstrated that in brainstem PEA increased the expression of steroidogenic acute regulatory protein (StAR) and cytochrome P450 side-chain cleavage (P450scc), both involved in neurosteroidogenesis. Accordingly, allopregnanolone (ALLO) levels were in turn higher in brainstem of PEA and pentobarbital treated mice vs pentobarbital alone, as revealed by quantitative analysis using gas chromatography-mass spectrometry. A Our results demonstrate that exogenous administration of PEA, through a PPAR-alpha-dependent mechanism, modulates neurosteroids formation increasing ALLO levels and leading to a positive modulation of GABA(A) receptor. These data further strengthen our previous data on the role of PPAR-alpha in PEA's actions and could provide a new framework to understand its role in the CNS., (Copyright 2009 Elsevier B.V. All rights reserved.)

The purpose of this study is to identify the hierarchy of importance amongst pathways involved in fatty acid (FA) metabolism and their regulators in the control of hepatic FA composition. A modeling approach was applied to experimental data obtained during fasting in PPARalpha knockout (KO) mice and wild-type mice. A step-by-step procedure was used in which a very simple model was completed by additional pathways until the model fitted correctly the measured quantities of FA in the liver. The resulting model included FA uptake by the liver, FA oxidation, elongation and desaturation of FA, which were found active in both genotypes during fasting. From the model analysis we concluded that PPARalpha had a strong effect on FA oxidation. There were no indications that this effect changes during the fasting period, and it was thus considered to be constant. In PPARalpha KO mice, FA uptake was identified as the main pathway responsible for FA variation in the liver. The models showed that FA were oxidized at a constant and small rate, whereas desaturation of FA also occurred during fasting. The latter observation was rather unexpected, but was confirmed experimentally by the measurement of delta-6-desaturase mRNA using real-time quantitative PCR (QPCR). These results confirm that mathematical models can be a useful tool in identifying new biological hypotheses and nutritional routes in metabolism.

Background: The peroxisome proliferators-activated receptor-alpha (PPARalpha) is important in lipid metabolism and regulation of inflammation. Recent studies have demonstrated the immunoregulatory effects of PPARalpha. This investigated the immunosuppressive effects of PPARalpha using its ligand, WY14643, on acute lung allograft rejection in a rat model and its mechanism of action., Method: The left lungs were transplanted orthotopically from Brown-Norway donors to F344 recipients. The recipients were then divided into control and WY14643 treatment groups. The allograft rejection was evaluated by daily chest X-ray imaging and was evaluated histologically on Day 7 after transplantation. The cytokine messenger RNA (mRNA) expression at Days 3 and 5 were also evaluated in allografts and recipient spleens., Results: The radiologic and histologic findings indicated that treatment with the WY14643 reduced acute allograft rejection. WY14643 also significantly extended the allograft survival time. This amelioration of acute rejection by WY14643 was also associated with up-regulated interleukin (IL)-4, IL-10, and transforming growth factor-beta (TGFbeta) mRNA expression in the lung allografts and spleens., Conclusion: This study demonstrated that the administration of the PPARa ligand, WY14643, ameliorates acute lung allograft rejection in rats. Treatment with WY14643 reduced histopathologic scores, prolonged graft survival, and up-regulated the expression of anti-inflammatory cytokine IL-4, IL-10, and TGFbeta mRNA compared with the control.

Former studies in rats demonstrated that starvation or treatment with the hypolipidemic drug clofibrate causes a marked increase in the concentration of carnitine in the liver. The molecular mechanisms underlying these phenomena in rats, however, have been largely unknown. Since both, fasting and clofibrate treatment lead to an activation of peroxisome proliferator-activated receptor alpha (PPARalpha), a ligand-activated transcription factor that acts as an important regulator of lipid metabolism and energy homeostasis, the hypothesis has been raised that activation of this nuclear receptor is responsible for the alterations in carnitine homeostasis observed in rodents by either stimulating carnitine uptake or carnitine biosynthesis or both of them. The present review summarizes recent evidence from studies with rodents and pigs supporting the hypothesis that activation of PPARalpha is responsible for the alterations in carnitine homeostasis previously observed. According to these novel results an essential role for PPARalpha in the regulation of carnitine uptake and carnitine biosynthesis in rodents and pigs has been clearly established. Due to the strong similarities in the gene response to PPARalpha agonists and the similar metabolic features and anatomic conditions between pigs and humans, it is likely that pharmacological PPARalpha agonists exert similar effects in humans.

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-activated transcription factor that belongs to the steroid hormone receptor superfamily. PPARalpha is expressed predominantly in tissues that have a high level of fatty acid catabolism, such as liver, heart, and muscle. PPARalpha regulates the expression of a number of genes critical for lipid and lipoprotein metabolism. PPARalpha ligand fibrates have been used for the treatment of dyslipidemia due to their ability to lower plasma triglyceride levels and elevate HDL cholesterol levels. PPARalpha activators have been shown to regulate obesity in rodents by both increasing hepatic fatty acid oxidation and decreasing the levels of circulating triglycerides responsible for adipose cell hypertrophy and hyperplasia. However, these effects of PPARalpha on obesity and lipid metabolism may be exerted with sexual dimorphism and seem to be influenced by estrogen. Estrogen inhibits the actions of PPARalpha on obesity and lipid metabolism through its effects on PPARalpha-dependent regulation of target genes. Thus, the use of fibrates seems to be effective in men and postmenopausal women with obesity and lipid disorders, but not in premenopausal women with functioning ovaries.

Glucocorticoids (GCs) are effective anti-inflammatory agents widely used in therapeutic approach to treatment of spinal cord trauma. Previous results suggest that peroxisome proliferator activated receptor alpha (PPAR-alpha), an intracellular transcription factor activated by fatty acids, plays a role in control of secondary inflammatory process associated with spinal cord injury (SCI). With the aim to characterize the role of PPAR-alpha in GC-mediated anti-inflammatory activity, we tested the efficacy of dexamethasone (DEX), a synthetic GC specific for glucocorticoid receptor (GR), in an experimental model of spinal cord trauma induced in mice by the application of vascular clips (force of 24 g) to the dura via a four-level T5-T8 laminectomy, and comparing mice lacking PPAR-alpha (PPAR-alphaKO) with wild type (WT) mice. Results indicate that DEX-mediated anti-inflammatory activity is weakened in PPAR-alphaKO mice, as compared to WT controls. In particular, DEX was less effective in PPAR-alphaKO, compared to WT mice, as evaluated by inhibition of the degree of spinal cord inflammation and tissue injury, neutrophil infiltration, nitrotyrosine formation, pro-inflammatory cytokine expression, NF-kappaB activation, inducible nitric-oxide synthase (iNOS) expression; and apoptosis. This study indicates that PPAR-alpha can contribute to the anti-inflammatory activity of GCs in SCI.

Heme is an essential prosthetic group of proteins involved in oxygen transport, energy metabolism and nitric oxide production. ALAS1 (5-aminolevulinate synthase) is the rate-limiting enzyme in heme synthesis in the liver and is highly regulated to adapt to the metabolic demand of the hepatocyte. In the present study, we describe human hepatic ALAS1 as a new direct target for the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha). In primary human hepatocytes and in HepG2 cells, PPARalpha agonists induced an increase in ALAS1 mRNA levels, which was abolished by PPARalpha silencing. These effects are mediated by two functional PPAR binding sites at positions -9 and -2.3 kb relative to the ALAS1 transcription start site. PPARalpha ligand treatment also up-regulated the mRNA levels of the genes ALAD (5-aminolevulinate dehydratase), UROS (uroporphyrinogen III synthase), UROD (uroporphyrinogen decarboxylase), CPOX (coproporphyrinogen oxidase) and PPOX (protoporphyrinogen oxidase) encoding for enzymes controlling further steps in heme biosynthesis. In HepG2 cells treated with PPARalpha agonists and in mouse liver upon fasting, the association of PPARalpha, its partner retinoid X receptor, PPARgamma co-activator 1alpha and activated RNA polymerase II with the transcription start site region of all six genes was increased, leading to higher levels of the metabolite heme. In conclusion, these data strongly support a role of PPARalpha in the regulation of human ALAS1 and of five additional genes of the pathway, consequently leading to increased heme synthesis.

Purpose: Peroxisome proliferator-activated receptors (PPAR's) are lipid sensors and when activated they modify gene expression of proteins regulating fatty acid (FA) metabolism in liver cells. The aim of the present study was to examine the in vivo effects of PPAR alpha and gamma activation combined with high fat diet (HFD) feeding on the lipid content and FA profile in the liver., Material/methods: We assessed whether in vivo activation of PPARs (alpha or gamma) affects lipid accumulation in the liver induced by HFD feeding. Furthermore, as PPAR activity may be a key factor regulating long chain fatty acids (LCFA) flux and subsequent LCFA utilization in the liver, we prompted to investigate also the FA profile in different lipid fractions in this tissue., Results: PPARalpha agonist (WY 14,643) treatment reduced the accumulation of liver lipids free fatty acids (FFA:-30%, diacylglycerols DAG: -27% and triacylglycerols TAG: -60%, p<0.05) evoked by HFD feeding. Interestingly, with PPARgamma stimulation liver lipid content was further elevated comparing to the effects of HFD (phospholipids PL: +48%, DAG: +231%, TAG: +346%, p<0.05)., Conclusions: These findings suggest that in vivo PPARalpha and PPARgamma activation combined with HFD feeding exert different effects on lipid content in rat's liver and in vivo PPARalpha activation may prevent lipid overload in the liver cells provoked by HFD feeding.

Eicosapentaenoic acid (EPA) is known to lower plasma cholesterol level and triglycerides, but its precise molecular mechanisms have not been reported. The objective of this study was to determine the mechanism of action of EPA in lowering plasma cholesterol and triglyceride levels. In this study, we found that long-term, highly purified EPA administration effectively reduced plasma and hepatic cholesterol levels in wild-type mice but not in peroxisome proliferator-activated receptor alpha (PPARalpha)-null mice. The significant down-regulation was detected at the transcriptional level on genes involved in cholesterol biosynthesis and cholesterol efflux in the liver only in wild-type mice. Limited changes were found in molecules involved in lipoprotein assembly and uptake, intracellular cholesterol transport, bile acid biosynthesis, and bile secretion. Transcription factors regulating cholesterol homeostasis were insignificantly modulated by the EPA treatment, except for sterol response element-binding protein-2 (SREBP-2). Based on these findings, EPA potentially lowers the plasma cholesterol levels by suppressing gene expression of cholesterol biosynthesis enzymes and a cholesterol efflux protein from the liver. In mature SREBP-2, processing ability appears to play an important role in the presence of PPARalpha. Our study provides novel evidence of an additional rationale for the use of EPA in the prevention and treatment of hypercholesterolemia.

Peroxisome proliferator chemicals are classic non-genotoxic carcinogens. These agents cause liver cancers when chronically administered to rats and mice. Peroxisome proliferators include the widely prescribed lipid and cholesterol lowering fibrate drugs. In contrast to the results in rodents, there is no evidence that fibrates are associated with elevated risk of liver cancer or any other neoplasms in humans thus indicating a species difference in the hepatocarcinogenic response. The biological effects of peroxisome proliferators are mediated by the peroxisome proliferator-activated receptor (PPAR)alpha. Pparalpha-null mice are resistant to all of the pleiotropic effects of peroxisome proliferators, including cell proliferation and hepatocarcinogenesis. The mechanism of hepatocellular proliferation involves downregulation of the microRNA let-7c gene by PPARalpha. Let-7c controls levels of proliferative c-myc by destabilizing its mRNA. Thus, upon suppression of let-7c, c-myc mRNA and protein are elevated resulting in enhanced hepatocellular proliferation. In contrast, PPARalpha-humanized mice, that respond to Wy-14,643 by lower serum triglycerides and induction of genes encoding fatty acid metabolizing enzymes, are resistant to peroxisome proliferator-induced cell proliferation and cancer. These mice do not exhibit downregulation of let-7c gene expression thus forming the basis for the resistance to hepatocellular carcinogenesis.

Background/aims: Hepatitis C virus (HCV) infected patients with high serum levels of bile acids (BAs) usually fail to respond to antiviral therapy. Besides, BAs are essential factors for replication of the porcine enteric calicivirus by inhibiting interferon signaling. The role of BAs on HCV RNA replication was thus assessed., Methods: BAs and other compounds were tested using an HCV-replication model containing a luciferase reporter gene., Results: BAs, especially chenodeoxycholate and deoxycholate, up-regulated genotype 1 HCV RNA replication by more than tenfold. Only free but not conjugated BAs were active, suggesting that their effect was mediated by a nuclear receptor. Only farnesoid X receptor (FXR) ligands stimulated HCV replication while FXR silencing and FXR antagonism by guggulsterone blocked the up-regulation induced by BAs. Furthermore, guggulsterone alone inhibited basal level of HCV replication by tenfold. Modulation of HCV replication by FXR ligands occurred in the same proportion in presence or absence of type I interferon, suggesting a mechanism of action independent of this control of viral replication. However, BAs or guggulsterone did not affect replication of genotype 2a-JFH1., Conclusions: Exposure to routinely measured concentrations of BAs increases HCV replication by a novel mechanism involving activation of the nuclear receptor FXR.

Patients with type-2 diabetes mellitus (T2DM) are considered to be at particularly high risk for cardiovascular disease. Over the last decade, the members of the peroxisome proliferator-activated receptor (PPAR) subfamily of nuclear receptors have emerged as valuable pharmacological targets whose activation can normalize metabolic dysfunctions and reduce some cardiovascular risk factors associated with T2DM. PPARalpha agonists, such as the fibrates, can correct dyslipidemia. PPARgamma agonists, such as the thiazolidinediones, act as insulin sensitizers and improve insulin resistance in patients with T2DM. Because of restricted potency and certain side-effects of PPAR agonists, as well as the increasingly epidemic incidence of T2DM, there is a real need for the development of selective PPAR agonists with improved clinical efficacy. This chapter focuses on the PPAR agonists currently used in the clinic, as well as on the discovery and development of the next generation of PPAR agonists.

Background: Peripheral blood mononuclear cells (PBMCs) are the only readily available cells in healthy humans. Various studies showed disease-characteristic gene expression patterns in PBMCs. However, little is known of nutritional effects on PBMC gene expression patterns. Fatty acids are nutrients that regulate gene expression by activating the nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha). PBMCs express PPARalpha, making these cells interesting to study FA-dependent gene expression., Objective: The aim of this study was to elucidate whether PBMC gene expression profiles also reflect nutrition-related metabolic changes. Furthermore, we focused on the specific role of PPARalpha in regulation of PBMC gene expression during fasting, when plasma free fatty acids are elevated., Design: Four healthy male volunteers fasted for 48 h. PBMC RNA was hybridized on Affymetrix whole genome microarrays. To elucidate the role of PPARalpha, PBMCs of 9 blood donors were incubated with the specific PPARalpha ligand Wy14643., Results: After 24 and 48 h of fasting, 1200 and 1386 genes were changed >1.4-fold, respectively. Many of those genes were involved in fatty acid beta-oxidation and are known PPARalpha target genes. Incubation of PBMCs with Wy14643 resulted in up-regulation of genes that were also up-regulated during fasting., Conclusions: We conclude that PBMC gene expression profiles reflect nutrition-related metabolic changes such as fasting and that part of the fasting-induced changes are likely regulated by PPARalpha.

Recent progress at the molecular level has revealed that nuclear receptors play an important role in the generation of mammalian circadian rhythms. To examine whether peroxisome proliferator-activated receptor alpha (PPARalpha) is involved in the regulation of circadian behavioral rhythms in mammals, we evaluated the locomotor activity of mice administered with the hypolipidemic PPARalpha ligand, bezafibrate. Circadian locomotor activity was phase-advanced about 3h in mice given bezafibrate under light-dark (LD) conditions. Transfer from LD to constant darkness did not change the onset of activity in these mice, suggesting that bezafibrate advanced the phase of the endogenous clock. Surprisingly, bezafibrate also advanced the phase in mice with lesions of the suprachiasmatic nucleus (SCN; the central clock in mammals). The circadian expression of clock genes such as period2, BMAL1, and Rev-erbalpha was also phase-advanced in various tissues (cortex, liver, and fat) without affecting the SCN. Bezafibrate also phase-advanced the activity phase that is delayed in model mice with delayed sleep phase syndrome (DSPS) due to a Clock gene mutation. Our results indicated that PPARalpha is involved in circadian clock control independently of the SCN and that PPARalpha could be a potent target of drugs to treat circadian rhythm sleep disorders including DSPS.

Previous studies in BALB/c mice revealed an adjuvant effect of di-(2-ethylhexyl) phthalate (DEHP) to simultaneously administered ovalbumin. DEHP is the most commonly used phthalate plasticizer. In vivo formed metabolites of DEHP are peroxisome-proliferator-activated receptor (PPAR) ligands, a group of chemicals that may have immunomodulatory properties. To study whether the PPARalpha receptor was involved in the adjuvant effect of DEHP, PPARalpha-deficient 129/Sv mice were exposed intraperitoneally to a mixture of OVA and DEHP, and the OVA-specific IgE, IgG1 and IgG2a responses were compared to the corresponding responses in the wild-type strain. The study showed that the adjuvant mechanism of DEHP is mediated through a PPARalpha-independent mechanism. Compared to mice only given OVA, DEHP induced highly increased levels of OVA-specific IgG1 and IgG2a, both in the wild-type and in the PPARalpha knock-out strains, indicating that DEHP is a mixed Th1/Th2 adjuvant.

Objective: Growth hormone (GH) enhances lipolysis in adipose tissue, thereby increasing the flux of fatty acids to other tissues. Moreover, GH increases hepatic triglyceride synthesis and secretion in rats and decreases the action of peroxisome proliferator-activated receptor (PPAR)alpha. PPARalpha is activated by fatty acids and regulates hepatic lipid metabolism in rodents. The aim of this study was to investigate the importance of PPARalpha for the effects of GH on hepatic gene expression and lipoprotein metabolism., Design: Bovine GH was given as a continuous infusion (5mg/kg/day) for 7 days to PPARalpha-null and wild-type (wt) mice. Plasma and liver lipids and hepatic gene expression were measured. In separate experiments, hepatic triglyceride secretion was measured., Results: GH treatment decreased hepatic triglyceride content and increased hepatic triglyceride secretion rate and serum cholesterol levels. Furthermore, GH increased hepatic acylCoA:diacylglycerol acyltransferase (DGAT)2 mRNA levels, but decreased the hepatic mRNA expression of acyl-CoA oxidase, medium-chain acyl-CoA dehydrogenase and PPARgamma1. All these GH effects were independent of PPARalpha. However, the effect of GH on Cyp4a10, PPARgamma2, and DGAT1 was different between the genotypes. GH treatment decreased Cyp4a10 mRNA expression in wt mice, but increased the expression in PPARalpha-null mice. In contrast, GH decreased the expression of DGAT1 and PPARgamma2 in PPARalpha-null mice, but not in wt mice., Conclusions: Most of the effects of GH on lipid and lipoprotein metabolism were independent of PPARalpha. However, GH had unique effects on Cyp4a10, DGAT1, and PPARgamma2 gene expression in PPARalpha-null mice showing cross-talk between GH and PPARalpha signalling in vivo.

PGC-1alpha induces mitochondrial biogenesis in muscle and its activity has been related to insulin sensitization. Here, we report that fibrates induce PGC-1alpha gene expression in muscle both in vivo and in vitro. However, only activation via PPARdelta but not PPARalpha underlies this effect. PPARdelta induces PGC-1alpha gene transcription through a PPAR-response element in the PGC-1alpha promoter. Moreover, PGC-1alpha coactivates the PPARdelta-responsiveness of its own gene. A further positive autoregulatory loop of control relies on the induction of PPARdelta expression by PGC-1alpha. These data point to a distinct value of PPARdelta rather than PPARalpha agonists in the improvement of oxidative metabolism in muscle.

Phytol, a branched-chain fatty alcohol, is the naturally occurring precursor of phytanic and pristanic acid, branched-chain fatty acids that are both ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor alpha (PPARalpha). To investigate the metabolism of phytol and the role of PPARalpha in its regulation, wild-type and PPARalpha knockout (PPARalpha-/-) mice were fed a phytol-enriched diet or, for comparison, a diet enriched with Wy-14,643, a synthetic PPARalpha agonist. After the phytol-enriched diet, phytol could only be detected in small intestine, the site of uptake, and liver. Upon longer duration of the diet, the level of the (E)-isomer of phytol increased significantly in the liver of PPARalpha-/- mice compared with wild-type mice. Activity measurements of the enzymes involved in phytol metabolism showed that treatment with a PPARalpha agonist resulted in a PPARalpha-dependent induction of at least two steps of the phytol degradation pathway in liver. Furthermore, the enzymes involved showed a higher activity toward the (E)-isomer than the (Z)-isomer of their respective substrates, indicating a stereospecificity toward the metabolism of (E)-phytol. In conclusion, the results described here show that the conversion of phytol to phytanic acid is regulated via PPARalpha and is specific for the breakdown of (E)-phytol.

Berberine (BBR), a compound purified from Cortidis rhizoma, reduces serum cholesterol, triglycerides, and LDL-cholesterol of hypercholesterolemic patients and high fat diet fed animals, and increases hepatic LDLR mRNA and protein levels through a post-transcriptional mechanism. BBR also enhances the hypoglycemic action of insulin in diabetic animal models. Here, we show that BBR inhibits the differentiation of 3T3-L1 preadipocytes induced by DM and suppresses the mitotic clonal expansion of 3T3-L1 preadipocytes in a time- and dose-dependent manner. Gene expression analysis and Western blot analysis reveal that the BBR inhibits the mRNA and protein levels of adipogenesis related transcription factors PPARgamma and C/EBPalpha and their upstream regulator, C/EBPbeta. Reporter gene assays demonstrate that the full-length PPARgamma and alpha transcription activities are inhibited by BBR. Using real-time PCR, we have also found that the PPAR target genes that are involved in adipocyte differentiation, such as aP2, CD36, ACO, LPL, and other adipocyte markers, are suppressed by BBR. These studies suggest that BBR works on multiple molecular targets as an inhibitor of PPARgamma and alpha, and is a potential weight reducing, hypolipidemic, and hypoglycemic drug.

The three peroxisome proliferator-activated receptors (PPAR alpha, PPAR beta, and PPAR gamma) are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily. They are regarded as being sensors of physiological levels of fatty acids and fatty acid derivatives. In the adult mouse skin, they are found in hair follicle keratinocytes but not in interfollicular epidermis keratinocytes. Skin injury stimulates the expression of PPAR alpha and PPAR beta at the site of the wound. Here, we review the spatiotemporal program that triggers PPAR beta expression immediately after an injury, and then gradually represses it during epithelial repair. The opposing effects of the tumor necrosis factor-alpha and transforming growth factor-beta-1 signalling pathways on the activity of the PPAR beta promoter are the key elements of this regulation. We then compare the involvement of PPAR beta in the skin in response to an injury and during hair morphogenesis, and underscore the similarity of its action on cell survival in both situations.

Hepatic peroxisome proliferation, increases in the numerical and volume density of peroxisomes, is believed to be closely related to peroxisome proliferator-activated receptor alpha (PPARalpha) activation; however, it remains unknown whether peroxisome proliferation depends absolutely on this activation. To verify occurrence of PPARalpha-independent peroxisome proliferation, fenofibrate treatment was used, which was expected to significantly enhance PPARalpha dependence in the assay system. Surprisingly, a novel type of PPARalpha-independent peroxisome proliferation and enlargement was uncovered in PPARalpha-null mice. The increased expression of dynamin-like protein 1, but not peroxisome biogenesis factor 11alpha, might be associated with the PPARalpha-independent peroxisome proliferation at least in part.

Ragaglitazar is a novel and potent dual peroxisome proliferators activated receptor (PPAR) alpha and gamma activator. The aim of this study is to investigate the effect of ragaglitazar on blood pressure and endothelial function in insulin resistant animal model and non-insulin resistant hypertensive models. The effects ragaglitazar were tested in Zucker fa/fa, spontaneously hypertensive rats (SHR), 2 kidney 1clip rat (2K1C) and Wistar Kyoto rats (WKY). Pioglitazone was taken as a comparative standard. Ragaglitazar showed significant reduction (P<0.001) of systolic blood pressure (SBP) in insulin resistant fa/fa rats, with concomitant reduction in plasma triglycerides (TG) and insulin levels while pioglitazone (10 mg kg(-1)) showed significant (P<0.05) but comparatively less reduction. Ragaglitazar in contrast to pioglitazone showed significant reduction (P<0.05) of SBP in SHR, 2K1C while the same dose did not have any effect on normotensive WKY. Ragaglitazar also showed significant improvement in acetylcholine-induced relaxation in isolated aorta of Zucker fa/fa, SHR, 2K1C and also potentiated the insulin-induced vasorelaxation in Zucker fa/fa rats. These findings summarize that ragaglitazar shows significant reduction of BP and improvement in endothelial function not only in insulin resistant but also in non-insulin resistant hypertensive models where standard thiazolidinediones are ineffective. These data indicates that dual PPARalpha and gamma activator ragaglitazar can be beneficial for the treatment of hypertension and vascular disease commonly associated with type 2 diabetes.

PPARs and sterol regulatory element-binding protein-1c (SREPB-1c) are fatty acid-regulated transcription factors that control lipid metabolism at the level of gene expression. This study compared a high oleic acid-rich safflower oil (ORSO) diet and a high-butter diet for their effect on adipose mass and expressions of genes regulated by PPAR and SREPB-1c in rats. Four groups of Wistar rats were fed 30S (30% ORSO), 5S (5% ORSO), 30B (29% butter + 1% ORSO), or 5B (4% butter plus 1% ORSO) diets for 15 wk. Compared with the 30B group, the 30S group had less retroperitoneal white adipose tissue (RWAT) mass and lower mRNA expressions of lipoprotein lipase, adipocyte fatty acid-binding protein, fatty acid synthase, acetyl CoA carboxylase, and SREBP-1c in the RWAT, higher mRNA expressions of acyl CoA oxidase, carnitine palmitoyl-transferase 1A, fatty acid binding protein, and mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase in the liver (P < 0.05). The 18:2(n-6) and 20:4(n-6) contents in the liver and RWAT of the 30S group were >2 fold those of the 30B group (P < 0.05). These results suggested that the smaller RWAT mass in rats fed the high-ORSO diet might be related to the higher tissue 18:2(n-6) and 20:4(n-6). This in turn could upregulate the expressions of fatty acid catabolic genes through the activation of PPARalpha in the liver and downregulate the expressions of lipid storage and lipogenic gene through the suppression of SREBP-1c in the RWAT.

Aquatic organisms living in coastal and estuarine areas are exposed to diverse contaminants which can cause peroxisome proliferation. Peroxisome proliferators are agonists of peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor superfamily. We have recently demonstrated expression of the three PPAR isoforms in liver of mullet Chelon labrosus and other fish species by immunohistochemistry. The goal of the present study was first to clone PPARalpha and second to investigate its expression pattern in various tissues of mullet. PCR-based screening of mullet cDNA with PPARalpha specific degenerate primers resulted in amplification, subcloning and sequencing of a 1090 bp cDNA fragment (AY618315) that encodes mullet PPARalpha and exhibits highest amino acid identity to fish Sparus aurata PPARalpha (90%). Semi-quantitative RT-PCR was used to characterize the expression of PPARalpha in brain, muscle, liver, spleen, gill, heart and female gonad of juvenile and adult male and female mullet. For this, mullet 18S-rRNA (AY825252), beta-actin (AY836368) and elongation factor alpha (AY836369) were cloned and used as internal reference for RT-PCR. Expression of PPARalpha was detected in all tissues, was highest in liver and lowest in adult male and female muscle.

The adipose differentiation-related protein (ADFP)/adipophilin belongs to a family of PAT (for perilipin, ADFP, and TIP47) proteins that associate on the surface of lipid droplets (LDs). Except for LD association, a clear role for ADFP has not been found. We demonstrate that ADFP is transcriptionally regulated by peroxisome proliferator-activated receptor alpha (PPARalpha) in mouse liver and rat and human hepatoma cells through a highly conserved direct repeat-1(DR-1) element. Although the ADFP mRNA is highly increased by a synthetic PPARalpha agonist, the ADFP protein is only substantially increased in cells containing LDs, such as hepatocytes incubated with fatty acids, and in livers of fasted mice. ADFP is induced by fasting even in the absence of a functional PPARalpha, in marked contrast to the PPARalpha target gene acyl-coenzyme A oxidase-1. Activation of LXRs, which stimulates LD formation through the activation of lipogenesis, does not affect ADFP mRNA levels. TIP47, another PAT member known to be expressed in liver, was unaffected by all treatments. This constitutively expressed PAT member seems to be less transcriptionally regulated than ADFP. These observations suggest that ADFP is primarily a fasting-induced protein in liver that coats the newly synthesized triacylglycerol-containing LDs formed during fasting.

Clinical, experimental and epidemiological research has shown the undeniable causal relationship between low HDL plasma concentrations and cardiovascular disease. Low HDL levels are present in about 10% of the general population and represent the most frequent form of dyslipidemia in patients with coronary disease. Reduced HDL concentrations seem to be unable to eliminate efficiently the cholesterol excess at vascular wall level, contributing to the onset of the inflammatory response that typically occurs in the pathogenesis of atherosclerosis right from its earliest stages. The results of numerous studies quite convincingly suggest that HDL is capable of exerting anti-inflammatory activity either directly or by modulating the expression of a number of acute phase proteins. Although the therapeutic options currently available for raising HDL levels still show modest efficacy, both in experimental and pre-clinical fields, genetic investigation and specifically aimed pharmacological treatment have produced more encouraging results, shedding some light on the concrete possibility of being able to treat this disease in the very near future.

Atherosclerosis is a primary cause of death in the United States, and the current obesity epidemic threatens to exacerbate its morbidity and mortality worldwide. Despite important cardiovascular treatment advances over the past few decades, new approaches are needed to curb dangerous health trends. Nuclear receptors are a superfamily of ligand-activated transcription factors. The discovery of subfamilies known as peroxisome proliferator-activated receptors (PPAR) and liver X receptors (LXR) as lipid-sensors that regulate lipid and glucose metabolism as well as inflammation offers new targets for nutritional and pharmacologic treatment of cardiovascular disease.

Peroxisome proliferator-activated receptor (PPAR)alpha is a pleiotropic regulator in many cell types and has recently been implicated in skin homeostasis. To determine the role of PPARalpha in skin physiology, transgenic mice were generated using the tetracycline Tet-off regulatory system to target constitutively activated PPARalpha to the epidermis and other stratified epithelia by the bovine keratin K5 promoter. Expression of the transgene during early development resulted in postnatal lethality within 2 days after birth. A thin epidermis, few hair follicles, and abnormal development of the tongue were observed in neonatal transgenic mice. Early mortality was not observed when transgenic PPARalpha expression was diminished by administration of doxycycline (dox) to the mothers. The alterations noted in neonatal mice were not observed in adult mice upon re-expression of the PPARalpha transgene by withdrawing dox. Attenuated hyperplasia of interfollicular epidermis after topical application of the tumor promotor 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was observed in adult mice expressing the PPARalpha transgene. In addition, expression of the PPARalpha transgene in mammary gland during pregnancy resulted in abnormal development of this organ and impaired lactation. Further investigations using primary keratinocytes revealed that expression of the transgene in keratinocytes resulted in increased differentiation and decreased proliferation, which may contribute to the observed phenotype in the transgenic mice. Thus, these results indicate that PPARalpha plays an important role in the development of stratified epithelia including skin, tongue, and mammary gland.

The liver plays a central role in the response to fasting. The hormonal profile in this condition, low insulin, and high concentrations of glucagon in plasma, induce the release of large amounts of fatty acids from adipose tissue. Prolonged starvation can therefore induce a dramatic change in the fatty acid oxidative capacity of liver metabolism. Modulation of gene expression by PPARalpha plays a crucial role in this response. While a major role for PPARalpha in the liver is to produce ketone bodies as fuel through beta-oxidation for peripheral tissues during fast, its participation in the control of CPT1A, the rate-limiting step of the pathway, remains controversial. Using Web-based software (VISTA) combining transcription factor binding site database searches with comparative sequence analyses, we have localized a conserved functional PPAR responsive element downstream of the transcriptional start site of the human CPT1A gene. We have shown that this sequence is fundamental for fatty acids or PGC1-induced transcriptional activation of the CPT1A gene. These results corroborate the hypothesis that PPARalpha regulates the limiting step in the oxidation of fatty acids in liver mitochondria.

Delta6 desaturase (D6D), the rate-limiting enzyme for highly unsaturated fatty acid (HUFA) synthesis, is induced by essential fatty acid-deficient diets. Sterol regulatory element-binding protein-1c (SREBP-1c) in part mediates this induction. Paradoxically, D6D is also induced by ligands of peroxisome proliferator-activated receptor alpha (PPARalpha). Here, we report a novel physiological role of PPARalpha in the induction of genes specific for HUFA synthesis by essential fatty acid-deficient diets. D6D mRNA induction by essential fatty acid-deficient diets in wild-type mice was diminished in PPARalpha-null mice. This impaired D6D induction in PPARalpha-null mice was not attributable to feedback suppression by tissue HUFAs because PPARalpha-null mice had lower HUFAs in liver phospholipids than did wild-type mice. Furthermore, PPARalpha-responsive genes were induced in wild-type mice under essential fatty acid deficiency, suggesting the generation of endogenous PPARalpha ligand(s). Contrary to genes for HUFA synthesis, the induction of other lipogenic genes under essential fatty acid deficiency was higher in PPARalpha-null mice than in wild-type mice even though mature SREBP-1c protein did not differ between the genotypes. The expression of PPARgamma was markedly increased in PPARalpha-null mice and might have contributed to the induction of genes for de novo lipogenesis. Our study suggests that PPARalpha, together with SREBP-1c, senses HUFA status and confers pathway-specific induction of HUFA synthesis by essential fatty acid-deficient diets.

Dietary fat regulates gene expression by controlling the activity or abundance of key transcription factors. In vitro binding and cell culture studies have identified many transcription factors as prospective targets for fatty acid regulation, including peroxisome proliferator-activated receptors (PPARalpha, beta, gamma1, and gamma2), sterol regulatory element binding protein-1c (SREBP-1c), hepatic nuclear factors (HNF-4alpha and gamma), retinoid X receptor (RXRalpha), liver X receptor (LXRalpha), and others. In vivo studies established that PPARalpha- and SREBP-1c-regulated genes are key targets for PUFA control of hepatic gene expression. PUFA activate PPARalpha by direct binding, leading to the induction of hepatic fatty acid oxidation. PUFA inhibit hepatic fatty acid synthesis by suppressing SREBP-1c nuclear abundance through several mechanisms, including suppression of SREBP-1c gene transcription and enhancement of proteasomal degradation and mRNA(SREBP1c) decay. Changes in intracellular nonesterified fatty acids (NEFA) correlate well with changes in PPARalpha activity and mRNA(SREBP-1c) abundance. Several mechanisms regulate intracellular NEFA composition, including fatty acid transport, acyl CoA synthetases and thioesterases, fatty acid elongases and desaturases, neutral and polar lipid lipases, and fatty acid oxidation. Many of these mechanisms are regulated by PPARalpha or SREBP-1c. Together, these mechanisms control hepatic lipid composition and affect whole-body lipid composition.

Peroxisome proliferator-activated receptor alpha (PPARalpha) belongs to the steroid/nuclear receptor superfamily. Two-dimensional (2D) SDS-PAGE analysis of brown adipose tissue (BAT) unexpectedly revealed six spots that were present only in PPARalpha-null mice. Proteomic analysis indicated that these proteins were tropomyosin-1 alpha chain, tropomyosin beta chain, myosin regulatory light chain 2, myosin light chain 3, and parvalbumin alpha. Analyses of mRNA have revealed that PPARalpha suppressed the genes encoding these proteins in a synchronous manner in adult wild-type mice. Histological and physiological analyses of BAT showed in adult wild-type mice, a marked suppression of BAT growth concurrent with a prominent decrease in lipolytic and thermogenesis activities. These results suggest that in adult mice, PPARalpha functions to suppress the expression of the proteins that may be involved in the architecture of BAT, and thus may function in keeping BAT in a quiescent state.