PPARalpha Ligand Research Articles

CLOFIBRATE TREATMENT IMPROVED THE STRUCTURAL DAMAGE ELICITED BY MYOCARDIAL ISCHEMIA THROUGH MODULATION OF RENIN-ANGIOTENSIN SYSTEM

Objective: Myocardial ischemia is an acute condition that, if not treated in a timely manner, produces the loss of heart tissue which can lead to heart failure or death of the patients. Our group has studied fibrates, exogenous ligands of PPAR, as an alternative to reduce processes associated with inflammation and we interested to know the exogenous ligand effect over damage in the cardiac tissue by RAS system. To study the effect of PPAR alpha ligand; clofibrate, on renin angiotensin system and on the structural morphology of the heart in myocardial infarcted subjects. Design and method: Male Wistar rats were separated in two groups: 1.- Sham, 2.- Myocardial infarct by coronary artery ligation. Seven days after, the rats were subdivided in vehicle (Vh)- or clofibrate treatment (Clof 100 mg/kg/day) administered for seven more days. At the end of the treatment (14 days in total), serum and left ventricle were analyzed. Results: Angiotensin converting enzyme (ACE), AT1 receptor and Ang II decreased in MI-Clof vs. MI-Vh, whereas non-classic RAS system components: ACE2, AT2 receptor, bradykinin, and Ang-(1–7) augmented in MI-Clof with respect to MI-Vh. VEGF also raised in clofibrate-treated animals. Clofibrate treatment preserved the structure of the sarcomere (fiber). Conclusions: Clofibrate treatment to MI rats exerts an antifibrotic effect and augmented the expression of non-classical axis of RAS system.

Involvement of the endocannabinoid system in the physiological response to transient common carotid artery occlusion and reperfusion

BackgroundThe transient global cerebral hypoperfusion/reperfusion achieved by induction of Bilateral Common Carotid Artery Occlusion followed by Reperfusion (BCCAO/R) may trigger a physiological response in an attempt to preserve tissue and function integrity. There are several candidate molecules among which the endocannabinoid system (ECS) and/or peroxisome-proliferator activated receptor-alpha (PPAR-alpha) may play a role in modulating oxidative stress and inflammation. The aims of the present study are to evaluate whether the ECS, the enzyme cyclooxygenase-2 (COX-2) and PPAR-alpha are involved during BCCAO/R in rat brain, and to identify possible markers of the ongoing BCCAO/R-induced challenge in plasma.MethodsAdult Wistar rats underwent BCCAO/R with 30 min hypoperfusion followed by 60 min reperfusion. The frontal and temporal-occipital cortices and plasma were analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS) to determine concentrations of endocannabinoids (eCBs) and related molecules behaving as ligands of PPAR-alpha, and of oxidative-stress markers such as lipoperoxides, while Western Blot and immunohistochemistry were used to study protein expression of cannabinoid receptors, COX-2 and PPAR-alpha. Unpaired Student’s t-test was used to evaluate statistical differences between groups.ResultsThe acute BCCAO/R procedure is followed by increased brain tissue levels of the eCBs 2-arachidonoylglycerol and anandamide, palmitoylethanolamide, an avid ligand of PPAR-alpha, lipoperoxides, type 1 (CB1) and type 2 (CB2) cannabinoid receptors, and COX-2, and decreased brain tissue concentrations of docosahexaenoic acid (DHA), one of the major targets of lipid peroxidation. In plasma, increased levels of anandamide and lipoperoxides were observed.ConclusionsThe BCCAO/R stimulated early molecular changes that can be easily traced in brain tissue and plasma, and that are indicative of the tissue physiological response to the reperfusion-induced oxidative stress and inflammation. The observed variations suggest that the positive modulation of the ECS and the increase of proinflammatory substances are directly correlated events. Increase of plasmatic levels of anandamide and lipoperoxides further suggests that dysregulation of these molecules may be taken as an indicator of an ongoing hypoperfusion/reperfusion challenge.

Dietary triacylglycerols with palmitic acid in the sn-2 position modulate levels of N-acylethanolamides in rat tissues.

BackgroundSeveral evidences suggest that the position of palmitic acid (PA) in dietary triacylglycerol (TAG) influences different biological functions. We aimed at evaluating whether dietary fat with highly enriched (87%) PA in sn-2 position (Hsn-2 PA), by increasing PA incorporation into tissue phospholipids (PL), modifies fatty acid profile and biosynthesis of fatty acid—derived bioactive lipids, such as endocannabinoids and their congeners.Study DesignRats were fed for 5 weeks diets containing Hsn-2 PA or fat with PA randomly distributed in TAG with 18.8% PA in sn-2 position (Lsn-2 PA), and similar total PA concentration. Fatty acid profile in different lipid fractions, endocannabinoids and congeners were measured in intestine, liver, visceral adipose tissue, muscle and brain.ResultsRats on Hsn-2 PA diet had lower levels of anandamide with concomitant increase of its congener palmitoylethanolamide and its precursor PA into visceral adipose tissue phospholipids. In addition, we found an increase of oleoylethanolamide, an avid PPAR alpha ligand, in liver, muscle and brain, associated to higher levels of its precursor oleic acid in liver and muscle, probably derived by elongation and further delta 9 desaturation of PA. Changes in endocannabinoids and congeners were associated to a decrease of circulating TNF alpha after LPS challenge, and to an improved feed efficiency.ConclusionsDietary Hsn-2 PA, by modifying endocannabinoids and congeners biosynthesis in different tissues may potentially concur in the physiological regulation of energy metabolism, brain function and body fat distribution.

Fibrates and fish oil upregulate the expression of the cholesteryl ester transfer protein (cetp) gene

Objectives: CETP is a plasma protein that reduces HDL-cholesterol levels and may increase atherosclerosis risk. n-3 and n-6 polyunsaturated fatty acids (PUFA) are natural ligands and fibrates are synthetic ligands for PPAR-alpha, a transcription factor that modulates lipid metabolism. In this study, we investigated the effects of PUFA oils and fibrates on the CETP expression.

Abstract 19434: The Novel PPARalpha-Selective Agonist K-877 Improves Dyslipidemia, Enhances Reverse Cholesterol Transport and Decreases Inflammation and Atherosclerosis

Background: Atherosclerosis is characterized by lipid accumulation and chronic inflammation in the arterial wall. Elevated levels of apolipoprotein (apo) B-containing lipoproteins are a risk factor for cardiovascular disease (CVD). By contrast, plasma levels of high-density lipoprotein (HDL) and apoA-I are protective against CVD by enhancing HDL functionality and reverse cholesterol transport (RCT). Activation of peroxisome proliferator-activated receptor-alpha (PPARalpha), a ligand-activated transcription factor, controls plasma lipid metabolism, macrophage cholesterol handling as well as the inflammatory response. Objective: To study whether pharmacological activation of PPARalpha with the highly potent PPARalpha ligand, K-877, improves lipid metabolism, macrophage cholesterol efflux, inflammation and consequently atherosclerosis development in human apoA-I transgenic mice and in the human apolipoprotein E2 knock-in mouse (apo E2KI) model of mixed dyslipidemia and atherosclerosis. Methods and results: In polarized Caco-2/TC7 human intestinal epithelium cells, K-877 treatment decreased apoB secretion and increased the expression of PPARalpha target genes involved in fatty acid oxidation and intestinal HDL production. Moreover, K-877 induced secretion of apoA-I in HDL particles. In primary human macrophages, K-877 promoted macrophage cholesterol efflux to HDL. K-877 treatment of human apoA-I transgenic mice induced plasma HDL cholesterol and apoA-I levels. Moreover, K-877 stimulated in vivo RCT in these mice. In addition, K-877 treatment exerted anti-inflammatory properties in murine and human macrophages. K-877 treatment not only improved the lipid profile, but also reduced inflammatory and macrophage marker gene expression in the aortic crosses as well as aortic atherosclerotic lesion burden in western diet-fed apo E2KI mice. Conclusion: These results demonstrate that the novel PPARalpha agonist K-877 exerts beneficial effects on lipid metabolism, RCT and inflammation resulting in anti-atherogenic properties.

Nutrient-dependent phosphorylation channels lipid synthesis to regulate PPARα

Peroxisome proliferator-activated receptor (PPAR)α is a nuclear receptor that coordinates liver metabolism during fasting. Fatty acid synthase (FAS) is an enzyme that stores excess calories as fat during feeding, but it also activates hepatic PPARα by promoting synthesis of an endogenous ligand. Here we show that the mechanism underlying this paradoxical relationship involves the differential regulation of FAS in at least two distinct subcellular pools: cytoplasmic and membrane-associated. In mouse liver and cultured hepatoma cells, the ratio of cytoplasmic to membrane FAS-specific activity was increased with fasting, indicating higher cytoplasmic FAS activity under conditions associated with PPARα activation. This effect was due to a nutrient-dependent and compartment-selective covalent modification of FAS. Cytoplasmic FAS was preferentially phosphorylated during feeding or insulin treatment at Thr-1029 and Thr-1033, which flank a dehydratase domain catalytic residue. Mutating these sites to alanines promoted PPARα target gene expression. Rapamycin-induced inhibition of mammalian/mechanistic target of rapamycin complex 1 (mTORC1), a mediator of the feeding/insulin signal to induce lipogenesis, reduced FAS phosphorylation, increased cytoplasmic FAS enzyme activity, and increased PPARα target gene expression. Rapamycin-mediated induction of the same gene was abrogated with FAS knockdown. These findings suggest that hepatic FAS channels lipid synthesis through specific subcellular compartments that allow differential gene expression based on nutritional status.

Lipid-lowering fibrates extend C. elegans lifespan in a NHR-49/PPARalpha-dependent manner

Compounds that delay aging in model organisms may be of significant interest to anti-aging medicine, since these substances potentially provide pharmaceutical approaches to promote healthy lifespan in humans. We here aimed to test whether pharmaceutical concentrations of three fibrates, pharmacologically established serum lipid-lowering drugs and ligands of the nuclear receptor PPARalpha in mammals, are capable of extending lifespan in a nematodal model organism for aging processes, the roundworm Caenorhabditis elegans. Adult C. elegans (wild-type N2 as well as two nhr-49-deficient strains, RB1716 and VC870) were maintained on agar plates and were fed E. coli strain OP50 bacteria. Bezafibrate, clofibrate, and fenofibrate were applied to the agar, respectively, to test whether they may promote longevity by quantifying survival in the presence and absence of the respective compounds. All three fibrates extended C. elegans N2 lifespan when applied at a concentration of 10 micromolar. Bezafibrate additionally extended C. elegans N2 lifespan at concentrations of 1 micromolar and 0.1 micromolar. In strains deficient for nhr-49, a functional orthologue of the mammalian peroxisome proliferator-activated receptor alpha (PPARalpha), all three compounds were incapable of extending lifespan. Taken together, fibrates promote C. elegans longevity in an NHR-49-dependent manner possibly by promoting mitohormesis and suggesting that these compounds may promote lifespan also in mammals.

Relationship of glucose and oleate metabolism to cardiac function in lipin-1 deficient (fld) mice

Lipin-1 is the major phosphatidate phosphatase (PAP) in the heart and a transcriptional coactivator that regulates fatty acid (FA) oxidation in the liver. As the control of FA metabolism is essential for maintaining cardiac function, we investigated whether lipin-1 deficiency affects cardiac metabolism and performance. Cardiac PAP activity in lipin-1 deficient [fatty liver dystrophy (fld)] mice was decreased by >80% compared with controls. Surprisingly, oleate oxidation and incorporation in triacylglycerol (TG), as well as glucose oxidation, were not significantly different in perfused working fld hearts. Despite this, [³H]oleate accumulation in phosphatidate and phosphatidylinositol was increased in fld hearts, reflecting the decreased PAP activity. Phosphatidate accumulation was linked to increased cardiac mammalian target of rapamycin complex 1 (mTORC1) signaling and endoplasmic reticulum (ER) stress. Transthoracic echocardiography showed decreased cardiac function in fld mice; however, cardiac dysfunction was not observed in ex vivo perfused working fld hearts. This showed that changes in systemic factors due to the global absence of lipin-1 could contribute to the decreased cardiac function in vivo. Collectively, this study shows that fld hearts exhibit unchanged oleate esterification, as well as oleate and glucose oxidation, despite the absence of lipin-1. However, lipin-1 deficiency increases the accumulation of newly synthesized phosphatidate and induces aberrant cell signaling.

VLDL hydrolysis by LPL activates PPAR-α through generation of unbound fatty acids

Recent evidence suggests that lipoproteins serve as circulating reservoirs of peroxisomal proliferator activated receptor (PPAR) ligands that are accessible through lipolysis. The present study was conducted to determine the biochemical basis of PPAR-alpha activation by lipolysis products and their contribution to PPAR-alpha function in vivo. PPAR-alpha activation was measured in bovine aortic endothelial cells following treatment with human plasma, VLDL lipolysis products, or oleic acid. While plasma failed to activate PPAR-alpha, oleic acid performed similarly to VLDL lipolysis products. Therefore, fatty acids are likely to be the PPAR-alpha ligands generated by VLDL lipolysis. Indeed, unbound fatty acid concentration determined PPAR-alpha activation regardless of fatty acid source, with PPAR-alpha activation occurring only at unbound fatty acid concentrations that are unachievable under physiological conditions without lipase action. In mice, a synthetic lipase inhibitor (poloxamer-407) attenuated fasting-induced changes in expression of PPAR-alpha target genes. Apolipoprotein CIII (apoCIII), an endogenous inhibitor of lipoprotein and hepatic lipase, regulated access to the lipoprotein pool of PPAR-alpha ligands, because addition of exogenous apoCIII inhibited, and removal of endogenous apoCIII potentiated, lipolytic PPAR-alpha activation. These data suggest that the PPAR-alpha response is generated by unbound fatty acids released locally by lipase activity and not by circulating plasma fatty acids.

Peroxisome proliferation activation receptor α modulation of Ca2+‐regulated exocytosis via arachidonic acid in guinea‐pig antral mucous cells

Indomethacin (IDM, 10 microm), not aspirin (ASA; 10 microm), enhanced the Ca(2+)-regulated exocytosis stimulated by 1 microm acetylcholine (ACh) in guinea-pig antral mucous cells. Indomethacin inhibits prostaglandin G/H (PGG/H) and 15R-hydroperoxy-eicosatetraenoic acid (15R-HPETE) production from arachidonic acid (AA), while ASA inhibits PGG/H production but accelerates 15R-HPETE production. This suggests that IDM accumulates AA. Arachidonic acid (2 microm) enhanced Ca(2+)-regulated exocytosis in antral mucous cells to a similar extent to IDM. Moreover, a stable analogue of AA, arachidonyltrifluoromethyl ketone (AACOCF(3)), also enhanced Ca(2+)-regulated exocytosis, indicating that AA, not products from AA, enhances Ca(2+)-regulated exocytosis. We hypothesized that AA activates peroxisome proliferation activation receptor alpha (PPARalpha), because AA is a natural ligand for PPARalpha. A PPARalpha agonist (WY14643; 1 microm) enhanced Ca(2+)-regulated exocytosis, and a PPARalpha blocker (MK886; 50 microm) abolished the enhancement of Ca(2+)-regulated exocytosis induced by AA, IDM, AACOCF(3) and WY14643. Western blotting and immunohistochemical examinations demonstrated that PPARalpha exists in antral mucous cells. Moreover, MK886 decreased the frequency of Ca(2+)-regulated exocytosis activated by 1 microm ACh or 2 microm thapsigargin alone by 25-30%. Thus, ACh stimulates AA accumulation via an [Ca(2+)](i) increase, which activates PPARalpha, leading to enhancement of Ca(2+)-regulated exocytosis in antral mucous cells. A novel autocrine mechanism mediated via PPARalpha enhances Ca(2+)-regulated exocytosis in guinea-pig antral mucous cells.

Leukotriene B4 Is a Physiologically Relevant Endogenous Peroxisome Proliferator-activated Receptor-α Agonist

Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription factors that play central roles in metabolism and inflammation. Although a variety of compounds have been shown to activate PPARs, identification of physiologically relevant ligands has proven difficult. In silico studies of lipid derivatives reported here identify specific 5-lipoxygenase products as candidate physiologically relevant PPAR-alpha activators. Subsequent studies show both in vitro and in a murine model of inflammation that 5-lipoxygenase stimulation induces PPAR-alpha signaling and that this results specifically from production of the inflammatory mediator and chemoattractant leukotriene B(4) (LTB(4)). Activation of PPAR-alpha is a direct effect of intracellularly generated LTB(4) binding to the nuclear receptor and not of secreted LTB(4) acting via its cell-surface receptors. Activation of PPAR-alpha reduces secretion of LTB(4) by stimulating degradation of this fatty acid derivative. We also show that the LTB(4) precursors leukotriene A(4) (LTA(4)) and 5-hydroperoxyeicosatetrenoic acid (5-HPETE) activate PPAR-alpha but have no significant endogenous effect independent of conversion to LTB(4). We conclude that LTB(4) is a physiologically relevant PPAR-alpha activator in cells of the immune system. This, together with previous findings, demonstrates that different types of lipids serve as endogenous PPAR-alpha ligands, with the relevant ligand varying between functionally different cell types. Our results also support the suggestion that regulation of inflammation may involve balancing proinflammatory effects of LTB(4), exerted through cell-surface receptors, and anti-inflammatory effects exerted through PPAR-alpha activation.

Endogenous ligand for an orphan receptor

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha) can be activated pharmacologically by fibrate drugs, lowering triglycerides and raising high-density lipoprotein. However, until recently, the endogenous ligand of PPARalpha had been unknown. A new study reports the identity of a physiologically relevant endogenous PPARalpha ligand as a phospholipid that is dependent upon a nutritionally responsive enzyme, fatty acid synthase. Mass spectrometry identified this phospholipid as 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (16/18-GPC) and as the endogenous ligand of PPARalpha. In vivo experiments involving portal vein infusion of 16/18-GPC induced PPARalpha-dependent expression of the fatty acid metabolism genes acyl CoA oxidase and carnitine palmitoyl transferase.

Bezafibrate Induces Plasminogen Activator Inhibitor-1 Gene Expression in a CLOCK-Dependent Circadian Manner

A functional interaction between peroxisome proliferator-activated receptor alpha (PPARalpha) and components of the circadian clock has been suggested, but whether these transcriptional factors interact to regulate the expression of their target genes remains obscure. Here we used a PPARalpha ligand, bezafibrate, to search for PPARalpha-regulated genes that are expressed in a CLOCK-dependent circadian manner. Microarray analyses using hepatic RNA isolated from bezafibrate treated-wild type, Clock mutant (Clk/Clk), and PPARalpha-null mice revealed that 136 genes are transcriptionally regulated by PPARalpha in a CLOCK-dependent manner. Among them, we focused on the plasminogen activator inhibitor-1 (PAI-1) gene, because its expression typically shows circadian variation, and it has transcriptional response elements for both PPAR and CLOCK. The bezafibrate-induced expression of PAI-1 mRNA was attenuated in Clk/Clk mice and in PPARalpha-null mice. The protein levels of PPARalpha were reduced in Clk/Clk hepatocytes. However, the overexpression of PPARalpha could not rescue bezafibrate-induced PAI-1 expression in Clk/Clk hepatocytes, suggesting that impaired bezafibrate-induced PAI-1 expression in Clk/Clk mice is not due to reduced PPARalpha expression. Luciferase reporter and chromatin immunoprecipitation analyses using primary hepatocytes demonstrated that DNA binding of both PPARalpha and CLOCK is essential for bezafibrate-induced PAI-1 gene expression. Pull-down assays in vitro showed that both PPARalpha and its heterodimerized partner retinoic acid receptor-alpha can serve as potential interaction targets of CLOCK. The present findings revealed that molecular interaction between the circadian clock and the lipid metabolism regulator affects the bezafibrate-induced gene expression.

Phosphatidylcholine and PPARα: A relevant connection in liver disease?

The nuclear receptors known as PPARs modulate metabolic and inflammatory pathways by responding to nutritional signals through ligand activation of transcription. They are targeted by drugs in use and in development for disease therapy. No endogenous PPARalpha ligand has been identified yet; the molecule that occupies the nuclear receptor-binding site in vivo while the receptor is actively driving transcription has been presently searched for by Chakravarthy et al. The group provides now a solid evidence that endogenous lipid synthesis generates a discrete phosphatidylcholine species, 1-palmitoyl 2-oleyl phosphatidylcholine (16:0/18:1 PC), that serves as an endogenous ligand for PPARalpha.

Elevated Production of Docosahexaenoic Acid in Females: Potential Molecular Mechanisms

Observational evidence suggests that in populations consuming low levels of n-3 highly unsaturated fatty acids, women have higher blood levels of docosahexaenoic acid (DHA; 22:3n-6) as compared with men. Increased conversion of alpha-linolenic acid (ALA; 18:3n-3) to DHA by females has been confirmed in fatty acid stable isotope studies. This difference in conversion appears to be associated with estrogen and some evidence indicates that the expression of enzymes involved in synthesis of DHA from ALA, including desaturases and elongases, is elevated in females. An estrogen-associated effect may be mediated by peroxisome proliferator activated receptor-alpha (PPARalpha), as activation of this nuclear receptor increases the expression of these enzymes. However, because estrogens are weak ligands for PPARalpha, estrogen-mediated increases in PPARalpha activity likely occur through an indirect mechanism involving membrane-bound estrogen receptors and estrogen-sensitive G-proteins. The protein kinases activated by these receptors phosphorylate and increase the activity of PPARalpha, as well as phospholipase A(2) and cyclooxygenase 2 that increase the intracellular concentration of PPARalpha ligands. This review will outline current knowledge regarding elevated DHA production in females, as well as highlight interactions between estrogen signaling and PPARalpha activity that may mediate this effect.

Regulatory role for phosphatidylcholine transfer protein/StarD2 in the metabolic response to peroxisome proliferator activated receptor alpha (PPARα)

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.

Role of Peroxisome Proliferator-activated Receptor-α in Hepatobiliary Injury Induced by Ammonium Perfluorooctanoate in Mouse Liver

Peroxisome proliferator-activated receptor-alpha (PPARalpha) has been suggested to protect against chemically induced hepatobiliary injuries in rodents. This function could mask the potential toxicities of perfluorooctanoic acid (PFOA) that is an emerging environmental contaminant and a weak ligand of PPARalpha. However its function has not been clarified. In this study, PFOA was found to elicit hepatocyte and bile duct injuries in Pparalpha-null mice after 4 wk treatment with PFOA ammonium salt (0, 12.5, 25, 50 micromol/kg/d, gavage). In wild-type mice, PFOA caused major hepatocellular damage dose-dependently and minor cholangiopathy observed only at 25 and 50 micromol/kg. In treated Pparalpha-null mice, PFOA produced marked fat accumulation, severe cholangiopathy, hepatocellular damage and apoptotic cells especially in bile ducts. Oxidative stress was also increased 4-fold at 50 micromol/kg and TNF-alpha mRNA was upregulated more than 3-fold at 25 micromol/kg in Pparalpha-null mice. Biliary bile acid/phospholipid ratios were higher in Pparalpha-null mice than in wild-type mice. Results from these studies suggest that PPARalpha is protective against PFOA and have a critical role in drug induced hepatobiliary injury.

Transgenic expression of proximal tubule peroxisome proliferator–activated receptor-α in mice confers protection during acute kidney injury

Our previous studies suggest that peroxisome proliferator-activated receptor-alpha (PPARalpha) plays a critical role in regulating fatty acid beta-oxidation in kidney tissue and this directly correlated with preservation of kidney morphology and function during acute kidney injury. To further study this, we generated transgenic mice expressing PPARalpha in the proximal tubule under the control of the promoter of KAP2 (kidney androgen-regulated protein 2). Segment-specific upregulation of PPARalpha expression by testosterone treatment of female transgenic mice improved kidney function during cisplatin or ischemia-reperfusion-induced acute kidney injury. Ischemia-reperfusion injury or treatment with cisplatin in wild-type mice caused inhibition of fatty-acid oxidation, reduction of mitochondrial genes of oxidative phosphorylation, mitochondrial DNA, fatty-acid metabolism, and the tricarboxylic acid cycle. Similar injury in testosterone-treated transgenic mice resulted in amelioration of these effects. Similarly, there were increases in the levels of 4-hydroxy-2-hexenal-derived lipid peroxidation products in wild-type mice, which were also reduced in the transgenic mice. Similarly, necrosis of the S3 segment was reduced in the two injury models in transgenic mice compared to wild type. Our results suggest proximal tubule PPARalpha activity serves as a metabolic sensor. Its increased expression without the use of an exogenous PPARalpha ligand in the transgenic mice is sufficient to protect kidney function and morphology, and to prevent abnormalities in lipid metabolism associated with acute kidney injury.

The Epoxygenases CYP2J2 Activates the Nuclear Receptor PPARα In Vitro and In Vivo

BackgroundPeroxisome proliferator-activated receptors (PPARs) are a family of three (PPARα, -β/δ, and -γ) nuclear receptors. In particular, PPARα is involved in regulation of fatty acid metabolism, cell growth and inflammation. PPARα mediates the cardiac fasting response, increasing fatty acid metabolism, decreasing glucose utilisation, and is the target for the fibrate lipid-lowering class of drugs. However, little is known regarding the endogenous generation of PPAR ligands. CYP2J2 is a lipid metabolising cytochrome P450, which produces anti-inflammatory mediators, and is considered the major epoxygenase in the human heart.Methodology/Principal FindingsExpression of CYP2J2 in vitro results in an activation of PPAR responses with a particular preference for PPARα. The CYP2J2 products 8,9- and 11-12-EET also activate PPARα. In vitro, PPARα activation by its selective ligand induces the PPARα target gene pyruvate dehydrogenase kinase (PDK)4 in cardiac tissue. In vivo, in cardiac-specific CYP2J2 transgenic mice, fasting selectively augments the expression of PDK4.Conclusions/SignificanceOur results establish that CYP2J2 produces PPARα ligands in vitro and in vivo, and suggests that lipid metabolising CYPs are prime candidates for the integration of global lipid changes to transcriptional signalling events.

The PPARα Agonist Fenofibrate Preserves Hippocampal Neurogenesis and Inhibits Microglial Activation After Whole-Brain Irradiation

Whole-brain irradiation (WBI) leads to cognitive impairment months to years after radiation. Numerous studies suggest that decreased hippocampal neurogenesis and microglial activation are involved in the pathogenesis of WBI-induced brain injury. The goal of this study was to investigate whether administration of the peroxisomal proliferator-activated receptor (PPAR) alpha agonist fenofibrate would prevent the detrimental effect of WBI on hippocampal neurogenesis. For this study, 129S1/SvImJ wild-type and PPARalpha knockout mice that were fed either regular or 0.2% wt/wt fenofibrate-containing chow received either sham irradiation or WBI (10-Gy single dose of (137)Cs gamma-rays). Mice were injected intraperitoneally with bromodeoxyuridine to label the surviving cells at 1 month after WBI, and the newborn neurons were counted at 2 months after WBI by use of bromodeoxyuridine/neuronal nuclei double immunofluorescence. Proliferation in the subgranular zone and microglial activation were measured at 1 week and 2 months after WBI by use of Ki-67 and CD68 immunohistochemistry, respectively. Whole-brain irradiation led to a significant decrease in the number of newborn hippocampal neurons 2 months after it was performed. Fenofibrate prevented this decrease by promoting the survival of newborn cells in the dentate gyrus. In addition, fenofibrate treatment was associated with decreased microglial activation in the dentate gyrus after WBI. The neuroprotective effects of fenofibrate were abolished in the knockout mice, indicating a PPARalpha-dependent mechanism or mechanisms. These data highlight a novel role for PPARalpha ligands in improving neurogenesis after WBI and offer the promise of improving the quality of life for brain cancer patients receiving radiotherapy.