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Palmitoleic acid (C16:1n7) has been identified as a regulator of physiological cardiac hypertrophy. In the present study, we aimed to investigate the molecular pathways involved in C16:1n7 responses in primary murine cardiomyocytes (PCM) and a mouse model of isoproterenol (ISO)-induced cardiac damage. PCMs were stimulated with C16:1n7 or a vehicle. Afterwards, RNA sequencing was performed using an Illumina HiSeq sequencer. Confirmatory analysis was performed in PCMs and HL-1 cardiomyocytes. For an in vivo study, 129 sv mice were orally treated with a vehicle or C16:1n7 for 22 days. After 5 days of pre-treatment, the mice were injected with ISO (25 mg/kg/d s. c.) for 4 consecutive days. Cardiac phenotyping was performed using echocardiography. In total, 129 genes were differentially expressed in PCMs stimulated with C16:1n7, including Angiopoietin-like factor 4 ( Angptl4 ) and Pyruvate Dehydrogenase Kinase 4 ( Pdk4 ). Both Angptl4 and Pdk4 are proxisome proliferator-activated receptor α/δ (PPARα/δ) target genes. Our in vivo results indicated cardioprotective and anti-fibrotic effects of C16:1n7 application in mice. This was associated with the C16:1n7-dependent regulation of the cardiac PPAR-specific signaling pathways. In conclusion, our experiments demonstrated that C16:1n7 might have protective effects on cardiac fibrosis and inflammation. Our study may help to develop future lipid-based therapies for catecholamine-induced cardiac damage.

N -retinylidene- N -retinylethanolamine (A2E) plays a central role in age-related macular degeneration (AMD) by inducing angiogenesis and inflammation. A2E effects are mediated at least partly via the retinoic acid receptor (RAR)-α. Here we show that A2E binds and transactivates also peroxisome proliferator-activated receptors (PPAR) and retinoid X receptors (RXR). 9'- cis -norbixin, a di-apocarotenoid is also a ligand of these nuclear receptors (NR). Norbixin inhibits PPAR and RXR transactivation induced by A2E. Moreover, norbixin reduces protein kinase B (AKT) phosphorylation, NF-κB and AP-1 transactivation and mRNA expression of the inflammatory interleukins (IL) -6 and -8 and of vascular endothelial growth factor (VEGF) enhanced by A2E. By contrast, norbixin increases matrix metalloproteinase 9 (MMP9) and C-C motif chemokine ligand 2 (CCL2) mRNA expression in response to A2E. Selective PPAR-α, -β/δ and -γ antagonists inhibit the expression of IL-6 and IL-8 while only the antagonist of PPAR-γ inhibits the transactivation of NF-κB following A2E exposure. In addition, a cocktail of all three PPARs antagonists and also HX531, an antagonist of RXR reproduce norbixin effects on inflammation. Altogether, A2E's deleterious biological effects could be inhibited through PPAR and RXR regulation. Moreover, the modulation of these NR by norbixin may open new avenues for the treatment of AMD.

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear receptors including PPARα, PPARγ, and PPARβ/δ, acting as transcription factors to regulate the expression of a plethora of target genes involved in metabolism, immune reaction, cell differentiation, and a variety of other cellular changes and adaptive responses. PPARs are activated by a large number of both endogenous and exogenous lipid molecules, including phyto- and endo-cannabinoids, as well as endocannabinoid-like compounds. In this view, they can be considered an extension of the endocannabinoid system. Besides being directly activated by cannabinoids, PPARs are also indirectly modulated by receptors and enzymes regulating the activity and metabolism of endocannabinoids, and, vice versa, the expression of these receptors and enzymes may be regulated by PPARs. In this review, we provide an overview of the crosstalk between cannabinoids and PPARs, and the importance of their reciprocal regulation and modulation by common ligands, including those belonging to the extended endocannabinoid system (or "endocannabinoidome") in the control of major physiological and pathophysiological functions.

A few studies suggested the contribution of PPARs to the etiology of schizophrenia (SCZ). However, it is still not clear whether variants in PPAR-encoding genes have a direct association with SCZ. The potential linkage between SCZ and the variants within PPAR encoding genes (PPARA, PPARD, and PPARG) was tested in a large cohort genome-wide association study (GWAS). Then, a mega-analysis was conducted using 14 gene expression profiling experiments in various human brain regions. Finally, the expression levels of the three PPAR-encoding genes were quantified in early-onset SCZ patients. Only one PPARG polymorphisms, rs62242085, presented a minor frequency deviation in the SCZ cohort (P-value = 0.035). None of the PPAR-encoding genes presented significant expression change within the brain regions profiled in 14 datasets acquired from different populations (P-value > 0.14) or in the whole blood of early-onset overall SCZ patients (P-value > 0.22). However, compared with healthy female controls, female early-onset SCZ patients presented a moderate but significant decrease in the expression level of PPARD (LFC = -0.55; P-value = 0.02) and a strong, but non-significant decrease in expression of PPARG (LFC = -1.30; P-value = 0.13). Our results do not support a significant association between variants in PPAR-encoding genes and SCZ, but suggest a necessity to explore the role of PPARD and PPARG in early SCZ phenotypes, specifically in females., (© 2020 The Author(s).)

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors with three isoforms (PPARα, PPARβ/δ, PPARγ) and can regulate pain, anxiety, and cognition. However, their role in conditioned fear and pain-fear interactions has not yet been investigated. Here, we investigated the effects of systemically administered PPAR antagonists on formalin-evoked nociceptive behaviour, fear-conditioned analgesia (FCA), and conditioned fear in the presence of nociceptive tone in rats. Twenty-three and a half hours following fear conditioning to context, male Sprague-Dawley rats received an intraplantar injection of formalin and intraperitoneal administration of vehicle, PPARα (GW6471), PPARβ/δ (GSK0660) or PPARγ (GW9662) antagonists, and 30 min later were re-exposed to the conditioning arena for 15 min. The PPAR antagonists did not alter nociceptive behaviour or fear-conditioned analgesia. The PPARα and PPARβ/δ antagonists prolonged context-induced freezing in the presence of nociceptive tone without affecting its initial expression. The PPARγ antagonist potentiated freezing over the entire trial. In conclusion, pharmacological blockade of PPARα and PPARβ/δ in the presence of formalin-evoked nociceptive tone, impaired short-term, within-trial fear-extinction in rats without affecting pain response, while blockade of PPARγ potentiated conditioned fear responding. These results suggest that endogenous signalling through these three PPAR isoforms may reduce the expression of conditioned fear in the presence of nociceptive tone.

Background: Peroxisome proliferator-activated receptors (PPARs) include the nuclear receptor superfamily of ligand-activated transcription factors involved in several metabolic processes, including carbohydrate and lipid metabolism., Material and Methods: In this study we examined PPARA: rs4253778, rs1800206, PPARD: rs2267668, rs2016520, rs1053049, PPARG rs1801282 and PPARGC1A rs8192678 polymorphisms in patients with unstable angina. This study included 246 patients with unstable angina confirmed by coronary angiography (defined by >70% stenosis in at least one major coronary artery) and 189 healthy controls., Results: We observed statistically significant difference in distribution of PPARG rs1801282 genotypes and alleles between patients and control group. Among patients there was the increased frequency of CG and GG genotypes and G alleles. The association between PPARG rs1801282 G allele and unstable angina was confirmed in multivariate regression analysis. There were no statistically significant differences in the distributions of other studied polymorphisms between patients with unstable angina and the control group., Conclusions: The results of our study suggest the association between PPARG rs1801282 G allele and unstable angina in Polish population., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Identification of new pharmacological approaches to inhibit the excessive fat intake-induced steatohepatitis and chronic kidney disease (CKD) is important. High-fat diet (HFD)-induced steatohepatitis and CKD share common pathogenesis involving peroxisome proliferator-activated receptor (PPAR)- α and - δ . Elafibranor, a dual PPAR α / δ agonist, can ameliorate the HFD-induced steatohepatitis. Nonetheless, the effects of HFD-induced CKD had not yet explored. This study investigated the effects of elafibranor (elaf) on the progression of HFD-induced CKD in mice. In vivo and in vitro renal effects were evaluated in HFD-elaf mice receiving 12 weeks of elafibranor (from 13 th to 24 th week of HFD feeding) treatment. In elafibranor-treated HFD mice, increased insulin sensitivity, reduced obesity and body fat mass, decreased severity of steatohepatitis, increased renal expression of PPAR α , PPAR δ , SIRT1, and autophagy (Beclin-1 and LC3-II) as well as glomerular/renal tubular barrier markers [synaptopodin (podocyte marker), zona occludin-1, and cubulin], reduced renal oxidative stress and caspase-3, and less urinary 8-isoprostanes excretion were observed. Aforementioned benefits of elafibranor were associated with low renal tubular injury and tubulointerstitial fibrosis scores, less albuminuria, low urinary albumin-to-creatinine ratio, and preserved glomerular filtration rate. Acute incubation of podocytes and HK-2 cells with elafibranor or recombinant SIRT1 reversed the HFD-sera-induced oxidative stress, autophagy dysfunction, cell apoptosis, barrier marker loss, albumin endocytosis, and reuptake reduction. Besides hepatoprotective and metabolic beneficial effects, current study showed that elafibranor inhibited the progression of HFD-induced CKD through activation of renal PPAR α , PPAR δ , SIRT1, autophagy, reduction of oxidative stress, and apoptosis in mice with steatohepatitis.

Peroxisome proliferator-activated receptors (PPARs) are a family of ligand-activated nuclear transcription factors, with three characterized subtypes: PPARα, PPARβ/δ, and PPARγ. The biological correlation between the two PPAR subtypes PPARα and γ and carcinogenesis is well-characterized; however, substantially less is known about the biological functions of PPARβ/δ. PPARβ/δ has been reported to repress transcription when PPARβ/δ and PPARα or PPARγ are simultaneously expressed in some cells, and MDA-MB-231 cells express functional levels of PPARβ/δ. We have previously reported that Δ 9 -tetrahydrocannabinol (Δ 9 -THC), a major cannabinoid component of the drug-type cannabis plant, can stimulate the expression of fatty acid 2-hydroxylase (FA2H) via upregulation of PPARα expression in human breast cancer MDA-MB-231 cells. Although the possibility of an inhibitory interaction between PPARα and PPARβ/δ has not been demonstrated in MDA-MB-231 cells, we reasoned if this interaction were to exist, Δ 9 -THC should make PPARα free to achieve FA2H induction. Here, we show that a PPARβ/δ-mediated suppression of PPARα function, but not of PPARγ, exists in MDA-MB-231 cells and Δ 9 -THC causes FA2H induction via mechanisms underlying the cancellation of PPARβ/δ-mediated inhibition of PPARα, in addition to the upregulation of PPARα., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Memory CD8 + T cells (T mem ) are superior mediators of adoptive cell therapy (ACT) compared with effector CD8 + T cells (T eff ) due to increased persistence in vivo . Underpinning T mem survival is a shift in cellular metabolism away from aerobic glycolysis towards fatty acid oxidation (FAO). Here we investigated the impact of the peroxisome proliferator-activated receptor (PPAR) agonist GW501516 (GW), an agent known to boost FAO in other tissues, on CD8 + T-cell metabolism, function, and efficacy in a murine ACT model. Via activation of both PPARα and PPARδ/β, GW treatment increased expression of carnitine palmitoyl transferase 1a, the rate-limiting enzyme of FAO, in activated CD8 + T cells. Using a metabolomics approach, we demonstrated that GW increased the abundance of multiple different acylcarnitines, consistent with enhanced FAO. T cells activated in the presence of GW and inflammatory signals, either mature dendritic cells or IL12, also demonstrated enhanced production of IFNγ and expression of T-bet. Despite high expression of T-bet, a characteristic of short-lived effector cells, GW-treated cells demonstrated enhanced persistence in vivo and superior efficacy in a model of ACT. Collectively, these data identify combined PPARα and PPARδ/β agonists as attractive candidates for further studies and rapid translation into clinical trials of ACT. SIGNIFICANCE: Dual activation of peroxisome proliferator-activated receptors α and δ improves the efficacy of adoptive cell therapy by reprogramming T-cell metabolism and cytokine expression., (©2018 American Association for Cancer Research.)

Objective: Genetic variation of disease susceptible genes is different in different ethnic groups and there is an evidence of association of polymorphisms of Peroxisome Proliferator Activated Receptors (PPARs) in Type 2 Diabetes Mellitus (T2DM). This research analyses the association of PPARs in early and late onset of T2DM in North Indian Population (NIP)., Methods: Total of 703 subjects were recruited from north of India and subjects were further divided into subjects of early onset (less than 25 years of onset, 26 T2DM and 26 controls) and late onset (more than 25 years of onset, 326 T2DM and 325 controls)., Result: The onset of T2DM begins from 15 years and continues further to maximum T2DM subjects to the age of 50 (76% of T2DM). High BMI and WHR, high blood pressure leading to early onset of hypertension, early mortality due to T2DM (7% of T2DM is above 75 years and 3% of T2DM has 20 years duration of onset) and high hyperglycemic NIP were the few outcomes of this research., Conclusion: There is a strong association of PPAR γ, PPAR α and PPAR δ genes on the susceptibility of T2DM in late onset but not with the early onset of T2DM subjects in North Indian Population: Dual association of PPAR γ was observed with its genotype G/G (Ala/Ala) favoring protection against T2DM and genotype C/C (Pro/Pro) favoring susceptibility to T2DM. Association of intron7 polymorphism of PPAR α and +T294C polymorphism of PPAR δ on the susceptibility to T2DM requires further analysis., (Copyright © 2017 Diabetes India. Published by Elsevier Ltd. All rights reserved.)

Background: The novel compound XH601 is a synthesized derivative of formononetin. The present study was to investigate the hypolipidemia effect and potential mechanism of XH601., Methods: Male Golden Syrian hamsters were induced by high-fat diet (HFD) for eight weeks and the hyperlipidemic model was established successfully. After XH601 treatment, serum and hepatic biochemistry parameters of hamsters were detected and the effect of XH601 on adipose tissue was also analyzed. Furthermore, 3 T3-L1 cell differentiation by Oil-Red-O staining was observed and the mRNA and protein expression of peroxisome proliferator-activated receptors (PPARs) were measured by qRT-PCR and Western-blot in mature adipocytes., Results: The in vivo results suggest that XH601 significantly decreased the adipose weight and levels of serum triglyceride (TG), total cholesterol (TC), low-density lipoprotein (LDL-C), apolipoprotein B (Apo-B), apolipoprotein E (Apo-E), while increased serum high-density lipoprotein (HDL-C). The in vitro results implied that XH601 up-regulated the mRNA and protein expression of both PPARα and PPARβ/δ in a dose-dependent manner., Conclusions: The study suggests that XH601 exhibited strong ability to improve the dyslipidemia in hamsters fed with high-fat diet. The potential mechanism of XH601 was associated with the up-regulation of PPARα and PPARβ/δ mRNA and protein expression.

Objectives: Risk of coronary heart disease (CHD) has been suggested to be associated with polymorphisms of peroxisome proliferator-activated receptors (PPARs), while the results were controversial. We aimed to systematically assess the association between PPAR polymorphisms and CHD risk., Methods: A case-control study with 446 subjects was conducted to evaluate the association between CHD risk and C161T polymorphism, which was of our special interest as this polymorphism showed different effects on risks of CHD and acute coronary syndrome (ACS). Meta-analyses were conducted to assess all PPAR polymorphisms. Either a fixed- or a random-effects model was adopted to estimate overall odds ratios (ORs)., Results: In the case-control study, T allele carriers of C161T polymorphism were not significantly associated with CHD risk (Odds ratio (OR) = 0.74, 95% confidence interval (CI) 0.47-1.15, P = 0.19), while T allele carriers showed higher risk of ACS (OR = 1.63, 95% CI 1.00-2.65, P = 0.048). The meta-analysis indicated that compared with CC homozygous, T allele carriers had lower CHD risk (OR = 0.69, 95% CI 0.59-0.82, P < 0.001) but higher ACS risk (OR = 1.43, 95% CI 1.09-1.87, P = 0.010). Three other polymorphisms were also found to be significantly associated with CHD risk under dominant model: PPAR-alpha intron 7G/C polymorphism (CC+GC vs GG, OR 1.42, 95% CI 1.13-1.78, P = 0.003), L162V polymorphism (VV+LV vs LL, OR 0.74, 95% CI 0.56-0.97, P = 0.031), and PPAR-delta +294T/C polymorphism (CC+TC vs TT, OR 1.51, 95% CI 1.12-2.05, P = 0.007)., Conclusions: The results suggested that PPAR-alpha intron 7G/C and L162V, PPAR-delta +294T/C and PPAR-gamma C161T polymorphisms could affect CHD susceptibility, and C161T polymorphism might have different effects on CHD and ACS.

Aims: Elevated low-density lipoprotein-cholesterol (LDL-C) is regarded as one of major risks of cardiovascular diseases and atherosclerotic events. It has been previously reported that peroxisome proliferator-activated receptors (PPARs) play an important role in the regulation of lipid metabolism. In this study, we aimed to investigate the influence of PPARα/δ/γ gene polymorphisms on LDL-C level. Eight hundred twenty unrelated participants were recruited. Ten single-nucleotide polymorphisms (SNPs) were genotyped to analyze the gene-gene interactions among these polymorphisms using the generalized multifactor dimensionality reduction (GMDR) method., Results: The results of single-locus analyses indicated that the genotypes with minor allele variants at the rs1800206, rs9794, rs1805192, rs709158, and rs3856806 loci are associated with higher LDL-C levels (p<0.05) after adjusting for covariates. In contrast, individuals that were homozygous for the major allele (CC) of rs10865710 had significantly higher LDL-C than those with either one or more minor type alleles (CG+GG, mean difference: -0.21 mM; 95% confidence interval [CI]: -0.37 to -0.04 mM; p=0.013). Significant gene-gene interactions among PPAR gene polymorphisms on LDL-C were identified by a generalized multifactor dimensionality reduction (GMDR) approach in 2- to 8-locus models (p<0.05)., Conclusion: Our results provide evidence that multiple PPARα/δ/γ gene polymorphisms are individually associated with increased LDL-C, and that interactions, among these alleles result in additional increased risk suggesting that PPAR genes may contribute substantially to the risk of cardiovascular diseases and atherosclerosis.

Selective killing of RPE cells in vivo by sodium iodate develops cardinal phenotypes of atrophic age-related macular degeneration. However, the molecular mechanisms are elusive. We tried to search for small cyto-protective molecules against sodium iodate and explore their mechanisms of action. Sodium iodate-mediated RPE cell death was associated with increased levels of reactive oxygen species (ROS) and IL-8. Resveratrol, a natural occurring polyphenol compound, was found to strongly protect RPE cells from sodium iodate with inhibition of production of ROS and IL-8. Resveratrol activated all isoforms of PPARs. Treatment with PPARα and PPARδ agonists inhibited sodium iodate-induced ROS production and protected RPE cells from sodium iodate. A PPARα antagonist significantly reduced resveratrol's protection of RPE cells from sodium iodate. Paradoxically, knocking down PPARδ also rendered RPE cells resistant to sodium iodate. Moreover, PPAR agonists reversed sodium iodate-induced production of IL-8. However, neutralizing extracellular IL-8 failed to protect RPE cells from sodium iodate. Taken together, these observations show that resveratrol protects RPE cells from sodium iodate injury through the activation of PPARα and alteration of PPARδ conformation. PPARα and δ modulators might ameliorate stress-induced RPE degeneration in vivo., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Genotype and allele frequencies of uncoupling proteins 2 and 3 genes (UCP2 and UCP3) and peroxisome proliferator-activated receptors genes (PPARA, PPARD and PPARG) were studied in 206 residents of the siege and in 139 individuals of more than 69 years old (control group). Studied polymorphisms included UCP2 (Ala55Val), UCP3 (C-55T), PPARA (G/C), PPARD (+294T/C), and PPARG (Pro12Ala). The G allele and the G/G genotype (PPARA) were overrepresented in the group of survivors and C/C (UCP3) genotype prevailed in the women of besieged Leningrad compared to relevant control groups of the persons of the same age who did not suffered hungry disaster. Feasible protective effects of PPARA gene allele G and C allele of UCP2 genes are briefly discussed.

Purpose of Review: This review provides an overview of newly described mechanisms by which peroxisome proliferator-activated receptors (PPARs) (α, γ, and δ) regulate several factors associated with cardiovascular risk., Recent Findings: PPAR agonists have known effects on plasma lipoprotein levels, inflammation, and insulin resistance all of which influence the risk of cardiovascular disease. Recent studies provide more detail regarding the mechanisms behind these changes. PPAR-α activation in the enterocyte on HDL and chylomicron formation. PPAR-γ agonists reduce inflammation, in part, through direct effects on adipocytes and regulatory T cells within visceral adipose. PPAR-δ also has a relatively high expression in the macrophage. Incubation of macrophages with PPAR-δ agonists was shown to inhibit foam cell formation induced excessive levels of VLDL remnants., Summary: Treatments that activate PPAR-α, PPAR-γ, and PPAR-δ alone or in combination have the potential to reduce cardiovascular risk although multiple independent mechanisms. Treatment with PPAR agonists can reduce the burden of atherogenic postprandial lipoproteins and improve vascular function, reduce inflammation and inhibit foam cell formation. All of these would be expected to have favorable effects on cardiovascular risk. The challenge remains to develop compounds that maximize these potential cardiovascular benefits while minimizing undesirable effects of these compounds.

High multivitamin intake (HV) during pregnancy increases body fat and weight and alters glucose and fatty acid metabolism in Wistar rat offspring. This study investigated the expression of peroxisome-proliferator activated receptors (PPARs) genes involved in regulation of glucose and fatty acid metabolism in their tissues. Dams received the AIN-93G diet with either the regular (RV) or 10-fold multivitamins (HV) during pregnancy. Male offspring were weaned to either the RV diet (RV-RV and HV-RV) or an obesogenic diet (RV-Ob and HV-Ob). Gene expression of PPARs in tissues was analyzed by real-time reverse transcriptase polymerase chain reaction. Gestational diet (GD) did not affect PPARs gene expression in offspring at either birth or weaning. In liver, at 14 weeks postweaning, PPAR-γ was 30% lower in the HV-RV and 30% higher in HV-Ob than in the RV-RV group [GD P=.76, postweaning diet (PD) P=.19, interaction P=.02, by two-way analysis of variance]. In muscle, PPAR-α expression was affected by GD and PD (GD P=.05, PD P<.01, interaction P=.07). In adipose tissue, PPAR-α expression was higher in all groups compared to RV-RV (GD P=.25, PD P=.85, interaction P=.03). PPAR-γ mRNA levels correlated with abdominal fat (r=0.45, P<.05) and insulin resistance index (r=0.39, P<.05). In liver, PPAR-γ expression correlated with insulin resistance index in offspring from RV (r=-0.62, P<.05), but not in those from HV dams (r=0.13, P>.05). In conclusion, the HV diet during pregnancy interacts with postweaning diets in determining the expression of PPARs genes in a tissue- and age-dependent manner and uncouples the relationship between these genes and glucose regulation and fat mass in the rat offspring., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The peroxisome proliferator-activated receptors (PPARs)-α,-β/δ and -γ are the ligand-activated transcription factors that function as the master regulators of glucose, fatty acid and lipoprotein metabolism, energy balance, cell proliferation and differentiation, inflammation and atherosclerosis. This study examined the main effects of both single-locus and multilocus interactions among genetic variants in Chinese Han individuals to test the hypothesis that PPAR-α/δ/γ polymorphisms may contribute to the etiology of hypertriglyceridemia independently and/or through such complex interactions. We genotyped 9 single nucleotide polymorphisms for PPAR-α/δ/γ. Participants were recruited from the Prevention of MetS and Multi-metabolic Disorders in Jiangsu Province of China Study. 820 subjects (474 non-hypertriglyceridemia subjects, 346 hypertriglyceridemia subjects) were randomly selected. Single-locus analyses showed that after adjusted for age, sex, smoking, alcohol consumption, body mass index, waist circumference and fasting glucose, rs1800206, rs9794, rs3856806 and rs1805192 were significantly associated with hypertriglyceridemia, the OR (95% CI) were 4.43(3.08-6.37), 1.49(1.10-2.02), 1.56(1.16-2.08), 2.43(1.80-3.29), respectively. Further, generalized multifactor dimensionality reduction method analysis showed that two-to-six-locus and eight-locus models were significant (p<0.05), which indicated a potential gene-gene interaction among PPAR-α/δ/γ polymorphisms. The results suggest that PPAR-α/δ/γ polymorphisms may contribute to the risk of hypertriglyceridemia independently and/or in an interactive manner., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Background: We investigated the association of 10 single-nucleotide polymorphisms (SNPs) in the peroxisome proliferator-activated receptors (PPARs) with obesity and the additional role of gene-gene interaction., Methods: Participants were recruited within the framework of the Prevention of Multiple Metabolic Disorders and MS in Jiangsu Province cohort population survey of an urban community in China. In total, 820 subjects (513 nonobese adults, 307 obese adults) were randomly selected, and no individuals were consanguineous. Ten SNPs (rs135539, rs4253778, rs1800206, rs2016520, rs9794, rs10865710, rs1805192, rs709158, rs3856806, and rs4684847) were genotyped and analyzed., Results: After covariate adjustment, minor alleles of rs2016520 in PPARδ and rs10865170 in PPARγ were associated with lower BMI (P < 0.01 for all). Generalized multifactor dimensionality reduction analysis showed significant gene-gene interaction among rs2016520, rs9794, and rs10865170 in 3-dimensional models (P = 0.0010); prediction accuracy was 0.6011 and cross-validation consistency was 9/10. It also showed significant gene-gene interaction between rs2016520 and rs10865170 in all 2-dimensional models (P = 0.0010); prediction accuracy was 0.6072 and cross-validation consistency was 9/10., Conclusions: rs2016520 and rs10865170 were associated with lower obesity risk. In addition, interaction was identified among rs2016520, rs9794, and rs10865170 in obesity.

Trans fatty acids (TFA) are hypothesized to have an impact not only on coronary heart diseases but also on the development of colon cancer. To analyze if TFA exhibit cellular and molecular effects which could be involved in colon tumor progression, cells of the human colorectal adenocarcinoma-derived cell line Caco-2 were treated with various TFA isomers differing in the number and position of trans double bonds. The TFA tested in this study did not increase cellular proliferation but displayed growth-inhibitory effects at concentrations higher than 500 μM. In case of the TFA isomer C18:3 t9, t11, t13, an IC50 value of 23 μM was estimated for cytotoxicity indicating a high cytotoxic potential of this compound. In addition to the cytotoxicity studies, the TFA isomers were tested for their ability to activate peroxisome proliferator-activated receptors (PPAR) by taking advantage of a PPAR-dependent reporter gene assay. In contrast to PPARγ that was not activated by the TFA isomers tested in this study, the substances were shown to moderately activate PPARα, and strong activation was observed for PPARδ. The putative impact of TFA on colon cancer development with respect to PPARδ activation is being discussed.

Based on X-ray crystallographic analysis of a peroxisome proliferator-activated receptor (PPAR) α/δ dual agonist complexed with human PPARs ligand binding domain (LBD), we previously reported the design and synthesis of a pyrene-based fluorescent PPARα/δ co-agonist 2. Here, we found that the fluorescence intensity of 2 increased upon binding to hPPARα-LBD, in a manner dependent upon the concentration of the LBD. But, surprisingly, the fluorescence intensity of 2 decreased concentration-dependently upon binding to hPPRδ-LBD. Site-directed mutagenesis of the two hPPAR subtypes clearly indicated that Trp264 of hPPARδ-LBD, located between H2' helix and H3 helix (omega loop), is critical for the concentration-dependent decrease in fluorescence intensity, which is suggested to be due to fluorescence resonance energy transfer (FRET) from the pyrene moiety of bound 2 to the nearby side-chain indole moiety of Trp264 in the hPPARδ-LBD., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: The occurrence of halogenated analogs of the xenoestrogen bisphenol A (BPA) has been recently demonstrated both in environmental and human samples. These analogs include brominated [e.g., tetrabromobisphenol A (TBBPA)] and chlorinated [e.g., tetrachlorobisphenol A (TCBPA)] bisphenols, which are both flame retardants. Because of their structural homology with BPA, such chemicals are candidate endocrine disruptors. However, their possible target(s) within the nuclear hormone receptor superfamily has remained unknown., Objectives: We investigated whether BPA and its halogenated analogs could be ligands of estrogen receptors (ERs) and peroxisome proliferator-activated receptors (PPARs) and act as endocrine-disrupting chemicals., Methods: We studied the activity of compounds using reporter cell lines expressing ERs and PPARs. We measured the binding affinities to PPARγ by competitive binding assays with [3H]-rosiglitazone and investigated the impact of TBBPA and TCBPA on adipocyte differentiation using NIH3T3-L1 cells. Finally, we determined the binding mode of halogenated BPAs to PPARγ by X-ray crystallography., Results: We observed that TBBPA and TCBPA are human, zebrafish, and Xenopus PPARγ ligands and determined the mechanism by which these chemicals bind to and activate PPARγ. We also found evidence that activation of ERα, ERβ, and PPARγ depends on the degree of halogenation in BPA analogs. We observed that the bulkier brominated BPA analogs, the greater their capability to activate PPARγ and the weaker their estrogenic potential., Conclusions: Our results strongly suggest that polyhalogenated bisphenols could function as obesogens by acting as agonists to disrupt physiological functions regulated by human or animal PPARγ.

Little is known about the role of the transcription factor peroxisome proliferator-activated receptor (PPAR) beta/delta in liver. Here we set out to better elucidate the function of PPARbeta/delta in liver by comparing the effect of PPARalpha and PPARbeta/delta deletion using whole genome transcriptional profiling and analysis of plasma and liver metabolites. In fed state, the number of genes altered by PPARalpha and PPARbeta/delta deletion was similar, whereas in fasted state the effect of PPARalpha deletion was much more pronounced, consistent with the pattern of gene expression of PPARalpha and PPARbeta/delta. Minor overlap was found between PPARalpha- and PPARbeta/delta-dependent gene regulation in liver. Pathways upregulated by PPARbeta/delta deletion were connected to innate immunity and inflammation. Pathways downregulated by PPARbeta/delta deletion included lipoprotein metabolism and various pathways related to glucose utilization, which correlated with elevated plasma glucose and triglycerides and reduced plasma cholesterol in PPARbeta/delta-/- mice. Downregulated genes that may underlie these metabolic alterations included Pklr, Fbp1, Apoa4, Vldlr, Lipg, and Pcsk9, which may represent novel PPARbeta/delta target genes. In contrast to PPARalpha-/- mice, no changes in plasma free fatty acid, plasma beta-hydroxybutyrate, liver triglycerides, and liver glycogen were observed in PPARbeta/delta-/- mice. Our data indicate that PPARbeta/delta governs glucose utilization and lipoprotein metabolism and has an important anti-inflammatory role in liver. Overall, our analysis reveals divergent roles of PPARalpha and PPARbeta/delta in regulation of gene expression in mouse liver.

Tetradecylthioacetic acid (TTA) is a hypolipidemic modified fatty acid and a peroxisome proliferator-activated receptor (PPAR) ligand. The mechanisms of TTA-mediated effects seem to involve the PPARs, but the effects have not been assigned to any specific PPAR subtype. PPARalpha-/- mice were employed to study the role of PPARalpha after TTA treatment. We also performed in vitro transfection assays to obtain mechanistic knowledge of how TTA affected PPAR activation in the presence of PPARgamma coactivator (PGC)-1 and steroid receptor coactivators (SRC)-1 and SRC-2, which are associated with energy balance and mitochondrial biogenesis. We show that TTA increases hepatic fatty acid beta-oxidation in PPARalpha-/- mice. TTA acts as a pan-PPAR ligand in vitro, and PGC-1, SRC-1 and SRC-2 have cell type and PPAR-specific effects together with TTA. In the absence of exogenous ligands, SRC-1 did not induce PPAR activity, while PGC-1 was the most potent PPAR coactivator. When the coactivators were overexpressed, pronounced effects of TTA were observed especially for PPARdelta and PPARgamma. We conclude that PPARalpha is involved in, but not required for, the hypolipidemic mechanisms of TTA. It appears that the activity of PPARdelta, with substantial contribution of nuclear receptor coactivators, PGC-1 in special, is conducive to TTA's mechanism of action.

Background: Hepatic PPARalpha acts as the primary mediator of the adaptive response to fasting by upregulation of a number of genes involved in fatty acid catabolism. Whether carnitine-acylcarnitine translocase (CACT), which mediates the import of acylcarnitines into the mitochondrial matrix for subsequent beta-oxidation of fatty acid moieties, is also regulated by PPARalpha in the liver has not yet been investigated., Methods and Results: Herein, we observed that hepatic mRNA abundance of CACT was increased by both, fasting and treatment with PPARalpha agonist WY-14,643 in wild-type mice but not PPARalpha-knockout mice (P<0.05). Cell culture experiments revealed that CACT mRNA abundance was higher in liver cells treated with either WY-14,643 or PPARdelta agonist GW0742, but not with PPARgamma agonist troglitazone (TGZ) than in control cells (P<0.05). In addition, reporter assays revealed activation of mouse CACT promoter by WY-14,643 and GW0742, but not TGZ. Moreover, deletion and mutation analyses of CACT promoter and 5'-UTR revealed one functional PPRE in the 5'-UTR of mouse CACT., General Significance: CACT is upregulated by PPARalpha and PPARdelta, probably by binding to a functional PPRE at position +45 to +57 relative to the transcription start site. The upregulation of CACT by PPARalpha and PPARdelta, which are both important for the regulation of fatty acid oxidation in tissues during fasting, may increase the import of acylcarnitine into the mitochondrial matrix during fasting.

Rationale: Phenotypic modulation of smooth muscle cells (SMCs), which are located in close proximity to endothelial cells (ECs), is critical in regulating vascular function. The role of flow-induced shear stress in the modulation of SMC phenotype has not been well defined., Objective: The objective was to elucidate the role of shear stress on ECs in modulating SMC phenotype and its underlying mechanism., Methods and Results: Application of shear stress (12 dyn/cm2) to ECs cocultured with SMCs modulated SMC phenotype from synthetic to contractile state, with upregulation of contractile markers, downregulation of proinflammatory genes, and decreased percentage of cells in the synthetic phase. Treating SMCs with media from sheared ECs induced peroxisome proliferator-activated receptor (PPAR)-alpha, -delta, and -gamma ligand binding activities; transfecting SMCs with specific small interfering (si)RNAs of PPAR-alpha and -delta, but not -gamma, inhibited shear induction of contractile markers. ECs exposed to shear stress released prostacyclin (PGI2). Transfecting ECs with PGI2 synthase-specific siRNA inhibited shear-induced activation of PPAR-alpha/delta, upregulation of contractile markers, downregulation of proinflammatory genes, and decrease in percentage of SMCs in synthetic phase. Mice with PPAR-alpha deficiency (compared with control littermates) showed altered SMC phenotype toward a synthetic state, with increased arterial contractility in response to angiotensin II., Conclusions: These results indicate that laminar shear stress induces synthetic-to-contractile phenotypic modulation in SMCs through the activation of PPAR-alpha/delta by the EC-released PGI2. Our findings provide insights into the mechanisms underlying the EC-SMC interplays and the protective homeostatic function of laminar shear stress in modulating SMC phenotype.

Macrophages adapt their response to micro-environmental signals. While Th1 cytokines promote pro-inflammatory M1 macrophages, Th2 cytokines promote an "alternative" anti-inflammatory M2 macrophage phenotype. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors expressed in macrophages where they control the inflammatory response. It has been shown that PPARgamma promotes the differentiation of monocytes into anti-inflammatory M2 macrophages in humans and mice, while a role for PPARbeta/delta in this process has been reported only in mice and no data are available for PPARalpha. Here, we show that in contrast to PPARgamma, expression of PPARalpha and PPARbeta/delta overall does not correlate with the expression of M2 markers in human atherosclerotic lesions, whereas a positive correlation with genes of lipid metabolism exists. Moreover, unlike PPARgamma, PPARalpha or PPARbeta/delta activation does not influence human monocyte differentiation into M2 macrophages in vitro. Thus, PPARalpha and PPARbeta/delta do not appear to modulate the alternative differentiation of human macrophages.

It is reported that arachidonic acid strongly induces the conformational change in vitro and transactivity of PPAR alpha in colorectal cancer cell line Caco-2. In this study, we demonstrated that the induction of conformational change and transactivity of PPAR delta by arachidonic acid, as well as other polyunsaturated fatty acids, was considerably lower than that of PPAR alpha. Mammalian two-hybrid assay showed that arachidonic acid enhanced binding of one of the coactivators, p300, to PPAR alpha but not to PPAR delta. Additionally, arachidonic acid induced in vitro binding of both PPAR alpha-RXR alpha and PPAR delta-RXR alpha heterodimers to several PPREs on CRBPII, L-FABP and ACO genes. Our results suggest that the lower transactivity of PPAR delta for arachidonic acid in Caco-2 cells, compared with PPAR alpha, is associated with the binding activity of p300 to the receptor.

Agonism of peroxisome proliferator-activated receptor (PPAR) alpha, a key regulator of lipid metabolism, leads to amelioration of lipid abnormalities in dyslipidemic patients. However, whether PPARalpha agonism is an effective form of therapy for obesity-related insulin resistance associated with lipid abnormalities is unclear. The present study investigated the effects of a potent and subtype-selective PPARalpha agonist, KRP-101, in a nonrodent insulin-resistant animal model under pair-fed conditions. Beagle dogs were fed a high-fat diet for 24 wk to induce insulin resistance. During the final 12 wk, 0.03 mg x kg(-1) x day(-1) KRP-101 (n = 5) or vehicle (n = 5) was administered orally once a day. KRP-101 administration resulted in a significantly lower weight of overall visceral fat, which is associated with increased adiponectin and decreased leptin in serum. KRP-101 administration improved hyperglycemia and hyperinsulinemia as well as dyslipidemia in dogs fed a high-fat diet. Oral glucose tolerance test showed that KRP-101 administration improved glucose intolerance. The KRP-101 group showed a markedly lower hepatic triglyceride concentration. Lipid oxidation was increased in the liver and skeletal muscles of the KRP-101 group. These findings in the dog model suggest that the use of potent and subtype-selective PPARalpha agonists as a potentially relevant therapeutic approach to treat human insulin resistance associated with visceral obesity.

Peroxisome proliferator activated receptor alpha (PPAR alpha) regulates fatty acid beta-oxidation (FAO) and plays a central role in the metabolic and energetic homeostasis of striated muscles. The thermodynamic consequences of the absence of PPAR alpha were investigated in diaphragm muscle of PPAR alpha knockout mice (KO). Statistical mechanics provides a powerful tool for determining entropy production, which quantifies irreversible chemical processes generated by myosin molecular motors and which is the product of thermodynamic force A/T (chemical affinity A and temperature T) and thermodynamic flow (myosin crossbridge (CB) cycle velocity upsilon). The behavior of both wild type (WT) and KO diaphragm was shown to be near-equilibrium and in a stationary state, but KO was farther from equilibrium than WT. In KO diaphragm, a substantial decrease in contractile function was associated with an increase in both A/T and upsilon and with profound histological injuries such as contraction band necrosis. There were no changes in PPAR delta and gamma expression levels or myosin heavy chain (MHC) patterns. In KO diaphragm, a marked increase in entropy production (A/T x upsilon) accounted for major thermodynamic dysfunction and a dramatic increase in irreversible chemical processes during the myosin CB cycle.

In the diabetic heart, chronic activation of the PPARalpha pathway drives excessive fatty acid (FA) oxidation, lipid accumulation, reduced glucose utilization, and cardiomyopathy. The related nuclear receptor, PPARbeta/delta, is also highly expressed in the heart, yet its function has not been fully delineated. To address its role in myocardial metabolism, we generated transgenic mice with cardiac-specific expression of PPARbeta/delta, driven by the myosin heavy chain (MHC-PPARbeta/delta mice). In striking contrast to MHC-PPARalpha mice, MHC-PPARbeta/delta mice had increased myocardial glucose utilization, did not accumulate myocardial lipid, and had normal cardiac function. Consistent with these observed metabolic phenotypes, we found that expression of genes involved in cellular FA transport were activated by PPARalpha but not by PPARbeta/delta. Conversely, cardiac glucose transport and glycolytic genes were activated in MHC-PPARbeta/delta mice, but repressed in MHC-PPARalpha mice. In reporter assays, we showed that PPARbeta/delta and PPARalpha exerted differential transcriptional control of the GLUT4 promoter, which may explain the observed isotype-specific effects on glucose uptake. Furthermore, myocardial injury due to ischemia/reperfusion injury was significantly reduced in the MHC-PPARbeta/delta mice compared with control or MHC-PPARalpha mice, consistent with an increased capacity for myocardial glucose utilization. These results demonstrate that PPARalpha and PPARbeta/delta drive distinct cardiac metabolic regulatory programs and identify PPARbeta/delta as a potential target for metabolic modulation therapy aimed at cardiac dysfunction caused by diabetes and ischemia.

Fatty acids in milk are thought to play an important role in intestinal maturation and gene expression in the postnatal small intestine. In this study, we determined the jejunal mRNA levels, in rats, of peroxisome proliferator-activated receptor alpha (PPARalpha) and PPARdelta which are nuclear receptors for fatty acids. We also measured expression of their target genes during the postnatal period, namely liver type fatty acid-binding protein (L-FABP) and cellular retinol-binding protein, type II (CRBPII). The mRNA levels of PPARalpha, L-FABP and CRBPII, but not PPARdelta, gradually increased during the suckling period and then sharply declined to a low level at the end of the weaning period. Rat pups at 17 d of age, weaned to a high-fat diet, showed significantly greater mRNA levels of PPARalpha, L-FABP and CRBPII than those weaned to a low-fat diet. Oral administration of PPARalpha ligand, WY14,643 during four consecutive days of the weanling period caused a parallel increase in the mRNA levels of PPARalpha, L-FABP and CRBPII genes. Furthermore, caprylic acid and oleic acid, which are major components of fatty acids in milk, induced jejunal PPARalpha, L-FABP and CRBPII gene expression. Our results suggest that fatty acids in milk may play a pivotal role in maintaining an enhanced level of expression of L-FABP and CRBPII genes in the small intestine, presumably by acting as inducers of PPARalpha gene expression.

Objective: To investigate the association of a polymorphism at position 294 (+294T/C) in the Peroxisome Proliferator-activated Receptor delta (PPARdelta) with body mass index (BMI) and the additional role of a gene-to-gene interaction between PPARdelta, PPARalpha and PPARgamma., Design: An association between genetic variations in PPARdelta, PPARalpha and PPARgamma and indices of obesity and metabolism., Subjects: A group of 462 moderately obese (mean BMI 28.9+/-7.7) and dyslipidemic, middle-aged (mean age 43.9+/-13.7), Caucasion men and women., Measurements: The three most frequent single-nucleotide-polymorphisms (snp) in PPARdelta (+294T/C), PPARalpha (L162V) and PPARgamma (P12A) were genotyped and associated with clinical parameters., Results: The C allele in PPARdelta was significantly associated with a lower body mass index. Moreover an interaction between the polymorphisms in PPARalpha and PPARdelta on body weight could be demonstrated., Conclusion: Our data provide further evidence for an involvement of PPARdelta in the regulation of BMI.

Peroxisome proliferator-activated receptors (PPARs) alpha, delta and gamma are nuclear transcription factors that control key genes involved in fatty acid metabolism and energy homeostasis. Little is known about PPAR activation in vivo and the existence of overlapping functions between PPARalpha, -delta and -gamma. As skeletal muscle is an important site for insulin action and acts as a significant sensor for life-style-induced influences in whole-body energy metabolism, we investigated the expression of PPARalpha, -delta and -gamma in rat skeletal muscle in response to exercise after four- and twelve-weeks of high-fat feeding, respectively. PPARalpha mRNA expression in skeletal muscle increased in parallel with other signs of developing metabolic syndrome such as increased visceral fat pad volymes, plasma free fatty acids and muscle triglyceride concentrations. PPARalpha mRNA expression was up-regulated 3-fold after four weeks of high-fat feeding (p<0.01). Exercise reversed the high-fat induced increase in PPARalpha expression in young lean rats (p<0.05), but did not change the PPARalpha, -delta and -gamma expression in the skeletal muscle in the normal nutritional state. The increase in PPARalpha expression declined during a longer term of high-fat feeding. In contrast, exercise increased PPARdelta mRNA and protein expression 3- to 6-fold in skeletal muscle after longer-term high-fat feeding (p<0.05). This effect was accompanied by a reduction in skeletal muscle fat content. These findings suggest that parallel activation of PPARalpha and -delta expression in skeletal muscle may be an important adaptive mechanism in response to increased fatty acid loads in young, lean animals, protecting them from insulin resistance, whereas exercise might be needed to mediate the same positive effects in older animals.

Objective: Tetradecylthioacetic acid (TTA) is a hypolipidemic antioxidant with immunomodulating properties involving activation of peroxisome proliferator-activated receptors (PPARs). Human endothelial cells express PPARs. We hypothesized that TTA could modulate endothelial cell activation at least partly through PPAR-related mechanisms., Methods and Results: We explored this hypothesis by different experimental approaches involving both in vitro studies in human endothelial cells (HUVECs) and in vivo studies in humans and PPAR-alpha-/- mice. Our main findings were as follows: (1) TTA suppressed the tumor necrosis factor alpha-induced expression of vascular cell adhesion molecule 1 (VCAM-1) and interleukin 8 (IL-8) in HUVECs. (2) No TTA-mediated attenuation of VCAM-1 and chemokine expression was seen in the liver of PPAR-alpha-/- mice. (3) Whereas TTA markedly enhanced PPAR-alpha-target genes in the liver of wild-type, but not of PPAR-alpha-/-, mice, no such effect on PPAR-alpha-target genes was seen in HUVECs. (4) The relevance of our findings to human disease was suggested by a TTA-mediated downregulation of serum levels of soluble VCAM-1 and IL-8 in psoriasis patients., Conclusions: We show that TTA has the ability to attenuate tumor necrosis factor alpha-mediated endothelial cell activation, further supporting antiinflammatory effects of this fatty acid, possibly involving both PPAR-alpha-dependent and -independent pathways.

Phthalate esters belong to a large class of compounds known as peroxisome proliferators (PP). PP include chemicals that activate different subtypes of the peroxisome proliferator-activated receptor (PPAR) family. The ability of phthalate esters and their metabolites to activate responses through different PPAR subtypes is not fully characterized. We investigated the ability of two phthalate esters di-(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP) and selected metabolites to activate PPAR (alpha, beta/delta, gamma) using a transient transfection assay. The monoester of DEHP, mono-(2-ethylhexyl) phthalate (MEHP) activated all three subtypes of PPAR, but preferentially activated PPARalpha. A second metabolite of DEHP, 2-ethylhexanoic acid (2-EHXA) was a weaker activator of all three subtypes. DBP, but not the primary metabolite mono-n-butyl phthalate weakly activated all three PPAR subtypes. MEHP and DBP but not DEHP and MBP interacted directly with human PPARalpha and PPARgamma as determined by scintillation proximity assays. Both DEHP and DBP activated expression of PP-inducible gene products in wild-type but not PPARalpha-null mice suggesting that both of these phthalates exert their effects by activation of PPARalpha in vivo. The preferential activation of PPARalpha by phthalate ester metabolites suggests that these phthalates mediate their toxic effects in rodent liver in a manner indistinguishable from other PP.

PPARalpha, beta/delta, and gamma regulate genes involved in the control of lipid metabolism and inflammation and are expressed in all major cell types of atherosclerotic lesions. In vitro studies have suggested that PPARs exert antiatherogenic effects by inhibiting the expression of proinflammatory genes and enhancing cholesterol efflux via activation of the liver X receptor-ABCA1 (LXR-ABCA1) pathway. To investigate the potential importance of these activities in vivo, we performed a systematic analysis of the effects of PPARalpha, beta, and gamma agonists on foam-cell formation and atherosclerosis in male LDL receptor-deficient (LDLR(-/-)) mice. Like the PPARgamma agonist, a PPARalpha-specific agonist strongly inhibited atherosclerosis, whereas a PPARbeta-specific agonist failed to inhibit lesion formation. In concert with their effects on atherosclerosis, PPARalpha and PPARgamma agonists, but not the PPARbeta agonist, inhibited the formation of macrophage foam cells in the peritoneal cavity. Unexpectedly, PPARalpha and PPARgamma agonists inhibited foam-cell formation in vivo through distinct ABCA1-independent pathways. While inhibition of foam-cell formation by PPARalpha required LXRs, activation of PPARgamma reduced cholesterol esterification, induced expression of ABCG1, and stimulated HDL-dependent cholesterol efflux in an LXR-independent manner. In concert, these findings reveal receptor-specific mechanisms by which PPARs influence macrophage cholesterol homeostasis. In the future, these mechanisms may be exploited pharmacologically to inhibit the development of atherosclerosis.

Fatty acids are an important ligand for peroxisome proliferator-activated receptor (PPAR) activation and transcriptional regulation of metabolic genes. To examine whether reduced plasma free fatty acid (FFA) availability affects the mRNA content of proteins involved in fuel metabolism in vivo, the skeletal muscle mRNA content of various transcription factors, transcriptional coactivators and genes encoding for lipid regulatory proteins were examined before and after 3 h of cycle exercise with (NA) and without (CON) pre-exercise ingestion of nicotinic acid (NA). NA resulted in a marked (3- to 6-fold) increase (P<0.05) in PPARalpha, PPARdelta and PPAR coactivator 1alpha (PGC1alpha) mRNA, but was without effect on nuclear respiratory factor-1 and Forkhead transcription factor, fatty acid transcolase/CD36, carnitine palmitoyl transferase 1, hormone sensitive lipase (HSL) and pyruvate dehydrogenase kinase 4. Exercise in CON was associated with increased (P<0.05) PPARalpha, PPARdelta and PGC1alpha mRNA, which was similar in magnitude to levels observed with NA at rest. Exercise was generally without effect on the mRNA content of lipid regulatory proteins in CON and did not affect the mRNA content of the measured subset of transcription factors, transcriptional co-activators and lipid regulatory proteins during NA. To determine the possible mechanisms by which NA might affect PGC1alpha expression, we measured p38 MAP kinase (MAPK) and plasma epinephrine. Phosphorylation of p38 MAPK was increased (P<0.05) by NA treatment at rest, and this correlated (r2=0.84, P<0.01) with increased PGC1alpha. Despite this close relationship, increasing p38 MAPK in human primary myotubes was without effect on PGC1alpha mRNA content. Plasma epinephrine was elevated (P<0.05) by NA at rest (CON: 0.27+/-0.06, NA: 0.72+/-0.11 nM) and throughout exercise. Incubating human primary myotubes with epinephrine increased PGC1alpha independently of changes in p38 MAPK phosphorylation. Hence, despite the fact that NA ingestion decreased FFA availability, it promoted the induction of PPARalpha/delta and PGC1alpha gene expression to a similar degree as prolonged exercise. We suggest that the increase in PGC1alpha may be due to the elevated plasma epinephrine levels. Despite these changes in transcription factors/coactivators, the mRNA content of lipid regulatory proteins was generally unaffected by plasma FFA availability.