Abstract: Fatty acid binding proteins (FABPs) act as intracellular shuttles for fatty acids as well as lipophilic xenobiotics to the nucleus, where these ligands are released to a group of nuclear receptors called the peroxisome proliferator activated receptors (PPARs). PPAR mediated gene activation is ultimately involved in maintenance of cellular homeostasis through the transcriptional regulation of metabolic enzymes and transporters that target the activating ligand. Here we show that liver- (L-) FABP displays a high binding affinity for PPAR subtype selective drugs. NMR chemical shift perturbation mapping and proteolytic protection experiments show that the binding of the PPAR subtype selective drugs produces conformational changes that stabilize the portal region of L-FABP. NMR chemical shift perturbation studies also revealed that L-FABP can form a complex with the PPAR ligand binding domain (LBD) of PPARα. This protein-protein interaction may represent a mechanism for facilitating the activation of PPAR transcriptional activity via the direct channeling of ligands between the binding pocket of L-FABP and the PPARαLBD. The role of L-FABP in the delivery of ligands directly to PPARα via this channeling mechanism has important implications for regulatory pathways that mediate xenobiotic responses and host protection in tissues such as the small intestine and the liver where L-FABP is highly expressed.

Abstract: Peroxisome proliferator-activated receptor- γ (PPAR γ ) agonists such as rosiglitazone and pioglitazone are used to improve insulin sensitivity in patients with diabetes mellitus. However, thiazolidinediones induce fluid retention, edema, and sometimes precipitate or exacerbate heart failure in a subset of patients. The mechanism through which thiazolidinediones induce fluid retention is controversial. Most studies suggest that this effect results from the increase in tubular sodium and water reabsorption in the kidney, but the role of specific nephron segments and sodium carriers involved is less clear. Some studies suggested that PPAR γ agonist stimulates Na(+) reabsorption in the collecting duct by activating epithelial Na(+) channel (ENaC), either directly or through serum and glucocorticoid-regulated kinase-1 (SGK-1). However, other studies did not confirm this mechanism and even report the suppression of ENaC. Alternative mechanisms in the collecting duct include stimulation of non-ENaC sodium channel or inhibition of chloride secretion to the tubular lumen. In addition, thiazolidinediones may augment sodium reabsorption in the proximal tubule by stimulating the expression and activity of apical Na(+)/H(+) exchanger-3 and basolateral Na(+)-HCO3 (-) cotransporter as well as of Na(+),K(+)-ATPase. These effects are mediated by PPAR γ -induced nongenomic transactivation of the epidermal growth factor receptor and downstream extracellular signal-regulated kinases (ERK).

Abstract: While TOFA (acetyl CoA carboxylase inhibitor) and C75 (fatty acid synthase inhibitor) prevent lipid accumulation by inhibiting fatty acid synthesis, the mechanism of action is not simply accounted for by inhibition of the enzymes alone. Liver fatty acid binding protein (L-FABP), a mediator of long chain fatty acid signaling to peroxisome proliferator-activated receptor-α (PPARα) in the nucleus, was found to bind TOFA and its activated CoA thioester, TOFyl-CoA, with high affinity while binding C75 and C75-CoA with lower affinity. Binding of TOFA and C75-CoA significantly altered L-FABP secondary structure. High (20 mM) but not physiological (6 mM) glucose conferred on both TOFA and C75 the ability to induce PPARα transcription of the fatty acid β-oxidative enzymes CPT1A, CPT2, and ACOX1 in cultured primary hepatocytes from wild-type (WT) mice. However, L-FABP gene ablation abolished the effects of TOFA and C75 in the context of high glucose. These effects were not associated with an increased cellular level of unesterified fatty acids but rather by increased intracellular glucose. These findings suggested that L-FABP may function as an intracellular fatty acid synthesis inhibitor binding protein facilitating TOFA and C75-mediated induction of PPARα in the context of high glucose at levels similar to those in uncontrolled diabetes.

Abstract: Peroxisome proliferator-activated receptors (PPAR) are members of the superfamily of nuclear hormone receptors involved in embryonic development and differentiation of several tissues including placenta, which respond to specific ligands such as polyunsaturated fatty acids by altering gene expression. Three subtypes of this receptor have been discovered, each evolving to achieve different biological functions. The PPARs also control a variety of target genes involved in lipid homeostasis. Similar to other nuclear receptors, the transcriptional activity of PPARs is affected not only by ligand-stimulation but also by crosstalk with other molecules. For example, both PPARs and the RXRs are ligand-activated transcription factors that coordinately regulate gene expression. In addition, several mechanisms underlying negative regulation of gene expression by PPARs have been shown. It is suggested that PPARs are key messengers responsible for the translation of nutritional stimuli into changes in gene expression pathways for placental development.

Abstract: Diabetic retinopathy (DR) remains as the leading cause of blindness among working age individuals in developed countries. Current treatments for DR (laser photocoagulation, intravitreal corticosteroids, intravitreal anti-VEGF agents, and vitreoretinal surgery) are applicable only at advanced stages of the disease and are associated with significant adverse effects. Therefore, new pharmacological treatments for the early stages of the disease are needed. Emerging evidence indicates that peroxisome proliferator-activator receptors (PPARs) agonists (in particular PPARα) are useful for the treatment of DR. However, the underlying molecular mechanisms are far from being elucidated. This paper mainly focuses on PPARs expression in the diabetic eye, its molecular implications, and the effect of PPAR agonists as a new approach for the treatment of DR. The availability of this new strategy will not only be beneficial in treating DR but may also result in a shift towards treating earlier stages of diabetic retinopathy, thus easing the burden of this devastating disease (Cheung et al. (2010)).

Abstract: PPARγ is a nuclear hormone receptor that functions as a master regulator of adipocyte differentiation and development. Full PPARγ agonists, such as the thiazolidinediones (TZDs), have been widely used to treat type 2 diabetes. However, they are characterized by undesirable side effects due to their strong agonist activities. Pseudoginsenoside F11 (p-F11) is an ocotillol-type ginsenoside isolated from Panax quinquefolium L. (American ginseng). In this study, we found that p-F11 activates PPARγ with modest adipogenic activity. In addition, p-F11 promotes adiponectin oligomerization and secretion in 3T3-L1 adipocytes. We also found that p-F11 inhibits obesity-linked phosphorylation of PPARγ at Ser-273 by Cdk5. Therefore, p-F11 is a novel partial PPARγ agonist, which might have the potential to be developed as a new PPARγ-targeted therapeutics for type 2 diabetes.

Abstract: Activation of the peroxisome proliferator activated receptor-gamma (PPAR)-γ is proposed as a neuroprotective strategy to treat neurodegenerative disorders. In this study, we examined if LSN862 (LSN), a novel non-thiazoledinedione partial PPAR-γ agonist, was neuroprotective in a mouse model of Parkinson’s disease (PD) and assessed possible mechanisms of action. LSN (3, 10, or 30 mg/kg) or vehicle was orally administered daily to C57BL/6 and antioxidant response element-human placental alkaline phosphatase (ARE-hPAP) reporter mice 3 days prior to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 30 mg/kg, i.p. × 5 days) or PBS administration. LSN elicited a dose-dependent preservation of dopaminergic nigrostriatal innervation that was not associated with inhibition of MPTP metabolism or activation of Nrf2-ARE, although changes in NQO1 and SOD2 mRNA were observed. A significant dose-dependent downregulation in MAC-1 and GFAP positive cells was observed in MPTP

Abstract: Expression of the brown adipocyte-specific gene, uncoupling protein 1 (UCP1), is increased by both PPAR stimulation and cAMP activation through their ability to stimulate the expression of the PPAR coactivator PGC1. In HIB1B brown preadipocytes, combination of the PPAR agonist, rosiglitazone, and the cAMP stimulator forskolin synergistically increased UCP1 mRNA expression, but PGC1 expression was only increased additively by the two drugs. The PPAR antagonist, GW9662, and the PKA inhibitor, H89, both inhibited UCP1 expression stimulated by rosiglitazone and forskolin but PGC1 expression was not altered to the same extent. Reporter studies demonstrated that combined rosiglitazone and forskolin synergistically activated transcription from a full length 3.1 kbp UCP1 luciferase promoter construct, but the response was only additive and much reduced when a minimal 260 bp proximal UCP1 promoter was examined. Rosiglitazone and forskolin in combination were able to synergistically stimulate promoters comprising of tandem repeats of either PPREs or CREs. We conclude that rosiglitazone and forskolin act together to synergistically activate the UCP1 promoter directly rather than by increasing PGC1 expression and by a mechanism involving cross-talk between the signalling systems regulating the CRE and PPRE on the promoters.

Abstract: Evidence had shown the detrimental effect of prostaglandin (PG) E2 in diabetic nephropathy (DN) of STZ-induced type-1 diabetes but its role in the development of DN of type-2 diabetes remains uncertain. The present study was undertaken to investigate the regulation of PGE2 synthetic pathway and the interaction between peroxisome proliferator-activated receptor (PPAR)γ and PGE2 synthesis in the kidneys of db/db mice. Strikingly, urinary PGE2 was remarkably elevated in db/db mice paralleled with the increased protein expressions of COX-2 and mPGES-1. In contrast, the protein expressions of COX-1, mPGES-2, cPGES, and 15-hydroxyprostaglandin dehydrogenase (15-PGDH) were not altered. Following 1-week rosiglitazone (Rosi) therapy, urinary PGE2, but not other prostanoids, was reduced by 57% in parallel with significant reduction of mPGES-1 protein and EP4 mRNA expressions. By immunohistochemistry, mPGES-1 was significantly induced in the glomeruli of db/db mice, which was almost entirely abolished by Rosi. In line with the reduction of glomerular mPGES-1, the glomerular injury score showed a tendency of improvement after 1 week of Rosi therapy. Collectively, the present study demonstrated an inhibitory effect of PPARγ activation on renal mPGES-1/PGE2/EP4 pathway in type-2 diabetes and suggested that mPGES-1 may potentially serve as a therapeutic target for treating type-2 diabetes-associated DN.

Abstract: The present study investigates the changes of peroxisome proliferator-activated receptors δ (PPARδ) expression and troponin phosphorylation in heart of rats which were treated with doxorubicin (DOX). Wistar rats which were treated with DOX according to a previous method. The protein levels of PPARδ and troponin phosphorylation were measured using Western blot. The PPARδ expression in heart was markedly reduced in DOX-treated rats showing a marked decrease in cardiac dP/dT and cardiac output. Also, cardiac troponin phosphorylation was lowered in DOX-treated rats. Meanwhile, combined treatment with the agonist of PPARδ (GW0742) reversed the decrease of cardiac dP/dT and cardiac output in DOX-treated rats. Then, primary cultured cardiomyocytes from neonatal rats were used to measure the changes of calcium concentration in cells. In addition to both decrease of PPARδ expression and troponin phosphorylation in neonatal cardiomyocytes by DOX, a marked decrease of calcium concentration was also observed. Our results suggest the mediation of cardiac PPARδ in DOX-induced cardiotoxicity in rats. Thus, activation of PPARδ may restore the expression of p-TnI and the cardiac performance in DOX-induced cardio toxicity in rats.

Abstract: Chronic kidney disease (CKD) is well known as a strong risk factor for both end stage renal disease and cardiovascular disease. To clarify the association of polymorphisms in the PPAR genes (PPARD, PPARG, and PPARGC1A) with the risk of CKD in Japanese, we examined this association among the Japanese subjects using the cross-sectional data of J-MICC (Japan Multi-Institutional Collaborative Cohort) Study. The subjects for this analysis were 3,285 men and women, aged 35–69 years, selected from J-MICC Study participants; genotyping was conducted by multiplex polymerase chain reaction-based Invader assay. The prevalence of CKD was determined for CKD stages 3–5 (defined as eGFR < 60 ml/min/1.73 m2). Participants with CKD accounted for 17.3% of the study population. When those with PPARD T-842C T/T were defined as reference, those with PPARD T-842C T/C and C/C demonstrated the OR for CKD of 1.26 (95%CI 1.04–1.53) and 1.31 (95%CI 0.83–2.06), respectively. There were no significant associations between the polymorphisms in other PPAR genes and the risk of CKD. The present study found a significantly increased risk of CKD in those with the C allele of PPARD T-842C, which may suggest the possibility of personalized risk estimation of this life-limiting disease in the near future.

Abstract: PPARγ receptor plays an important role in oxidative stress response. Its agonists can influence vascular contractility in experimental hypertension. Our study was focused on the effects of a PPARγ agonist pioglitazone (PIO) on blood pressure regulation, vasoactivity of vessels, and redox-sensitive signaling at the central (brainstem, BS) and peripheral (left ventricle, LV) levels in young prehypertensive rats. 5-week-old SHR were treated either with PIO (10 mg/kg/day, 2 weeks) or with saline using gastric gavage. Administration of PIO significantly slowed down blood pressure increase and improved lipid profile and aortic relaxation after insulin stimulation. A significant increase in PPARγ expression was found only in BS, not in LV. PIO treatment did not influence NOS changes, but had tissue-dependent effect on SOD regulation and increased SOD activity, observed in LV. The treatment with PIO differentially affected also the levels of other intracellular signaling components: Akt kinase increased in the the BS, while β-catenin level was down-regulated in the BS and up-regulated in the LV. We found that the lowering of blood pressure in young SHR can be connected with insulin sensitivity of vessels and that β-catenin and SOD levels are important agents mediating PIO effects in the BS and LV.

Abstract: There has been a tremendous amount of information produced on peroxisome proliferator-activated receptors (PPARs). The interest in PPARs was originally driven largely by their role in hypolipidemia and hepatocarcinogenesis, but it soon became evident that they played important roles in the metabolic syndrome and overall health of organisms including regeneration of tissues, differentiation, insulin signaling, overall lipid metabolism, and immune response (reviewed in [1–7]). From a nutritional standpoint, the PPARs are of extreme importance because of their ability to bind and be activated by long-chain fatty acids and their metabolites. Therefore, the PPARs are recognized as ideal candidates for therapeutic use in order to improve metabolism and overall health through diet. At present, there is substantial interest in therapeutic applications tailored to regulate PPARs via synthetic drugs (e.g., [8]), but the exploitation of dietary approaches is not a reality yet. Most of our knowledge on PPARs has been produced by studies carried out in rodents and humans and little from other species, bovine and pig being the most studied among livestock species. The multitude of roles of PPARs and the possibility of regulating them through dietary approaches are also of interest in animal food production. Therefore, a comparative approach to bring together physiological and nutritional roles of PPARs across species appears critical. For this reason, this special issue was dedicated to PPARs interspecies comparisons with a larger emphasis on livestock species compared to animal models or humans. Among the 6 papers published, 3 focused specifically on ruminants and one on chicken. The review from Bionaz et al. assembled all the information pertaining to ruminant PPARs, with emphasis on functions, activation, and potential targets for nutrigenomics approaches to improve animal production and wellbeing. The review underscored that the information about PPARs in ruminants accumulated quickly in the last decade owing to the recognition of their potential importance in those mammalian species. The functional comparison among ruminant, mouse, and human highlighted a similar role of PPAR isotypes on lipid metabolism between species. However, the data highlighted differences in the response to long-chain fatty acids. Monogastrics are more sensitive to unsaturated while ruminants, particularly bovine, are more sensitive to saturated long-chain fatty acids. Based on PPARs data generated in nonruminants and ruminants, they proposed an integrative and dynamic model encompassing the activation (by long-chain fatty acids) of the three PPAR isotypes in order to optimize the adaptation to lactation. Among others, they also reviewed the data supporting a role of PPARγ in controlling milk fat synthesis in ruminants and demonstrated that this feature is not shared by mouse or, likely, other monogastrics. A pivotal role of PPARγ in controlling milk fat synthesis was confirmed by the paper of Shi et al. published in the present special issue. Those authors demonstrated, using a combination of PPARγ specific activator, gene expression, luciferase-PPRE assay, and siRNA techniques, that this nuclear receptor controls the expression of milk fat-related genes also in primary goat mammary epithelial cells. The activation of PPARγ using oral administration of 2,4-thiazolidinedione (TZD) in growing beef bulls was assessed by Arevalo-Turrubiarte et al. The authors aimed to test the effect of PPARγ activation on intramuscular fat (i.e., marbling). They observed a greater amount of TZD in liver of the treated animals, demonstrating an uptake of the drug via oral administration. The TZD treatment had no effect on carcass quality but had a strong effect on the expression of all three PPAR isotypes in liver (all decreased) and in muscle (increase only of PPARα). They observed also an overall increase in cell size and decrease of cellular synthesis in muscle and perirenal adipose tissue, but the opposite was observed in subcutaneous adipose. This effect was explained by higher insulin sensitivity due to the treatment. Activation of PPARγ with oral administration of a TZD in growing pigs also had no significant effect on marbling, but it did increase muscle fiber oxidative capacity regardless of fiber type [9]. As for bovine, the activation of PPARγ in swine may be useful to influence metabolism overall, but more studies are needed to examine this possibility. Takada and Kobayashi provided the first review of the three PPAR isotypes in poultry, particularly in chickens. Interestingly, they also provided a comparison with human PPARs both structurally and functionally. They uncovered several peculiar and unique functions in chicken PPARs and differences between chickens, and human PPARs. These data prompt for more chicken-specific studies in order to exploit the ability of PPARs to control lipid and glucose metabolism in this species. Mandard and Patsouris reviewed recent evidence establishing that PPARs are critical regulators of inflammation in mammals. In the last decade, PPARs have emerged as modulators of inflammatory responses. Therefore, the potential therapeutic usefulness of PPARα and PPARγ activation in the control of obesity and diabetes-induced chronic (low-grade) inflammation has extensively been studied over the last couple of years using rodents. The authors discussed different aspects of the interaction of PPARγ with adipose inflammation. In the light of the recent findings, it has become clear that, besides activating PPARγ in the adipocyte, pharmacological activation of this receptor extends to a much broader range of cell types, such as T regulatory cells, which is likely beneficial in the suppression of obesity-associated inflammation in white adipose tissue, as far as rodents are concerned. The impact of the pharmacological activation of mouse PPARα in the context of obesity-induced hepatic inflammation is also reviewed as well as the potential relevance of PPARβ/δ as a molecular drug target to fight liver inflammation in the case of nonalcoholic fatty liver disease. A growing body of evidence also indicates that PPARs are potent negative regulators of the acute-phase response in different species, ranging from mouse, rat, pig, cattle and humans. The review article by Mandard and Patsouris also expands on the potential beneficial use of PPAR (ant)agonists in the routine of livestock to prevent bacterial-induced excessive inflammatory reaction and associated diseases such as mastitis in dairy cows. PPARα is also known to be critical for energy homeostasis. In line with this, the review paper by Ringseis et al. thoroughly summarizes the implication of PPARα in carnitine homeostasis in no less than six different species including rat, mouse, pig, cattle, chicken, and human. The comparative analysis performed by the authors led them to conclude that PPARα displays a key regulator role in carnitine homeostasis in general. It is the process of cellular carnitine uptake, with the key role of the PPARα target carnitine transporter novel organic cation transporter 2, that is particularly well conserved across the above-mentioned species. All the papers in this special issue emphasized on one hand a similar function of PPARs among species, particularly related to lipid metabolism, but also, and more importantly, accentuated the differences and the species-specific functions and response to agonists. In summary, the analysis of PPARs across species highlighted the following: interspecies conserved functional roles of those nuclear receptors (e.g., regulation of lipid metabolism and inflammation); the potential for therapeutic intervention through nutritional modulation of PPARs in all species in order to prevent diseases and improve animal production; differences between species that prompt for more species-specific studies in order to fully exploit the abovementioned therapeutic roles through nutrition. Massimo Bionaz Gary J. Hausman Juan J. Loor Stephane Mandard

Abstract: The liver X receptors (LXRs) have been shown to be crucially involved in maternal-fetal cholesterol transport and placentation. The aim of this study was to investigate the expression pattern and frequency of LXR under normal physiological circumstances and in spontaneous abortion and/or recurrent miscarriage. A total of 29 (12 physiologic pregnancies/10 spontaneous abortions/7 recurrent miscarriages) human pregnancies in first trimester were analysed for LXR expression. Expression changes were evaluated by immunohistochemistry for receptor and quantitative RT-PCR (TaqMan) was performed to determine the level of LXR mRNA expression. We also stained for RXRα and PPARγ as possible heterodimers of LXR. LXR expression was downregulated in the syncytiotrophoblast of spontaneous abortion placentas compared to normal pregnancy. In recurrent miscarriage there was a trend for a downregulation. Decidua showed an even stronger downregulation in both groups. In the syncytiotrophoblast we found a positive correlation for the combination of LXR/PPARγ in abortions and a negative correlation for LXR/RXRα. In addition, double-immunofluorescence staining showed that LXR as well as RXRα and PPARγ are expressed by the extravillous trophoblast. Finally, RXRα and LXR showed coexpression in the same extravillous trophoblast cells. To conclude, our data show that LXR expression is decreased in miscarriage.

Abstract: While an understanding of lipid metabolism in chickens is critical for a further improvement of food production, there are few studies concerning differences in lipid metabolism mechanisms between chickens and other species at a molecular level. Chickens have three PPAR gene subtypes (α, β, and γ) that function differently from those present in humans and mice. The chicken PPAR-gamma (cPPARγ) gene is shorter than that in humans and lacks a γ2 isoform. Moreover, in serum-free media, cPPARγ shows high transcriptional activity without exogenous ligands. Luciferase reporter assays were used to examine the effect of sera on cPPAR transcriptional activities and showed that adult bovine serum and chicken serum highly activate cPPARα and β functions. Moreover, we found that bezafibrate induces the transactivation function of cPPARβ, but not human PPARδ (human PPARβ ortholog). This ligand selectivity relies on one amino acid residue (chicken: Val419, human: Met444). These results show the possibilities for unique functions of cPPARs on chicken-specific lipid glucose metabolism. As such, a better understanding of the molecular mechanisms of lipid metabolism in chickens could result in higher productivity for the poultry industry.

Abstract: 15-Deoxy--prostaglandin J2 (15d-PGJ2) and activin are implicated in the control of apoptosis, cell proliferation, and inflammation in cells. We examined both the mechanism by which 15d-PGJ2 regulates the transcription of activin-induced activin receptors (ActR) and Smads in HepG2 cells and the involvement of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) pathways in this regulation. Activin A (25 ng/mL) inhibited HepG2 cell proliferation, whereas 15d-PGJ2 (2 μM and 5 μM) had no effect. Activin A and 15d-PGJ2 showed different regulatory effects on ActR and Smad expression, NF-κB p65 activity and MEK/ERK phosphorylation, whereas they both decreased IL-6 production and increased IL-8 production. When co-stimulated with 15d-PGJ2 and activin, 15d-PGJ2 inhibited the activin-induced increases in ActR and Smad expression, and decreased activin-induced IL-6 production. However, it increased activin-induced IL-8 production. In addition, 15d-PGJ2 inhibited activin-induced NF-κB p65 activity and activin-induced MEK/ERK phosphorylation. These results suggest that 15d-PGJ2 suppresses activin-induced ActR and Smad expression, down-regulates IL-6 production, and up-regulates IL-8 production via suppression of NF-κB and MAPK signaling pathway in HepG2 cells. Regulation of ActR and Smad transcript expression and cytokine production involves NF-κB and the MAPK pathway via interaction with 15d-PGJ2/activin/Smad signaling.

Abstract: The present trial aimed to investigate the effects of pioglitazone on the serum level of asymmetric dimethylarginine (ADMA), a marker of endothelial function, and some indices of inflammation and glucose and lipid metabolism in nondiabetic metabolic syndrome patients. 104 eligible participants (57% female; age between 20 and 70) were enrolled in a double-blind placebo-controlled trial and were randomized to receive either pioglitazone (uptitrated to 30 mg/day) or matching placebo for 24 weeks. Participants were clinically examined and a blood sample was obtained at baseline and at the end of the trial. Pioglitazone significantly improved C-reactive protein level irrespective of changes in insulin sensitivity. Compared with the placebo group, alanine and aspartate transaminases were decreased and high-density lipoprotein cholesterol was increased after treatment with pioglitazone. A considerably greater weight gain was also recorded in the intervention group. We failed to observe any significant changes in serum ADMA in either group and between groups with and without adjustment for age, sex, and components of the metabolic syndrome. In a nutshell, pioglitazone seems to have positive effects on lipid profile, liver transaminases, and systemic inflammation. However, its previously demonstrated endothelial function-improving properties do not seem to be mediated by ADMA.

Abstract: We aimed to determine whether epidermal growth factor receptor (EGFR) inhibition, in addition to a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, prevents high-glucose-induced proximal tubular fibrosis, inflammation, and sodium and water retention in human proximal tubule cells exposed to normal glucose; high glucose; high glucose with the PPARγ agonist pioglitazone or with the P-EGFR inhibitor, gefitinib; or high glucose with both pioglitazone and gefitinib. We have shown that high glucose increases AP-1 and NFκB binding activity, downstream phosphorylation of EGFR and Erk1/2, and fibronectin and collagen IV expression. Pioglitazone reversed these effects but upregulated NHE3 and AQP1 expression. Gefitinib inhibited high glucose induced fibronectin and collagen IV, and EGFR and Erk1/2 phosphorylation and reversed pioglitazone-induced increases in NHE3 and AQP1 expression. Our data suggests that combination of an EGFR inhibitor and a PPARγ agonist mitigates high-glucose-induced fibrosis and inflammation and reverses the upregulation of transporters and channels involved in sodium and water retention in human proximal tubule cells. Hence EGFR blockade may hold promise, not only in limiting tubulointerstitial pathology in diabetic nephropathy, but also in limiting the sodium and water retention observed in patients with diabetes and exacerbated by PPARγ agonists.

Abstract: Leu162Val PPARα and Pro12Ala PPARγ2 were investigated for their individual and their interactive impact on MS and renal functionality (RF). 522 subjects were investigated for biochemical and anthropometric measurements. The diagnosis of MS was based on the IDF definition (2009). The HOMA 2 was used to determine HOMA-β, HOMA-S and HOMA-IR from FPG and FPI concentrations. RF was assessed by estimating the GFR. PCR-RFLP was performed for DNA genotyping. Allele frequencies were 0.845 for Pro and 0.155 for Ala, and were 0.915 for Leu and 0.085 for Val. We showed that carriers of the PPARα Val 162 allele had lower urea, UA and higher GFR compared to those homozygous for the Leu162 allele. Subjects carried by PPARγ2Ala allele had similar results. They also had reduced FPG, FPI and HOMA-IR, and elevated HOMA-β and HOMA-S compared to those homozygous for the Pro allele. Subjects were divided into 4 groups according to the combinations of genetic alleles of the 2 polymorphisms. Subjects carrying the Leu/Val with an Ala allele had lower FPG, PPI, HOMA-IR, urea, UA levels, higher HOMA-β, HOMA-S and GFR than different genotype combinations. Leu162Val PPARα and Pro12Ala PPARγ2 can interact with each other to modulate glucose and insulin homeostasis and expand their association with overall better RF.

Abstract: Obesity and type 2 diabetes mellitus (T2D) are two major public health problems that have motivated the scientific community to investigate the high contribution of genetic factors to these disorders. The peroxisome proliferator activated by gamma 2 (PPAR2) plays an important role in the lipid metabolism. Since PPAR2 is expressed mainly in adipose tissue, a moderate reduction of its activity influences the sensitivity to insulin, diabetes, and other metabolic parameters. The present study aims to contribute to the elucidation of the impact of the Pro12Ala polymorphism associated with T2D and obesity through a meta-analysis study of the literature that included approximately 11500 individuals, from which 3870 were obese and 7625 were diabetic. Statistical evidence supports protective effect in T2D of polymorphism Pro12Ala of PPAR2 (OR = 0.702 with 95% CI: 0.622; 0.791, ). Conversely the same polymorphism Pro12Ala of PPAR2 seems to favor obesity since 1.196 more chance than nonobese was found (OR = 1.196 with 95% CI: 1.009; 1.417, ). Our results suggest that Pro12Ala polymorphism enhances both adipogenic and antidiabetogenic physiological role of PPAR. Does Pro12Ala polymorphism represent an evolutionary step towards the stabilization of the molecular function of PPAR transcription factor signaling pathway?

Abstract: Chronic kidney disease (CKD) is characterised by specific lipoprotein abnormalities and insulin resistance. Dual activation of the peroxisome proliferators-activated receptors (PPAR) α and γ can significantly improve insulin sensitivity. The aim of the study was to investigate the effects of a dual PPAR α / γ agonist on lipoprotein abnormalities in patients with CKD. One mg of the dual PPAR α / γ agonist tesaglitazar was given once daily during six weeks to CKD patients, and to healthy subjects. Plasma lipids, apolipoproteins (apo) and discrete lipoprotein subclasses were measured at baseline and end of treatment. In the CKD patients apoA-I increased significantly by 9%, and apoB decreased by 18%. There was an increase of apoC-III in HDL by 30%, and a parallel decrease of apoC-III in VLDL + LDL by 13%. Both the apoB-containing cholesterol-rich and the triglyceride-rich subclasses decreased significantly. With the exception of ApoC-III,all plasma lipids apolipoproteins and lipoprotein subclasses were reduced by treatment down to similar levels as the baseline levels of a healthy group of reference subjects. This study suggests that by improving insulin sensitivity a dual PPAR α / γ agonist has the potential to normalise most of the lipoprotein abnormalities in patients with CKD.

Abstract: During the last years accumulating evidence demonstrated that the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPARgamma) regulates the expression of renin gene and thus the overall renin production. This review summarizes the current knowledge of the transcriptional control of the renin gene by PPARgamma received from variety of models ranging from cell culture to transgenic animals. The molecular mechanisms of the PPARgamma action on renin are particularly interesting because they are featured by two newly described characteristics: one of them is the recently identified PPARgamma target sequence Pal3 which is specific for the human renin gene and mediates exceptionally high sensitivity to transactivation; the other is the potentiating effect of PPARgamma on the cAMP signaling in the renin-producing cells. Furthermore, I discuss the need for generating of additional transgenic animal models which are more appropriate with regard to the role of the PPARgamma-dependent regulation of the renin gene expression in human diseases such as arterial hypertension and metabolic syndrome.

Abstract: Pediatric primary nephrotic syndrome (PNS) is a chronic disease promoted by metabolic and immune dysfunctions. Peroxisome proliferator-activated receptor (PPAR) polymorphisms have been associated with a variety of metabolic and kidney disorders. We therefore hypothesized that PPAR polymorphisms might be involved in the pathophysiology of PNS. We compared the distributions of the PPAR-γ Pro12Ala and Val290Met, PPAR-γ coactivator-α (PGC-1α) Gly482Ser, and PPAR-α Leu162Val single nucleotide polymorphisms (SNPs) between children with PNS and normal controls and analyzed their correlations with clinical and metabolic indicators and steroid responsiveness. There were no significant differences in distributions of any of the polymorphisms between PNS cases and controls. However, PNS patients with the PPAR-γ (Pro12Ala) PP genotype had significantly higher fasting serum insulin, IgA, and HOMA-IR levels and lower insulin sensitivity than did patients with PA and AA genotypes. Additionally, the PGC-1α (Gly482Ser) A allele was associated with lower CD8+ T-cell counts and higher triglyceride and complement C3 levels compared with the G allele. No polymorphisms were related to hormone sensitivity. These results suggest that the PPAR-γ (Pro12Ala) and PGC-1α (Gly482Ser) SNPs may influence insulin and triglyceride metabolism in children with PNS and may thus be relevant to the prognosis of this chronic condition.

Abstract: This special issue of PPAR Research contains four interesting reviews and a research article examining the relevance of PPARs to liver diseases. Peroxisome proliferation-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily and have been implicated in a variety of pathologic processes. PPARs require heterodimerization with retinoid X receptors (RXRs) to function. PPARs α/β/δ/γ, with RXR, are important nuclear receptors expressed in the liver and contribute to the control of glucose and lipid metabolism, cell proliferation and inflammation, and so forth. PPARs were considered target molecules of human metabolic disease such as nonalcoholic fatty liver diseases (NAFLDs) including nonalcoholic steatohepatitis (NASH), a condition that might progress to cirrhosis. In this special issue, two review articles mention the relationship between PPARs and NAFLD. In regard to inflammation, a review article summarizes the antioxidant stress and anti-inflammation of PPARα. On the other hand, a research article mentions that PPARγ exacerbated concanavalin A (Con A)-induced liver injury. In our review article, we summarize the relevance of PPARs and hepatocellular carcinoma (HCC) including cancer stem cells. These five articles have interesting and valuable points of views regarding PPARs and liver diseases. In the review article “Antioxidant stress and anti-inflammation of PPARα on warm hepatic ischemic-reperfusion injury” by Z. Gao and Y. H. Li, the authors focus on hepatic ischemic-reperfusion injury, since PPARα could have a role in organ protection in addition to regulating lipid and lipoprotein metabolism. They concluded that oxidant stress and inflammation are the most critical mechanisms in organ pathophysiology after warm hepatic ischemia reperfusion. The most significant mechanisms of PPARα hepatoprotective abilities have been demonstrated through antioxidant stress and anti-inflammation functions. Moreover, they mention that PPARα agonists such as N-3 polyunsaturated fatty acids, eicosapentaenoic acid, and docosahexaenoic acid could decrease the expression of proinflammatory genes by preventing IκB phosphorylation and NF-κB translocation into the nucleus. On the other hand, Y. Ogawa et al. published the research article “Peroxisome proliferation-activated receptor gamma exacerbates concanavalin A-induced liver injury via suppressing the translocation of NF-κB into the nucleus.” Using a mice model, this article surprisingly shows that the administration of PPARγ ligands exacerbated Con A-induced liver injury. They concluded that PPARγ suppressed the translocation of NF-κB into the nucleus, thereby inhibiting the suppression of liver cell apoptosis. In clinical settings, liver damage would occur with inflammation and apoptosis. Therefore, we need to consider the opposite effects of PPARs on liver injury. NAFLD, a major cause of progressive liver disease, is increasing worldwide at an alarming rate. Defined by an increased hepatic lipid content, NAFLD varies widely from simple steatosis to NASH and has a strong genetic component. PPARs, including PPARα, PPARγ, and PPARδ, play an important role in hepatic lipid metabolism and also have several genetic variants (polymorphisms). In the review article “Peroxisome proliferator-activated receptor genetic polymorphisms and nonalcoholic fatty liver disease: any role in disease susceptibility?” by P. Dongiovanni et al., the authors conducted a meta-analysis of previously reported evidence based upon which they describe the possible association between PPARs genetic polymorphisms and the susceptibility to NAFLD and NASH in specific subgroups. This review may contribute to new insight into the management of a therapeutic strategy for NAFLD, targeting PPARs. In the review article “Misregulation of PPAR functioning and Its pathogenic consequences associated with nonalcoholic fatty liver disease in human obesity” by L. A. Videla and P. Pettinelli, the authors mention that NASH is involved in the misregulation of PPARs signaling, accompanied by PPAR-γ and SREBP-1c-mediated metabolic disturbances (obesity-induced oxidative stress and related long-chain polyunsaturated fatty acid n-3 (LCPUFA n-3) depletion, insulin resistance, hypoadiponectinemia, and ER stress, due to lipogenesis and fatty acid oxidation. Targeting PPAR-α is problematic since fibrates have poor effectiveness, thiazolidinediones have weight gain limitations, and dual PPAR-α/γ agonists have safety concerns. The authors describe that supplementation of LCPUFA n-3 is a novel therapeutic modality since it reduces liver steatosis scores and inflammatory response, since the LCPUFA n-3 depletion reduces PPAR-α, leading to enhanced DNA binding of proinflammatory factors (NF-κB and AP-1) and the progression of steatosis to steatohepatitis. In our review article “PPAR could contribute to the pathogenesis of hepatocellular carcinoma,” we summarize the relevance of PPARs to the pathogenesis of HCC and cancer stem cells and possible therapeutic options through modifying PPAR signaling, since PPARs could contribute to the mechanisms of cell cycling, anti-inflammatory responses, and apoptosis. Abnormal stimulation of PPARα generates HCC through fatty liver. In HCCs, it is not clear whether PPARγ promotes cancer or can control it. PPARs might be useful target cancer stem cells in inducing the differentiation of HCC, because the expression of PPARs has been implicated in the regulation of the cell cycling of hepatocytes. In conclusion, we hope that you will find these recent advances in elucidating the roles of PPARs in the various kinds of liver diseases. We expect that the reviews presented in this special issue, on the interplay between PPARs and liver disease, will be highly useful for those with interest in this field. Yasuteru Kondo Kenji Uno Keigo Machida Masanori Terajima

Abstract: 1 Centre de Recherche INSERM-UMR866 “Lipides, Nutrition, Cancer” Faculte de Medecine, Universite de Bourgogne 7, Boulevard Jeanne d’Arc, 21079 Dijon Cedex, France 2 Laboratoire CarMeN, UMR INSERM U1060/INRA 1235, Universite Lyon 1, Faculte de Medecine Lyon Sud, 165 Chemin du Grand Revoyet, 69921 Oullins, France 3 Department of Chemical Physiology,The Scripps Research Institute, MB-24, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA

Abstract: Adaptive immunity has evolved as a very powerful and highly specialized tool of host defense. Its classical protagonists are lymphocytes of the T- and B-cell lineage. Cytokines and chemokines play a key role as effector mechanisms of the adaptive immunity. Some autoimmune and inflammatory diseases are caused by disturbance of the adaptive immune system. Recent advances in understanding the pathogenesis of autoimmune diseases have led to research on new molecular and therapeutic targets. PPARγ are members of the nuclear receptor superfamily and are transcription factors involved in lipid metabolism as well as innate and adaptive immunity. PPARγ is activated by synthetic and endogenous ligands. Previous studies have shown that PPAR agonists regulate T-cell survival, activation and T helper cell differentiation into effector subsets: Th1, Th2, Th17, and Tregs. PPARγ has also been associated with B cells. The present review addresses these issues by placing PPARγ agonists in the context of adaptive immune responses and the relation of the activation of these receptors with the expression of cytokines involved in adaptive immunity.

Abstract: To explore the function of PPAR γ in the goat mammary gland, we cloned the whole cDNA of the PPAR γ gene. Homology alignments revealed that the goat PPAR γ gene is conserved among goat, bovine, mouse, and human. Luciferase assays revealed that rosiglitazone enhanced the activity of the PPAR γ response element (PPRE) in goat mammary epithelial cells (GMECs). After rosiglitazone (ROSI) treatment of GMECs, there was a significant (P < 0.05) increase in the expression of genes related to triacylglycerol synthesis and secretion: LPL, FASN, ACACA, PLIN3, FABP3, PLIN2, PNPLA2, NR1H3, SREBF1, and SCD. The decreases in expression observed after knockdown of PPAR γ relative to the control group (Ad-NC) averaged 65%, 52%, 67%, 55%, 65%, 58%, 85%, 43%, 50%, and 24% for SCD, DGAT1, AGPAT6, SREBF1, ACACA, FASN, FABP3, SCAP, ATGL, and PLIN3, respectively. These results provide direct evidence that PPAR γ plays a crucial role in regulating the triacylglycerol synthesis and secretion in goat mammary cells and underscore the functional importance of PPAR γ in mammary gland tissue during lactation.

Abstract: PPARβ/δ is a ligand-activated transcription factor that regulates various cellular functions via induction of target genes directly or in concert with its associated transcriptional repressor, BCL-6. Matrix remodeling proteinases are frequently over-expressed in pancreatic cancer and are involved with metastasis. The present study tested the hypothesis that PPARβ/δ is expressed in human pancreatic cancer cells and that its activation could regulate MMP-9, decreasing cancer cells ability to transverse the basement membrane. In human pancreatic cancer tissue there was significantly higher expression of MMP-9 and PPARβ/δ, and lower levels of BCL-6 mRNA. PPARβ/δ activation reduced the TNFα-induced expression of various genes implicated in metastasis and reduced the invasion through a basement membrane in cell culture models. Through the use of short hairpin RNA inhibitors of PPARβ/δ, BCL-6, and MMP-9, it was evident that PPARβ/δ was responsible for the ligand-dependent effects whereas BCL-6 dissociation upon GW501516 treatment was ultimately responsible for decreasing MMP-9 expression and hence invasion activity. These results suggest that PPARβ/δ plays a role in regulating pancreatic cancer cell invasion through regulation of genes via ligand-dependent release of BCL-6 and that activation of the receptor may provide an alternative therapeutic method for controlling migration and metastasis.

Abstract: Nonalcoholic fatty liver disease (NAFLD) defines a wide spectrum of liver diseases that extend from simple steatosis, that is, increased hepatic lipid content, to nonalcoholic steatohepatitis (NASH), a condition that may progress to cirrhosis with its associated complications. Nuclear hormone receptors act as intracellular lipid sensors that coordinate genetic networks regulating lipid metabolism and energy utilization. This family of transcription factors, in particular peroxisome proliferator-activated receptors (PPARs), represents attractive drug targets for the management of NAFLD and NASH, as well as related conditions such as type 2 diabetes and the metabolic syndrome. The impact on the regulation of lipid metabolism observed for PPARs has led to the hypothesis that genetic variants within the human PPARs genes may be associated with human disease such as NAFLD, the metabolic syndrome, and/or coronary heart disease. Here we review the available evidence on the association between PPARs genetic polymorphism and the susceptibility to NAFLD and NASH, and we provide a meta-analysis of the available evidence. The impact of PPAR variants on the susceptibility to NASH in specific subgroup of patients, and in particular on the response to therapies, especially those targeting PPARs, represents promising new areas of investigation.