PPAR Isotypes Research Articles

WED-523 - Unraveling the individual contributions of the PPAR isotypes to the pan-PPAR agonist Lanifibranor-induced improvements of the vascular alterations and liver histology in a rat model of early NAFLD

WED-523 - Unraveling the individual contributions of the PPAR isotypes to the pan-PPAR agonist Lanifibranor-induced improvements of the vascular alterations and liver histology in a rat model of early NAFLD

A randomised, double-blind, placebo-controlled, multi-centre, dose-range, proof-of-concept, 24-week treatment study of lanifibranor in adult subjects with non-alcoholic steatohepatitis: Design of the NATIVE study

BackgroundNon-alcoholic steatohepatitis (NASH), a multifactorial disease, can progress to hepatic fibrosis and cirrhosis. The Peroxysomal Proliferator-Activated Receptors, PPARα, β/δ and γ, play a central role in the regulation of glucose and lipid metabolism and of the inflammatory and fibrogenic pathways in liver and in other organs that all contribute to NASH pathogenesis. Lanifibranor (IVA337), a panPPAR agonist, by acting on these three different PPAR isotypes, combines pharmacological effects that could address the different components of the disease as demonstrated in preclinical models.ObjectivesNATIVE study (EudraCT: 2016–001979-70, NCT: NCT03008070) aims to assess the safety and the efficacy of a 24-week treatment with lanifibranor (800 and 1200 mg/day) in adult non-cirrhotic NASH patients. The primary efficacy endpoint is a 2-point reduction in the activity part of the Steatosis Activity Fibrosis (SAF) histological score (combining inflammation and ballooning) without worsening of fibrosis.DesignNATIVE is a Phase 2b randomised, placebo-controlled, double-blind, parallel-assignment, dose-range study. Eligible adult patients with a confirmed histological diagnosis of NASH should have a SAF Activity score of 3 or 4 (>2) and a SAF Steatosis score ≥ 1. There is no specific criterion related to the fibrosis score except that patients with cirrhosis (F4) were excluded.SummaryThis study will evaluate the efficacy of a 24-week treatment of NASH with lanifibranor based on histological evaluations (SAF score) by biopsy. The number of responders according to the SAF Activity score-based definition from baseline to 24 weeks will be compared between groups and serves as primary endpoint.

Pioglitazone prevents sevoflurane‑induced neuroinflammation and cognitive decline in a rat model of chronic intermittent hypoxia by upregulating hippocampal PPAR‑γ

Post‑operative cognitive dysfunction is a common complication after anesthesia and surgery. Sevoflurane(SEV), a widely used inhalational anesthetic, can exaggerate neuroinflammation and cause cognitive dysfunction under chronic intermittent hypoxia(CIH) conditions by downregulating hippocampal peroxisome proliferator‑activated receptor‑γ(PPAR‑γ). In the present study, it was examined whether treatment with PPAR‑γ agonist pioglitazone(PIO) is beneficial in counteracting SEV‑induced neuroinflammation and cognitive decline in a rat model of CIH. Rats were exposed to CIH for 4weeks. After 2weeks of CIH, these animals underwent either 2.6%SEV or control(CON) exposure for 4h. PIO (60mg/kg) or vehicle (VEH) was administered orally twice daily for 2weeks, starting one day prior to SEV or CON exposure. Compared with CIH‑CON+VEH rats, CIH‑SEV+VEH rats exhibited significant cognitive decline as indicated by increased latency to locate the hidden platform and shorter dwell‑time in the goal quadrant in the Morris Water Maze task. Molecular studies revealed that CIH‑SEV+VEH rats had increased proinflammatory cytokine expression and microglial activation in the hippocampus, which were associated with decreased PPAR‑γ activity. Notably, SEV‑induced cognitive decline and increases in proinflammatory cytokine expression and microglial activation were prevented by PIO, which increased hippocampal PPAR‑γ activity. PIO also increased hippocampal PPAR‑γ activity in CIH‑CON rats but did not alter proinflammatory cytokine expression and microglial activation as well as cognitive function. Additionally, expression of hippocampal PPAR‑α and PPAR‑β, two other PPAR isotypes, were comparable among the groups. These data suggest that PIO prevents SEV‑induced exaggeration of neuroinflammation and cognitive decline under CIH conditions by upregulating hippocampal PPAR‑γ. PIO may have the potential to prevent anesthetic SEV‑induced cognitive decline in surgical patients with obstructive sleep apnea.

Sex-dependent changes in lipid metabolism, PPAR pathways and microRNAs that target PPARs in the fetal liver of rats with gestational diabetes

Gestational diabetes mellitus (GDM) is a prevalent disease that impairs fetal metabolism and development. We have previously characterized a rat model of GDM induced by developmental programming. Here, we analyzed lipid content, the levels of the three PPAR isotypes and the expression of microRNAs that regulate PPARs expression in the liver of male and female fetuses of control and GDM rats on day 21 of pregnancy. We found increased levels of triglycerides and cholesterol in the livers of male fetuses of GDM rats compared to controls, and, oppositely, reduced levels of triglycerides, cholesterol, phospholipids and free fatty acids in the livers of female fetuses of GDM rats compared to controls. Although GDM did not change PPARα levels in male and female fetal livers, PPARγ was increased in the liver of male fetuses of GDM rats, a change that occurred in parallel to a reduction in the expression of miR-130, a microRNA that targets PPARγ. In livers of female fetuses of GDM rats, no changes in PPARγ and miR-130 were evidenced, but PPARδ was increased, a change that occurred in parallel to a reduction in the expression of miR-9, a microRNA that targets PPARδ, and was unchanged in the liver of male fetuses of GDM and control rats. These results show clear sex-dependent changes in microRNAs that target different PPAR isotypes in relation to changes in the levels of their targets and the differential regulation of lipid metabolism evidenced in fetal livers of GDM pregnancies.

Localization of PPAR isotypes in the adult mouse and human brain.

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that act as ligand-activated transcription factors. PPAR agonists have well-documented anti-inflammatory and neuroprotective roles in the central nervous system. Recent evidence suggests that PPAR agonists are attractive therapeutic agents for treating neurodegenerative diseases as well as addiction. However, the distribution of PPAR mRNA and protein in brain regions associated with these conditions (i.e. prefrontal cortex, nucleus accumbens, amygdala, ventral tegmental area) is not well defined. Moreover, the cell type specificity of PPARs in mouse and human brain tissue has yet to be investigated. We utilized quantitative PCR and double immunofluorescence microscopy to determine that both PPAR mRNA and protein are expressed ubiquitously throughout the adult mouse brain. We found that PPARs have unique cell type specificities that are consistent between species. PPARα was the only isotype to colocalize with all cell types in both adult mouse and adult human brain tissue. Overall, we observed a strong neuronal signature, which raises the possibility that PPAR agonists may be targeting neurons rather than glia to produce neuroprotection. Our results fill critical gaps in PPAR distribution and define novel cell type specificity profiles in the adult mouse and human brain.

Using a large-scale knowledge database on reactions and regulations to propose key upstream regulators of various sets of molecules participating in cell metabolism

BackgroundMost of the existing methods to analyze high-throughput data are based on gene ontology principles, providing information on the main functions and biological processes. However, these methods do not indicate the regulations behind the biological pathways. A critical point in this context is the extraction of information from many possible relationships between the regulated genes, and its combination with biochemical regulations. This study aimed at developing an automatic method to propose a reasonable number of upstream regulatory candidates from lists of various regulated molecules by confronting experimental data with encyclopedic information.ResultsA new formalism of regulated reactions combining biochemical transformations and regulatory effects was proposed to unify the different mechanisms contained in knowledge libraries. Based on a related causality graph, an algorithm was developed to propose a reasonable set of upstream regulators from lists of target molecules. Scores were added to candidates according to their ability to explain the greatest number of targets or only few specific ones. By testing 250 lists of target genes as inputs, each with a known solution, the success of the method to provide the expected transcription factor among 50 or 100 proposed regulatory candidates, was evaluated to 62.6% and 72.5% of the situations, respectively. An additional prioritization among candidates might be further realized by adding functional ontology information. The benefit of this strategy was proved by identifying PPAR isotypes and their partners as the upstream regulators of a list of experimentally-identified targets of PPARA, a pivotal transcriptional factor in lipid oxidation. The proposed candidates participated in various biological functions that further enriched the original information. The efficiency of the method in merging reactions and regulations was also illustrated by identifying gene candidates participating in glucose homeostasis from an input list of metabolites involved in cell glycolysis.ConclusionThis method proposes a reasonable number of regulatory candidates for lists of input molecules that may include transcripts of genes and metabolites. The proposed upstream regulators are the transcription factors themselves and protein complexes, so that a multi-level description of how cell metabolism is regulated is obtained.

Rosiglitazone as a regulator of innate immunity in a cell model of hyperglycemia

Epidemiological studies have shown that severe inflammatory responses occur in patients with hyperglycemia. The molecular nature of these changes is currently under intense investigations. A central role of nuclear receptors PPAR has been shown in the regulation of metabolic changes associated with hyperglycemia, a selective agonist of nuclear receptor PPARγ rosiglitazone is used as a hypoglycemic drug. Rosiglitazone is known to have anti-inflammatory effects, but its properties as an anti-inflammatory drug in hyperglycemic conditions have not been studied. This was an aim of our work. We used a human cell culture model of hyperglycemia: HeLa cells incubated in the conditions of 25 mM glucose for 3 days. Control cells were incubated with 5 mM glucose. The cells were stimulated with lipopolysaccharide (LPS) that is known to trigger innate immune response through activation of Toll-like receptor 4 and influence mRNA expression levels of three of PPAR (α, β/δ, γ) isotypes as well as cyclooxygenase (COX-1 and COX-2). We have shown that under hyperglycemic conditions expression levels of PPARα and PPARβ/δ decreased almost twofold, expression level of COX-2 also decreased, while expression levels of COX-1 and PPARγ remained unchanged compared to those under normal glucose concentration. LPS administration in control cells leads to a 1.5–2.5-fold stimulation of expression of COX-2 and PPAR isotypes. In contrast, under hyperglycemia, LPS exhibited no effect on expression of COX-2 and the PPAR isotypes, which indicates potential mechanisms of hyperglycemia-related alterations in innate immunity. Rosiglitazone, an agonist of PPARγ, decreased expression level of PPARβ/δ and abolished the effect of LPS under hyperglycemia. Rosiglitazone also reduced expression level of COX-1 and COX-2, which indicates on the agonist possible role as an anti-inflammatory agent under high glucose concentrations. These data broaden applicability of rosiglitazone as an anti-inflammatory agent in hyperglycemic conditions.

Review: Effects of PPAR activation in the placenta and the fetus: Implications in maternal diabetes

Peroxisome proliferator-activated receptors (PPARα, PPARδ and PPARγ) are ligand-activated transcription factors that regulate metabolic, anti-inflammatory and developmental processes. The maternal and fetal metabolic impairments, the intrauterine pro-inflammatory environment and the developmental defects induced by maternal diabetes make PPARs an interesting focus of investigation. Therefore, research has been conducted in experimental models of diabetes throughout gestation. During embryo organogenesis, impaired PPARδ signaling pathways are related to the induction of congenital malformations. In fetuses from diabetic rats, both lipid metabolism and several pro-inflammatory markers are regulated by the activation of PPAR isotypes. In the placenta from diabetic animals, activation of different PPAR isotypes regulates lipid metabolism and anti-inflammatory pathways, whereas in term placentas from diabetic patients PPARγ reduces the production of nitric oxide. Decreased PPARγ and PPARα protein expression are found in term placentas of diabetic animals and diabetic patients. In addition, a deficiency in polyunsaturated fatty acids (PUFAs) and impaired formation of arachidonic acid derivatives that activate PPARs is found in several diabetic intrauterine tissues. PPARs can be activated by both natural and pharmacological activators. Intrauterine activation of PPARs can be achieved by the administration of maternal diets enriched in PUFAs. This review summarizes recent advances highlighting the possible beneficial role of PPAR activation on embryonic and feto-placental development in maternal diabetes.

PPARs as therapeutic targets in cardiovascular disease

Importance of the field: The role of peroxisome proliferator-activated receptors PPARα, PPARδ and PPARγ in cardiovascular disease is receiving widespread attention. As ligand-activated nuclear receptors, they play a role in regulation of lipid and glucose metabolism. This feature of the PPARs has been successfully exploited to treat systemic metabolic diseases, like hyperlipidemia and type-2 diabetes. Indirectly, their lipid lowering effect also leads to a reduction of the risk for cardiovascular diseases, primarily atherosclerosis.Areas covered in this review: The pleiotropic effects of each of the PPAR isotypes on vascular and cardiac disease are discussed, with special emphasis on the molecular mechanism of action and on preclinical observations. The mechanism underlying the beneficial effect of PPARs is not confined to whole body metabolism, but also includes modulation of other vital processes, such as inflammation and cell fate (proliferation, differentiation, apoptosis).What the reader will gain: A large body of preclinical studies indicates that, in addition to their effect on atherogenesis, PPAR ligands also impact on ischemic heart disease and the development of cardiac failure. It remains to be established to what extent these intriguing observations can be translated into clinical practice.Take home message: The versatile mechanism of action extends the potential therapeutic profile of the PPARs enormously. Conversely, this versatility makes it harder to attain a specific therapeutic effect, without increasing the risk of undesirable side effects. The future challenge will be to design PPAR-based therapeutic strategies that minimize the detrimental side effects.

Altering PPARγ Ligand Selectivity Impairs Adipogenesis by Thiazolidinediones But Not Hormonal Inducers

Peroxisome proliferator-activated receptor gamma (PPARgamma) acts as a ligand-dependent transcription factor with a key role in mediating adipocyte differentiation and insulin sensitivity. Recently, we and others have shown that PPARgamma recruits the nuclear corepressors NCoR and silencing mediator for retinoid and thyroid hormone receptors (SMRT) to modulate adipogenesis. While the synthetic ligands for PPARgamma, the thiazolidinediones (TZD), are widely used in the treatment of type 2 diabetes mellitus, the biologically relevant endogenous PPARgamma ligand involved in adipogenesis remains unidentified. To further understand the role of ligand binding and corepressor interaction in PPARgamma-mediated adipogenesis, a mutation was introduced in the ligand-binding domain (LBD) of murine PPARgamma. PPARgammamut was created via two amino acid substitutions known to be major determinants of ligand selectivity among PPAR isotypes, H323Y and R288M. These mutations alter PPARgamma to the corresponding residues of the PPARalpha. Characterizing the in vitro functional properties of this mutant, we show that PPARgammamut preferentially responds to the PPARalpha agonist, WY-14643, over the TZD, pioglitazone. When expressed in 3T3-L1 preadipocytes using recombinant adenovirus, wild-type PPARgamma leads to adipocyte formation with both hormonal and TZD treatment. PPARgammamut blocks the upregulation of adipocyte-specific proteins by TZD, but surprisingly, not by standard hormonal inducers. Our data suggest that TZDs and the purported endogenous ligand do not interact in the same way with the PPARgamma LBD. We propose that the endogenous ligand has distinct properties that allow for promiscuity within the hydrophobic PPAR ligand-binding pocket, yet fosters appropriate cofactor recruitment and release to allow adipogenesis to proceed.

Peroxisome Proliferator Activated Receptor β/δ Activation Prevents Extracellular Regulated Kinase 1/2 Phosphorylation and Protects the Testis From Ischemia and Reperfusion Injury

Testicular torsion is a medical emergency that requires immediate diagnosis and treatment to avoid subsequent testicular injury and infertility. PPARs are a family of nuclear hormone receptors belonging to the steroid receptor superfamily. Three PPAR isotypes (alpha, beta/delta and gamma) encoded by separate genes and showing different tissue distribution patterns have been identified. PPARbeta/delta is expressed in testis and its role is largely unknown. We tested whether pharmacological activation of PPARbeta/delta might protect the testis from ischemia and reperfusion injury. Adult male Sprague-Dawley rats were subjected to 1-hour testicular ischemia, followed by 24 hours of reperfusion. Sham testicular ischemia-reperfusion rats served as controls. The animals were randomized to receive immediately after detorsion 1) L-165,041 (4 mg/kg intraperitoneally), a potent agonist of PPARbeta/delta, 2) GW9662 (Calbiochem(R)) (4 mg/kg intraperitoneally), an antagonist of PPAR, 3) L-165,041 (4 mg/kg intraperitoneally) plus GW9662 (4 mg/kg intraperitoneally) concomitantly or 4) vehicle (1 ml/kg 10% dimethyl sulfoxide/NaCl solution). We evaluated testicular extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 by Western blot. We also investigated PPARbeta/delta activation by Western blot, mRNA expression and organ damage. Testicular ischemia-reperfusion injury caused a significant increase in extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 expression in each testis. Furthermore, histological examination revealed marked damage. L-165,041 administration increased the PPARbeta/delta message and protein, inhibited extracellular signal regulated kinase, tumor necrosis factor-alpha and interleukin-6 expression, and decreased histological damage. Concomitant administration of GW9662 reversed the protection exerted by PPARbeta/delta agonist. These findings indicate that PPARbeta/delta agonists might be an attractive therapeutic candidate for managing testicular torsion.

Seasonal and gender variation of peroxisome proliferator activated receptors expression in brown trout liver

PPAR isotypes have been previously identified in the teleost brown trout ( Salmo trutta f. fario) and their organ distribution pattern established. Being that the liver is a vital metabolic organ presenting expression of all isotypes and also knowing that estrogens/estrogen receptors seem to interact with PPARs, we hypothesized that the latter may very well change seasonally. So, we studied the expression of these receptors in the liver, along the annual reproductive cycle and in both genders. According to real-time RT-PCR, PPARα mRNA expression in females was significantly higher in May and lower in September than in other seasons. No significant variation was observed along the year in males. A significant difference between genders occurred in May, when PPARα expression was higher for females. PPARβ expression showed little variation along the reproductive cycle in females, but in males it was significantly higher in December than in the other seasons. No significant differences existed between genders. PPARγ was more expressed in February than in September and December, for females. As to males, it was more expressed in February than in all other seasons. No significant differences were observed between genders. The study proved our hypothesis that PPARs gene expression varies along the year. Moreover, PPARα expression in females followed the same annual variation pattern as peroxisome volumes and enzyme activities, and an inverse pattern relatively to the salmonid type annual plasma estradiol levels. The data agrees with the idea that PPARα is under estradiol modulation and that cross-talk between this receptor and the estrogen receptor possibly exists.

Development of Synthetic Modulators of PPARs: Current Challenges and Future Opportunities

The cloning of the mouse PPAR alpha gene in 1990 by Issemann and Green [1] stimulated intense interest in this family of nuclear receptors, and research efforts over the next decade established important roles for the PPAR isotypes in glucose and lipoprotein metabolism, inflammation, and atherosclerosis. Though the fibrates (PPAR-α agonists) had been used for the treatment of dyslipidemia for nearly 40 years, the discovery of the insulin-sensitizing effects of PPAR-γ agonists brought about the development and commercialization of the thiazolidinedione (TZD) class of oral anti-hyperglycemic medications: troglitazone, approved by the FDA in 1997, and pioglitazone and rosiglitazone, both approved by the FDA in 1999. The withdrawal of troglitazone from the market in 2000 was an early indicator of the potential safety issues of PPAR drugs. Even so, the clinical use of fibrates and TZDs has allowed for a better understanding of the safety profiles and safety issues of PPAR-α and PPAR-γ agonists [2, 3]. At the beginning of this decade, many pharmaceutical companies had development programs focused on delivering “new and improved” PPAR agonists to the market. For example, several programs were developing PPAR-α/γ dual agonists (i.e., glitazars) for the treatment of type 2 diabetes. Although preliminary data from various PPAR-α/γ dual agonist research programs was promising, nearly all of these research programs were discontinued due to safety issues identified during clinical testing and/or during preclinical testing [4–6]. More recently, the highly publicized (and controversial) meta-analysis of rosiglitazone reported by Nissen and Wolski [7] called into question the safety of the TZDs and prompted changes to the labels of both rosiglitazone and pioglitazone. And yet, the promise of the therapeutic potential of PPAR drugs remains. A PubMed search using the term “peroxisome proliferator-activated receptor” yielded 1578 manuscripts (161 of which were review articles) between January 1 and December 1, 2008. In addition to the roles of the PPAR isotypes in lipid/lipoprotein/glucose metabolism, additional roles in diverse physiological processes and disease states are currently being investigated. As additional functions are identified; the PPARs will continue to be important molecular targets for identifying ligands (drugs) with potential applications to reproduction and fertility, normal development; function of the reproductive, gastrointestinal, respiratory, and central nervous systems; skin biology and wound healing; and cell cycle control and cancer. Reports highlighting both challenges and opportunities in PPAR drug development are included in this special issue. For example, edema, weight gain, and a reduction in bone mass (particularly in women) are challenges limiting the clinical utility of the currently marketed TZDs. The renal and vascular mechanisms of TZD-induced fluid retention are reviewed by Yang and Soodvilai, and the recent clinical data describing the effects of TZDs on bone are reviewed by Schwartz. In contrast, several reports highlight opportunities in PPAR drug development. Deeg and Tan compare the effects of rosiglitazone and pioglitazone on lipids, lipoproteins, and apolipoproteins as reported in head-to-head, randomized clinical studies. Two papers describe the effects of PPARs/PPAR ligands on immune/inflammatory responses; Fernandez reviews the roles of the PPARs in modulating the immune/inflammatory response in atherosclerosis, while Yamashita reviews the receptor-independent effects of PPAR-α and PPAR-γ ligands on cysteinyl leukotriene production in mast cells as it relates to the development of potential anti-asthma medications. Technological and methodological approaches that may prove useful in the identification and assessment of new PPAR drugs are also reported. Clarke et al. describe an approach used to determine the species differences in plasma protein binding to MBX-102, a novel PPAR-γ agonist currently in Phase 2 clinical development, and the corresponding differences in PPAR-γ activation across species. Cho et al. review the role of PPARs in metabolic disorders as well as various strategies and technologies used in the identification and assessment of PPAR drugs. Finally, Miyachi and Hashimoto describe the synthesis and SAR of subtype-specific PPAR agonists derived from a single 3,4-disubstituted phenylpropanoic acid “versatile template” scaffold, and Higgins and Mantzoros review the development and safety profile of INT-131, a potent non-TZD selective PPAR modulator (SPPARM) currently in Phase 2 clinical development. In conclusion, though the full therapeutic potential of PPARs has yet to be realized, and serious safety issues are associated with the currently marketed PPAR drugs (PPAR-α and PPAR-γ), there remains intense interest in exploring new physiological roles of the PPARs and in the identification of new and improved PPAR agonists drugs. Jane A. Pinaire Anne Reifel Miller Francine M. Gregoire

PPARs/RXRs in Cardiovascular Physiology and Disease

The PPAR family of nuclear receptor transcription factors are important regulators of cardiovascular function and metabolism. Because of this, PPARs are potentially interesting pharmacologic targets for treating cardiometabolic disease. The reviews in this series discuss the regulatory functions of PPARs in maintaining metabolic and physiologic homeostasis in a variety of cells and tissues. Additionally, the therapeutic potential and mechanisms of action of ligands of the different PPAR isotypes are discussed. The review series is started by an examination of the effects of PPARs on lipoprotein metabolism. This is one of the first identified functions of PPARs. Indeed, ligands for PPARα were in clinical use as lipid-lowering agents even before their pharmacological target, PPARα, were known. The second review evaluates the important anti-inflammatory effects of PPARs in platelets, which is emerging as an important mechanism of their beneficial effects. Next, the critical role that PPARα and its transcriptional coactivator protein PGC-1α play in regulating energy metabolism and function of the myocardium is discussed. Then, a series of reviews focuses on the potentially beneficial effects of PPARγ agonists on the cardiovascular system. Several aspects are presented. The effects of PPAR activation on the cardiovascular system as a whole, on the vascular smooth muscle cell, and in the context of diabetic cardiovascular disease are each discussed at length. A review by Demers et al. also discusses the potential input of the hexarelin signaling pathway in regulating PPARγ activity and its potential impact on cardiometabolic disease. The genes encoding the PPARs are rich with genetic variation and the impact of these polymorphisms and haplotypes on the response to PPAR activators is only beginning to be understood. Thus, the “pharmacogenomics” of PPARs are discussed in a review by Dr. Sharon Cresci. Finally, the potential toxicity and adverse outcomes of PPAR agonism are summarized in detail by Jennifer Robinson. The timeliness of this discussion is outstanding given the recent reports of increased cardiovascular morbidity associated with use of rosiglitazone and the failure of PPAR dual agonists at different stages of development. Several of the other reviews in this series also touch this controversial issue at least briefly. We are also pleased to present two original research reports. The first report found associations between PPARγ gene polymorphisms and several cardiometabolic indices, but found no link with cardiovascular morbidity and mortality. Second, Buroker et al. report an important role for PGC- 1α in postnatal metabolic maturation. This preprogrammed burst in cardiac oxidative metabolism is an important developmental response that also has implications for other physiologic states wherein the demand for ATP production is rapidly induced. We hope that you will find this issue enjoyable and informative. Brian N. Finck Giulia Chinetti Bart Staels

The Roles of PPARs in the Fetal Origins of Metabolic Health and Disease

Beyond the short-term effects on fertility, there is increasing evidence that obesity or the consumption of an inappropriate diet by the mother during pregnancy adversely affects the long-term health of her offspring. PPAR and RXR isotypes are widely expressed in reproductive tissues and in the developing fetus. Through their interactions with fatty acids, they may mediate adaptive responses to the changes in the maternal diet. In the maturing follicle, PPAR- has an important role in the granulosa cells that surround the maturing oocyte. After fertilisation, PPAR- and PPAR- are essential regulators of placentation and the subsequent development of key metabolic tissues such as skeletal muscle and adipose cells. Activation of PPAR- and PPAR- during fetal development has the potential to modify the growth and development of these tissues. PPAR- is expressed at low levels in the fetal liver, however, this expression may be important, as changes in the methylation of DNA in its promoter region are reported to take place during this period of development. This epigenetic modification then programmes subsequent expression. These findings suggest that two separate PPAR-dependent mechanisms may be involved in the fetal adaptations to the maternal diet, one, mediated by PPAR- and PPAR-, regulating cell growth and differentiation; and another adapting long-term lipid metabolism via epigenetic changes in PPAR- to optimise postnatal survival.

PPARs Expression in Adult Mouse Neural Stem Cells: Modulation of PPARs during Astroglial Differentiaton of NSC

PPAR isotypes are involved in the regulation of cell proliferation, death, and differentiation, with different roles and mechanisms depending on the specific isotype and ligand and on the differentiated, undifferentiated, or transformed status of the cell. Differentiation stimuli are integrated by key transcription factors which regulate specific sets of specialized genes to allow proliferative cells to exit the cell cycle and acquire specialized functions. The main differentiation programs known to be controlled by PPARs both during development and in the adult are placental differentiation, adipogenesis, osteoblast differentiation, skin differentiation, and gut differentiation. PPARs may also be involved in the differentiation of macrophages, brain, and breast. However, their functions in this cell type and organs still awaits further elucidation. PPARs may be involved in cell proliferation and differentiation processes of neural stem cells (NSC). To this aim, in this work the expression of the three PPAR isotypes and RXRs in NSC has been investigated.

PPAR and human metabolic disease

The nuclear receptor family of PPARs was named for the ability of the original member to induce hepatic peroxisome proliferation in mice in response to xenobiotic stimuli. However, studies on the action and structure of the 3 human PPAR isotypes (PPARalpha, PPARdelta, and PPARgamma) suggest that these moieties are intimately involved in nutrient sensing and the regulation of carbohydrate and lipid metabolism. PPARalpha and PPARdelta appear primarily to stimulate oxidative lipid metabolism, while PPARgamma is principally involved in the cellular assimilation of lipids via anabolic pathways. Our understanding of the functions of PPARgamma in humans has been increased by the clinical use of potent agonists and by the discovery of both rare and severely deleterious dominant-negative mutations leading to a stereotyped syndrome of partial lipodystrophy and severe insulin resistance, as well as more common sequence variants with a much smaller impact on receptor function. These may nevertheless have much greater significance for the public health burden of metabolic disease. This Review will focus on the role of PPARgamma in human physiology, with specific reference to clinical pharmacological studies, and analysis of PPARG gene variants in the abnormal lipid and carbohydrate metabolism of the metabolic syndrome.

Rosiglitazone induces interleukin‐1 receptor antagonist in interleukin‐1β–stimulated rat synovial fibroblasts via a peroxisome proliferator–activated receptor β/δ–dependent mechanism

To study the potency of 2 peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-deoxy-PGJ(2)) and rosiglitazone, to modulate the expression of interleukin-1 receptor antagonist (IL-1Ra) in rat synovial fibroblasts. Levels of messenger RNA for IL-1Ra and PPAR isotypes (alpha, beta/delta, gamma) were assessed by real-time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL-1beta. PPAR levels were assessed by Western blotting and secreted IL-1Ra levels by immunoassay. The potency of PPARgamma agonists and the PPARbeta/delta agonist GW-501516 on IL-1Ra levels was tested in the range of 1-10 microM and at 100 pM, respectively. The contribution of PPARgamma to the effects of rosiglitazone on IL-1Ra secretion was examined either by its overexpression or by inhibition using wild-type or dominant-negative constructs and the antagonist GW-9662 (10 microM), respectively. The dominant-negative strategy was also performed to investigate the possible contribution of PPARbeta/delta and NF-kappaB activation. IL-1beta-induced IL-1Ra production was increased by 10 microM rosiglitazone but was reduced dose-dependently by 15-deoxy-PGJ(2). Both agonists lowered IL-1beta secretion, but rosiglitazone alone reduced the imbalance of IL-1beta/IL-1Ra toward basal levels. Enhancement of IL-1beta-induced IL-1Ra production by rosiglitazone was not affected by PPARgamma overexpression or by its inhibition with dominant-negative PPARgamma or GW-9662. Inhibition of NF-kappaB was also ineffective against rosiglitazone but abolished the stimulating effect of IL-1beta on IL-1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARgamma decreased dramatically upon IL-1beta exposure, whereas PPARbeta/delta remained stable. Dominant-negative PPARbeta/delta abolished the enhancement of IL-1Ra by rosiglitazone, whereas GW-501516 reproduced the effect of rosiglitazone on IL-1Ra secretion. Rosiglitazone stimulates IL-1Ra production by a PPARbeta/delta mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.

Peroxisome proliferator-activated receptor gamma and its ligands in controlling interleukin-1beta target gene expression: A confusing story

Antiinflammatory effects by peroxisome proliferator-activated receptor gamma (PPARgamma) agonists have been previously reported. However, PPARgamma dependency and the molecular mechanism involved in these effects require more investigation to clearly demonstrate whether PPARgamma is a key modulator of the antiinflammatory process. This would permit the design of more specific agonists or antagonists able to address the gamma subtype without cross reactions with other transcription factors, thus preventing undesirable side effects. However, several hurdles need to be taken into consideration, such as the coexpression of several PPAR isotypes in the same cell type. As PPARgamma and -alpha seem to play equal antiinflammatory roles, determining the subset of specific PPAR subtype target genes appears to be crucial. The work described here is our current understanding of the modulations of interleukin-1 target gene expression by PPARgamma and its ligands.

Immunolocalization of peroxisome proliferator-activated receptors and retinoid x receptors in the adult rat CNS

Peroxisome proliferator-activated and retinoid X receptors (PPARs and RXRs) are transcription factors belonging to the steroid hormone receptor superfamily. Upon activation by their ligands, PPARs and RXRs bind to their target genes as heterodimers. Ligands of these receptors include lipophylic molecules, such as retinoids, fatty acids and eicosanoids, the importance of which in the metabolism and functioning of the nervous tissue is well documented. The immunohistochemical distribution of PPARs and RXRs in the CNS of the adult rat was studied by means of a sensitive biotinyl-tyramide method. All PPAR (α, β/δ and γ) and RXR (α, β and γ) isotypes were detected and found to exhibit specific patterns of localization in the different areas of the brain and spinal cord. The presence of the nuclear receptors was observed in both neuronal and glial cells. While PPAR β/δ and RXR β showed a widespread distribution, α and γ isotypes exhibited a more restricted pattern of expression. The frontal cortex, basal ganglia, reticular formation, some cranial nerve nuclei, deep cerebellar nuclei, and cerebellar Golgi cells appeared rather rich in all studied receptors. Based on our data, we suggest that in the adult CNS, PPARs and RXRs, besides playing roles common to many other tissues, may have specific functions in regulating the expression of genes involved in neurotransmission, and therefore play roles in complex processes, such as aging, neurodegeneration, learning and memory.