Regional distribution of PPARbeta in the cerebellum of the rat

Synthesis and evaluation of an orally available "Y"-shaped biaryl peroxisome proliferator-activated receptor δ agonist

In this study, we designed and synthesized several novel "Y"-shaped biaryl PPARδ agonists. Structure-activity relationship (SAR) studies demonstrated that compound 3a was the most active agonist with an EC₅₀ of 2.6 nM. We also synthesized and evaluated enantiospecific R and S isomers of compound 3a to confirm that R isomer (EC₅₀ = 0.7 nM) shows much more potent activity than S isomer (EC₅₀ = 6.1 nM). Molecular docking studies between the PPAR ligand binding domain and enantiospecific R and S isomers of compound 3a were performed. In vitro absorption, distribution, metabolism, excretion, and toxicity (ADMET) and in vivo PK profiles show that compound 3a possesses superior drug-like properties including good bioavailability. Our overall results clearly demonstrate that this orally administrable PPARδ agonist 3a is a viable drug candidate for the treatment of various PPARδ-related disorders.

Prenatal fat exposure and hypothalamic PPAR β/δ: Possible relationship to increased neurogenesis of orexigenic peptide neurons

Gestational exposure to a fat-rich diet, while elevating maternal circulating fatty acids, increases in the offspring's hypothalamus and amygdala the proliferation and density of neurons that express neuropeptides known to stimulate consummatory behavior. To understand the relationship between these phenomena, this study examined in the brain of postnatal offspring (day 15) the effect of prenatal fat exposure on the transcription factor, peroxisome proliferator-activated receptor (PPAR) β/δ, which is sensitive to fatty acids, and the relationship of PPAR β/δ to the orexigenic neuropeptides, orexin, melanin-concentrating hormone, and enkephalin. Prenatal exposure to a fat-rich diet compared to low-fat chow increased the density of cells immunoreactive for PPAR β/δ in the hypothalamic paraventricular nucleus (PVN), perifornical lateral hypothalamus (PFLH), and central nucleus of the amygdala (CeA), but not the hypothalamic arcuate nucleus or basolateral amygdaloid nucleus. It also increased co-labeling of PPAR β/δ with the cell proliferation marker, BrdU, or neuronal marker, NeuN, and the triple labeling of PPAR β/δ with BrdU plus NeuN, indicating an increase in proliferation and density of new PPAR β/δ neurons. Prenatal fat exposure stimulated the double-labeling of PPAR β/δ with orexin or melanin-concentrating hormone in the PFLH and enkephalin in the PVN and CeA and also triple-labeling of PPAR β/δ with BrdU and these neuropeptides, indicating that dietary fat increases the genesis of PPAR β/δ neurons that produce these peptides. These findings demonstrate a close anatomical relationship between PPAR β/δ and the increased proliferation and density of peptide-expressing neurons in the hypothalamus and amygdala of fat-exposed offspring.

The PPARβ/δ Agonist GW0742 Induces Early Neuronal Maturation of Cortical Post-Mitotic Neurons: Role of PPARβ/δ in Neuronal Maturation

Increasing evidences support that signaling lipids participate in synaptic plasticity and cell survival, and that the lipid signaling is closely associated with neuronal differentiation, learning, and memory and with pathologic events, such as epilepsy and Alzheimer's disease. The Peroxisome Proliferator-Activated Receptors (PPAR) are strongly involved in the fatty acid cell signaling, as many of the natural lypophylic compounds are PPAR ligands. We have previously shown that PPARβ/δ is the main isotype present in cortical neuron primary cultures and that during neuronal maturation, PPARβ/δ is gradually increased and activated. To get more insight into the molecular mechanism by which PPARβ/δ may be involved in neuronal maturation processes, in this work a specific PPARβ/δ agonist, GW0742 was used administered alone or in association with a specific PPARβ/δ antagonist, the GSK0660, and the parameters involved in neuronal differentiation and maturation were assayed. The data obtained demonstrated the strong involvement of PPARβ/δ in neuronal maturation, triggering the agonist an anticipation of neuronal differentiation, and the antagonist abolishing the observed effects. These effects appear to be mediated by the activation of BDNF pathway.

Involvement of peroxisome proliferator-activated receptor β/δ (PPAR β/δ) in BDNF signaling during aging and in Alzheimer disease: possible role of 4-hydroxynonenal (4-HNE)

Aging and many neurological disorders, such as AD, are linked to oxidative stress, which is considered the common effector of the cascade of degenerative events. In this phenomenon, reactive oxygen species play a fundamental role in the oxidative decomposition of polyunsaturated fatty acids, resulting in the formation of a complex mixture of aldehydic end products, such as malondialdehyde, 4-hydroxynonenal, and other alkenals. Interestingly, 4-HNE has been indicated as an intracellular agonist of peroxisome proliferator-activated receptor β/δ. In this study, we examined, at early and advanced AD stages (3, 9, and 18 months), the pattern of 4-HNE and its catabolic enzyme glutathione S-transferase P1 in relation to the expression of PPARβ/δ, BDNF signaling, as mRNA and protein, as well as on their pathological forms (i.e., precursors or truncated forms). The data obtained indicate a novel detrimental age-dependent role of PPAR β/δ in AD by increasing pro-BDNF and decreasing BDNF/TrkB survival pathways, thus pointing toward the possibility that a specific PPARβ/δ antagonist may be used to counteract the disease progression.

Peroxisome proliferator-activated receptor (PPAR)β/δ, a possible nexus of PPARα- and PPARγ-dependent molecular pathways in neurodegenerative diseases: Review and novel hypotheses

Peroxisome proliferator-activated receptors (PPARα, -β/δ and -γ) are lipid-activated transcription factors. Synthetic PPARα and PPARγ ligands have neuroprotective properties. Recently, PPARβ/δ activation emerged as the focus of a novel approach for the treatment of a wide range of neurodegenerative diseases. To fill the gap of knowledge about the role of PPARβ/δ in brain, new hypotheses about PPARβ/δ involvement in neuropathological processes are requested. In this paper, we describe a novel hypothesis, claiming the existence of tight interactions between the three PPAR isotypes, which we designate the "PPAR triad". We propose that PPARβ/δ has a central control of the PPAR triad. The majority of studies analyze the regulation only by one of the PPAR isotypes. A few reports describe the mutual regulation of expression levels of all three PPAR isotypes by PPAR agonists. Analysis of these studies where pairwise interactions of PPARs were described allows us to support the existence of the PPAR triad with central role for PPARβ/δ. In the present review, we propose the hypothesis that in a wide range of brain disorders, PPARβ/δ plays a central role between PPARα and PPARγ. Finally, we prove the advantages of the PPAR triad concept by describing hypotheses of PPARβ/δ involvement in the regulation of myelination, glutamate-induced neurotoxicity, and signaling pathways of reactive oxygen species/NO/Ca(2+).

Nuclear control of the inflammatory response in mammals by peroxisome proliferator-activated receptors

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that play pivotal roles in the regulation of a very large number of biological processes including inflammation. Using specific examples, this paper focuses on the interplay between PPARs and innate immunity/inflammation and, when possible, compares it among species. We focus on recent discoveries establishing how inflammation and PPARs interact in the context of obesity-induced inflammation and type 2 diabetes, mostly in mouse and humans. We illustrate that PPAR γ ability to alleviate obesity-associated inflammation raises an interesting pharmacologic potential. In the light of recent findings, the protective role of PPAR α and PPAR β / δ against the hepatic inflammatory response is also addressed. While PPARs agonists are well-established agents that can treat numerous inflammatory issues in rodents and humans, surprisingly very little has been described in other species. We therefore also review the implication of PPARs in inflammatory bowel disease; acute-phase response; and central, cardiac, and endothelial inflammation and compare it along different species (mainly mouse, rat, human, and pig). In the light of the data available in the literature, there is no doubt that more studies concerning the impact of PPAR ligands in livestock should be undertaken because it may finally raise unconsidered health and sanitary benefits.

Discovery, design and synthesis of Y-shaped peroxisome proliferator-activated receptor δ agonists as potent anti-obesity agents in vivo

We have discovered and demonstrated the in vitro and in vivo PPARδ-selective activity of novel Y-shaped agonists. These compounds activated hPPARδ with EC(50) values between 1 and 523 nM. Surprisingly, compounds 10a, 11d, 11e and 11f were the most potent and most selective hPPARδ agonists with 10(4)-fold selectivity over the other two subtypes, namely, hPPARα and hPPARγ. The PPARδ ligands 10a, 11e and 11f showed good bioavailability and in vivo efficacy.

Neuroprotective Mechanisms of PPARδ: Modulation of Oxidative Stress and Inflammatory Processes

Peroxisome proliferator-activated receptors (PPARα, δ, and γ) are ligand-activated transcription factors that regulate a wide range of cellular processes, including inflammation, proliferation, differentiation, metabolism, and energy homeostasis. All three PPAR subtypes have been identified in the central nervous system (CNS) of rodents. While PPARα and PPARγ are expressed in more restricted areas of the CNS, PPARδ is ubiquitously expressed and is the predominant subtype. Although data regarding PPARδ are limited, studies have demonstrated that administration of PPARδ agonists confers neuroprotection following various acute and chronic injuries to the CNS, such as stroke, multiple sclerosis, and Alzheimer's disease. The antioxidant and anti-inflammatory properties of PPARδ agonists are thought to underly their neuroprotective efficacy. This review will focus on the putative neuroprotective benefits of therapeutically targeting PPARδ in the CNS, and specifically, highlight the antioxidant and anti-inflammatory functions of PPARδ agonists.

PPARs as new therapeutic targets for the treatment of cerebral ischemia/reperfusion injury

Stroke is a leading cause of death and long-term disability in industrialized countries. Despite advances in understanding its pathophysiology, little progress has been made in the treatment of stroke. The currently available therapies have proven to be highly unsatisfactory (except thrombolysis) and attempts are being made to identify and characterize signaling proteins which could be exploited to design novel therapeutic modalities. The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that control lipid and glucose metabolism. PPARs regulate gene expression by binding with the retinoid X receptor (RXR) as a heterodimeric partner to specific DNA sequences, termed PPAR response elements. In addition, PPARs may modulate gene transcription also by directly interfering with other transcription factor pathways in a DNA-binding independent manner. To date, three different PPAR isoforms, designated alpha, beta/delta, and gamma, have been identified. Recently, they have been found to play an important role for the pathogenesis of various disorders of the central nervous system and accumulating data suggest that PPARs may serve as potential targets for treating ischemic stroke. Activation of all PPAR isoforms, but especially of PPARgamma, was shown to prevent post-ischemic inflammation and neuronal damage in several in vitro and in vivo models, negatively regulating the expression of genes induced by ischemia/ reperfusion (I/R). This paper reviews the evidence and recent developments relating to the potential therapeutic effects of PPAR-agonists in the treatment of cerebral I/R injury.

Peroxisome proliferator-activated receptors (PPARs) and related transcription factors in differentiating astrocyte cultures

Peroxisome proliferator-activated receptors (PPARs), retinoid X receptors (RXRs), CCAAT/enhancer binding proteins (C/EBPs) and beta-catenin are transcription factors involved in cell differentiation. The aim of this work was to investigate the occurrence and variations of these proteins during astrocyte differentiation. Primary cultures of mouse cortical astrocytes were characterized using nestin, A2B5 and glial fibrillary acidic protein (GFAP) as differentiation markers, during a period of 21 days in vitro (DIV). Glycogen and triglyceride accumulation were also studied. At 3 DIV the cultures were mainly constituted by neural progenitor cells, as assessed by their immunofluorescent pattern. At this time PPARs and beta-catenin were localized to the cytoplasm. Interestingly, some cells contained Oil Red O-positive lipid droplets. Between 7 and 21 DIV, nestin decreased, while GFAP increased, indicating ongoing astroglial differentiation. beta-catenin, predominantly nuclear at 7 DIV, later localized to membranes. Redistribution of all three PPAR isotypes from the cytoplasm to the nucleus was observed starting from 7 DIV. Between 7 and 14 DIV, C/EBPalpha, PPARalpha, RXRalpha and glycogen content increased. Between 14 and 21 DIV, PPARbeta/delta decreased, while PPARgamma, C/EBPbeta and delta and lipid droplet-containing cells increased. At 21 DIV both A2B5-/GFAP+ and A2B5+/GFAP+ cells were predominantly observed, indicating differentiation toward type-1 and type-2 astrocytes, although the presence of GFAP- cells demonstrates the persistence of neural precursors in the culture even at this time point. In conclusion, our results, reporting modifications of PPARs, RXRs, C/EBPs and beta-catenin during culture time, strongly suggest the involvement of these transcription factors in astrocyte differentiation. Specifically, beta-catenin translocation from the nucleus to plasma membrane, together with PPARbeta/delta decrease and C/EBPalpha increase, could be related to decreased proliferation at confluence, while PPARalpha and gamma and all C/EBPs could participate in differentiation processes, such as glycogenesis and lipidogenesis.

Expression of peroxisome proliferator-activated receptors (PPARs) and retinoic acid receptors (RXRs) in rat cortical neurons

Neuronal differentiation is a complex process involving the sequential expression of several factors. The important role of lipid molecules in brain development is well known. Many fatty acid cell signaling activities are mediated by peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated transcription factors belonging to the steroid, thyroid and retinoid nuclear receptor superfamily. They are activated by fatty acids and their derivatives. Different isotypes of PPARs (alpha, beta/delta and gamma) have distinct physiological functions depending on their different ligand activation profiles and tissue distribution. PPARs have been involved in neural cell differentiation and death as well as in inflammation and neurodegeneration. Although PPARs have been described in neurons by in situ studies, the presence and possible modulation of these receptors during neuronal differentiation has not been explored yet. In this study we analyzed the expression of PPARs and of their heterodimeric partners, RXRs, in embryonic rat cortical neurons during their in vitro maturation. Our results demonstrate the presence of PPARs alpha, beta/delta and gamma and of RXRs beta and gamma. PPARalpha, beta/delta and gamma are differentially modulated during culture time suggesting that they may be involved in neuronal maturation. In particular, we point toward the PPARbeta/delta isotype as a key factor in neuronal differentiation.

The human semaphorin 6B gene is down regulated by PPARs

The peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors and belong to the nuclear hormone receptor superfamily. They form heterodimers with the retinoid X receptor and bind to specific peroxisome proliferator-response elements. The latter are direct repeat elements of two hexanucleotides with the consensus sequence TG(A/T)CCT separated by a single nucleotide spacer. Such a sequence, or a similar one, has been found in numerous PPAR-inducible genes. We developed an affinity method to isolate human genomic fragments containing binding sites for PPARs and to identify novel PPAR target genes. For this, an antibody raised against all PPAR subtypes was used. Immunoselected fragments were amplified and sequenced and one of them, ISF5148, was found to bind specifically to PPARs in gel mobility shift, supershift, and competition assays and to exhibit a down transregulation potentiality in transfection experiments under clofibrate (a PPARalpha agonist) treatment. ISF5148 was mapped by BLAST analysis 8.5 kb upstream of the human semaphorin 6B [(HSA)SEMA6B] gene. The latter encodes a member of the semaphorin family of axon guidance molecules. Expression of this gene in human glioblastoma T98G cells was strongly down regulated after treatment with clofibrate or Wy-14,643, two PPARalpha agonists. Our study establishes for the first time that PPAR activators diminish the expression of the human (HSA)SEMA6B gene. These data are relevant to the fact that PPARs are implicated in brain development, neuronal differentiation, and lipid metabolism in the central nervous system. In addition, cross talk between the peroxisome proliferator and retinoic acid pathways is suggested.

Effect of the peroxisome proliferator-activated receptor beta activator GW0742 in rat cultured cerebellar granule neurons

The ligand-activated transcription factor peroxisome proliferator-activated receptor beta (PPARbeta) is present in the brain and is implicated in the regulation of genes with potential roles in neurotoxicity. We sought to examine the role of PPARbeta in neuronal cell death by using the PPARbeta ligand GW0742. Primary cultures of rat cerebellar granule neurons were prepared from 7-day-old pups. Reverse transcriptase-polymerase chain reaction and in situ hybridization were used to verify that PPARbeta mRNA was present in neurons. After 10-12 days in culture, the neuronal cells were incubated in the presence of GW0742, and cell death was measured with a lactate dehydrogenase release (LDH) assay. After 24 hr of exposure, PPARbeta activation by GW0742 was not inherently toxic to cerebellar granule neurons. However, toxicity was observed after 48 hr, with cell death mediated via an apoptotic mechanism. In an effect opposite to that observed with PPARalpha-activating ligands, PPARbeta activation exhibited neuroprotective properties. Treatment with GW0742 significantly reduced cell death during a 12-hr exposure to low-KCl media. These results clearly reinforce very specific roles for the PPAR isoforms in neurons and suggest that PPARbeta is worthy of further investigation regarding its potential role as a therapeutic target in neurodegenerative states.

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 (alpha, beta/delta and gamma) and RXR (alpha, beta and gamma) 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 beta/delta and RXR beta showed a widespread distribution, alpha and gamma 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.

Differential effects of polyunsaturated fatty acids on sterol synthesis rates in adult and fetal tissues of the hamster: consequence of altered sterol balance

Cholesterol is necessary for the proper growth and development of the fetus. Consequently, disruptions in cholesterol biosynthesis lead to abnormal fetal development. It has been shown that in cells exposed to polyunsaturated fatty acids (PUFA), the expressions of genes and activities of enzymes involved in cholesterol synthesis are reduced. Similarly, we found that adult male hamsters fed PUFA-enriched diets had an approximately 60% reduction in in vivo hepatic sterol synthesis rates. If fetal tissues respond to PUFA in the same manner as do adult livers, then maternal dietary PUFA could lead to a reduction in fetal sterol synthesis rates and possibly abnormal development. To investigate the impact of maternal dietary fatty acids on fetal sterol synthesis rates, female hamsters were fed diets enriched in various fatty acids before and throughout gestation. In vivo sterol synthesis rates were measured in fetuses at mid- and late gestation. At both gestational stages, dietary PUFA had no effect on fetal sterol synthesis rates. This lack of effect was not a consequence of a lack of PUFA enrichment in fetal fatty acids or the lack of PUFA receptor expression in the fetus. We hypothesize that the fetus may experience a dysregulation of sterol synthesis as the result of the fetus being in a negative sterol balance; the PUFA-induced suppression of sterol synthesis in the adult male hamster liver was ablated by creating a net negative sterol balance across the adult hepatocyte.

Localization of PPARdelta in murine central nervous system: expression in oligodendrocytes and neurons

The peroxisome proliferator-activated receptors (PPARs), PPARdelta, PPARgamma and PPARalpha, comprise a subclass of the supergene family of nuclear receptors. As such they are ligand-regulated transcription factors whose major effects are mediated by altering expression of target genes. PPARdelta has been shown to be ubiquitously expressed in mammals. However, its primary biological role(s) has yet to be defined. Several recent studies have demonstrated that PPARdelta is the most highly expressed PPAR isoform in the central nervous system, but ambiguity still exists as to the specific brain sub-regions and cells in which it is expressed. Here, utilizing novel, isoform-selective PPARdelta riboprobes and an anti-peptide antibody, we performed a series of in situ hybridization and immunolocalization studies to determine the distribution of PPARdelta in the central nervous system (CNS) of mice. We found that PPARdelta mRNA and protein is expressed throughout the brain, with particularly high levels in the entorhinal cortex, hypothalamus and hippocampus, and lower levels in the corpus callosum and caudate putamen. At the cellular level, PPARdelta mRNA and protein were found to be expressed in oligodendrocytes and neurons but not astrocytes. Such results suggest a role for PPARdelta in both myelination and neuronal functioning within the CNS.

Evidence for the presence of both peroxisome proliferator-activated receptors alpha and beta in the rat spinal cord

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily. Different subtypes of PPARs (alpha, beta, and gamma) have been described. Their distinct physiological functions depend on their differential ligand activation profiles but also on their specific tissue expression. Previous studies have described their presence in the central nervous system. However, their expression in the adult rat spinal cord in normal physiological conditions has never been investigated. We demonstrated by using reverse-transcription-polymerase chain reaction, and Western blotting, the mRNA and protein expression of PPARalpha and PPARbeta, but not PPARgamma in cervical, thoracic, and lumbar segments of the spinal cord. Using immunohistochemistry, we also showed for the first time the specific cellular distribution of these transcription factors in the different segments of the spinal cord. In the gray matter, the distribution of PPARalpha was homogenous whereas PPARbeta was specifically localized in motoneurons and in medial part of laminae IV, V, VI, VII, VIII, and X. These latter areas are known as nociceptive afferent pathways to supra-spinal structures such as the medulla reticular nucleus and the thalamus. In the white matter, PPARalpha was localized exclusively in astrocytes while PPARbeta was present in oligodendrocytes. The possible functions of PPARalpha and PPARbeta expressed in both white and gray matters of the spinal cord will be discussed but need further studies.

The mechanisms of action of PPARs

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPAR gamma, PPAR alpha, and PPAR delta, encoded by different genes. PPARs are ligand-regulated transcription factors that control gene expression by binding to specific response elements (PPREs) within promoters. PPARs bind as heterodimers with a retinoid X receptor and, upon binding agonist, interact with cofactors such that the rate of transcription initiation is increased. The PPARs play a critical physiological role as lipid sensors and regulators of lipid metabolism. Fatty acids and eicosanoids have been identified as natural ligands for the PPARs. More potent synthetic PPAR ligands, including the fibrates and thiazolidinediones, have proven effective in the treatment of dyslipidemia and diabetes. Use of such ligands has allowed researchers to unveil many potential roles for the PPARs in pathological states including atherosclerosis, inflammation, cancer, infertility, and demyelination. Here, we present the current state of knowledge regarding the molecular mechanisms of PPAR action and the involvement of the PPARs in the etiology and treatment of several chronic diseases.

Long-term n-3 FA deficiency modifies peroxisome proliferator-activated receptor beta mRNA abundance in rat ocular tissues

Peroxisomal proliferator-activated receptors (PPAR) are a FA-response system involved in diverse cellular responses. FA regulate PPAR activity and modulate PPAR mRNA abundance. Increasing evidence indicates that PUFA are required for optimal neuronal development and function. To gain insight into the mechanism for nutrition-induced impairment of neuronal development and function we investigated the effect of chronic n-3 FA deficiency on PPAR mRNA levels in rat brain and ocular tissues. Rats were fed for three generations a diet designed to reduce DHA levels in tissues, and the abundance of PPARalpha and PPARbeta transcripts was measured by hybridization with specific probes. Chronic consumption of the a-linolenic acid (LNA)-insufficient diet caused a remarkable modification in DHA content in membrane phospholipids. The results reported here indicate that PPARa mRNA levels did not exhibit significant variation in ocular, hepatic, or nervous tissues from rats fed the experimental diet. In contrast, PPARalpha mRNA normalized to beta-actin mRNA was 21% higher in ocular tissue from F3 generation rats consuming the LNA-deficient diet but was independent of diet in hepatic and nervous tissues. The absolute abundance of PPARbeta transcripts showed a 17% increase in ocular tissue from rats consuming the LNA-deficient diet (F3 generation). The biological significance of the reported changes in PPARbeta mRNA in ocular tissue remains to be determined.

Activation of the peroxisome proliferator-activated receptor-alpha enhances cell death in cultured cerebellar granule cells

Peroxisome proliferator-activated receptor-alpha (PPARalpha) is a member of the steroid hormone receptor superfamily. In rodents, PPARalpha alters genes involved in cell cycle regulation in hepatocytes. Some of these genes are implicated in neuronal cell death. Therefore, in this study, we examined the toxicological consequence of PPARalpha activation in rat primary cultures of cerebellar granule neurons. Our studies demonstrated the presence of PPARalpha mRNA in cultures by reverse transcriptase-polymerase chain reaction. After 10 days in vitro, cerebellar granule neuron cultures were incubated with the selective PPARalpha activator 4-chloro-6-(2,3-xylidino)2-pyrimidinylthioacetic acid (Wy-14,643). The inherent toxicity of Wy-14,643 and the effect of PPARalpha activation following toxic stimuli were assessed. In these studies, neurotoxicity was induced through reduction of extracellular [KCl] from 25 mM to 5.36 mM. We observed no inherent toxicity of Wy-14,643 (24 hr) in cultured cerebellar granule cells. However, after reduction of [KCl], cerebellar granule cell cultures incubated with Wy-14,643 showed significantly greater toxicity than controls. These results suggest a possible role for PPARalpha in augmentation of cerebellar granule neuronal death after toxic stimuli.

Fatty acid regulation of gene expression

Over the past 10 years it has become evident that fatty acids regulate cellular functions by modulating gene expression. Fatty acids and fatty acid metabolites exert some of their effects on gene expression by affecting the activity of nuclear transcription factors, peroxisome proliferator-activated receptors and sterol regulatory element binding protein type 1. The present review describes the latest developments in the field, with particular emphasis on the physiological roles of the various peroxisome proliferator-activated receptor isotypes, including their implication in the control of proliferation and differentiation of normal and malignant cells, and on the mechanisms implicated in the regulation of sterol regulatory element binding protein type 1 activity by polyunsaturated fatty acids.