title: Peroxisome proliferator-activated receptor (PPAR)-gamma positively controls and PPARalpha negatively controls cyclooxygenase-2 expression in rat brain astrocytes through a convergence on PPARbeta/delta via mutual control of PPAR expression levels.
abstract: Peroxisome proliferator-activated receptor (PPAR) transcription factors are pharmaceutical drug targets for treating diabetes, atherosclerosis, and inflammatory degenerative diseases. The possible mechanism of interaction between the three PPAR isotypes (alpha, beta/delta, and gamma) is not yet clear. However, this is important both for understanding transcription factor regulation and for the development of new drugs. The present study was designed to compare the effects of combinations of synthetic agonists of PPARalpha [2-[4-[2-[4-cyclohexylbutyl (cyclohexylcarbamoyl)amino]ethyl]phenyl] sulfanyl-2-methylpropanoic acid (GW7647)], PPARbeta/delta [4-(3-(2-propyl-3-hydroxy-4-acetyl)phenoxy)propyloxyphenoxy acetic acid, (L-165041)], and PPARgamma (rosiglitazone, ciglitazone) on inflammatory gene regulation in rat primary astrocytes. We measured cyclooxygenase-2 (COX-2) expression and prostaglandin E(2) synthesis in lipopolysaccharide (LPS)-stimulated cells. PPARalpha, PPARbeta/delta, and PPARgamma knockdown models served to delineate the contribution of each PPAR isotype. Thiazolidinediones enhanced the LPS-induced COX-2 expression via PPARgamma-dependent pathway, whereas L-165041 and GW7647 had no influence. However, the addition of L-165041 potentiated the effect of PPARgamma activation through PPARbeta/delta-dependent mechanism. On the contrary, PPARalpha activation (GW7647) suppressed the effect of the combined L-165041/rosiglitazone application. The mechanism of the interplay arising from combined applications of PPAR agonists involves changes in PPAR expression levels. A PPARbeta/delta overexpression model confirmed that PPARbeta/delta expression level is the point at which PPARgamma and PPARalpha pathways converge in control of COX-2 gene expression. Thus, we discovered that in primary astrocytes, PPARgamma has a positive influence and PPARalpha has a negative influence on PPARbeta/delta expression and activity. A positive/negative-feedback loop is formed by PPARbeta/delta-dependent increase in PPARalpha expression level. These findings elucidate a novel principle of regulation in the signaling by synthetic PPAR agonists that involves modulating the interaction between PPARalpha,-beta/delta, and -gamma isoforms on the level of their expression.
authors.affiliation: Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Institut für Neurobiochemie, Magdeburg, Germany.
authors.forename: Stepan
authors.initials: S
authors.lastname: Aleshin
authors.forename: Sevil
authors.initials: S
authors.lastname: Grabeklis
authors.forename: Theodor
authors.initials: T
authors.lastname: Hanck
authors.forename: Marina
authors.initials: M
authors.lastname: Sergeeva
authors.forename: Georg
authors.initials: G
authors.lastname: Reiser
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D001921:Brain / Q000166:cytology; D002087:Butyrates / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D004338:Drug Combinations; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D047493:PPAR alpha / Q000819:agonists / Q000378:metabolism; D047494:PPAR delta / Q000819:agonists / Q000378:metabolism; D047495:PPAR gamma / Q000819:agonists / Q000378:metabolism; D048068:PPAR-beta / Q000819:agonists / Q000378:metabolism; D047492:Peroxisome Proliferator-Activated Receptors / Q000819:agonists* / Q000378:metabolism; D010642:Phenoxyacetates / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D010671:Phenylurea Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D020033:Protein Isoforms / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D051381:Rats; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology*; D013997:Time Factors
chemical_list: C520164:4-(3-(2-propyl-3-hydroxy-4-acetyl)phenoxy)propyloxyphenoxy acetic acid; D015415:Biomarkers; D002087:Butyrates; D004338:Drug Combinations; C453899:GW 7647; D005904:Glial Fibrillary Acidic Protein; D008070:Lipopolysaccharides; D047493:PPAR alpha; D047494:PPAR delta; D047495:PPAR gamma; D048068:PPAR-beta; D047492:Peroxisome Proliferator-Activated Receptors; D010642:Phenoxyacetates; D010671:Phenylurea Compounds; D020033:Protein Isoforms; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D051546:Cyclooxygenase 2; C039671:ciglitazone