RESUMEN
BACKGROUND: Glucocorticoids (GC) are potent anti-inflammatory and immunosuppressive steroid hormones, mainly produced by the adrenal glands. However, increasing evidence supports the idea of additional extra-adrenal sources of bioactive GC. The lung epithelium is constantly exposed to a plethora of antigenic stimuli, and local GC synthesis could contribute to limit uncontrolled immune reactions and tissue damage. METHODS: Expression of steroidogenic enzymes and GC synthesis in ex vivo organ cultures was studied in mouse lung tissue after in vivo stimulation of immune cells. RESULTS: Mouse lung tissue was found to express steroidogenic enzymes required for the synthesis of corticosterone from cholesterol and to synthesize corticosterone in large quantities after immune cell activation by anti-CD3 antibody, lipopolysaccharide, or TNFα. In marked contrast, ovalbumin-induced allergic airway inflammation failed to promote lung GC synthesis. Although the lung expresses all steroidogenic enzymes necessary for de novo synthesis of corticosterone from cholesterol, functional data indicated that inactive serum-derived dehydrocorticosterone is converted to active corticosterone by 11ß-hydroxysteroid dehydrogenase 1. CONCLUSION: Our results support the notion that local GC synthesis represents a novel immunoregulatory mechanism to limit uncontrolled immune responses in the lung and indicate that defective local steroidogenesis may contribute to the pathogenesis of allergic airway inflammation.
Asunto(s)
Glucocorticoides/biosíntesis , Pulmón/inmunología , Pulmón/metabolismo , Hipersensibilidad Respiratoria/inmunología , Hipersensibilidad Respiratoria/metabolismo , 11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 1/metabolismo , Animales , Línea Celular Tumoral , Modelos Animales de Enfermedad , Células HEK293 , Humanos , Técnicas In Vitro , Pulmón/patología , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Noqueados , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Hipersensibilidad Respiratoria/genética , Esteroide Hidroxilasas/genética , Esteroide Hidroxilasas/metabolismo , Factor de Necrosis Tumoral alfa/metabolismoRESUMEN
Organisms adapt their metabolism to meet ever changing environmental conditions. This metabolic adaptation involves at a cellular level the fine tuning of mitochondrial function, which is mainly under the control of the transcriptional co-activator proliferator-activated receptor gamma co-activator (PGC)-1alpha. Changes in PGC-1alpha activity coordinate a transcriptional response, which boosts mitochondrial activity in times of energy needs and attenuates it when energy demands are low. Reversible acetylation has emerged as a key way to alter PGC-1alpha activity. Although it is well established that PGC-1alpha is deacetylated and activated by Sirt1 and acetylated and inhibited by GCN5, less is known regarding how these enzymes themselves are regulated. Recently, it became clear that the energy sensor, AMP-activated kinase (AMPK) translates the effects of energy stress into altered Sirt1 activity by regulating the intracellular level of its co-substrate nicotinamide adenine dinucleotide (NAD)(+). Conversely, the enzyme ATP citrate lyase (ACL), relates energy balance to GCN5, through the control of the nuclear production of acetyl-CoA, the substrate for GCN5's acetyltransferase activity. We review here how these metabolic signaling pathways, affecting GCN5 and Sirt1 activity, allow the reversible acetylation-deacetylation of PGC-1alpha and the adaptation of mitochondrial energy homeostasis to energy levels.
Asunto(s)
Factores de Transcripción/metabolismo , Acetilación , Animales , Humanos , Mitocondrias/metabolismo , Transducción de Señal , Transactivadores/metabolismoRESUMEN
Incretin-based therapies have shown promise in the treatment of type 2 diabetes. Here we review our current understanding of TGR5 as a target to induce glucagon-like peptide-1 (GLP-1) secretion. These new observations suggest that TGR5 agonists may constitute a novel approach to treat type 2 diabetes, as well as complications of diabetes, such as non-alcoholic fatty liver disease.
Asunto(s)
Diabetes Mellitus Tipo 2/tratamiento farmacológico , Diabetes Mellitus Tipo 2/metabolismo , Receptores Acoplados a Proteínas G/agonistas , Inhibidores de la Dipeptidil-Peptidasa IV/farmacología , Péptido 1 Similar al Glucagón/análogos & derivados , Péptido 1 Similar al Glucagón/metabolismo , Glucosa/metabolismo , Humanos , Receptores Acoplados a Proteínas G/fisiologíaRESUMEN
Thiazolidinediones (TZDs) form a new class of oral antidiabetic agents. They improve insulin sensitivity and reduce glycemia, lipidemia and insulinemia in patients with type 2 diabetes. Their mechanism is original, since they activate the nuclear receptor Peroxisome Proliferator-Activated Receptor gamma (PPARgamma), altering the expression of genes involved in glucose and lipid homeostasis. Stimulating PPARgamma improves insulin sensitivity via several mechanisms: 1) it raises the expression of GLUT4 glucose transporter; 2) it regulates release of adipocyte-derived signaling factors that affect insulin sensitivity in muscle, and 3) it contributes to a turn-over in adipose tissue, inducing the production of smaller, more insulin sensitive adipocytes. TZDs also affect free fatty acids (FFA) lipotoxicity on islets, improving pancreatic B-cell function. In addition, triglycerides and FFA levels are lowered by TZDs. Two TZDs, rosiglitazone and pioglitazone, have recently obtained the European commercial licence, but their use is restricted to the association with metformin or sulfonylureas. At the moment, they are indicated in type 2 diabetes but could be of interest in a broader array of diseases related to insulin resistance. As for side effects, rosiglitazone and pioglitazone may cause increased plasma volume, edema and dose-related weight gain. TZDs offer an attractive option in the treatment of type 2 diabetes, though it may be too soon to determine if they prevent vascular complications, as do other oral antidiabetic agents. An important issue for the future will be to assess the influence of weight gain in the long time.
Asunto(s)
Diabetes Mellitus Tipo 2/tratamiento farmacológico , Hipoglucemiantes/uso terapéutico , Receptores Citoplasmáticos y Nucleares/fisiología , Tiazoles/uso terapéutico , Tiazolidinedionas , Factores de Transcripción/fisiología , Adipocitos/efectos de los fármacos , Adipocitos/fisiología , Diabetes Mellitus Tipo 2/sangre , Ácidos Grasos no Esterificados/sangre , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Insulina/sangre , Insulina/metabolismo , Secreción de Insulina , Receptores Citoplasmáticos y Nucleares/efectos de los fármacos , Receptores Citoplasmáticos y Nucleares/genética , Transducción de Señal/fisiología , Factores de Transcripción/efectos de los fármacos , Factores de Transcripción/genética , Triglicéridos/sangreAsunto(s)
Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Proteínas de Unión al ADN/metabolismo , ADN/metabolismo , Elementos E-Box/genética , Vectores Genéticos , Luciferasas/genética , Factores de Transcripción , Sitios de Unión , Proteína 1 de Unión a los Elementos Reguladores de EsterolesRESUMEN
The ligand-dependent nuclear receptors PPARgamma and RXRalpha/beta were recently determined to be essential for murine placental development and trophoblast differentiation. In the current study we examined the expression and role of the PPARgamma/RXRalpha heterodimers in human invasive trophoblasts. We first report that in human first trimester placenta, PPARgamma and RXRalpha are highly expressed in cytotrophoblasts at the feto-maternal interface, especially in the extravillous cytotrophoblasts involved in uterus invasion. The coexpression of PPARgamma and RXRalpha genes in extravillous cytotrophoblast nuclei were then confirmed by immunocytochemistry, immunoblot, and real-time quantitative PCR using cultured purified primary extravillous cytotrophoblasts. We next examined, using the extravillous cytotrophoblast culture model, the biological role of PPARgamma/RXRalpha heterodimers in vitro, and we showed that both synthetic (rosiglitazone) and natural [15-deoxy-delta-(12,14)PGJ(2)] PPARgamma agonists inhibit extravillous cytotrophoblast invasion in a concentration-dependent manner and synergize with pan-RXR agonists. Conversely, PPARgamma or pan-RXR antagonists promoted extravillous cytotrophoblast invasion. Furthermore, the pan-RXR antagonist abolished the inhibitory effect of the PPARgamma agonists. Together these data underscore an important function of PPARgamma/RXRalpha heterodimers in the modulation of trophoblast invasion.
Asunto(s)
Receptores Citoplasmáticos y Nucleares/fisiología , Receptores de Ácido Retinoico/fisiología , Factores de Transcripción/fisiología , Trofoblastos/fisiología , Diferenciación Celular , Dimerización , Femenino , Humanos , ARN Mensajero/análisis , Receptores Citoplasmáticos y Nucleares/química , Receptores Citoplasmáticos y Nucleares/genética , Receptores de Ácido Retinoico/química , Receptores de Ácido Retinoico/genética , Receptores X Retinoide , Factores de Transcripción/química , Factores de Transcripción/genéticaRESUMEN
Recent studies performed with null mice suggested a role of either RXR alpha or PPAR gamma in murine placental development. We report here that both PPAR gamma and RXR alpha are strongly expressed in human villous cytotrophoblasts and syncytiotrophoblasts. Moreover, specific ligands for RXRs or PPAR gamma (but not for PPAR alpha or PPAR delta) increase both human CG beta transcript levels and the secretion of human CG and its free beta-subunit. When combined, these ligands have an additive effect on human CG secretion. Pan-RXR and PPAR gamma ligands also have an additive effect on the synthesis of other syncytiotrophoblast hormones such as human placental lactogen, human placental GH, and leptin. Therefore, in human placenta, PPAR gamma/RXR alpha heterodimers are functional units during cytotrophoblast differentiation into the syncytiotrophoblast in vitro. Elements located in the regulatory region of the human CG beta gene (beta 5) were found to bind RXR alpha and PPAR gamma from human cytotrophoblast nuclear extracts, suggesting that PPAR gamma/RXR alpha heterodimers directly regulate human CG beta transcription. Altogether, these data show that PPAR gamma/RXR alpha heterodimers play an important role in human placental development.
Asunto(s)
Gonadotropina Coriónica Humana de Subunidad beta/fisiología , Receptores Citoplasmáticos y Nucleares/fisiología , Receptores de Ácido Retinoico/fisiología , Factores de Transcripción/fisiología , Trofoblastos/fisiología , Diferenciación Celular/fisiología , Células Cultivadas , Dimerización , Femenino , Humanos , Receptores X Retinoide , Transducción de Señal , Trofoblastos/citologíaRESUMEN
The peroxisome proliferator-activated receptor gamma (PPARgamma) is highly expressed in the colon mucosa and its activation has been reported to protect against colitis. We studied the involvement of PPARgamma and its heterodimeric partner, the retinoid X receptor (RXR) in intestinal inflammatory responses. PPARgamma(1/)- and RXRalpha(1/)- mice both displayed a significantly enhanced susceptibility to 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis compared with their wild-type littermates. A role for the RXR/PPARgamma heterodimer in the protection against colon inflammation was explored by the use of selective RXR and PPARgamma agonists. TNBS-induced colitis was significantly reduced by the administration of both PPARgamma and RXR agonists. This beneficial effect was reflected by increased survival rates, an improvement of macroscopic and histologic scores, a decrease in tumor necrosis factor alpha and interleukin 1beta mRNA levels, a diminished myeloperoxidase concentration, and reduction of nuclear factor kappaB DNA binding activity, c-Jun NH(2)-terminal kinase, and p38 activities in the colon. When coadministered, a significant synergistic effect of PPARgamma and RXR ligands was observed. In combination, these data demonstrate that activation of the RXR/PPARgamma heterodimer protects against colon inflammation and suggest that combination therapy with both RXR and PPARgamma ligands might hold promise in the clinic due to their synergistic effects.
Asunto(s)
Colitis/tratamiento farmacológico , Receptores Citoplasmáticos y Nucleares/agonistas , Receptores de Ácido Retinoico/agonistas , Tiazolidinedionas , Factores de Transcripción/agonistas , Animales , Colitis/inducido químicamente , Dimerización , Sinergismo Farmacológico , Ratones , Ratones Mutantes , Receptores Citoplasmáticos y Nucleares/genética , Receptores de Ácido Retinoico/genética , Receptores X Retinoide , Rosiglitazona , Tetrahidronaftalenos/uso terapéutico , Tiazoles/uso terapéutico , Factores de Transcripción/genética , Activación Transcripcional , Ácido Trinitrobencenosulfónico/efectos adversosRESUMEN
Cholesterol and bile acid metabolism is tightly controlled by nuclear receptors. The liver X receptor, an oxysterol-activated nuclear receptor, limits cholesterol accumulation in the body both by stimulating reverse cholesterol transport and by inhibiting intestinal cholesterol absorption. The liver X receptor stimulates the adenosine triphosphate binding cassette transporter (types 1 and 8)-mediated cholesterol efflux from peripheral tissues to apolipoprotein AI and the expression of the cholesterol ester transfer protein, hence facilitating cholesterol transfer to the liver. In the liver, the liver X receptor alpha induces the cholesterol 7alpha-hydroxylase (CYP7A1) gene, which controls the rate-limiting step in bile acid synthesis, the major cholesterol excretion pathway. The liver X receptor also limits cholesterol entry in the body by promoting cholesterol efflux from enterocytes into the intestinal lumen, again via an adenosine triphosphate binding cassette transporter type-mediated process. Whereas the liver X receptor is a master controller of cholesterol metabolism, the farnesol X receptor, a bile acid-activated receptor, coordinates bile acid homeostasis. Bile acids facilitate the solubilization of dietary lipids and their subsequent absorption. Bile acids enter the enterocyte through the ileal bile acid transporter and activate the farnesol X receptor, which upregulates the ileal bile acid binding protein, a carrier protein facilitating their re-uptake by the gut. Bile acids are then delivered into the portal blood and taken up in the hepatocytes by the sodium taurocholate co-transporting polypeptide. Inside the hepatocytes, activated farnesol X receptor will decrease further bile acid uptake by reducing the levels of sodium taurocholate co-transporting polypeptide, and stimulating the export of bile acid by increasing the expression of the bile salt export pump. Furthermore, the farnesol X receptor induces the small heterodimer partner, an atypical nuclear receptor, which attenuates bile acid synthesis by inhibiting the action of the orphan nuclear receptor, liver receptor homolog-1, which is a competence factor for CYP7A1 transcription. The farnesol X receptor hence stimulates bile acid re-uptake and controls bile acid production through a regulatory circuit involving both a nuclear receptor regulatory cascade and a number of specific transporter proteins.
Asunto(s)
Colesterol/metabolismo , Proteínas de Unión al ADN/fisiología , Hígado/metabolismo , Receptores Citoplasmáticos y Nucleares/fisiología , Factores de Transcripción/fisiología , Animales , Ácidos y Sales Biliares/metabolismo , Ácidos y Sales Biliares/farmacología , Transporte Biológico , Humanos , Lipoproteínas/metabolismo , Receptores X del Hígado , Receptores Nucleares HuérfanosRESUMEN
Intracellular and extracellular cholesterol levels are tightly maintained within a narrow concentration range by an intricate transcriptional control mechanism. Excess cholesterol can be converted into oxysterols, signaling molecules, which modulate the activity of a number of transcription factors, as to limit accumulation of excess of cholesterol. Two key regulatory pathways are affected by oxysterols. The first pathway involves the uptake and de novo synthesis of cholesterol and is controlled by the family of sterol response element binding proteins, whose activity is regulated by a sterol-dependent feedback mechanism. The second pathway, which only recently has become a topic of interest, involves the activation by a feedforward mechanism of cholesterol utilization for either bile acid or steroid hormone synthesis by oxysterol-activated nuclear receptors, such as liver X receptor and steroidogenic factor-1. Furthermore, biosynthesis and enterohepatic reabsorption of bile acids are regulated by the farnesol X receptor, a receptor activated by bile acids. Both the feedback inhibition of cholesterol uptake and production and the stimulation of cholesterol utilization will ultimately result in a lowering of the intracellular cholesterol concentration and allow for a fine-tuned regulation of the cholesterol concentration.
Asunto(s)
Proteínas Potenciadoras de Unión a CCAAT/farmacología , Colesterol/metabolismo , Proteínas de Unión al ADN/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Factores de Transcripción/farmacología , Animales , Ácidos y Sales Biliares/biosíntesis , Colesterol/análisis , Colesterol/biosíntesis , Proteínas de Unión al ADN/metabolismo , Endopeptidasas/metabolismo , Factores de Transcripción Fushi Tarazu , Proteínas de Homeodominio , Receptores X del Hígado , Receptores Nucleares Huérfanos , Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Ácido Retinoico/metabolismo , Receptores de Hormona Tiroidea/metabolismo , Factor Esteroidogénico 1 , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Esteroles/biosíntesis , Factores de Transcripción/metabolismoRESUMEN
Overexpression of the adipocyte differentiation and determination factor-1 (ADD-1) or sterol regulatory element binding protein-1 (SREBP-1) induces the expression of numerous genes involved in lipid metabolism, including lipoprotein lipase (LPL). Therefore, we investigated whether LPL gene expression is controlled by changes in cellular cholesterol concentration and determined the molecular pathways involved. Cholesterol depletion of culture medium resulted in a significant induction of LPL mRNA in the 3T3-L1 preadipocyte cell line, whereas addition of cholesterol reduced LPL mRNA expression to basal levels. Similar to the expression of the endogenous LPL gene, the activity of the human LPL gene promoter was enhanced by cholesterol depletion in transient transfection assays, whereas addition of cholesterol caused a reversal of its induction. The effect of cholesterol depletion upon the human LPL gene promoter was mimicked by cotransfection of expression constructs encoding the nuclear form of SREBP-1a, -1c (also called ADD-1) and SREBP-2. Bioinformatic analysis demonstrated the presence of 3 potential sterol regulatory elements (SRE) and 3 ADD-1 binding sequences (ABS), also known as E-box motifs. Using a combination of in vitro protein-DNA binding assays and transient transfection assays of reporter constructs containing mutations in each individual site, a sequence element, termed LPL-SRE2 (SRE2), was shown to be the principal site conferring sterol responsiveness upon the LPL promoter. These data furthermore underscore the importance of SRE sites relative to E-boxes in the regulation of LPL gene expression by sterols and demonstrate that sterols contribute to the control of triglyceride metabolism via binding of SREBP to the LPL regulatory sequences.
Asunto(s)
Colesterol/farmacología , Lipoproteína Lipasa/genética , Elementos de Respuesta/genética , Factores de Transcripción , Activación Transcripcional/efectos de los fármacos , Adipocitos/efectos de los fármacos , Adipocitos/metabolismo , Animales , Secuencia de Bases , Sitios de Unión , Proteínas Potenciadoras de Unión a CCAAT/genética , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Línea Celular , Colesterol/metabolismo , ADN/genética , ADN/metabolismo , Huella de ADN , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Desoxirribonucleasa I/metabolismo , Genes Reporteros , Humanos , Ratones , Datos de Secuencia Molecular , Regiones Promotoras Genéticas/genética , Unión Proteica , ARN Mensajero/genética , ARN Mensajero/metabolismo , Eliminación de Secuencia/genética , Factor de Transcripción Sp1/metabolismo , Células Madre/efectos de los fármacos , Células Madre/metabolismo , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Transfección , Células Tumorales CultivadasRESUMEN
AIMS/HYPOTHESIS: Thiazolidinediones are reported to improve pancreatic islet morphology and beta-cell function in rodents, supporting the hypothesis of a direct action of thiazolidinediones on endocrine islet cells. In this study we examined the expression of the peroxisome proliferator-activated receptor gamma, a nuclear receptor that is activated by naturally occurring fatty acids and synthetic thiazolidinediones, in normal human endocrine pancreatic cells. METHODS: Human islets were isolated from pancreata harvested in ten brain-dead lean non-diabetic adult donors. We analysed the gene and protein expression of the human peroxisome proliferator-activated receptor gamma and evaluated the effects of peroxisome proliferator-activated receptor gamma agonist on insulin secretion in human islet preparations. RESULTS: The RT-PCR carried out on total RNA from four distinct human islet preparations demonstrated the presence of peroxisome proliferator-activated receptor gamma mRNA. Western blot analysis showed the consistent expression of peroxisome proliferator-activated receptor gamma protein. Peroxisome proliferator-activated receptor gamma was shown to be present in all three endocrine cell types studied (alpha, beta and delta cells) by immunohistochemistry. CONCLUSION/INTERPRETATION: We found that peroxisome proliferator-activated receptor gamma is highly expressed in human islet endocrine cells, both at the mRNA and protein levels. These results support the hypothesis of a direct influence of peroxisome proliferator-activated receptor gamma agonist on human pancreatic endocrine cells.
Asunto(s)
Islotes Pancreáticos/fisiología , Receptores Citoplasmáticos y Nucleares/genética , Factores de Transcripción/genética , Transcripción Genética , Tejido Adiposo/citología , Tejido Adiposo/metabolismo , Adulto , Proteínas de Unión al ADN/genética , Glucagón/análisis , Humanos , Inmunohistoquímica , Insulina/análisis , Insulina/metabolismo , Secreción de Insulina , Islotes Pancreáticos/citología , Islotes Pancreáticos/metabolismo , ARN Mensajero/genética , Receptores Citoplasmáticos y Nucleares/análisis , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Somatostatina/análisis , Factores de Transcripción/análisisRESUMEN
The catabolism of cholesterol into bile acids is regulated by oxysterols and bile acids, which induce or repress transcription of the pathway's rate-limiting enzyme cholesterol 7alpha-hydroxylase (CYP7A1). The nuclear receptor LXRalpha binds oxysterols and mediates feed-forward induction. Here, we show that repression is coordinately regulated by a triumvirate of nuclear receptors, including the bile acid receptor, FXR; the promoter-specific activator, LRH-1; and the promoter-specific repressor, SHP. Feedback repression of CYP7A1 is accomplished by the binding of bile acids to FXR, which leads to transcription of SHP. Elevated SHP protein then inactivates LRH-1 by forming a heterodimeric complex that leads to promoter-specific repression of both CYP7A1 and SHP. These results reveal an elaborate autoregulatory cascade mediated by nuclear receptors for the maintenance of hepatic cholesterol catabolism.
Asunto(s)
Ácidos y Sales Biliares/biosíntesis , Homeostasis/fisiología , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Animales , Células Cultivadas , Colesterol/metabolismo , Colesterol 7-alfa-Hidroxilasa/genética , Colesterol 7-alfa-Hidroxilasa/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Retroalimentación/fisiología , Regulación Enzimológica de la Expresión Génica/fisiología , Humanos , Riñón/citología , Receptores X del Hígado , Ratones , Receptores Nucleares Huérfanos , Regiones Promotoras Genéticas/fisiología , Proteínas Represoras/genética , Proteínas Represoras/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Transcripción Genética/fisiologíaRESUMEN
Thiazolidinediones, which are being developed for the treatment of insulin resistance and type 2 diabetes mellitus, bind and activate peroxisome proliferator-activated receptor gamma, a nuclear receptor that regulates the expression of several genes involved in metabolism. This receptor controls adipocyte differentation, lipid storage, and insulin sensitisation. Besides metabolic activities, thiazolidinediones have effects as diverse as the control of host defence, cell proliferation, and tumorigenesis.
Asunto(s)
Tiazoles/farmacología , Tiazolidinedionas , Tejido Adiposo/efectos de los fármacos , Proteínas de Unión al ADN/farmacología , Diabetes Mellitus/tratamiento farmacológico , Humanos , Resistencia a la Insulina , Conformación Molecular , Receptores Citoplasmáticos y Nucleares/análisis , Transducción de Señal/efectos de los fármacos , Tiazoles/uso terapéutico , Factores de Transcripción/análisisRESUMEN
The isoprenoids farnesol and juvenile hormone III (JH), metabolites of the cholesterol biosynthetic pathway, have been shown to stimulate fetal epidermal development in rodents. In this study we determined whether this effect might be attributed to a direct induction of keratinocytes differentiation and examined the mechanisms responsible for these effects. Rates of cornified envelope formation, a marker of keratinocyte terminal differentiation, as well as protein and mRNA levels of two proteins required for cornified envelope formation, involucrin (INV) and transglutaminase, increased 2- to 3-fold in normal human keratinocytes (NHK) treated with either farnesol or JH, even at low calcium concentrations (0.03 mM), which otherwise inhibit differentiation. In contrast, neither cholesterol nor mevalonate affected INV or transglutaminase mRNA levels. Effects of farnesol and JH on INV and transglutaminase mRNA levels were additive with high calcium concentrations (1.2 mM) that independently stimulate keratinocyte differentiation. In contrast, keratinocyte DNA synthesis was inhibited by these compounds. Both farnesol and JH stimulated INV and transglutaminase promoter activity, suggesting regulation at the transcriptional level. A series of truncation and deletion experiments revealed a farnesol-responsive region (-2452 to -1880 base pairs (bp)) in the INV gene. This region contained an AP-1 site. A single base pair mutation of the AP-1 site at -2116 to -2110 bp abolished farnesol responsiveness, identical to effects by peroxisome proliferator-activated receptor (PPARalpha) activators. Farnesoid X-activated receptor mRNA was not detected in NHK, but farnesol treatment increased activities of both a PPAR response element and PPARalpha mRNA levels in NHK. Furthermore, the increase in PPRE activity by farnesol was dependent upon PPARalpha in CV-1 cells. Finally, topical applications of farnesol increased mRNA and protein levels of the differentiation-specific genes, profilaggrin and loricrin, determined by immunohistochemistry and in situ hybridization, in wild-type but not in PPARalpha-/- murine epidermis. These findings suggest a novel role for selected isoprenoid cholesterol intermediates in the regulation of differentiation-specific gene transcription and a convergence of PPARalpha with the cholesterol synthetic pathway.
Asunto(s)
Proteínas Potenciadoras de Unión a CCAAT , Farnesol/farmacología , Queratinocitos/efectos de los fármacos , Receptores Citoplasmáticos y Nucleares/fisiología , Factores de Transcripción/fisiología , Animales , Diferenciación Celular/efectos de los fármacos , División Celular/efectos de los fármacos , Células Cultivadas , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/fisiología , Humanos , Ratones , Ratones Pelados , Proteínas Nucleares/fisiología , Precursores de Proteínas/genética , ARN Mensajero/análisis , Elementos de Respuesta , Sesquiterpenos/farmacología , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Factores de Transcripción/genética , Transcripción GenéticaRESUMEN
Statins are hypolipidemic drugs which not only improve cholesterol but also triglyceride levels. Whereas their cholesterol-reducing effect involves inhibition of de novo biosynthesis of cellular cholesterol through competitive inhibition of its rate-limiting enzyme 3-hydroxy-3-methylglutaryl CoA reductase, the mechanism by which they lower triglycerides remains unknown and forms the subject of the current study. Treatment of normal rats for 4 days with simvastatin decreased serum triglycerides significantly, whereas it increased high density lipoprotein cholesterol moderately. The decrease in triglyceride concentrations after simvastatin was caused by a reduction in the amount of very low density lipoprotein particles which were of an unchanged lipid composition. Simvastatin administration increased the lipoprotein lipase mRNA and activity in adipose tissue and heart. This effect on lipoprotein lipase was accompanied by decreased mRNA as well as plasma levels of the lipoprotein lipase inhibitor apolipoprotein C-III. These results suggest that the triglyceride-lowering effect of statins involves a stimulation of lipoprotein lipase-mediated clearance of triglyceride-rich lipoproteins.
Asunto(s)
Apolipoproteínas C/sangre , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacología , Lipoproteína Lipasa/sangre , Simvastatina/farmacología , Triglicéridos/sangre , Animales , Apolipoproteína A-I/sangre , Apolipoproteína A-II/sangre , Apolipoproteína C-III , Apolipoproteínas C/efectos de los fármacos , Colesterol/sangre , HDL-Colesterol/sangre , Lipoproteína Lipasa/efectos de los fármacos , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor implicated in adipocyte differentiation and insulin sensitivity. We investigated whether PPARgamma expression is dependent on the activity of adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1 (ADD-1/SREBP-1), another transcription factor associated with both adipocyte differentiation and cholesterol homeostasis. Ectopic expression of ADD-1/SREBP-1 in 3T3-L1 and HepG2 cells induced endogenous PPARgamma mRNA levels. The related transcription factor SREBP-2 likewise induced PPARgamma expression. In addition, cholesterol depletion, a condition known to result in proteolytic activation of transcription factors of the SREBP family, induced PPARgamma expression and improved PPRE-driven transcription. The effect of the SREBPs on PPARgamma expression was mediated through the PPARgamma1 and -3 promoters. Both promoters contain a consensus E-box motif that mediates the regulation of the PPARgamma gene by ADD-1/SREBP-1 and SREBP-2. These results suggest that PPARgamma expression can be controlled by the SREBP family of transcription factors and demonstrate new interactions between transcription factors that can regulate different pathways of lipid metabolism.
Asunto(s)
Adipocitos/metabolismo , Proteínas Potenciadoras de Unión a CCAAT , Proteínas de Unión al ADN/fisiología , Regulación del Desarrollo de la Expresión Génica , Proteínas Nucleares/fisiología , Receptores Citoplasmáticos y Nucleares/biosíntesis , Factores de Transcripción/biosíntesis , Adipocitos/citología , Diferenciación Celular/genética , Colesterol/metabolismo , Colesterol/farmacología , Secuencia de Consenso , Ácidos Grasos/farmacología , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Humanos , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacología , Metabolismo de los Lípidos , Familia de Multigenes , Proliferadores de Peroxisomas/farmacología , Regiones Promotoras Genéticas , Receptores Citoplasmáticos y Nucleares/genética , Simvastatina/farmacología , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Factores de Transcripción/genética , Factores de Transcripción/fisiologíaRESUMEN
Treatment with fibrates, a widely used class of lipid-modifying agents, results in a substantial decrease in plasma triglycerides and is usually associated with a moderate decrease in LDL cholesterol and an increase in HDL cholesterol concentrations. Recent investigations indicate that the effects of fibrates are mediated, at least in part, through alterations in transcription of genes encoding for proteins that control lipoprotein metabolism. Fibrates activate specific transcription factors belonging to the nuclear hormone receptor superfamily, termed peroxisome proliferator-activated receptors (PPARs). The PPAR-alpha form mediates fibrate action on HDL cholesterol levels via transcriptional induction of synthesis of the major HDL apolipoproteins, apoA-I and apoA-II. Fibrates lower hepatic apoC-III production and increase lipoprotein lipase--mediated lipolysis via PPAR. Fibrates stimulate cellular fatty acid uptake, conversion to acyl-CoA derivatives, and catabolism by the beta-oxidation pathways, which, combined with a reduction in fatty acid and triglyceride synthesis, results in a decrease in VLDL production. In summary, both enhanced catabolism of triglyceride-rich particles and reduced secretion of VLDL underlie the hypotriglyceridemic effect of fibrates, whereas their effect on HDL metabolism is associated with changes in HDL apolipoprotein expression.
Asunto(s)
Hipolipemiantes/farmacología , Metabolismo de los Lípidos , Lipoproteínas/metabolismo , Humanos , Hiperlipidemias/tratamiento farmacológico , Hipolipemiantes/efectos adversos , Hipolipemiantes/uso terapéutico , Receptores Citoplasmáticos y Nucleares/fisiología , Factores de Transcripción/fisiologíaRESUMEN
It is currently thought that the effects of PPARgamma activation on glucose homeostasis may be due to the effect of this nuclear receptor on the production of adipocyte-derived signalling molecules, which affect muscle glucose metabolism. Potential signalling molecules derived from adipocytes and modified by PPARgamma activation include TNFalpha and leptin, which both interfere with glucose homeostasis. In addition to its effects on these proteins, PPARgamma also profoundly affects fatty acid metabolism. Activation of PPARgamma will selectively induce the expression of several genes involved in fatty acid uptake, such as lipoprotein lipase, fatty acid transport protein and acyl-CoA synthetase, in adipose tissue without changing their expression in muscle tissue. This co-ordinate regulation of fatty acid partitioning by PPARgamma results in an adipocyte 'FFA steal' causing a relative depletion of fatty acids in the muscle. Based on the well established interference of muscle fatty acid and glucose metabolism it is hypothesized that reversal of muscle fatty acid accumulation will contribute to the improvement in whole body glucose homeostasis.
Asunto(s)
Adipocitos/metabolismo , Ácidos Grasos/metabolismo , Glucosa/metabolismo , Homeostasis/fisiología , Receptores Citoplasmáticos y Nucleares/metabolismo , Factores de Transcripción/metabolismo , Animales , HumanosRESUMEN
Intracellular fatty acid (FA) concentrations are in part determined by a regulated import/export system that is controlled by two key proteins, i.e. fatty acid transport protein (FATP) and acyl-CoA synthetase (ACS), which respectively facilitate the transport of FAs across the cell membrane and their esterification to prevent their efflux. The aim of this investigation was to analyze the expression pattern of FATP and ACS and to determine whether their expression was altered by agents that affect FA metabolism through the activation of peroxisome proliferator-activated receptors (PPAR) such as the fibrates and thiazolidinediones. FATP mRNA was ubiquitously expressed, with highest levels being detected in adipose tissue, heart, brain, and testis. Fibrate treatment, which is known to preferentially activate PPARalpha, induced FATP mRNA levels in rat liver and intestine and induced ACS mRNA levels in liver and kidney. The antidiabetic thiazolidinedione BRL 49653, which is a high-affinity ligand for the adipocyte-specific PPARgamma form, caused a small induction of muscle but a robust induction of adipose tissue FATP mRNA levels. BRL 49653 did not affect liver FATP and had a tendency to decrease heart FATP mRNA levels. ACS mRNA levels in general showed a similar pattern after BRL 49653 as FATP except for the muscle where ACS mRNA was induced. This regulation of FATP and ACS expression by PPAR activators was shown to be at the transcriptional level and could also be reproduced in vitro in cell culture systems. In the hepatocyte cell lines AML-12 or Fa 32, fenofibric acid, but not BRL 49653, induced FATP and ACS mRNA levels, whereas in the 3T3-L1 preadipocyte cell line, the PPARgamma ligand induced FATP and ACS mRNA levels quicker than fenofibric acid. Inducibility of ACS and FATP mRNA by PPARalpha or gamma activators correlated with the tissue-specific distribution of the respective PPARs and was furthermore associated with a concomitant increase in FA uptake. Most interestingly, thiazolidinedione antidiabetic agents seem to favor adipocyte-specific FA uptake relative to muscle, perhaps underlying in part the beneficial effects of these agents on insulin-mediated glucose disposal.