Asunto(s)
Antígenos Ly/genética , Queratodermia Palmoplantar/metabolismo , Linfocitos/metabolismo , Mutación Missense/genética , Activador de Plasminógeno de Tipo Uroquinasa/genética , Antígenos Ly/química , Moléculas de Adhesión Celular/química , Moléculas de Adhesión Celular/genética , Moléculas de Adhesión Celular/metabolismo , Proteínas Ligadas a GPI/química , Proteínas Ligadas a GPI/genética , Proteínas Ligadas a GPI/metabolismo , Heterogeneidad Genética , Humanos , Queratodermia Palmoplantar/genética , Unión Proteica , Activador de Plasminógeno de Tipo Uroquinasa/química , Activador de Plasminógeno de Tipo Uroquinasa/metabolismo , Receptor Nicotínico de Acetilcolina alfa 7/metabolismoRESUMEN
Lipoprotein lipase (LPL) is produced by parenchymal cells, mainly adipocytes and myocytes, but is involved in hydrolysing triglycerides in plasma lipoproteins at the capillary lumen. For decades, the mechanism by which LPL reaches its site of action in capillaries was unclear, but this mystery was recently solved. Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1), a glycosylphosphatidylinositol-anchored protein of capillary endothelial cells, 'picks up' LPL from the interstitial spaces and shuttles it across endothelial cells to the capillary lumen. When GPIHBP1 is absent, LPL is mislocalized to the interstitial spaces, leading to severe hypertriglyceridaemia. Some cases of hypertriglyceridaemia in humans are caused by GPIHBP1 mutations that interfere with the ability of GPIHBP1 to bind to LPL, and some are caused by LPL mutations that impair the ability of LPL to bind to GPIHBP1. Here, we review recent progress in understanding the role of GPIHBP1 in health and disease and discuss some of the remaining unresolved issues regarding the processing of triglyceride-rich lipoproteins.
Asunto(s)
Proteínas Portadoras , Células Endoteliales/fisiología , Hipertrigliceridemia , Lipoproteína Lipasa , Receptores de Lipoproteína , Animales , Capilares/metabolismo , Proteínas Portadoras/genética , Proteínas Portadoras/metabolismo , Quilomicrones/metabolismo , Endotelio Vascular/fisiología , Predisposición Genética a la Enfermedad , Humanos , Hipertrigliceridemia/genética , Hipertrigliceridemia/metabolismo , Lipólisis/genética , Lipoproteína Lipasa/genética , Lipoproteína Lipasa/metabolismo , Ratones , Mutación Missense , Transporte de Proteínas/genética , Receptores de Lipoproteína/genética , Receptores de Lipoproteína/metabolismo , Triglicéridos/metabolismoRESUMEN
Peroxisome proliferator-activated receptors (PPARs) are transcription factors that play an important role in the regulation of genes involved in lipid utilization and storage, lipoprotein metabolism, adipocyte differentiation, and insulin action. The three isoforms of the PPAR family, i.e. alpha, delta, and gamma, have distinct tissue distribution patterns. PPAR-alpha is predominantly present in the liver, and PPAR-gamma in adipose tissue, whereas PPAR-delta is ubiquitously expressed. A recent study reported increased PPAR-gamma messenger RNA (mRNA) expression in the liver in ob/ob mice; however, it is not known whether increased PPAR-gamma expression in the liver has any functional consequences. The expression of PPAR-alpha and -delta in the liver in obesity has not been determined. We have now examined the mRNA levels of PPAR-alpha, -delta, and -gamma in three murine models of obesity, namely, ob/ob (leptin-deficient), db/db (leptin-receptor deficient), and serotonin 5-HT2c receptor (5-HT2cR) mutant mice. 5-HT2cR mutant mice develop a late-onset obesity that is associated with higher plasma leptin levels. Our results show that PPAR-alpha mRNA levels in the liver are increased by 2- to 3-fold in all three obese models, whereas hepatic PPAR-gamma mRNA levels are increased by 7- to 9-fold in ob/ob and db/db mice and by 2-fold in obese 5-HT2cR mutant mice. PPAR-delta mRNA expression is not altered in ob/ob or db/db mice. To determine whether increased PPAR-gamma expression in the liver has any functional consequences, we examined the effect of troglitazone treatment on the hepatic mRNA levels of several PPAR-gamma-responsive adipose tissue-specific genes that have either no detectable or very low basal expression in the liver. The treatment of lean control mice with troglitazone significantly increased the expression of adipocyte fatty acid-binding protein (aP2) and fatty acid translocase (FAT/CD36) in the liver. This troglitazone-induced increase in the expression of aP2 and FAT/CD36 was markedly enhanced in the liver in ob/ob mice. Troglitazone also induced a pronounced increase in the expression of uncoupling protein-2 in the liver in ob/ob mice. In contrast to the liver, troglitazone did not increase the expression of aP2, FAT/CD36, and uncoupling protein-2 in adipose tissue in lean or ob/ob mice. Taken together, our results suggest that the effects of PPAR-gamma activators on lipid metabolism and energy homeostasis in obesity and type 2 diabetes may be partly mediated through their effects on PPAR-gamma in the liver.
Asunto(s)
Tejido Adiposo/metabolismo , Cromanos/farmacología , Diabetes Mellitus/metabolismo , Regulación de la Expresión Génica/efectos de los fármacos , Hígado/metabolismo , Obesidad , Receptores Citoplasmáticos y Nucleares/genética , Tiazoles/farmacología , Tiazolidinedionas , Factores de Transcripción/genética , Animales , Northern Blotting , Masculino , Ratones , Ratones Endogámicos C57BL , ARN Mensajero/metabolismo , TroglitazonaRESUMEN
The acute phase response (APR) is associated with decreased hepatic expression of many proteins involved in lipid metabolism. The nuclear hormone receptors peroxisome proliferator-activated receptor alpha (PPARalpha) and liver X receptor (LXR) play key roles in regulation of hepatic lipid metabolism. Because heterodimerization with RXR is crucial for their action, we hypothesized that a decrease in RXR may be one mechanism to coordinately down-regulate gene expression during APR. We demonstrate that lipopolysaccharide (LPS) induces a rapid, dose-dependent decrease in RXRalpha, RXRbeta, and RXRgamma proteins in hamster liver. Maximum inhibition was observed at 4 h for RXRalpha (62%) and RXRbeta (50%) and at 2 h for RXRgamma (61%). These decreases were associated with a marked reduction in RXRalpha, RXRbeta, and RXRgamma mRNA levels. Increased RNA degradation is likely responsible for the repression of RXR, because LPS did not decrease RXRbeta and RXRgamma transcription and only marginally inhibited (38%) RXRalpha transcription. RXR repression was associated with decreased LXRalpha and PPARalpha mRNA levels and reduced RXR x RXR, RXR x PPAR and RXR x LXR binding activities in nuclear extracts. Furthermore, LPS markedly decreased both basal and Wy-14,643-induced expression of acyl-CoA synthetase, a well characterized PPARalpha target. The reduction in hepatic RXR levels alone or in association with other nuclear hormone receptors could be a mechanism for coordinately inhibiting the expression of multiple genes during the APR.
Asunto(s)
Reacción de Fase Aguda/metabolismo , Hígado/metabolismo , Receptores de Ácido Retinoico/metabolismo , Factores de Transcripción/metabolismo , Reacción de Fase Aguda/genética , Animales , Cricetinae , Citocinas/farmacología , Proteínas de Unión al ADN , Dimerización , Regulación de la Expresión Génica/efectos de los fármacos , Lipopolisacáridos/farmacología , Receptores X del Hígado , Masculino , Mesocricetus , Receptores Nucleares Huérfanos , ARN Mensajero/metabolismo , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Ácido Retinoico/genética , Receptores X Retinoide , Factores de Tiempo , Factores de Transcripción/genéticaRESUMEN
Apolipoproteins A-II and C-III, which participate in the control of cholesterolemia and triglyceridemia, are negative acute phase proteins. Treatment of HepG2 cells with TNFalpha showed that apoA-II and apoC-III mRNA levels were decreased. Using transient transfection, we found that apoC-III gene expression is controlled at the transcriptional level. By competition and supershift experiments, we demonstrate that TNFalpha-induced complexes were related to C/EBPdelta/NF-IL6beta and p50 and that overexpression of C/EBPdelta was able to reproduce the inhibitory effect of TNFalpha on the apoC-III promoter. RT-PCR failed to detect the IL-1 transcript in TNFalpha-treated HepG2 cells, suggesting that activation of C/EBPdelta by TNFalpha is not related to the IL-1-signalling pathway.
Asunto(s)
Apolipoproteínas C/genética , Proteínas Potenciadoras de Unión a CCAAT , Proteínas de Unión al ADN/metabolismo , Regulación Neoplásica de la Expresión Génica , Interleucina-1/metabolismo , Proteínas Nucleares/metabolismo , Factores de Transcripción/metabolismo , Factor de Necrosis Tumoral alfa/farmacología , Apolipoproteína A-II/genética , Apolipoproteína A-II/metabolismo , Apolipoproteína C-III , Apolipoproteínas C/metabolismo , Proteína delta de Unión al Potenciador CCAAT , Carcinoma Hepatocelular , Cloranfenicol O-Acetiltransferasa/genética , Cloranfenicol O-Acetiltransferasa/metabolismo , Proteínas de Unión al ADN/genética , Humanos , FN-kappa B/genética , FN-kappa B/metabolismo , Subunidad p50 de NF-kappa B , Proteínas Nucleares/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Factores de Transcripción/genética , Transcripción Genética , Transfección , Células Tumorales CultivadasRESUMEN
Tissue-specific transcription of the apolipoprotein C-III (apoC-III) gene is mainly regulated by synergistic interactions between the liver-enriched transcription factor HNF-4, which binds to the proximal promoter, and ubiquitous factors, which bind to the upstream enhancer region. Here we show that apoC-III expression in HepG2 cells is negatively regulated in response to interleukin-1 (IL-1), and this inhibition is mainly due to transcriptional repression. CAAT enhancer-binding protein delta (C/EBPdelta) was found to be the main mediator of IL-1-induced suppression. Analysis of the apoC-III promoter revealed two IL-1 response elements. The first is located in the proximal promoter region D and the second in the distal enhancer region I. Proximal element D is a high affinity binding site for C/EBPdelta, while the enhancer element I is not directly recognized by this transcription factor. Functional analysis of different combinations of homologous and heterologous promoter constructs revealed that indirect interaction of C/EBPdelta with site I, in the context of the full promoter, leads to repression. C/EBPdelta is activated by phosphorylation during IL-1-induced signal transduction pathway. This modification is important for both DNA binding activity and indirect transrepression of the apoC-III promoter.
Asunto(s)
Apolipoproteínas C/metabolismo , Proteínas Potenciadoras de Unión a CCAAT , Proteínas de Unión al ADN/metabolismo , Interleucina-1/farmacología , Proteínas Nucleares/metabolismo , Animales , Apolipoproteína C-III , Apolipoproteínas C/genética , Secuencia de Bases , Proteína delta de Unión al Potenciador CCAAT , Células COS , Línea Celular , Regulación hacia Abajo , Humanos , FN-kappa B/metabolismo , Regiones Promotoras Genéticas , Factores de Transcripción/metabolismoRESUMEN
The effect of cyclosporin A (CsA) on tumor necrosis factor (TNF) or interleukin-6 (IL-6) production was evaluated in vivo in primed or unprimed mice challenged with lipopolysaccharide (LPS). Both pretreatment with BCG infection or with muramyl dipeptide (MDP) prior to LPS challenge resulted in an increase in the cytokine bioactivity level in the blood. CsA administration inhibited the TNF production. In unprimed mice, either normal or sensitized to LPS lethality by galactosamine treatment, a marked decrease in the cytokine level was observed after injection of CsA. After adrenalectomy, the yield of both TNF and IL-6 following LPS injection was markedly elevated but decreased by CsA administration. Ex vivo experiments have shown that the inhibitory effect of CsA could be demonstrated at the level of macrophages from mice previously given the drug. If mice had received MDP, in vitro responses of cells to LPS were enhanced but again CsA decreased the mRNA expression and protein secretion.
Asunto(s)
Acetilmuramil-Alanil-Isoglutamina/farmacología , Toxinas Bacterianas/farmacología , Ciclosporina/farmacología , Endotoxinas/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Inmunosupresores/farmacología , Interleucina-6/biosíntesis , Lipopolisacáridos/farmacología , Factor de Necrosis Tumoral alfa/biosíntesis , Adrenalectomía , Animales , Ciclosporina/uso terapéutico , Interacciones Farmacológicas , Femenino , Galactosamina/farmacología , Inmunosupresores/uso terapéutico , Macrófagos/efectos de los fármacos , Macrófagos/fisiología , Ratones , Mycobacterium bovis/inmunología , Organismos Libres de Patógenos Específicos , Tuberculosis/inmunologíaRESUMEN
Cyclosporin A (CsA) administration reduced mortality in mice sensitized to endotoxic toxicity by various agents, such as muramyl dipeptide (MDP) or a lipophilic derivative. CsA is an inhibitor of a variety of T cell responses, suggesting that muramyl peptides could influence LPS-induced effects via the release of lymphokine. The potentiation of TNF production by pretreatment with muramyl peptides was comparable in nude mice and in controls, indicating that it is a T-independent mechanism, and CsA produced a similar inhibition in both groups. Neutralizing antibody to IFN-gamma did not change the elevated TNF level obtained in the blood when LPS was given after a muramyl peptide. However, the same treatment with anti-IFN-gamma MAb prevented the death of mice challenged with LPS plus MDP or plus a lipophilic derivative displaying similar effects. In comparing three selected muramyl peptides, we also show that the priming effect could be dissociated from the toxic synergism with LPS.