RESUMEN
The functional effects of the common 27- or 24-amino-acid (aa) variants in the human apoB signal peptide (SP) on intracellular and secreted apoB17 were investigated in vitro. Only in the presence of oleate was a significant difference in intracellular and secreted SP27-B17 compared to SP24-B17 observed (P = 0.01 and P < 0.0007, respectively), although in the presence or absence of oleate mRNA levels from the two constructs were similar. After fractionation, oleate treatment enhanced microsomal SP27-B17 by 150% (P < 0.0005) with a modest but significant effect on SP24-B17 (32% P = 0.007). Oleate stimulated SP24-B17 accumulation in the nonmicrosomal fraction. The data suggest that the presence of oleate leads to inefficient translocation of the 24-amino-acid signal peptide, possibly resulting in increased retrograde translocation into the cytoplasm and reduced intracellular and secreted levels compared to the "wildtype" 27 aa SP. This implies a direct role of the SP variants in the regulation of apoB intracellular metabolism.
Asunto(s)
Apolipoproteínas B/metabolismo , Variación Genética , Señales de Clasificación de Proteína/fisiología , Animales , Apolipoproteínas B/genética , Células COS , Carcinoma Hepatocelular/metabolismo , Fraccionamiento Celular , Citosol/metabolismo , Humanos , Líquido Intracelular/metabolismo , Riñón/citología , Riñón/efectos de los fármacos , Riñón/metabolismo , Microsomas/metabolismo , Ácido Oléico/farmacología , Polimorfismo Genético , Señales de Clasificación de Proteína/genética , Transporte de Proteínas/efectos de los fármacos , Transporte de Proteínas/genética , ARN Mensajero/análisis , ARN Mensajero/metabolismo , Ratas , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transfección , Células Tumorales CultivadasRESUMEN
We have investigated the effects of chronic physical training and acute intensive exercise on plasma fibrinogen levels and the relationship of these responses to beta-fibrinogen G-453-A polymorphism genotype. One hundred fifty-six male British Army recruits were studied at the start of their 10-week basic training, which emphasizes physical fitness. Cohorts were restudied between 0.5 and 5 days after a major 2-day strenuous military exercise (ME) undertaken in their final week of training. Changes in fibrinogen concentration were adjusted for the effects of age, body mass index, and smoking history. Compared with baseline values, fibrinogen concentrations were significantly lower (11.9%, P=.04) at day 5 after ME, consistent with the beneficial effect of training. However, they were higher on days 1 through 3 after ME (suggesting an "acute-phase" response to strenuous exercise) and were maximal on days 1 and 2 (27.2%, P<.001 and 37.1%, P<.001 respectively). Fibrinogen genotype was available in 149 individuals. As expected from previous studies, men with one or more fibrinogen gene A-453 alleles had plasma fibrinogen concentration slightly but significantly higher at baseline (4.5%, P=.11). During the acute-phase response (days 2 and 3), however, the degree of rise was strongly related to the presence of the A allele, being 26.7+/-5.4% (mean+/-SE), 36.5+/-11.0%, and 89.2+/-30.7 for the GG, GA, and AA genotypes, respectively (P=.01). These results confirm that chronic exercise training lowers plasma fibrinogen levels, that intensive exercise generates an acute-phase rise in levels, and that this acute response is strongly influenced by the G/A polymorphism of the beta-fibrinogen gene.
Asunto(s)
Ejercicio Físico , Fibrinógeno/genética , Polimorfismo Genético , Adolescente , Adulto , Fibrinógeno/análisis , Genotipo , Humanos , MasculinoRESUMEN
Hepatic lipase (HL) is almost exclusively synthesized in the liver. Its gene is located on chromosome 15 in man, on chromosome 9 in rat, and has 9 exons and 8 introns. Inhibitory and activator sequences have been found at the 5' end of the gene, upstream to the initiation site, as well as several consensus sequences such as TRE, SRE, AP-2, CEBP, ERE, AF1 and OCT-1. Glycosylation is an essential step for full active mature protein. The catalytic site is in the N-terminal part of the lipase gene while the lipid binding site is at its C-terminal end. HL is generally thought to be active as a dimer. This enzyme hydrolyses the acyl ester bonds of glycerides and phospholipids as well as the acyl CoA-thiol ester bonds. After being secreted by the hepatocytes, HL remains on the surface of hepatic endothelial cells and hepatocytes, bound to heparan sulfate proteoglycans, where it acts on the uptake of chylomicron remnants, IDL and HDL cholesterol ester. HL also participates in the VLDL to IDL and LDL cascade and in the conversion of HDL2 to HDL3 and pre-beta 1 HDL. Thus, HL plays an important role in lipoprotein metabolism and in reverse cholesterol transport and may thus be involved in atherogenic processes. Moreover, HL expression is regulated by hormones and nutritional state in the pre- and post-natal periods. Therefore, it appears of interest to gain further insight into the regulation of HL gene expression in order to better understand plasma lipoprotein metabolism.
Asunto(s)
Lipasa/genética , Hígado/enzimología , Animales , Regulación Enzimológica de la Expresión Génica , Genes , Humanos , Lipasa/química , Lipasa/deficiencia , Lipasa/metabolismo , Lipoproteínas/metabolismoRESUMEN
Male and female rats fed a cystine-rich diet (5% L-cystine) became hypercholesterolemic after 2 months, with 2-fold higher cholesterol levels carried mainly by the HDL1 and HDL2 lipoprotein fractions. Post-heparin lipoprotein lipase activity was increased in male rats only (60%, P < 0.01), while hepatic lipase (HL) activity was increased in both males and females (48%, P < 0.001 and 27%, P < 0.01, respectively). In the liver, HL activity and mRNA levels were increased in males (30%, P < 0.01, and 70%, P < 0.001, respectively), but not in females. A higher correlation between HDL1-cholesterol and liver HL activity was found in male rats than in female rats. In the latter, although the cystine diet induced a virtually identical increase in HDL1-cholesterol, HL gene expression was not promoted. It is suggested that HL gene expression may be triggered by the uptake of HDL1-cholesterol in male rats, while oestrogens in female rats would counteract this effect.
Asunto(s)
Cistina/farmacología , Hipercolesterolemia/enzimología , Lipasa/metabolismo , Hígado/enzimología , Animales , HDL-Colesterol/metabolismo , Dieta , Femenino , Expresión Génica/efectos de los fármacos , Lipasa/genética , Masculino , ARN Mensajero/análisis , Ratas , Ratas Wistar , Factores Sexuales , Regulación hacia ArribaRESUMEN
Female lean Zucker rats were fed for four weeks with either a control diet or the same diet enriched with 2% (w/w) cholesterol and cholic acid (0.5%, w/w). This treatment resulted in a 6-fold increase in plasma total cholesterol. A 30% decrease was observed in plasma post-heparin HL activity, in contrast with lipoprotein lipase, which was unmodified in the cholesterol/cholate-fed rats. HL activity measured in liver homogenate from these rats was also decreased (-30%, p < 0.05), as was its protein mass, quantified by immunoblot analysis (-57%, (p < 0.01), whereas HL mRNA levels were 3-fold lower in the cholesterol/cholate-fed rats. We conclude that the cholesterol/cholate-enriched diet decreases the HL gene expression by acting at the transcriptional level and/or by affecting HL mRNA stability, or both.
Asunto(s)
Colesterol en la Dieta/farmacología , Lipasa/genética , Hígado/enzimología , ARN Mensajero/análisis , Animales , Colesterol/metabolismo , Femenino , Ratas , Ratas ZuckerRESUMEN
The effects of a fish oil concentrate on blood lipids and lipoproteins were examined in relation to their effects on liver fatty acid synthase (FAS), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, adipose tissue lipoprotein lipase (LPL), and hepatic triglyceride lipase (H-TGL). For 15 days, 2-mo-old rats were fed a control diet (10% of calories from fat, 4% fat by weight) or diets with 50% of calories (25% wt/wt) provided by lard, lard and fish oil calories (35%/15%), or lard and corn oil (35%/15%). The high-lard diet increased plasma chylomicron and liver triglycerides. The high-lard diet greatly decreased FAS, HMG-CoA reductase, and LPL activities; it also reduced H-TGL activity. Compared with the lard diet, the lard-fish oil diet decreased plasma TG by drastically lowering chylomicron (4-fold, P < 0.001) and very-low-density lipoprotein levels (P < 0.001). It also reduced high-density lipoprotein levels. The lard-fish oil diet prevented hepatic triglyceride accumulation and decreased FAS activity and mass by 3.5-fold (P < 0.001) but did not further decrease HMG-CoA reductase activity. Adipose tissue LPL activity was 2.5-fold (P < 0.001) higher with the lard-fish oil diet than with the lard diet, and H-TGL activity decreased significantly (-32%, P < 0.01), despite unaltered levels of H-TGL mRNA. These effects were significant with only 10% fish oil concentrate in the lard diet. They were not observed with the lard-corn oil diet.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Grasas de la Dieta/farmacología , Ácido Graso Sintasas/metabolismo , Aceites de Pescado/farmacología , Lipólisis , Lipoproteínas/sangre , Hígado/enzimología , Animales , Epidídimo/enzimología , Hidroximetilglutaril-CoA Reductasas/metabolismo , Lipasa/genética , Lípidos/sangre , Lipoproteína Lipasa/metabolismo , Masculino , ARN Mensajero/análisis , Ratas , Ratas WistarRESUMEN
The aim of this study was to assess whether diets enriched in cholesterol, sodium cholate and drugs known to modify liver cholesterol biosynthesis can modulate hepatic lipase (H-TGL) expression and activity in vivo. Female lean Zucker rats, known to be good responders to cholesterol, were fed for 7 days with a control C diet or the C diet supplemented (w/w) with either 2% cholesterol, 0.5% sodium cholate, 2% cholestyramine or simvastatin (0.1%) added to the cholestyramine diet or given by gavage (10 mg/rat) for 3 days. H-TGL activity decreased by 34% with cholesterol, and by 27% when both cholesterol and cholate were administered to the rats. Under these conditions, H-TGL mRNA decreased by 34% and 87%, respectively. The sharp decrease in H-TGL expression was associated with a strong increase in cholesteryl ester in total liver and in the liver microsome fraction. H-TGL activity decreased by 33% with cholestyramine and the mRNA level decreased by 47%. Simvastatin lowered H-TGL activity by 55% when added to the cholestyramine diet, probably because of a reduction in food intake. When administrated by gavage, simvastatin increased both the H-TGL activity (by 28%) and mRNA (by 23%). These variations may be linked to the availability of mevalonate-derived sterol and non-sterol products.