Srivastava R A, Jiao S, Tang J J, Pfleger B A, Kitchens R T, Schonfeld G
Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO 63110.
Biochim Biophys Acta. 1991 Oct 15;1086(1):29-43. doi: 10.1016/0005-2760(91)90151-7.
Two proteins that may be important in the hypercholesterolemia and atherosclerosis produced by dietary fat and/or cholesterol are apoB and the LDL-receptor. We evaluated the molecular and genetic regulation of these two proteins by two important components of atherogenic diets: dietary fatty acids and dietary cholesterol. The control diet (C) contained 5% corn oil; the high cholesterol (HC) diets, 5% corn oil plus 0.5% or 2% cholesterol; the high fat diet (HF) 1% corn oil and 20% hydrogenated coconut oil; the fat plus cholesterol diets (HF/C) were the same as HF diet plus either 0.5% or 2% cholesterol. Ten strains of inbred mice were fed the C and HF/C (2% cholesterol) diets. Three strains; C3H, C57BL and SWR, were studied in greater detail. In them the effects of dietary fat and cholesterol were assessed separately and together. These three strains were fed all six diets. Lipoprotein profiles of plasma and indexes of lipoprotein composition were obtained by gel filtration chromatography and in selected strains by gradient ultracentrifugation. Relative rates of transcription of LDL-receptor mRNA and apoB mRNA were measured in purified mouse liver nuclei and levels of LDL-receptor mRNA and apoB mRNA in liver and intestine were quantified by RNA excess solution hybridization assays. The HF/C diet produced rises in plasma total-, VLDL- and LDL-cholesterol and apoB concentrations in the ten strains. VLDL and LDL became cholesterol-enriched and the proportion of total cholesterol transported in VLDL and LDL rose at the expense of HDL. This general pattern of HF/C diet-induced changes was similar in all strains, but there were marked quantitative differences between strains with respect to lipid and lipoprotein concentrations, and compositions and the distribution of cholesterol on both the HC and HF/C diets. The strain-related differences were not due to differences in absorption of dietary cholesterol because, for any given diet, hepatic cholesterol levels increased to the same extent in all strains. Nor were the strain-related differences related to alleles of the apoB gene as determined by RFLP analyses. In the three strains, hepatic LDL-receptor mRNA transcription was suppressed by all diets. But, LDL-receptor mRNA levels in both intestine and liver were suppressed only by the HC and HF/C diets and not by the HF diet. Thus, dietary cholesterol decreased LDL-receptor mRNA levels by mechanisms operating at the transcriptional level, while dietary fatty acids, in addition to inhibiting transcription also appeared to enhance mRNA stability.(ABSTRACT TRUNCATED AT 400 WORDS)
两种在膳食脂肪和/或胆固醇所致高胆固醇血症及动脉粥样硬化中可能起重要作用的蛋白质是载脂蛋白B和低密度脂蛋白受体。我们通过致动脉粥样化饮食的两个重要成分：膳食脂肪酸和膳食胆固醇，评估了这两种蛋白质的分子和遗传调控。对照饮食（C）含有5%玉米油；高胆固醇（HC）饮食，5%玉米油加0.5%或2%胆固醇；高脂肪饮食（HF），1%玉米油和20%氢化椰子油；脂肪加胆固醇饮食（HF/C）与HF饮食相同，但分别添加0.5%或2%胆固醇。给10个近交系小鼠喂食C和HF/C（2%胆固醇）饮食。对三个品系：C3H、C57BL和SWR进行了更详细的研究。在这些品系中，分别评估了膳食脂肪和胆固醇的影响以及它们共同的影响。给这三个品系喂食所有六种饮食。通过凝胶过滤色谱法获得血浆脂蛋白谱和脂蛋白组成指标，并在选定品系中通过梯度超速离心法获得。在纯化的小鼠肝细胞核中测量低密度脂蛋白受体mRNA和载脂蛋白B mRNA的相对转录速率，并通过RNA过量溶液杂交试验定量肝和肠中低密度脂蛋白受体mRNA和载脂蛋白B mRNA的水平。HF/C饮食使10个品系的血浆总胆固醇、极低密度脂蛋白胆固醇、低密度脂蛋白胆固醇和载脂蛋白B浓度升高。极低密度脂蛋白和低密度脂蛋白富含胆固醇，且极低密度脂蛋白和低密度脂蛋白中运输的总胆固醇比例上升，而高密度脂蛋白的比例下降。HF/C饮食诱导的这种总体变化模式在所有品系中相似，但在脂质和脂蛋白浓度、组成以及胆固醇在HC和HF/C饮食中的分布方面，品系间存在显著的定量差异。品系相关差异并非由于膳食胆固醇吸收的差异，因为对于任何给定饮食，所有品系的肝胆固醇水平均以相同程度升高。品系相关差异也与通过限制性片段长度多态性分析确定的载脂蛋白B基因等位基因无关。在这三个品系中，所有饮食均抑制肝低密度脂蛋白受体mRNA转录。但是，仅HC和HF/C饮食抑制肠和肝中的低密度脂蛋白受体mRNA水平，而HF饮食则无此作用。因此，膳食胆固醇通过转录水平的机制降低低密度脂蛋白受体mRNA水平，而膳食脂肪酸除了抑制转录外，似乎还增强mRNA稳定性。（摘要截断于400字）
