Plasma Apolipoprotein Mutants and their Implication on Lipoprotein Metabolism

对199例CCU心绞痛或心肌梗死患者和211例健康体检者的血清脂蛋白和载脂蛋白E进行了分析。CCU组载脂蛋白E4频率高于对照组，而E2频率低于对照组。载脂蛋白E突变体E7和E5在CCU组中也很常见。当我们根据载脂蛋白E表型检测血清脂蛋白时，E3/2表型的受试者血清低密度脂蛋白水平降低，极低密度脂蛋白(VLDL)浓度升高，而E4/3表型的受试者血清低密度脂蛋白水平升高。提示E4和E2同工蛋白分别是动脉粥样硬化的阳性和阴性危险因素。动脉粥样硬化的机制之一与载脂蛋白E对血清低密度脂蛋白水平的作用有关，我们已发现载脂蛋白E的独特的等位蛋白(载脂蛋白E5和E7)与高脂血症和动脉粥样硬化有关。E5的基因分析表明，G到A的替换导致了…在成熟蛋白质的第三位，更多的是谷氨酸到赖氨酸的替代。F，7有两个G到A的取代，导致在第244和245位的-Glu-Glu-to-Lys-Lys-取代。我们鉴定了载脂蛋白E5和载脂蛋白E7与人成纤维细胞上的低密度脂蛋白受体结合的活性。Apo E5的亲和力是野生型apo E3的两倍。然而，载脂蛋白E7的受体亲和力低于载脂蛋白E3。载脂蛋白E5的高亲和力可能导致肝脏对含有载脂蛋白E5的脂蛋白的高摄取，并导致肝脏低密度脂蛋白受体的下调。我们建立了一种快速、准确、灵敏的测定载脂蛋白E分子类型的方法，并利用该方法研究了载脂蛋白E同工蛋白与儿童血清脂蛋白代谢的关系。对767名7岁、10岁和13岁学龄儿童的载脂蛋白E表型和血清脂蛋白水平进行了测定。等电聚焦凝胶免疫印迹法检测载脂蛋白E表型。血清样本在脱脂前用神经氨酸酶处理。血清胆固醇和低密度脂蛋白-胆固醇浓度在各年龄组按E3/2-&Gt；1/2E3/3-&Gt；E4/3顺序升高。载脂蛋白E基因多态性对血清载脂蛋白B水平的影响趋势与胆固醇水平一致，但对血清载脂蛋白E浓度的影响则相反。值得注意的是，载脂蛋白E亚型对血清脂蛋白的影响早在儿童时期就被揭示出来。我们认为，高脂蛋白血症和动脉粥样硬化性偏头痛有可能通过在生命早期根据载脂蛋白E表型进行饮食控制来预防。较少

Serum lipoproteins and apo E were analyzed from 199 patients in CCU, having angina pectoris or myocardial infarction, and from 211 healthy subjects. The frequency of apo E4 was higher and that of E2 was lower in the CCU group than in the control group. Apo E mutants, E7 and E5, were also frequent in the CCU group. When we examined serum lipoproteins by the apo E phenotypes, the subjects with an E3/2 phenotype had reduced LDL and increased very low density lipoprotein (VLDL) concentrations, and those with an E4/3 phenotype had increased LDL levels in serum. The results suggested that the E4 and E2 isoproteins were positive and negative risk factors for atherosclerosis, respectively. One of the mechanisms of atherosclerosis is associated with the action of apo E isoproteins on serum LDL levels.We have previously demonstrated unique isoproteins of apo E (apo E5 and E7) associated with liyperlipidemia and atlierosclerosis. Gene analysis of E5 showed that a G to A substitution had resulted … More in a Glu to Lys substitution at the third position of the mature protein. F, 7 had two G to A substitutions, resulting in -Glu-Glu- to -Lys-Lys- substitution at positions 244 and 245. We characterized the activity of apo E5 and apo E7 binding to LDL receptors on human fibroblasts. The affinity of apo E5 was twice that of wild form of apo E3. Apo E7, however, had a lower receptor affinity than apo E3. The high affinity, of apo E5 may result in a high uptake of apo E5-containing lipoproteins by the liver and lead to a down-regulation of LDL receptors in the liver. We can postulate that the subjects with apo E5 are susceptible to hypercholesterolemia and in consequence to atherosclerosis.We developed a rapid, accurate, and sensitive method for determining apo E molecular species, and to utilize this method we investigated the relationship between apo E isoproteins and serum lipoprotein metabolism in children. Apo E phenotypes and serum lipoprotein levels were determined in 767 school children aged 7, 10 and 13 years old. Apo E phenotyping was performed by immunoblotting of an isoelectric focusing gel. Serum samples were treated with neuraminidase before delipidation. Serum cholesterol and LDL-cholesterol concentrations increase'd in the order of E3/2 -> 1/2 E3/3 -> E4/3 in each agegroup. The effect of the apo E polymorphism in serum apo B was the same tendency as cholesterol levels, but the opposite effect on serum apo E concentrations was observed. It was noteworthy that the effect of apo E isoforms on serum lipoproteins had been revealed even in childhood. We suggest the possibility that hyperlipoproteinemia and atherosclerosis miglit be prevent by dietary control based on apo E phenotypes early in life. Less