Autosomal recessive hypercholesterolemia caused by mutations in a putative LDL receptor adaptor protein

Atherogenic low density lipoproteins are cleared from the circulation by hepatic low density lipoprotein receptors (LDLR). Two inherited forms of hypercholesterolemia result from loss of LDLR activity: autosomal dominant familial hypercholesterolemia (FH), caused by mutations in the LDLR gene, and autosomal recessive hypercholesterolemia (ARH), of unknown etiology. Here we map the ARH locus to an approximately 1-centimorgan interval on chromosome 1p35 and identify six mutations in a gene encoding a putative adaptor protein (ARH). ARH contains a phosphotyrosine binding (PTB) domain, which in other proteins binds NPXY motifs in the cytoplasmic tails of cell-surface receptors, including the LDLR. ARH appears to have a tissue-specific role in LDLR function, as it is required in liver but not in fibroblasts.     

Apolipoprotein E: cholesterol transport protein with expanding role in cell biology

Apolipoprotein E is a plasma protein that serves as a ligand for low density lipoprotein receptors and, through its interaction with these receptors, participates in the transport of cholesterol and other lipids among various cells of the body. A mutant form of apolipoprotein E that is defective in binding to low density lipoprotein receptors is associated with familial type III hyperlipoproteinemia, a genetic disorder characterized by elevated plasma cholesterol levels and accelerated coronary artery disease. Apolipoprotein E is synthesized in various organs, including liver, brain, spleen, and kidney, and is present in high concentrations in interstitial fluid, where it appears to participate in cholesterol redistribution from cells with excess cholesterol to those requiring cholesterol. Apolipo-protein E also appears to be involved in the repair response to tissue injury; for example, markedly increased amounts of apolipoprotein E are found at sites of peripheral nerve injury and regeneration. Other functions of apolipoprotein E, unrelated to lipid transport, are becoming known, including immunoregulation and modulation of cell growth and differentiation.     

Lipoprotein uptake by neuronal growth cones in vitro

Macrophages that rapidly enter injured peripheral nerve synthesize and secrete large quantities of apolipoprotein E. This protein may be involved in the redistribution of lipid, including cholesterol released during degeneration, to the regenerating axons. To test this postulate, apolipoprotein E-associated lipid particles released from segments of injured rat sciatic nerve and apolipoprotein E-containing lipoproteins from plasma were used to determine whether sprouting neurites, specifically their growth cones, possessed lipoprotein receptors. Pheochromocytoma (PC12) cells, which can be stimulated to produce neurites in vitro, were used as a model system. Apolipoprotein E-containing lipid particles and lipoproteins, which had been labeled with fluorescent dye, were internalized by the neurites and their growth cones; the unmetabolized dye appeared to be localized to the lysosomes. The rapid rate of accumulation in the growth cones precludes the possibility of orthograde transport of the fluorescent particles from the PC12 cell bodies. Thus, receptor-mediated lipoprotein uptake is performed by the apolipoprotein B,E(LDL) (low density lipoprotein) receptors, and in the regenerating peripheral nerve apolipoprotein E may deliver lipids to the neurites and their growth cones for membrane biosynthesis.     

Type III hyperlipoproteinemia associated with apolipoprotein E deficiency

Subjects with type III hyperlipoproteinemia develop premature atherosclerosis and have hyperlipidemia due to an increase in cholesterol-rich very low density lipoproteins (VLDL) of abnormal electrophoretic mobility. Apolipoprotein E is a major protein constituent of VLDL and appears to be important for the hepatic uptake of triglyceride-rich lipoproteins. A new kindred of patients with type III hyperlipoproteinemia is described in which no plasma apolipoprotein E could be detected, consistent with the concept that type III hyperlipoproteinemia may be due to an absence or striking deficiency of apolipoprotein E.     

Expression of the familial hypercholesterolemia gene in heterozygotes: mechanism for a dominant disorder in man

Studies in ctltured fibroblasts indicate that the primary genetic abnormality in familial hypercholesterolemia involves a deficiency in a cell surface receptor for low density lipoproteins (LDL). In normal cells, binding of LDL to this receptor regulates cholesterol metabolism by suppressing cholesterol synthesis and increasing LDL degradation. In cells from heterozygotes, a 60 percent reduction in LDL receptors leads to a concentration-dependent defect in regulation, so that attainment of equal rates of cholesterol synthesis and LDL degradation in normal and heterozygous cells requires a two- to threefold higher concentration of LDL in the heterozygote. The identification of this genetic regulatory defect in fibroblasts of heterozygotes makes available an in vitro system for studying the effects of a dominant mutation on gene expression in mammalian cells.     

Diet-induced hypercholesterolemia in mice: prevention by overexpression of LDL receptors

The current studies were designed to determine whether chronic overexpression of low density lipoprotein (LDL) receptors in the liver would protect mice from the increase in plasma LDL-cholesterol that is induced by high-fat diets. A line of transgenic mice was studied that express the human LDL receptor gene in the liver under control of the transferrin promoter. When fed a diet containing cholesterol, saturated fat, and bile acids for 3 weeks, the transgenic mice, in contrast to normal mice, did not develop a detectable increase in plasma LDL. The current data indicate that unregulated overexpression of LDL receptors can protect against diet-induced hypercholesterolemia in mice.     

Human lipoprotein lipase complementary DNA sequence

Lipoprotein lipase is a key enzyme of lipid metabolism that acts to hydrolyze triglycerides, providing free fatty acids for cells and affecting the maturation of circulating lipoproteins. It has been proposed that the enzyme plays a role in the development of obesity and atherosclerosis. The human enzyme has been difficult to purify and its protein sequence was heretofore undetermined. A complementary DNA for human lipoprotein lipase that codes for a mature protein of 448 amino acids has now been cloned and sequenced. Analysis of the sequence indicates that human lipoprotein lipase, hepatic lipase, and pancreatic lipase are members of a gene family. Two distinct species of lipoprotein lipase messenger RNA that arise from alternative sites of 3'-terminal polyadenylation were detected in several different tissues.     

极低密度脂蛋白受体的研究

极低密度脂蛋白受体(VLDL-R)是一种存在细胞表面的、可识别多种配体的跨膜蛋白,是含有载脂蛋白E(ApoE)的脂蛋白颗粒的受体,在动物体内富含三酰甘油(TG)的脂蛋白的代谢中发挥重要作用。该受体在禽类机体内发挥着介导卵子发生发育的重要生理功能,在哺乳动物机体中主要是参与脂蛋白代谢,可能还有其他生理功能有待于进一步研究。就极低密度脂蛋白受体的分子结构、分布部位、生物学功能以及其基因序列作了简要综述。     

胆碱对鹅体内脂质代谢及肝脏FAS基因mRNA表达的影响

【目的】探讨胆碱对青农灰鹅体内脂质转运、代谢的作用及脂肪酸合成酶FAS（fatty acid synthase）基因表达的影响,确定鹅日粮中胆碱的最适添加量。【方法】将180只1日龄青农灰鹅随机分为6个处理组,每处理组3个重复,每个重复10只。试验在玉米-豆粕型饲粮的基础上各组的胆碱添加量分别为0、600、1 200、1 800、2 400和3 000 mg•kg-1,试验期15周。屠宰后测定肝脏和血清总胆固醇、甘油三酯,血清低密度脂蛋白胆固醇、高密度脂蛋白胆固醇、葡萄糖、胰岛素、胰高血糖素水平,肝脏脂蛋白酯酶、肝脂酶及血清胆碱酯酶活性和肝脏脂肪酸合成酶（FAS）基因表达量。【结果】①4周龄时,饲粮中添加胆碱显著降低肝脏和血清总胆固醇、甘油三酯、血清低密度脂蛋白胆固醇、胰岛素水平和血清胆碱酯酶活性（P＜0.05或P＜0.01）;显著提高肝脏脂蛋白酯酶、肝脂酶活性和血清胰高血糖素水平（P＜0.05）;但对血清高密度脂蛋白胆固醇、葡萄糖含量影响不显著（P＞0.05）。15周龄时,饲粮中添加胆碱显著降低肝脏和血清总胆固醇、甘油三酯、低密度脂蛋白胆固醇含量与胰岛素水平及血清胆碱酯酶活性（P＜0.05或P＜0.01）;显著提高肝脏脂蛋白酯酶、肝脂酶活性和血清高密度脂蛋白胆固醇、胰高血糖素水平（P＜0.05）;但对血清葡萄糖含量影响不显著（P＞0.05）。②饲粮中添加胆碱显著提高肝脏FAS基因的表达量（P＜0.01）,且肝脏脂肪酸合成酶基因表达量随胆碱添加水平呈先下降后上升趋势。【结论】综合考虑胆碱对鹅肝脏脂质代谢的影响,1—4和5—15周龄鹅饲粮中胆碱适宜添加量分别为1 200—1 800和1 200 mg•kg-1。     

Identity of very low density lipoprotein apoproteins of plasma and liver Golgi apparatus

In the rat, very low density lipoproteins isolated from hepatocyte Golgi apparatus, liver perfusates, and whole plasma appear identical in many respects. With specific immunochemical techniques and polyacrylamide-gel electrophoresis it can be demonstrated that the very low density lipoproteins from all three sources contain the same major lipoprotein apoproteins.     

Mutation in LDL receptor: Alu-Alu recombination deletes exons encoding transmembrane and cytoplasmic domains

The molecular size of the plasma LDL (low density lipoprotein) receptor synthesized by cultured fibroblasts from a patient with the internalization-defective form of familial hypercholesterolemia (FH 274) was smaller by 10,000 daltons than the size of the normal LDL receptor. The segment of the gene encoding the truncated portion of the FH 274 receptor was cloned into bacteriophage lambda. Comparison of the nucleotide sequences of the normal and FH 274 genes revealed a 5-kilobase deletion, which eliminated the exons encoding the membrane-spanning region and the carboxyl terminal cytoplasmic domain of the receptor. The deletion appeared to be caused by a novel intrastrand recombination between two repetitive sequences of the Alu family that were oriented in opposite directions. The truncated receptors lack membrane-spanning regions and cytoplasmic domains; they are largely secreted into the culture medium, but a small fraction remains adherent to the cell surface. The surface-adherent receptors bind LDL, but they are unable to cluster in coated pits, thus explaining the internalization-defective phenotype.     

新生仔猪脂类代谢功能发育性变化的研究

选择新生仔猪 15头 ,分别于出生 0 (当日 )、 3和 7d屠宰取样 ,测定肝脏和血浆中多项生化指标和 β 羟基 β 甲戊二酸单酰CoA还原酶 (HMGCoA还原酶 )mRNA的丰度。结果显示 ,血浆中甘油三酯和葡萄糖的浓度在出生后 3d迅速升高 (P <0 0 1) ,4～ 7d保持稳定 ;血浆游离脂肪酸在出生后 3d明显下降 (P <0 0 5 ) ;肝脏中苹果酸脱氢酶的活性也在出生后 3d显著上升 (P <0 0 5 ) ;0～ 7d ,血浆总胆固醇、低密度脂蛋白胆固醇和高密度脂蛋白胆固醇的浓度都极显著提高 (P <0 0 1) ;0和 3dHMGCoA还原酶基因的表达水平接近。结果提示 ,仔猪出生后一周 ,脂肪酸合成、脂质转运和脂质中间代谢的能力迅速提高 ,血浆胆固醇水平的升高与采食初乳有关     

铁木周果实对大鼠血糖血脂的影响

[目的]研究铁果实的降血糖、降血脂作用。[方法]通过给正常大鼠饲喂高糖高脂饲料,建立高糖高脂大鼠模型;将实验大鼠随机分为正常组、高糖脂模型组、高糖脂模型对照组、铁果实粉低、中、高剂量组,测定各组大鼠的血糖(GLU)、总胆固醇(TC)、甘油三酯(TG)、低密度脂蛋白(LDL-C)、高密度脂蛋白(HDL-C)、载脂蛋白A1(APO-A1)、载脂蛋白B(APO-B)、超敏C反应蛋白(HsCRP)等各项指标。[结果]饲喂铁果实粉后高糖脂模型大鼠的GLUT、CT、G和LDL-C等均显著降低(P<0.01)。[结论]铁果实粉具有明显的降血糖和降血脂作用。     

饲料脂肪水平对鳡幼鱼生长、体成分及血清生化指标的影响

将初始均质量(8.26±0.81)g的鳡(Elopichthys bambusa)300尾,随机分为5组,分别投喂5种脂肪水平(A组:3%、B组:6%、C组:9%、D组:12%、E组:15%)的等氮(45.64%±0.20%)、等能(16.82±0.11MJ/kg)饲料56d,研究饲料脂肪水平对鳡幼鱼生长、体成分及血清生化指标的影响。结果表明:随着饲料脂肪水平的升高,增重率、特定生长率(SGR)先升后降,B组显著高于A、E组(P<0.05),回归分析得出,饲料脂肪含量为7.71%时SGR最高;随着饲料脂肪水平的增加,饵料系数先降后升,B组显著低于A、D、E组(P<0.05),蛋白质效率先升后降,B组最高;肝体比(HSI)随饲料脂肪含量增加而升高,A组显著低于C、D、E组(P<0.05);鱼体脂肪、肝脏脂肪含量的变化趋势同HSI,体蛋白含量先升后降;随饲料脂肪水平上升,血清谷丙转氨酶、谷草转氨酶、碱性磷酸酶活力及总胆汁酸含量呈上升趋势,总蛋白、总胆固醇、甘油三酯、高密度脂蛋白胆固醇和低密度脂蛋白胆固醇含量呈降低趋势。经分析认为,鳡最适饲料脂肪含量为7.71%,含量过高使鳡生长缓慢,脂肪代谢异常。     

左卡尼汀对高脂血症大鼠血脂代谢的影响及抗氧化作用

为了观察左卡尼汀( L-carnitine,LC)对高脂血症大鼠血脂代谢的影响及抗氧化作用,将50只健康SD大鼠随机分成5组,分别接受标准饲料、高脂饲料、高脂饲料加低、中、高剂量[(0.25、0.50、1.00g/(kg·d)]LC灌胃处理.连续灌服给药28 d后,测定大鼠血清总胆固醇(TC)、甘油三酯(TG)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)含量及血清和肝脏中超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量.结果表明,与高脂模型组相比,给予LC可显著降低血清TC、TG、LDL-C含量,增加HDL-C含量;血清和肝脏中SOD活性提高、MDA含量降低(P＜0.05).表明LC对高脂血症大鼠有明显的降血脂和改善体内抗氧化能力的作用.     

Compositional relatedness between histocompatibility antigens and human serum lipoproteins

Human histocompatibility antigens and the protein part of Lp(a) lipoprotein and low density lipoprotein of human serum appear to be related when the amino acid compositions are compared. The Lp(a) lipoprotein appears to be closely related also to murine H-2(d) antigen. The results support the concept of a relation between serum lipoproteins and histocompatibility antigens on cell membranes.     

乳化剂对樱桃谷鸭生产性能、肌肉品质和脂类代谢的影响

将540只1日龄樱桃谷鸭随机分为3组,每组6个重复,每重复30只,分别饲喂添加0(对照组)、200、400 mg·kg-1乳化剂的试验日粮,试验期为42 d,研究不同含量乳化剂对樱桃谷鸭生长性能、肌肉品质和脂类代谢的影响.结果表明:添加400 mg·kg-1乳化剂可显著降低樱桃谷鸭前期料重比(P<0.05),提高42 d体重(P<0.05);添加200 mg·kg-1乳化剂可显著降低胸肌48 h滴水损失(P<0.05),提高胸肌24 h的pH(P<0.05).与对照组和200 mg·kg-1乳化剂组相比,添加400 mg·kg-1乳化剂可显著提高血清中的甘油三酯(TG)含量(P<0.05).添加200 mg·kg-1乳化剂可显著降低血清中的低密度脂蛋白胆固醇(LDL-C)含量(P<0.05),添加乳化剂对血清中的高密度脂蛋白胆固醇(HDL-C)、极低密度脂蛋白胆固醇(VLDL-C)和血清中的总胆固醇(TC)含量均无显著影响(P>0.05).结果提示,日粮中添加400 mg·kg-1乳化剂可提高樱桃谷鸭生产性能,添加200 mg·kg-1可改善胸肌肌肉品质,添加不同含量乳化剂均能不同程度改善脂类代谢.     

填饲期肥肝鹅脂肪沉积、血脂成分和脂类代谢酶的变化规律

【目的】通过对不同填饲期肥肝鹅体内脂肪沉积、血脂成分和脂类代谢酶等指标的测定分析,探讨肥肝鹅脂肪代谢规律。【方法】选取同批孵化、相同饲养条件下育成的85日龄体重差异不显著（P＞0.05）的肝用型公鹅200只进行填饲,填饲期30 d。从预试期结束起,分别于填饲0、6、12、18、24、30 d取血、屠宰1次;每次随机选取30只体重相近的试验鹅,每只为1个重复,以填饲0 d作为对照。分别测定肝重、皮脂重、腹脂重、肠脂重、皮脂率、腹脂率、肠脂率、血脂成分和脂类代谢相关指标。所有试验鹅填饲同一种饲粮,填饲量定量一致。将经过筛选的玉米粒倒入水锅内,煮沸5-10 min后,捞出沥干,趁热加入1%鹅油、0.3%的食盐并充分拌匀,冷却后作为填饲饲粮;采用双人机械填饲方法。试验鹅采用地面圈养填饲,分栏饲养。【结果】①腹脂重、皮脂重、肠脂重随着填饲时间的延长而增加,填饲12-18 d腹脂、皮脂、肠脂、肥肝脂肪沉积增重最快,填饲30 d时皮脂重＞腹脂重＞肠脂重;②除了填饲6 d皮脂率与肥肝重呈显著负相关（r=-0.869）外,不同填饲期肥肝鹅腹脂重、皮脂重、肠脂重、腹脂率、皮脂率、肠脂率与肝脏重均呈极显著正相关（P＜0.01）。③填饲显著改变游离脂肪酸（non-estesterified fatty acid,NEFA）和载脂蛋白A（apolipoprotein- A,Apo-A）的含量;在整个填饲过程中,载脂蛋白B（apolipoprotein- B,Apo-B）的含量随着填饲时间的延长有下降的趋势,但各填饲阶段之间差异均不显著（P＞0.05）;随着填饲时间的延长,甘油三酯（Triglyceride,TG）、总胆固醇（total cholesterol,TC）、高密度脂蛋白胆固醇（high density lipoprotein-cholesterol,HDL-C）、低密度脂蛋白胆固醇（low density lipoprotein-cholesterol,LDL-C）和极低密度脂蛋白胆固醇（very low density lipoprotein-cholesterol,VLDL-C）的含量逐渐增加。④胆碱酯酶（cholinesterase,CHE）、脂肪酶（lipase,LPS）、脂蛋白脂酶（lipoprotein lipase,LPL）和肝脂酶（lipoprotein lipase,HL）和总脂酶（LPL+HL）活性最大值分别出现在填饲18-24 d,并呈先升高后降低趋势。【结论】填饲显著改变肥肝鹅的机体脂肪组成;填饲能够显著改变肥肝鹅血脂成分含量,肝重与机体脂肪沉积均呈极显著正相关（P＜0.01）;填饲12-24 d是机体脂肪代谢最旺盛的时期,沉积量最多,肥肝增重最快。     

油脂来源及使用量对小鼠生长、健康、血脂和肝脏胆固醇代谢指标的影响

【目的】观察饲料中添加不同种类和不同剂量的油脂对小鼠生长性能、健康状态、血脂指标和肝脏胆固醇代谢关键基因相对表达量的影响,探讨日粮中不同油脂来源及使用量对肝脏胆固醇代谢的作用机制,为哺乳动物筛选较为适宜的油脂类型及其添加量提供理论参考。【方法】试验选取3周龄体重16-19 g的健康昆明种小鼠48只,随机分为4组,每组4个重复,每个重复3只。4组分别饲喂正常小鼠饲料（对照组）和添加4%豆油（B组）、4%乳化椰子粉（L组）以及8%乳化椰子粉（H组）的饲料14 d。试验期间,记录每天的饲喂次数、每次饲喂量、饲料剩余量,所有试验动物均自由采食和饮水。分析试验期间小鼠的体重变化和平均日采食量（ADFI）、平均日增重（ADG）以及料重比（F/G）等生长性能指标,分析小鼠的血液分布和健康指数等健康状态指标,测定小鼠的肝脏重以及甘油三酯（TG）、总胆固醇（TC）、高密度脂蛋白胆固醇（HDL-C）、低密度脂蛋白胆固醇（LDL-C）等血清脂质指标,运用实时荧光定量PCR技术检测小鼠肝脏组织中胆固醇7-α羟化酶（CYP7A1）、低密度脂蛋白受体（LDLR）和3-羟-3-甲基戊二酸单酰辅酶A还原酶（HMGCR）这3个基因的mRNA表达水平。【结果】①生长性能方面,添加4%豆油组的小鼠体重变化、平均日采食量和肝脏脏器指数与对照组差异显著（P＜0.05）,而平均日增重、料重比和肝脏重与对照组差异不显著（P＞0.05）;添加4%乳化椰子粉组的小鼠各生长性能指标与对照组差异不显著（P＞0.05）;8%乳化椰子粉显著提高小鼠的平均日采食量（P＜0.05）,其他指标差异不显著（P＞0.05）。②健康状态方面,各试验组小鼠的血液分布和健康指数与对照组相比均无显著性差异（P＞0.05）。③血脂指标方面,与对照组相比,添加4%豆油显著降低了小鼠血清中TC和HDL-C含量（P＜0.05）,对TG和LDL-C的影响差异不显著（P＞0.05）,添加4%乳化椰子粉对小鼠的各项血脂指标均无显著性影响（P＞0.05）,添加8%乳化椰子粉能显著降低血清TC含量（P＜0.05）,但对TG、HDL-C和LDL-C无显著性影响（P＞0.05）;④肝脏胆固醇相关基因方面,添加8%乳化椰子粉组肝脏中CYP7A1基因mRNA表达量显著高于对照组（P＜0.05）,而4%豆油组和4%乳化椰子粉组与对照组相比无显著差异（P＞0.05）。肝脏HMGCR基因和LDLR基因mRNA表达水平与对照组差异不显著（P＞0.05）。【结论】日粮中添加豆油增加了小鼠日采食量和体重等指标,降低了血清总胆固醇和高密度脂蛋白胆固醇;高剂量乳化椰子粉的添加提高了小鼠日采食量,降低了血清总胆固醇,并增加了肝脏CYP7A1基因mRNA的表达。相比于添加高剂量乳化椰子粉,低剂量乳化椰子粉在改善小鼠脂代谢方面应用效果并不好。添加油脂可能是通过调控肝脏中胆固醇代谢相关酶的基因表达量来影响小鼠肝脏胆固醇的代谢,从而维持体内的胆固醇代谢的稳态。     

Human apolipoprotein B: structure of carboxyl-terminal domains, sites of gene expression, and chromosomal localization

Apolipoprotein (apo-) B is the ligand responsible for the receptor-mediated catabolism of low density lipoproteins, the principal cholesterol-transporting lipoproteins in plasma. The primary structure of the carboxyl-terminal 30 percent (1455 amino acids) of human apo-B (apo-B100) has been deduced from the nucleotide sequence of complementary DNA. Portions of the protein structure that may relate to its receptor binding function and lipid binding properties have been identified. The apo-B100 messenger RNA is about 19 kilobases in length. The apo-B100 gene is expressed primarily in liver and, to a lesser extent, in small intestine, but in no other tissues. The gene for apo-B100 is located in the p24 region (near the tip of the short arm) of chromosome 2.