Mutation in apolipoprotein B associated with hypobetalipoproteinemia despite decreased binding to the low density lipoprotein receptor

Mutations in apolipoprotein B (APOB) may reduce binding of low density lipoprotein (LDL) to the LDL receptor and cause hypercholesterolemia. We showed that heterozygotes for a new mutation in APOB have hypobetalipoproteinemia, despite a reduced binding of LDL to the LDL receptor. APOB R3480P heterozygotes were identified among 9,255 individuals from the general population and had reduced levels of apoB-containing lipoproteins. Most surprisingly, R3480P LDL bound with lower affinity to the LDL receptor than non-carrier LDL in vitro, and these results were confirmed by turnover studies of LDL in vivo. In very low density lipoprotein (VLDL) turnover studies, the amount of VLDL converted to LDL in R3480P heterozygotes was substantially reduced, suggesting that this was the explanation for the hypobetalipoproteinemia observed in these individuals. Our findings emphasized the importance of combining in vitro studies with both human in vivo and population-based studies, as in vitro studies often have focused on very limited aspects of complex mechanisms taken out of their natural context.     

Antisense oligonucleotide-induced alternative splicing of the <Emphasis Type="Italic">APOB</Emphasis> mRNA generates a novel isoform of APOB

Background  

Apolipoprotein B (APOB) is an integral part of the LDL, VLDL, IDL, Lp(a) and chylomicron lipoprotein particles. The APOB pre-mRNA consists of 29 constitutively-spliced exons. APOB exists as two natural isoforms: the full-length APOB100 isoform, assembled into LDL, VLDL, IDL and Lp(a) and secreted by the liver in humans; and the C-terminally truncated APOB48, assembled into chylomicrons and secreted by the intestine in humans. Down-regulation of APOB100 is a potential therapy to lower circulating LDL and cholesterol levels.     

A novel pathogenic variant of the LDLR gene in the Asian population and its clinical correlation with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a disease implicated with defects in either, Low density lipoprotein receptor gene (LDLR), Apolipoprotein B-100 gene (APOB), the Proprotein convertase subtilisin/kexin type 9 gene (PCSK9) or other related genes of the lipid metabolism pathway. The general characterization of heterozygous FH is by elevated low-density lipoprotein (LDL) cholesterol and early-onset cardiovascular diseases, while the more severe type, the homozygous FH results in extreme elevated levels of LDL cholesterol and usually death of an affected individual by early twenties. We present here a novel non-synonymous, missense mutation in exon 14 of the LDLR gene in two siblings of the Malay ethnicity discovered during an in-house genetic test. We postulate that their elevated cholesterol is due to this novel mutation and they are positive for homozygous FH. This is the first report of a C711Y mutation in patients with elevated cholesterol in Asia.     

LDL的氧化修饰和氧化修饰LDL的组成和结构变化

与低密度脂蛋白(LDL)相比,氧化修饰LDL(O-LDL)的组成、结构和生物学特性发生了深刻的变化,而组成和结构的改变是生物学特性改变的基础.本文根据最近文献资料.结合我们实验室的工作.对LDL的氧化修饰、O-LDL的组成、结构改变,以及它们的机理作一简要综述.     

Hepatic lipase: a marker for cardiovascular disease risk and response to therapy

PURPOSE OF REVIEW: Hepatic lipase plays a key role in the metabolism of pro-atherogenic and anti-atherogenic lipoproteins affecting their plasma level as well as their physico-chemical properties. However, controversial evidence exists concerning whether hepatic lipase is pro or anti-atherogenic. The goal of this review is to summarize recent evidence that connects the enzyme to cardiovascular disease. The potential impact of genetic determinants of hepatic lipase activity in modulating both the development of coronary and carotid atherosclerosis will be discussed based on hepatic lipase proposed roles in lipoprotein metabolism. RECENT FINDINGS: Twenty to 30% of individual variation of hepatic lipase activity is accounted for by the presence of a common polymorphism in the promoter region (-514 C to T) of the hepatic lipase gene (LIPC). This polymorphism, via its impact on hepatic lipase synthesis and activity, appears to contribute to (1) individual susceptibility to cardiovascular disease: the presence of the T allele (low hepatic lipase activity) may carry a marginally increased risk of atherosclerosis; (2) carotid plaque composition and individual susceptibility to cerebrovascular events: the presence of the C allele (high hepatic lipase activity) is associated with increased carotid intima-media thickness and abundance of macrophages in the carotid plaque (unstable plaque); and (3) response of cardiovascular disease patients to lipid-lowering therapy: patients with the CC genotype have the greatest clinical benefit from intensive lipid-lowering therapy. SUMMARY: Convincing evidence shows that hepatic lipase plays a key role in remnant lipoprotein catabolism as well as in remodeling of LDL and HDL particles. The anti or pro-atherogenic role of hepatic lipase is likely to be modulated by the concurrent presence of other lipid abnormalities (i.e. increased LDL cholesterol levels) as well as by the genetic regulation of other enzymes involved in lipoprotein metabolism. Characterization of patients by their LIPC genotype will contribute to a better definition of individual risk of coronary and cerebrovascular events, specifically in patients with qualitative (small, atherogenic LDL and low HDL2 cholesterol) rather than quantitative lipid abnormalities for whom the routine lipid profile may underestimate the risk of coronary and cerebrovascular disease.     

Apolipoprotein E Structure and Substrate and Receptor-Binding Activities of Triglyceride-Rich Human Plasma Lipoproteins in Normo- and Hypertriglyceridemia

Cysteine-arginine interchanges along the primary sequence of human plasma apolipoprotein E (apoE) play an important role in determining its biological functions due to a high mutation frequency of cytosine in CGX triplet that codes 33 of 34 apolipoprotein arginine residues. The contribution of apoE secondary structure to apolipoprotein-lipid interaction is described. The significance of apolipoprotein in triglyceride synthesis, lipoprotein lipolysis, and receptor-mediated clearance of lipolytic remnants of triglyceride-rich lipoproteins is discussed as well. The metabolic flow of lipoproteins in normo- and hypertriglyceridemia can be described by separate compartments that contribute to lipoprotein interaction with at least six different receptors: 1) low density lipoprotein (LDL) receptor; 2) LDL receptor-related protein (LRP); 3) apoB(48) macrophage receptor for hypertriglyceridemic very low density lipoproteins (VLDL); 4) scavenger receptors; 5) VLDL receptor; 6) lipolysis-stimulated receptor. The contribution of the exposure of apoE molecules on the surface of triglyceride-rich particles sensitive both to lipolysis and plasma triglyceride content to the interaction with LDL receptor and LRP is emphasized.     

The lipoprotein subfraction profile: heritability and identification of quantitative trait loci

The HDL and LDL subclass profile is an emerging cardiovascular risk factor. Yet, the biological and genetic mechanisms controlling the lipoprotein subclass distribution are unclear. Therefore, we aimed 1) to determine the heritability of the entire spectrum of LDL and HDL subclass features and 2) to identify gene loci influencing the lipoprotein subfraction pattern. Using NMR spectroscopy, we analyzed the lipoprotein subclass distribution in 1,275 coronary artery disease patients derived from the Regensburg Myocardial Infarction Family Study. We calculated heritabilities, performed a microsatellite genome scan, and calculated linkage. HDL and LDL subclass profiles showed heritabilities ranging from 23% to 67% (all P < 10(-3)) of traits using univariate calculation. After multivariate adjustment, we found heritabilities of 27-48% (all P < 0.05) for HDL and 21-44% for LDL traits. The linkage analysis revealed a significant logarithm of the odds (LOD) score (3.3) for HDL particle concentration on chromosome 18 and a highly suggestive signal for HDL particle size on chromosome 12 (2.9). After multivariate adjustment, we found a significant maximum LOD score of 3.7 for HDL size. Our study is the first to analyze heritability and linkage for the entire spectrum of LDL and HDL subclass features. Our findings may lead to the identification of genes controlling the lipoprotein subclass distribution.     

Familial hypercholesterolemia in St. Petersburg: diversity of mutations argues against a strong founder effect

Examination of low-density lipoprotein (LDL) receptor, its promoter, and major exon-intron boundaries from a sample of patients with familial hypercholesterolemia (FH) from 74 probands of St. Petersburg revealed 34 mutations and 8 widely spread polymorphisms at this locus. Only four mutations were considered silent, while the other 30 are likely associated with familial hypercholesterolemia (FH). Mutations in the LDL receptor gene, inducing the disease, were identified in 41 (55%) out of 74 families with FH. Mutation R3500Q in apolipoprotein B (APOB) gene was not detected in all probands. Therefore in the families lacking mutations hypercholesterolemia was induced by mutations in the introns of the LDL receptor gene or by other genetic factors. Nineteen mutations causing disease progression were described in St. Petersburg for the first time, while 18 of them are specific for Russia. Among Ashkenazi Jews, major mutation G197del was detected in 30% (7 out of 22) of patients with FH. In the Slavic population of St. Petersburg, no major mutations were detected. Only five mutations were identified in two families, while 24 were found in isolated families. These data are indicative of the lack of a strong founder effect for FH in the St. Petersburg population.     

Mutations affecting the binding,internalization, and lysosomal hydrolysis of low density lipoprotein in cultured human fibroblasts,lymphocytes, and aortic smooth muscle cells

Studies comparing the metabolism of low density lipoprotein (LDL) in normal cells and in cells cultured from patients with homozygous familial hypercholesterolemia have disclosed the existence of a receptor for plasma LDL. This receptor has been identified on the surface of human fibroblasts, lymphocytes, and aortic smooth muscle cells. An extension of these studies to cell strains derived from patients with other single gene defects in cholesterol metabolism has provided additional insight into the normal mechanisms by which cells regulate their cholesterol content and how alterations in these genetic control mechanisms may predispose to atherosclerosis in man.     

Recognition of lipoproteins by scavenger receptor class A members

Scavenger receptor class A (SR-A) proteins are type II transmembrane glycoproteins that form homotrimers on the cell surface. This family has five known members (SCARA1 to 5, or SR-A1 to A5) that recognize a variety of ligands and are involved in multiple biological pathways. Previous reports have shown that some SR-A family members can bind modified low-density lipoproteins (LDLs); however, the mechanisms of the interactions between the SR-A members and these lipoproteins are not fully understood. Here, we systematically characterize the recognition of SR-A receptors with lipoproteins and report that SCARA1 (SR-A1, CD204), MARCO (SCARA2), and SCARA5 recognize acetylated or oxidized LDL and very-low-density lipoprotein in a Ca²⁺-dependent manner through their C-terminal scavenger receptor cysteine-rich (SRCR) domains. These interactions occur specifically between the SRCR domains and the modified apolipoprotein B component of the lipoproteins, suggesting that they might share a similar mechanism for lipoprotein recognition. Meanwhile, SCARA4, a SR-A member with a carbohydrate recognition domain instead of the SRCR domain at the C terminus, shows low affinity for modified LDL and very-low-density lipoprotein but binds in a Ca²⁺-independent manner. SCARA3, which does not have a globular domain at the C terminus, was found to have no detectable binding with these lipoproteins. Taken together, these results provide mechanistic insights into the interactions between SR-A family members and lipoproteins that may help us understand the roles of SR-A receptors in lipid transport and related diseases such as atherosclerosis.     

Dual roles for lipolysis and oxidation in peroxisome proliferation-activator receptor responses to electronegative low density lipoprotein

Low density lipoprotein (LDL) exists in various forms that possess unique characteristics, including particle content and metabolism. One circulating subfraction, electronegative LDL (LDL(-)), which is increased in familial hypercholesterolemia and diabetes, is implicated in accelerated atherosclerosis. Cellular responses to LDL(-) remain poorly described. Here we demonstrate that LDL(-) increases tumor necrosis factor alpha (TNFalpha)-induced inflammatory responses through NF kappa B and AP-1 activation with corresponding increases in vascular cell adhesion molecule-1 (VCAM1) expression. LDL receptor overexpression increased these effects. In contrast, exposing LDL(-) to the key lipolytic enzyme lipoprotein lipase (LPL) reversed these responses, inhibiting VCAM1 below levels seen with TNFalpha alone. LPL is known to act on lipoproteins to generate endogenous peroxisomal proliferator-activated receptor alpha (PPAR alpha) ligand, thus limiting inflammation. These responses varied according to the lipoprotein substrate triglyceride content (very low density lipoprotein > LDL > high density lipoprotein). The PPAR alpha activation seen with LDL, however, was disproportionately high. We show here that MUT LDL activates PPAR alpha to an extent proportional to its LDL(-) content. As compared with LDL(-) alone, LPL-treated LDL(-) increased PPAR alpha activation 20-fold in either cell-based transfection or radioligand displacement assays. LPL-treated LDL(-) suppressed NF kappa B and AP-1 activation, increasing expression of the PPAR alpha target gene I kappa B alpha, although only in the genetic presence of PPAR alpha and with intact LPL hydrolysis. Mass spectrometry reveals that LPL-treatment of either LDL or LDL(-) releases hydroxy-octadecadienoic acids (HODEs), potent PPAR alpha activators. These findings suggest LPL-mediated PPAR alpha activation as an alternative catabolic pathway that may limit inflammatory responses to LDL(-).     

The age dependency of gene expression for plasma lipids, lipoproteins, and apolipoproteins.

The aim of this study was to investigate and disentangle the genetic and nongenetic causes of stability and change in lipids and (apo)lipoproteins that occur during the lifespan. Total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides, apolipoprotein A1 (ApoA1), apolipoprotein B (ApoB), and lipoprotein(a) (Lp[a]) were measured in a group of 160 middle-aged parents and their twin offspring (first project) and in a group of 203 middle-aged twin pairs (second project). Combining the data of both projects enabled the estimation of the extent to which measured lipid parameters are influenced by different genes in adolescence and adulthood. To that end, an extended quantitative genetic model was specified, which allowed the estimation of heritabilities for each sex and generation separately. Heritabilities were similar for both sexes and both generations. Larger variances in the parental generation could be ascribed to proportional increases in both unique environmental and additive genetic variance from childhood to adulthood, which led to similar heritability estimates in adolescent and middle-aged twins. Although the magnitudes of heritabilities were similar across generations, results showed that, for total cholesterol, triglycerides, HDL, and LDL, partly different genes are expressed in adolescence compared to adulthood. For triglycerides, only 46% of the genetic variance was common to both age groups; for total cholesterol this was 80%. Intermediate values were found for HDL (66%) and LDL (76%). For ApoA1, ApoB, and Lp(a), the same genes seem to act in both generations.     

Sortilin: an unusual suspect in cholesterol metabolism: from GWAS identification to in vivo biochemical analyses, sortilin has been identified as a novel mediator of human lipoprotein metabolism

The concentration of low-density lipoprotein (LDL) cholesterol (C) in plasma is a key determinant of cardiovascular disease risk and human genetic studies have long endeavoured to elucidate the pathways that regulate LDL metabolism. Massive genome-wide association studies (GWASs) of common genetic variation associated with LDL-C in the population have implicated SORT1 in LDL metabolism. Using experimental paradigms and standards appropriate for understanding the mechanisms by which common variants alter phenotypic expression, three recent publications have presented divergent and even contradictory findings. Interestingly, although these reports each linked SORT1 to LDL metabolism, they did not agree on a mechanism to explain the association. Here, we review recent mechanistic studies of SORT1 - the first gene identified by GWAS as a determinant of plasma LDL-C to be evaluated mechanistically.     

Evidence for a third genetic locus causing familial hypercholesterolemia. A non-LDLR, non-APOB kindred.

Monogenically inherited hypercholesterolemia is most commonly caused by mutations at the low density lipoprotein receptor (LDLR) locus causing familial hypercholesterolemia (FH) or at the apolipoprotein B (APOB) locus causing the disorder familial defective apoB (FDB). Probands from 47 kindreds with a strict clinical diagnosis of FH were selected from the Cardiovascular Genetics Research Lipid Clinic, Utah, for molecular genetic analysis. Using a combination of single-strand conformation polymorphism (SSCP) and direct sequencing, 12 different LDLR gene mutations were found in 16 of the probands. Three of the probands were carriers of the APOB R3500Q mutation. In five of the remaining 28 pedigrees where no mutation had been detected, samples from enough relatives were available to examine co-segregation with the LDLR region using the microsatellite marker D19S221, which is within 1 Mb centromeric of the LDLR locus, and D19S394, sited within 150 kb telomeric of the LDLR locus. In four of the families there was strong evidence for co-segregation between the LDLR locus and the phenotype of hypercholesterolemia, but in one large family with 18 living affected members and clear-cut bimodal hypercholesterolemia, there were numerous exclusions of co-segregation. Using length polymorphic markers within and outside the APOB gene, linkage of phenotype in this family to the APOB region was similarly excluded. In this large family, the degree of hypercholesterolemia, prevalence of tendon xanthomata, and occurrence of early coronary disease were indistinguishable from the other families studied. In summary, the data provide unequivocal evidence that a third locus can be etiological for monogenic familial hypercholesterolemia and should be reinvigorating to research in this field.     

Vitamin C protects low-density lipoprotein from homocysteine-mediated oxidation

Homocysteine, an atherogenic amino acid, promotes iron-dependent oxidation of low-density lipoprotein (LDL). We investigated whether vitamin C, a physiological antioxidant, could protect LDL from homocysteine-mediated oxidation. LDL (0.2 mg of protein/ml) was incubated at 37 degrees C with homocysteine (1000 microM) and ferric iron (10-100 microM) in either the absence (control) or presence of vitamin C (5-250 microM). Under these conditions, vitamin C protected LDL from oxidation as evidenced by an increased lag time preceding lipid diene formation (> or = 5 vs. 2.5 h for control), decreased thiobarbituric acid-reactive substances accumulation (< or = 19 +/- 1 nmol/mg when vitamin C > or = 10 microM vs. 32 +/- 3 nmol/mg for control, p <.01), and decreased lipoprotein anodic electrophoretic mobility. Near-maximal protection was observed at vitamin C concentrations similar to those in human blood (50-100 microM); also, some protection was observed even at low concentrations (5-10 microM). This effect resulted neither from altered iron redox chemistry nor enhanced recycling of vitamin E in LDL. Instead, similar to previous reports for copper-dependent LDL oxidation, we found that vitamin C protected LDL from homocysteine-mediated oxidation through covalent lipoprotein modification involving dehydroascorbic acid. Protection of LDL from homocysteine-mediated oxidation by vitamin C may have implications for the prevention of cardiovascular disease.     

Further characterization of apolipoprotein B genetic variations in Taiwanese.

Apolipoprotein B (apoB, protein; APOB, gene) is the main protein component of low-density lipoprotein (LDL) and plays an important role in blood lipid metabolism. Previously, we have reported four APOB coding regions, 5' signal peptide, and 3' repeat sequence polymorphisms in our population. In this report, we further characterize other APOB genetic variations. The results illustrate that the mutation frequencies for Arg3500Gln (1/846 alleles), Arg4019Trp (2/786 alleles), -265 C/T promoter region (0/264 alleles), and intron 2 A/G (0/450 alleles) are very low. Our population showed a frequency of 68.9% for the B4311 Ser allele. The B4311 Asn allele was associated with a higher apoB level than the Ser group (p < 0.05) in normal controls. In the normal controls, a higher B4311 Asn/Asn genotype frequency was found in the group with total cholesterol (TC) > 200 mg/dL and apoB concentration > 85 mg/dL than in the group with a TC < 200 mg/dL and apoB < 85 mg/dL (p = 0.03 for TC comparison).     

Neutral glycosphingolipids of serum lipoproteins in Fabry's disease.

The neutral glycosphingolipid compositions of lipoprotein fractions of serum from eight healthy male volunteers and three patients with Fabry's disease were determined. Four fractions were studied: very low density lipoprotein (VLDL, d less than 1.006); low density lipoprotein (LDL, d 1.006-1.063); high density lipoprotein (HDL, d 1.063-1.21); and ultracentrifugal residue (Residue, d less than 1.21). All lipoprotein fractions contained the four major neutral glycosphingolipids (glucosylceramide, lactosylceramide, galactosylgalactosylglucosylceramide and N-acetylgalactosaminylgalactosylgalactosylglucosylceramide). The LDL and HDL, however, accounted for most of the total glycosphingolipid (69 and 20%, respectively); only small amounts were demonstrated in the VLDL and Residue. The relative distributions of the glycosphingolipids within the LDL and HDL fractions were similar to the distribution in unfractionated serum. Galactosylgalactosylglucosylceramide levels were 3-5 times normal in all three patients with Fabry's disease, and in two the distribution of the excess lipid among the major lipoprotein fractions was similar to that in the control group. In the third patient, who exhibited the presence of "sinking pre-beta lipoprotein", the amount of glycosphingolipid isolated with the HDL was greater than that in the LDL.     

Synthesis of cinnamic acid derivatives and their inhibitory effects on LDL-oxidation, acyl-CoA:cholesterol acyltransferase-1 and -2 activity, and decrease of HDL-particle size

A series of cinnamic acid derivatives were synthesized and their biological abilities on lipoprotein metabolism were examined. Among the tested compounds, 4-hydroxycinnamic acid (l-phenylalanine methyl ester) amide (1) and 3,4-dihydroxyhydrocinammic acid (l-aspartic acid dibenzyl ester) amide (2) inhibited human acyl-CoA:cholesterol acyltransferase-1 and -2 activities with apparent IC(50) around 60 and 95 microM, respectively. Compounds 1 and 2 also served as an antioxidant against copper mediated low-density lipoproteins (LDL) oxidation with apparent IC(50)=52 and 3 microM, compound 1 and 2, respectively. Additionally, decrease of HDL-particle size under presence of LDL was inhibited by the 1 at 307 microM of final concentration. Treatment of the 1 or 2 did not influence normal growth of RAW264.7 without detectable cytotoxic activity from a cell viability test. These results suggest that the new cinnamic acid derivatives possess useful biological activity as an anti-atherosclerotic agent with inhibition of cellular cholesterol storage and transport by the both ACAT, inhibition of LDL-oxidation, HDL particle size rearrangement.     

Characterization and quantification of serum lipoprotein subfractions by capillary isotachophoresis: relationships with lipid, apolipoprotein, and lipoprotein levels.

Human serum lipoproteins are currently defined according to their density as well as according to their electrophoretic mobility. They can be fractionated into discrete subspecies which exhibit variations in their structure and function. Capillary electrophoresis has been suggested to be a potential analytical strategy in understanding metabolic lipoprotein heterogeneity. In a sample of 35 normolipidemic subjects, we analyzed ceramide-labeled serum lipoproteins by capillary isotachophoresis linked to laser-induced fluorescent detection. Capillary isotachophoresis showed advantage to be an automated, rapid (6 min) and reproducible (CV < 7%) separation mode, on-line monitoring lipoprotein subfractions according to net charge. HDL were separated into three subfractions: i) the fast migrating HDL correlated positively with serum apoA-I (P < 0.05) and negatively with triglyceride (P < 0.01) concentrations, ii) the intermediate migrating HDL involved in HDL-cholesterol delivery and inversely related to LDL particles concentration (P < 0.001), and iii) the slow migrating prebeta(1)HDL. Triglyceride level was significantly associated with two fractions: i) the VLDL fraction correlated positively with apoE serum concentration (P < 0.01), and ii) the IDL fraction closely and positively associated with apoC-III-containing lipoprotein level (P < 0.001). Two LDL subfractions were positively related to LDL-cholesterol (0.05 相似文献