Low density lipoprotein receptors in cultured skin fibroblasts from psoriasis patients

Low density lipoprotein (LDL) receptor activity, measured as 125I-LDL association and degradation at 37 degrees C, was determined in cultured fibroblasts from involved as well as uninvolved skin obtained from 20 psoriasis patients. The same analyses were conducted in fibroblasts from two reference groups consisting of 19 heterozygotes for familial hypercholesterolemia and 16 normal subjects, respectively. Psoriasis patients had significantly lower LDL receptor activity than normals, and it was comparable to that of the heterozygotes for familial hypercholesterolemia. The reduced LDL receptor activity was not accompanied by an increase in total serum cholesterol. The psoriasis patients had a significant reduction in apo-B concentration, but did not differ from the normals in the other serum lipid or lipoprotein parameters. There was no difference in LDL receptor activity between involved and uninvolved skin from psoriasis patients. These results suggest that there is an abnormal cell membrane in dermal fibroblasts from psoriasis patients. Since their total serum cholesterol is normal, their low LDL receptor activity may be confined to dermal cells, leaving the hepatic lipid metabolism normal. The pathogenetic significance of this finding is unknown.     

Lp(a) lipoprotein enters cultured fibroblasts independently of the plasma membrane low density lipoprotein receptor

Lp(a) lipoprotein shares the apoB antigen with low density lipoprotein (LDL). The Lp(a) antigen is unique for Lp(a) lipoprotein. Fibroblast association (i.e. plasma membrane binding plus intracellular accumulation), plasma membrane binding, intracellular accumulation and degradation of 125I-Lp(a) lipoprotein were studied in strains from subjects with or without autosomal dominant hypercholesterolemia (HC). Subjects without HC (non-HCs) have cell surface receptors for low density lipoprotein (LDL receptors). On the average, HC heterozygotes have half-normal LDL receptor activity and "receptor-negative" HC homozygous cell strains lack functional receptors. Fibroblast processing of 125I-Lp(a) lipoprotein was compared to fibroblast processing of 125I-LDL. LDL receptor-dependent processing of 125I-LDL was saturated at about 50 microgram apo 125I-LDL.ml-1 in non-HC fibroblasts. 125I-Lp(a) lipoprotein was, however, largely processed independently of receptor mechanisms by non-HC cells (highest concentration examined 150 microgram apo 125I-Lp(a) lipoprotein . ml-1). Lp(a) lipoprotein did not interfere with 125I-LDL for fibroblast association, but inhibited 125I-LDL degradation. The interference with 125I-LDL degradation was time dependent. Only slightly higher 125I-Lp(a) lipoprotein processing values were found in non-HC and HC heterozygous strains than in "receptor-negative" HC homozygous strains. However, non-HC cells had more than tenfold higher 125I-LDL processing values than "receptor-negative" HC homozygous cells.     

Low density lipoprotein receptor expression and function in human polymorphonuclear leucocytes

Low density lipoprotein receptors (LDLR), capable of internalizing LDL, are expressed in polymorphonuclear neutrophils (PMN). The expression was assessed using anti-LDLR antibody by flow cytometry. The internalization of LDL was assessed by: (i) quantification of the uptake of labelled LDL with 1,1′-dioctadecyl-3,3,3′,3′ tetramethyl-indocarboxycyanine perchlorate (DiI) by flow cytometry; and (ii) the binding of LDL-¹²⁵I. In fresh purified cells, Lineweaver–Burk analysis of LDL binding (LDL-DiI) revealed that the calculated Kd (internalized LDL) for PMN (15.0 × 10⁻⁹ m) is lower than the Kd for monocytes (1.1 × 10⁻⁷ m) and the Kd for lymphocytes (3.2 × 10⁻⁷ m). Scatchard analysis (LDL-¹²⁵I) revealed 25 000 binding sites and a Kd of 9.6 × 10⁻⁹ m for PMN. The interaction of LDL with its receptor caused a two-fold fast (peak at 1 min) and transient increase in the oxidative burst, measured by the formation of 2′,7′ dicholoflurescein (DCF) by flow cytometry. This effect was not observed in monocytes or lymphocytes, and it was blocked by anti-LDLR antibody. The stimulation of LDL was optimal at 10 μg of protein/ml. LDL was able to suppress DCF formation induced by phorbol myristate acetate (PMA) and PMA was unable to further stimulate LDL-treated cells, suggesting protein kinase-C (PKC) involvement in LDL effects. Using a PKC assay, LDL was shown to induce a two-fold increase in PKC translocation to the membrane. Thus, LDL increases PMN oxidative burst through a PKC-dependent pathway.     

Genetics of the low density lipoprotein receptor:

Fibroblast association (plasma membrane binding plus intracellular accumulation) and degradation of radioiodinated low density lipoprotein (125I-LDL) index plasma membrane LDL receptor activity. Cultured fibroblasts from 23 subjects affected with familial hypercholesterolemia (HC) and from 95 subjects without HC (non-HCs) were tested for 125I-LDL association and degradation. Both LDL receptor activity indices were twice as high in non-HC and HC heterozygous cell strains. This is compatible with a major gene effect on LDL receptor activity. However, a considerable overlap between non-HC and HC heterozygous values was found in the 125I-LDL association assay [median (range) 970 (330-2500), and 450 (250-490), respectively] and in the degradation assay [median (range) 810 (280-2020), and 470 (160-790), respectively]. The values are expressed as ng 125I-LDL X mg cell protein-1 X 4.5 h-1. These great overlaps in the LDL receptor activity indices support the view that the influence of LDL receptor activity on the HC phenotype may be smaller than believed previously. Furthermore, for the diagnosis of HC, these LDL receptor activity assays are far more expensive and have less sensitivity and specificity than simple serum cholesterol determination. The LDL receptor-dependent 125I-LDL association values for the HC heterozygous individuals clustered into four groups. Family data supported the hypothesis that this variation could be due to four different LDL receptor variants, each coded for by different alleles at the LDL receptor locus. If confirmed, this finding may have implications for the understanding of the variable expression of HC and also of the genetic impact on lipoprotein metabolism and susceptibility to atherosclerosis in non-HCs.     

Genetics of the low density lipoprotein receptor:

Fibroblast low density lipoprotein (LDL) plasma membrane receptor activity, measured as 125I-LDL association (plasma membrane binding plus intracellular accumulation) and degradation was determined in cell strains from 14 monozygotic (MZ) and 21 like-sexed dizygotic (DZ) normolipidemic twin pairs. The twins were between 57 and 62 years old and had liver apart for an average of 38 years (range 0-60). The intrapair differences were significantly smaller in MZ than in DZ twin pairs in fibroblast 125I-LDL association as well as degradation assays (P less than 0.05). These findings suggest a genetic influence on normal variation in LDL receptor activity in vitro. In two MZ pairs discordant for psoriasis, the psoriatic twin had markedly lower LDL receptor activity than the cotwin.     

Low density lipoprotein receptor (LDLR) gene mutations in Canadian subjects with familial hypercholesterolemia,but not of French descent

Heterozygous familial hypercholesterolemia (FH) is a relatively common autosomal dominant disorder, which is characterized by elevated plasma concentrations of low density lipoprotein (LDL) cholesterol and early coronary heart disease. FH results from mutations in the gene encoding the LDL receptor (LDLR). In Canada, there is a founder effect for LDLR mutations in FH among individuals of French descent, most of whom reside in the province of Quebec. However, the spectrum of mutations in other regions, specifically in the populous and predominantly English‐speaking province of Ontario, has not been studied. We sequenced the coding regions, promoter and intron‐exon boundaries of the LDLR gene in 60 Ontario FH subjects from a variety of ethnic backgrounds other than French Canadian. We found 25 LDLR mutations in 34 subjects. Eleven LDLR mutations were novel, including two in‐frame deletions of a single amino acid (one each in exons 2 and 4), two larger deletions that shifted the reading frame (one each in exons 4 and 10), five missense mutations (C42R, A370T, T413M, L561P and E760D) and two splice acceptor mutations (one each in introns 3 and 8). The results indicate that FH is more genetically diverse in Ontario than in Quebec. The results are also consistent with findings from investigations of the LDLR in FH conducted in other countries, in which PCR‐based, exon‐by‐exon sequencing uncovers small mutations in about half of the subjects screened. The gap in molecular diagnosis suggests that lesions not found by this sequencing strategy, such as larger scale LDLR mutations that cannot be amplified, may underlie a substantial number of cases of FH. Alternatively, there might be genetic heterogeneity underlying the FH phenotype, with contributions from other single or multiple genes. Hum Mutat 18:359, 2001. © 2001 Wiley‐Liss, Inc.     

Characterization of low density lipoprotein receptor (LDLR) gene mutations in Albania

Introduction

Familial hypercholesterolaemia (FH) is a clinical syndrome characterised by elevated serum total cholesterol (TCHOL) levels due to an increase in low-density lipoprotein (LDL) cholesterol, by tendon xanthomata and clinical manifestations of ischaemic heart disease in early life. Typically, it results from mutations in the low-density lipoprotein receptor (LDLR) gene. So far, more than 800 mutations have been reported for the LDLR gene and account for FH. The nature of LDLR gene mutations varies among different ethnicities. Until now no mutations of LDLR have been reported in the Albanian population.

Material and methods

We assessed the contribution of the LDLR gene mutations as causes of FH in an Albanian population. Fifty probands with a clinical diagnosis of FH were included. We analysed all the exons and the promoter of the LDLR gene by using restriction isotyping or direct sequencing.

Results

Twenty-one patients were heterozygous for the 1646G>A mutation (FH Genoa) in exon 11 and 9 patients were heterozygous for the 81T>C mutation in exon 2 of the LDLR gene.

Conclusions

This report describes two LDLR gene mutations accounting for FH in Albania (1646G>A, 81T>C).     

Maximal low density lipoprotein receptor activity and the effect of lipid lowering diet on total serum cholesterol

This study was undertaken to test if the effect of lipid lowering diet on total serum cholesterol, is influenced by maximal low density lipoprotein (LDL) receptor activity. LDL receptor activity was determined in cultured skin fibroblasts from hypercholesterolemic, male subjects after lipid lowering diet intervention. The LDL receptor values from 15 subjects (responders) who had responded well to a lipid lowering diet and from 14 subjects (non-responders) who had responded poorly, were compared. The responders had a reduction in total serum cholesterol of 29.4%, and the non-responders had a reduction of 8.2% (p less than 0.0001). The higher values for LDL receptor activity among the responders did not reach statistical significance. For all 29 subjects there were non-significant positive correlations between reductions in total serum cholesterol and values for association or degradation of 125I-LDL at 37 degrees C (r = 0.16, p = 0.40 and r = 0.17, p = 0.38, respectively). Thus, it seems that maximal LDL receptor activity is not a major predictor for the response of lipid lowering diet on total serum cholesterol levels in hypercholesterolemic subjects without autosomal dominant familial hypercholesterolemia.     

A 9.6 kilobase deletion in the low density lipoprotein receptor gene in Norwegian familial hypercholesterolemia subjects

Haplotype analysis of the low density lipoprotein receptor (LDLR) gene was performed in Norwegian subjects heterozygous for familial hypercholesterolemia (FH). Southern blot analysis of genomic DNA, using an exon 18 specific probe and the restriction enzyme NcoI, showed that two out of 57 unrelated FH subjects had an abnormal 3.6 kb band. Further analyses revealed that this abnormal band was due to a 9.6 kb deletion that included exons 16 and 17. The 5' deletion breakpoint was after 245 bp of intron 15, and the 3' deletion breakpoint was in exon 18 after nucleotide 3390 of cDNA. Thus, both the membrane-spanning and cytoplasmatic domains of the receptor had been deleted. A polymerase chain reaction (PCR) method was developed to identify this deletion among other Norwegian FH subjects. As a result of this screening one additional subject was found out of 124 subjects screened. Thus, three out of 181 (1.7%) unrelated Norwegian FH subject possessed this deletion. The deletion was found on the same haplotype in the three unrelated subjects, suggesting a common mutagenic event. The deletion is identical to a deletion (FH-Helsinki) that is very common among Finnish FH subjects. However, it is not yet known whether the mutations evolved separately in the two countries.     

内源性高甘油三酯血症患者血浆VLDL、LDL及HDL对血凝的影响

目的：研究内源性高甘油三酯血症(HTG)患血浆极低密度脂蛋白(VLDL)、低密度脂蛋白(LDL)及高密度脂蛋白(HDL)是否发生了氧化修饰及其对血凝的影响。方法：对2l例内源性高甘油三酯血症患与2l例年龄性别相近的正常人的血脂、脂质过氧化物进行了分析。用一次性密度梯度超速离心法分离血浆VLDL、LDL及HDL,测定这三种脂蛋白的234nm光吸收、相对电泳迁移率(REM)和硫代巴比妥酸反应物质(TBARS),分别将这三种脂蛋白加入由正常人新鲜混合血浆构成的反应系统中,按试剂盒分别测定凝血酶原时间(PT)及活化部分凝血酶原时间(APIT)。结果：内源性HTG患血浆TG含量平均升高2．73倍,HDLC下降l.7l倍,同时LPO升高1．22倍;HTG组VLDL、LDL及HDL的REM、234nm光吸收值、TBARS含量均较对照组显增加(P＜0．01),表明内源性HTG患血浆VLDL、LDL及LDL均发生了氧化修饰生成Ox—VLDL、Ox-LDL.PT及APTT在分别加入HTG组的VLDL、LDL及HDL后均比加入相应正常组脂蛋白明显缩短(P均＜0．05)。相关分析表明,HTG组血浆VLDL及HDL相对电泳迁移率(REM)与PT呈负相关(P＜0．01)。结论：HTG患血浆VLDL、LDL及HDL发生了氧化修饰,并使PT及APTT明显缩短。     

低密度脂蛋白受体相关蛋白5基因的基因组结构

目的 确定2低密度脂蛋白受体相关蛋白5（low density lipoprotein receptor related protein,5 LRP5）的基因组结构。方法 以LRP5基因的cDNA序列为线索，采用计算机杂交方法首先通过对比分析该基因的cDNA序列和基因组序列，初步确定LRP5基因的基因组结构，按分析得到的基因组结构设计引物，扩增并测定外显子序列和外显子内含子接头序列，确定该基因的基因组结构。结果 LRP5基因的基因组DNA全长为131.6kb，含4有23个外显子和22个内含子；在编码序列中检测到3个单核苷酸多态，即位于第2外显子的A459G，位于第10外显子的C2220T和位于第21外显子的G4416C；LRP5基因含有4个已知的短串联重复序列，即D11S1917，D11S4087，D11S1337和D11S4178，它们分别位于该基因的5'端和第1，4，13内含子内。结论 LRP5基因的基因组结构的确定，为分析该基因突变和功能研究奠定了基础。     

肝细胞生长因子对人Tenon's囊成纤维细胞低密度脂蛋白受体表达的影响

目的:探讨人Tenon's囊成纤维细胞(HTFs)在肝细胞生长因子(HGF)刺激下,其低密度脂蛋白受体(LDLr)表达的动态变化。方法:分别以0、10、20、40、80和160μg/L的HGF刺激人Tenon's囊成纤维细胞12、24和48 h;应用MTT法检测HTFs的增殖率;real-time PCR定量分析不同增殖状态的HTFs上LDLr mRNA的表达水平;Western blot法检测不同增殖状态HTFs上LDLr蛋白表达水平的变化。结果:HTFs上LDLr mRNA及蛋白的表达水平均与HTFs的增殖率呈正相关,HGF以时间和浓度依赖的方式促进HTFs的增殖,同时以时间和浓度依赖的方式促进LDLr的表达(P0.05)。结论:在HGF刺激下,增殖活跃的HTFs上LDLr呈高表达状态,提示增殖异常活跃的HTFs上高表达的LDLr,可能成为一种新型的抗代谢药物作用靶点,尤其是在抗青光眼术后滤过泡瘢痕化的研究中可能得到广泛应用。     

动脉粥样硬化性脑梗塞与低密度脂蛋白受体基因NcoI、AvaⅡ多态性的关系

目的 探讨动脉粥样硬化性脑梗死（atherosclerotic cerebral infarction,ACI)与低密度脂蛋白受体（low density lipoprotein receptor,LDL-R)基因NcoI、AvaⅡ多态性的关系。方法 用聚合酶链反应技术检测113名辽宁藉汉族健康人和77例ACI患者的LD－R基因NcoI、AvaⅡ多态性及血脂、载脂蛋白的含量。结果 LDL－R基因NcoI、AvaⅡ等位基因频率健康人N^ 为0．667、A^ 为0．230；ACI组N^ 为0．662、A^ 为0．125。A^-A^-与N^ N^ 联合存在时ACI的发病相对风险率（RR）为5．56（P＜0．001），引起血清TG、TC、LDL－C、LP（a)升高的相对风险率依次为4．29、7．67、9．33、3．09（P＜0．05）。结论 LDL－R基因A^-A^-与N^ N^ 联合存在影响血脂、脂蛋白的含量，与ACI密切相关。     

Association of HincII RFLP of low density lipoprotein receptor gene with obesity in essential hypertensives

Obese (BMI 26 kg/m²; n=51) and lean (BMI <26 kg/m²; n=61) Caucasian patients with severe, familial essential hypertension, were compared with respect to genotype and allele frequencies of a Hin cII RFLP of the low density lipoprotein receptor gene ( LDLR ). A similar analysis was performed in obese (n=28) and lean (n=68) nonmotensives. A significant association of the C allele of the T → C variant responsible for this RFLP was seen with obesity ( x ²=4.6, P =0.029) in the hypertensive, but not in the normotensive, group (odds ratio=3.0 for the CC genotype and 2.7 for CT ). Furthermore, BMI tracked with genotypes of this allele in the hypertensives ( P =0.046). No significant genotypic relationship was apparent for plasma lipids. Significant linkage disequilibrium was, moreover, noted between the Hin cII RFLP and an Apa LI RFLP ( x ²=33, P <0.0005) that has previously shown even stronger association with obesity (odds ratio 19.6 for cases homozygous for the susceptibility allele and 15.2 for heterozygotes). The present study therefore adds to our previous evidence implicating LDLR as a locus for obesity in patients with essential hypertension.     

Normal DNA polymorphism at the low density lipoprotein receptor (LDLR) locus associated with serum cholesterol level

A restriction fragment length polymorphism (RFLP) at the low density lipoprotein receptor (LDLR) locus detectable with the restriction enzyme PvuII exhibits association with total serum cholesterol level. People who are homozygous for absence of the PvuII restriction site have a significantly higher total cholesterol level than heterozygotes (the number of homozygotes for presence of the restriction site was too small to permit meaningful comparison). This difference is significant at the 2% level. Thus, this study of sex- and age-adjusted cholesterol levels in a sample of healthy people yields additional evidence and sustains our previous proposal that normal alleles at the LDLR locus contribute to the population variation in total cholesterol levels. Absence of the PvuII site appears to confer an odds ratio of approximately 2.7 for having a cholesterol level in the top quartile of the population distribution.     

Characterization and geographic distribution of the low density lipoprotein receptor (LDLR) gene mutations in northwestern Greece

Familial Hypercholesterolaemia (FH) is a clinical syndrome characterised by elevated serum total cholesterol levels due to an increase in low density lipoprotein (LDL) cholesterol, by tendon xanthomata and clinical manifestations of ischaemic heart disease in early life. Typically, it results from mutations in the low-density lipoprotein receptor (LDLR) gene. So far, over 600 mutations have been reported for the LDLR gene and account for FH. The nature of LDLR gene mutations is different in various ethnicities and has also regional distribution within each ethnicity. Eleven mutations have already been described in the Greek population. This report describes seven LDLR gene mutations accounting for FH in Northwestern Greece (81T>G, 517T>C, 858C>A, 1285G>A, 1352T>C, 1646G>A and 1775G>A) and their geographic distribution. We have recently described one of these mutations (1352T>C) as a novel point mutation in a Greek family originating from Northwestern Greece. Furthermore, two previously identified mutations (81T>C, 1775G>A) were also detected in the Greek FH patients for the first time. The 1775G>A mutation was responsible for all the homozygous patients in our area, indicating a founder effect. These data will favor the development of tailed information and screening programs in Northwestern Greece for the primary prevention of cardiovascular disease in FH patients.     

Cellular glycosaminoglycans and low density lipoprotein receptor are involved in hepatitis C virus adsorption

The initial binding of Hepatitis C virus (HCV) to the cell membrane is a critical determinant of pathogenesis. Two putative HCV receptors have been identified, CD81 and low-density lipoprotein receptor (LDLr). CD81 interacts in vitro with the HCV E2 envelope glycoprotein, and LDLr interacts with HCV present in human plasma. In order to characterize these potential receptors for HCV, virus from plasma, able to replicate in cell culture, was inoculated on Vero cells or human hepatocarcinoma cells. HCV adsorption was assessed by quantitating cell-associated viral RNA by a real-time RT-PCR method. Anti-LDLr antibody, low and very low density lipoproteins inhibited significantly HCV adsorption, confirming the role of LDLr as HCV receptor. Only one out of the two anti-CD81 antibodies used in this study led to a partial inhibition of HCV binding. This study also highlights a role for glycosaminoglycans (GAGs) in HCV adsorption: treatment of virus with heparin led to 70% inhibition of attachment, as did desulfation of cellular GAGs. Treatment of Vero cells with heparin-lyase significantly inhibited virus attachment but by only 30%. These results demonstrate the complexity of the HCV binding step in which LDLr interacts strongly with HCV, whereas the interaction of HCV with GAGs and particularly with CD81 seem to be more moderate.     

Sphingomyelinase in cultured skin fibroblasts from normal and Niemann-Pick type C patients

The spingomyelinase activities of extracts of normal cultured skin fibroblasts were compared with those obtained from Niemann-Pick disease Type A and B patients, and from a number of patients with a provisional clinical diagnosis of Niemann-Pick disease Type C. Even though fibroblasts from Type A and B patients were shown to be clearly deficient (<5% residual activity) the activity in Type C fibroblasts varied from approximately 50% of the lowest control value to normal activity.
Isoelectric focussing of extracts of normal cultured skin fibroblasts on polyacrylamide gels revealed the presence of sphingomyelinase heterogeneity. However, no characteristic change in the behaviour of the enzyme in corresponding extracts from Niemann-Pick Type C cells was observed, suggesting that, if the defect in this condition is expressed in fibroblasts, it does not manifest biochemically in the appearance or disappearance of a specific sphingomyelinase isoenzyme.
Our data suggest that the heterogeneity observed in fibroblast extracts may simply reflect an interaction of the enzyme either with itself or with other hydrophobic components present in the cellular extracts.     

两个家族性高胆固醇血症纯合子家系低密度脂蛋白受体基因分析

目的：分析家族性高胆固醇血症（familial hypercholesterolemia,FH)低密度脂蛋白受体（low density lipoprotein receptor,LDLR)的基因突变。方法：提取5个彼此无亲缘关系临床诊断为FH的纯合子患儿及其家系成员的基因组DNA,用聚合酶链反应－单链构象多态性分析方法,对LDLR基因的启动子和全部18个外显子进行突变检测,并对结果异常者进行DNA测序。结果：在两个家系分别发现A606T和C263R两种突变。结论：LDLR基因在以上两位点的突变可引起FH,中国FH患者的LDLR基因可能存在特有的突变位点。