July 9, 2001
Here GNN posts abstracts to articles about Tangier disease related to the feature story Trafficking in Cholesterol: Investigating the Human ABCA1 Gene
Tangier disease (TD) is characterized by severe high-density lipoproteins (HDL) deficiency, hypercatabolism of HDL constituents, impaired cellular cholesterol efflux, and mutations in the gene of ATP-binding cassette 1 (ABC-1). In the present study, we determined plasma lipid and apolipoprotein levels, and HDL subpopulations, in 110 subjects from a large TD kindred in which the proband was homozygous for an A-->C missense mutation at nucleotide 5338 of the ABC-1 transcript. In the proband HDL-C, apoA-I, and apoA-II concentrations were 2, 1, and 2 mg/dl, respectively, apoA-I was present only in prebeta(1), while apoA-II was found free of apoA-I in two distinct alpha mobility subpopulations with different sizes. The smaller size particles contained only apoA-II while the larger one contained apoA-II and apo(a). Relative to unaffected male relatives (n=30), male heterozygotes (n=21) had significant reductions (P<0.001) in plasma HDL-C (-45%), apoA-I (-34%), apoA-II (-59%), apoA-IV (-40%), Lp(a) (-62%), and apoB (-55%) concentrations, and a significant increase (P<0.05, +33%) in plasma apoC-III levels. Female heterozygotes (n=11) similarly had significant reductions (P<0.001) in the concentrations of plasma HDL-C (-42%), apoA-I (-27%), apoA-II (-52%), Lp(a) (-27%), and (P<0.01) apoA-IV (-28%), apoB (-13%), and a significant increase (P<0.05) in plasma apoE levels (+29%) as compared to unaffected female relatives (n=41). Large size HDL subpopulations, especially the two LpA-I particles: alpha(1) and prealpha(1) were dramatically reduced in both male and female heterozygotes relative to their unaffected family members. Since apoA-II decreased more than apoA-I in both male and female heterozygotes, the ratios of apoA-I/apoA-II were significantly (P<0.01) increased. The prevalence of CHD was 60% higher in the 32 heterozygotes than in the 71 unaffected relatives even though the latter group was on average 7 years older. We conclude that TD homozygotes have only prebeta(1) apoA-I-containing HDL subpopulations, while heterozygotes have HDL that is selectively depleted in the large alpha(1), prealpha(1), and alpha(2), prealpha(2) subpopulations, resulting in HDL particles that are small in size, poor in cholesterol, but relatively enriched in apoA-I compared to those of their unaffected relatives. These abnormalities appear to result in a higher risk of CHD in heterozygotes than in unaffected controls.
Atherosclerosis 2001 May;156(1):217-25.
Several members of the ATP-binding cassette (ABC) transporter family are involved in cholesterol efflux from cells. A defect in one member, ABCA1, results in Tangier disease, a condition characterized by cholesterol accumulation in macrophages and virtual absence of mature circulating high-density lipoproteins. Expression of a second member, ABCG1, is increased by cholesterol-loading in human macrophages. We now show that ABCG1, which we identified by differential display RT-PCR in foamy macrophages, is overexpressed in macrophages from patients with Tangier disease compared to control macrophages. On examination by confocal laser scanning microscopy, ABCG1 was present in perinuclear structures within the cell. In addition, a combination of in situ hybridization and indirect immunofluorescence microscopy revealed that ABCG1 is expressed in foamy macrophages within the atherosclerotic plaque. These data indicate that not only ABCA1 but also ABCG1 may play a role in the cholesterol metabolism of macrophages in vitro and in the atherosclerotic plaque. Copyright 2001 Academic Press.
Biochem Biophys Res Commun 2001 May 18;283(4):821-30.
Identification of mutations in the ATP binding cassette transporter (ABCA1) gene in patients with Tangier disease, who exhibit reduced HDL cholesterol (HDL-C) and apolipoprotein A1 (apoA1) levels and premature coronary atherosclerosis, has led to the hypothesis that common polymorphisms in the ABCA1 gene could determine HDL-C and apoA1 levels and the risk of coronary atherosclerosis in the general population. We sequenced a 660-bp 5' fragment of the ABCA1 gene in 24 subjects and identified 3 novel polymorphisms: -477C/T, -419A/C, and -320G/C. We developed assays, genotyped 372 participants in the prospective Lipoprotein Coronary Atherosclerosis Study (LCAS), and determined the association of the variants with fasting plasma lipids and indices of quantitative coronary angiograms obtained at baseline and 2.5 years after randomization to fluvastatin or placebo. Distribution of -477C/T and -320G/C genotypes were 127 CC, 171 CT, and 74 TT and 130 GG, 168 GC, and 75 CC, respectively, and were in complete linkage disequilibrium (P<0.0001). Data for -477C/T are presented. The -419A/C variant was uncommon (present in 1 of 63 subjects). Heterozygous subjects had a modest reduction in HDL-C (P=0.09) and apoA1 (P=0.05) levels and a lesser response of apoA1 to treatment with fluvastatin (P=0.04). The mean number of coronary lesions causing 30% to 75% diameter stenosis was greater in subjects with the TT genotype (3.1+/-2.1) or CT genotype (2.9+/-1.9) than in subjects with the CC genotype (2.2+/-1.8) (P=0.002). Similarly, compared with subjects with the CC genotype, greater numbers of subjects with the TT or CT genotype had >/=1 coronary lesion (P=0.001). No association between the genotypes and progression of coronary atherosclerosis or clinical events was detected. We conclude that ABCA1 genotypes are potential risk factors for coronary atherosclerosis in the general population.
Circ Res 2001 May 11;88(9):969-73.
The role of the ATP-binding cassette transporter 1 (ABCA1) in cellular lipid efflux and high density lipoprotein metabolism has been recently documented by mutations in genetic HDL deficiency syndromes such as classical Tangier disease. Analysis of ABCA1 knockout mice and overexpression studies have established the importance of ABCA1 as a major determinant of HDL cholesterol in plasma. These studies also indicate that ABCA1 is critically involved in cellular trafficking of cholesterol and choline-phospholipids and in total body lipid homeostasis, such as intestinal cholesterol and fat-soluble vitamin absorption and in the modulation of steroidogenesis. First insights into the upregulation of ABCA1 gene expression by cellular cholesterol and cAMP have identified critical ABCA1 promoter elements, which bind the transcription factors liver X receptor, retinoid X receptor, Sp1 and E-box proteins. The finding that a lipid sensitive subgroup of ABC transporters is able to translocate cholesterol and phospholipids supports the concept that in ABCA1 deficiency, compensatory mechanisms possibly involving MDR1, MDR3 and MRP-family members could be active. This suggests that a network of ABC transporters involved in cellular lipid transport exists, which is under the tight control of energy pathways directly linked to high density lipoprotein metabolism and atherogenesis.
Curr Opin Lipidol 2001 Apr;12(2):129-40.
The proband is a 50 year-old woman born from a consanguineous marriage. She has been suffering from angina pectoris since the age of 38 and underwent coronary bypass surgery for three-vessel disease at 48. The presence of low plasma levels of total cholesterol and high density lipoprotein (HDL) cholesterol (2.4 and 0.1 mmol/l) and apo AI (<15 mg/dl), associated with corneal lesions and a mild splenomegaly suggested the diagnosis of Tangier disease. However, none of the other features of Tangier disease, including hepatomegaly, anemia and peripheral neuropathy, were present. The analysis of the dinucleotide microsatellites located in chromosome 9q31 region demonstrated that the proband was homozygous for the alleles of D9S53, D9S1784 and D9S1832. The mother and son of the proband, both with low levels of HDL cholesterol, shared one of the proband's haplotypes, whereas neither of these haplotypes was present in the normolipidemic proband's sister. The sequence of ATP-binding cassette transporter 1 (ABC1-1) cDNA obtained by reverse transcription-PCR (RT-PCR) of total RNA isolated from cultured fibroblasts showed that the proband was homozygous for a C>T transition in exon 13, which caused a tryptophane for arginine substitution (R527W). This mutation was confirmed by direct sequencing of exon 13 amplified from genomic DNA. It can be easily screened, as the nucleotide change introduces a restriction site for the enzyme Afl III. R527W substitution occurs in a highly conserved region of the NH2 cytoplasmic domain of ABC1 protein. R527W co-segregates with the low HDL phenotype in the family and was not found in 200 chromosomes from normolipidemic individuals.
Atherosclerosis 2001 Feb 15;154(3):599-605.
Familial HDL deficiency (FHD) is the heterozygous form of Tangier disease (TD). Mutations of the ABCA1 gene cause FHD and TD. FHD/TD cells are unable to normally efflux cholesterol onto nascent HDL particles, which are rapidly catabolized. TD fibroblasts have an abnormal pattern of PLC and PLD activation following cell stimulation with HDL(3) or apolipoprotein A-I (apoA-I). We examined cellular cholesterol efflux in FHD and TD fibroblasts by phospholipid-derived-molecules, compared with that of normal cells. We used the PKC agonist 1,2-dioctanoylglycerol (DOG) and phorbol myristate acetate (PMA) to activate PKC, calphostin C, and GO 6976, as inhibitors of PKC; phosphatidic acid (PA), which is the product of PLD, and lysophosphatidic acid (LPA), phosphatidylcholine, sphingomyelin, and beta-cyclodextrin to investigate their potential effect in modulating cellular cholesterol efflux in [(3)H]cholesterol-labeled and cholesterol-loaded fibroblasts. Phosphatidylcholine, sphingomyelin, and beta-cyclodextrin promoted cholesterol efflux in an identical fashion in control, FHD, or TD fibroblasts. In a dose-dependent fashion, DOG (0-200 microM) increased apoA-I-mediated cellular cholesterol efflux by 40% in controls, 71% in FHD, and 242% in TD cells. PMA similarly increased cholesterol efflux to a maximum of 256% in controls, 182% in FHD, and 191% in TD cells. This effect was inhibited by calphostin C. PA (100 microM) also increased cholesterol efflux by 25% in control, 44% in FHD, and 100% in TD cells. Conversely, LPA reduced cholesterol efflux in a dose-dependent fashion in control and FHD cells (-50%, 200 microM) but not in TD cells, where efflux was increased by 140%. Propranolol (100 microM) significantly increased cholesterol efflux at 24 h in all three cell lines. n-Butanol partially decreased the DOG-mediated increase in cholesterol efflux. The inhibitory effect of calphostin C on DOG-stimulated cholesterol efflux could be partially overcome by propranolol, suggesting that PA is a downstream mediator of PKC-stimulated cholesterol efflux.We conclude that PLC and PLD activities are required for apoA-I-mediated cellular cholesterol efflux, and modulating cellular PA concentration can correct, at least partially, the cholesterol efflux defect in FHD and TD.
J Lipid Res 2001 Feb;42(2):249-57.
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