Impaired secretion of apolipoprotein E2 from macrophages.
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Human apoE is a multifunctional and polymorphic protein synthesized and secreted by liver, brain, and tissue macrophages. Here we show that apoE isoforms and mutants expressed through lentiviral transduction display cell-specific differences in secretion efficiency. Whereas apoE3, apoE4, and a natural mutant of apoE4 (apoE-Cys(142)) were efficiently secreted from macrophages, apoE2 and a non-natural apoE mutant (apoE-Cys(112)/Cys(142)) were retained in the perinuclear region and only minimally secreted. The secretory block for apoE2 in macrophages was not affected by the ablation of LDLR (low density lipoprotein receptor), ABCA-1, or SR-BI (scavenger receptor class B type I) but was released in the absence of low density lipoprotein receptor related protein (LRP). In co-immunoprecipitation experiments, an anti-apoE antibody pulled down two times more LRP in apoE2-transduced macrophages than in apoE3-expressing macrophages. Non-reducing SDS-PAGE/Western blot analyses showed that macrophage apoE2 is mostly dimeric and multimeric, whereas apoE3 is predominantly monomeric. ApoE2 retention and multimer formation also occurred in human macrophages derived from the monocyte cell line THP-1. These results were specific for macrophages, as in transduced mouse primary hepatocytes: 1) ApoE2 was secreted as efficiently as apoE3 and apoE4; 2) all isoforms were exclusively in monomeric form; 3) there was no co-immunoprecipitation of apoE and LRP. A microsomal triglyceride transfer protein (MTP) inhibitor nearly deleted apoB100 secretion from hepatocytes without affecting apoE secretion. These data show that macrophages retain apoE2, a highly expressed protein carried by about 8% of the human population. Given the role of locally produced apoE in regulating cholesterol efflux, modulating inflammation, and controlling oxidative stress, this unique property of apoE2 may have important impacts on atherogenesis. (+info)
Patient characteristics are important determinants of neurodevelopmental outcome at one year of age after neonatal and infant cardiac surgery.
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OBJECTIVE: Many studies of neurodevelopmental outcomes after neonatal and infant cardiac surgery have focused on potentially modifiable risk factors for adverse outcomes, primarily intraoperative management strategies and the use of deep hypothermic circulatory arrest. There is increasing evidence that patient-specific factors are more important determinants of outcome. METHODS: We investigated predictors of neurodevelopmental outcomes at 1 year of age after neonatal and infant cardiac surgery in a subgroup of infants enrolled in a prospective study of apolipoprotein E (APOE) genotype and neurodevelopmental outcome. Children with a variety of 2-ventricle cardiac defects repaired with only 1 operation with cardiopulmonary bypass and no more than 1 episode of deep hypothermic circulatory arrest were included. Neurodevelopmental outcomes at 1 year of age included the Bayley Scales of Infant Development-II, which yield 2 indices, the Mental Developmental Index and the Psychomotor Developmental Index. RESULTS: Two hundred forty-seven infants underwent surgical repair between October 1998 and April 2003 with 1 hospital death and 3 deaths before 1 year of age. Neurodevelopmental evaluation was performed in 188 (77%) of 243 survivors, including 56 patients with tetralogy of Fallot, 39 with transposition of the great arteries with intact ventricular septum, 34 with ventricular septal defects, and 59 with other defects. The median age at operation was 56 days (1-186 days), including 72 (38%) neonates. Confirmed or suspected genetic syndromes were present in 59 (31%) of 188 infants. Deep hypothermic circulatory arrest was used in 67 (35%) infants with a median duration of 34 minutes (1-80 minutes). For the entire cohort, the mean Mental Developmental Index was 90.6 +/- 14.9 and the mean Psychomotor Developmental Index was 81.6 +/- 17.2. For patients without genetic syndromes, the mean Mental Developmental Index was 93.7 +/- 13.6 and the mean Psychomotor Developmental Index was 85.1 +/- 14.6. For the entire cohort, predictors of lower scores for both the Mental Developmental Index and Psychomotor Developmental Index were presence of a confirmed or suspected genetic syndrome, lower birth weight, and presence of the APOE epsilon2 allele (all P < .04). Black race was associated with higher scores on the Psychomotor Developmental Index (P = .018). Lower nasopharyngeal temperature during cardiopulmonary bypass was associated with a lower score on the Psychomotor Developmental Index (P = .03) and was the only intraoperative factor that was a significant predictor of either the Mental or Psychomotor Developmental Index. CONCLUSIONS: The strongest predictors of a worse neurodevelopmental outcome at 1 year of age were patient-specific factors including presence of a genetic syndrome, low birth weight, and presence of the APOE epsilon2 allele. Patient-specific factors eclipsed the use and duration of deep hypothermic circulatory arrest as predictors of worse neurodevelopmental outcomes. (+info)
Residues Leu261, Trp264, and Phe265 account for apolipoprotein E-induced dyslipidemia and affect the formation of apolipoprotein E-containing high-density lipoprotein.
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Overexpression of apolipoprotein E (apoE) induces hypertriglyceridemia in apoE-deficient mice, which is abrogated by deletion of the carboxy-terminal segment of residues 260-299. We have used adenovirus-mediated gene transfer in apoE-/- and apoA-I-/- mice to test the effect of three sets of apoE mutations within the region of residues 261-265 on the induction of hypertriglyceridemia, the esterification of cholesterol of very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL), and the formation of spherical or discoidal apoE-containing HDL. A single-amino acid substitution (apoE4[Phe265Ala]) induced hypertriglyceridemia in apoE-/- or apoA-I-/- mice, promoted the accumulation of free cholesterol in the very low-density lipoprotein (VLDL) and HDL region, and decreased HDL cholesterol levels. A double substitution (apoE4[Leu261Ala/Trp264Ala]) induced milder hypertriglyceridemia and increased HDL cholesterol levels. A triple substitution (apoE4[Leu261Ala/Trp264Ala/Phe265Ala] or apoE2[Leu261Ala/Trp264Ala/Phe265Ala]) did not induce hypertriglyceridemia and increased greatly the HDL cholesterol levels. Electron microscopy (EM) analysis of the HDL fractions showed that apoE4[Leu261Ala/Trp264Ala/Phe265Ala] and apoE2[Leu261Ala/Trp264Ala/Phe265Ala] contained spherical HDL, apoE4[Leu261Ala/Trp264Ala] contained mostly spherical and few discoidal HDL particles, and apoE4[Phe265Ala] contained discoidal HDL. We conclude that residues Leu261, Trp264, and Phe265 play an important role in apoE-induced hypertriglyceridemia, the accumulation of free cholesterol in VLDL and HDL, and the formation of discoidal HDL. Substitution of these residues with Ala improves the apoE functions by preventing hypertriglyceridemia and promoting formation of spherical apoE-containing HDL. (+info)
Dissociation of neuropathologic findings and cognition: case report of an apolipoprotein E epsilon2/epsilon2 genotype.
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BACKGROUND: The apolipoprotein E (APOE) epsilon2 allele has been suggested as having a protective effect and delaying the age at onset of Alzheimer disease. OBJECTIVE: To describe a dissociation between neuropathologic findings with normal cognition in a woman with severe Alzheimer disease with the APOE epsilon2/epsilon2 genotype. DESIGN: Case report from a community-based prospective study of persons 90 years or older (The 90+ Study). PARTICIPANT: A 92-year-old woman without dementia with the APOE epsilon2/epsilon2 genotype who lived independently without significant cognitive or functional loss and was a participant in The 90+ Study. She died in December 2004, and postmortem examination of her brain was performed. INTERVENTION: Neurologic examination and a battery of neuropsychological tests were performed 6 months and 1 month before death. Neuropathologic examination included Braak and Braak staging for senile plaques and neurofibrillary tangles. RESULTS: Neuropathologic examination of the brain revealed advanced senile plaque and neurofibrillary tangle disease consistent with a high likelihood of Alzheimer disease. At clinical evaluation, the participant demonstrated no dementia and only mild cognitive deficits. CONCLUSIONS: The APOE genotype may have contributed to maintenance of cognition despite advanced neuropathologic findings of Alzheimer disease. This case suggests that the APOE epsilon2 isoform may have a protective effect against cognitive decline in Alzheimer disease that may be independent from senile plaques and neurofibrillary tangles. (+info)
Apolipoprotein E gene polymorphism in the Mongolian population.
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Apolipoprotein E plays a key role in the regulation of lipid metabolism. ApoE function is determined by the presence of three common alleles (epsilon2, epsilon3, epsilon4). The apo epsilon3 allele is the most prevalent, apo epsilon2 is associated with dysbetalipoproteinaemia, and apo epsilon4 is frequently associated with an increased risk for cardiovascular and Alzheimer's diseases. Mongolian population has a high rate of cardiovascular mortality and morbidity and there might be genetic susceptibility of the population to cardiovascular disease. The aim of our study was to establish the frequency of apoE genotypes in 744 Mongolian subjects and to compare the results with findings from other Asian populations. The apo E sequence was amplified using polymerase chain reaction and apo E genotyping was performed by restriction enzyme cleavage with CfoI. The relative apoE allele frequencies were epsilon2 = 3.7%, epsilon3 = 80.8%, and epsilon4 = 15.5%, the genotype frequencies were epsilon2/epsilon2 = 0% (N = 0), epsilon2/epsilon3 = 5.7% (N = 42), epsilon2/epsilon4 = 1.7% (N = 13), epsilon3/epsilon3 = 65.3% (N = 486), epsilon3/epsilon4 = 25.4% (N = 189), epsilon4/epsilon4 = 1.9% (N = 14); the occurrence of the risk epsilon4 allele in Mongolia is among the highest in Asia. The high frequency of the apo epsilon4 allele may increase the susceptibility of Mongolian population to cardiovascular diseases. (+info)
The D9N, N291S and S447X variants in the lipoprotein lipase (LPL) gene are not associated with Type III hyperlipidemia.
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BACKGROUND: Type III hyperlipidemia (Type III HLP) is associated with homozygosity for the epsilon2 allele of the APOE gene. However only about 10% of epsilon2 homozygotes develop Type III HLP and it is assumed that additional genetic and/or environmental factors are required for its development. Common variants in the LPL gene have been proposed as likely genetic co-factors. METHODS: The frequency of the LPL SNPs D9N, N291S and S447X in 100 patients with hyperlipidemia and APOE2/2 genotype has been determined and compared to that in healthy blood donors and patients with hyperlipidemia. RESULTS: There were no statistically significant difference in the frequencies of the variants between APOE2/2 patients and controls. CONCLUSION: It is unlikely that the D9N, N291S or S447X variants in the LPL gene play an important role in the development of Type III HLP. (+info)
Human apolipoprotein E2 transgenic mice show lipid accumulation in retinal pigment epithelium and altered expression of VEGF and bFGF in the eyes.
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We investigated the human apolipoprotein E2 (apoE2) transgenic mouse as an animal model system for age-related macular degeneration (AMD). Transgenic mice expressing human apoE2 and C57BL/6J mice were fed normal chow or a high-fat diet for 4 weeks. Eyes were collected from the mice and lipid deposits in retinal pigment epithelium (RPE) were assessed using electron microscopy. The expressions of apoE, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and pigment-epithelium derived factor (PEDF), which are molecular markers for angiogenesis, were assessed with immunohistochemistry. Eyes from apoE2 mice, regardless of diet, contained lipid accumulation in RPE under electron microscopy, whereas control C57BL/6J eyes did not. Lipid accumulation was found predominantly in the RPE and the Bruch's membrane and increased in the eyes of apoE2 mice after one month of a high-fat diet (8 +/- 2 per 50 microm2 for normal chow and 11 +/- 2 per 50 microm2, p < 0.05). ApoE expression was similar in the apoE2 and control mice; however, VEGF and bFGF were overexpressed in the retinal pigment epithelium of apoE2 eyes compared with control eyes, and PEDF expression was slightly decreased. These expression patterns of VEGF, bFGF, and PEDF suggest angiogenesis is progressing in apoE2 eyes. In conclusion, the eyes of apoE2 mice develop typical lipid accumulations, a common characteristic of AMD, making them a suitable animal model for AMD. The expression profile of VEGF and bFGF on the retinal pigment epithelium suggests that apoE2 may induce neovascularization by altering angiogenic cytokines. (+info)
Apolipoprotein E gene and retinal microvascular signs in older people: the Cardiovascular Health Study.
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PURPOSE: To examine the association between apolipoprotein E (APOE) gene polymorphism and retinal microvascular signs in an older population. METHODS: Retinal photographs were taken of 2,152 participants (1,831 whites, and 321 African-Americans), aged 69-96 years, who were participating in a population-based study of four United States communities. We used standardized protocols to assess photographs for the presence of retinal microvascular signs (retinopathy, arterio-venous nicking, and focal arteriolar narrowing) and a computer-assisted method to measure retinal vessel diameters. We analyzed DNA extracted from blood samples of participants for common allelic variants of the APOE gene. RESULTS: After adjusting for age, gender, systolic blood pressure, smoking, total serum cholesterol, and other risk factors, we found white participants carrying the epsilon2 and epsilon4 alleles were more likely to have arterio-venous nicking than the epsilon3/epsilon3 homozygotes, with odds ratio (OR) of 1.70 and confidence interval (CI) 95% (1.03-2.83) for the epsilon2 carriers and OR 1.74 (95% CI 1.06-2.84) for the epsilon4 carriers. Among white participants without hypertension, the associations remained significant for the epsilon4 carriers (OR 2.32, 95% CI 1.18-4.57). Whites, normotensive carriers of the epsilon2 allele had significantly narrower retinal arteriolar diameters (adjusted mean arteriolar diameter of 163.5 mum, 95% CI 160.1-167.0, p=0.03) compared to the epsilon3/epsilon3 homozygotes (167.8 mum, 95% CI 166.0-169.6). APOE gene polymorphism was not associated with retinopathy, focal narrowing, or retinal venular diameters in white participants. There were insufficient numbers of African-Americans for separate multivariate analysis. CONCLUSIONS: This study provides little evidence that the APOE gene polymorphism plays a significant role in the pathogenesis of retinal microvascular changes in the general population. In the older white population, APOE epsilon2 and epsilon4 allele carriers were more likely to have arterio-venous nicking. Other retinal signs, however, were not related to APOE gene polymorphism. (+info)