Specific regional transcription of apolipoprotein E in human brain neurons.
In central nervous system injury and disease, apolipoprotein E (APOE, gene; apoE, protein) might be involved in neuronal injury and death indirectly through extracellular effects and/or more directly through intracellular effects on neuronal metabolism. Although intracellular effects could clearly be mediated by neuronal uptake of extracellular apoE, recent experiments in injury models in normal rodents and in mice transgenic for the human APOE gene suggest the additional possibility of intraneuronal synthesis. To examine whether APOE might be synthesized by human neurons, we performed in situ hybridization on paraffin-embedded and frozen brain sections from three nondemented controls and five Alzheimer's disease (AD) patients using digoxigenin-labeled antisense and sense cRNA probes to human APOE. Using the antisense APOE probes, we found the expected strong hybridization signal in glial cells as well as a generally fainter signal in selected neurons in cerebral cortex and hippocampus. In hippocampus, many APOE mRNA-containing neurons were observed in sectors CA1 to CA4 and the granule cell layer of the dentate gyrus. In these regions, APOE mRNA containing neurons could be observed adjacent to nonhybridizing neurons of the same cell class. APOE mRNA transcription in neurons is regionally specific. In cerebellar cortex, APOE mRNA was seen only in Bergmann glial cells and scattered astrocytes but not in Purkinje cells or granule cell neurons. ApoE immunocytochemical localization in semi-adjacent sections supported the selectivity of APOE transcription. These results demonstrate the expected result that APOE mRNA is transcribed and expressed in glial cells in human brain. The important new finding is that APOE mRNA is also transcribed and expressed in many neurons in frontal cortex and human hippocampus but not in neurons of cerebellar cortex from the same brains. This regionally specific human APOE gene expression suggests that synthesis of apoE might play a role in regional vulnerability of neurons in AD. These results also provide a direct anatomical context for hypotheses proposing a role for apoE isoforms on neuronal cytoskeletal stability and metabolism. (+info)
Transcription factor AP-2 activity is modulated by protein kinase A-mediated phosphorylation.
We recently reported that APOE promoter activity is stimulated by cAMP, this effect being mediated by factor AP-2 [Garcia et al. (1996) J. Neurosci. 16, 7550-7556]. Here, we study whether cAMP-induced phosphorylation modulates the activity of AP-2. Recombinant AP-2 was phosphorylated in vitro by protein kinase A (PKA) at Ser239. Mutation of Ser239 to Ala abolished in vitro phosphorylation of AP-2 by PKA, but not the DNA binding activity of AP-2. Cotransfection studies showed that PKA stimulated the effect of AP-2 on the APOE promoter, but not that of the S239A mutant. Therefore, cAMP may modulate AP-2 activity by PKA-induced phosphorylation of this factor. (+info)
Age of onset in Huntington disease: sex specific influence of apolipoprotein E genotype and normal CAG repeat length.
Age of onset (AO) of Huntington disease (HD) is known to be correlated with the length of an expanded CAG repeat in the HD gene. Apolipoprotein E (APOE) genotype, in turn, is known to influence AO in Alzheimer disease, rendering the APOE gene a likely candidate to affect AO in other neurological diseases too. We therefore determined APOE genotype and normal CAG repeat length in the HD gene for 138 HD patients who were previously analysed with respect to CAG repeat length. Genotyping for APOE was performed blind to clinical information. In addition to highlighting the effect of the normal repeat length upon AO in maternally inherited HD and in male patients, we show that the APOE epsilon2epsilon3 genotype is associated with significantly earlier AO in males than in females. Such a sex difference in AO was not apparent for any of the other APOE genotypes. Our findings suggest that subtle differences in the course of the neurodegeneration in HD may allow interacting genes to exert gender specific effects upon AO. (+info)
Competition of Abeta amyloid peptide and apolipoprotein E for receptor-mediated endocytosis.
The genetic polymorphism of apolipoprotein E (apoE) is associated with the age of onset and relative risk of Alzheimer's disease (AD). In contrast to apoE3, the wild type allele, apoE4 confers an increased risk of late-onset AD. We demonstrate that the beta-amyloid peptide isoforms Abeta (1-28), Abeta (1-40), and Abeta (1-43) compete for the cellular metabolism of apoE3 and apoE4 containing beta-very low density lipoproteins. An antibody raised against Abeta (1-28) cross-reacted with recombinant apoE. Epitope mapping revealed positive amino acid clusters as common epitopes of Abeta (13 through 17; HHQKL) and apoE (residues 144 through 148; LRKRL), both regions known to be heparin binding domains. Abeta in which amino acids 13 through 17 (HHQKL) were replaced by glycine (GGQGL) failed to compete with the cellular uptake of apoE enriched betaVLDL. These observations indicate that Abeta and apoE are taken up into cells by a common pathway involving heparan sulfate proteoglycans. (+info)
Mass spectral study of polymorphism of the apolipoproteins of very low density lipoprotein.
New isoforms of apolipoprotein (apo)C-I and apoC-III have been detected in delipidated fractions from very low density lipoprotein (VLDL) using matrix-assisted laser desorption (MALDI) and electrospray ionization (ESI) mass spectrometry (MS). The cleavage sites of truncated apoC-III isoforms have also been identified. The VLDL fractions were isolated by fixed-angle single-spin ultracentrifugation using a self-generating sucrose density gradient and delipidated using a newly developed C18 solid phase extraction protocol. Fifteen apoC isoforms and apoE were identified in the MALDI spectra and the existence of the more abundant species was verified by ESI-MS. The relative intensities of the apoCs are closely correlated in three normolipidemic subjects. A fourth subject with type V hyperlipidemia exhibited an elevated apoC-III level and a suppressed level of the newly discovered truncated apoC-I isoform. ApoC-II was found to be particularly sensitive to in vitro oxidation. The dynamic range and specificity of the MALDI assay shows that the complete apoC isoform profile and apoE phenotype can be obtained in a single measurement from the delipidated VLDL fraction. (+info)
beta-amyloid load is not influenced by the severity of cardiovascular disease in aged and demented patients.
BACKGROUND AND PURPOSE: This study was conducted to analyze the association between reported risk factors for Alzheimer's disease, apolipoprotein E epsilon4 allele, and cardiovascular disease and neuropathological changes essential for the diagnosis of Alzheimer's disease. METHODS: Our data are based on clinical and postmortem evaluations of a cohort of nondemented (n=118) and demented (n=107) individuals. A cardiovascular index was calculated at autopsy to estimate the extent of cardiovascular disease. Neuropathological lesions such as senile/neuritic plaques, neurofibrillary tangles, beta-amyloid load, cerebral amyloid angiopathy, and the load of paired helical filaments were determined. RESULTS: The aforementioned neuropathological lesions did not show any positive significant correlation with cardiovascular index. In contrast, the extent of Alzheimer's lesions was significantly higher in those nondemented and demented patients carrying the apolipoprotein E epsilon4 allele than in those without this allele. CONCLUSIONS: Our results demonstrate that the apolipoprotein E epsilon4 allele, but not cardiovascular disease, indeed influences the extent of Alzheimer's lesions seen in the brain tissue of demented patients as well as asymptomatic controls. (+info)
Apo E phenotype and changes in serum lipids in adult patients during growth hormone replacement.
OBJECTIVE: To determine whether apo E phenotype influences changes in lipid profiles induced by growth hormone replacement in growth hormone (GH)-deficient adults. DESIGNS: Patients were treated for 6 months with recombinant human GH (hGH), given in a dose of 0.125 U/kg per week for 4 weeks followed by 0.25 U/kg per week thereafter. The effects on serum lipids and the influence of apo E phenotype were examined. METHODS: Thirty patients (aged 35.1+/-11.8 years: mean +/- S.D.) with adult growth hormone deficiency with included in the study. Fasting serum samples were analysed for apo E phenotype total cholesterol, high-density lipoprotein (HDL)-cholesterol, triglycerides, lipoprotein (a) (Lp(a)) and IGF-I. Low-density lipoprotein (LDL)-cholesterol was calculated using the Friedwald formula. RESULTS: Six months of replacement treatment with hGH resulted in a reduction in HDL-cholesterol from 0.90+/-0.10 to 0.68+/-0.08 mmol/l (P<0.01), and a small, non-significant reduction in total cholesterol from 6.14+/-0.40 to 5.99+/-0.35 mmol/l (P = 0.06). There was no significant change in the other lipid parameters. The decrease in HDL-cholesterol concentration was greater in patients carrying the apo E2 allele (0.40+/-0.07 mmol/l, P<0.05) than in patients homozygous for the apo E3 allele (0.23+/-0.04 mmol/l) and patients carrying the apo E4 allele (0.15+/-0.36 mmol/l). Patients with the apo E4 allele had lower baseline cholesterol concentrations than patients lacking the apo E4 allele, and this persisted after treatment with hGH (P<0.05). CONCLUSIONS: Apo E phenotype may be a determining factor in the response of HDL-cholesterol to hGH in GH-deficient adults. (+info)
Iron-deficient diet reduces atherosclerotic lesions in apoE-deficient mice.
BACKGROUND: Iron deposition is evident in human atherosclerotic lesions, suggesting that iron may play a role in the development of atherosclerosis. To test this idea, the correlation between the extent of iron deposition and the severity of atherosclerosis in apolipoprotein E (apoE)-deficient mice was investigated. Furthermore, the effect of a low-iron diet on the progression of atherosclerotic lesions in these animals was evaluated. METHODS AND RESULTS: Iron deposition in tissues of apoE-deficient mice was examined by Perls' staining method. The results clearly demonstrated that iron deposits are present in atherosclerotic lesions and tissue sections of heart and liver in an age-dependent manner. When the young mice received a low-iron diet for 3 months, the hematocrit, serum iron, hemoglobin, and cholesterol concentrations were not significantly altered compared with those of littermates placed on a chow diet. However, the serum ferritin level of animals in the iron-restricted group was 27% to 30% lower than that of the control group in either sex. Furthermore, the lipoproteins isolated from the iron-restricted group exhibited greater resistance to copper-induced oxidation. Histological examination revealed that atherosclerotic lesions developed in mice fed a low-iron diet were significantly smaller than those found in control littermates. Likewise, the iron deposition as well as tissue iron content was much less in aortic tissues of the iron-restricted animals. Circulating autoantibodies to oxidized LDL and immunostains for epitopes of malondialdehyde-modified LDL detected on lesions were also significantly lower in mice fed a low-iron diet. CONCLUSIONS: Iron deposition is closely associated with the progression of atherosclerosis in apoE-deficient mice. Restriction in dietary iron intake leads to significant inhibition of lesion formation in these animals. These results suggest that the beneficial effect of a low-iron diet may be mediated, at least in part, by the reduction of iron deposition as well as LDL oxidation in vascular lesions. (+info)