Binding of Human Apolipoprotein E to Synthetic Amyloid Beta Peptide: Isoform-Specific Effects and Implications for Late-Onset Alzheimer Disease (original) (raw)
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Association of human, rat, and rabbit apolipoprotein E with β‐amyloid
Journal of Neuroscience Research, 1997
In humans, apolipoprotein E (apoE) has three major isoforms, E2 (Cys 112 , Cys 158 ), E3 (Cys 112 , Arg 158 ), and E4 (Arg 112 , Arg 158 ). While e4 is a genetic risk factor for Alzheimer's disease (AD), e2 may protect against late-onset AD. Using native preparations of apoE from conditioned tissue culture media or plasma lipoproteins, we have previously shown that when equivalent amounts of apoE3 or E4 were incubated with b-amyloid (Ab), apoE3 formed 20 times as much SDS-stable complex with the peptide as apoE4. This preferential binding of Ab to apoE3 was abolished when apoE was purified by a process which includes delipidation and denaturation. Here we expand these observations to include Ab binding to lipoprotein-associated and purified apoE2. Lipoproteins isolated from the plasma of individuals homozygous for either e2 or e3 were incubated with Ab(1-40). SDS-stable complex formation was analyzed by a non-reducing gel shift assay, followed by immunoblotting with either Ab or apoE antibodies. ApoE2:Ab complex formation was comparable to apoE3:Ab in both native and purified preparations of apoE. In addition, lipoprotein-associated rat apoE (Arg 112 , Arg 158 ), like human apoE4, did not form complex with Ab, while lipoprotein-associated rabbit apoE (Cys 112 , Arg 158 ) did bind the peptide. These binding studies provide one possible explanation for protective effects of both apoE2 and E3 against the development of Alzheimer's disease.
2005
The major protein component of the extracellular deposits in Alzheimer's disease (AD) is a 4 kDa peptide termed amyloid-β (Aβ). This peptide is known to bind apolipoprotein E (apoE), a key mediator of lipoprotein transport, in an isoform specific manner. Whilst these isoform specific effects on apoE are well recognized, the functional significance of this interaction is poorly understood. Here, we investigated the influence of Aβ on apoE-mediated lipoprotein binding to cells using fluorescently tagged lipoprotein-like emulsions. Using this approach, we demonstrate that Aβ enhanced the normally poor binding of apoE2 lipoprotein-like particles to fibroblasts in culture, whilst markedly reducing the binding of apoE3 and apoE4. This suggests that the action of apoE isoforms on cellular lipoprotein or cholesterol metabolism is differentially modulated by Aβ. This also suggests that Aβ may also compromise apoE function in the Alzheimer disease affected brain. . Despite the well established association of the APOE ε4 allele with AD , the mechanistic link between apoE and the pathogenesis of AD remains poorly understood. Initial investigations examining this link in vitro revealed that Aβ, the major protein component of the AD senile plaque, formed SDS resistant complexes with purified apoE in an isoform specific manner . It was found that the apoE4 isoform had the strongest affinity for Aβ whilst apoE3 exhibited weaker affinity .
Apolipoprotein E is immunochemically localized to the senile plaques, vascular amyloid, and neuroflbril-lary tangles of Alzheimer diwase. In vitro, apolipoprotein E in cerebrospinal fluid binds to synthetic 13A4 peptide (the primary constituent of the senile plaque) with high avidity. Amino acids 12-28 of the flA4 peptide are required. The gene for apolipo-protein E is located on chromosome 19q13.2, within the region previously associated with linkage of late-onset familial Alz-heimer diseas. Analysis of apolipoprotein E alleles in Alzhei-mer disease and controls demonstrated that there was a highiy significant assocition of apolipoprotein E type 4 alele (APOE-e4) and late-onset familil Alzheimer disea. The alele frequency of the APOE-e4 in 30 random affected patients, each from a different Azheimer disease family, was 0.50 t 0.06; the aUlele frequency of APOE-e4 in 91 age-matched unrelated controls was 0.16 ± 0.03 (Z = 2.44, P = 0.014). A functional role of the apolipoprotein E-E4 isoform in the pathogenesis of late-onset familial Alzheimer dise is suggested.
Journal of Neurochemistry, 2002
The 4allele of apolipoprotein E (apoE, protein; APOE, gene) is a major risk factor for Alzheimer's disease (AD). Genetically, the frequency of the 4 allele is enriched in early-onset sporadic, late-onset familial, and common late-onset sporadic AD. ApoE is found in the extracellular amyloid-/3 (A~i9)deposits that are characteristic features of AD. In this study, we examined the interaction between A/3 and apoE isoforms. The apoE isoforms used in this study were either produced by stably transfected Chinese hamster ovary cells (CHO) or were from human plasma. We report that when similar concentrations of the apoE isoforms were used, native nonpurifled apoE3 from recombinant CHO-derived sources bound A~,but apoE4 did not. In fact, in our system, binding of recombinant apoE4 to A/3 was never detectable, even after incubation for 4 days. Furthermore, using the same assay conditions, native apoE2, like apoE3, binds A/I avidly. Furthermore, when human plasma apoE isoforms are tested in A/3 binding experiments, apoE3 bound A/I more avidly than apoE4, and a major apoE/ A/I complex (the 40-kDa form) was observed with plasma apoE3 but not apoE4. These data extend our understanding of apoE isoform-dependent binding of A/3 by associating apoE2 with efficient apoE/A/I complex formation and demonstrate that native apoE3 (whether recombinant or derived from human plasma) forms sodium dodecyl sulfate-stable apoE/A/I complexes more readily than native apoE4. The different A/I-binding properties of native apoE4 versus native apoE3 provide insight into the molecular mechanisms by which the APOE 4 allele exerts its risk factor effects in AD.
Journal of Alzheimer's disease : JAD, 2005
The major protein component of the extracellular deposits in Alzheimer's disease (AD) is a 4 kDa peptide termed amyloid-beta (Abeta). This peptide is known to bind apolipoprotein E (apoE), a key mediator of lipoprotein transport, in an isoform specific manner. Whilst these isoform specific effects on apoE are well recognized, the functional significance of this interaction is poorly understood. Here, we investigated the influence of Abeta on apoE-mediated lipoprotein binding to cells using fluorescently tagged lipoprotein-like emulsions. Using this approach, we demonstrate that Abeta enhanced the normally poor binding of apoE2 lipoprotein-like particles to fibroblasts in culture, whilst markedly reducing the binding of apoE3 and apoE4. This suggests that the action of apoE isoforms on cellular lipoprotein or cholesterol metabolism is differentially modulated by Abeta. This also suggests that Abeta may also compromise apoE function in the Alzheimer disease affected brain.
Apolipoprotein E isoforms in Alzheimer's disease pathology and etiology
Microscopy Research and Technique, 2000
The apolipoprotein E (apoE) ⑀4 allele increases risk of Alzheimer's disease (AD), perhaps by accelerating plaque formation, or by impairing neuron repair. Considerable evidence supports both mechanisms. AD patients with ⑀4 have more and earlier amyloid deposits than do patients without ⑀4. The same is true of non-demented control subjects. In vitro, all apoE isoforms inhibit amyloid  protein (A) aggregation, but apoE4 less effectively than apoE3. Transgenic amyloid-producing mice expressing apoE3 or apoE4 develop less A deposition than apoE knockout mice. These observations are consistent with an effect of apoE isoforms on A aggregation in AD. ApoE is important for neurite maintenance since apoE knockout mice lose neurites and suffer behavioral deficits with aging or treatment with excitotoxins. ApoE4 mice show similar defects, but apoE3 mice are normal. AD patients with ⑀4 show more neuritic deficits than ⑀3 carriers. ApoE ⑀4 also worsens neurological impairment in head injury, stroke, and multiple sclerosis. Thus, apoE4 is less effective at neurite maintenance. Perhaps ⑀4 increases AD risk by both mechanisms: allowing amyloid deposition and failing to repair neurites. In either case, introducing apoE3 or apoE2 into the brain, for example by gene therapy or cell grafts, might delay AD progression.