Abstract
Variation at the apolipoprotein E locus on chromosome 19 plays a role in more cases of Alzheimer's disease than does any other identified genetic determinant. We have previously reported the isoform-specific interaction of native human apolipoprotein E (APOE, gene; apoE, protein) epsilon 3 with the amyloid-ss peptide, Ass(1-40), the major component of the cerebral amyloid deposits that appear to cause Alzheimer's disease. In order to investigate the apoE: A beta interaction further, a modified assay was developed based on co-immunoprecipitation of the complex using an anti-apoE antibody (anti-apoE IP assay). Application of this assay demonstrated that the interaction of Ass(1-40) and apoE can be distinguished into two types: sodium dodecyl sulfate (SDS) -resistant and SDS-releasable. The SDS-resistant interaction between epsilon;3 and Ass(1-40) is apparently maximal at an Ass(1-40) concentration of approximately 75 micro M, and an Ass(1-40) /epsilon 3 molar ratio of about 250:1. The major apoE-isoform-specific difference in interaction with Ass(1-40) is the ability of Ass(1-40) to form SDS- resistant complexes with epsilon 3 but not with epsilon 4. Using the anti-apoE co-IP assay, we found that human cerebrospinal fluid (CSF) epsilon 3 can also form an SDS-resistant complex with Ass(1-40) but human CSF epsilon;4 cannot. However, when compared with apoE epsilon;3 collected from the conditioned medium of APOE epsilon 3-transfected cells, the competence of equal concentrations of CSF apoE epsilon 3 to form SDS-resistant complexes with Ass(1-40) is apparently diminished. A 1:1 mixture of CSF plus apoE epsilon 3-containing conditioned medium is associated with diminished Ass(1-40) /epsilon;3 complex formation to a greater extent than that observed when an identical volume of phosphate-buffered saline is added to apoE epsilon;3 medium. These results suggest the presence in CSF of factors that interfere with the formation of complexes between synthetic Ass(1-40) and apoE epsilon 3.
Highlights
Alzheimer’s disease (AD) is characterized by the invariable deposition of brain amyloid plaques [1]
We have previously reported the preferential interaction of Aß1–40 with native human 3 derived from mammalian cell lines [16,17], confirming the results of an earlier study by LaDu, Frail, and
In order to perform a more comprehensive study of a apoE/Aß interactions, we developed a modified protocol utilizing a polyclonal anti-apoE antibody to immunoprecipitate all apoE molecules following a preincubation reaction with Aß1–40
Summary
Alzheimer’s disease (AD) is characterized by the invariable deposition of brain amyloid plaques [1]. The incorporation of apoE into brain amyloid plaques [8,9], the existence of SDS-resistant apoE/Aß complexes in AD brain [10], and the increased amyloid plaque density in AD patients and nondemented elderly individuals carrying an 4 allele [11,12,13,14] all emphasize the likely importance of isoform-specific interactions between apoE and Aß peptides. We have previously reported the isoform-specific interaction of native human apolipoprotein E (APOE, gene; apoE, protein) 3 with the amyloid-ß peptide, Aß1–40, the major component of the cerebral amyloid deposits that appear to cause Alzheimer’s disease. When compared with apoE 3 collected from the conditioned medium of APOE 3-transfected cells, the competence of equal concentrations of CSF apoE 3 to form SDS-resistant complexes with Aß1–40 is apparently diminished. A 1:1 mixture of CSF plus apoE 3-containing conditioned medium is associated with diminished Aß1–40/3 complex formation to a greater extent than that observed when an identical volume of phosphate-buffered saline is added to apoE 3 medium
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