ISOFORM-SPECIFIC BINDING OF APOLIPOPROTEIN-E TO BETA-AMYLOID

Apolipoprotein E (apoE), particularly the e4 allele, is genetically li nked to the incidence of Alzheimer's disease, ApoE is present in the e xtracellular senile plaques and intracellular neurofibrillary tangles associated with Alzheimer's disease. In vitro, apoE has been shown to bind beta-amyloid (A beta), an amyloidogenic proteolytic product of am yloid precursor protein. To analyze the interaction of A beta and apoE , we used Western immunoblotting of human A beta-(1-40)-peptide incuba ted with conditioned medium from HEK-293 cells transfected with either human apoE3 or apoE4 (products of the e3 and e4 alleles, respectively ) cDNA. Nonreducing SDS-polyacrylamide gel electrophoresis revealed th e presence of an similar to 45-kDa complex with both A beta and apoE i mmunoreactivity. The level of the apoE3 A beta complex was similar to 20-fold greater than that of the apoE4.A beta complex. This apoE isofo rm-specific binding pattern was maintained from pH 5.0 to 9.0, from 2 min to 24 h of peptide incubation, and at concentrations of apoE from 5 to 100 mu g/ml and of A beta from 10 mu M to 1 mM. The higher level of apoE3 binding to A beta is in contrast to previously published data using purified apoE (Strittmatter, W. J., Weisgraber, K. H., Huang, D . Y., Dong, L.-M., Salvesen, G. S., Pericak-Vance, M., Schmechel, D., Saunders, A. M., Goldgaber, D., and Roses, A. D. (1993) Proc. Natl. Ac ad. Sci. U. S. A. 90, 8098-8102). Factors responsible for the isoform- specific interactions between apoE and A beta will require further stu dy before the apparent discrepancy between these data can be reconcile d.