ASSOCIATION OF HUMAN, RAT, AND RABBIT APOLIPOPROTEIN-E WITH BETA-AMYLOID

In humans, apolipoprotein E (apoE) has three major isoforms, E2 (Cys(1 12), Cys(158)), E3 (Cys(112), Arg(158)), and E4 (Arg(112), Arg(158)). While epsilon 4 is a genetic risk factor for Alzheimer's disease (AD), epsilon 2 may protect against late-onset AD. Using native preparation s 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 beta-amyloid (A beta), apoE3 formed 20 times as m uch SDS-stable complex with the peptide as apoE4. This preferential bi nding of A beta to apoE3 was abolished-when apoE was purified by a pro cess which includes delipidation and denaturation. Here we expand thes e observations to include A beta binding to lipoprotein-associated and purified apoE2. Lipoproteins isolated from the plasma of individuals homozygous for either epsilon 2 or epsilon 3 were incubated with A bet a(1-40). SDS-stable complex formation was analysed by a non-reducing g el shift assay, followed by immunoblotting with either A beta or apoE antibodies. ApoE2:A beta complex formation was comparable to apoE3:A b eta in both native and purified preparations of apoE. In addition, lip oprotein-associated rat apoE (Arg(112), Arg(158)), like human apoE4, d id not form complex with A beta, while lipoprotein-associated rabbit a poE (Cys(112), Arg(158)) did bind the peptide. These binding studies p rovide one possible explanation for protective effects of both apoE2 a nd E3 against the development of Alzheimer's disease. (C) 1997 Wiley-L iss, Inc.