Interaction of Nascent ApoE2, ApoE3, and ApoE4 Isoforms Expressed in Mammalian Cells with Amyloid Peptide β (1−40). Relevance to Alzheimer's Disease

Aug 26, 1997Biochemistry

How newly made ApoE2, ApoE3, and ApoE4 proteins in cells interact with amyloid beta peptide and their relevance to Alzheimer's disease

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Abstract

Apolipoprotein E isoforms show varying efficiencies in binding to amyloid beta, with apoE2 demonstrating the highest binding efficiency.

Apolipoprotein E4 is associated with a higher incidence and earlier onset of late-onset familial Alzheimer's disease.
In vitro studies indicate different binding reactivities of apoE isoforms with amyloid beta peptide and tau protein.
A dimeric form of apoE is formed with apoE2 and apoE3, but not with apoE4.
The order of efficiency for apoE monomer-Abeta complex formation is apoE2 > apoE3 >> apoE4.
Binding behavior of monomeric apoE differs from that of plasma-derived apoE isoforms.
The efficiency of binding among the apoE isoforms correlates inversely with the risk of developing late-onset familial Alzheimer's disease.

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Population studies have established that one of the common isoforms of apolipoprotein E, the apoE4, is associated with higher incidence and earlier age of onset of late onset familial Alzheimer's disease (AD), whereas apoE2 may have the opposite effect. The apoE3 and apoE4 isoforms were shown to display different binding reactivities with amyloid beta peptide (Abeta) and tau protein in vitro. On the basis of these findings, it has been proposed that the apoE isoforms may modulate positively or negatively the formation of either the neurofibrillary tangles or the amyloid deposits in the brain of patients with AD. To study the interaction of Abeta with nascent apoE isoforms we have expressed their cDNAs in baby hamster kidney (BHK-21) cells using the Semliki Forest Virus expression system. Analysis of the secreted apoE by one- and two-dimensional gel electrophoresis and immunoblotting showed that the nascent apoE is heavily modified with carbohydrate chains containing sialic acid. A dimeric form of apoE is formed with apoE2 and apoE3 but not with apoE4 isoforms. Analysis of the interaction of nascent apoE2, apoE3, and apoE4 produced by BHK-21 cells with Abeta (1-40) under physiological conditions (pH 7.4, 37 degrees C) showed that the efficiency of the apoE monomer-Abeta complex formation follows the order apoE2 > apoE3 >> apoE4. In addition, the apoE2 dimer formed a complex with Abeta more efficiently than the apoE3 dimer. The isoform-specific differences in binding were temperature-dependent and are attenuated upon decrease of the temperature. The binding behavior of the monomeric apoE is different from that reported for plasma apoE3 and apoE4 or commercially available apoE3 and apoE4 preparations and similar to that described for apoE3 and apoE4 produced by human embryonic kidney (HEK-293) cells. It appears that the efficiency of binding between each of three main apoE isoforms and Abeta correlates inversely with the risk of developing late-onset familial AD and may indicate possible involvement of apoE in the binding and clearance of Abeta in vivo.

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Interaction of Nascent ApoE2, ApoE3, and ApoE4 Isoforms Expressed in Mammalian Cells with Amyloid Peptide β (1−40). Relevance to Alzheimer's Disease

Abstract

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