The apolipoprotein E epsilon4 allele contributes to the genetic susceptibility underlying a large proportion (~40-60%) of typical, sporadic Alzheimer disease. Apolipoprotein E deficient mice made transgenic for human apolipoprotein E epsilon4 accumulate excess cerebral amyloid when compared to similarly prepared mice expressing human apolipoprotein E epsilon3. Therefore, it is important to search for relevant interactions(s) between apolipoprotein E epsilon4 and Abeta in order to clarify the biological role for apolipoprotein E epsilon4 in Alzheimer disease. Using a thioflavine T (ThT)-based assay, we have investigated the effects of native human apolipoprotein E isoforms on the kinetics of Abeta fibrillogenesis. No obvious profibrillogenic activity was detected in Abeta1-40-based assays of any native apolipoprotein E isoform. However, when ThT assays were repeated using Abeta1-42, modest, but statistically significant, profibrillogenic activity was detected in both apolipoprotein E epsilon3- and apolipoprotein E epsilon4-containing media and was similar in magnitude for the two isoforms. These data demonstrate that native apolipoprotein E possesses "pathological chaperone"-type activity for Abeta: in other words, the data indicate that a chaperone-like misfolding reaction can occur between native apolipoprotein E and Abeta. However, the equipotent activities of the apolipoprotein E epsilon3 and epsilon4 isoforms suggests the possibility that either extended co-incubation of apolipoprotein E and Abeta, or, perhaps, the inclusion in the reaction of other fibrillogenesis-modulation co-factors (such as metal ions, or inflammatory mediators such as reactive oxygen species, alpha2-macroglobulin, apolipoprotein J, etc.) may be required for modeling in vitro the apolipoprotein E-isoform-specific-regulation of extracellular Abeta accumulation that occurs in vivo. Alternatively, other events, such as differential apolipoprotein E-isoform-mediated clearance of Abeta or of apolipoprotein E/Abeta complexes may underlie apolipoprotein E-isoform-dependent Abeta accumulation.

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Published in Journal of Neuroinflammation, v. 1, 15.

© 2004 Sweeney et al; licensee BioMed Central Ltd.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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