Received for publication October 2, 2006.
Revised December 22, 2006.
Accepted for publication December 27, 2006.

DOMINANCE OF AMYLOID PRECURSOR PROTEIN SEQUENCE OVER HOST CELL SECRETASES IN DETERMINING -AMYLOID PROFILES STUDIES OF INTERSPECIES VARIATION AND DRUG ACTION BY INTERNALLY STANDARDIZED IMMUNOPRECIPITATION/MASS SPECTROMETRY

Abstract

-amyloid peptides, tentatively regarded as the principal neurotoxins responsible for Alzheimer's Disease, make up a set of products that varies significantly between different biological systems. The full implications of this complexity and its variations have yet to be defined. In this work, A peptide populations were extracted from animal brain tissue or cell-conditioned media, immunoprecipitated with specific antibodies, and analyzed by matrix-assisted laser desorption time-of-flight mass spectrometry. ¹⁵N-Substituted A internal standards were added to gauge variations in the profile of captured peptides. Results from a range of species, including guinea pig, dog, rabbit and wild-type and transgenic mice, showed that the A peptide population in each system was mainly determined by the species of origin of the amyloid precursor protein (APP) and not by the host tissue or cell line. The same method was used to gauge the effect on the A peptide profile of an inhibitor of -secretase, one of the two proteinases that excises A peptides from the precursor protein with different effects on specific peptides. Overall, the results demonstrate that the species of origin of the APP substrate dictates the products of -secretase processing, and not the origin of the enzyme, an important consideration when choosing model systems.

Key words: amyloid, animal models, beta secretase, gamma secretase, mass spectrometry, transgenic mice