AGGREGATION OF SECRETED AMYLOID BETA-PROTEIN INTO SODIUM DODECYL SULFATE-STABLE OLIGOMERS IN CELL-CULTURE

Filamentous aggregates of the 40-42-residue amyloid beta-protein (A be ta) accumulate progressively in the limbic and cerebral cortex in Alzh eimer's disease, where they are intimately associated with neuronal an d glial cytopathology, Attempts to model this cytotoxicity in vitro us ing synthetic peptides have shown that monomeric A beta is relatively inert, whereas aggregated A beta reproducibly exerts a variety of neur otoxic effects, The processes that mediate the conversion of monomeric A beta into a toxic aggregated state are thus of great interest. Prev ious studies of this conversion have employed high concentrations (10( -5)-10(-3) M) of synthetic A beta peptides under nonbiological conditi ons, We report here the detection of small amounts (<10(-9) M) of SDS- stable A beta oligomers in the culture media of Chinese hamster ovary cells expressing endogenous or transfected amyloid beta-protein precur sor genes, The identity of these oligomers (primarily dimers and trime rs) was established by immunoprecipitation with a panel of A beta anti bodies, by electrophoretic comigration with synthetic A beta oligomers , and by amino acid sequencing, The oligomeric A beta species comprise d similar to 10-20% of the total immunoprecipitable A beta in these cu ltures. A truncated A beta species beginning at Arg 5 was enriched in the oligomers, suggesting that amino-terminal heterogeneity can influe nce A beta oligomerization in this system. Addition of Congo red (10 m u M) during metabolic labeling of the cells led to increased monomeric and decreased oligomeric A beta. The ability to detect and quantitate oligomers of secreted A beta peptides in cell culture should facilita te dynamic studies of the critical process of initial A beta aggregati on under physiological conditions.