O2‐04‐05: A cell‐based model for presenilin 1 early‐onset familial Alzheimer's disease (EOFAD): Dominant negative effects and relative stabilities of presenilin 1 with EOFAD mutations

Abstract

The most frequent cause of Early-onset familial Alzheimer's disease (EOFAD) is the autosomal dominant inheritance of a missense mutation in the presenilin 1 (PS1) gene (PSEN). Since EOFAD results from a mutation in a single allele of PSEN, both wild type and the PSEN variant gene products are co-expressed. The potential for the mutant PS1 protein to affect the function of wild-type PS1 (e.g., a dominant negative effect) and the relative amount of wild type and mutant PS1 incorporated into the gamma secretase complex are important factors that are relevant to the understanding and the treatment of PS1 EOFAD. We have generated five PS1 EOFAD cell lines (M146V, A431E, H163R, delta9, E280A and WT control in H4 neuroglioma cells) in which recombinant mutant PS1 expression, in the presence of endogenous wild type PS1, is under the control of the TETrepressor. We measured Ab42and Ab40 levels as a function of the ratio of wild type to mutant PS1 in the gamma secretase complex and demonstrated that all EOFAD PS1 mutants tested exhibit dominant negative behavior for Ab42 and total Ab production. In contrast, over-expression of wild type PS1 had no effect on Ab42 or total Ab production. Although equal gene dosage of mutant and wild type PS1 is expected in EOFAD, the actual ratio of mutant to wild type PS1 in the gamma secretase complex will be dependent on the relative stability (i.e., multiple factors such as mutant holo-PS1 stability, its ability to interact with other gamma secretase components and the stability of the resulting gamma secretase complex). In PS1 EOFAD, the relative stability of the PS1 variant could impact the degree of a dominant negative effect and thus make a significant contribution to disease severity and age of onset. We determined the relative stability of the PS1 mutants by measuring the amount of mutant PS1 incorporated into the gamma secretase complex as a function of recombinant mRNA levels. Our results suggest that increasing the ratio of wild type to mutant PS1 may promote normalization of gamma secretase function and could be a promising therapeutic approach for PS1 EOFAD.