alpha-secretase-derived product of beta-amyloid precursor protein is decreased by presenilin 1 mutations linked to familial Alzheimer's disease

Recent reports indicate that missense mutations on presenilin (PS) 1 are likely responsible for the main early-onset familiar forms of Alzheimer's disease (FAD). Consensual data obtained through distinct histopathological, cell biology, and molecular biology approaches have led to the conclusion that these PS1 mutations clearly trigger an increased production of the 42-amino-acid-long species of beta-amyloid peptide (A beta). Here we show that overexpression of wild-type PS1 in HK293 cells increases A beta 40 secretion. By contrast, FAD-linked mutants of PS1 trigger increased secretion of both A beta 40 and A beta 42 but clearly favor the production of the latter species. We also demonstrate that overexpression of the wild-type PSI augments the alpha-secretase-derived C-terminally truncated fragment of beta-amyloid precursor protein (APP alpha) recovery, whereas transfectants expressing mutated PS1 secrete drastically lower amounts of APP alpha when compared with cells expressing wild-type PS1. This decrease was also observed when comparing double transfectants overexpressing wild-type beta-amyloid precursor protein and either PS1 or its mutated congener M146V-PS1. Altogether, our data indicate that PS mutations linked to FAD not only trigger an increased ratio of A beta 42 over total A beta secretion but concomitantly downregulate the production of APP alpha.