Flexible and Accurate Substrate Processing with Distinct Presenilin/γ-Secretases in Human Cortical Neurons.

Mutations in the genes (, ) have been linked to the majority of familial Alzheimer's disease (AD). Although great efforts have been made to investigate pathogenic mutations, which ultimately cause an increase in the toxic form of β-amyloid (Aβ), the intrinsic physiological functions of PS in human neurons remain to be determined. In this study, to investigate the physiological roles of PS in human neurons, we generated conditional knock-out (KO) induced pluripotent stem cells (iPSCs), in which PS1 can be selectively abrogated under Cre transduction with or without additional KO. We showed that iPSC-derived neural progenitor cells (NPCs) do not confer a maintenance ability in the absence of both PS1 and PS2, showing the essential role of PS in Notch signaling. We then generated -null human cortical neurons, where PS1 was intact until full neuronal differentiation occurred. Aβ40 production was reduced exclusively in human /-null neurons along with a concomitant accumulation of amyloid β precursor protein (APP)-C-terminal fragments CTFs, whereas Aβ42 was decreased in neurons devoid of Unlike previous studies in mice, in which APP cleavage is largely attributable to PS1, γ-secretase activity seemed to be comparable between PS1 and PS2. In contrast, cleavage of another substrate, N-cadherin, was impaired only in neurons devoid of Moreover, PS2/γ-secretase exists largely in late endosomes/lysosomes, as measured by specific antibody against the γ-secretase complex, in which Aβ42 species are supposedly produced. Using this novel stem cell-based platform, we assessed important physiological PS1/PS2 functions in mature human neurons, the dysfunction of which could underlie AD pathogenesis.