Probing sporadic and familial Alzheimer?s disease using induced pluripotent stem cells.

Our understanding of Alzheimer’s disease (AD) pathogenesis is currently limited by difficulties in obtaining live neurons from patients and the inability to model the sporadic form of AD. It may be possible to overcome these challenges by reprogramming primary cells from patients into induced pluripotent stem cells (iPSCs). We reprogrammed primary fibroblasts from two patients with familial AD (both caused by a duplication of APP1, APPDp), two with sporadic AD (sAD1, 2) and two non-demented control individuals (NDCs) into iPSC lines. Neurons from differentiated cultures were FACS-purified and characterized. Purified cultures contained >90% neurons, clustered with fetal brain mRNA samples by microarray criteria, and could form functional synaptic contacts. Virtually all cells exhibited normal electrophysiological activity. Relative to controls, iPSC-derived, purified neurons from the two APPDp patients and patient sAD2 exhibited significantly higher levels of secreted Aβ1-40, phospho-tauThr231 (pTau) and active GSK3β (aGSK3β). Neurons from APPDp and sAD2 patients also accumulated large Rab5-positive early endosomes compared to controls. Treatment of purified neurons with β-secretase inhibitors, but not g-secretase inhibitors, caused significant reductions in pTau and aGSK3β levels. These results suggest a direct relationship between APP proteolytic processing, but not Aβ, in GSK3β activation and tau phosphorylation in human neurons. Additionally, we observed that neurons with the genome of one sAD patient exhibited the phenotypes seen in familial AD samples. More generally, we demonstrate that iPSC technology can be used to observe phenotypes relevant to AD, even though it can take decades for overt disease to manifest in patients.