“Patient-specific Alzheimer-like pathology in trisomy 21 cerebral organoids reveals BACE2 as a gene-dose-sensitive AD-suppressor in human brain”

Alić, Ivan; Goh, Pollyanna A; Murray, Aoife; Portelius, Erik; Gkanatsiou, Eleni; Gough, Gillian; Mok, Kin Y; Koschut, David; Brunmeir, Reinhard; Yeap, Yee Jie; O’Brien, Niamh L; Groet, Jurgen; Shao, Xiaowei; Havlicek, Steven; Dunn, N Ray; Kvartsberg, Hlin; Brinkmalm, Gunnar; Hithersay, Rosalyn; Startin, Carla; Hamburg, Sarah; Phillips, Margaret; Pervushin, Konstantin; Turmaine, Mark; Wallon, David; Rovelet-Lecrux, Anne; Soininen, Hilkka; Volpi, Emanuela; Martin, Joanne E; Foo, Jia Nee; Becker, David L; Rostagno, Agueda; Ghiso, Jorge; Krsnik, Željka; Šimić, Goran; Kostović, Ivica; Mitrečić, Dinko; Francis, Paul T; Blennow, Kaj; Strydom, Andre; Hardy, John; Zetterberg, Henrik; Nižetić, Dean

A population of >6 million people worldwide at high risk of Alzheimer’s disease (AD) are those with Down Syndrome (DS, caused by trisomy 21 (T21)), 70% of whom develop dementia during lifetime, caused by an extra copy of β-amyloid-(Aβ)-precursor-protein gene. We report AD-like pathology in cerebral organoids grown in vitro from non-invasively sampled strands of hair from 71% of DS donors. The pathology consisted of extracellular diffuse and fibrillar Aβ deposits, hyperphosphorylated/pathologically conformed Tau, and premature neuronal loss. Presence/absence of AD-like pathology was donor-specific (reproducible between individual organoids/iPSC lines/experiments). Pathology could be triggered in pathology-negative T21 organoids by CRISPR/Cas9-mediated elimination of the third copy of chromosome-21-gene BACE2, but prevented by combined chemical β and γ-secretase inhibition. We found that T21-organoids secrete increased proportions of Aβ-preventing (Aβ1-19) and Aβ-degradation products (Aβ1-20 and Aβ1-34). We show these profiles mirror in cerebrospinal fluid of people with DS. We demonstrate that this protective mechanism is mediated by BACE2-trisomy and cross-inhibited by clinically trialled BACE1-inhibitors. Combined, our data prove the physiological role of BACE2 as a dose-sensitive AD-suppressor gene, potentially explaining the dementia delay in ∼30% of people with DS. We also show that DS cerebral organoids could be explored as pre-morbid AD-risk population detector and a system for hypothesis-free drug screens as well as identification of natural suppressor genes for neurodegenerative diseases.