Novel presenilin 1 and 2 double knock-out cell line for in vitro validation of PSEN1 and PSEN2 mutations

Mutations in APP (amyloid precursor protein), PSEN1 (presenilin 1) or PSEN2 (presenilin 2) are the main cause of early-onset familial forms of Alzheimer's disease (autosomal dominant AD or ADAD). These genes affect γ-secretase-dependent generation of Amyloid β (Aβ) peptides, the main constituent of amyloid plaques and one of the pathological hallmarks of AD. Evaluation of patients with ADAD includes assessment of family history, clinical presentation, biomarkers, neuropathology when available and DNA sequencing data. These analyses frequently uncover novel variants of unknown significance in ADAD genes. This presents a barrier to recruitment of such individuals into clinical trials, unless a biochemical test can demonstrate that a novel mutation results in altered APP processing in a manner consistent with pathogenicity. Here we describe generation and characterization of a novel presenilin 1 and 2 double knock-out in N2A mouse neuroblastoma cells using CRISPR/Cas9, which results in complete ablation of Aβ production, decreased Pen-2 expression and Nicastrin glycosylation. Because of the absence of background Aβ secretion from endogenous γ-secretases, these cells can be used for validation of PSEN1 and PSEN2 variant effects on production of Aβ or other γ-secretase substrates and for biochemical studies of γ-secretase function using novel variants. We examined several PSEN1 and PSEN2 mutations of known and unknown pathogenicity. Known mutants increased Aβ42/Aβ40 ratio with varying effect on Aβ40, Aβ42, total Aβ levels and Pen-2 expression, which aligns with previous work on these mutants. Our data on novel PSEN1 V142F, G206V and G206D mutations suggest that these mutations underlie the reported clinical observations in ADAD patients. We believe our novel cell line will be valuable for the scientific community for reliable validation of presenilin mutations and helpful in defining their pathogenicity to improve and facilitate evaluation of ADAD patients, particularly in the context of enrollment in clinical trials.