NOVEL METHOD FOR OLIGOMERIC Aβ DETECTION REVEALS INTRACELLULAR ACCUMULATION OF Aβ UPON LOW-DOSE TREATMENT WITH A GAMMA-SECRETASE INHIBITOR

As the focus for Aβ-induced Alzheimer's disease (AD) pathology has shifted towards the oligomeric forms, there is a need for specific and sensitive detection of oligomeric Aβ (oAβ). Additionally, clinical trials using γ-secretase inhibitors have been halted due to lack of clinical efficacy and/or side effects. Recent in vitro studies suggest that low doses of γ-secretase inhibitors (GSI) may increase Aβ production. We hypothesised that low-dose treatment with the GSI DAPT could cause intracellular accumulation of oAβ and developed a novel method to monitor this process. A novel method for specific detection of oligomeric Aβ (oAβ) was developed using Duolink techology, where an Aβ N-terminal specific antibody was conjugated to Duolink PLUS and MINUS probes, respectively. The method was optimized using oAβ-fed SH-SY5Y cells and was thereafter used to study intracellular accumulation of oAβ in iPSC-derived human cortical neurons exposed to low doses of DAPT. Secreted levels of Aβ were also investigated upon DAPT treatment using mass spectrometry and immunocytochemical methods. Duolink probe-labelled 82E1 antibody successfully detected oAβ in cultured SH-SY5Y cells. The method was sensitive (lower limit of detection <125 nM) (Figure 1) and specific for the oligomeric form (no cross-reactivity with monomeric N-terminal Aβ fragments). Furthermore, low-dose treatment (2 and 20 nM) with DAPT increased the secretion of several Aβ peptides from iPSC derived human cortical neurons. This was accompanied by intracellular accumulation oAβ (Figure 2).