Low-dose γ-secretase inhibition increases secretion of Aβ peptides and intracellular oligomeric Aβ

Abstract

γ-Secretase inhibitors have been considered promising drug candidates against Alzheimer's disease (AD) due to their ability to reduce amyloid-β (Aβ) production. However, clinical trials 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 may instead increase Aβ production. Using a stem cell-derived human model of cortical neurons and low doses of the γ-secretase inhibitor DAPT, the effects on a variety of Aβ peptides were studied using mass spectrometry. One major focus was to develop a novel method for specific detection of oligomeric Aβ (oAβ), and this was used to study the effects of low-dose γ-secretase inhibitor treatment on intracellular oAβ accumulation. Low-dose treatment (2 and 20nM) with DAPT increased the secretion of several Aβ peptides, especially Aβx-42. Furthermore, using the novel method for oAβ detection, we found that 2nM DAPT treatment of cortical neurons resulted in increased oAβ accumulation. Thus, low dose-treatment with DAPT causes both increased production of long, aggregation-prone Aβ peptides and accumulation of intracellular Aβ oligomers, both believed to contribute to AD pathology.

Partial reduction of amyloid β production by β-secretase inhibitors does not decrease synaptic transmission

“…Inhibition of γ-secretase using LY411575 decreased secretion of both Aβ40 and Aβ42 equally at all three doses, although the decrease of Aβ42 did not reach statistical significance. The preferential inhibition of Aβ40 over Aβ42 has earlier been shown for other γ-secretase inhibitors, by our group and others [44,45]. This biased inhibition results in an increased Aβ42 to Aβ40 ratio, which is believed to be more amyloidogenic and could be negative for synaptic function [46].…”

Identification of the Aβ37/42 peptide ratio in CSF as an improved Aβ biomarker for Alzheimer's disease

“…39 We treated both the HEK293-APPsw and the human iPSC-derived neurons with a very potent GSM, GSM4 (Figure 2C), as reported 40 ; this compound was resynthesized and characterized by us recently. 41 We observed the expected dose-dependent increase in short Aβs (37,38) and decrease in long Aβs (40, 42) (Figure 2D, E). In the HEK293-APPsw cells, GSM4 at as low as 0.29 pM could elevate Aβ37 by 118% but only decrease Aβ42 by 23% (Figure 2D).…”

“…Secreted Aβx‐37, x‐38, x‐40, and x‐42 were quantified in the conditioned media (Figure 2B). We observed the “paradoxical” increase of Aβ generation, especially x‐42, in the 20 nM to 200 nM low dose range of DAPT, an effect reported multiple times with GSIs (eg, 38 ). Further analysis of the pattern of DAPT inhibition showed that Aβ37 was more suppressed by DAPT than Aβ40 or Aβ42, suggesting that Aβ37 production is somewhat more sensitive to the pharmacological action of a γ‐secretase inhibitor.…”

Based on molecular structures: Amyloid-β generation, clearance, toxicity and therapeutic strategies

“…Surprisingly, recent in vitro studies have found that low doses of GSI may increase Aβ generation. Low doses of DAPT (a GSI) increased the generation of several Aβ peptides, particularly Aβ x– 42 , and increased Aβ oligomers were found in cortical neurons treated with low doses of DAPT ( Agholme et al, 2017 ). Other studies have found rebound effects caused by GSI, such as increased levels of PS1 and other γ-secretase subunits.…”