Alzheimer’s-Causing Mutations Shift Aβ Length by Destabilizing γ-Secretase-Aβn Interactions

Abstract

Alzheimer's disease (AD)-linked mutations in Presenilins (PSEN) and the amyloid precursor protein (APP) lead to production of longer amyloidogenic Aβ peptides. The shift in Aβ length is fundamental to the disease; however, the underlying mechanism remains elusive. Here, we show that substrate shortening progressively destabilizes the consecutive enzyme-substrate (E-S) complexes that characterize the sequential γ-secretase processing of APP. Remarkably, pathogenic PSEN or APP mutations further destabilize labile E-S complexes and thereby promote generation of longer Aβ peptides. Similarly, destabilization of wild-type E-S complexes by temperature, compounds, or detergent promotes release of amyloidogenic Aβ. In contrast, E-Aβ stabilizers increase γ-secretase processivity. Our work presents a unifying model for how PSEN or APP mutations enhance amyloidogenic Aβ production, suggests that environmental factors may increase AD risk, and provides the theoretical basis for the development of γ-secretase/substrate stabilizing compounds for the prevention of AD.

Both positional and chemical variables control in vitro proteolytic cleavage of a presenilin ortholog

“…1D, Table 1). For mIAP L275F , corresponding to the presenilin L435F FAD mutant (34)(35)(36), catalytic efficiency is similar to WT, but this is due to the countering effect of a ~60% decrease in Vmax combined with 50% improvement in Km (Fig. 1D, Table 1).…”

Aβ43‐producing PS1 FAD mutants cause altered substrate interactions and respond to γ‐secretase modulation

“…Source data are available online for this figure. ª 2019 The Authors EMBO reports 21: e47996 | 2020 trimming pathway and the generation of the pathogenic longer Ab species [31,38]. Source data are available online for this figure. ª 2019 The Authors EMBO reports 21: e47996 | 2020 trimming pathway and the generation of the pathogenic longer Ab species [31,38].…”

CRISPR Transcriptional Activation Analysis Unmasks an Occult γ-Secretase Processivity Defect in Familial Alzheimer’s Disease Skin Fibroblasts

“…We hypothesize that once GS carboxypeptidase activity is placed under substrate pressure, due to increased expression of APP or BACE1 , such as seen in neuronal cultures, a carboxypeptidase activity deficit is revealed in the FAD fibroblast cultures, leading to a further shift in the Aβ42/Aβ40 ratio (Figure 4G). PSEN FAD-associated mutations have been reported to cause a premature release of longer, intermediary substrates/products during the sequential carboxypeptidase cleavage (Chavez-Gutierrez et al, 2012), and a recent publication showed that this is a consequence of impaired catalytic γ-Secretase activity (Szaruga et al, 2017). It is possible that increased concentrations of longer Aβ forms, in the context of PSEN mutations, drive competition at the GS catalytic site in a concentration-dependent manner, thus impairing GS processivity (Figure 4G), but this remains to be demonstrated.…”

“…A traditional loss of function hypothesis propose that overall loss of PSEN function, due to the lower endopeptidase activity, causes age-dependent neurodegeneration, and cognitive impairment, without increasing Aβ (Saura et al, 2004; Shen and Kelleher, 2007; Heilig et al, 2010; Wines-Samuelson et al, 2010; Watanabe et al, 2012; Heilig et al, 2013; Xia et al, 2015; Xia et al, 2016; Sun et al, 2017). Recently, several reports have proposed that PSEN mutations increase the Aβ42/Aβ40 due to a dominant reduction in GS carboxypeptidase activity (Quintero-Monzon et al, 2011; Chavez-Gutierrez et al, 2012; Fernandez et al, 2014; Szaruga et al, 2015; Szaruga et al, 2017). Data herein obtained from human fibroblasts suggest that both a neomorphic mutation shifting GS endopeptidase activity to the Aβ48 product line, and a loss of carboxypeptidase function that is unmasked under substrate pressure contribute to the increased Aβ42/Aβ40 ratio.…”