Attenuated Aβ42 Responses to Low Potency γ-Secretase Modulators Can Be Overcome for Many Pathogenic Presenilin Mutants by Second-generation Compounds

Abstract

Sequential processing of the ␤-amyloid precursor protein by ␤-and ␥-secretase generates the amyloid ␤-peptide (A␤), which is widely believed to play a causative role in Alzheimer disease. Selective lowering of the pathogenic 42-amino acid variant of A␤ by ␥-secretase modulators (GSMs) is a promising therapeutic strategy. Here we report that mutations in presenilin (PS), the catalytic subunit of ␥-secretase, display differential responses to non-steroidal anti-inflammatory drug (NSAID)-type GSMs and more potent second-generation compounds. Although many pathogenic PS mutations resisted lowering of A␤ 42 generation by the NSAID sulindac sulfide, the potent NSAID-like second-generation compound GSM-1 was capable of lowering A␤ 42 for many but not all mutants. We further found that mutations at homologous positions in PS1 and PS2 can elicit differential A␤ 42 responses to GSM-1, suggesting that a positive GSM-1 response depends on the spatial environment in ␥-secretase. The aggressive pathogenic PS1 L166P mutation was one of the few pathogenic mutations that resisted GSM-1, and Leu-166 was identified as a critical residue with respect to the A␤ 42 -lowering response of GSM-1. Finally, we found that GSM-1-responsive and -resistant PS mutants behave very similarly toward other potent second-generation compounds of different structural classes than GSM-1. Taken together, our data show that a positive A␤ 42 response for PS mutants depends both on the particular mutation and the GSM used and that attenuated A␤ 42 responses to low potency GSMs can be overcome for many PS mutants by second generation GSMs. The amyloid ␤-peptide (A␤)4 is a 37-43-amino acid secreted peptide and an invariant pathological hallmark of Alzheimer disease (AD). The 42-amino acid variant A␤ 42 has been suggested to be causative for the disease by triggering the amyloid cascade, a sequence of pathogenic events that ultimately leads to neurodegeneration and dementia in affected patients (1). The pathogenic peptide is generated by a sequential cleavage of the ␤-amyloid precursor protein (APP) by ␤-and ␥-secretase (2). After ␤-secretase cleavage, ␥-secretase cleaves the C-terminal fragment of APP that is left in the membrane by an intramembrane cleavage to release the various A␤ species (3-5). Although A␤ 42 is normally a minor species produced by this cleavage besides the major A␤ 40 species, its production is enhanced by familial AD (FAD) mutations in presenilin (PS) 1 and PS2, the catalytic component of ␥-secretase (6), as well as by a subset of FAD mutations in APP. Targeting ␤-and ␥-secretase by specific inhibitors is one of the current approaches toward an effective AD treatment (7). With respect to ␥-secretase, however, ␥-secretase inhibitors also block the cleavage of Notch1, a major physiological ␥-secretase substrate and, thus, the generation of the Notch1 intracellular domain (NICD), which is a crucial signaling molecule controlling cell differentiation (7). Interfering with the cleavage of this substrate accounts for adverse side effects in...

Specific Triazine Herbicides Induce Amyloid-β42 Production

“…1A, 1B): ametryn, prometryn, dipropetryn, terbutryn, cybutryne, dimethametryn. As observed with aftins [13,14], Aβ 42 production was strongly inhibited by β-(inhibitor IV) and γ-secretases (BMS 299897, DAPT) inhibitors and by a γ-secretase modulator ('Torrey Pines' compound) (the latter induces a dose-dependent increase in Aβ 38 and a decrease in Aβ 42 and Aβ 40 ) [30,31] (Fig. 1C).…”

“…A panel of 236 triazines was selected in a large triazines library constructed as described previously [30,31]. Twenty products displayed some activity (45-65) (Supplementary Table S5).…”

“…The γ-secretase modulator ('Torrey Pines' compound) was synthesized as previously described [14,30,31]. DMSO, Nonidet P-40, Tween-20, CHAPSO (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonate), dithiothreitol (DTT), bovine serum albumin (BSA), Na 2 CO 3 , NaHCO 3 , citric acid monohydrate, Na 2 HPO 4 .2H 2 …”

Novel γ-Secretase Enzyme Modulators Directly Target Presenilin Protein

“…Characterization of GSMs-Modulatory activities of GSMs, including dose-response curves, were analyzed in cell-based and cell-free ␥-secretase assays as described previously (13)(14)(15). Additional details are described in the supplemental material, including cell lines and antibodies used for analysis.…”

Cleavage of amyloid precursor protein by an archaeal presenilin homologue PSH

“…Considerable effort has been dedicated to the discovery of modulators that, upon binding to γ-secretase, may decrease the Aβ42/Aβ40 ratio. The small molecules GSM-1 and E2012 are known to achieve this effect by inhibiting the production of Aβ42 (24)(25)(26)(27) (Fig. S3).…”