Insensitivity to Aβ42-lowering Nonsteroidal Anti-inflammatory Drugs and γ-Secretase Inhibitors Is Common among Aggressive Presenilin-1 Mutations

Abstract

A␤42-lowering nonsteroidal anti-inflammatory drugs (NSAIDs) constitute the founding members of a new class of ␥-secretase modulators that avoid side effects of pan-␥-secretase inhibitors on NOTCH processing and function, holding promise as potential disease-modifying agents for Alzheimer disease (AD). These modulators are active in cell-free ␥-secretase assays indicating that they directly target the ␥-secretase complex. Additional support for this hypothesis was provided by the observation that certain mutations in presenilin-1 (PS1) associated with early-onset familial AD (FAD) change the cellular drug response to A␤42-lowering NSAIDs. Of particular interest is the PS1-⌬Exon9 mutation, which provokes a pathogenic increase in the A␤42/A␤40 ratio and dramatically reduces the cellular response to the A␤42-lowering NSAID sulindac sulfide. This FAD PS1 mutant is unusual as a splice-site mutation results in deletion of amino acids Thr 291 -Ser 319 including the endoproteolytic cleavage site of PS1, and an additional amino acid exchange (S290C) at the exon 8/10 splice junction. By genetic dissection of the PS1-⌬Exon9 mutation, we now demonstrate that a synergistic effect of the S290C mutation and the lack of endoproteolytic cleavage is sufficient to elevate the A␤42/A␤40 ratio and that the attenuated response to sulindac sulfide results partially from the deficiency in endoproteolysis. Importantly, a wider screen revealed that a diminished response to A␤42-lowering NSAIDs is common among aggressive FAD PS1 mutations. Surprisingly, these mutations were also partially unresponsive to ␥-secretase inhibitors of different structural classes. This was confirmed in a mouse model with transgenic expression of the PS1-L166P mutation, in which the potent ␥-secretase inhibitor LY-411575 failed to reduce brain levels of soluble A␤42. In summary, these findings highlight the importance of genetic background in drug discovery efforts aimed at ␥-secretase, suggesting that certain AD mouse models harboring aggressive PS mutations may not be informative in assessing in vivo effects of ␥-secretase modulators and inhibitors.

Generation of Aβ38 and Aβ42 Is Independently and Differentially Affected by Familial Alzheimer Disease-associated Presenilin Mutations and γ-Secretase Modulation

“…Sulindac sulfide is known to modulate ␥-secretase activity by shifting the cleavage from amino acid 42 to amino acid 38 (10). In line with previous findings, the PS1 M146L mutation showed slightly greater sensitivity to treat- ment with sulindac sulfide, whereas the PS1 ⌬exon9 and PS1 L166P mutations failed to respond to the A␤ 42 -lowering activity (13,31) (Fig. 2).…”

“…However, many laboratories use transgenic mice overexpressing APP in combination with more or less aggressive PS mutations to enhance and accelerate amyloid plaque formation. Our data from the PS2 N141I mouse are in agreement with recent data from the PS1 L166P mouse (31). Such 38 .…”

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

“…Two exceptionally strong PS mutants, PS1 L166P and PS2 N141I, have been tested so far with GSM-1 and also do not respond to this highly potent compound (9). This has led to the concept that many pathogenic PS mutations, in particular those that generate high amounts of A␤ 42 , lock ␥-secretase in a GSM-resistant conformation such that the aberrant generation of A␤ 42 is maintained (9,22,23). Surprisingly, when we now analyzed the PS1 G384A mutant, which causes a similarly strong increase of the A␤ 42 to total A␤ ratio (total A␤ ϭ A␤ 38 ϩ A␤ 40 ϩ A␤ 42 ) as the PS1 L166P mutant as assessed by a highly sensitive and specific A␤ immunoassay (Fig.…”

“…Likewise, both familial and synthetic mutations at the ␥-secretase cleavage site domain showed the typical GSM responses (13). In contrast, although FAD mutations in PS still increase A␤ 38 in response to NSAIDs, lowering of A␤ 42 is not effective for the majority of these mutants (9,22,23). This was seen mostly for aggressive mutations with early disease onset that cause a strong increase of A␤ 42 , such as the PS1 L166P mutant, which was also resistant to the potent compound GSM-1 (9).…”

Amyloid beta 42 peptide (Aβ42)-lowering compounds directly bind to Aβ and interfere with amyloid precursor protein (APP) transmembrane dimerization

“…CHO cells stably overexpressing wild-type human APP751 and wild-type human PS1 were cultured as described previously (20). Cells were treated with compounds at 60 μM or DMSO for 24 h. Aliquots of medium (10 μL for detection of Aβ40, 100 μL for Aβ42) were analyzed for secreted Aβ peptides by ELISA using the monoclonal Aβ antibody IC16 as capture antibody and HRP-labeled antibodies against Aβ40 (BAP-24) or Aβ42 (BAP-15) (33) for detection.…”