Substrate-targeting gamma-secretase modulators

Area of Science:

• Neuroscience
• Biochemistry
• Pharmacology

Background:

• Alzheimer's disease (AD) therapy targets lowering amyloid-beta 42 (Abeta42) using gamma-secretase modulators (GSMs).
• The precise molecular target of GSMs within the gamma-secretase pathway remains incompletely understood.
• Identifying GSM targets is crucial for developing effective AD therapeutics.

Purpose of the Study:

• To identify the direct molecular targets of small-molecule gamma-secretase modulators (GSMs).
• To elucidate the mechanism by which GSMs modulate Abeta42 production and amyloid-beta aggregation.
• To explore the therapeutic potential of substrate-targeting GSMs for Alzheimer's disease.

Main Methods:

• Development and application of biotinylated photoactivatable GSMs (photoprobes).
• Affinity labeling assays in human neuroglioma H4 cells to identify protein targets.
• Competition assays with various GSMs and substrate-specific labeling experiments.
• Site-directed mutagenesis of the amyloid precursor protein (APP) binding site.

Main Results:

• GSM photoprobes labeled the amyloid precursor protein (APP), its carboxy-terminal fragments, and amyloid-beta peptide, but not core gamma-secretase components.
• GSM interaction was localized to residues 28-36 of amyloid-beta, a region critical for aggregation.
• GSMs altered the production of cell-derived amyloid-beta oligomers, and APP mutations affected GSM sensitivity.
• Substrate labeling by GSMs was more efficient for APP than for Notch.

Conclusions:

• GSMs act by directly targeting the APP substrate, not the gamma-secretase enzyme complex.
• This substrate-targeting mechanism links modulation of Abeta42 production with inhibition of amyloid-beta aggregation.
• This dual action offers a potentially synergistic therapeutic strategy for Alzheimer's disease, broadening the concept of druggable targets.