Independent relationship between amyloid precursor protein (APP) dimerization and γ-secretase processivity

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Altered amyloid precursor protein (APP) processing is linked to Alzheimer's disease (AD).
• APP dimerization, particularly of the C99 fragment, has been hypothesized to influence amyloid-beta (Aβ) production by gamma-secretase.
• Previous studies present conflicting data on whether APP dimers are substrates for gamma-secretase.

Purpose of the Study:

• To investigate the impact of substrate multimerization on gamma-secretase cleavage and Aβ production.
• To evaluate the role of specific APP mutations (3xK-APP) in Aβ production and dimerization.
• To determine how substrate sequence and multimerization affect gamma-secretase processivity.

Main Methods:

• Generation of recombinant wild-type (WT) and 3xK-C100 APP carboxyl-terminal fragment (CTF) substrates.
• Isolation and purification of monomeric, dimeric, and trimeric forms of these substrates.
• Assessment of gamma-secretase ε-cleavage site utilization and Aβ production from different substrate forms.

Main Results:

• Substrate multimerization significantly impedes gamma-secretase cleavage, regardless of the substrate sequence.
• The monomeric form of the 3xK-C100 mutant increased long Aβ production without altering initial ε-cleavage site utilization.
• These findings confirm that dimeric substrates are inefficient substrates for gamma-secretase.

Conclusions:

• APP substrate multimerization is a critical factor that impedes gamma-secretase activity.
• Specific primary sequence determinants within APP substrates can alter gamma-secretase processivity, independent of multimerization.
• Understanding these mechanisms is crucial for developing therapeutic strategies targeting Aβ production in Alzheimer's disease.