ADAM10 is the physiologically relevant, constitutive α-secretase of the amyloid precursor protein in primary neurons

The amyloid precursor protein (APP) undergoes constitutive shedding by a protease activity called α-secretase. This is considered an important mechanism preventing the generation of the Alzheimer's disease amyloid-β peptide (Aβ). α-Secretase appears to be a metalloprotease of the ADAM family, but its identity remains to be established. Using a novel α-secretase-cleavage site-specific antibody, we found that RNAi-mediated knockdown of ADAM10, but surprisingly not of ADAM9 or 17, completely suppressed APP α-secretase cleavage in different cell lines and in primary murine neurons. Other proteases were not able to compensate for this loss of α-cleavage. This finding was further confirmed by mass-spectrometric detection of APP-cleavage fragments. Surprisingly, in different cell lines, the reduction of α-secretase cleavage was not paralleled by a corresponding increase in the Aβ-generating β-secretase cleavage, revealing that both proteases do not always compete for APP as a substrate. Instead, our data suggest a novel pathway for APP processing, in which ADAM10 can partially compete with γ-secretase for the cleavage of a C-terminal APP fragment generated by β-secretase. We conclude that ADAM10 is the physiologically relevant, constitutive α-secretase of APP.