P4–267: ADAM10 activation is required for green tea EGCG–induced alpha–secretase cleavage of amyloid precursor protein

Since α–secretase cleaves within the Aβ peptide domain, its activation may even have the double advantage of not only precluding the neurotoxic Aβ peptide formation but also generating the putatively neuroprotective sAPP–α. Thus, it would appear highly advantageous to shift APP cleavage from the amyloidogenic β–secretase to the non–amyloidogenic α–secretase cleavage. Indeed, we have recently shown that green tea polyphenol (–)–epigallocatechin–3–gallate (EGCG) exerts a beneficial role on reducing brain Aβ levels, resulting in mitigation of cerebral amyloidosis in a mouse model of Alzheimer's disease (AD). EGCG seems to accomplish this by modulating amyloid precursor protein (APP) processing, resulting in enhanced cleavage of the α–C–terminal fragment (α–CTF) of APP and corresponding elevation of the N–terminal APP product, soluble APP–α (sAPP–α). These beneficial effects were associated with increased α–secretase cleavage activity, but no significant alteration in β– or γ–secretase activities. To gain insight into the molecular mechanism whereby EGCG modulates APP processing, we evaluated the involvement of three candidate α–secretase enzymes, α–disintegrin–and–metalloprotease (ADAM) 9, 10, or 17, in EGCG–induced non–amyloidogenic APP metabolism. Results show that EGCG treatment of N2a cells stably transfected with “Swedish” mutant human APP (SweAPP N2a cells) leads to markedly elevated active (∼60 kDa mature form) ADAM10 protein. Elevation of active ADAM10 significantly correlated with increased α–CTF cleavage, and elevated sAPP–α in vitro and in vivo. To definitively test the contribution of ADAM10 to non–amyloidogenic APP metabolism, small interfering RNA knock–down of ADAM9, 10, or 17 mRNA was employed. Results show that ADAM10 (but not ADAM9 or 17) is critical for EGCG–mediated α–secretase cleavage activity. In summary, ADAM10 activation is necessary for EGCG promotion of non–amyloidogenic (α–secretase cleavage) APP processing. Thus, ADAM10 represents an important pharmacotherapeutic target for the treatment of cerebral amyloidosis in AD.