Although there is considerable evidence suggesting that altered metabolism
of beta-amyloid precursor protein (APP) and accumulation of its beta-amyloi
d fragment are key features of Alzheimer's disease (AD), the normal physiol
ogical function of APP remains elusive. We investigated the potential role
of APP in neurons using the monoclonal antibody 22C11, which binds to the e
xtracellular domain of the human, rat, or mouse APP. Exposure of cortical n
eurons to 22C11 induced morphological changes including neurite degeneratio
n, nuclear condensation, and internucleosomal DNA cleavage that were consis
tent with neurons dying by apoptosis, Supporting a role for 22C11-mediated
apoptosis occurring by binding to APP were data demonstrating that preincub
ation of 22C11 with either purified APP or a synthetic peptide (APP(66-81))
that contains the epitope for 22C11 significantly attenuated neuronal dama
ge induced by 22C11. The specificity of 22C11 was further supported by data
showing no apparent effects of either mouse IgG or the monoclonal antibody
P2-1, which is specific for the aminoterminal end of human but not rat APP
. In addition, biochemical features indicative of apoptosis were the format
ion of 120- and 150-kDa breakdown products of fodrin following treatment of
cortical neurons with 22C11. Both the morphological and the biochemical ch
anges induced by 22C11 were prevented following pretreatment of neurons wit
h the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(O-methyl)-f
luoromethyl ketone. Prior incubation of cortical neurons with GSH ethyl est
er (GEE), a cell-permeable form of GSH, resulted in complete protection fro
m the 22C11 insult, thus implicating an oxidative pathway in 22C11-mediated
neuronal degeneration. This was further supported by the observation that
prior treatment of neurons with buthionine sulfoximine, an inhibitor of gam
ma-glutamylcysteinyl synthetase, potentiated the toxic effects of 22C11. Fi
nally, with use of compartmented cultures of hippocampal neurons, it was al
so demonstrated that selective application of 22C11 caused local neuritic d
egeneration that was prevented by the addition of GEE to the neuritic compa
rtment. Thus, the binding of a monoclonal antibody to APP initially trigger
s neurite degeneration that is followed by caspase-dependent apoptosis in n
euronal cultures and illustrates a novel property of this protein in neuron
s that may contribute to the profound neuronal cell death associated with A
D.