A monoclonal antibody to amyloid precursor protein induces neuronal apoptosis

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.