Cell death induced by a caspase-cleaved transmembrane fragment of the Alzheimer amyloid precursor protein

The Alzheimer amyloid precursor protein (APP) is a transmembrane protein whose abnormal processing is associated with the pathogenesis of Alzheimer's disease. Activated caspases cleave APP and generate its carboxyl-terminally truncated fragment (APPdeltaC31). We have previously reported that overexpression of wild-type APP induces caspase-3 activation and apoptosis in postmitotic neurons. We now report that APPdeltaC31 potentially plays pathophysiological roles in neuronal death. Adenovirus-mediated overexpression of wild-type APP695 induced activation of caspase-3 and accumulation of APPdeltaC31 in postmitotic neurons derived from human NT2 embryonal carcinoma cells, whereas an APP mutant lacking the Abeta(1-20) region induced neither caspase-3 activation nor APPdeltaC31 generation. Inhibition of caspase-3 suppressed the generation of APPdeltaC31 in APP-overexpressing neurons. Forced expression of APPdeltaC31 induced apoptotic changes of neurons and non-neuronal cells, but failed to activate caspase-3. The cytotoxicity of APPdeltaC31 was also dependent on the Abeta(1-20) region. These results suggest that accumulation of wild-type APP activates neuronal caspase-3 to generate APPdeltaC31 that mediates caspase-3-independent cell death.