Activation of calpain in cultured neurons overexpressing Alzheimer amyloid precursor protein

We have previously reported that overexpression of wild-type amyloid precursor protein (APP) in postmitotic neurons induces cleavage-dependent activation of caspase-3 both in vivo and in vitro. In this study. we investigated the mechanism underlying APP-induced caspase-3 activation using adenovirus-mediated gene transfer into postmitotic neuron,, derived front human embryonal carcinoma NT2 cells. Overexpression of wild-type APP significantly increased intracellular Ca-45(2+) content prior to the activation of caspase-3 in NT2-derived neurons. Chelation of intracellulax Ca2+ markedly suppressed APP-induced activation of caspase-3. Furthermore, calpain, a Ca2+-dependent cysteine protease, was activated in neurons overexpressing APP as assessed by increased levels of calpain-cleaved alpha-fodrin and autolytic mu-calpain fragments. Neither calpain nor caspase-3 was activated in neuron,., expressing an APP mutant defective in the Abeta(1-20) domain. Calpain inhibitors almost completely suppressed APP-induced activation of neuronal caspase-3. E64d, a membrane permeable inhibitor of calpain. significantly suppressed APP-induced neuronal death. These results suggest that overexpression of wild-type APP activates calpain that mediates caspase-3 activation in postmitotic neurons. (C) 2002 Elsevier Science B.V. All rights reserved.