Endoplasmic reticulum stress-induced cysteine protease activation in cortical neurons - Effect of an Alzheimer's disease-linked presenilin-1 knock-inmutation

Endoplasmic reticulum (ER) stress elicits protective responses of chaperone induction and translational suppression and, when unimpeded, leads to casp ase-mediated apoptosis. Alzheimer's disease-linked mutations in presenilin- 1 (PS-1) reportedly impair ER stress-mediated protective responses and enha nce vulnerability to degeneration. We used cleavage site-specific antibodie s to characterize the cysteine protease activation responses of primary mou se cortical neurons to ER stress and evaluate the influence of a PS-1 knock -in mutation on these and other stress responses. Two different ER stressor s lead to processing of the ER-resident protease procaspase-12, activation of calpain, caspase-3, and caspase-6, and degradation of ER and non-ER prot ein substrates. Immunocytochemical localization of activated caspase-3 and a cleaved substrate of caspase-6 confirms that caspase activation extends i nto the cytosol and nucleus. ER stress-induced proteolysis is unchanged in cortical neurons derived from the PS-1 P264L knock-in mouse. Furthermore, t he PS-1 genotype does not influence stress-induced increases in chaperones Grp78/BiP and Grp94 or apoptotic neurodegeneration. A similar lack of effec t of the PS-1 P264L mutation on the activation of caspases and induction of chaperones is observed in fibroblasts. Finally, the PS-1 knock-in mutation does not alter activation of the protein kinase PKR-like ER kinase (PERK), a trigger for stress-induced translational suppression. These data demonst rate that ER stress in cortical neurons leads to activation of several cyst eine proteases within diverse neuronal compartments and indicate that Alzhe imer's disease-linked PS-1 mutations do not invariably alter the proteolyti c, chaperone induction, translational suppression, and apoptotic responses to ER stress.