Amyloid β-protein potentiates tunicamycin-induced neuronal death in organotypic hippocampal slice cultures

We have assessed amyloid beta protein (A beta)-induced neurotoxicity, with and without added tunicamycin (TM), an inhibitor of N-glycosylation in the encloplasmic reticulum (ER), in rat organotypic hippocampal slice cultures (OHCs). In the rat OHCs cultured for 3 weeks, there was little neurotoxicity after treatment with A beta(25-35) (25 mu M) alone for 48 h. However, with TM alone, concentration-dependent neuronal death was observed at concentrations between 20 and 80 mu g/mL. When amyloid-beta protein was combined with tunicamycin (A beta+TM), cell death was more acute than with TM alone. Western blot analysis revealed that calpain activity and the active forms of caspase-12 and caspase-3 was increased after exposure to A beta+TM as compared with exposure to TM alone. In contrast, the levels of glucose regulated protein (GRP)94, GRP78 and C/EBP homologous protein (CHOP) were not changed in the presence of A beta. A beta potentiation of TM neurotoxicity was reversibly blocked by S-allyl-L-cysteine (SAC), an organosulfur compound purified from aged garlic extract, and the L-type calcium channel blocker, nifeclipine, in a restricted neuronal area of the OHCs. Simultaneously applied SAC also reversed the increases in calpain activity and the active forms of caspase-12 and caspase-3 by A beta+TM with no change in the increased levels of GRP94, GRP78 and CHOP. These data indicate that AP facilitates the calpain-caspase-12-caspase-3 pathway, thus potentiating TM-induced neuronal death in the hippocampus. (c) 2007 IBRO. Published by Elsevier Ltd. All rights reserved.