Fibroblasts from FAD-linked presenilin 1 mutations display a normal unfolded protein response but overproduce Aβ42 in response to tunicamycin

Many patients affected by early onset familial Alzheimer's disease (FAD), carry mutations in the presenilin 1 (PSI) gene. Since it has been suggested that FAD-linked PSI mutations impair the unfolded protein response (UPR) due to endoplasmic reticulum (ER) stress, we analyzed the UPR and amyloid beta-protein processing in fibroblasts hearing various PSI mutations. Neither in normal conditions nor after induction of ER stress with DTT or tunicamycin were the mRNA levels of UPR-responsive genes (BiP and PDI) significantly different in control and FAD fibroblasts. DTT, which blocked APP transport to the Golgi, caused a 30% decrease of secreted Abeta42 in wild type and PSI mutant fibroblasts. In contrast, tunicamycin, which allowed exit of APP from the ER, increased secreted Abeta42 only in PSI mutant fibroblasts. Our findings suggest that, although the UPR is active in fibroblasts from FAD patients, mutant PSI may selectively increase Abeta42 secretion when N-glycosylation is impaired. (C) 2004 Elsevier Inc. All rights reserved.