Increased Aβ1-42 Production Sensitizes Neuroblastoma Cells for ER Stress Toxicity

Alzheimer's disease ( AD) is characterized by the aggregation and subsequent deposition of misfolded beta-amyloid (A beta) peptide. The unfolded protein response ( UPR) is activated by misfolded protein stress in the endoplasmic reticulum ( ER). In previous studies we demonstrated mild activation of the UPR by extracellularly applied oligomeric but not fibrillar A beta(1-42). In addition, we showed that oligomeric A beta(1-42) is internalized by cells, whereas fibrillar A beta(1-42) remains on the outside of the cell. Inhibition of A beta uptake specifically inhibits toxicity of A beta(1-42) oligomers, underscoring the toxic potential of intracellular A beta Therefore, in the present study, we investigated the connection between intracellularly produced A beta and the ER stress response, using human neuroblastoma cells overexpressing either wild type APP695 ( APPwt) or APP695(V717F) ( APPmut). Both cell lines secrete higher levels of A beta(1-40) and A beta(1-42) compared to the parental line. In addition, APPmut produces more A beta(1-42) than APPwt. Whereas the basal levels of UPR markers are not different, we find augmented UPR induction in response to ER stress in both APP overproducing cell lines compared to the parental cell line, with the strongest UPR activation in APPmut cells. In addition, ER stress toxicity was highest in APPmut cells, strongly suggesting a connection with the production of A beta(1-42). The difference in ER stress mediated toxicity between the APPwt and APPmut cell lines is alleviated by pretreatment with gamma-secretase inhibitor, indicating that it is dependent on A beta production and in particular on A beta(1-42). Our data indicate that increased A beta(1-42) production sensitizes neuroblastoma cells for ER stress toxicity.