Impact of sustained exposure to ß-amyloid on calcium homeostasis and neuronal integrity in model nerve cell system expressing α4ß2 nicotinic acetylcholine receptors.

Although the interaction between ß-amyloid (Aß) and nicotinic acetylcholine receptors has been widely studied, the impact of prolonged exposure to Aß on nAChR expression and signaling is not known. In this study, we employed a neuronal culture model to better understand the impact of sustained exposure of Aß on the regulation of cellular and synaptic function. The differentiated rodent neuroblastoma cell line NG108-15 expressing exogenous high-affinity α4ß2 nAChRs was exposed to soluble oligomeric Aß for several days. Ca(2+) responses, expression levels of α4ß2 nAChRs, rate of mitochondrial movement, mitochondrial fission, levels of reactive oxygen species, and nuclear integrity were compared between Aß-treated and untreated cells, transfected or not (mock-transfected) with α4ß2 nAChRs. Sustained exposure of Aß(1-42) to α4ß2 nAChR-transfected cells for several days led to increased Ca(2+) responses on subsequent acute stimulation with Aß(1-42) or nicotine, paralleled by increased expression levels of α4ß2 nAChRs, likely the result of enhanced receptor recycling. The rate of mitochondrial movement was sharply reduced, whereas the mitochondrial fission protein pDrp-1 was increased in α4ß2 nAChR-transfected cells treated with Aß(1-42). In addition, the presence of α4ß2 nAChRs dramatically enhanced Aß(1-42)-mediated increases in reactive oxygen species and nuclear fragmentation, eventually leading to apoptosis. Our data thus show disturbed calcium homeostasis coupled with mitochondrial dysfunction and loss of neuronal integrity on prolonged exposure of Aß in cells transfected with α4ß2 nAChRs. Together, the results suggest that the presence of nAChRs sensitizes neurons to the toxic actions of soluble oligomeric Aß, perhaps contributing to the cholinergic deficit in Alzheimer disease.