Impact of Sustained Exposure to β-Amyloid on Calcium Homeostasis and Neuronal Integrity in Model Nerve Cell System Expressing α4β2 Nicotinic Acetylcholine Receptors

Although the interaction between beta-amyloid (A beta) and nicotinic acetylcholine receptors has been widely studied, the impact of prolonged exposure to A beta 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 A beta on the regulation of cellular and synaptic function. The differentiated rodent neuroblastoma cell line NG108-15 expressing exogenous high-affinity alpha 4 beta 2 nAChRs was exposed to soluble oligomeric A beta for several days. Ca2+ responses, expression levels of alpha 4 beta 2 nAChRs, rate of mitochondrial movement, mitochondrial fission, levels of reactive oxygen species, and nuclear integrity were compared between A beta-treated and untreated cells, transfected or not (mock-transfected) with alpha 4 beta 2 nAChRs. Sustained exposure of A beta(1-42) to alpha 4 beta 2 nAChR-transfected cells for several days led to increased Ca2+ responses on subsequent acute stimulation with A beta(1-42) or nicotine, paralleled by increased expression levels of alpha 4 beta 2 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 alpha 4 beta 2 nAChR-transfected cells treated with A beta(1-42). In addition, the presence of alpha 4 beta 2 nAChRs dramatically enhanced A beta(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 A beta in cells transfected with alpha 4 beta 2 nAChRs. Together, the results suggest that the presence of nAChRs sensitizes neurons to the toxic actions of soluble oligomeric A beta, perhaps contributing to the cholinergic deficit in Alzheimer disease.