Preventing Expression of the Nicotinic Receptor Subunit α7 in SH-SY5Y Cells with Interference RNA Indicates that this Receptor may Protect Against the Neurotoxicity of Aβ

The present aim was to characterize the influence of the alpha 7 nicotinic acetylcholine receptor (nAChR) on BACE, the enzyme that cleaves the amyloid precursor protein (APP) at the beta-site, as well as on the oxidative stress induced by amyloid-beta peptide (A beta). To this end, human neuroblastoma SH-SY5Y cells were transfected with siRNAs targeting the alpha 7 nAChR subunit and/or exposed to A beta(1-42). For alpha 7 nAChR, BACE1 (cleaving at the beta-site of APP) and BACE2 (cleaving within the A beta domain), alpha-secretase (ADAM10), and the two components of gamma-secretase, PS and NCT, the mRNA and protein levels were determined by real-time PCR and Western blotting, respectively. The level of A beta(1-42) in the cell culture medium was determined by an ELISA procedure. The extent of lipid peroxidation and activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were assayed spectrophotometrically. In the transfected SH-SY5Y cells, expression of alpha 7 nAChR was reduced; the level of BACE1 increased and that of BACE2 decreased; the amount of ADAM10 lowered; and the level of PS raised. Moreover, the level of A beta(1-42) in the culture medium was elevated. Treatment of non-transfected cells with A beta elevated the level of malondialdehyde (MDA) and lowered the activities of SOD and GSH-Px and these changes were potentiated by inhibiting expression of alpha 7 nAChR. These results indicate that alpha 7 nAChR plays a significant role in amyloidogenic metabolism of APP and the oxidative stress evoked by A beta, suggesting that this receptor might help protect against the neurotoxicity of A beta.