The influence of inhibiting or stimulating the expression of the α3 subunit of the nicotinic receptor in SH-SY5Y cells on levels of amyloid-β peptide and β-secretase.

To examine the effects of the α3 subunit of the nicotinic acetylcholine receptor (nAChR) on the expression of β-secretase and the concomitant level of amyloid-β (Aβ), SH-SY5Y neuroblastoma cells were either transfected with small interference RNAs (siRNAs) specifically targeting this subunit or exposed to nicotine. The levels of α3 nAChR mRNA and protein, as well as the corresponding levels of BACE1 (which cleaves the β-site of APP) and BACE2 (cleaving in the Aβ domain) were determined by real-time PCR and Western blotting, respectively. The levels of Aβ(1-42) in culture media were determined by an Elisa procedure. In SH-SY5Y cells transfected with siRNA, the levels of α3 nAChR mRNA and protein were reduced by 96% and 88%, respectively; the levels of BACE1 mRNA and protein were significantly enhanced, while those of BACE2 were reduced; and the level of Aβ in the culture medium was elevated. In contrast, when untransfected SH-SY5Y cells were exposed to nicotine, the levels of both α3 nAChR mRNA and protein were enhanced; while the levels of BACE1 mRNA and protein were diminished and the corresponding levels of BACE2 enhanced; and the level of Aβ in the culture medium was attenuated. These results indicate that the α3 subunit of nAChR inhibits the production of Aβ by reducing the expression of BACE1 and elevating the expression of BACE2, suggesting that this subunit might play an important neuroprotective role in connection with the pathogenesis of AD.