Expression levels of the α7 nicotinic acetylcholine receptor in the brains of patients with Alzheimer's disease and their effect on synaptic proteins in SH-SY5Y cells.

Alzheimer's disease (AD) is a chronic neurodegenerative, and abnormal aggregation of the neurotoxic ß amyloid (Aß) peptide is an early event in AD. The present study aimed to determine the correlation between the nicotinic acetylcholine receptor α7 subunit (α7 nAChR) and Aß in the brains of patients with AD, and to investigate whether the increased expression levels of the α7 nAChR could alter the neurotoxicity of Aß. The expression levels of α7 nAChR and Aß in the brains of patients with AD and healthy brains were analyzed using immunofluorescence. Moreover, SH­SY5Y cells were used to stably overexpress or silence α7 nAChR expression levels, prior to the treatment with or without 1 µmol/l Aß1­42 oligomer (AßO). The mRNA and protein expression levels of α7 nAChR, synaptophysin (SYP), postsynaptic density of 95 kDa (PSD­95) and synaptosomal­associated protein of 25 kDa (SNAP­25) were subsequently analyzed using reverse transcription­quantitative PCR and western blotting. In addition, the concentration of acetylcholine (ACh) and the activity of acetylcholinesterase (AChE) were analyzed using spectrophotometry, while the cell apoptotic rate was determined using flow cytometry. The expression of Aß in the brains of patients with AD was found to be significantly increased, whereas the expression of α7 nAChR was significantly decreased compared with the healthy control group. In vitro, the expression levels of α7 nAChR were significantly increased or decreased following the overexpression or silencing of the gene, respectively. Consistent with these observations, the mRNA and protein expression levels of SYP, PSD­95 and SNAP­25 were also significantly increased following the overexpression of α7 nAChR and decreased following the genetic silencing of the receptor. In untransfected or negative control cells, the expression levels of these factors and the apoptotic rate were significantly reduced following the exposure to AßO, which was found to be attenuated by α7 nAChR overexpression, but potentiated by α7 nAChR RNA silencing. However, no significant differences were observed in either the ACh concentration or AChE activity following transfection. Collectively, these findings suggested that α7 nAChR may protect the brains of patients with AD against Aß, as α7 nAChR overexpression increased the expression levels of SYP, SNAP­25 and PSD­95, and attenuated the inhibitory effect of Aß on the expression of these synaptic proteins and cell apoptosis. Overall, this indicated that α7 nAChR may serve an important neuroprotective role in AD.

[Effects of α3 neuronal nicotinic acetylcholine receptor on cell apoptosis and p38 MAPK signal transduction pathway in SH-SY5Y cells].

OBJECTIVE: To investigate the effects of α3 neuronal nicotinic acetylcholine receptor (nAChR) on apoptosis and p38 signal transduction pathway in SH-SY5Y cells and to assess the roles of α3 nAChR in the pathogenesis of Alzheimer's disease (AD). METHODS: The levels of α3 nAChR mRNA and protein were measured by real-time PCR and Western blot, respectively, in SH-SY5Y cells transfected with α3 nAChR siRNA. The mRNA level of bcl-2 and bax was measured by the real-time PCR. The siRNA transfected SH-SY5Y cells and control were then treated with 10 µmol/L Aß25-35 for another 48 h, and the change in apoptotic rate and the levels of p-p38 and p38 were measured by flow cytometry and Western blot. Subsequently these SH-SY5Y cells were exposed to a blocker of p38 protein, and the apoptotic rate was measured again. RESULTS: Compared to the controls, the expression of α3 nAChR at mRNA and protein levels in the SH-SY5Y cells transfected with α3 nAChR siRNA decreased by 95% and 86%, respectively; the mRNA levels of bax increased 2.11 times and that for bcl-2 decreased 0.53 times. The apoptotic rate was unaffected (3.40% ± 0.20%); but it increased after Aß25-35 treatment (24.52% ± 1.59%); the level of p-p38 protein also increased by 178% in the α3 nAChR inhibited cells treated with Aß25-35. Compared to controls, the Aß25-35-treated SH-SY5Y cells and the Aß25-35-treated and siRNA-transfected cells both showed a reduction in apoptosis after treatment with p38 blocker, especially in the former. CONCLUSION: The siRNA silencing of α3 nAChR mRNA may enhance the effect of Aß25-35 on the cell apoptosis by increasing the levels of p38 protein and bax mRNA and decreasing the level of bcl-2 mRNA, which may play a role in the pathogenesis of AD.

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 Aß.

The present aim was to characterize the influence of the α7 nicotinic acetylcholine receptor (nAChR) on BACE, the enzyme that cleaves the amyloid precursor protein (APP) at the ß-site, as well as on the oxidative stress induced by amyloid-ß peptide (Aß). To this end, human neuroblastoma SH-SY5Y cells were transfected with siRNAs targeting the α7 nAChR subunit and/or exposed to Aß1-42. For α7 nAChR, BACE1 (cleaving at the ß-site of APP) and BACE2 (cleaving within the Aß domain), α-secretase (ADAM10), and the two components of γ-secretase, PS and NCT, the mRNA and protein levels were determined by real-time PCR and Western blotting, respectively. The level of Aß1-42 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 α7 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 Aß1-42 in the culture medium was elevated. Treatment of non-transfected cells with Aß elevated the level of malondialdehyde (MDA) and lowered the activities of SOD and GSH-Px and these changes were potentiated by inhibiting expression of α7 nAChR. These results indicate that α7 nAChR plays a significant role in amyloidogenic metabolism of APP and the oxidative stress evoked by Aß, suggesting that this receptor might help protect against the neurotoxicity of Aß.