The consequences of reducing expression of the α7 nicotinic receptor by RNA interference and of stimulating its activity with an α7 agonist in SH-SY5Y cells indicate that this receptor plays a neuroprotective role in connection with the pathogenesis of Al

In order to examine the neuroprotective effects of the α7 nicotinic receptor (nAChR) in relationship to the pathogenesis of Alzheimer's disease (AD), neuroblastoma (SH-SY5Y) cells were transfected with small interference RNAs (siRNAs) that targets specifically towards α7 nAChR or exposed to 20 μM 3-[2,4-dimethoxybenzylidene] anabaseine (DMXB), a selective agonist of this same receptor. The levels of α7 nAChR mRNA and protein were measured by RT-PCR and Western blotting, respectively. The levels of the α-form of secreted amyloid precursor protein (αAPPs), total APP and the extracellular signal-regulated kinase 1/2 (ERK1/2) were also determined by Western blotting. SH-SY5Y cells transfected with siRNA or exposed to DMXB were then treated with 1 μM Aβ25–35, following which the levels of lipid peroxidation and rate of reduction of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] were characterized by utilizing spectrophotometric procedures. Compared to controls, SH-SY5Y cells transfected with siRNA expressed the decreases in the levels of α7 nAChR mRNA and protein by 81% and 69% lower levels, respectively; exhibited reduced levels of the αAPPs and ERK1/2 proteins; and demonstrated enhanced lipid peroxidation and a decreased rate of MTT reduction. In cells exposed to DMXB, the level of α7 nAChR protein was elevated by 23%, with no alteration in the content of the corresponding mRNA; the levels of the αAPPs and ERK1/2 proteins were increased. Inhibition of the expression of the α7 nAChR gene enhanced the toxicity exerted by Aβ, whereas stimulation of this receptor attenuated this toxicity exerted. These findings indicate that α7 nAChR may play a significant neuroprotective role by enhancing cleavage of APP by α-secretase, regulating signal transduction, improving antioxidant defenses and inhibiting the toxicity of Aβ, which is connected with the pathogenesis of AD.