title: Effect of beta-amyloid peptide 1-42 on the cytoprotective action mediated by alpha7 nicotinic acetylcholine receptors in growth factor-deprived differentiated PC-12 cells.
abstract: Brain deposition of beta-amyloid peptide (Abeta1-42)-containing senile plaques is a consistent finding in Alzheimer's disease (AD). However, the link between Abeta1-42 and neuronal degeneration remains unclear. It has been reported that Abeta peptides bind with selectivity to alpha7 nicotinic acetylcholine receptors (alpha7nAChRs) and that the two proteins are associated in human AD brain tissue. A potential functional interaction between alpha7nAChRs and Abeta1-42 also has been suggested through the ability of nicotine to inhibit Abeta1-42-induced cytotoxicity. Differentiated PC-12 cells share several features in common with cholinergic basal forebrain neurons. The cells express alpha7nAChRs, they require growth factor stimulation for their maintenance and survival, and nicotine protects against cytotoxicity subsequent to growth factor withdrawal. Using these cells as a model system, we designed experiments to more directly determine whether Abeta peptides (Abeta1-42 and Abeta1-40) interfere with a potential nicotinic cytoprotective action and with the ability of nicotine to increase intracellular Ca2+. Differentiated PC-12 cells were preloaded with fura 2/acetoxymethyl ester and intracellular free Ca2+ levels were determined by fluorescent imaging. Nicotine-induced Ca2+ signals were inhibited by pretreatment with the alpha7nAChR-selective antagonists alpha-bungarotoxin and methyllycaconitine, and they were completely absent in cells maintained in Ca2+-free medium. The nicotine response also was blocked by pretreatment with 100 nM Abeta1-42. Nicotine (1-1000 muM) produced a concentration-dependent increase in cell viability in differentiated PC-12 cells that underwent nerve growth factor withdrawal for 24 h. Cell viability was maintained near 100% by 100 muM nicotine. The cytoprotective action of nicotine was efficiently antagonized by cotreatment with alpha7nAChR antagonists. A concentration-dependent inhibition of the cytoprotective action of nicotine also was produced by cotreatment with Abeta1-42 (1-100 nM), but not with Abeta40 -1. It is possible, therefore, that in AD, as growth factor support to basal forebrain cholinergic neurons declines, the interaction of Abeta peptides with alpha7nAChRs may enhance toxicity by interfering with an important nicotinic signal for neuronal viability.
authors.affiliation: Alzheimer's Research Center, Medical College of Georgia, Augusta, GA 30912-2300, USA.
authors.forename: Xinyu D
authors.initials: XD
authors.lastname: Li
authors.forename: Jerry J
authors.initials: JJ
authors.lastname: Buccafusco
mesh_terms: D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000818:Animals; D019610:Cytoprotection / Q000187:drug effects; D006133:Growth Substances / Q000378:metabolism*; D016716:PC12 Cells; D010446:Peptide Fragments / Q000494:pharmacology*; D020011:Protective Agents / Q000494:pharmacology*; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D016229:Amyloid beta-Peptides; C579167:Chrna7 protein, human; C579165:Chrna7 protein, rat; D006133:Growth Substances; D010446:Peptide Fragments; D020011:Protective Agents; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C075222:amyloid beta-protein (1-42)