Beta-Amyloid Blockade of Hippocampal Nicotinic Alpha7-R*

University Of California San Diego, La Jolla CA

Investigators

Abstract

Alzheimer's Disease Drug Discovery. Alzheimer's disease is a physiologically devastating condition that is threatening to reach epidemic proportions as the population ages. Cholinergic deficit is a widely recognized aspect of Alzheimer's disease, and is now thought to include nicotinic signaling as a critical component. One of the most interesting nicotinic receptors is the subtype composed of alpha7 subunits because it is widely expressed in the nervous system and has a high relative permeability to calcium which enables it to control diverse cellular functions. Recently it has been shown that alpha7-containing receptors bind the beta-amyloid peptide (amino acids 1-42) in the pM- nM range. The mammalian hippocampus is an interesting system for studying such interactions because alpha7-containing receptors are relatively abundant there, and the hippocampus is centrally involved in memory formation which is a major target of Alzheimer's disease. In preliminary studies we have found that the beta-amyloid peptide in the nM range reversibly inhibits alpha7-containing nicotinic receptors on hippocampal neurons in culture. Surprisingly, certain peptides applied exogenously can quickly and reversibly potentiate the alpha7- containing receptor response by an order of magnitude. This raises the real possibility that drugs capable of accessing the same site may be able to compensate for beta-amyloid inhibition of the receptors. This pilot proposal will examine the interactive of beta-amyloid peptide with hippocampal alpha7-containing receptors both functionally and physically. In addition, it will test the hypothesis that exogenous application of appropriate regulatory molecules will overcome the inhibition mediated by beta-amyloid peptide. The approach will use whole-cell patch clamp recording (usually in perforated patch mode) from the neurons while applying test compounds in desired sequences from a multi-bore rapid applicator. Competition binding experiments with radiolabeled probes will also be used to assess direct interactions. Functional characterization will include modulation of spontaneous synaptic events in the cultures by alpha7-containing receptors, and determining the impact of beta-amyloid peptide on the modulation in the presence of absence of the candidate potentiators. If this pilot study proves successful (as the preliminary experiments encourage us to think it will), the results will provide the basis for a subsequent full-scale follow-up to analyze beta-amyloid effects on CNS alpha7-containing nicotinic receptors, to analyze Alzheimer's brain tissue for specific involvement of alpha7-receptors in the disease, and to evaluate compounds capable of crossing the blood-brain barrier and potentiating the receptors in situ as a possible therapeutic strategy.