Chronic exposure to nicotine is a crosscutting phenomenon, leading to nicotine dependence as well as to inadvertent therapeutic effects such as protection against Parkinson's disease. The project tests the novel suggestion that effects of chronic nicotine exposure depend on intracellular nicotine-not on conventional signal transduction via receptors at the plasma membrane. It is known that nicotine passively enters cells and recent studies suggest that nicotine also enters organelles such as endoplasmic reticulum (ER). In ER, nicotine may pharmacologically chaperone nascent nicotinic acetylcholine receptors (nAChRs), matchmaking subunits as pentameric receptors assemble. Other studies suggest additional potential sequelae of intracellular nicotine-nAChR interactions: decreasing unfolded protein responses, escorting other proteins from ER, or abducting proteins to abnormal pathways. The proposed mechanism is inside-out, because it begins in the ER rather than on the plasma membrane. Nicotine's sustained inside-out effects proceed at concentrations much lower than its transient activation of plasma membrane nAChR channels. The project will invent new techniques to measure and control the initial steps in inside-out nicotinic pharmacology. We will develop NanoSIMS for measuring drug binding, and we will develop compartmentalized nicotinic ligands. We will also employ other state-of-the-art techniques: reconstitution of COPII vesicle budding, and FRET. Sub-Approach A invents tools measuring the compartmentalization of nicotine action. Sub-Approach B invents tools for confining pharmacology to the ER, both for nicotine and for the clinically important alpha4beta2 nAChR-selective ligand, varenicline. Sub-Approach C tests for interactions between nAChRs and candidate genes discovered by previous experiments. Inside-out pharmacology is a transformative concept that may reveal new therapeutic targets for addiction and neurodegeneration.
Nicotine dependence and neurodegenerative disease are devastating problems and require better therapeutic drugs. The project attempts to understand what happens in the brain of a person chronically exposed to nicotine. The project suggests a new, 'inside-out' mechanism of action, and this mechanism may reveal new therapeutic targets for addiction, neurodegeneration, and psychiatry.
