Evaluation of the nicotinic acetylcholine receptor-associated proteome at baseline and following nicotine exposure in human and mouse cortex

Abstract

Nicotinic acetylcholine receptors (nAChRs) support initiation and maintenance of smoking, but long-term changes in the protein complex as a result of smoking and nicotine in tobacco is not known. Human studies and animal models have also demonstrated that increasing cholinergic tone increases behaviors related to depression, suggesting that the nAChR-associated proteome could be altered in individuals with mood disorders. We therefore immunopurified nAChRs and associated proteins for quantitative proteomic assessment of changes in protein:protein interactions of high affinity nAChRs containing the β2 subunit (β2* nAChRs) from either cortex of mice treated with saline or nicotine, or postmortem human temporal cortex tissue from tobacco-exposed and –non-exposed individuals, with a further comparison of diagnosed mood disorder to controls. We observed significant effects of nicotine exposure on the β2* nAChR-associated proteome in human and mouse cortex, particularly in the abundance of the nAChR subunits themselves, as well as putative interacting proteins that make up core components of neuronal excitability (Na/K ATPase subunits), presynaptic neurotransmitter release (syntaxins, SNAP25, synaptotagmin), and a member of a known nAChR protein chaperone family (14-3-3ζ). These findings identify candidate signaling proteins that could mediate changes in cholinergic signaling via nicotine or tobacco use. Further analysis of identified proteins will determine whether these interactions are essential for primary function of nAChRs at presynaptic terminals. Identification of differences in the nAChR-associated proteome and downstream signaling in subjects with various mood disorders may also identify novel etiological mechanisms and reveal new treatment targets.

Significance Statement: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels responsible for rapid excitatory acetylcholine signaling, which modulate numerous circuits involved in complex behaviors. In addition, nAChRs are the primary targets for the reinforcing effects of nicotine in tobacco products. Proteins associated with nAChRs are critical for receptor trafficking, localization and function. Identifying core elements of the nAChR-associated proteome that are conserved across human and mouse brain is essential for understanding how these receptors are regulated and how their functions and interactions are altered by chronic exposure to nicotine.