Lynx1 and Aβ1-42 bind competitively to multiple nicotinic acetylcholine receptor subtypes

Lynx1 regulates synaptic plasticity in the brain by regulating nicotinic acetylcholine receptors (nAChRs). It is not known to which extent Lynx1 can bind to endogenous nAChR subunits in the brain or how this interaction is affected by Alzheimer's disease pathology. We apply affinity purification to demonstrate that a water-soluble variant of human Lynx1 (Ws-Lynx1) isolates alpha 3, alpha 4, alpha 5, alpha 6, alpha 7, beta 2, and beta 4 nAChR subunits from human and rat cortical extracts, and rat midbrain and olfactory bulb extracts, suggesting that Lynx1 forms complexes with multiple nAChR subtypes in the human and rodent brain. Incubation with Ws-Lynx1 decreases nicotine-mediated extracellular signal-regulated kinase phosphorylation in PC12 cells and striatal neurons, indicating that binding of Ws-Lynx1 is sufficient to inhibit signaling downstream of nAChRs. The effect of nicotine in PC12 cells is independent of alpha 7 or alpha 4 beta 2 nAChRs, suggesting that Lynx1 can affect the function of native non-alpha 7, non-alpha 4 beta 2 nAChR subtypes. We further show that Lynx1 and oligomeric beta-amyloid(1-42) compete for binding to several nAChR subunits, that Ws-Lynx1 prevents beta-amyloid(1-42)-induced cytotoxicity in cortical neurons, and that cortical Lynx1 levels are decreased in a transgenic mouse model with concomitant beta-amyloid and tau pathology. Our data suggest that Lynx1 binds to multiple nAChR subtypes in the brain and that this interaction might have functional and pathophysiological implications in relation to Alzheimer's disease. (C) 2016 The Author(s). Published by Elsevier Inc.