Granulocytes as models for human protein marker identification following nicotine exposure

α9α10 nicotinic acetylcholine receptors regulate murine bone marrow granulocyte functions

Polymorphonuclear neutrophilic granulocytes (PMNs) are extremely important in defense of the organism against infections and in inflammatory processes including neuroinflammation and pain sensation. Different subtypes of nicotinic acetylcholine receptors (nAChRs) are involved in modulation of PMN activities. Earlier we determined expression of α2-7, α9, β3, β4 subunits and regulatory role of α7 and α3β2 nAChR subtypes in functions of inflammatory PMNs. Other authors detected mRNA of α9 subunit in bone marrow neutrophils (BM-PMNs). Murine BM-PMNs coming out from the bone marrow, where they develop, to blood were characterized as mature. There was no data for α10 and for the presence of functionally active α9α10 nAChRs in BM-PMNs. Here we detected for the first time mRNA expression of the α10 nAChR subunit in BM-PMNs and confirmed the expression of mRNA for α9 nAChR. With the help of α-conotoxins RgIA and Vc1.1, highly selective antagonists of α9α10 nAChRs, we have revealed participation of α9 and/or α9α10 nAChRs in regulation of cytosolic Ca²⁺ concentration, cell adhesion, and in generation of reactive oxygen species (ROS). Nicotine, choline, RgIA, and Vc1.1 induced Ca²⁺ transients in BM-PMNs, enhanced cell adhesiveness and decreased production of ROS indicating involvement of α9, possibly co-assembled with α10, nAChRs in the BM-PMN activity for recruitment and cytotoxicity.

Brain Region-Specific nAChR and Associated Protein Abundance Alterations Following Chronic Nicotine and/or Menthol Exposure

The identification of biomarkers that are altered following nicotine/tobacco exposure can facilitate the investigation of tobacco-related diseases. Nicotinic acetylcholine receptors (nAChRs) are pentameric cation channels expressed in the mammalian central and peripheral nervous systems and the neuromuscular junction. Neuronal nAChR subunits (11) have been identified in mammals (α2-7, α9-10, β2-4). We examined changes in β2 nAChR subunit protein levels after chronic nicotine, (±)-menthol, or nicotine co-administered with (±)-menthol in nine murine brain regions. Our investigation of β2 nAChR subunit level changes identified the hypothalamus as a novel region of interest for menthol exposure that demonstrated increased β2 nAChR levels after (±)-menthol plus nicotine exposure compared to nicotine exposure alone. Using mass spectrometry, we further characterized changes in membrane protein abundance profiles in the hypothalamus to identify potential biomarkers of (±)-menthol plus nicotine exposure and proteins that may contribute to the elevated β2 nAChR subunit levels. In the hypothalamus, 272 membrane proteins were identified with altered abundances after chronic nicotine plus menthol exposure with respect to chronic nicotine exposure without menthol. A comprehensive investigation of changes in nAChR and non-nAChR protein expression resulting from (±)-menthol plus nicotine in the brain may establish biomarkers to better understand the effects of these drugs on addiction and addiction-related diseases.

Proteomic Investigation of Murine Neuronal α7-Nicotinic Acetylcholine Receptor Interacting Proteins

The α7-nicotinic acetylcholine receptor (α7-nAChR) is a ligand-gated ion channel that is expressed widely in vertebrates and is the principal high-affinity α-bungarotoxin (α-bgtx) binding protein in the mammalian CNS. α7-nAChRs associate with proteins that can modulate its properties. The α7-nAChR interactome is the summation of proteins interacting or associating with α7-nAChRs in a protein complex. To identify an α7-nAChR interactome in neural tissue, we isolated α-bgtx-affinity protein complexes from wild-type and α7-nAChR knockout (α7 KO) mouse whole brain tissue homogenates using α-bgtx-affinity beads. Affinity precipitated proteins were trypsinized and analyzed with an Orbitrap Fusion mass spectrometer. Proteins isolated with the α7-nAChR specific ligand, α-bgtx, were determined to be α7-nAChR associated proteins. The α7-nAChR subunit and 120 additional proteins were identified. Additionally, 369 proteins were identified as binding to α-bgtx in the absence of α7-nAChR expression, thereby identifying nonspecific proteins for α7-nAChR investigations using α-bgtx enrichment. These results expand on our previous investigations of α7-nAChR interacting proteins using α-bgtx-affinity bead isolation by controlling for differences between α7-nAChR and α-bgtx-specific proteins, developing an improved protein isolation methodology, and incorporating the latest technology in mass spectrometry. The α7-nAChR interactome identified in this study includes proteins associated with the expression, localization, function, or modulation of α7-nAChRs, and it provides a foundation for future studies to elucidate how these interactions contribute to human disease.

Preface: Cholinergic Mechanisms

This special issue is a companion to the meeting 'XVth International Symposium on Cholinergic Mechanisms', and is edited by Israel Silman, Marco Prado and Pascale Marchot. In the review articles, renowned researchers in the field capture key mechanisms of cholinergic neurotransmission, from genomic amplification of cholinesterase genes, splicing and post-translational modifications; features of the neuromuscular junction, implications of cholinergic circuitry that are relevant to addiction, anxiety and mood, to preclinical models, protein biomarkers, and clinical findings that are relevant to pathology, for example, developmental neurotoxicity. The broad variety of features reflects the impact of cholinergic mechanisms on many physiological events and emphasizes the importance of research in this area. This is the Preface for the special issue XVth International Symposium on Cholinergic Mechanisms.