The Nicotinic Receptor Alpha7 Impacts the Mouse Lung Response to LPS through Multiple Mechanisms

March The Nicotinic Receptor Alpha7 Impacts the Mouse Lung Response to LPS through Multiple Mechanisms Elena Y. Enioutina 0 1 2 3 Elizabeth J. Myers 0 1 2 3 Petr Tvrdik 0 1 2 3 John R. Hoidal 0 1 2 3 Scott W. Rogers 0 1 2 3 Lorise C. Gahring 0 1 2 3 0 Funding: This work was supported by a Veterans Administration Merit Grant 1BX001798, and a National Institutes of Health grant R01DA025057. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript 1 Data Availability Statement: All relevant data are within the paper 2 Academic Editor: Brij Singh, School of Medicine and Health Sciences, University of North Dakota, UNITED STATES 3 1 Geriatric Research, Education and Clinical Center (GRECC), Veterans Affairs Medical Center , Salt Lake City , Utah, United States of America, 2 Department of Internal Medicine, Division of Geriatrics, University of Utah School of Medicine , Salt Lake City , Utah, United States of America, 3 Department of Pathology, Division of Microbiology and Immunology, University of Utah School of Medicine , Salt Lake City , Utah, United States of America, 4 Department of Human Genetics, University of Utah School of Medicine , Salt Lake City , Utah, United States of America, 5 Department of Internal Medicine, Division of Pulmonary Medicine, University of Utah School of Medicine , Salt Lake City , Utah, United States of America, 6 Veterans Affairs Medical Center , Salt Lake City , Utah, United States of America, 7 Department of Neurobiology and Anatomy, University of Utah School of Medicine , Salt Lake City, Utah , United States of America The nicotinic acetylcholine receptor alpha7 (7) is expressed by neuronal and non-neuronal cells throughout the body. We examined the mechanisms of the lung inflammatory response to intranasal (i.n.) lipopolysaccharide (LPS) regulated by 7. This was done in mice using homologous recombination to introduce a point mutation in the 7 receptor that replaces the glutamate residue 260 that lines the pore with alanine (7E260A), which has been implicated in controlling the exceptional calcium ion conductance of this receptor. The 7E260A mice exhibit normal inflammatory cell recruitment to the blood in response to i.n. LPS administration. This differs from the 7knock-out (7KO) in which upstream signaling to initiate the recruitment to the blood following i.n. LPS is significantly impaired. While hematopoietic cells are recruited to the bloodstream in the 7E260A mouse, they fail to be recruited efficiently into both the interstitium and alveolar spaces of the lung. Bone marrow reconstitution experiments demonstrate that the responsiveness of both CD45+ and CD45- cells of the 7E260A mouse are impaired. The expression of several pro-inflammatory cytokine and chemokine RNAs including TNF, IL-1, Ccl2 and Cxcl10 are decreased in the 7E260A mouse. However, there is a substantial increase in IL-13 expression by CD45- lung interstitial cells in the 7E260A mouse. Our results support the conclusion that 7 functional pleiotropy contributes to modulating the tissue response to an inflammatory insult through impacting upon a variety of mechanisms reflecting the individual cell composition of the lung. - Among the most abundant agents in cigarette smoke (CS) is nicotine, which in addition to being the addictive substance of CS also modulates inflammatory responses [14]. In the body nicotine interacts with ionotropic nicotinic acetylcholine receptors (nAChR) that are expressed by both neuronal and non-neuronal cells that together modulate a multitude of cellular responses which in many instances govern how normal and pathological processes progress [5]. Physiological interaction with nicotine from CS, or other sources such as electronic-cigarettes (e-cigarettes), occurs first through the oral cavity followed by the lung. A prominent nAChR subtype expressed in the lung whose function is implicated in the response to nicotine is alpha7 (7) [69]. This nicotinic receptor is well-recognized to modulate both central and peripheral neurotransmission, but it also modifies inflammation through mechanisms that directly alter non-neuronal cell responses including immune cells, epithelial cells and adipocytes [10]. This impact is explained in part by the unique ion channel properties of 7 that in addition to the normal sodium/potassium current include an exceptional permeability to calcium [5]. In this case, the calcium current is sufficient to modulate multiple calcium-mediated intracellular processes which have been suggested to resemble metabotropic-like properties in addition to its contribution to depolarization responses [11]. Thus, the broad distribution of 7 expression must be considered when defining how activation of this receptor impacts on responses throughout the body. The role of 7 in inflammation has been supported by studies examining the 7KO mouse that elicits greater inflammatory cytokine responses in a tissue specific manner including more cellular infiltration into a site of inflammation [3,1214]. Notably, 7-modulatory processes can be imparted through: 1) through parasympathetic nerve function; 2) direct impact on hematopoietic cells such as macrophages that express this receptor; and 3) cells and tissues such as keratinocytes of the skin where parasympathetic innervation is absent [12,13,15]. However, as would be predicted, should these processes converge in a single tissue, the impact of 7 on the tissue response through modulation of different pathways may not always be obvious in the 7KO. Further, the possibility of functional compensation of 7 in the knock-out animal by other nAChRs or other cellular signaling systems could obscure the specific contribution of this receptor makes to the inflammatory process. In the lung previous studies identified 7 expression by multiple resident non-hematopoietic cells such as lung macrophages derived from the hematopoietic system and bronchial epithelium and endothelium [6,8,1618]. Lung macrophages fall into two categories broadly defined as alveolar macrophages (AM), which are resident in bronchial alveolar lavage fluid (BALF) of normal mice, and interstitial tissue macrophages (IM) of the lung tissue parenchyma [19]. AMs are distinguished by their expression of the CD11c marker which is traditionally associated with dendritic cells [2022] in contrast to IMs that express predominantly the CD11b (MAC1) surface marker and are infrequently CD11c+. Lung airway inflammation is characterized by an influx of macrophages as well as granulocytes such as polymorphonuclear cells (PMN) into both the alveolar space and interstitial tissue, which is an integral part of the acute response to an airway irritant [23]. The initiation of lung inflammation also involves the cellular activation of epithelial cells which also express 7 receptors [6,8,24]. Maouche et al. [24] found that 7 expressed by epithelium plays a role in the regulation of th (...truncated)