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

Abstract

The nicotinic acetylcholine receptor alpha7 (α7) 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 α7. This was done in mice using homologous recombination to introduce a point mutation in the α7 receptor that replaces the glutamate residue 260 that lines the pore with alanine (α7E260A), which has been implicated in controlling the exceptional calcium ion conductance of this receptor. The α7E260A mice exhibit normal inflammatory cell recruitment to the blood in response to i.n. LPS administration. This differs from the α7knock-out (α7KO) 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 α7E260A 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 α7E260A mouse are impaired. The expression of several pro-inflammatory cytokine and chemokine RNAs including TNFα, IL-1α, Ccl2 and Cxcl10 are decreased in the α7E260A mouse. However, there is a substantial increase in IL-13 expression by CD45- lung interstitial cells in the α7E260A mouse. Our results support the conclusion that α7 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.

Nicotinic alpha 7 receptor expression and modulation of the lung epithelial response to lipopolysaccharide

“…Also notable was the reduction of inflammatory cell infiltration into the α7 E260A:G lung as measured in the bronchial alveolar lavage fluid (BALF) despite the relatively normal recruitment of inflammatory cells into the blood from the bone-marrow. Notably, in reciprocal chimeric mice constructed from bone marrow of differing α7 genotypes it was shown that the non-hematopoietic cells of the α7 E260A:G mouse lung dominated this overall inefficient LPS-response and the poor recruitment of bone-marrow derived inflammatory cells to the lung [14]. This study extends those findings to examine the α7 E260A:G CD45 - resident cell transcriptional responses to i.n.…”

“…Pharmacological agents specific to α7 suppress the response to LPS [7,10], a result that was confirmed and extended in the lung of α7 E260A:G mice [14]. In the α7 E260A:G mouse the inflammatory response by both hematopoietic and local non-hematopoietic cells to intranasal (i.n.)…”

“…To better understand these mechanisms, we used a genetic approach [12–14]. Through homologous recombination, mice were constructed in which a bi-cistronic IRES-driven tau:green fluorescent protein (tGFP) extension of the native α7 transcript provides a reporter of receptor gene transcription (α7 G ; [12]).…”

“…Through homologous recombination, mice were constructed in which a bi-cistronic IRES-driven tau:green fluorescent protein (tGFP) extension of the native α7 transcript provides a reporter of receptor gene transcription (α7 G ; [12]). In this background a precise point mutation was introduced to change the glutamic acid 260 to an alanine and specifically limit the relatively high calcium current through this receptor (α7 E260A:G ; [4,14–16]). This effectively uncouples the α7 from calcium signaling mechanisms with minimal perturbation to genomic context or other receptor functions.…”

“…In the α7 E260A:G mouse the inflammatory response by both hematopoietic and local non-hematopoietic cells to intranasal (i.n.) LPS was overall significantly decreased [14]. Also notable was the reduction of inflammatory cell infiltration into the α7 E260A:G lung as measured in the bronchial alveolar lavage fluid (BALF) despite the relatively normal recruitment of inflammatory cells into the blood from the bone-marrow.…”