Extracellular Nucleotide Regulation of Airway Epithelial Cell Immunological Mediator Release

Kountz, Timothy

doi:https://doi.org/10.21985/n2-n9ys-n854

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Extracellular Nucleotide Regulation of Airway Epithelial Cell Immunological Mediator Release

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The airway epithelial cells (AECs) lining the conducting passageways of the lung secrete a variety of immunomodulatory factors. One interesting pair of molecules produces by AECs is IL-6 and prostaglandin E2 (PGE2). PGE2 limits lung inflammation and promotes bronchodilation. By contrast, IL-6 drives intense airway inflammation, remodeling, and fibrosis. The signaling that differentiates the production of these opposing mediators is not understood. In this thesis, we find that the production of PGE2 and IL-6 following stimulation of AECs by the danger associated molecule pattern (DAMP), extracellular ATP, share a common requirement for Ca2+ release-activated Ca2+ (CRAC) channels. ATP-mediated synthesis of PGE2 required activation of cell surface metabotropic P2Y2 receptors and CRAC channel-mediated cPLA2 signaling. By contrast, ATP-evoked synthesis of IL-6 occurred via activation of P2X receptors and CRAC channel-mediated calcineurin/NFAT signaling. In contrast to ATP, which elicited the production of both PGE2 and IL-6, the uridine nucleotide, UTP, stimulated PGE2 but not IL-6 production. These results reveal that AECs employ unique receptor-specific signaling mechanisms with CRAC channels as a signaling nexus to regulate release of opposing immunomodulatory mediators. Collectively, our results identify P2Y2 receptors, CRAC channels, and P2X receptors as potential intervention targets for airway diseases. The airway epithelial cells (AECs) lining the conducting airways of the lung form the first line of defense against a variety of inhaled pathogens, allergens and environmental irritants. When a respiratory virus infects cells within the airway epithelium, it provokes the release of numerous immunomodulatory mediators. One essential component of a productive antiviral response is the production of interferons, a family of cytokines known to exhibit powerful antiviral influences. Cells derived from asthmatic patients are known to exhibit diminished interferon release. However, the cellular basis of this phenomenon is not well understood. In this thesis work, we find that two mediators known to be elevated in asthmatic airways, namely extracellular nucleotides and histamine, both potently inhibit the release of interferons from airway epithelial cells. Pharmacological evidence demonstrated that activation of G-protein coupled P2Y2 and H1 receptors elicited this effect. Differentiation of airway epithelial cells at an air-liquid interface confirmed that this phenotype is conserved following differentiation to develop mucociliary function. Mechanistically, receptor signaling through PKC was required to exert these inhibitory effects on interferon release. Significantly, histamine and ATP inhibited interferon release from airway cells infected with live influenza A virus. These results reveal a conserved role for G-protein coupled receptor signaling restraining release of interferons from airway epithelial cells. Collectively, our results provide a potential cellular and molecular basis for the observed limited interferon responses in asthmatic cells.

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