Mechanisms of IL-33 secretion in allergic diseases

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PROJECT SUMMARY/ABSTRACT The long-term objective of this project is to investigate the fundamental immunological mechanisms involved in the development of asthma and allergic diseases. It is becoming increasingly clear that cytokines produced by epithelial cells, including thymic stromal lymphopoietin, IL-25, and IL-33, play an important role in shaping type 2 immunity and in the pathophysiology of allergic diseases. However, major gaps remain in our knowledge concerning the molecular and cellular control of production and secretion of these cytokines. In this application, we will investigate the mechanisms involved in IL-33 secretion. IL-33 is primarily stored in the nucleus of non-hematologic cells; nuclear localization is a unique feature of this cytokine. We previously found that exposure of human airway epithelial cells to a fungal allergen, Alternaria alternata, evokes rapid extracellular release of ATP, which triggers sustained increases in intracellular calcium concentration and IL-33 secretion into the extracellular milieu. We also found that airway epithelial cells release acetylcholine (ACh) extracellularly following Alternaria or house dust mite allergen exposure. Importantly, blocking M3 muscarinc receptors (M3R) on epithelial cells suppressed ATP release and IL-33 secretion, suggesting an autocrine role for ACh. Therefore, we hypothesize that allergen-induced ACh secretion by the airway epithelium plays a pivotal role in triggering a sequence of intracellular events that lead to extracellular release of IL-33. The experiments described in this proposal will investigate key steps of this process in detail. In Aim 1, we will deterimne how airborne allergen exposure triggers ACh secretion and early cellular responses in airway epithelial cells in vitro. In Aim 2, we will investigate how epithelium-derived ACh facilitates IL-33 secretion by focusing on the autocrine ACh/M3R signaling pathway and protein kinase C-dependent phosphorylation of key regulatory proteins. In Aim 3, we will investigate the role of epithelial ACh/M3R signaling in allergen-induced IL- 33 secretion and initiation of type 2 immunity in the lung by using mouse models of allergic inflammation. We will employ a combination of complementary expertise in molecular and cell biology, pharmacology and immunology in the laboratories of Dr. O’Grady and Dr. Kita. Novel and robust in vitro and in vivo models have been developed for this project. These studies will provide a better understanding of how the epithelium responds to environmental allergens and will define key cellular and molecular mechanisms responsible for secretion of IL-33. Ultimately, these studies will characterize critical mechanism(s) involved in allergen-induced immune responses, allowing for identification of novel therapeutic target(s) to treat and ideally prevent immune-mediated airway diseases, such as asthma, chronic rhinosinusitis, and other allergic disorders.