The Role and Mechanisms of High Affinity Ige Receptor and E-Cadherin in Ige-Mediated Alarmins Expression in Airway Epithelial Cell of Severe Asthma(1/2)

Severe asthma affecting about 10 percent of the asthma patient, is characterized by corticosteroid insensitivity, persistent airway inflammation related to predominance of eosinophils, neutrophils, or Th17 cells, and prominent airway structural changes. In response to allergens, viruses or mucosal injury, airway epithelial cells produce three alarmin cytokines, IL-33, IL-25, and thymic stromal lymphopoietin (TSLP), which promote type 2 inflammation by enhancing differentiation of Th2 cells and activation of mast cells and type 2 innate lymphoid cells (ILC2) to trigger the Th2 cytokines. These are implicated in the airway inflammatory responses in severe asthma. Epidermal growth factor receptor (EGFR) through activation of downstream signaling pathways Akt, ERK1/2 and NF-B, has been demonstrated a critical regulator of IL-33, IL-25 and TSLP expression. Expression of high affinity IgE receptors are found up-regulated in asthmatic airway epithelium. IgE binding to high affinity IgE receptor (FcεRI) activates Src family kinases (SFK) leading to Syk activation. The downstream signaling pathways for Syk activation include Ras/Raf, MEK and MAPK/ERK, which has been shown to suppress E-cadherin and mediate ligand-independent EGFR transactivation. E-cadherin, an intercellular junction protein suppresses intracellular signaling pathways. Loss of E-cadherin may result in reduced suppression of EGFR-dependent signaling pathways. SFK activation by IgE/FcεRI receptor coupling has been shown to induce E-cadherin deregulation. Thus, it is also possible that IgE/FcεRI receptor interaction may induce ligand-independent EGFR activation directly or indirectly via E-cadherin deregulation to increase IL-33, IL-25 and TSLP expression in airway epithelium. This 3-year project aims to investigate whether FcRI, is implicated in the production of alarmins in airway epithelial cells of severe allergic asthma patients, and to investigate the role of E-cadherin and EGFR transaction in IgE-induced alarmins expression. 1st year project: To investigate the molecular mechanisms underlying IgE induced expression of IL-33, IL-25, and TSLP in primary epithelial cell culture (PHEC) from patients with severe allergic asthma and mild asthma.2nd years project: To investigate the implication role of E-cadherin and EGFR in IgE-induced IL-33, IL-25 and TSLP expression, by transfection of epithelial cells with SiRNA against E-cadherin, pretreatment with EGFR tyrosine kinase inhibitor or a pan HDAC inhibitor or specific inhibitors of signaling pathways.3rd years project: Immunohistochemistry and Immunological profiles studies of bronchial tissues before and after anti-IgE treatment. Therapeutic effects of Gefitinib or HDAC inhibitors (MPT0E028) on ovalbumin challenged mice will confirm the role of EGFR transaction and E-cadherin.This project will for the first time elucidate the role of FcRI on airway epithelium in regulation of severe allergic asthma exacerbation. Through our preliminary data, we have shown IgE induces IL-33, IL-25 and TSLP synthesis in PHEC of severe allergic asthma. IgE induced loss of E-cadherin, EGFR transactivation and increased IL-33, IL-25 and TSLP expression, suggesting a causal-effect relationship between IgE-mediated responses and E-cadherin. Based on our preliminary results, we believe this project is feasible and will disclose a novel mechanism for pathogenesis of severe allergic asthma.