The Pro-Inflammatory but not Protective Effects of Protease-Activated-Receptor-2 In the Airways are Abolished in Beta-Arrestin-2 Mice in OVA, Cockroach Frass and Alternaria-Induced Models of Allergic Asthma

ABSTRACT OF THE DISSERTATIONThe Pro-Inflammatory but not Protective Effects of Protease-Activated-Receptor-2 In the Airways are Abolished in Beta-Arrestin-2 Mice in OVA, Cockroach Frass and Alternaria-Induced Models of Allergic AsthmabyHeddie Lynn NicholsDoctor of Philosophy, Graduate Program in Biomedical SciencesUniversity of California, Riverside, December 2012Dr. Kathryn A. DeFeaProteinase Activated Receptor-2 (PAR2), a G Protein Coupled Receptor (GPCR) activated by serine-like proteases, is reported to have both protective and pro-inflammatory effects in the airway. Given these dual and apparently opposing actions, both inhibitors and activators of PAR2 have been proposed as therapeutics for asthma. PAR2 can signal through two independent pathways: a G-protein-dependent and a beta--arrestin-2-dependent/G-protein-independent one. The beta-arrestin-dependent pathway promotes leukocyte migration, while bronchiolar smooth muscle relaxation requires G-protein signaling intermediates. These studies address the hypothesis that inflammatory responses to PAR2 activation are mediated by beta-arrestins, while prostaglandin production and smooth muscle relaxation are not. Our initial studies focused on a mouse ovalbumin model for PAR2-modulated airway inflammation to focus specifically on PAR2 effects. During the course of our studies, two models of PAR2 dependent airway inflammation were introduced. They are: Alternaria alternata, a fungus that commonly grows in homes and on plant; and Cockroach Frass from Blatella germanica a common household pest. These models induce a more robust inflammatory response and are more physiologically relevant as they used common household allergens. As determined by flow cytometry, cytospin and immunohistochemistry, PAR2-induced overall lung inflammation, mucus production, airway responsiveness and recruitment of eosinophils and CD4+-lymphocytes to the Broncho Alveolar Lavage Fluid (BALF) were abolished in beta-arrestin-2-/-, compared with wild type mice. These results were exacerbated in our AltA and BG models. In contrast, PAR2 promoted equivalent bronchial epithelium-dependent tracheal smooth muscle relaxation and production of PGE2 in both wild type and beta-arrestin-2-/- mice. Our data suggest that the PAR2-enhanced inflammatory process is beta-arrestin-2-dependent, while the `protective' anti-constrictor effect of bronchial epithelial PAR2 is beta-arrestin-independent