Mast cells (MCs), granulocytes, and lymphocytes are integral to the development of an allergic response. Allergic inflammation may also be generated through activation of receptors coupled to heterotrimeric G proteins (GPCRs). The purpose of this study is to understand mechanisms of G protein-mediated signal transduction in immune cells, with a focus on GPCR-mediated trafficking of leukocytes to sites of allergic inflammation. GPCRs activate a core pathway of heterotrimeric G proteins, which bind guanosine triphosphate (GTP) in exchange for guanosine diphosphate (GDP). The GTP-bound form of the G protein alpha subunit induces downstream signaling cascades, including intracellular calcium flux responsible for MC/basophil degranulation. This project focuses on a family of regulators of G protein signaling (RGS proteins), which inhibit the function of G alpha-i and G alpha-q, but not G alpha-s, proteins by increasing their GTPase activity. G alpha subunits oscillate between GDP- (inactive) and GTP- (active) bound forms based on ligand occupancy of the associated receptor. The GTPase accelerating (GAP) activity of RGS proteins limits the time of interaction of active G-alpha and its effectors, resulting in desensitization of GCPR signaling. Despite a growing body of knowledge concerning the biochemical mechanisms of RGS action, relatively little is known about the physiological role of these proteins in allergic inflammation. A major area of investigation is the recruitment of inflammatory cells to sites of inflammation. Chemokines are a major class of compounds acting on leukocyte GPCRs, which orchestrate immune cell trafficking, and RGS proteins including RGS13 and RGS16 inhibit chemokine signaling by desensitizing GPCR signals. In FY14, we determined the mechanisms by which RGS13 promotes the generation of pathogenic autoantibodies in GCs using BXD2-Rgs13-/- mice. In spleens of BXD2 mice, RGS13 was mainly expressed by GC B cells and was stimulated by IL-17 but not IL-21. BXD2-Rgs13-/- mice had smaller GCs and lower adenosine induced deaminase (AID) levels, suggesting lower somatic hypermutation and affinity maturation during the antibody response. There were, however, increased IgMbright plasmablasts, upregulation of plasma program genes Irf4, Blimp1, Xbp1 and pCREB target genes Fosb and Obf1, with downregulation of GC program genes Aicda, Pax5 and Bach2 in GC B cells of BXD2-Rgs13-/- mice. BXD2-Rgs13-/- mice showed lower titers of IgG autoantibodies and IgG deposits in the kidney glomeruli, suggesting reduced autoantibody pathogenicity. These results indicate that RGS13 deficiency is associated with reduction in GC program genes and exit of less pathogenic IgM plasmablasts in BXD2 mice. A prolonged GC program, mediated by upregulation of RGS13, enhanced AID expression and enabled generation of pathogenic autoantibodies in autoreactive GCs. A second research area is the trafficking of mast cells and granulocytes during allergic responses. Many allergens contain intrinsic proteolytic activity and bind protease activated GPCRs. Although sensitization to protease allergens, such as papain, helminth infection, chronic allergic skin inflammation, and nasal rhinitis are associated with basophil recruitment to inflamed tissue or to draining lymph nodes (LNs), the precise role of basophils and mechanisms involved in their recruitment is incompletely understood. We are generating mouse strains containing mast cells or basophils hyper- or hyporesponsive to chemokines in order to study the contribution of these cells to various allergic responses. A final area of investigation is the role of RGS5 in neutrophil trafficking. Using Rgs5-/- mice, we discovered in FY14 that neutrophils deficient in RGS5 do not traffic to the lungs followed ozone exposure or to the peritoneum following thioglycollate injection, which are typically strong inducers of neutrophilic inflammation. Neutrophils isolated from Rgs5 gene deleted mice display nearly absent chemotaxis to chemokines known to be involved in these responses.
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