Strategic targeting of GPRC5A and GPRC5B in airway smooth muscle

Thomas Jefferson University, Philadelphia PA

Investigators

Abstract

ABSTRACT Asthma involves airway hyperresponsiveness (AHR) with impaired bronchodilation, and airway remodeling (cell proliferation). In spite of improved mechanistic understanding, there is substantial unmet clinical need to address both AHR and remodeling that are not alleviated by current therapies. Here, airway smooth muscle (ASM) is a key cell type regulating contractility, remodeling and local inflammatory milieu. In fact, GPCRs that remain a major aspect of asthma all target the ASM (e.g. β2-adrenoceptor agonists and muscarinic receptor antagonists). Asthmatic airways are also associated with several orphan receptors of unknown physiological significance, highlighting a potentially novel area for therapeutic exploration. We intend to explore two novel orphan GPCRs, retinoic acid (RA)-induced Class C GPCRs GPRC5A (RAIG1; 5A) and GPRC5B (RAIG2; 5B) in the context of asthma. Relevance of RAIGs in asthma lies in emerging roles for RA receptor signaling and a detrimental effect of RA deficiency. There is currently no information on 5A or 5B in airways, ASM or asthma. Preliminary studies using human samples from non-asthmatic vs. asthmatics show both receptors are expressed in ASM, increased by RA, and higher in asthmatics or with inflammatory cytokines. Our data show functional importance of these RAIGs but interestingly in opposing fashion: as a Gs-coupled GPCR, 5A plays a protective, potentially therapeutic role in asthma, while 5B, as a Gq-coupled (or additionally Gi-coupled) GPCR plays a pathogenic role. We therefore hypothesize that GPRC5A blunts while GPRC5B exacerbates airway contractility and remodeling in inflammation and asthma: making both 5A and 5B potentially targetable for benefit but in opposing ways (i.e. 5A activation vs. 5B inhibition). We will test our model via the following aims. Aim 1: Establish the expression profile and G protein coupling of GPRC5A vs. GPRC5B in human ASM cells in the context of asthma; Aim 2: Establish the roles of GPRC5A vs. GPRC5B in airway contractility and remodeling; Aim 3: Test the efficacy of novel compounds targeting GPCR5A (activation) and GPRC5B (inhibition) using human ASM cells and a murine model of asthma. Using human samples from non-asthmatics vs. asthmatics (Core B) and a mixed allergen mouse model of asthma, we will explore baseline and RA-induced expression and cellular localization of 5A vs. 5B with/without cytokines important in asthma. Coupling of 5A to Gs vs. 5B to Gi or Gq, the linkage to cAMP (Project 2) and DAG (Project 3), and downstream influence on ASM Ca2+/contractility or cell proliferation as well as effector signaling mechanisms are evaluated using complementary imaging, genetic and pharmacological tools. Novel 5A and 5B agonists, antagonists or allosteric modulators including those developed by Core A are evaluated in human cell/tissue and mouse models towards alleviating AHR and remodeling. We thus initially establish clinical significance of 5A vs. 5B as pleiotropic, protective vs. detrimental mechanisms and novel therapeutic targets in asthma.