Agonists of the beta-2-adrenoceptor (2AR), commonly referred to as -agonists, have been a cornerstone of asthma treatment for nearly half a century. Despite their utility, however, -agonists used in asthma management have problems, including functional tachyphylaxis, deterioration of asthma control, and mortality concerns. The inability to understand why such problems exist and the failure to significantly improve 2AR pharmacology is reflected by over 2 decades of NIH Program announcements declaring the need for safer, more efficacious alternatives to asthma treatment. Our recent published and unpublished studies provide compelling insight into why -agonists are problematic while offering a solution to their clinical application. Our data strongly suggest that 2AR agonism plays a permissive role in the development of allergic lung inflammation and associated airway hyperresponsiveness (AHR), and that endogenous (epinephrine) as well as exogenous -agonists invoke pathogenic mechanisms promoting the asthma phenotype. New data suggest that 2ARs transduce 2 qualitatively distinct signaling pathways in airway cells: pro-inflammatory signaling mediated by -arrestin2, and anti-inflammatory and bronchoprotective signaling mediated by Gs proteins. We propose studies to solve the asthma 2AR paradox by establishing the cell-specific role of these 2AR signaling pathways in regulating the asthma phenotype, and identifying from among current and newly generated 2AR ligands or modulators those with biased signaling properties that are optimal in their ability to antagonize pathogenic 2AR signaling via arrestins, yet promote beneficial G protein signaling. We will employ many systems, including cell, tissue, and in vivo models, to test the central hypothesis that 2AR signaling via -arrestin2 in airway epithelia is critical to the allergen-induced asthma phenotype, and biased 2AR ligands or modulators that antagonize -arrestin2 signaling while enabling Gs protein signaling are more efficacious in the treatment of asthma.
Aim 1 will employ genetic strategies enabling cell-specific 2AR gene ablation or expression to establish the requirement and sufficiency of 2AR agonism in airway epithelial and smooth muscle cells in mediating allergic lung inflammation, mucin production, and AHR.
Aim 2 will employ similar genetic approaches to establish the roles of 2AR-mediated PKA- and arrestin-dependent signaling in regulating the asthma phenotype in vivo, as well as molecular biology approaches to characterize PKA- and arrestin-dependent regulation of mucin production and inflammatory agents in both human and murine airway epithelial cells.
Aim 3 will utilize pharmacological and genetic approaches, and determine the biased signaling properties of approved and new 2AR ligands to conclusively establish the roles for PKA and arrestin signaling in regulating the asthma phenotype. Collectively, these studies will significantly advance the fields of asthma biology and asthma pharmacology by identifying a fundamental pathogenic signaling mechanism involved in allergic lung inflammation, and by characterizing the optimal 2AR ligands used to manage asthmatics.
This project is relevant to public health because it has a high likelihood of finding new, or improving current, asthma medications. Furthermore, the results could alter our understanding of the beta-2-adrenergic receptor in asthma at a paradigm-shifting level. Finally, the theories we use in this project to find these drugs could be applied to drug discovery for many other diseases.
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