Asthma is a chronic inflammatory disease of the lungs that is characterized by airway obstruction and bronchospasm. While there are many factors that contribute to development of asthma and other inflammatory airway diseases, the generation of reactive oxygen species (ROS) within the airway can lead to exasperation of airway inflammation and contributes greatly to pathophysiology of airway disorders like asthma. The gold- standard for treatment of asthma and other bronchoconstrictive disorders is inhalation of ?2-adrenergic receptor (?2AR) agonists, which quickly relax the airway tissues and reduce bronchospasms, allowing for greater pulmonary function. Recently, our laboratory has demonstrated that agonism of ?2AR leads to robust formation of ROS. However, our work also shows that ROS are required for ?2AR function, as inhibition of ROS abrogates all ?2AR signaling. These results suggest that some level of ROS are required for stabilization of functional ?2AR, and indeed, we show in airway epithelial cells that ROS regulate the ?2AR by directly oxidizing it. Importantly, the oxidation of ?2AR is decreased in tissue from mice that lack appropriate ROS- generating enzymes, and also regulates the receptors function in human airway cells, suggesting that ROS interplay may be important for homeostatic pulmonary function of ?2AR. The overall goal of this project is to examine the ROS generation and ROS-mediated oxidation of ?2AR in normal and asthma-diseased airways. In this regard, we plan to: 1) Localize the exact site(s) of the ?2-receptor that are oxidized by ROS, and assess the functional consequences of this oxidation in normal and asthma-diseased cells. 2) Characterize the signaling pathways that facilitate both ROS generation and ?2-recptor oxidation in normal and asthma- diseased cells. Results of this work will shed light on the role of ROS as regulators of GPCR function, and establish a knowledge base towards understanding the ROS-?2-receptor linkage in mammalian airway cells that modulate the clinical response to ?2AR-agonist treatment. This work will also reveal if there are differences in the ?2AR-ROS axis in asthma diseased airways.
The ?2-adrenergic receptor mediates the body's responses to epinephrine and norepinephrine and is critical in the normal functioning of the heart, lungs, and kidneys, amongst other organs. Clinically, activation of ?2-receptors with inhaled bronchodilators provides relief from symptoms of asthma. We have previously shown that ?2-receptors can increase levels of reactive oxygen species (ROS) inside cells and that such increases feedback to oxidize the receptor, keeping it in a signal- capable state. This project will allow us to characterize ?2-receptor ROS generation and its oxidation within cells of the human lung that are responsible for bronchodilation and bronchoconstriction. Overall, this work will significantly impact our understanding for the requirement of ROS in ?2AR function in the pulmonary system.
