Cystic fibrosis is characterized by defective epithelial ion transport in the airways, bacterial infection, and intense, leukocyte-dominated inflammation. Together, these processes contribute to the progressive airway destruction characteristic of the disease. Mutations in CFTR initiate this cascade, creating an abnormal airway surface liquid microenvironment. While CF-specific abnormalities in ion transport and inflammation have been described and are currently under intense investigation, the factors within the airway microenvironment that modulate both fundamental aspects of CF airway disease are not clearly identified. Adenosine is an endogenous autocoid that is an attractive candidate molecule, activating C1- secretion across airway and other CFTR-expressing epithelia, and modulating many important aspects of leukocyte (neutrophil and macrophage) function. Evidence also suggests that both airway epithelia and inflammatory cells export adenosine nucleotides which are metabolized in the extracellular environment to adenosine. Cellular signaling is primarily through adenosine receptors, including A2 receptors. This proposal is intended to characterize how the inflammatory regulator adenosine, through A2 receptors, activates CFTR. Our preliminary results suggest that A2 receptors activate CFTR through phospholipase A2 (PLA2) and arachidonic acid. This signaling pathway represents a novel, previously undescribed mechanism to modulate CFTR activity. The studies outlined in this proposal will: (1) characterize A2 receptor activation of CFTR-dependent Cl transport in living cells and across airway epithelia in vivo, (2) determine whether adenosine is a predominant nucleotide in the airway microenvironment, and (3) help to develop and test strategies to improve the detection of wildtype CFTR activity, and to improve the function of mutant CFTRs in vitro and in vivo. Adenosine signaling provides a new framework in which to consider the interactions between the epithelia and immune system within the airway microenvironment, helping to bridge the gap between inflammation, CFTR, and Cl- secretion. The experiments outlined also identify a new way to regulate CFTR, and therefore may help define new therapeutic targets in the disease.
