Mechanisms of Nucleotide release by Airway Epithelia

Univ Of North Carolina Chapel Hill, Chapel Hill NC

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Abstract

[unreadable] Nucleotides within the liquid film lining the epithelia of the airways control the mucociliary (MCC) clearance[unreadable] process that removes inhaled noxious materials. ATP, UTP, UDP, and adenosine activate a subset of[unreadable] purinergic receptors that regulate ion secretion, increase ciliary beat frequency, and promote mucin[unreadable] secretion. In addition, UTP, ATP, and UDP-glucose are potent neutrophil chemoattractants, suggesting that[unreadable] nucleotides released onto airway surfaces may induce neutrophil migration in response to airway stress.[unreadable] Therefore, understanding the mechanism(s) of nucleotide release by airway epithelia has important[unreadable] pathophysiological and therapeutic implications for the lung. Circumstantial evidence exists for two modes of[unreadable] ATP release from epithelial cells onto the airway surface: (i) ion channels and/or transporters and (ii)[unreadable] vesicles. However, whether nucleotides are released from the cytosol, from vesicles, or both compartments[unreadable] is not unambiguously known. Recognition that airway epithelial cells release UDP-sugars, donor substrates[unreadable] of glycosylation reactions in the endoplasmic reticulum and Golgi lumen, in addition to ATP, suggests that[unreadable] nucleotides entering these organelles may be released by exocytosis. Preliminary data illustrating that[unreadable] enhanced mucin secretion by cultured goblet-like cells is accompanied by release of UDP-glucose and ATP[unreadable] suggest that nucleotide release by goblet cells reflects an exocytotic process associated with mucin[unreadable] secretion. Preliminary data also suggests that NMP antiporters mediate the release of cytosolic UDP-sugars[unreadable] in non-goblet cells. This application outlines a plan to define the role of vesicle and mucin granule exocytosis[unreadable] and of antiporter mechanisms in the release of nucleotides by airway epithelia. To accomplish this goal, we[unreadable] propose the following Specific Aims: (1) to test the hypothesis that NTP/NDP release is vesicular, (2) to test[unreadable] the hypothesis that nucleotide/NMP antiporters facilitate nucleotide release, and (3) to delineate the[unreadable] relationship between nucleotide release and mucin secretion. We will assess the extent to which nucleotide[unreadable] release reflects vesicle exocytosis, is modified by Golgi nucleotidases, involves Golgi and/or cell surface[unreadable] translocators, and is mechanistically associated with mucin secretion. Completion of these studies will[unreadable] establish mechanism(s) for the physiologically important process of nucleotide release, and accordingly will[unreadable] delineate potential drug targets for airway diseases associated with poor MCC clearance.