In response to tissue damage or
inflammation, adenosine-5'-triphosphate (
ATP) is released into the extracellular compartment and has been demonstrated to augment
inflammation via
purinergic P2 receptors (P2Rs). Recently,
ATP has been shown to be increased in the airways of
COPD patients. In the present study, we examined the possible involvement of extracellular
ATP in airway mucus hypersecretion during viral-induced
COPD exacerbations.
METHODS: The involvement of extracellular
ATP in the release of a major airway
mucin, MUC5AC, and its signal pathway was examined after stimulation with polyinosine-
polycytidylic acid [
poly(I:C)], a synthetic analog of dsRNA to mimic
viral infection, and rhinovirus (RV)
infection in NCI-H292 cells and differentiated airway epithelial cells from
COPD patients.
RESULTS: Treatment with
poly(I:C) significantly increased the amount of extracellular
ATP and induced MUC5AC release in NCI-H292 cells. Pre-treatment with a pannexin channel inhibitor,
carbenoxolone (CBX), reduced the amount of extracellular
ATP and suppressed MUC5AC release from
poly(I:C)-treated cells. Pre-treatment with the P2R antagonist
suramin significantly reduced the expression and release of MUC5AC. The inhibitory effects of CBX and
suramin on the release of
ATP and/or MUC5AC were replicated with RV
infection. Pre-treatment with
suramin also significantly reduced the expression and amount of extracellular EGFR
ligands and the phosphorylation of EGFR and ERK in
poly(I:C)-treated cells. In addition, pre-treatment with a
P2Y2 receptor siRNA significantly suppressed the
poly(I:C)-potentiated EGFR
ligands and MUC5AC release. After
poly(I:C) stimulation, the expression of MUC5AC in the differentiated cells from
COPD patients was significantly higher than those from healthy subjects and the values of MUC5AC expression were inversely related with forced expiratory volume in 1 s (FEV1) % predicted. The inhibitory effects of CBX and
suramin on
poly(I:C)-potentiated MUC5AC expression were confirmed in differentiated airway epithelium from
COPD patients.
CONCLUSIONS: These results demonstrate that dsRNA induces the release of
ATP via pannexin channel and that the extracellular
ATP is involved in the expression and release of MUC5AC, mainly via P2Y2R, in an autocrine manner. Modulation of this pathway could be a therapeutic target for viral-induced mucus hypersecretion in
COPD exacerbations.