Silencing of MUC8 by siRNA increases P2Y2-induced airway inflammation

Mucin hypersecretion and overproduction are frequent manifestations of respiratory disease. Determining the physiological function of airway mucin is presently considered more important than identifying the relevant signaling pathways. The lack of a full-length human mucin 8 (MUC8) cDNA sequence has hindered the generation of a Muc8 knockout mouse line. Thus, the precise physiological functions of MUC8 are unclear. Herein, we investigated the function of MUC8 using a small-interfering RNA (siRNA)-mediated genetic silencing approach in human airway epithelial cells. Herein, intracellular IL-1 alpha production was stimulated by an ATP/P2Y(2) complex. While ATP/P2Y(2) increased IL-1 alpha secretion in a time-dependent manner, treatment with P2Y(2)-specific siRNA significantly decreased IL-1 alpha secretion. Moreover, ATP increased P2Y(2)-mediated upregulation of MUC8 expression; however, IL-1 alpha significantly decreased the extent to which ATP/P2Y(2) upregulated MUC8 expression. Interestingly, treatment with MUC8-specific siRNA decreased the production of anti-inflammatory cytokines (TGF-beta and IL-1 receptor antagonist) and increased the production of inflammatory cytokines (IL-1 alpha and IL-6) in our system. In addition, siRNA-mediated knockdown of MUC8 expression dramatically increased the secretion of inflammatory chemokines and resulted in an approximately threefold decrease in cell chemotaxis. We propose that MUC8 may function as an anti-inflammatory mucin that participates in inflammatory response by attracting immune cells/cytokines to the site of inflammation. Our results provide new insight into the physiological function of MUC8 and enhance our understanding of mucin overproduction during airway inflammation.