PROJECT SUMMARY
Cystic Fibrosis (CF) is a genetic disease caused by mutations in the Cystic Fibrosis Transmembrane
conductance Regulator (CFTR), an ion channel responsible for the transport of chloride and bicarbonate
across the apical cell surface. CF affects multiple organs, and in the lungs, results in mucus stasis, chronic
infection/lung damage, and mortality. Mucus stasis is a pathologic hallmark of CF, and many of the gel-forming
properties of airway mucus are provided by the gel-forming mucins, MUC5B and MUC5AC. These gel-forming
mucins are extensively O-linked glycosylated, and terminal sialylation of these glycans contributes to their
negative charges and interaction with the ionic microenvironment established by CFTR. Changes in O-linked
sialylation of gel-forming mucins would therefore be expected to alter their physiochemical characteristics.
Early evidence shows that defective CFTR can reduce mucin sialylation, however, the mechanistic basis for
this, its relationship to impaired CFTR anion transport, and its consequences on mucus function are unknown.
Furthermore, low charged mucin glycoforms have been linked to pathologic mucus in multiple airway diseases,
but the consequences of altered sialylation on mucin structure and mucus physiology have not been
determined. Our preliminary data shows that sialyltransferase expression is downregulated in CF primary
human bronchial epithelial cells, and that inhibiting sialylation in vitro and in vivo leads to impairment of
mucociliary transport independent of mucus hydration. Through this proposed study, we will identify the role of
CFTR anion transport on mucin sialylation and determine the functional consequences of altered mucin
sialylation on mucin structure and mucus transport. Our overarching hypothesis is that impaired CFTR ion
transport downregulates the sialylation of mucins, which decreases their negative charge, resulting in mucin
structural abnormalities and mucus stasis in CF. To test this, we have developed two specific aims. In aim 1,
we will determine the effect of CFTR anion transport on mucin sialylation by pharmacologically inhibiting or
restoring anion transport in vitro and in vivo, followed by assessing changes in sialylation by quantifying
sialyltransferase expression, sialyltransferase protein levels, and mucin sialylation. In aim 2, we will directly
downregulate or upregulate global or specific sialyltransferase activity and assess the changes in MUC5B or
MUC5AC electrostatic properties, conformation, and physiology to define the consequences of altered
sialylation on gel forming airway mucins. These studies will advance the field by revealing a new mechanism of
mucus stasis in CF, while identifying novel therapeutic targets for treatment of CF and possibly other diseases
of mucus stasis.