Targeting ENaC as a Molecular Suspect in Cystic Fibrosis.

Cystic fibrosis (CF) is the most common life shortening autosomal inherited disorder, affecting 1 in 2500 newborns in the Caucasian population. In CF the lung pathology is associated with dehydration of the airways epithelial surface which in part results from Na(+) hyperabsorption via the epithelial sodium channel (ENaC). The molecular mechanisms of this Na(+) hyperabsorption and its correlation with the underlying genetic defect in the cystic fibrosis transmembrane conductance regulator (CFTR) are not fully understood. However, it is obvious that a reduced Cl(-) secretion by CFTR and an enhanced Na+ absorption through ENaC lead to the so far incurable disease. Therefore, it could be indicated to pursue a double-tracked strategy in that way enabling Cl(-) secretion by a reconstitution of the defect CFTR as well as blocking ENaC to prevent Na(+) hyperabsorption. Since the cloning of CFTR great efforts have been done in delivery of CFTR for the correction of the reduced Cl(-) secretion. Positive benefits for the inhibition of the CF related Na(+) hyperabsorption offer technologies using small molecule inhibitors like ASOs or siRNA, which target translation and knockdown of ENaC, respectively. In this review we discuss possible CFTR/ENaC interactions in the context of CF, describe ENaC structure as well as some of the numerous attempts that were performed to prevent the Na(+) hyperabsorption in CF related lung disease. Thus, we give a short summary of e.g. amiloride therapy approaches and focus on inventive blocking efforts using ASOs and siRNA.