Upregulated expression of ENaC in human CF nasal epithelium

Abstract

Cystic fibrosis (CF) is characterised by the absence of CFTR function resulting in a reduced Cl(-) secretion and an increase in Na+ absorption. This Na+ hyperabsorption is mediated by the human amiloride-sensitive epithelial sodium channel (ENaC), but the underlying mechanisms are still unknown. After demonstrating functional differences of the Na+ absorption in CF and non-CF epithelia in Ussing chamber experiments with human primary cultures, we compared ENaC sequences from CF and non-CF human nasal tissue (hnENaC), investigated the mRNA transcription levels via real-time PCR and studied the protein expression in Western blot analyses. We found no differences in the sequences of CF and non-CF hnENaC, but identified some polymorphisms. The real-time experiments revealed an enhanced mRNA amount of all three hnENaC subunits in CF tissue. By comparing the two groups on the protein level, we observed differences in the abundance of the Na+ channel. While the alpha- and beta-hnENaC protein amount was increased in CF tissue the gamma-hnENaC was decreased. We conclude that the Na+ hyperabsorption in CF is not caused by mutations in hnENaC, but by an increase in the transcription of the hnENaC subunits. This could be induced by a disturbed regulation of the channel in CF.

Ion Transport by Pulmonary Epithelia

“…In agreement with the general dogma that all airway epithelia (nasal, tracheal, bronchial) are Na + absorptive, an amiloride-sensitive, ENaC-mediated component of baseline ion transport has been detected in airway epithelia of human and a variety of mammalian species such as rabbit, dog, and mouse [18, 20–23]. In addition to that, Cl − secretion on the apical side is an important parameter for airway epithelial function, because Na + absorption and Cl − secretion regulate passive transepithelial H 2 O flow and, thus, the height of the ASL (see above [13]).…”

“…The amiloride-sensitive, Na + -absorptive ENaC has been characterised in human airway epithelium [19, 20]. It has been well established that ENaC forms a trimer usually consisting of the αβγ -subunits [29].…”

“…It has been well established that ENaC forms a trimer usually consisting of the αβγ -subunits [29]. This isoform is widely distributed in human superficial airway and nasal epithelium [19, 20]. However, this is only part of the story, because, during recent years, two different isoforms ( δ 1 and δ 2) of a fourth subunit, the δ -subunit, have been detected [30].…”

AF17 Competes with AF9 for Binding to Dot1a to Up-regulate Transcription of Epithelial Na+ Channel α

“…Failure of Na ϩ homeostasis contributes to hypertension, cardiovascular disease, and respiratory diseases such as cystic fibrosis (1). The importance of the epithelial Na ϩ channel (ENaC) 3 in the regulation of salt homeostasis and blood pressure is demonstrated by the association of gain-and loss-offunction mutations in its subunits with genetic hypertensive and hypotensive diseases, such as Liddle syndrome (2) and pseudohypoaldosteronism type 1 (3).…”

Anaerobiosis ofPseudomonas aeruginosa: Implications for Treatments of Airway Infection

“…In CF, hyperactivation of epithelial Na + channel (ENaC), an event that occurs due to the mutation in the CFTR gene (35), drives the isotonic absorption of H 2 O and ions into the airway epithelium resulting in the dehydration of PLL and thus the formation of a stagnant mucus layer (1). Bronchiectasis (BE) is a disease state where the bronchial tree is irreversibly dilated.…”