| مستخلص: |
The amiloride-sensitive Epithelial Na+ Channel (ENaC) plays a pivotal role in regulating salt and fluid transport in salt absorbing epithelia in the kidney, lung, intestine and other tissues, and is involved in controlling blood pressure. An important regulator of ENaC stability at the plasma membrane is the ubiquitin ligase Nedd4L (Nedd4-2), which promotes ENaC ubiquitination and endocytosis, thus down regulating the channel by targeting it for lysosomal degradation. In vivo, knockout of Nedd4L in mouse kidney was shown (by the Staub and Yang groups) to increase abundance of both ENaC and the Na+/Cl-co-transporter, leading to salt-induced hypertension. The in vivo role of Nedd4L in the lung was not known. To investigate the role of Nedd4L in the lung, we knocked it out specifically in lung epithelia (in SPC-expressing Type II and airway epithelial cells). Our results show that these mice developed cystic fibrosis-like lung disease, with airway mucus obstruction, goblet cell hyperplasia, massive inflammation, fibrosis and death by 3-weeks of age. Cystic fibrosis is caused by impaired ion transport due to mutated CFTR, accompanied by elevated activity of ENaC. These effects of Nedd4L loss in the lung were likely caused by enhanced ENaC function, as reflected by increased ENaC protein levels, increased lung dryness at birth, amiloride-sensitive dehydration of lung explants, and elevated ENaC currents in primary alveolar-Type II cells analyzed by patch clamp recordings. Moreover, the lung defects could be rescued with administration of amiloride into the lungs of young knockout pups via nasal instillation. Our results therefore suggest that the ubiquitin ligase Nedd4L normally opposes the onset of cystic fibrosis symptoms by inhibiting ENaC in lung epithelia. More recently, we have begun investigating the role of Nedd4L in the intestine, by knocking out Nedd4L specifically in intestinal epithelium (in Villin-expressing cells). The results of these studies will be presented. [ABSTRACT FROM AUTHOR] |
