INCREASED EPITHELIAL SODIUM CHANNEL (ENAC) ACTIVITY PROTECTS PRETERM LUNGS FROM HYPEROXIA‐INDUCED LUNG INJURY
Authors: Goh Ethan , Coca Camila , Helms My 
Published: June 2021

Background and Significance

Oxygen supplementation is an important component of intensive care for preterm infants and many patients with water in the lungs. Immature preterm lungs have 25% more water in the lungs than term infants. ENaC serves as the rate limiting step for net salt (and then water) transport across an epithelium, and therefore, plays a very important role in resolving lung water. Our lab has previously shown that during high O2 exposure, the level of glutathione disulfide (GSSG) is significantly increased, and that GSSG significantly decreases lung αβγ ENaC activity. Herein, we investigated whether supplemental oxygen contributes to lung injury via GSSG down‐regulation of ENaC activity using a mouse model of preterm lung injury. Results from our studies could lead to new treatment options for hyperoxia‐induced lung injury.

Hypothesis

We hypothesize that GSSG down‐regulation of ENaC plays an important role in hyperoxia‐induced lung injury.

Methods

We employed the term mouse model of hyperoxia‐induced lung injury, and a gain‐of‐ENaC function C57Bl6 mouse model which overexpresses the Scnn1b gene under the Clara cell secretory protein promoter (referred to as Scnn1b hereafter). Scnn1b and their WT litter mates were maintained on 85% or 21% O2 (hyperoxia or normoxia, respectively) from birth up to postnatal day (PN) 11. A subset of normoxic WT C57Bl6 mice were nasally insufflated with 400 μM GSSG from PN 1 through PN 11. Lung injury and development were assessed by morphometric analysis (radial alveolar counts) of Masson's trichrome stained tissue. The Evan's blue assay was used to determine alveolar fluid clearance.

Results

Our studies show that newborn mice maintained on 85% O2 from birth up to PN 11 can be used as a biologically relevant model for hyperoxia‐induced lung injury since chronic hyperoxia correlated with increased lung fibrosis and attenuated lung development. Importantly, our study shows that Scnn1b mice were protected from high O2 injury; Masson's Trichrome staining showed less fibrotic tissue (stained blue) in hyperoxic Scnn1b mice compared to hyperoxic WT littermates, and radial alveolar counts (a reliable measure of lung maturation) increased from 8.1±0.29 in (hyperoxia) WT pups to 9.9±0.35 in (hyperoxia) Scnn1b pups; n=8, p<.01. Overexpression of lung ENaC, under both normoxic and hyperoxic conditions, correlated positively with increased alveolar fluid clearance. Nasal insufflation of GSSG into WT lung (under normoxic conditions) significantly decreased alveolar fluid clearance in PN11 pups compared to age‐matched control mice insufflated with saline under normoxia. Together, these data support our novel paradigm which suggests that GSSG inhibition of ENaC plays a critically important role in hyperoxia‐induced lung injury

Conclusion

Scnn1b over‐expression in mouse lung increases ENaC activity, which translates into improved fluid clearance rates and protection from hyperoxia‐induced injury.

Support or Funding Information

Scnn1b mice with gain‐of‐ENaC function was a kind gift from Dr. Alessandra Livraghi‐Butrico (University of North Carolina at Chapel Hill). This project was made possible by support from the University of Utah Pulmonary Division Investigator Initiated Grant awarded to MNH.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.