Expression of chloride channels in trachea-occluded hyperplastic lungs and nitrofen-induced hypoplastic lungs in rats.
BACKGROUND
Congenital diaphragmatic hernia is accompanied by pulmonary hypoplasia. Fetal lung growth is dependent on the secretion of lung liquid, in which Cl(-) secretion by the pulmonary epithelium plays a crucial role. A decrease of lung liquid production during fetal development renders marked pulmonary hypoplasia, while accelerated fetal lung growth in the form of pulmonary hyperplasia can be achieved by in utero tracheal occlusion (TO). Cl(-) secretion presumably involves NKCC-1, the primary basolateral Cl(-) entry pathway in airway epithelia, coupled to an apical Cl(-) exit pathway. The chloride channels ClC-2, -3 and -5, members of the CLC gene family, are all localized to the apical membrane of fetal respiratory epithelia, which makes them possible candidates for being mediators of fetal apical Cl(-) secretion. The aim of the study was to examine the potential of ClC-2, -3 and -5 as alternative apical airway epithelial Cl(-) channels in normal lung development and their possible role in the development of hypoplastic lungs in CDH. We also wanted to examine ClC-2, -3 and -5 together with the NKCC-1 in hyperplastic lungs created by TO.


METHODS
Pregnant Sprague-Dawley rat dams were given nitrofen on gestational day 9.5 to induce pulmonary hypoplasia. Controls were given only olive oil. The rat fetuses were removed on days 17, 19 and 21. Hyperplastic lungs were created by intrauterine TO of rat fetuses on day 19 and the lungs were harvested on day 21. The pulmonary expression of ClC-2, -3, -5 and NKCC-1 was then analyzed using Western blot.


RESULTS
We found that the temporal expression of ClC-2 and -3 in normal fetal lungs points toward a developmental regulation. ClC-2 and -3 were also both down-regulated on day 21 in hypoplastic CDH lungs. In TO induced hyperplastic lungs, the levels of ClC-2 were found to be significantly up-regulated. NKCC-1 showed a tendency toward up-regulation in hyperplastic lungs, while ClC-3 showed a tendency to be down-regulated, but no statistically significant changes could be seen. There was no difference between controls and any of the groups for the expression of ClC-5.


CONCLUSIONS
We show that the developmental changes in ClC-2 and ClC-3 protein expression are negatively affected in hypoplastic CDH lungs. Lung hyperplasia created by TO up-regulates the expression of ClC-2. ClC-2 is therefore an interesting potential target in the development of novel, non-invasive, therapies for CDH treatment.
Ringman Uggla
Andreas
A
Research Laboratory Q2:09, Department of Woman and Child Health, Nordic Centre of Excellence for Research in Water Imbalance Related Disorders, Astrid Lindgren Children's Hospital, Karolinska University Hospital, Karolinska Institutet, 171 76 Stockholm, Sweden. andreas.ringman.uggla@ki.se
Zelenina
Marina
M
Eklöf
Ann-Christine
AC
Aperia
Anita
A
Frenckner
Björn
B
D000818:Animals; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D006548:Hernia, Diaphragmatic / Q000139:chemically induced; D065630:Hernias, Diaphragmatic, Congenital; D006965:Hyperplasia; D008168:Lung / Q000196:embryology / Q000378:metabolism* / Q000473:pathology*; D008171:Lung Diseases / Q000139:chemically induced; D010575:Pesticides / Q000009:adverse effects; D010647:Phenyl Ethers / Q000009:adverse effects; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D064506:Solute Carrier Family 12, Member 2; D014132:Trachea / Q000601:surgery; D015854:Up-Regulation
D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; C115376:ClC-3 channel; D010575:Pesticides; D010647:Phenyl Ethers; C578879:Slc12a2 protein, rat; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; C007350:nitrofen