Krüppel-like Factor 4 (Klf4) in human and mouse lung development: Regulation of ATII Cell Homeostasis in Lungs of Newborn Mice Exposed to HYX

Background: Premature infants, who require high O2, often develop bronchopulmonary dysplasia, a neonatal chronic lung disease, characterized by a reduced alveolarization. Prior studies showed that lung growth arrest is linked to reduced Kruppel-like factor 4 (Klf4), a transcription factor regulating cell pluripotency and survival. Aim: To study (1) spatiotemporal expression of Klf4 in type II alveolar epithelial cells (ATII) in human and murine lung development; (2) if hyperoxia-induced lung injury is linked to reduced Klf4 in ATII cells. Methods: (1) Investigation of human fetal and murine lungs. (2) Newborn mice or cultured murine ATII cells (MLE-12) were exposed to 85% O2 (HYX) or room air (NOX). Klf4 was overexpressed in MLE-12 using sleeping beauty transposon system. Results: (1) Klf4 was localized in CDH1 or surfactant protein C (SfptC) positive cells during human and murine lung development, respectively, by immunofluorescence. (2) Decreased SftptC and aquaporin 5 coupled with reduced radial alveolar count and increased mean linear intercept after HYX was related to diminished lung Klf4 gene and protein expression. Lower cell survival of MLE-12 and increased markers of epithelial-mesenchymal transition after HYX were linked to reduced Klf4 mRNA and protein abundance. Overexpression of Klf4, however, aggravated the anti-proliferative effect of HYX on MLE-12. Conclusion: Our study does not only identify Klf4 in epithelial cells during murine and human lung development, but also as a potential novel regulator of AECII homeostasis in hyperoxia-induced lung injury, and thereby also as a target to enable lung regeneration.