Abstract 19929: Delta Like Ligand 4 -Notch1 Signaling Inhibits Postnatal Lung Alveolarization by Endothelial Cell and Epithelial Cell Communication
Postnatal lung development involves two processes, angiogenesis and alveolarization. It is well known that angiogenesis is essential for alveolarization, however the mechanism is still unknown. Previously, we demonstrated that G protein–coupled receptor kinase 2–interacting protein-1 (GIT1) knockout mice showed impaired lung angiogenesis and alveolarization and that GIT1 inhibited retinal sprouting angiogenesis by suppressing Dll4-Notch1 pathway. Recent transcriptome analysis predicts that Notch signaling plays an inhibitory role in perinatal lung maturation. Dll4 is exclusively expressed in endothelial cell (EC) but Notch1 is expressed in both EC and airway epithelial cell (AEC). We hypothesize that increased Dll4 in EC mediates Notch1 activation in AEC, which contributes to impaired alveolarization in GIT1-KO mice. To test this hypothesis, we measured Dll4 mRNA and protein expression and found 3 fold and 7 fold increases respectively in lungs of GIT1-KO mice compared to WT mice. Notch1 is the major receptor of Dll4. Notch1 activation, measured by intracellular domain of Notch 1 (N1-ICD) protein expression, was increased 4 fold in lungs of GIT1-KO mice. Most importantly, immunohistochemistry staining demonstrated that Dll4 is enhanced in EC of GIT1-KO mice. In contrast, N1-ICD increased in both EC and AEC in GIT1-KO mice, which suggests Dll4 in EC activated Notch1 in AEC. In vitro, we studied the effects of Dll4 on AEC. Immobilized Dll4 significantly activated Notch1 and its downstream target genes Hey1 and Hes1. Dll4 treatment decreased AEC proliferation and increased apoptosis as demonstrated by BrdU incorporation and the level of cleaved Caspase 3 respectively. Similarly, the proliferation of AEC was decreased and apoptosis increased when they were co-cultured with GIT1-KO lung ECs compared to those with WT lung ECs. These data suggest that EC derived Dll4 activates Notch 1 in AEC to inhibit AEC proliferation and increase apoptosis. In summary, we describe a novel mechanism for how angiogenesis affects alveolarization. This observation furthers our knowledge of postnatal lung development, and suggests that Dll4 is a potential therapeutic target for lung development related diseases, such as bronchopulmonary dysplasia.
Author Disclosures: G. zhu: None. S. Majumder: None. X. Xu: None. M. Sowden: None. S. Senchanthisai: None. M. Reilly: None. J. Pang: None.
- © 2016 by American Heart Association, Inc.