Mild hypoxia impairs alveolarization in the endothelial nitric oxide synthase-deficient mouse.
In addition to its vasodilator properties, nitric oxide (NO) promotes angiogenesis in the systemic circulation and tumors. However, the role of NO in promoting normal lung vascular growth and its impact on alveolarization during development or in response to perinatal stress is unknown. We hypothesized that NO modulates lung vascular and alveolar growth and that decreased NO production impairs distal lung growth in response to mild hypoxia. Litters of 1-day-old mouse pups from parents that were heterozygous for endothelial nitric oxide synthase (eNOS) deficiency were placed in a hypobaric chamber at a simulated altitude of 12,300 ft (Fi(O(2)) = 0.16). After 10 days, the mice were killed, and lungs were fixed for morphometric and molecular analysis. Compared with wild-type controls, mean linear intercept (MLI), which is inversely proportional to alveolar surface area, was increased in the eNOS-deficient (eNOS -/-) mice [51 +/- 2 micro m (eNOS -/-) vs. 41 +/- 1 micro m (wild type); P < 0.01]. MLI was also increased in the eNOS heterozygote (+/-) mice (44 +/- 1 micro m; P < 0.03 vs. wild type). Vascular volume density was decreased in the eNOS -/- mice compared with wild-type controls (P < 0.03). Lung vascular endothelial growth factor (VEGF) protein and VEGF receptor-1 (VEGFR-1) protein content were not different between the study groups. In contrast, lung VEGFR-2 protein content was decreased from control values by 63 and 34% in the eNOS -/- and eNOS +/- mice, respectively (P < 0.03). We conclude that exposure to mild hypoxia during a critical period of lung development impairs alveolarization and reduces vessel density in the eNOS-deficient mouse. We speculate that NO preserves normal distal lung growth during hypoxic stress, perhaps through preservation of VEGFR-2 signaling.
Balasubramaniam
Vivek
V
Pediatric Heart Lung Center and Section of Pediatric Pulmonary Medicine, University of Colorado School of Medicine, Denver, Colorado 80218, USA. vivek.balasubramaniam@uchsc.edu
Tang
Jen-Ruey
JR
Maxey
Anne
A
Plopper
Charles G
CG
Abman
Steven H
SH
D000818:Animals; D000831:Animals, Newborn; D001835:Body Weight; D016228:Endothelial Growth Factors / Q000096:biosynthesis; D006548:Hernia, Diaphragmatic / Q000378:metabolism / Q000473:pathology; D065630:Hernias, Diaphragmatic, Congenital; D006976:Hypertension, Pulmonary / Q000378:metabolism / Q000473:pathology; D000860:Hypoxia / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis; D008222:Lymphokines / Q000096:biosynthesis; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009389:Neovascularization, Pathologic / Q000151:congenital / Q000378:metabolism / Q000473:pathology; D019001:Nitric Oxide Synthase / Q000235:genetics*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010100:Oxygen / Q000494:pharmacology; D010641:Phenotype; D011650:Pulmonary Alveoli / Q000002:abnormalities* / Q000378:metabolism* / Q000473:pathology; D042461:Vascular Endothelial Growth Factor A; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000096:biosynthesis; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000096:biosynthesis; D042442:Vascular Endothelial Growth Factors
D016228:Endothelial Growth Factors; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D010100:Oxygen