Critical role of the axonal guidance cue EphrinB2 in lung growth, angiogenesis, and repair.

RATIONALE: Lung diseases characterized by alveolar damage currently lack efficient treatments. The mechanisms contributing to normal and impaired alveolar growth and repair are incompletely understood. Axonal guidance cues (AGC) are molecules that guide the outgrowth of axons to their targets. Among these AGCs, members of the Ephrin family also promote angiogenesis, cell migration, and organogenesis outside the nervous system. The role of Ephrins during alveolar growth and repair is unknown. OBJECTIVES: We hypothesized that EphrinB2 promotes alveolar development and repair. METHODS: We used in vitro and in vivo manipulation of EphrinB2 signaling to assess the role of this AGC during normal and impaired lung development. MEASUREMENTS AND MAIN RESULTS: In vivo EphrinB2 knockdown using intranasal siRNA during the postnatal stage of alveolar development in rats arrested alveolar and vascular growth. In a model of O(2)-induced arrested alveolar growth in newborn rats, air space enlargement, loss of lung capillaries, and pulmonary hypertension were associated with decreased lung EphrinB2 and receptor EphB4 expression. In vitro, EphrinB2 preserved alveolar epithelial cell viability in O(2), decreased O(2)-induced alveolar epithelial cell apoptosis, and accelerated alveolar epithelial cell wound healing, maintained lung microvascular endothelial cell viability, and proliferation and vascular network formation. In vivo, treatment with intranasal EphrinB2 decreased alveolar epithelial and endothelial cell apoptosis, preserved alveolar and vascular growth in hyperoxic rats, and attenuated pulmonary hypertension. CONCLUSION: The AGC EphrinB2 may be a new therapeutic target for lung repair and pulmonary hypertension.

Blunted hypoxic pulmonary vasoconstriction in experimental neonatal chronic lung disease.

RATIONALE: Neonatal chronic lung disease (CLD), caused by prolonged mechanical ventilation (MV) with O(2)-rich gas, is the most common cause of long-term hospitalization and recurrent respiratory illness in extremely premature infants. Recurrent episodes of hypoxemia and associated ventilator adjustments often lead to worsening CLD. The mechanism that causes these hypoxemic episodes is unknown. Hypoxic pulmonary vasoconstriction (HPV), which is partially controlled by O(2)-sensitive voltage-gated potassium (K(v)) channels, is an important adaptive response to local hypoxia that helps to match perfusion and ventilation in the lung. OBJECTIVES: To test the hypothesis that chronic lung injury (CLI) impairs HPV. METHODS: We studied preterm lambs that had MV with O(2)-rich gas for 3 weeks and newborn rats that breathed 95%-O(2) for 2 weeks, both of which resulted in airspace enlargement and pulmonary vascular changes consistent with CLD. MEASUREMENTS AND MAIN RESULTS: HPV was attenuated in preterm lambs with CLI after 2 weeks of MV and in newborn rats with CLI after 2 weeks of hyperoxia. HPV and constriction to the K(v)1.x-specific inhibitor, correolide, were preferentially blunted in excised distal pulmonary arteries (dPAs) from hyperoxic rats, whose dPAs exhibited decreased K(v)1.5 and K(v)2.1 mRNA and K(+) current. Intrapulmonary gene transfer of K(v)1.5, encoding the ion channel that is thought to trigger HPV, increased O(2)-sensitive K(+) current in cultured smooth muscle cells from rat dPAs, and restored HPV in hyperoxic rats. CONCLUSIONS: Reduced expression/activity of O(2)-sensitive K(v) channels in dPAs contributes to blunted HPV observed in neonatal CLD.