Endothelial Adenosine Monophosphate-Activated Protein Kinase-Alpha1 Deficiency Potentiates Hyperoxia-Induced Experimental Bronchopulmonary Dysplasia and Pulmonary Hypertension.

Bronchopulmonary dysplasia and pulmonary hypertension, or BPD-PH, are serious chronic lung disorders of prematurity, without curative therapies. Hyperoxia, a known causative factor of BPD-PH, activates adenosine monophosphate-activated protein kinase (AMPK) α1 in neonatal murine lungs; however, whether this phenomenon potentiates or mitigates lung injury is unclear. Thus, we hypothesized that (1) endothelial AMPKα1 is necessary to protect neonatal mice against hyperoxia-induced BPD-PH, and (2) AMPKα1 knockdown decreases angiogenesis in hyperoxia-exposed neonatal human pulmonary microvascular endothelial cells (HPMECs). We performed lung morphometric and echocardiographic studies on postnatal day (P) 28 on endothelial AMPKα1-sufficient and -deficient mice exposed to 21% O2 (normoxia) or 70% O2 (hyperoxia) from P1-P14. We also performed tubule formation assays on control- or AMPKα1-siRNA transfected HPMECs, exposed to 21% O2 or 70% O2 for 48 h. Hyperoxia-mediated alveolar and pulmonary vascular simplification, pulmonary vascular remodeling, and PH were significantly amplified in endothelial AMPKα1-deficient mice. AMPKα1 siRNA knocked down AMPKα1 expression in HPMECs, and decreased their ability to form tubules in normoxia and hyperoxia. Furthermore, AMPKα1 knockdown decreased proliferating cell nuclear antigen expression in hyperoxic conditions. Our results indicate that AMPKα1 is required to reduce hyperoxia-induced BPD-PH burden in neonatal mice, and promotes angiogenesis in HPMECs to limit lung injury.

Adrenomedullin Deficiency Potentiates Lipopolysaccharide-Induced Experimental Bronchopulmonary Dysplasia in Neonatal Mice.

Lung inflammation interrupts alveolarization and causes bronchopulmonary dysplasia (BPD). Besides mechanical ventilation and hyperoxia, sepsis contributes to BPD pathogenesis. Adrenomedullin (Adm) is a multifunctional peptide that exerts anti-inflammatory effects in the lungs of adult rodents. Whether Adm mitigates sepsis-induced neonatal lung injury is unknown. The lung phenotype of mice exposed to early postnatal lipopolysaccharide (LPS) was recently shown to be similar to that in human BPD. This model was used to test the hypothesis that Adm-deficient neonatal mice will display increased LPS-induced lung injury than their wild-type (WT) littermates. Adm-deficient mice or their WT littermates were intraperitoneally administered 6 mg/kg of LPS or vehicle daily on postnatal days (PNDs) 3 to 5. The lungs were harvested at several time points to quantify inflammation, alveolarization, and vascularization. The extent of LPS-induced lung inflammation in Adm-deficient mice was 1.6-fold to 10-fold higher than their WT littermates. Strikingly, Adm deficiency induced STAT1 activation and potentiated STAT3 activation in LPS-exposed lungs. The severity of LPS-induced interruption of lung development was also greater in Adm-deficient mice at PND7. At PND14, LPS-exposed WT littermates displayed substantial improvement in lung development, whereas LPS-exposed Adm-deficient mice continued to have decreased lung development. These data indicate that Adm is necessary to decrease lung inflammation and injury and promote repair of the injured lungs in LPS-exposed neonatal mice.