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A6109 - Endothelial Calcitonin Receptor-Like Receptor Is Necessary to Protect Neonatal Mice Against Experimental Bronchopulmonary Dysplasia
Author Block: B. Shivanna, A. Shrestha, R. Menon; Pediatrics, Baylor College of Medicine, Houston, TX, United States.
Rationale: Interrupted pulmonary angiogenesis is a hallmark of bronchopulmonary dysplasia (BPD), the most common chronic lung disease of preterm infants. Adrenomedullin (AM) is a multifunctional peptide that mediates its angiogenic effects via calcitonin receptor-like receptor (Calcrl) and receptor activity-modifying protein (RAMP) -2. We observed that global AM-deficient mice have an increased susceptibility to neonatal hyperoxic lung injury. However, the endothelial cell-specific contribution and mechanisms of AM-mediated effects on developing lungs are unknown. Therefore, we tested the hypothesis that endothelial AM signaling-deficient neonatal mice will display increased susceptibility to hyperoxia-induced experimental BPD compared with wild-type mice. Methods: In vivo studies: To disrupt endothelial AM signaling, we decreased the expression of the AM receptor, Calcrl, in the mouse lung endothelial cells by breeding Calcrlflox/flox mice with Tie-Cre mice. One-day-old endothelial Calcrl-sufficient (eCalcrl +/+) or -deficient (eCalcrl +/-) mice were exposed to air (FiO2 21%) or hyperoxia (FiO2 70%) for up to 14 d, following which the mouse lungs were harvested to determine angiogenesis and alveolarization, and the expression of Calcrl. In vitro studies: For mechanistic studies, we used fetal human pulmonary artery endothelial cells (HPAECs) and human pulmonary artery microvascular endothelial cells (HPMECs) and determined the effects of Calcrl antagonist, Calcrl knockdown, and AM on angiogenesis and activation of extracellular signal-regulated kinase (ERK)-1/2 and endothelial nitric oxide synthase (eNOS). Results: Exposure of neonatal mice to 70% oxygen decreased the expression of endothelial Calcrl expression. Further, endothelial Calcrl deficiency augmented hyperoxia-induced alveolar and pulmonary vascular simplification in neonatal mice. Mechanistically, inhibition or knockdown of Calcrl in human fetal lung endothelial cells decreased eNOS expression, ERK1/2 activation, and in vitro angiogenesis. Additionally, inhibition of ERK1/2 and eNOS signaling in these cells decreased AM-mediated angiogenesis. Conclusion: We conclude that endothelial AM signaling protects against hyperoxia-induced experimental BPD via ERK1/2 and eNOS pathways. Our results indicate that AM and Calcrl-RAMP2 interface are potential therapeutic targets for the management of BPD in preterm infants.