Mechanistic Roles of Adrenomedullin and its Signaling Receptors in Experimental Bronchopulmonary Dysplasia and Pulmonary Hypertension

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Abstract/Summary Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of preterm infants; development of pulmonary hypertension (PH) in these infants increases BPD-associated mortality and morbidity. Interrupted angiogenesis and alveolarization, endothelial cell dysfunction, and pulmonary vascular remodeling contribute to the pathogenesis of BPD and PH, a disease for which there are no specific therapies. Adrenomedullin (AM) is an endogenous peptide that regulates angiogenesis and endothelial cell survival and function, making this peptide an ideal target to develop therapies for this disease. AM signals through its cognate receptors, calcitonin-receptor like receptor (Calcrl) and receptor activity-modifying protein (RAMP)-2. Recent studies indicate that AM signaling is necessary for lung development and to ameliorate lung injury in neonatal rodents. However, it is unclear if AM improves BPD-associated lung and pulmonary vascular dysfunction in these animals. Further, the cellular and molecular mechanisms by which AM signaling protects against neonatal lung injury are unknown. So, we propose to address these knowledge gaps using an established neonatal mouse model of hyperoxic lung injury. Our preliminary studies indicate that AM signaling is necessary for healthy lung development and to mitigate hyperoxia-induced lung injury in neonatal mice. Further, we observed that AM regulates extracellular signal-regulated kinase (ERK) 1/2 activation and endothelial nitric oxide synthase (eNOS) expression in the lungs of neonatal mice and in fetal human pulmonary endothelial cells. Based on these data, we will test the central hypothesis that endothelial-specific AM signaling activates ERK 1/2 and eNOS to promote angiogenesis and prevent endothelial cell dysfunction in neonatal lungs, which in turn will mitigate hyperoxia-induced experimental BPD and PH. We will use a unique combination of molecular, cellular, functional, and translational approaches to test this hypothesis. In Aim 1, we will use transgenic mice to determine if endothelial-specific AM signaling is necessary and sufficient to protect neonatal mice against hyperoxia-induced lung and pulmonary vascular injury and dysfunction. In Aim 2, we will use double transgenic mice to examine the interactions between AM, ERK 1/2 signaling, and eNOS activity in the developing lungs exposed to hyperoxia. Aim 3, which has two sub-aims, is designed to examine the translational potential of our proposal. In sub-aim 1, we will examine if AM signaling regulates hyperoxia-induced injury in human pulmonary endothelial cells. In sub-aim 2, we will determine the expression of AM and its receptors in the lungs of infants with and without BPD. We expect that successful completion of these studies would provide a mechanistic rationale for targeting AM, Calcrl, or RAMP2 to develop meaningful therapies for BPD and PH. Further, these studies could provide a scientific premise for clinical trials with AM to treat BPD patients with PH. Our studies could also positively impact other angiogenesis- and PH-related research areas, such as congenital diaphragmatic hernia and congenital lung hypoplasia.