P1.153: Platelets are Activated and Increased in the Lungs of Neonatal Mice with Experimental Bronchopulmonary Dysplasia and Pulmonary Hypertension

Background: Pulmonary hypertension (PH) is a life-threatening condition characterized by inflammation, pulmonary vascular remodeling, and vasoconstriction. In the neonatal population, 25-60% of former-preterm infants with severe bronchopulmonary dysplasia (BPD) demonstrate co-existing PH. Current therapies primarily target vasoconstriction and are often ineffective in severe disease; thus, identification of novel mechanisms driving PH is of important clinical relevance. Accumulating data from adult studies demonstrate platelets are mediators of pulmonary vascular inflammation and play a role in the pathogenesis of PH, but whether platelets contribute to pulmonary vascular remodeling in neonatal PH is unknown.

Methods: C57BL/6 neonatal mice remained in normoxia or were placed in hypobaric hypoxia at day of life (DOL 1). Lung injury was established at DOL 15 by mean linear intercept (MLI) and PH was assessed by right ventricular systolic pressure (RVSP) and right ventricular hypertrophy (RVH). Whole blood was obtained via right ventricle cardiac puncture and cell surface markers of platelet activation were quantified by flow cytometry. Lungs were inflated for immunohistochemistry or homogenized for ELISA. Data were analyzed using unpaired t test and reported as mean SE with significance defined as p< 0.05.

Results: Hypoxia resulted in increased MLI (51.41.0 vs. 40.61.9 [m], p< 0.001), increased RVSP (29.71.8 vs. 21.50.3 [mmHg], p< 0.0001), and RVH (0.40.0 vs. 0.30.0 [RV/LV+S], p< 0.01). Platelets from hypoxic mice were activated with increased expression of platelet P-selectin (11.71.9 vs. 3.31.0 [%], p< 0.01) and activation of the transmembrane integrin α2βB3 (14.02.6 vs. 4.20.7 [%], p< 0.01). Platelets were increased in the lungs of hypoxic mice, with more CD41+ cells (2.260.7 vs. 0.930.1 [%], p< 0.05) on immunostaining and increased platelet factor 4 (PF4), in lung homogenates (3331474 vs. 1256248 [ng/mL], p< 0.01).

Conclusion: Neonatal platelets are activated in the circulation and increased in the lungs of mice with BPD and PH. However, whether platelets promote pulmonary vascular remodeling and the development of PH remains unclear. Our parallel clinical study will assess platelet activation in infants with BPD-associated PH, and future translational investigation will determine the contribution of platelets to PH using the thrombocytopenic mouse. These findings have the potential to lead to a paradigm shift in our understanding of BPD-associated neonatal PH, laying the foundation for the development of targeted, individualized therapies for this population.