Abstract
Background:
Premature infants requiring mechanical ventilation and supplemental oxygen for respiratory support are at increased risk for bronchopulmonary dysplasia (BPD), wherein inflammation have been proposed as a driver of hyperoxia-induced injuries, including persistent loss of endothelial progenitor cells (EPCs), impaired vascularization and eventual alveolar simplification in BPD lungs. However, the underlying mechanisms linking these phenomena remain poorly defined.
Methods:
We used clodronate liposomes to deplete macrophages in a mouse model of neonatal hyperoxia-induced lung injury to evaluate if EPC loss in BPD lungs could be an effect of macrophage infiltration. We further generated in vitro culture systems initiated with cord blood (CB)-derived CD34+ EPCs and neonatal macrophages either polarized from CB-derived monocytes or isolated from tracheal aspirates of human preterm infants requiring mechanical ventilation and oxygen supplementation, to identify EV-transmitted molecular mechanism that is critical for inhibitory actions of hyperoxic macrophages on EPCs.
Results:
Initial experiments using mouse model identified the crucial role of macrophage infiltration in eliciting significant reduction of c-Kit+ EPCs in BPD lungs. Further examination of this concept in human system, we found that hyperoxia-exposed neonatal macrophages hamper human CD34+ EPC maintenance and impair endothelial function in the differentiated progeny via the EV transmission of miR-23a-3p. Notably, treatment with antagomiR-23a-3p to silence miR-23a-3p in vivo enhances c-Kit+ EPC maintenance, and increases capillary density, and consequently mitigates simplified alveolarization in BPD lungs.
Conclusion:
Our findings highlight the importance of pulmonary intercellular communication in the pathophysiology of BPD, by identifying a linkage through vesicle transfer of miR-23a-3p from hyperoxic macrophages to EPCs, and thus demonstrating potential for novel therapeutic target in BPD.