AQP1 and edema: Currently, mechanisms underlying pulmonary edema at an early stage of BPD mainly involve increased permeability of lung vasculature induced by inflammatory factors [6, 37], defects in pulmonary fluid clearance induced by aquaporin-1 and amiloride-sensitive sodium channel upregulation on the surface of AEC-II [38], and disruption of the pulmonary vascular endothelial barrier induced by downregulation of connexin proteins [8].