Postnatal upregulation of cyclooxygenase-2 (COX-2) drives anatomical closure of the ductus arteriosus

Postnatal environmental changes markedly facilitate functional closure of the ductus arteriosus (DA). Vascular remodeling during both fetal and postnatal periods is essential for achieving permanent anatomical DA closure; however, molecular mechanisms driving postnatal DA remodeling have yet to be fully elucidated. Single-cell RNA sequencing (scRNA-seq) revealed that postnatal mouse smooth muscle cells (SMCs) formed a transcriptionally distinct cluster compared with fetal ductus arteriosus smooth muscle cells (DASMCs), whereas other cell types remained in the same cluster after birth, highlighting a critical role for SMCs in postnatal DA remodeling. Transcriptome analysis identified genes differentially expressed in postnatal DASMCs compared with the adjacent arteries, among which cyclooxygenase-2 (COX-2) exhibited the most robust induction. Exposure to hydrogen peroxide, simulating oxidative stress encountered after birth, significantly increased COX-2 mRNA and protein expression in DASMCs. Given that platelet adhesion is a postnatal event in the DA and platelets are a major source of thromboxane A₂, we administered thromboxane A₂ receptor agonist to DASMCs and found marked COX-2 upregulation. Lentiviral-based overexpression of COX-2 led to prostaglandin E₂ (PGE₂) production. PGE₂ stimulation increased expression of <i>Nr4a1</i> via PGE₂ receptor EP4. <i>Nr4a1</i> silencing inhibited DASMC proliferation. To assess the in vivo relevance of COX-2, we maternally administered a selective COX-2 inhibitor, SC-236, and found impaired postnatal DA closure in mice. These data suggest that postnatal upregulation of COX-2 in DASMCs promotes anatomical closure, potentially involving <i>Nr4a1</i>; inhibition of COX-2 at the very early postnatal period may interfere with DA closure.<b>NEW & NOTEWORTHY</b> Postnatal environmental changes promote anatomical closure of the ductus arteriosus (DA). This study identifies cyclooxygenase-2 (COX-2) as a key driver of postnatal DA remodeling. DA smooth muscle cells (SMCs) undergo transcriptional changes after birth, with COX-2 markedly upregulated by oxidative stress and thromboxane A₂. COX-2-derived prostaglandin E₂ enhanced SMC proliferation, potentially involving <i>Nr4a1</i>. In vivo COX-2 inhibition impaired DA closure, highlighting its essential role and potential vulnerability to early postnatal COX-2 suppression.