Mutations in bone morphogenetic protein type II receptor (BMPR2) have been found in patients with congenital heart disease-associated pulmonary arterial hypertension (CHD-PAH). Our study aimed to clarify whether deficient BMPR2 signalling acts through downstream effectors, inhibitors of DNA-binding proteins (IDs), during heart development to contribute to the progress of PAH in CHD patients. To confirm that IDs are downstream effectors of BMPR2 signalling in cardiac mesoderm progenitors (CMPs) and contribute to PAH, we generated Cardiomyocytes (CMs)-specific Id 1/3 knockout mice (Ids cDKO), and 12/25 developed mild PAH with altered haemodynamic indices and pulmonary vascular remodelling. Moreover, we generated ID1 and ID3 double-knockout (IDs KO) human embryonic stem cells that recapitulated the BMPR2 signalling deficiency of CHD-PAH iPSCs. CMs differentiated from induced pluripotent stem cells (iPSCs) derived from CHD-PAH patients with BMPR mutations exhibited dysfunctional cardiac differentiation and reduced Ca2+ transients, as evidenced by confocal microscopy experiments. Smad1/5 phosphorylation and ID1 and ID3 expression were reduced in CHD-PAH iPSCs and in Bmpr2 +/- rat right ventricles. Moreover, Ultrasound revealed that 33% of Ids cDKO mice had detectable defects in their ventricular septum and pulmonary regurgitation. CMs isolated from the mouse right ventricles also showed reduced Ca2+ transients and shortened sarcomeres. Single-cell RNA(scRNA)-seq analysis revealed impaired differentiation of CMPs and downregulated USP9X expression in IDs KO cells compared with wild-type (WT) cells. We found that BMPR2 signals through IDs and USP9X to regulate cardiac differentiation, and the loss of ID1 and ID3 expression contributes to CM dysfunction in CHD-PAH patients with BMPR2 mutations.
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