Endocardium-to-coronary artery differentiation during heart development and regeneration involves sequential roles of Bmp2 and Cxcl12/Cxcr4.

Endocardial cells lining the heart lumen are coronary vessel progenitors during embryogenesis. Re-igniting this developmental process in adults could regenerate blood vessels lost during cardiac injury, but this requires additional knowledge on molecular regulators. Here, we use mouse genetics and scRNAseq to identify novel regulators of endocardial angiogenesis and precisely assess the role of CXCL12/CXCR4 signaling. Time-specific lineage tracing demonstrated that endocardial cells differentiated in coronary endothelial cells primarily at mid-gestation. A new mouse line reporting CXCR4 activity—along with cell-specific gene deletions—revealed it was specifically required for artery morphogenesis rather than angiogenesis. Integrating scRNAseq data of endocardial-derived coronary vessels from mid- and late-gestation identified a Bmp2-expressing transitioning population specific to mid-gestation. Bmp2 stimulated endocardial angiogenesis in vitro and in injured neonatal mouse hearts. Our data shed light on how understanding the molecular mechanisms underlying endocardial angiogenesis can identify new potential therapeutic targets promoting revascularization of the injured heart. Overall design: E17.5 BmxCreERT2;Rosa26tdTomato lineage-labeled hearts in which the Cxcr4flox allele was removed from endo cells at E9.5. FACS-sorted CD31+/tdTomato+ cells from Cxcr4 heterozygous (Cxcr4fl/+, control) and Cxcr4 knock-out (Cxcr4fl/fl, mutant) hearts were collected and processed using the 10X Genomics platform