Bmp9 regulates Notch signaling and the temporal dynamics of angiogenesis via Lunatic Fringe

Sprouting angiogenesis and blood vessel stabilization require precise coordination between endothelial cells (ECs) and pericytes. Bone Morphogenic Protein 9 (Bmp9), whose signaling through activin receptor-like kinase 1 (Alk1) is dysregulated in several diseases, was thought to regulate these processes by independently activating Notch target genes in an additive fashion with canonical Notch signaling. Here, through predictive computational modeling validated in mice, zebrafish, and human cell lines, we uncover that Bmp9 enhances Notch activity synergistically by upregulating Lunatic Fringe (Lfng) in ECs. Specifically, Bmp9-induced Lfng enhances Notch receptor activation, most strongly when Delta-like ligand 4 (Dll4) is also present. This Lfng regulation alters vessel branching by modulating the timing of EC phenotype selection and rearrangement during angiogenesis. Lfng also contributes to pericyte-driven vessel stabilization by mediating Jagged1 upregulation in Bmp9-stimulated ECs. In summary, Bmp9-upregulated Lfng enhances Dll4-Notch1 signaling in ECs and Jag1-Notch3 activation in pericytes, shaping angiogenic sprouting and stabilization outcomes.