An organ-specific angiogenic control mechanism for endothelial tailoring

Each organ of the human body requires locally-adapted blood vessels. The gain of such organotypic vessel specializations is often deemed molecularly unrelated to the process of organ vascularization. Opposing this model, we reveal a molecular mechanism for brain-specific angiogenesis, that operates under the control of Wnt7a/b ligands, well-known blood-brain barrier maturation signals. The control mechanism relies on Wnt7a/b-dependent expression of Mmp25 in brain endothelial cells. This hitherto poorly characterized GPI-anchored matrix metalloproteinase is selectively required in endothelial tip cells to enable their initial migration across the pial basement membrane lining the brain surface, which distinctive molecular composition is controlled by embryonic pial fibroblasts. Mechanistically, Mmp25 confers brain invasive competence by cleaving the pial basement membrane-enriched Col4a5/6 within a short non-collagenous region of the central helical part of the heterotrimer. Upon genetic interference with pial basement membrane composition, the Wnt/ß-catenin-dependent organotypic control of brain angiogenesis is lost, resulting in properly patterned, yet blood-brain barrier-defective cerebrovasculatures. This work reveals an organ-specific angiogenesis mechanism, sheds light on tip cell mechanistic angiodiversity, and thereby illustrates how organs, by imposing local constraints on angiogenic tip cells, can select vessels matching their distinctive physiological requirements. Overall design: The samples in this submission are single cells, sorted into single wells of a 96 or 384 well plates. The cells were lysed and transcriptomic sequencing data was obtained using Smart-seq2 chemistry