Project description:Each organ of the human body requires locally-adapted blood vessels1–3. 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 signals4–6. 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 which lines the brain surface, and whose 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/β-catenin-dependent organotypic control of brain angiogenesis is lost, resulting in a properly patterned, yet blood-brain barrier-defective cerebrovasculature. 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.
Project description: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/β-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.
Project description:To address the role of endothelial Wnt/β-catenin signaling in CNS angiogenesis, we compared the bulk transcriptomes of WT and Wnt/β-catenin signaling-deficient PHBC endothelial cells, prior to CNS vascular invasion. To this end, we used three approaches to abrogate endothelial Wnt/β-catenin signaling: Morpholino-mediated knock-down of gpr124, reck or wnt7aa. We find that the expression of mmp25b is decreased in PHBC endothelial cells of all Wnt/β-catenin signaling deficient conditions as compared to the WT controls.
Project description:The endothelium first forms in the blood islands in the extra-embryonic yolk sac and then throughout the embryo to establish circulatory networks that further acquire organ-specific properties during development to support diverse organ functions. Here, we investigated the properties of endothelial cells (ECs), isolated from four human major organsthe heart, lung, liver, and kidneys in individual fetal tissues at three months' gestation, at gene expression, and at cellular function levels. We showed that organ-specific ECs have distinct expression patterns of gene clusters, which support their specific organ development and functions. These ECs displayed distinct barrier properties, angiogenic potential, and metabolic rate and support specific organ functions. Our findings showed the link between human EC heterogeneity and organ development and can be exploited therapeutically to contribute in organ regeneration, disease modeling, as well as guiding differentiation of tissue-specific ECs from human pluripotent stem cells.
Project description:Angiogenesis is a highly regulated process essential for organ development and maintenance, and its deregulation contributes to inflammation, cardiac disorders and cancer. The Ca2+/Nuclear Factor of Activated T-cells (NFAT) signaling pathway is central to endothelial cell angiogenic responses, and it is activated by stimuli like the vascular endothelial growth factor A (VEGF). NFAT phosphorylation by dual-specificity tyrosine phosphorylation-regulated kinases (DYRKs) is thought to be an inactivating event. Contrary to expectations, we show that the DYRK family member DYRK1A positively regulates VEGF-dependent NFAT transcriptional responses in primary endothelial cells. DYRK1A silencing reduces intracellular Ca2+ influx in response to VEGF, which dampens NFAT activation. The effect is exerted at the level of VEGFR2 accumulation leading to impairment in PLCg1 activation. Notably, Dyrk1a heterozygous mice show defects in developmental retinal vascularization. Our data establish a regulatory circuit, DYRK1A/ Ca2+/NFAT, to fine-tune endothelial cell proliferation and angiogenesis.
Project description:To identify previously unknown determinants of endothelial cell sprouting, we defined and exploited a pharmacological strategy for the manipulation of angiogenic cell behavior in vivo. Whereas high vascular endothelial growth factor receptor (Vegfr) signaling is known to promote tip cell (TC) specification, activation of the Notch receptor via its ligand Delta-like 4 (Dll4) represses the TC phenotype to promote stalk cell (SC) fate. Conversely, suppression of Notch activity upon antagonistic interaction with its ligand Jagged1 pro- motes TC formation. Hence, specification of TCs involves tight spatiotemporal control of Vegfr/Notch signaling. Consequently, we hypothesized that the pharmacological manipulation of Vegfr/Notch signaling selectively during zebrafish intersegmental vessel (ISV) angiogenesis would enable the precise control of angiogenic EC behavior and sprouting- associated gene expression in vivo. For more information, see Herbert et al., 2012, PMID 22921365.