Transforming growth factor-β1 (TGFβ1), a major promoter of myofibroblast differentiation, induces α-smooth muscle (sn) actin, modulates the expression of adhesive receptors, and enhances the synthesis of extracellular matrix (ECM) molecules including ED-A fibronectin (FN), an isoform de novo expressed during wound healing and fibrotic changes. We report here that ED-A FN deposition precedes α-SM actin expression by fibroblasts during granulation tissue evolution in vivo and after TGFβ1 stimulation in vitro. Moreover, there is a correlation between in vitro expression of α-SM actin and ED-A FN in different fibroblastic populations. Seeding fibroblasts on ED-A FN does not elicit per se α-SM actin expression; however, incubation of fibroblasts with the anti-ED-A monoclonal antibody IST-9 specifically blocks the TGFβ1-triggered enhancement of α-SM actin and collagen type I, but not that of plasminogen activator inhibitor-1 mRNA. Interestingly, the same inhibiting action is exerted by the soluble recombinant domain ED-A, but neither of these inhibitory agents alter FN matrix assembly. Our findings indicate that ED-A–containing polymerized FN is necessary for the induction of the myofibroblastic phenotype by TGFβ1 and identify a hitherto unknown mechanism of cytokine-determined gene stimulation based on the generation of an ECM-derived permissive outside in signaling, under the control of the cytokine itself.

The motility and morphogenesis of endothelial cells is controlled by spatio-temporally regulated activation of integrin adhesion receptors, and integrin activation is stimulated by major determinants of vascular remodelling. In order for endothelial cells to be responsive to changes in activator gradients, the adhesiveness of these cells to the extracellular matrix must be dynamic, and negative regulators of integrins could be required. Here we show that during vascular development and experimental angiogenesis, endothelial cells generate autocrine chemorepulsive signals of class 3 semaphorins (SEMA3 proteins) that localize at nascent adhesive sites in spreading endothelial cells. Disrupting endogenous SEMA3 function in endothelial cells stimulates integrin-mediated adhesion and migration to extracellular matrices, whereas exogenous SEMA3 proteins antagonize integrin activation. Misexpression of dominant negative SEMA3 receptors in chick embryo endothelial cells locks integrins in an active conformation, and severely impairs vascular remodelling. Sema3a null mice show vascular defects as well. Thus during angiogenesis endothelial SEMA3 proteins endow the vascular system with the plasticity required for its reshaping by controlling integrin function.

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contributed equally to this workIn vertebrates, networks of capillary vessels supply tissues with nutrients. Capillary patterns are closely mimicked by endothelial cells cultured on basement membrane proteins that allow single randomly dispersed cells to self-organize into vascular networks.Here we provide a model including chemoattraction as the fundamental mechanism for cell-to-cell communication in order to identify key parameters in the complexity of the formation of vascular patterns. Bȳ anking biological experiments, theoretical insights and numerical simulations, we provide strong evidence that endothelial cell number and the range of activity of a chemoattractant factor regulate vascular network formation and size. We propose a mechanism linking the scale of formed endothelial structures to the range of cell-to-cell interaction mediated by the release of chemoattractants.

Neuropilin 1 (Nrp1) is a coreceptor for vascular endothelial growth factor A165 (VEGF-A165, VEGF-A164 in mice) and semaphorin 3A (SEMA3A). Nevertheless, Nrp1 null embryos display vascular defects that differ from those of mice lacking either VEGF-A164 or Sema3A proteins. Furthermore, it has been recently reported that Nrp1 is required for endothelial cell (EC) response to both VEGF-A165 and VEGF-A121 isoforms, the latter being incapable of binding Nrp1 on the EC surface. Taken together, these data suggest that the vascular phenotype caused by the loss of Nrp1 could be due to a VEGF-A164/SEMA3A-independent function of Nrp1 in ECs, such as adhesion to the extracellular matrix. By using RNA interference and rescue with wild-type and mutant constructs, we show here that Nrp1 through its cytoplasmic SEA motif and independently of VEGF-A165 and SEMA3A specifically promotes α5β1-integrin-mediated EC adhesion to fibronectin that is crucial for vascular development. We provide evidence that Nrp1, while not directly mediating cell spreading on fibronectin, interacts with α5β1 at adhesion sites. Binding of the homomultimeric endocytic adaptor GAIP interacting protein C terminus, member 1 (GIPC1), to the SEA motif of Nrp1 selectively stimulates the internalization of active α5β1 in Rab5-positive early endosomes. Accordingly, GIPC1, which also interacts with α5β1, and the associated motor myosin VI (Myo6) support active α5β1 endocytosis and EC adhesion to fibronectin. In conclusion, we propose that Nrp1, in addition to and independently of its role as coreceptor for VEGF-A165 and SEMA3A, stimulates through its cytoplasmic domain the spreading of ECs on fibronectin by increasing the Rab5/GIPC1/Myo6-dependent internalization of active α5β1. Nrp1 modulation of α5β1 integrin function can play a causal role in the generation of angiogenesis defects observed in Nrp1 null mice.