194 Growth factor gradients in vascular patterning Andrea Lundkvist, Sunyoung Lee*, Luisa Iruela-Arispe*, Christer Betsholtz † and Holger Gerhardt 1 Vascular Biolog y Laboratory, Cancer Research UK London Research Institute, 44 Lincoln’s Inn Fields, London WC2A 3PX, UK, *Molecular Biolog y Institute, Jonsson Comprehensive Cancer Center and Department of Molecular, Cell and Developmental Biolog y, University of California, Los Angeles, 611 Charles E. Young Drive Ea., Los Angeles, CA 99095, USA and † Laboratory of Vascular Biolog y, Division of Matrix Biolog y, Department of Medical Biochemistry and Biophysics, Scheeles vag 2, Karo- linska Institutet, SE-171 77 Stockholm, Sweden Abstract. Growth factor gradients regulate many developmental processes. VEGF-A is distributed in a graded fashion in growing tissues in order to direct sprouting of new vessels. Growth factor gradients can be formed by regulated production, retention, controlled release and degradation. VEGF-A production is controlled by hypoxia while its retention depends on the C-terminal heparin-binding motifs present in the longer splice-isoforms, VEGF164 and 188. This motif confers binding to the cell surface and the surrounding extracelluar matrix. The short isoform VEGF120 is diffusible and hence fails to direct endothelial tip cell migration. Conditional inactivation of heparan sulfate proteoglycans in the cells that produce VEGF results similarly in misguidance of the tip cells. Studying retinal developmental angiogenesis and pathological neovascu- larization side-by-side in the mouse retina, we find that endothelial tip cell guidance and stalk cell proliferation control are disrupted in neovascularization due to a loss of VEGF- A retention. The cause for this is proteolytic cleavage of VEGF-A by matrix metallo- proteases (MMP) derived mostly from macrophages infiltrating the ischaemic retinal areas. Genetic or pharmacological inhibition of macrophage infiltration or MMP activity can rescue guided revascularization at the expense of pre-retinal neovascularization. Disruption of VEGF-A gradients provides a novel concept for the mechanism underly- ing pathological patterning in ocular disease. 2007 Vascular development. Wiley, Chichester (Novartis Foundation Symposium 283) p 194–206 Growth factor and morphogen gradients are versatile tools for patterning previ- ously uniform space into distinct domains, to fine tune cellular responses like differentiation and proliferation and to direct cellular migration (Charron & Tessier-Lavigne 2005). VEGF-A is involved in early differentiation processes of the haemangioblast lineage (Damert et al 2002), but also fulfils numerous func- 1 This paper was presented at the symposium by Holger Gerhardt, to whom correspondence should be addressed.