1. Departments of
2. Molecular Oncology, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA
3. Protein Chemistry, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA
4. Assay Development, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA
5. Organic Chemistry, Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA

Correspondence to: Hans-Peter Gerber¹ Correspondence and requests for materials should be addressed to H.-P.G. (e-mail: Email: gerberhp@gene.com).

Abstract

Vascular endothelial growth factor (VEGF) is a principal regulator of blood vessel formation and haematopoiesis^{1, 2}, but the mechanisms by which VEGF differentially regulates these processes have been elusive. Here we describe a regulatory loop by which VEGF controls survival of haematopoietic stem cells (HSCs). We observed a reduction in survival, colony formation and in vivo repopulation rates of HSCs after ablation of the VEGF gene in mice. Intracellularly acting small-molecule inhibitors of VEGF receptor (VEGFR) tyrosine kinase dramatically reduced colony formation of HSCs, thus mimicking deletion of the VEGF gene. However, blocking VEGF by administering a soluble VEGFR-1, which acts extracellularly, induced only minor effects. These findings support the involvement in HSC survival of a VEGF-dependent internal autocrine loop mechanism (that is, the mechanism is resistant to inhibitors that fail to penetrate the intracellular compartment). Not only ligands selective for VEGF and VEGFR-2 but also VEGFR-1 agonists rescued survival and repopulation of VEGF-deficient HSCs, revealing a function for VEGFR-1 signalling during haematopoiesis.