VEGF modulates NMDA receptors activity in cerebellar granule cells through Src-family kinases before synapse formation.

NMDA type glutamate receptors (NMDARs) are best known for their role in synaptogenesis and synaptic plasticity. Much less is known about their developmental role before neurons form synapses. We report here that VEGF, which promotes migration of granule cells (GCs) during postnatal cerebellar development, enhances NMDAR-mediated currents and Ca(2+) influx in immature GCs before synapse formation. The VEGF receptor Flk1 forms a complex with the NMDAR subunits NR1 and NR2B. In response to VEGF, the number of Flk1/NR2B coclusters on the cell surface increases. Stimulation of Flk1 by VEGF activates Src-family kinases, which increases tyrosine phosphorylation of NR2B. Inhibition of Src-family kinases abolishes the VEGF-dependent NR2B phosphorylation and amplification of NMDAR-mediated currents and Ca(2+) influx in GCs. These findings identify VEGF as a modulator of NMDARs before synapse formation and highlight a link between an activity-independent neurovascular guidance cue (VEGF) and an activity-regulated neurotransmitter receptor (NMDAR).

VEGF mediates commissural axon chemoattraction through its receptor Flk1.

Growing axons are guided to their targets by attractive and repulsive cues. In the developing spinal cord, Netrin-1 and Shh guide commissural axons toward the midline. However, the combined inhibition of their activity in commissural axon turning assays does not completely abrogate turning toward floor plate tissue, suggesting that additional guidance cues are present. Here we show that the prototypic angiogenic factor VEGF is secreted by the floor plate and is a chemoattractant for commissural axons in vitro and in vivo. Inactivation of Vegf in the floor plate or of its receptor Flk1 in commissural neurons causes axon guidance defects, whereas Flk1 blockade inhibits turning of axons to VEGF in vitro. Similar to Shh and Netrin-1, VEGF-mediated commissural axon guidance requires the activity of Src family kinases. Our results identify VEGF and Flk1 as a novel ligand/receptor pair controlling commissural axon guidance.

HRG inhibits tumor growth and metastasis by inducing macrophage polarization and vessel normalization through downregulation of PlGF.

Polarization of tumor-associated macrophages (TAMs) to a proangiogenic/immune-suppressive (M2-like) phenotype and abnormal, hypoperfused vessels are hallmarks of malignancy, but their molecular basis and interrelationship remains enigmatic. We report that the host-produced histidine-rich glycoprotein (HRG) inhibits tumor growth and metastasis, while improving chemotherapy. By skewing TAM polarization away from the M2- to a tumor-inhibiting M1-like phenotype, HRG promotes antitumor immune responses and vessel normalization, effects known to decrease tumor growth and metastasis and to enhance chemotherapy. Skewing of TAM polarization by HRG relies substantially on downregulation of placental growth factor (PlGF). Besides unveiling an important role for TAM polarization in tumor vessel abnormalization, and its regulation by HRG/PlGF, these findings offer therapeutic opportunities for anticancer and antiangiogenic treatment.

Matrix-binding vascular endothelial growth factor (VEGF) isoforms guide granule cell migration in the cerebellum via VEGF receptor Flk1.

Vascular endothelial growth factor (VEGF) regulates angiogenesis, but also has important, yet poorly characterized roles in neuronal wiring. Using several genetic and in vitro approaches, we discovered a novel role for VEGF in the control of cerebellar granule cell (GC) migration from the external granule cell layer (EGL) toward the Purkinje cell layer (PCL). GCs express the VEGF receptor Flk1, and are chemoattracted by VEGF, whose levels are higher in the PCL than EGL. Lowering VEGF levels in mice in vivo or ectopic VEGF expression in the EGL ex vivo perturbs GC migration. Using GC-specific Flk1 knock-out mice, we provide for the first time in vivo evidence for a direct chemoattractive effect of VEGF on neurons via Flk1 signaling. Finally, using knock-in mice expressing single VEGF isoforms, we show that pericellular deposition of matrix-bound VEGF isoforms around PC dendrites is necessary for proper GC migration in vivo. These findings identify a previously unknown role for VEGF in neuronal migration.

From vessel sprouting to normalization: role of the prolyl hydroxylase domain protein/hypoxia-inducible factor oxygen-sensing machinery.

The accepted model of vessel branching distinguishes several endothelial cell fates. At the forefront of a vessel sprout, "tip cells" guide the sprouting vessel toward an angiogenic stimulus. Behind the tip, "stalk cells" proliferate to elongate the vessel branch and create a lumen. In mature vessels, endothelial cells acquire a streamlined shape to optimally conduct blood flow. For this purpose, endothelial cells switch to the "phalanx" cell fate, which is characterized by quiescent and nonproliferating cells aligned in a tight cobblestonelike layer. Vessel maturation also requires the recruitment of mural cells (ie, smooth muscle cells and pericytes). These cell fates are often altered in pathological conditions, most prominently during the formation of tumor vasculature. Given the essential role of hypoxia as the driving force for initiating angiogenesis, it is not surprising that the hypoxia-sensing machinery controls key steps in physiological and pathological angiogenesis.