gms | German Medical Science

Initially characterized through their involvement in neuronal development, recently Ephs and ephrins have been found to be critical for vascular development. We addressed the question, whether EphB4 signaling might also be involved in pathophysiological conditions in adulthood, like tumor angiogenesis.

To identify potential targets for genetic manipulations, we determined the expression profiles of Eph family members in human glioma cell lines, xenografts, and surgical specimens. To examine the role of EphB4 in the vascular system in vivo, we used ecotropic retroviruses encoding for wild-type (EphB4-wt) and truncated dominant-negative mutants of EphB4 (EphB4-dn). Virus producing cells, together with human glioma cell lines or alone, were implanted into dorsal skinfold chamber preparations of nude mice. Intravital fluorescence microscopy was used to study tumor angiogenesis and microcirculation.

RT-PCR analysis revealed, that Eph receptors and ephrins are differentially expressed by both, tumor cells and blood vessels, during glioma progression. EphB4-wt and EphB4-dn did not affect tumor angiogenesis, as indicated by a comparable functional tumor blood vessel density, but led to circumferential vessel growth, resulting in giant diameter vessels, reduced vascular branching and a reduced leakiness of blood vessels. Pericyte association to transgenic endothelial cells was not significantly altered, instead an altered Ang1/Ang2 ratio in EphB4 overexpressing endothelial cells suggests a molecular link between the EphB4- and Ang-1/Tie2 system. Implantation of Virus producing cells alone yielded a similar phenotype, as observed for glioma coimplantations.

For the complex process of microvascular organization and morphogenesis our in vivo studies have revealed, that EphB4 signalling is rather involved in the microvascular network formation and microvascular organization than in angiogenic sprouting during tumor vascularization. Moreover, since changes in vascular morphology were independent from tumor angiogenesis, EphB4 signalling seems to play a physiological rolefor adult vascular- remodelling and morphogenesis.