Vascular Endothelial Growth Factor-A (VEGF) is the master regulator of vascular growth and it can induce either normal or aberrant angiogenesis depending on its dose in the microenvironment around each producing cell in vivo, and not on the total amount. However, stimulation of pericyte recruitment by co-expression of Platelet Derived Growth Factor-BB (PDGF-BB) could prevent aberrant structures despite heterogeneous and high VEGF levels and switch to homogeneously normal angiogenesis.
Here we dissected the role of specific pericyte-mediated signaling pathways in the switch between normal and aberrant angiogenesis by VEGF.
Monoclonal populations of transduced myoblasts were used to homogeneously express specific VEGF doses, inducing either normal or aberrant angiogenesis, and were further transduced to secrete soluble blockers of the TGFβ-1/TGFβ-R, Tie2/Angiopoietin or EphB4/EphrinB2 pathways (LAP, sTie2Fc and sEphB4, respectively). Two weeks after implantation into mouse limb muscles, neither TGFβ nor Angiopoietin blockade altered the normal angiogenesis by low VEGF, whereas EphrinB2/EphB4 inhibition caused a switch to aberrant angioma-like structures, similar to the effects of blocking pericyte recruitment. Conversely, gain-of-function of EphB4 signaling by systemic treatment with recombinant EphrinB2-Fc completely prevented aberrant angiogenesis by high VEGF levels and yielded normal networks of mature capillaries.
We recently found that VEGF over-expression in muscle induces angiogenesis without sprouting, but by circumferential enlargement and longitudinal splitting (intussusception). EphB4 inhibition increased both endothelial proliferation and the diameter of initial enlargements induced by low VEGF (4 days), leading to a failure of splitting and progressive angioma growth. However, it did not interfere with pericyte recruitment, contrary to high VEGF alone. Conversely, EphB4 stimulation decreased both endothelial proliferation and the diameter of enlargements induced by high VEGF to values similar to low VEGF alone, and accelerated splitting into pericyte-covered capillary networks.
In conclusion, EphrinB2/EphB4 signaling can prevent VEGF-induced aberrant angiogenesis by regulating intussusception.
Split for the cure: VEGF, PDGF-BB and intussusception in therapeutic angiogenesis
