Contribution of macrophages to angiogenesis induced by vascular endothelial growth factor receptor-3-specific ligands.

Vascular endothelial growth factor receptor (VEGFR)-2 is a major stimulator of hemangiogenesis (HA), whereas VEGFR-3 stimulates lymphangiogenesis (LA). Contrary to this understanding, we demonstrate that implantation of pellets containing VEGFR-3-specific ligands (VEGF-C156S and recombinant murine VEGF-D) into the corneal stroma induce not only LA but also robust HA characterized by blood vessels that are positive for VEGFR-3 expression. The implantation of pellets containing VEGFR-3-specific ligands also leads to the recruitment of VEGF-A-secreting macrophages. Depletion of these infiltrating macrophages using clodronate-liposome administration shows a significant reduction in HA as well as LA. Blockade of either VEGFR-2 or VEGFR-3 signaling reduces both HA and LA; however, the percent reduction of HA is greater in the VEGFR-2 blockade group. In addition, in the VEGFR-3 blockade group, the percent reduction of HA is significantly greater with VEGFR-3-specific ligands than that by VEGF-A or VEGF-C. Collectively, our data suggest that VEGFR-3-specific signaling can induce new blood vessels, to which macrophages contribute a major role, and signify its potential as an additional therapeutic target to the existing VEGF-A/VEGFR-2 signaling-based antiangiogenesis strategies.