Delta-like ligand 4–Notch signaling regulates bone marrow–derived pericyte/vascular smooth muscle cell formation

Delta-like ligand 4 (DLL4) is essential for the formation of mature vasculature. However, the role of DLL4-Notch signaling in pericyte/vascular smooth muscle cell (vSMC) development is poorly understood. We sought to determine whether DLL4-Notch signaling is involved in pericyte/vSMC formation in vitro and during vasculogenesis in vivo using 2 Ewing sarcoma mouse models. Inhibition of DLL4 with the antibody YW152F inhibited pericyte/vSMC marker expression by bone marrow (BM) cells in vitro. Conversely, transfection of 10T1/2 cells with the active domains of Notch receptors led to increased expression of pericyte/vSMC markers. Furthermore, the blood vessels of Ewing sarcoma tumors from mice treated with YW152F had reduced numbers of BM-derived pericytes/vSMCs, fewer open lumens, and were less functional than the vessels in tumors of control-treated mice. Tumor growth was also inhibited. These data demonstrate a specific role for DLL4 in the formation of BM-derived pericytes/vSMCs and indicate that DLL4 may be a novel therapeutic target for the inhibition of vasculogenesis.