Endomucin Plays a Role in Retinal Vascular Development and in VEGF‐Induced Endothelial Cell Migration, Growth, and Morphogenesis

Abstract

Angiogenesis is central to both normal and pathologic processes. Endothelial cells (ECs) express high levels of O‐glycoproteins that are believed to play important roles in vascular development and stability. Endomucin‐1 (EMCN) is a type I O‐glycosylated, sialic‐rich glycoprotein, specifically expressed by venous and capillary endothelium. Although ECs express high levels of EMCN, its possible role in vascular development has not been examined. A role for EMCN in angiogenesis was studied by modulating gene expression in vitro and in vivo. Postnatal day (P) four C57BL/6 mice were injected intravitreally with siEMCN or scramble siRNA (siCtrl). Knockdown of EMCN mRNA was significant at 48 hrs after injection compared to siCtrl mice. We observed a delay in radial expansion of the developing mouse vasculature in siEMCN‐injected P6 mice (51±2.2 vs. 69±1.8%, P<0.0001), accompanied by reduced vessel density (49±1.9 vs. 66±4.8%, P<0.01), branch point number (43±1.1 vs. 64±4.0 mm2, P<0.0001), and tip cell number (18±0.6 vs. 28± 2.1 mm, P<0.05) when compared to siCtrl mice. Knockdown of EMCN in human retinal ECs led to a reduction in VEGF‐induced migration (22±1.3 vs. 59±2.7%, P<0.0001), proliferation (1.51 x 104±125.0 vs. 2.25 x 104±1500 cell/cm2, P<0.05), and morphogenesis (7201±86 vs. 9157±273.0 mm, P<0.005) compared to siCtrl cells, without compromising cell survival. VEGF stimulation of siEMCN transfected ECs showed reduction in phospho‐VEGFR2, phospho‐ERK1/2 and phospho‐Akt levels. Taken together, our study indicates a novel role for EMCN as an important regulator of angiogenesis.