Abstract
Angiogenesis is central to both normal and pathologic processes. Endothelial cells (ECs) express 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. Evidence has pointed to a potential role for EMCN in angiogenesis but it had not been directly investigated. In this study, we examined the role of EMCN in angiogenesis by modulating EMCN levels both in vivo and in vitro. Reduction of EMCN in vivo led to the impairment of angiogenesis during normal retinal development in vivo. To determine the cellular basis of this inhibition, gain- and loss-of-function studies were performed in human retinal EC (HREC) in vitro by EMCN over-expression using adenovirus or EMCN gene knockdown by siRNA. We show that EMCN knockdown reduced migration, inhibited cell growth without compromising cell survival, and suppressed tube morphogenesis of ECs, whereas over-expression of EMCN led to increased migration, proliferation and tube formation. Furthermore, knockdown of EMCN suppressed VEGF-induced signaling as measured by decreased phospho-VEGFR2, phospho-ERK1/2 and phospho-p38-MAPK levels. These results suggest a novel role for EMCN as a potent regulator of angiogenesis and point to its potential as a new therapeutic target for angiogenesis-related diseases.
Highlights
Angiogenesis, the process through which new vessels grow from existing vessels via branching morphogenesis[1], is central to many physiological and pathological processes such as embryonic development, wound healing, tumor growth and metastasis, as well as several ocular diseases[2,3]
The morphogenic response of adenovirus encoding EMCN (AdEMCN) infected cells was increased by 1.4- and 1.3-fold over that observed in AdGFP infected control cells in the absence or presence of vascular endothelial growth factor-A (VEGF) at 12 hr, respectively (Fig. 7d–f)
To gain insight into the mechanism by which EMCN influences angiogenesis we investigated whether EMCN is involved in VEGF-VEGF receptor 2 (VEGFR2) signaling
Summary
Angiogenesis, the process through which new vessels grow from existing vessels via branching morphogenesis[1], is central to many physiological and pathological processes such as embryonic development, wound healing, tumor growth and metastasis, as well as several ocular diseases[2,3]. Treatment of human retinal endothelial cells (HREC) with siRNA sequences against EMCN (siEMCN) resulted in knockdown of EMCN expression by approximately 93% at 24 hr and about 85% after 48 hr, measured by qRT-PCR compared to siCtrl (Fig. 4a).
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