Human CD93, an epidermal growth factor (EGF)-like domain containing transmembrane protein, is predominantly expressed in the vascular endothelium. Studies have shown that AA4, the homolog of CD93 in mice, may mediate cell migration and angiogenesis in endothelial cells. Soluble CD93 has been detected in the plasma of healthy individuals. However, the role of soluble CD93 in the endothelium remains unclear. Recombinant soluble CD93 proteins with EGF-like domains (rCD93D123, with domains 1, 2, and 3; and rCD93D23, with domains 2 and 3) were generated to determine their functions in angiogenesis. We found that rCD93D23 was more potent than rCD93D123 in stimulating the proliferation and migration of human umbilical vein endothelial cells (HUVECs). Production of matrix-metalloproteinase 2 increased after the HUVECs were treated with rCD93D23. Further, in a tube formation assay, rCD93D23 induced cell differentiation of HUVECs through phosphoinositide 3-kinase/Akt/endothelial nitric oxide synthase and extracellular signal-regulated kinases-1/2 signaling. Moreover, rCD93D23 promoted blood vessel formation in a Matrigel-plug assay and an oxygen-induced retinopathy model in vivo. Our findings suggest that the soluble EGF-like domain containing CD93 protein is a novel angiogenic factor acting on the endothelium.

IntroductionAngiogenesis is involved in physiologic processes such as embryogenesis, wound healing, and the female reproductive cycle, and also contributes to the pathogenesis of numerous disorders, including atherosclerosis, ischemic disease, arthritis, and cancer. 1 Normally, angiogenesis is strictly controlled by the balance between angiogenic promoters and inhibitors.Thrombomodulin (TM) is a type I-glycosylated membrane protein composed of 5 distinct domains. At the NH 2 -terminal is a C-type lectin-like domain followed by 6 consecutively repeated epidermal growth factor (EGF)-like domains and an O-glycosylation site-rich domain. Connected to these extracellular domains is a transmembrane domain followed by a short cytoplasmic tail. 2 TM functions as part of the anticoagulant pathway; it binds thrombin on the cell surface and catalyzes proteolytic activation of protein C. 2 Soluble TM fragments have been detected in the medium of cultured TM-expressing cells 3 and human plasma and urine, 4-6 but the physiologic significance of the soluble TM fragments remains unclear. Our previous study showed that the recombinant EGF-like domain plus the O-glycosylation site-rich domain of TM (rTMD23) promotes angiogenesis in vitro and in vivo. 7 The multiple mechanisms underlying the anti-inflammatory activity of the recombinant lectin-like domain of TM have been demonstrated recently. [8][9][10][11] Lewis Y Ag (LeY) belongs to the type II Lewis Ag family, which is structurally related to the determinants of the ABH blood group system. LeY is expressed on the cell membrane along with phospholipids, 12 EGF receptors, 13 and mucins, 14 and its soluble form is up-regulated in the synovial fluid of human angiogenic rheumatoid arthritis. 15 LeY has been suggested to be a participant in cell-cell interaction, 16 arthritis, 15 and cancer. 17 In addition, ablation in endothelial cells of fucosyltransferase I, which is crucial for generation of the precursor of type II Lewis Ag, resulted in defective tube formation, suggesting the role of LeY in endothelial cell-cell contacts. 18 Previously, we demonstrated that recombinant lectin-like domain of TM (rTMD1) suppressed lipopolysaccharide-induced inflammation through interaction with LeY-conjugated lipopolysaccharide. 11 However, the biologic significance of the interaction between rTMD1 and LeY on the endothelial cell surface has never been investigated. In this study, the biologic function of LeY on endothelial cells and the antiangiogenic function of rTMD1 were investigated. In addition, recombinant adeno-associated virus (AAV) expression vector carrying TMD1 (AAV-TMD1) resulted in efficient suppression of angiogenesis with a single injection of AAV in mice. An Inside Blood analysis of this article appears at the front of this issue.The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance ...

The membrane glycoprotein thrombomodulin (TM) has been implicated in keratinocyte differentiation and wound healing, but its specific function remains undetermined. The epidermis-specific TM knockout mice were generated to investigate the function of TM in these biological processes. Primary cultured keratinocytes obtained from TM(lox/lox); K5-Cre mice, in which TM expression was abrogated, underwent abnormal differentiation in response to calcium induction. Poor epidermal differentiation, as evidenced by downregulation of the terminal differentiation markers loricrin and filaggrin, was observed in TM(lox/lox); K5-Cre mice. Silencing TM expression in human epithelial cells impaired calcium-induced extracellular signal-regulated kinase pathway activation and subsequent keratinocyte differentiation. Compared with wild-type mice, the cell spreading area and wound closure rate were lower in keratinocytes from TM(lox/lox); K5-Cre mice. In addition, the lower density of neovascularization and smaller area of hyperproliferative epithelium contributed to slower wound healing in TM(lox/lox); K5-Cre mice than in wild-type mice. Local administration of recombinant TM (rTM) accelerated healing rates in the TM-null skin. These data suggest that TM has a critical role in skin differentiation and wound healing. Furthermore, rTM may hold therapeutic potential for the treatment of nonhealing chronic wounds.

rTMD23 induced angiogenesis via FGFR1, a process that is independent of the APC pathway.