Tumor Endothelial Marker 1 (TEM1/Endosialin/CD248) Enhances Wound Healing by Interacting with Platelet-Derived Growth Factor Receptors.

Tumor endothelial marker 1 (TEM1), also known as endosialin or CD248, is a type I transmembrane glycoprotein containing a C-type lectin-like domain. It is highly expressed in pericytes and fibroblasts. Dermal fibroblasts play a pivotal role during cutaneous wound healing, especially in the proliferative phase. However, the physiological function of TEM1 in wound healing is still undetermined. During the process of wound healing, the expression of both TEM1 and platelet-derived growth factor (PDGF) receptor α was highly upregulated in myofibroblasts. In vivo, fibroblast activation and collagen deposition in granulation tissues were attenuated, and wound healing was retarded in TEM1-deleted mice. In vitro, the migration, adhesion, and proliferation of NIH3T3 cells were suppressed following TEM1 knockdown by short hairpin RNA. In PDGF-BB-treated NIH3T3 cells, the downstream signal and mitogenic, and chemoattractive effects were inhibited by TEM1 knockdown. In addition, TEM1 and PDGF receptor α were colocalized in subcellular organelles in fibroblasts, and the association of TEM1 and PDGF receptor α was demonstrated by coimmunoprecipitation. In summary, these findings suggested that TEM1, in combination with PDGF receptor α, plays a critical role in wound healing by enhancing the mitogenic and chemoattractive effects of PDGF-BB and collagen deposition in myofibroblasts.

Sustained release of recombinant thrombomodulin from cross-linked gelatin/hyaluronic acid hydrogels potentiate wound healing in diabetic mice.

Thrombomodulin (TM) is a type-I transmembrane glycoprotein expressed on the surfaces of endothelial cells and epidermal keratinocytes. It is known to regulate blood coagulation, inflammation, and cell-cell adhesion. A recombinant TM, which contains an epidermal growth factor-like domain and serine/threonine-riches domain, has been demonstrated to stimulate cell proliferation and migration of keratinocytes and wound healing. In this study, we developed the biodegradable hydrogels and evaluated the efficacy of sustained release of rhTM from the hydrogel for the treatment of diabetic wounds. The hydrogels were composed of gelatin with or without hyaluronic acid, and fabricated by chemical cross-linking followed by lyophilization. Gelatin-based hydrogels had porous structure, good swelling property, and were biodegradable with characteristics of slow rhTM release in a short term. The once every-3-day rhTM-loaded hydrogel (with hyaluronic acid) markedly promoted wound healing and were superior to rhTM solution, once daily rhTM hydrogel (without hyaluronic acid), hydrogel controls, and once every-3-day rhEGF hydrogel treatment groups. The rhTM hydrogels enhanced granulation tissue formation, re-epithelialization, collagen deposition, and angiogenesis in wound repair. The once every-3-day rhTM hydrogel was stable and drug release was maintained up to 11-month of storage at 4 °C. The developed rhTM hydrogels could meet the needs for clinical practice, and may have future medical applications for wound care in diabetic patients.

Thrombomodulin promotes focal adhesion kinase activation and contributes to angiogenesis by binding to fibronectin.

Angiogenesis promotes tumor growth and metastasis. Cell adhesion molecules interact with the extracellular matrix (ECM) and increase cell adhesion and migration during angiogenesis. Thrombomodulin (TM) is a cell surface transmembrane glycoprotein expressed in endothelial cells. However, the function and significance of TM in cell-matrix interactions and angiogenesis remain unclear. Here, we first demonstrated that recombinant lectin-like domain of TM interacts with an ECM protein, fibronectin, and identified the N-terminal 70-kDa domain of fibronectin as the TM-binding site. Exogenous expression of TM in TM-deficient A2058 melanoma cells enhanced cell adhesion and migration on fibronectin and invasion on Matrigel. In addition, TM increased focal adhesion kinase (FAK) phosphorylation and matrix metalloproteinase-9 production. In mice bearing subcutaneous B16F10 melanoma tumors, immunofluorescence analysis indicated that TM was highly expressed and co-localized with fibronectin on the tumor vasculature. The interaction between TM and fibronectin in tumor blood vessels was also validated by the proximity ligation assay. In human umbilical vein endothelial cells, up-regulation of TM by vascular endothelial growth factor (VEGF), a tumor angiogenic factor, promoted cell adhesion and tube formation, whereas TM knockdown by RNA interference attenuated VEGF-induced cell adhesion and tube formation. In summary, TM promotes angiogenesis by enhancing cell adhesion, migration, and FAK activation through interaction with fibronectin. TM may represent a novel target for inhibiting tumor angiogenesis.

Membrane-Bound Thrombomodulin Regulates Macrophage Inflammation in Abdominal Aortic Aneurysm.

OBJECTIVE: Thrombomodulin (TM), a glycoprotein constitutively expressed in the endothelium, is well known for its anticoagulant and anti-inflammatory properties. Paradoxically, we recently found that monocytic membrane-bound TM (ie, endogenous TM expression in monocytes) triggers lipopolysaccharide- and gram-negative bacteria-induced inflammatory responses. However, the significance of membrane-bound TM in chronic sterile vascular inflammation and the development of abdominal aortic aneurysm (AAA) remains undetermined. APPROACH AND RESULTS: Implicating a potential role for membrane-bound TM in AAA, we found that TM signals were predominantly localized to macrophages and vascular smooth muscle cells in human aneurysm specimens. Characterization of the CaCl2-induced AAA in mice revealed that during aneurysm development, TM expression was mainly localized in infiltrating macrophages and vascular smooth muscle cells. To investigate the function of membrane-bound TM in vivo, transgenic mice with myeloid- (LysMcre/TM(flox/flox)) and vascular smooth muscle cell-specific (SM22-cre(tg)/TM(flox/flox)) TM ablation and their respective wild-type controls (TM(flox/flox) and SM22-cre(tg)/TM(+/+)) were generated. In the mouse CaCl2-induced AAA model, deficiency of myeloid TM, but not vascular smooth muscle cell TM, inhibited macrophage accumulation, attenuated proinflammatory cytokine and matrix metalloproteinase-9 production, and finally mitigated elastin destruction and aortic dilatation. In vitro TM-deficient monocytes/macrophages, versus TM wild-type counterparts, exhibited attenuation of proinflammatory mediator expression, adhesion to endothelial cells, and generation of reactive oxygen species. Consistently, myeloid TM-deficient hyperlipidemic mice (ApoE(-/-)/LysMcre/TM(flox/flox)) were resistant to AAA formation induced by angiotensin II infusion, along with reduced macrophage infiltration, suppressed matrix metalloproteinase activities, and diminished oxidative stress. CONCLUSIONS: Membrane-bound TM in macrophages plays an essential role in the development of AAA by enhancing proinflammatory mediator elaboration, macrophage recruitment, and oxidative stress.

Thrombomodulin promotes corneal epithelial wound healing.

PURPOSE: To determine the role of thrombomodulin (TM) in corneal epithelial wound healing, and to investigate whether recombinant TM epidermal growth factor-like domain plus serine/threonine-rich domain (rTMD23) has therapeutic potential in corneal epithelial wound healing. METHODS: TM localization and expression in the murine cornea were examined by immunofluorescence staining. TM expression after injury was also studied. The effect of rTMD23 on corneal wound healing was evaluated by in vitro and in vivo assays. RESULTS: TM was expressed in the cornea in normal adult mice. TM expression increased in the early phase of wound healing and decreased after wound recovery. In the in vitro study, platelet-derived growth factor-BB (PDGF-BB) induced TM expression in murine corneal epithelial cells by mediating E26 transformation-specific sequence-1 (Ets-1) via the mammalian target of rapamycin (mTOR) signaling pathway. The administration of rTMD23 increased the rate of corneal epithelial wound healing. CONCLUSIONS: TM expression in corneal epithelium was modulated during the corneal wound healing process, and may be regulated by PDGF-BB. In addition, rTMD23 has therapeutic potential in corneal injury.

Thrombomodulin promotes diabetic wound healing by regulating toll-like receptor 4 expression.

Keratinocyte-expressed thrombomodulin (TM) and the released soluble TM (sTM) have been demonstrated to promote wound healing. However, the effects of high glucose on TM expression in keratinocytes and the role of TM in diabetic ulcer remain unclear. In this study, we demonstrated that expressions of TM and Toll-like receptor 4 (TLR4) were both downregulated in high-glucose cultured human keratinocytes and in skin keratinocytes of diabetic patients. In addition, the wound-triggered upregulation of TM and sTM production was abolished in both high-glucose cultured human keratinocytes and streptozotocin-induced diabetic mouse skin. Furthermore, supplementation of recombinant sTM could increase TLR4 expression and promote cutaneous wound healing in both high-glucose cultured human keratinocytes and diabetic mice. However, in Tlr4-deleted mice, which exhibited delayed wound healing, the therapeutic benefit of recombinant sTM was abrogated. Moreover, our results showed that tumor necrosis factor-α (TNF-α) expression in keratinocytes was dose-dependently upregulated by glucose, and TNF-α treatment downregulated the expression of TM and TLR4. Taken together, high-glucose environment reduces the expression of TM and TLR4 in keratinocytes possibly through the action of TNF-α, and recombinant sTM can increase the TLR4 expression and promote wound healing under diabetic condition.

Thrombomodulin regulates keratinocyte differentiation and promotes wound healing.

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.

Thrombomodulin is an ezrin-interacting protein that controls epithelial morphology and promotes collective cell migration.

Adhesive interactions between cells are needed to maintain tissue architecture during development, tissue renewal and wound healing. Thrombomodulin (TM) is an integral membrane protein that participates in cell-cell adhesion through its extracellular lectin-like domain. However, the molecular basis of TM-mediated cell-cell adhesion is poorly understood. Here, we demonstrate that TM is linked to the actin cytoskeleton via ezrin. In vitro binding assays showed that the TM cytoplasmic domain bound directly to the N-terminal domain of ezrin. Mutational analysis of the TM cytoplasmic domain identified (522)RKK(524) as important ezrin-binding residues. In epidermal epithelial A431 cells, TM colocalized with ezrin and actin filaments at cell-cell contacts. Knockdown of endogenous TM expression by RNA interference induced morphological changes and accelerated cell migration in A431 cells. Moreover, epidermal growth factor, upstream of ezrin activation, stimulated the interaction between ezrin and TM. In skin wound healing of mice, TM and ezrin were highly expressed in neoepidermis, implying that both proteins are key molecules in reepithelialization that requires collective cell migration of epithelial cells. Finally, exogenous expression of TM in TM-deficient melanoma A2058 cells promoted collective cell migration. In summary, TM, which associates with ezrin and actin filaments, maintains epithelial morphology and promotes collective cell migration.