Expression of Thrombomodulin and Consequences of Thrombomodulin Deficiency during Healing of Cutaneous Wounds

Abstract

Thrombomodulin is a cell surface anticoagulant that is expressed by endothelial cells and epidermal keratinocytes. Using immunohistochemistry , we examined thrombomodulin expression during healing of partial-thickness wounds in human skin and fullthickness wounds in mouse skin. We also examined thrombomodulin expression and wound healing in heterozygous thrombomodulin-deficient mice , compound heterozygous mice that have <1% of normal thrombomodulin anticoagulant activity , and chimeric mice derived from homozygous thrombomodulin-deficient embryonic stem cells. In both human and murine wounds , thrombomodulin was absent in keratinocytes at the leading edge of the neoepidermis , but it was expressed strongly by stratifying keratinocytes within the neoepidermis. No differences in rate or extent of reepithelialization were observed between wild-type and thrombomodulin-deficient mice. In chimeric mice , both thrombomodulin-positive and thrombomodulin-negative keratinocytes were detected within the neoepidermis. Compared with wild-type mice , heterozygous and compound heterozygous thrombomodulin-deficient mice exhibited foci of increased collagen deposition in the wound matrix. These findings demonstrate that expression of thrombomodulin in keratinocytes is regulated during cutaneous wound healing. Severe deficiency of thrombomodulin anticoagulant activity does not appear to alter reepithelialization but may influence collagen production by fibroblasts in the wound matrix. (Am J Pathol 1999, 155:1569 -1575)Thrombomodulin is an anticoagulant glycoprotein that is expressed on the surface of vascular endothelial cells and epidermal keratinocytes.

Thrombomodulin Regulates Keratinocyte Differentiation and Promotes Wound Healing

“…Skin injury promotes TM expression in the neoepidermis (Peterson et al, 1999), suggesting that TM plays a role in wound healing and epidermis development. To unveil the functions of epithelial TM, several heterozygous transgenic mice and keratinocyte specific TM overexpression mice have been generated because TM knockout in mice results in lethality (Healy et al, 1995;Peterson et al, 1999;Raife et al, 1998).…”

“…Expression of TM is highly enhanced in the HE during the early phases of cutaneous wound healing in humans and mice (Peterson et al, 1999). The in vivo effects of TM expression in keratinocytes were examined using a wound healing model in mice, in which a full thickness transdermal incision 10 was made along the dorsal spine and the rate of wound closure was measured.…”

“…The last three EGF-like structures of TMD2 are required for protein C-activating cofactor activity and also anticoagulant activity (Zushi et al, 1989). During the early phase of cutaneous wound healing, TM expression has been highly augmented in the hyperproliferative epithelium (HE) in humans and mice (Peterson et al, 1999), yet its function remains controversial. Keratinocyte-specific overexpression of human TM using the keratin 14 promoter did not have a significant impact on the squamous differentiation or re-epithelialization of cutaneous wounds but modulated collagen reconstitution of the wound matrix (Raife et al, 1998).…”

“…Keratinocyte-specific overexpression of human TM using the keratin 14 promoter did not have a significant impact on the squamous differentiation or re-epithelialization of cutaneous wounds but modulated collagen reconstitution of the wound matrix (Raife et al, 1998). On the other hand, no significant differences in the rate or extent of re-epithelialization during cutaneous wound healing were observed in various TM-deficient mice such as heterozygous TM-deficient (TM +/-), compound heterozygous (TM pro/-), and TM -/-chimeric mice (Peterson et al, 1999). The ectodomain of TM protein, which includes the EGF-like domain (TMD2), has mitogenic activity toward fibroblasts and also promotes angiogenesis (Hamada et al, 1995;Shi et al, 2005).…”

Genetically modified mouse models in studies on cutaneous wound healing

“…injection of galardin, a broad inhibitor of matrix metalloproteinases (Lund et al 1999 (Healy et al 1995). For this reason, wound healing studies were performed in the TM heterozygous mouse, the compound heterozygous TM proÏ-and TM chimeric mice (Peterson et al 1999). Neither of these mouse lines demonstrated differences in re-epithelialization.…”