Expression and activity of thrombomodulin in human gingival epithelium: in vivo and in vitro studies

Epidermal keratinocytes thrombomodulin (TM) has been shown to regulate thrombin at sites of cutaneous injury in addition to a role for epidermal differentiation. TM, a major anticoagulant proteoglycan of the endothelial cell membrane, is a thrombin receptor that acts as a co-factor for protein C activation. Thrombin has pro-inflammatory effects for periodontitis. However, little is known about TM in gingival tissue with periodontitis. We used immunohistochemistry to examine expression of TM in gingival epithelium from patients with periodontitis. In vitro, we observed TM expression at varying Ca2+ concentrations by confocal laser scanning microscopy, examined the expression of TM mRNA and tested TM co-factor activity. Furthermore, we measured TM concentration in gingival crevicular fluid (GCF) from 11 severe adult cases of periodontitis using enzyme-linked immunosorbent assay. Immunoreactive TM was present in gingival epithelium and junctional epithelium, and was reduced in inflamed gingival epithelium compared to healthy gingival epithelium. Ultrastructurally, TM, including microvilli, was observed on the cell membrane. TM localization in cells cultured in 0.09 mM Ca2+ differed from that in cells exposed to 1.2 mM Ca2+. Northern analysis demonstrated TM mRNA in gingival keratinocytes more than in human umbilical vein endothelial cells (HUVEC). Gingival keratinocytes also facilitated protein C activation by thrombin, although less strongly than HUVEC. TM in GCF at sites with bleeding on probing in patients was significantly elevated (p < 0.001, Student's t-test). TM in gingival epithelium may regulate thrombin activity at sites of coagulation and inflammation with periodontal disease, although inflammation may impair this regulation of thrombin.