Degradation of Vascular Endothelial Thrombomodulin by Arginine‐ and Lysine‐Specific Cysteine Proteases From Porphyromonas gingivalis

Background: The endothelial cell surface glycoprotein thrombomodulin (TM) inhibits vascular coagulation and inflammation via regulation of thrombin‐mediated activation of protein C. Porphyromonas gingivalis is the major periodontopathic bacterium and has been found in vessel walls and atherosclerotic lesions in humans. P. gingivalis‐derived cysteine proteases (gingipains) are known to enhance inflammatory and coagulant responses of vascular endothelial cells. However, it has not been elucidated whether gingipains affect vascular endothelial TM. Methods: Purified arginine‐specific gingipains (Rgps) and lysine‐specific gingipain (Kgp) from P. gingivalis were used to investigate the effects of gingipains on recombinant human TM by immunoblot analyses. Flow cytometry and activated protein C assay were carried out to examine the effects of gingipains on vascular endothelial cell surface TM. Immunohistochemistry was performed to investigate TM expression in microvascular endothelia in gingival tissues taken from patients with periodontitis. Results: Rgps and Kgp cleaved TM in vitro. Endothelial cell surface TM was also degraded by Rgps. Thrombin‐mediated activation of protein C was reduced by Rgps through TM inactivation. Gingival microvascular endothelial TM was reduced in patients with periodontitis. Conclusions: P. gingivalis gingipains induced the degradation and inactivation of endothelial TM, which may promote vascular coagulation and inflammation. In addition, in vivo relevance was demonstrated by reduced expression of TM in gingival microvascular endothelia in patients with periodontitis, which may be involved in the pathogenesis of periodontitis.