Reduced thrombomodulin in human peripheral nerve microvasculature

Thrombin downregulates thrombomodulin expression and activity in primary human endothelial cells

Thrombomodulin (TM) is a cell surface anticoagulant glycoprotein that plays a key role in the protein C pathway. TM expression in endothelial cells may be modulated by a variety of extracellular signals. Most notably, TM has been shown to be downregulated by inflammatory mediators, such as tumor necrosis factor-alpha and lipopolysaccharide. The objective of this study was to determine the effect of thrombin on TM expression and activity. Thrombin resulted in reduced TM in primary cultures of human endothelial cells by approximately 40% at the level of mRNA, protein, and activity. These effects were blocked by the thrombin inhibitor hirudin. These results suggest that activation of the coagulation cascade may result in a positive-feedback loop consisting of thrombin-mediated repression of TM-dependent protein C activation.

Thrombin in inflammatory brain diseases

Inflammatory brain diseases such as multiple sclerosis (MS) include hyperactivation of the coagulation pathway which includes thrombin. In the experimental autoimmune encephalomyelitis (EAE) model we have found significantly higher levels of thrombin inhibitors which include the very early elevation of protease nexin 1. The physiological importance of excess thrombin in neural tissue is demonstrated by recent experiments which link thrombin with conduction block in the sciatic nerve.