Abstract 5480: Laminin Receptor Activation Inhibits Endothelial Tissue Factor Expression
Background. Tissue factor (TF) is an important trigger of arterial thrombosis. The extracellular matrix glycoprotein laminin is a major compound of the basement membrane contributing to vessel wall integrity. The green tea catechin epigallocatechin-3-gallate (EGCG) is a ligand of the 67 kDa laminin receptor (67-LR). This study investigates the effect of 67-LR activation by laminin and EGCG on endothelial TF expression.
Methods and Results. Immunofluorescence demonstrated that human aortic endothelial cells expressed 67-LR abundantly. Western blot analysis demonstrated that cells grown on laminin expressed less TF in response to TNF-α than those grown on fibronectin (n=6; p<0.001). EGCG inhibited TNF-α and histamine induced TF expression and activity in endothelial cells in a concentration-dependent manner (1–30 μM) resulting in a 87% reduction of TF expression (n=5; p<0.001). In contrast, expression of tissue factor pathway inhibitor was not affected (n=4; p=NS). Real-time PCR and promoter studies revealed that inhibition of TF expression occurred at the transcriptional level. EGCG (30μM) impaired activation of the mitogen-activated protein (MAP) kinase c-Jun terminal NH2 kinase (JNK), but not ERK or p38. The JNK inhibitor SP600125 (1μM) reduced TF promoter activity (n±4, p±0.001) and protein expression (n=4; p<0.001). 67-LR blocking antibodies blunted the inhibitory effect of EGCG on JNK activation and TF expression. Expression of Vascular cell adhesion molecule 1 (VCAM-1) was not regulated by JNK, and its expression was not affected by 67-LR activation.
Conclusions. Laminin receptor activation inhibits endothelial TF expression by impairing JNK phosphorylation. This study identifies a new mechanism by which the basement membrane contributes to hemostatic balance of the endothelium in intact vessels and suggests 67-LR as a potential target for the development of novel anti-thrombotic therapies.