OBJECTIVEThrombin and factor Xa are key players in the process of arterial thrombi formation and lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) is a cell surface endocytosis receptor for atherogenic oxidized LDL (ox-LDL). Here we investigate whether thrombin and factor Xa can induce LOX-1 protein expressions in cell-associated forms and soluble forms in cultured bovine aortic smooth muscle cells (BSMCs).

METHODSBSMCs were treated with thrombin or factor Xa in the presence or absence of AG1478, an epidermal growth factor (EGF) receptor-associated tyrosine kinase inhibitor. Total cell lysates and concentrated culture medium were then analyzed by Western blot using a mouse anti-LOX-1 monoclonal antibody.

RESULTSLOX-1 protein levels in cell lysates and culture medium were significantly increased by thrombin and factor Xa in a concentration- and time-dependent manner. Upregulation of LOX-1 protein expressions in cell lysates and concentrated culture medium was observed at concentrations above 2.0 and 3.0 U/ml of thrombin and 50 and 100 nmol/L of factor Xa, respectively. Increased LOX-1 protein expressions in cell lysates and cell culture medium were detectable as early as 4 h and peaked at 12 h after treatment with thrombin or factor Xa. LOX-1 expression induced by thrombin and factor Xa could be blocked by pretreatment with AG1478.

CONCLUSIONSThrombin and factor Xa can act as LOX-1 inducers via tyrosine kinase activation.