AGGREGATED LOW-DENSITY LIPOPROTEIN INDUCES TISSUE FACTOR EXPRESSION AND ACTIVITY IN VASCULAR CELLS THROUGH A MECHANISM SUSCEPTIBLE TO PRAVASTATIN-MEDIATED INHIBITION

Introduction. Aggregated low-density lipoprotein (agLDL) strongly induces tissue factor (TF) expression and activation in human vascular smooth muscle cells (VSMC). The aim of this study was to investigate the mechanism involved in agLDL-TF overexpression and agLDL-TF activation, as well as regulation of this mechanism by pravastatin. Methods. VSMC were preincubated with pravastatin (0.5 mM) with or without mevalonate (0.1 mM), geranylgeranyl pyrophosphate (GGPP) (10 mu M) and farnesyl pyrophosphate (FPP) (10 mu M). The cells were then exposed to native LDL (nLDL) or agLDL (100 mu g/ml) for 18 h. TF expression was measured by real-time PCR. TF activity was analyzed by the factor Xa generation test. Rho A traslocation was determined by detection of Rho A antigen in cytoplasmic and membrane fractions. The effect of Rho A inhibition on TF expression and activity was analyzed by preincubation of VSMC with exoenzyme C3 (25 mu g/ml, 24 hours). Results. AgLDL significantly increased TF expression and activity concomitantly with an increase in Rho A membrane levels (by 2-fold). Pravastatin (0.5 mM) inhibited agLDL-TF mRNA overexpression and agLDL-TF activation by 52.33 +/- 5.17% and 28 +/- 2%, respectively. These effects were reverted by GGPP but not by FPP, suggesting involvement of a geranylgeranyl protein. Exoenzyme C3 (a specific Rho A inhibitor) prevented agLDL-TF overexpression and activation by 42 +/- 3.3% and 41 +/- 2.5%, respectively. Conclusion. AgLDL internalization increases TF expression and activation through Rho A activation while pravastatin prevents this effect by impairing Rho A traslocation. Our results help to explain the major role of Rho A activation in the pathogenesis of atherothrombosis and the potential of statins in atherothrombosis prevention.