Phosphatidic Acid Enhances Procoagulant Activity and Thrombosis through Phosphatidylserine Exposure in Human Erythrocytes.

The increased phospholipase D (PLD) activity and phosphatidic acid (PA) level are frequently observed in various disease states including cancers, diabetes, inflammation, sepsis, and thrombosis. While PA has been previously regarded as a precursor for lysophosphatidic acid (LPA) and diacylglycerol (DAG), increasing evidence suggests the biological activities of PA, itself. Here we demonstrated that the PA can enhance procoagulant activities in human erythrocytes and thrombus formation mediated through phosphatidylserine (PS) exposure. Conspicuously, the PS exposure by PA was substantially greater than that of LPA and we examined its mechanism of action in an effort to elucidate the biological significance of PA. In human erythrocytes, PA treatment resulted in PS exposure without microvesicle generation or hemolysis as determined by flow cytometry. These effects were not attenuated by inhibitors of phospholipase A₂ and phosphatidate phosphatase, that convert PA to LPA and DAG, respectively, suggesting that PA directly induced PS exposure. PA exposed erythrocytes showed significantly high intracellular calcium level and resultant protein kinase C (PKC) a activation. Consistent with these findings, the activity of scramblase was enhanced by PA treatment, while that of flippase was inhibited. Furthermore, PA-exposed erythrocytes were aggregated, accelerated thrombin generation, and increased adherence to endothelial cells, implying PA treatment enhanced the thrombogenic activities of erythrocytes indeed. Of note, these procoagulant activations by PA were confirmed in rat in vivo venous thrombosis model. These results suggest that PA can contribute to enhanced thrombosis, mediated through PS exposure on erythrocytes. With this study, we believe a novel insight was given into the role of PA in cardiovascular diseases.