Protein S on the surface of plasma lipoproteins: a potential mechanism for protein S delivery to the atherosclerotic plaques?

The anticoagulant protein S (PS) binds phospholipids with very high affinity, but PS interaction with lipoproteins and lipidrich atherosclerotic plaques remains still poorly defined. We investigated PS in plasma lipoproteins and in atherosclerotic plaques from ten patients undergoing endarterectomy. PS was detected by Western blotting after exposure of the necrotic core to liposomes and was found to maintain its ability to bind phosphatidylserine micelles. The amounts of PS bound to low/very low-density lipoproteins in patient’ plasmas were higher and more variable than those detected in healthy subjects. A direct correlation between bound PS and low-density lipoproteins (LDL), plasma levels was found only in patients (r=0.921, p<0.001), thereby leading to hypothesize that the PS-phospholipids binding may increase by oxidative processes of LDL in atherosclerotic patients. The presence of the PS into the necrotic core of atherosclerotic plaques and on the surface of lipoproteins, particularly the atherogenic LDL, suggests a LDL-based delivery of PS to the atherosclerotic plaques and emphasizes the deep link between plasma lipids and coagulation in cardiovascular diseases.