Human Platelets Internalize Pregnancy-Specific Glycoprotein-1 (PSG1)

It has been long suggested that the placenta "educates" maternal platelets to contribute to a healthy pregnancy. Several studies have also demonstrated unique changes in platelet function and ultrastructure during pregnancy, some of which may drive hypertensive complications of pregnancy. One of the few proteins that are differentially found in the plasma of pregnant females when compared with non-pregnant females and males are the members of the pregnancy-specific glycoprotein (PSG) family, and PSG1 is one of the highest expressed and best characterized of all human PSGs. Because PSGs are secreted into the maternal circulation (by the trophoblast cells of the placenta), platelets may be picking up placental exosomes containing PSGs. Also, platelets may directly incorporate circulating PSGs, which are found in high concentration, as has been shown for other serum proteins, including fibrinogen. In this image report, we have utilized a state-of-the-art high-resolution imaging approach to examine the interactions of labeled recombinant PSG1 with non-permeabilized human platelets. Strikingly, we observed that human platelets internalize PSG1 and express PSGs during pregnancy.