Differential Localization of CEACAM-1 in Distinct Platelet Populations

Carcinoembryonic antigen-related cell adhesion molecule-1 (CEACAM-1) is a platelet receptor recognized as a negative regulator of platelet activity. During thrombus formation, platelets differentiate into distinct populations, but whether CEACAM-1 is preferentially associated with specific platelet phenotypes remains unclear. Here, we investigated CEACAM-1 localization in different platelet populations, focusing on the accessibility of its extracellular domain. In platelets adherent to poly-L-lysine, the CEACAM-1 signal was predominantly intracellular and decreased following treatment with acetylsalicylic acid (ASA), whereas glucose increased this signal. During integrin-dependent spreading on fibrinogen, CEACAM-1 was undetectable by immunofluorescence, irrespective of αIIbβ3 inhibition with tirofiban, although its presence was confirmed by Western blotting. Flow cytometry revealed that ASA reduced the percentage of CEACAM-1-positive platelets following ADP stimulation under both normoglycemic and hyperglycemic conditions. Confocal microscopy demonstrated co-localization of CEACAM-1 with phosphatidylserine (PS)-positive regions, a hallmark of the procoagulant platelet phenotype. In thrombi formed on collagen fibers under flow, ASA reduced the CEACAM-1-positive area under both conditions. However, a reduction in the ratio of CEACAM-1-positive area to PS-exposing area was observed only under normoglycemic conditions. In fibrin–platelet clots, CEACAM-1 was detected only after prolonged clot incubation and subsequent platelet permeabilization. Collectively, these findings reveal differences in CEACAM-1 localization and detectability across platelet populations and experimental settings, suggesting an association with platelet functional specialization.