Involvement of ICOS and ICOSL System in Platelet Function 2327673

Abstract Introduction Platelets are non-nucleated, megakaryocyte-derived cell fragments involved in hemostasis and thrombosis. Beyond this activity, they express T cell co-stimulatory/co-inhibitory molecules, including CD40L, CD86, and PD-L1. ICOS and ICOSL are T-cell co-stimulatory molecules that belong to the CD28 and B7 families, respectively. Recent studies show that the ICOS-ICOSL axis also influences non-immune processes including wound healing and endothelial cell function, but its role in platelet biology is poorly defined. This study aimed to evaluate the role of ICOS and ICOSL in platelets formation and function in mice. Methods ADP-induced platelet aggregation was assessed by light transmission aggregometry using platelet-rich plasma from wild-type (WT) mice and mice deficient for ICOS (ICOS⁻/⁻) or ICOSL (ICOSL⁻/⁻). Then, platelet activation induced by thrombin (0.05 and 0.1u/mL) was assessed by staining the activation markers CD62P and GPIIb/IIIa and flow cytometry analysis. Differentiation of primary bone marrow megakaryocytes was evaluated by DNA ploidy analysis by flow cytometry. Results Platelets from ICOS-/- or ICOSL-/- mice exhibited significantly impaired aggregation compared to that detected in WT mice. Thrombin fully activated wild-type platelets at both 0.1 and 0.05 U/ml, whereas platelets from ICOS-/- and ICOSL-/- mice were fully activated by 0.1 U/ml thrombin only. ICOSL-/- mice displayed a reduction in the 2N and 4N megakaryocyte populations compared to WT (p < 0.05), indicating impaired megakaryocyte maturation, whereas maturation was normal in ICOS-/- mice. Primary mouse megakaryocytes were found to express both ICOS and ICOSL in wild-type mice, as determined by confocal microscopy. Conclusion These findings show that ICOS and ICOSL are involved in platelet function and early megakaryocyte development. The mechanisms of this activity deserve further investigation. Funding Source this project is funded by AIRC -Italian Association for Cancer Research Topic Categories Immune Response Regulation: Molecular Mechanisms (IRM)