CONTROLS EARLY THROMBUS FORMATION AND STABILITY BY FACILITATING ΑIIBΒ3 OUTSIDE-IN SIGNALING IN MICE

Key points: 1. TLT-1 modulates αIIbβ3 fibrinogen-mediated inside-out signaling while stabilizes outside-in signaling. 2. Anti-TLT-1 reduced mortality in the pulmonary embolism model demonstrating therapeutic potential for TLT-1. Platelets regulate inflammation as well as hemostasis. Inflammatory insults often induce hemostatic function through mechanisms that are not always understood. The triggering receptor expressed in myeloid cells (TREM)-like transcript 1 (TLT-1) is an abundantly expressed platelet receptor and its deletion leads to hemorrhage and edema after lipopolysaccharide and TNF- treatment. To define a role for TLT-1 in immune derived bleeding we used a CXCL-2 mediated local inflammatory reaction in the vessels of the cremaster muscle of treml1-/- and wild type mice. Our whole mount immunofluorescent staining of the cremaster muscle demonstrated a 50% reduction in clot size and increased extravasation of plasma molecules in treml1-/- mice compared to wild type. We demonstrate that the decreased clotting in treml1-/- mice is associated with a 2X reduction in integrin β3 phosphorylation on residue Y773 after platelet activation, which is consistent with treml1-/- mice displaying reduced outside-in signaling and smaller thrombi. We further substantiate TLT-1?s role in the regulation of immune derived bleeding using the reverse arthus reaction and demonstrate TLT-1?s role in thrombosis using the thromboplastin initiated and collagen/epinephrine models of pulmonary embolism. Thus, the data presented here demonstrate that TLT-1 regulates early clot formation though the stabilization of αIIbβ3 outside-in signaling.