TLT-1-CONTROLS EARLY THROMBUS FORMATION AND STABILITY BY FACILITATING AIIBB3 OUTSIDE-IN SIGNALING IN MICE.

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-α 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.