PB0783 - Characterization of P-selectin and TLT-1 interaction to regulate hemostatic function.

Background: Platelets play a key role in hemostasis and immunity. While hemostasis is well described, mechanisms underlying platelet immunological function remain enigmatic. TREM-like transcript-1 (TLT-1) and P-selectin are both found in platelet alpha-granules and seem to affect leukocyte’s function. P-selectin mediates initial leukocyte interactions and TLT-1 plays a role in the release before leukocyte transmigration. We created mice deficient TLT-1 and P-selectin (PT-DKO) to characterize platelet altered hemostatic and immune functionality. The literature suggests that these two mouse models phenocopy one another.

Aims: Assess the hemostatic and immune functionality in P-selectin/TLT-1 single and double knockout mouse models (KO).

Methods: Selp-/- and Treml1-/- mice were intercrossed on a C57BL/6J background to generate PT-DKO. Bleeding time and hemoglobin assay, platelet spreading, whole blood aggregometry, and mesenteric assays were used to evaluate the hematological parameters in our mice. Cremaster, and lung studies were utilized to assess murine immune functionality.

Results: Our data show that Selp-/- and treml1-/- mice have significant increased bleeding time and hemoglobin loss, compared to WT and, surprisingly to PT-DKO. However, Platelet adhesion on fibrinogen was only significantly decreased in treml1-/- mice compared to any other genotype. While whole blood aggregation with collagen was not affected in any of the genotypes, a decreased ATP release was found in treml1-/- and PT-DKO. Interestingly, plasma fibrinogen levels are normal in Selp-/- and PT-DKO but are significantly reduced in lysates from treml1-/- mice.

Conclusion(s): The PT-DKO demonstrate a complex phenotype. In bleeding assays, PT-DKO mice phenocopy WT phenotype mice. Our findings in treml1-/- and PT-DKO mice suggest decreased ATP release, despite a functional aggregation. However, the lack of TLT-1 seems to decrease platelet’s capability to bind fibrinogen. These differences should help us unravel nuances in platelet immune function. The current state of this study will be presented at this poster.