PB0780 - Using Itga2b-creERT2 and Itga2b-creERT2-treml1 transgenic mice to decipher TLT-1’s role in platelet interaction with fibrinogen

Background: aIIb (CD41), a lineage-specific receptor, plays an important role in hemostasis due to functional interactions with fibrinogen that promote platelet interaction and clot formation. TREM-Like Transcript-1 (TLT-1) is a lineage-specific receptor stored in platelet -granules, which translocates to the platelet surface following agonist-induced platelet activation. TLT-1 also binds fibrinogen during platelet activation. However, the relevant role of TLT-1 during this process has not been fully elucidated yet.

Aims: To elucidate the role of TLT-1 as a fibrinogen receptor by establishing and characterizing a conditional knockout mice model of IIb (ITGA2B) under the regulation of a tamoxifen-inducible Cre-recombinase (CreER/T2) and subsequently crossing this mouse on to the treml-/- background to study fibrinogen binding

Methods: Tamoxifen was used to induce CRE and remove exons 2 – 4 of ITGA2b. These mice were crossed into the treml1-/- mouse line to assess TLT-1 binding to fibrinogen and to characterize the phenotype, mice were fed tamoxifen and evaluated by immunological and hematological techniques

Results: We found the 2-week tamoxifen diet-induced repression of GPIIb on Itga2b-creERT2 platelets, but not on other platelet receptors such as GPIb or TLT-1. GPIIIa is expressed intracellularly, but not on the platelet surface. These mice displayed a Glanzmann Thrombasthenia phenotype with severely reduced fibrinogen binding. However, at low-dose thrombin, a distinct binding of fibrinogen is removed in Itga2b-creERT2-treml1-/- mice. We plan to exploit this difference to delineate the differential interactions of IIb2 and TLT-1 with fibrinogen. The current characterization of this model will be shown in this presentation

Conclusion(s): These transgenic mice are likely to be a valuable tool to study the function of platelet TLT-1 involved in immunological response and hemostatic regulation