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Bleeding diathesis in mice lacking JAK2 in platelets

Updated: May 11, 2022

The tyrosine kinase JAK2 protein is critical for the JAK/STAT cytokine signaling of hematopoietic cells.

The somatic JAK2 V617F mutation is common in myeloproliferative neoplasms (MPNs), on which venous and arterial thrombosis is the leading cause of death.

However, the role of JAK2 in hemostasis remains unclear. Thus, researchers at the Versiti Blood Research Institute investigated the role of this protein in platelet hemostasis in JAK2 knockout mice.

Study Overview

The study used mice lacking JAK2 in platelets and megakaryocytes (MKs). The researchers collected the animal´s blood and tissues to analyse complete blood count, blood smear, plasma Von Willebrand factor (WWF) levels, and immunohistochemistry of the femur. They also determined the tail-bleeding time.

Platelet analysis

For platelet preparation, the researchers collected blood from the retroorbital plexus and anticoagulated it in acid citrate dextrose. They isolated the platelets by centrifugation and resuspended them in a buffer solution.

They used these samples to analyse platelet surface glycoproteins, platelet proteins, and platelet aggregation.

Ex vivo perfusion assay

First, the researchers pre-coated the microchannels of Cellix’s Vena8 Fluoro+ biochips with Type 1 collagen. After washing and blocking, the researchers used Cellix’s VenaFlux platform to perfuse the blood collected from the mice through the collagen-coated biochip. The researchers analysed JAK2Plt-/-’s ability in whole blood to adhere to type 1 collagen and form thrombi under arterial shear rate (1500 s -1), see Fig. 3 A-B.

Figure 3. from Falet et al. Reduced thrombus formation of JAK2Plt-/- platelets at arterial shear rates. PPACK-anticoagulated whole blood from Jak2Plt1/1 and Jak2Plt2/2 mice was labeled and perfused on a type 1 collagen–immobilized surface at an arterial shear rate of 1500 s21. (A) Representative still images at 3 minutes. Bars represent 100 mm. (B) Fluorescence intensity at 3 minutes. Results represent mean ± SD and were compared by using the unpaired Student t-test (n = 3 in each group; P=.0317).