JAK2-V617F promotes venous thrombosis through β1/β2 integrin activation
Bärbel Edelmann, … , Andreas J. Müller, Thomas Fischer
Bärbel Edelmann, … , Andreas J. Müller, Thomas Fischer
Published July 19, 2018
Citation Information: J Clin Invest. 2018;128(10):4359-4371. https://doi.org/10.1172/JCI90312.
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Research Article Hematology

JAK2-V617F promotes venous thrombosis through β1/β2 integrin activation

Abstract

JAK2-V617F–positive chronic myeloproliferative neoplasia (CMN) commonly displays dysfunction of integrins and adhesion molecules expressed on platelets, erythrocytes, and leukocytes. However, the mechanism by which the 2 major leukocyte integrin chains, β1 and β2, may contribute to CMN pathophysiology remained unclear. β1 (α4β1; VLA-4) and β2 (αLβ2; LFA-1) integrins are essential regulators for attachment of leukocytes to endothelial cells. We here showed enhanced adhesion of granulocytes from mice with JAK2-V617F knockin (JAK2+/VF mice) to vascular cell adhesion molecule 1– (VCAM1-) and intercellular adhesion molecule 1–coated (ICAM1-coated) surfaces. Soluble VCAM1 and ICAM1 ligand binding assays revealed increased affinity of β1 and β2 integrins for their respective ligands. For β1 integrins, this correlated with a structural change from the low- to the high-affinity conformation induced by JAK2-V617F. JAK2-V617F triggered constitutive activation of the integrin inside-out signaling molecule Rap1, resulting in translocation toward the cell membrane. Employing a venous thrombosis model, we demonstrated that neutralizing anti–VLA-4 and anti–β2 integrin antibodies suppress pathologic thrombosis as observed in JAK2+/VF mice. In addition, aberrant homing of JAK2+/VF leukocytes to the spleen was inhibited by neutralizing anti-β2 antibodies and by pharmacologic inhibition of Rap1. Thus, our findings identified cross-talk between JAK2-V617F and integrin activation promoting pathologic thrombosis and abnormal trafficking of leukocytes to the spleen.

Authors

Bärbel Edelmann, Nibedita Gupta, Tina M. Schnoeder, Anja M. Oelschlegel, Khurrum Shahzad, Jürgen Goldschmidt, Lars Philipsen, Soenke Weinert, Aniket Ghosh, Felix C. Saalfeld, Subbaiah Chary Nimmagadda, Peter Müller, Rüdiger Braun-Dullaeus, Juliane Mohr, Denise Wolleschak, Stefanie Kliche, Holger Amthauer, Florian H. Heidel, Burkhart Schraven, Berend Isermann, Andreas J. Müller, Thomas Fischer

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Figure 6

MELC of JAK+/+ and JAK2+/VF spleens.

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MELC of JAK+/+ and JAK2+/VF spleens. (A) Segmentation of JAK2+/+ (n = 5)...
(A) Segmentation of JAK2+/+ (n = 5) and JAK2+/VF (n = 5) splenic tissue of into red pulp (RP), white pulp (WP), and marginal zone (MZ) based on the signals of VCAM1 and ICAM1. Scale bars: 50 μm. (B) Fluorescence signal of VCAM1 (white) and ICAM1 (magenta) for JAK+/+ and JAK2+/VF spleen. (C) MFI of VCAM1 (left panel) and ICAM1 (right panel) for the regions defined in A. (D) The fluorescence signal of VCAM1 and ICAM1 was overlaid with the neutrophil marker protein CD11b. (E) Quantification of all neutrophils is depicted within the respective areas of the spleen based on fluorescence data shown in D. (F) MFI of CD11b signals in defined small objects that directly interact with VCAM1 (left panel) or ICAM1 (right panel). The definition of small objects is described in Supplemental Figure 5. An overlap of any small object of more than 0% and less than 20% with the regions positive for VCAM1 or ICAM1 is defined as directly interacting small object. Data were generated from 5 individual fields of view from 3 independent mice for each genotype. Horizontal bars represent the mean. *P < 0.05, **P < 0.01 (unpaired, 2-tailed Student’s t test).