A study on the effects of calreticulin del52 mutation on neutrophil adhesion : Results from CALRdel52 knock-in mice and characterization of a novel CALRdel52 Catchup mouse model

Abstract

In the pathophysiology of classical Philadelphia-negative myeloproliferative neoplasms (MPNs), JAK2- V617F represents the most prevalent underlying disease driver mutation followed by deletion mutations in the gene encoding the endoplasmatic reticulum chaperone calreticulin (CALR). Patients harboring CALRdel mutations are at a lower risk of thrombosis as opposed to JAK2-V617F mutation carriers, but this difference in thrombotic risk has yet not been clarified at the molecular level. Our research group has shown for the first time that a JAK2-V617F-mediated shift of neutrophil-bound integrins to the high- affinity conformation leads to increased thrombus formation by strengthening neutrophil adhesion to the endothelial adhesion molecule vascular cell adhesion molecule 1 and lymphocyte function- associated antigen 1. Contrary to JAK2-V617F, much remains unknown regarding the effect CALRdel on neutrophil biology. In this doctoral thesis, we employ a novel neutrophil-specific CALRdel Catchup model and a hematopoietic-specific VavCre CALRdel mouse model to evaluate the impact of CALRdel on neutrophil function. In both murine models, CALRdel was not associated with increased integrin- mediated adhesion. Interestingly, a decreased binding of CALR-mutated neutrophils to E-selectin under flow and partially under static conditions was observed. In addition, CALRdel-expressing neutrophils were not capable of inducing a chronic myeloproliferative phenotype as assessed by similar blood counts and spleen size of CALRdel/+ Catchup mice compared to their wild-type counterparts. As opposed to a recently described JAK2-V617F Catchup mouse model, CALRdel/+ Catchup mice did not exhibit elevated levels of key pro-inflammatory cytokines, which points towards a minor role of CALRdel- expressing granulocytes in chronic non-resolving inflammation of MPNs. Our findings indicate that JAK2- V617F and CALRdel differentially regulate neutrophil-related adhesion and inflammation in the pathogenesis of MPNs.