Important Role Of CXCR3 In Hematopoietic System And MPNs

Chemokines in hematopoietic microenvironment are important factors in regulating behaviors of hematopoietic stem cell(HSC),which play a role of mediating cell migration,proliferation,differentiation,apoptosis and cytokine release by binding to chemokine receptor on cytomembrane and activating intracellular signal cascade.C-X-C chemokine receptor Type 3(CXCR3),a member of GPCR family,is mainly expressed in NK cells,DC cells and effector T cells,which regulated by T-bet and IFN-?.CXCR3 mediates signals related to migration,proliferation,and calcium influx in leukocytes,but vascular inhibition and pro-apoptotic signals in endothelial cells.Therefore,CXCR3-mediated biological processes are very complex,which role of CXCR3 mainly depends on the subtype of CXCR3,the type of ligand that binds to CXCR3and the microenvironment of cells.Myeloproliferative neoplasms(MPNs)are caused by the malignant cloning of hematopoietic stem cells,They mainly include Polycythemia vera(PV),essential thrombocythemia(ET)and primary myelofibrosis(PMF).Clinically,the driving mutations that cause MPNs mainly involve Somatic mutations occur in Janus kinase 2(JAK2),calreticulin(CALR)and Myeloative leukemia virus oncogene(MPL).Although there are multiple symptoms of MPNs and driver mutations that cause MPNs,they eventually lead to constitutive activation of the JAK2-STAT signaling pathway.The ligands of CXCR3,CXCL4,CXCL9,CXCL10,and CXCL11,are all IFN-?induced by JAK/STATs signal mediated expression,and CXCL9 also acts as an upstream signal to activate the JAK/STATs pathway to induce downstream gene expression.Therefore,CXCR3 may be closely to MPNs induced by JAK2 constitutive activation,and CXCR3-mediated inflammatory response is also an important factor promoting the development of myelofibrosis in the later stage of MPNs.In this paper,CXCR3 gene expression was detected in hematopoietic cells,and it was found that T cells were accompanied by CXCR3 gene expression during development.Next,phenotypes of CXCR3 conventional knockout mice were detected,and it was found that T cells in the peripheral blood and spleen of CXCR3^-/-mice were reduced,and a subset of CD3e⁺B220^int cells appeared in bone marrow and spleen,which was very noticeable.The absence of CXCR3 also resulted in the accumulation of immature granulocytes in peripheral blood,while in bone marrow it was mainly the reduction of neutrophils and GMP.Colony formation assay showed that CXCR3deficiency significantly reduced the number of CFU-GEMM.This result was consistent with the low concentration of short-term hematopoietic stem cells in the bone marrow of CXCR3^-/-mice.ST-HSC play a major role in cell renewal of the hematopoietic system in steady-state hematopoiesis,and the reduction of ST-HSC in bone marrow of CXCR3^-/-mice suggests that CXCR3 plays a supplementary role in the maintenance of HSC.To explore the reasons for the low chimerism of CXCR3^-/-cells in competitive transplantation experiments,we then analyzed the homing ability of hematopoietic stem cells in mice.The results revealed that CXCR3^-/-hematopoietic stem cells have poor ability of resideing in the bone marrow,especially myeloid progenitor cells.In WT-JAK2^V617F and CXCR3^-/--JAK2^V617F mouse models,it was found that absence of CXCR3 inhibited erythrocytosis in MPNs and destruction of healthy spleen structure,and reduced proliferation of bone marrow fibroblasts.By colony-forming assay,it was found that CXCR3deletion reduced the proliferation capacity of mouse bone marrow c-Kit⁺cells with JAK2^V617Fmutation and human leukemia cell line HEL 92.1.7.Our results indicate that CXCR3 regulates hematopoietic stem cell stemness maintenance,lineage differentiation and migration,and may serve as a novel potential therapeutic target for MPNs induced by JAK2^V617F.