Reduced retention of radioprotective hematopoietic cells within the bone marrow microenvironment in CXCR4–/– chimeric mice

Abstract

The physiologic role of CXCR4 on hematopoietic stem/progenitor cells (HSPCs) is not fully understood. Here, we show that radioprotection of lethally irradiated mice by embryonic day 14.5 (E14.5) CXCR4 ؊/؊ fetal liver (FL) cells was markedly impaired when compared with CXCR4 ؉/؉ counterparts, but this defect was rescued when hosts were engrafted with high cell numbers. This quantitative defect contrasted with a similar content in hematopoietic colony-forming cells (CFCs), splenic colony-forming units (CFUs-S), and Lin ؊ Sca-1 ؉ c-kit ؉ cells in E14.5 CXCR4 ؊/؊ and CXCR4 ؉/؉ livers. In addition, the homing of HSPCs in the bone marrow was not altered as detected with a CFSE-staining assay. In contrast, a 30-fold increase in CFCs was seen in the circulation of mice stably reconstituted with CXCR4 ؊/؊ FL cells and this increment was already observed before hematopoiesis had reached a steady-state level. Together, the data strongly suggest that impaired retention may, at least in shortterm hematopoietic reconstitution, lead to a diminution in the number of available progenitors required for radioprotection. IntroductionThe CXC chemokine ligand 12 (CXCL12)/stromal cell-derived factor-1 (SDF-1)/pre-B cell growth-stimulating factor (PBSF) 1,2 mediates the homing of hematopoietic stem/progenitor cells (HSPCs) to the bone marrow (BM) by binding to its receptor CXCR4. 3 SDF-1/CXCR4 interactions play pleiotropic roles during development, as revealed by the phenotype of mice with a homozygous targeted gene disruption that die from defects in multiples organs. [4][5][6][7] In fetal hematopoiesis, CXCR4 Ϫ/Ϫ or SDF-1 Ϫ/Ϫ embryos display more profound defects in the marrow than in the fetal liver (FL), suggesting a major role for the CXCR4/SDF-1 axis in marrow colonization. [4][5][6][7] In adult hematopoiesis, CXCR4 receptors are involved in numerous biologic processes, including cell migration, 8 proliferation, and survival. [9][10][11][12][13][14] Several data suggest that SDF-1 and CXCR4 play a critical role in the homing of HSPCs with SDF-1 acting as a major chemoattractant for severe combined immunodeficiency (SCID)-repopulating cells and leukemic cells. 8,15,16 Blocking CXCR4 function on CD34 ϩ cells with anti-CXCR4 antibodies prevented hematopoietic reconstitution in nonobese diabetic (NOD)/SCID mice, 17 whereas CXCR4 overexpression increased their abilities to engraft NOD/SCID mice. 9 In mice, it has been reported that CXCR4 Ϫ/Ϫ FL cells can successfully reconstitute hematopoiesis of lethally irradiated mice, 18-20 whereas secondary transplantation experiments showed defective reconstitution. 20 A critical role for CXCR4 in mobilization, the egress of HSPCs from BM to the peripheral blood, was recently suggested. For instance, a rapid mobilization of HSPCs was obtained by treatment with the CXCR4 antagonist AMD3100, 21,22 as well as by induction of SDF-1 plasma elevation. 23,24 In addition, G-CSF-induced HSPC mobilization coincides in vivo with a decrease in BM SDF-1 concentration related to SDF-1 cleavage by marrow seri...

Evidence that β7 Integrin Regulates Hematopoietic Stem Cell Homing and Engraftment Through Interaction with MAdCAM-1

“…Although some recent studies have questioned the role of CXCR4 in HSC homing in fetal liver hematopoiesis [31] and CXCR4-overexpression studies [32], it is commonly accepted that the CXCR4/CXCL12 axis plays a significant role in the BM homing of transplanted HSPCs [33,34]. Consistent with the role of CXCR4 in HSC homing, we observed that b7KO HSCs were impaired in their ability to migrate toward CXCL12 in vitro and home to BM in vivo (Fig.…”

Ptk7-Deficient Mice Have Decreased Hematopoietic Stem Cell Pools as a Result of Deregulated Proliferation and Migration

“…Alternatively, it may be that a homing assay performed with total liver cells reveals a constitutive promigratory function of PTK7, in contrast to long-term engraftment reflecting BM microenvironmental signaling through PTK7 in HSCs. Similar complex mechanisms of cell cycle regulation and differential homing of mature cells versus HSPCs homing to the BM were also attributed to CXCR4 (51)(52)(53)(54). Whether PTK7 and CXCR4 signaling share more in common remains to be addressed.…”

CXCR4 is required for the quiescence of primitive hematopoietic cells

“…Early transplantation experiments demonstrated that primitive hematopoietic cells required CXCR4 and CXCL12 interaction for effi cient engraftment ( 12,18 ). Later studies involved transplantation of CXCR4-inactivated primitive hematopoietic cells into irradiated hosts, and showed that the recovery of these cells in the BM within 24 h was quantitatively normal compared with that of WT cells ( 13,19 ). These results imply that early BM homing of primitive hematopoietic cells might be CXCR4 independent, but BM retention of these cells requires CXCR4.…”