Targeted gene deletion demonstrates that the cell adhesion molecule ICAM-4 is critical for erythroblastic island formation

Abstract

Erythroid progenitors differentiate in erythroblastic islands, bone marrow niches composed of erythroblasts surrounding a central macrophage. Evidence suggests that within islands adhesive interactions regulate erythropoiesis and apoptosis. We are exploring whether erythroid intercellular adhesion molecule 4 (ICAM-4), an immunoglobulin superfamily member, participates in island formation. Earlier, we identified ␣ V integrins as ICAM-4 counterreceptors. Because macrophages express ␣ V , ICAM-4 potentially mediates island attachments. To test this, we generated ICAM-4 knock-out mice and developed quantitative, live cell techniques for harvesting intact islands and for re-forming islands in vitro. We observed a 47% decrease in islands reconstituted from ICAM-4 null marrow compared to wild-type marrow. We also found a striking decrease in islands formed in vivo in knock-out mice. Further, peptides that block ICAM-4/␣ V adhesion produced a 53% to 57% decrease in reconstituted islands, strongly suggesting that ICAM-4 binding to macrophage ␣ V functions in island integrity. Importantly, we documented that ␣ V integrin is expressed in macrophages isolated from erythroblastic islands. Collectively, these data provide convincing evidence that ICAM-4 is critical in erythroblastic island formation via ICAM-4/␣ V adhesion and also demonstrate that the novel experimental strategies we developed will be valuable in exploring molecular mechanisms of erythroblastic island formation and their functional role in regulating erythropoiesis. IntroductionErythroid progenitors proliferate, differentiate, and enucleate within specialized bone marrow niches, termed erythroblastic islands. [1][2][3][4] These structural units are composed of developing erythroblasts surrounding a central macrophage. It is apparent from ultrastructural studies that extensive cell-cell interactions, both erythroblastmacrophage, as well as erythroblast-erythroblast, occur within these 3-dimensional structures. However, little is known regarding either the molecular nature or functional role of the specific adhesive interactions. We are exploring the potential function of erythroid ICAM-4, a recently characterized member of the immunoglobulin superfamily, in erythroblastic island formation. ICAM-4 expression is limited to erythroid and placental tissue 5 but, to date, there is no information on its role in erythropoiesis. We earlier identified ␣ 4 ␤ 1 and ␣ V family integrins as ICAM-4-binding partners. 6 Because macrophages express ␣ V and erythroblasts exhibit ␣ 4 ␤ 1 , ICAM-4 is an attractive candidate for mediating erythroblast-erythroblast interactions via ICAM-4/␣ 4 ␤ 1 binding and regulating adhesion of erythroblasts to central macrophages via ICAM-4/␣ V binding.ICAM-4, which carries the Lansteiner Wiener (LW) blood group antigen system, has strong sequence homology with other members of the ICAM protein superfamily. 7,8 It is composed of 2 extracellular immunoglobulin-like domains, an N-terminal I set and a membrane proximal I2 set, and a single membr...

c-Maf plays a crucial role for the definitive erythropoiesis that accompanies erythroblastic island formation in the fetal liver

“…6 Thus, c-Maf and Palladin are important for erythroblastic islands in the embryonic stage, but their importance in the adult stage is still unconfirmed. However, a previous study found that ICAM-4 is critical for erythroblastic island formation in adult marrow, 41 but the role of ICAM-4 in the embryonic stage has been left for future study. Overall, previous studies and our results indicate that there might be different mechanisms or regulation processes or both between fetal liver and adult marrow/spleen erythroblastic island formation and maintenance.…”

Hypoxic stress underlies defects in erythroblast islands in the Rb-null mouse

“…However, our data predict that the expression and/or interaction of key adhesion molecules on the surfaces of the red cells and macrophages may be sensitive to oxygen tension. It will therefore be interesting to determine whether adhesion molecules known to mediate macrophage-erythroblast interactions, such as ICAM-4 and ␣ 5 -integrin 33 or ␣ 4 -integrin and VCAM-1, 34 are altered in their expression or activity by changes in oxygen tension.…”

CD14+ cells from peripheral blood positively regulate hematopoietic stem and progenitor cell survival resulting in increased erythroid yield

“…[9][10][11][12] However, macrophage colony-stimulating factor (M-CSF)-deficient op/op mice and CSFR -/-mice, which display reduced F4/80 tissue-resident macrophages, are characterized by hypocellularity of the bone marrow and reduced erythroid burst-forming units (BFU-E), 13 which indicates a major effect of macrophages on HSPC. In addition, erythroblast proliferation in bone marrow was unchanged in myeloablated mice and the ratios between the different stages during erythroblast maturation were comparable.…”