Lee Gloria, Lo Annie, Short Sarah A, Mankelow Tosti J, Spring Frances, Parsons Stephen F, Yazdanbakhsh Karina, Mohandas Narla, Anstee David J, Chasis Joel Anne
Life Sciences Division, University of California, Lawrence Berkeley National Laboratory, Bldg 74, 1 Cyclotron Road, Berkeley, CA 94720, USA.
Blood. 2006 Sep 15;108(6):2064-71. doi: 10.1182/blood-2006-03-006759. Epub 2006 May 11.
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 alpha(V) integrins as ICAM-4 counterreceptors. Because macrophages express alpha(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/alpha(V) adhesion produced a 53% to 57% decrease in reconstituted islands, strongly suggesting that ICAM-4 binding to macrophage alpha(V) functions in island integrity. Importantly, we documented that alpha(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/alpha(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.
红系祖细胞在成红细胞岛中分化，成红细胞岛是由围绕中央巨噬细胞的成红细胞组成的骨髓生态位。有证据表明，在这些岛状结构中，黏附相互作用调节着红细胞生成和细胞凋亡。我们正在探索免疫球蛋白超家族成员红系细胞间黏附分子4（ICAM - 4）是否参与岛状结构的形成。此前，我们已确定α(V)整合素是ICAM - 4的反受体。由于巨噬细胞表达α(V)，ICAM - 4可能介导岛状结构的附着。为了验证这一点，我们培育了ICAM - 4基因敲除小鼠，并开发了定量活细胞技术，用于收集完整的岛状结构以及在体外重新形成岛状结构。我们观察到，与野生型骨髓相比，由ICAM - 4基因缺失的骨髓重建的岛状结构减少了47%。我们还发现基因敲除小鼠体内形成的岛状结构显著减少。此外，阻断ICAM - 4/α(V)黏附的肽使重建的岛状结构减少了53%至57%，这有力地表明ICAM - 4与巨噬细胞α(V)的结合对岛状结构的完整性起作用。重要的是，我们记录到α(V)整合素在从成红细胞岛分离出的巨噬细胞中表达。总体而言，这些数据提供了令人信服的证据，证明ICAM - 4通过ICAM - 4/α(V)黏附在成红细胞岛形成中起关键作用，同时也表明我们开发的新实验策略在探索成红细胞岛形成的分子机制及其在调节红细胞生成中的功能作用方面将具有重要价值。
