Study of the Roles of SDF1 and CXCR4 in Hematopoiesis

我们小组和其他人以前的研究已经确定了趋化因子CXCL 12/SDF 1及其受体CXCR 4在骨髓中保留和动员髓样细胞中的关键作用。CXCL 12在骨髓的非造血细胞中是丰富的，特别是在CAR（CXCL 12丰富的网状细胞）和骨髓中的其他间充质细胞中。骨髓造血细胞通常表达CXCR 4，并且CXCL 12/CXCR 4之间的信号传导相互作用用于将造血细胞保留在骨髓中。G-CSF是粒细胞生成的重要生理调节因子：携带集落刺激因子（G-CSF）或其受体纯合缺失的小鼠严重缺乏，G-CSFR的显性阴性突变与粒细胞生成的严重缺陷有关。G-CSF的施用诱导骨髓中髓系细胞的扩增，并促进成熟髓系细胞和造血祖细胞从骨髓释放到外周血。因此，药理学浓度的G-CSF被广泛用于诱导粒细胞生成和动员造血祖细胞到外周血。在功能上，G-CSF通过多种机制降低骨髓中的CXCR 4和CXCL 12水平。因此，将造血细胞保留在骨髓中的胶减少，并且实现了成熟和未成熟造血细胞的大量退出。CXCR 4竞争性抑制剂AMD 3100/Plerixlavor已被FDA批准，并与G-CSF联合用作造血前体的动员剂。最近，我们的研究旨在进一步了解HSPC动员已经检测到受体/配体对EphrinB 2/EphB 4的重要作用。我们揭示了EphB 4受体在血窦中和EphrinB 2配体在造血细胞中的相互排斥的骨髓分布，并发现了控制HSPC动员的EphB 4/EphrinB 2依赖性途径。EphB 4/EphrinB 2的阻断减少了HSPC和其他骨髓细胞向循环的动员。在源自骨髓的造血细胞促进肿瘤生长的鼠癌症模型中，EphB 4/EphrinB 2阻断减少了HSPC的肿瘤浸润和肿瘤进展。这些结果确定EphB 4/EphrinB 2信号传导对于从骨髓动员造血细胞至关重要，并提供了通过靶向骨髓来减少癌症进展的新策略。其他正在进行的研究集中在从主动脉内皮生成造血细胞，以及表征这一关键发育步骤的生化要求。成人型胚胎内造血起源于背主动脉（DA）的特化内皮细胞。尽管这种特化内皮对于造血干细胞和成体造血谱系的建立至关重要，但调节其出现的机制尚不完全清楚。我们发现EphrinB 2是内皮细胞功能的主要调节因子，它控制着内皮细胞生成成人型造血的发展。EphrinB 2的缺乏损害DA衍生的造血。跨膜EphrinB 2及其EphB 4受体在新生的DA中相互作用，其瞬时地窝藏EphrinB 2+和EphB 4+内皮细胞，从而提供双向细胞间信号传导的机会以控制生血内皮的出现。胚胎干（ES）细胞衍生的EphrinB 2+细胞富含生血内皮前体。EphrinB 2沉默损害造血细胞的ES生成，但不损害内皮细胞的生成。EphrinB 2作为成人造血的重要调节因子的鉴定为早期造血定型的调节提供了重要的见解。

Previous studies from our group and others have identified a critical role of the chemokine CXCL12/SDF1 and its receptor CXCR4 in the retention and mobilization of myeloid cells from the bone marrow. CXCL12 is abundant in the non hematopoietic cells of bone marrow, particular in the CAR (CXCL12 abundant reticular) and in other mesenchymal cells in the bone marrow. The bone marrow hematopoietic cells generally express CXCR4, and the signaling interaction between CXCL12/CXCR4 serves to retain hematopoietic cells in the bone marrow. G-CSF is a critical physiological regulator of granulopoiesis: mice carrying homozygous deletions of colony-stimulating factor (G-CSF) or its receptor are severely neutropenic, and dominant-negative mutations of G-CSFR have been linked to severe defects of granulopoiesis. Administration of G-CSF induces an expansion of myeloid lineage cells in the bone marrow, and promotes the release of mature myeloid cells and hematopoietic progenitor cells from the bone marrow to the peripheral blood. Thus, G-CSF at pharmacologic concentrations is widely used to induce granulopoiesis and to mobilize hematopoietic progenitors to the peripheral blood. Functionally, G-CSF reduces CXCR4 and CXCL12 levels in the bone marrow through a variety of mechanisms. As a consequence, the glue that retains hematopoietic cells in the bone marrow is decreased and massive exit of mature and immature hematopoietic cells is achieved. A CXCR4 competitive inhibitor, AMD3100/Plerixafluor, has been approved by FDA and a mobilizing agent for hematopoitic precursors in conjunction with G-CSF. Recently, our studies designed to further understanding of HSPC mobilization have detected an important role of the receptor/ligand pair EphrinB2/EphB4. We unveiled the mutually exclusive bone marrow distribution of EphB4 receptors in the sinusoids and EphrinB2 ligands in hematopoietic cells, and discovered an EphB4/EphrinB2-dependent pathway that controls HSPCs mobilization. Blockade of EphB4/EphrinB2 reduced HSPCs and other myeloid cells mobilization to the circulation. In murine cancer models, in which hematopoietic cells derived from the bone marrow promote tumor growth, EphB4/EphrinB2 blockade reduced tumor infiltration with HSPCs and tumor progression. These results identify EphB4/EphrinB2 signaling as critical to hematopoietic cells mobilization from bone marrow and provide a new strategy for reducing cancer progression by targeting the bone marrow. Other ongoing studies have focused on the generation of hematopoietic cells from aortic endothelium, and the characterization of the biochemical requirements underlying this critical developmental step. Adult-type intraembryonic hematopoiesis arises from specialized endothelial cells of the dorsal aorta (DA). Despite the critical importance of this specialized endothelium for establishment of hematopoietic stem cells and adult hematopoietic lineages, the mechanisms regulating its emergence are incompletely understood. We show that EphrinB2, a principal regulator of endothelial cell function, controls the development of endothelium producing adult-type hematopoiesis. The absence of EphrinB2 impairs DA-derived hematopoiesis. Transmembrane EphrinB2 and its EphB4 receptor interact in the emerging DA, which transiently harbors EphrinB2+ and EphB4+ endothelial cells, thereby providing an opportunity for bi-directional cell-to-cell signaling to control the emergence of the hemogenic endothelium. Embryonic Stem (ES) cell-derived EphrinB2+ cells are enriched with hemogenic endothelial precursors. EphrinB2 silencing impairs ES generation of hematopoietic cells but not generation of endothelial cells. The identification of EphrinB2 as an essential regulator of adult hematopoiesis provides important insight in the regulation of early hematopoietic commitment.