Bone and the Hematopoietic System

骨髓腔的发育是一个协调的过程，在这个过程中，造血干细胞(HSC)迁移并定植于胚胎骨和软骨形成的空间。因此，在生命早期，骨细胞(成骨细胞或OBS)和HSCs之间就建立了密切的物理联系。这些研究的重点是，骨骼和血液之间的这种空间关系是否也反映了这两个组织之间的功能相互依赖。我们假设，成骨和造血是由细胞间直接相互作用调节的相互关联和相互依赖的发育过程。这项建议的总体目标是明确正常和异常造血中HSC-OB相互作用的具体机制和后果。根据我们的初步数据，我们将描绘HSC来源的细胞因子是否与OB中间体建立旁分泌环，进而释放HSC生存所必需的细胞因子(目标1A)。我们将确定造血干细胞本身是否会改变OBS产生的细胞因子，以响应造血应激(目标1B)。这种干扰可能发生在对影响OB细胞因子产生或影响OB成熟的功能需求的反应中。此外，我们还了解到，唾液酸化的N-连接糖蛋白介导了HSCs与OBS的最初连接，HSCs上的LFA-1和VLA-4受体提供了牢固的细胞-细胞联系，从而确保了HSCs在OBS上的存活。在第二个目标中，将制备针对候选受体蛋白的单抗，以进一步鉴定导致造血干细胞与OBS最初连接的唾液酸化N-连接糖蛋白(目标2A)。在这个目标的第二部分，我们将通过改变HSCs的黏附分子的表达来确定OBS对HSCs的反应，以及VLA-4和LFA-1的可溶性重组受体配体是否可以取代HSCs与OBS之间的直接接触以确保HSC在体外的存活(Aim 2A)。在最终目标中，我们将利用转基因小鼠(目标3A)确定活动物骨髓内的造血干细胞存活是否需要OB(目标3A)，以及不同成熟阶段的OBS是否支持HSC存活(目标3B)。这些研究的结果将为了解血液和骨骼在健康和疾病中相互作用的生物学本质提供重要的新见解。这些研究最终将导致治疗造血和骨科疾病的新策略。

The development of the bone marrow cavity is an coordinated process in which hematopoietic stem cell (HSC) migrate and colonize spaces carved out of embryonic bone and cartilage. Thus, an intimate physical association between bone cells (osteoblasts or OBs) and HSCs is established early in life. The focus of these studies relate to whether this spatial relationship between bone and blood also mirrors a functional interdependence between the two tissues. We hypothesize that osteogenesis and hematopoiesis are interrelated and interdependent developmental processes regulated by direct cell- to-cell interaction. The overall goal of this proposal is to define the specific mechanisms and consequences of HSC-OB interactions in normal as well as in abnormal hematopoiesis. Based upon our preliminary data we will delineate if HSC-derived cytokines establish a paracrine loop with OB intermediaries, which in turn release cytokines necessary for HSC survival (Aim 1A). We will determine whether HSCs themselves alter the cytokines produced by OBs in response to hematopoietic stresses (Aim 1B). Such perturbations may arise in response to functional demands that affect OB cytokine production or that influence OB maturation. Furthermore, we have also learned that sialated-N-linked glycoproteins mediate the initial tethering of HSCs to OBs and LFA-1 and VLA-4 receptors on HSCs provide firm cell-cell contact thereby assuring the survival of HSCs on OBs. In the second aim monoclonal antibodies to candidate receptor proteins will be made to further characterize the sialated N-linked glycoproteins responsible for the initial tethering of HSCs to OBs (Aim 2A). In the second part of this aim, we will determine of OBs respond to HSCs by altering the expression of their adhesion molecules, and if soluble recombinant receptor ligands to VLA-4 and LFA-1 will substitute for direct contact between HSCs and OBs to ensure HSC survival in vitro (Aim 2A). In the final aim, we will determine if OBs are required for survival of HSCs within the bone marrow of living animals using transgenic mice which allow us to induce the death of mature OBs (Aim 3A), and if OBs at different stages of maturation support HSC survival (Aim 3B). The results of these investigations will provide important new insights into the nature of the interactive biology of blood and bone in health and disease. These investigations will ultimately lead to new strategies for the treatment of hematopoietic and osseous disorders.