Structural microenvironment of bone marrow stem cells

描述(申请人提供)：骨髓(BM)中成体干细胞生态位的定义及其受外部因素的调节是组织工程和骨骼再生医学的首要研究重点，也是骨髓切除治疗后造血功能及其重建的关键方面。与指定功能离散的骨髓微环境的关于细胞类型、细胞间相互作用和可溶信号的丰富信息不同，人们对细胞外基质(ECM)在利基功能中的作用知之甚少，这不利于开发更有效的基于干细胞的疗法。我们的初步发现首次表明纤维蛋白-1参与其中，这是一种独特的ECM蛋白，调节组织的空间组织和物理属性以及内源性(局部)转化生长因子家族信号的生物利用度。这一发现提出了一种令人兴奋的可能性，即骨髓基质的结构成分通过确定常驻干细胞的物理微环境并协调其中的调节信号来控制骨、血液和免疫细胞的产生。纤维蛋白-1是马凡综合征(MFS)的突变蛋白，其多效性表现为进行性骨丢失(骨量减少)。我们以前曾证明，MFS小鼠的骨量减少反映了由于局部合成代谢和分解代谢信号的校准受损而导致的骨重建受扰。正在进行的研究表明，纤维蛋白-1是骨髓微环境的重要组成部分，它规定了间充质干细胞(MSC)和造血干细胞(HSC)的性能。这种高风险/高回报的R21应用程序的目标是回答以下两个问题：(A)缺乏纤维蛋白-1对骨髓成骨和造血的表型后果是什么？(B)纤维蛋白-1是否协调MSC支持的HSC的表现？因此，我们建议：(目标1)表征附件骨骼中缺乏纤维蛋白-1的小鼠的MSC活性受损和骨丢失进展，并对这些突变动物的造血异常提供完整的描述；(目的2)验证纤维蛋白-1在协调中的作用 在特定基质细胞群中条件灭活Fbn1的小鼠中，MSC支持的HSC分化。通过证明纤维蛋白-1是骨髓壁龛不可或缺的功能成分，这些实验将为未来探讨纤维蛋白-1调节骨髓壁龛的机制奠定基础；通过将纤维蛋白-1与免疫系统功能联系起来，它们还可能导致对导致MFS主动脉疾病进展的细胞事件的全新理解，并带来意想不到的治疗机会。总体而言，这一极具创新性的建议有望为年龄相关的骨丢失提供新的见解，促进干细胞生物学的基础知识，影响再生医学中的各种翻译应用，并可能改善MFS中危及生命的主动脉表现的临床管理。

DESCRIPTION (provided by applicant): The definition of adult stem cell niches in the bone marrow (BM) and their regulation by extrinsic factors is a top research priority in tissue engineering and skeletal regenerative medicine, as well as a critical aspect of hematopoietic function and its reconstitution after marrow ablation therapy. Unlike the wealth of information regarding the cell types, cell-cell interactions and soluble signals that specify functionally discrete BM microenvironments, significantly less is known about the role of the extracellular matrix (ECM) in niche function to the detriment of developing more effective stem cell-based therapies. Our preliminary findings are the first to indicate involvement of fibrillin-1, a unique ECM protein that regulates the spatial organization and physical properties of tissues as well as the bioavailability of endogenous (local) TGF¿ family signals. This discovery raises the exciting possibility that a structural component of the marrow matrix controls the production of bone, blood and immune cells by determining the physical microenvironment of resident stem cells and by coordinating regulatory signals within it. Fibrillin-1 is the mutated protein in Marfan syndrome (MFS), whose pleiotropic manifestations include progressive bone loss (osteopenia). We previously demonstrated that osteopenia in MFS mice reflects perturbed bone remodeling due to impaired calibration of local anabolic and catabolic signals. Ongoing investigations have implied that fibrillin-1 is an essential component of the BM microenvironment that specifies the performance of mesenchymal stem cells (MSC) and hematopoietic stem cells (HSC). The goal of this high risk/high reward R21 application is to answer the following two questions: (a) What are the phenotypic consequences of fibrillin-1 deficiency for BM-based osteogenesis and hematopoiesis? ; (b) Does fibrillin-1 coordinate MSC-supported HSC performance? Accordingly, we propose to: (Aim 1) Characterize impaired MSC activity and bone loss progression in mice lacking fibrillin-1 in the appendicular skeleton and to provide a full account of hematopoietic abnormalities in these mutant animals; and (Aim 2) Validate the role of fibrillin-1 in coordinating MSC-supported HSC differentiation using mice with conditional Fbn1 inactivation in a specific stromal cells population. By demonstrating that fibrillin-1 is an indispensable functional component of BM niches, the experiments will establish the basis for future interrogation of the mechanism mediating fibrillin-1 regulation of marrow niches; and by implicating fibrillin-1 in immune system function, they may also lead to a radically new understanding of the cellular events responsible for aortic disease progression in MFS with unanticipated opportunities for therapy. Overall, this highly innovative proposal is expected to yield novel insights into age-related bone loss, advance fundamental knowledge of stem cell biology, impact a variety of translational applications in regenerative medicine, and perhaps improve the clinical management of life- threatening aortic manifestations in MFS.