Structural microenvironment of bone marrow stem cells

描述（申请人提供）：骨髓成体干细胞壁龛的定义及其受外部因素的调控是组织工程和骨骼再生医学的研究重点，也是骨髓消融治疗后造血功能及其重建的关键方面。与关于细胞类型、细胞间相互作用和可溶信号的丰富信息不同，这些信息指定了功能离散的骨髓微环境，但对细胞外基质（ECM）在生态位功能中的作用知之甚少，这不利于开发更有效的干细胞疗法。我们的初步研究结果首次表明了纤颤蛋白-1的参与，这是一种独特的ECM蛋白，调节组织的空间组织和物理特性以及内源性（局部）TGF¿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决定驻留干细胞的物理微环境和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是马凡氏综合征（MFS）的突变蛋白，其多种表现包括进行性骨质流失（骨质减少）。我们之前证明，MFS小鼠的骨质减少反映了由于局部合成代谢和分解代谢信号校准受损而导致的骨重塑紊乱。正在进行的研究表明，纤原蛋白-1是骨髓微环境的一个重要组成部分，它指定间充质干细胞（MSC）和造血干细胞（HSC）的性能。这项高风险/高回报的R21应用的目标是回答以下两个问题：(a)纤维蛋白-1缺乏对基于骨髓的成骨和造血的表型后果是什么？;(b)纤颤蛋白-1是否协调msc支持的HSC性能？因此，我们建议：（目标1）表征小鼠阑尾骨骼中缺乏纤维蛋白-1的MSC活性受损和骨质流失进展，并提供这些突变动物造血异常的完整描述；（Aim 2）验证纤颤蛋白-1在协调中的作用

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.