Role of osteogenic stem cells in bone regeneration and repair in vivo

描述(申请人提供)：骨系细胞在骨骼的终生再生过程中特别重要。它们在骨髓微环境中也是至关重要的，在那里它们控制着造血，并可能参与白血病和癌症转移。然而，尽管成骨细胞在维持骨骼和造血方面起着关键作用，但这些细胞在体内的起源、寿命和动力学仍然是一个根本未解的问题。因此，我们的目标是确定成骨细胞的寿命及其在稳态和损伤条件下的替代来源。我们最近使用遗传脉冲追逐技术和延时活体动物荧光成像相结合的研究表明，功能性成骨细胞和成骨细胞前体的寿命很短，并在体内由其祖细胞持久维持。此外，我们发现‘间充质干细胞’(根据体外多系能力的定义)在体内没有这样的功能。相反，它们在正常的动态平衡中是骨线受限的前体细胞。这些成骨前体细胞可以通过瞬时激活粘病毒抗性-1(Mx1)启动子来进行遗传学标记。我们证明了Mx1标记的成骨前体细胞具有血管周围起源，有效地迁移到损伤部位，并为 大多数新生的成骨细胞在骨折愈合中。此外，它们与血管周围巢蛋白MSCs的子集重叠。我们现在有了独特的阶段特异性诱导模型，可以标记成骨干/祖细胞、前成骨细胞和成熟成骨细胞。本研究的目的是了解成骨细胞及其干/祖细胞在体内骨再生和修复中的作用。我们还将探索成骨干细胞的临床相关性，目的是逆转退行性骨病的状况。因此，我们建议：1.检测Mx1和Nestin双标记物是否在体内特异性成骨干细胞。2.检测成骨干细胞移植对骨折愈合的促进作用。3.检测成骨干细胞在骨丢失疾病中的作用。通过研究三个特定的、与临床相关的问题，我们将进一步定义在生理条件下成骨干细胞的新的生物学和临床见解。

DESCRIPTION (provided by applicant): Osteo-lineage cells are of particular importance in the life-long regenerative processes of bone. They are also critical in the bone marrow microenvironment where they control hematopoiesis and likely participate in leukemia and cancer metastasis. However, despite the pivotal roles of osteogenic cells in the maintenance of bones and hematopoiesis, the in vivo origin, lifespan, and dynamics of these cells remain fundamentally unanswered questions. Therefore, we aimed to define the lifespan of bone-forming osteoblasts and their source of replacement under homeostatic and injury conditions. Our recent studies using genetic pulse-chase techniques in combination with time-lapse live-animal fluorescent imaging have revealed that functional osteoblasts and osteoblast precursors have a short lifespan and are durably maintained by their progenitor cells in vivo. Additionally, we found that the 'mesenchymal stem cells' (as defined by in vitro multilineage capacity) have no such function in vivo. Rather, they serve as osteolineage-restricted progenitors in normal homeostasis. These osteogenic progenitors can be genetically marked by transient activation of the myxovirus resistance-1 (Mx1) promoter. We demonstrated that Mx1-labeled osteogenic progenitor cells have a perivascular origin, migrate efficiently to sites of injury, and supply the majority of new osteoblasts in fracture healing. Further, they overlap with a subset of perivascular nestin¿ MSCs. We now have distinct stage-specific inducible models that can label osteogenic stem/progenitors, pre-osteoblasts and mature osteoblasts. The goal of this study is to understand the role of mature osteoblasts and their stem/progenitor cells in the context of bone regeneration and repair in vivo. We will also explore the clinical relevance of osteogenic stem cells with the goal of reversing conditions of degenerative bone disease. We thus propose to: 1. Test if Mx1 and nestin double labeling specify osteogenic stem cells in vivo. 2. Test if te transplantation of osteogenic stem cells improves the restoration of bone fracture. 3. Test the role of osteogenic stem cells in bone loss diseases. By studying three specific, clinically relevan questions, we will further define new biological and clinical insights of osteogenic stem cells in physiological conditions.