Trap+ Mononuclear Cells in Periosteal Bone Formation

项目总结/摘要 骨膜骨生长和建模发生在皮质骨外表面的骨膜中。 骨膜覆盖整个骨表面，除了包含关节软骨的骨部分。 软骨是体内最成骨的组织之一，在皮质扩张中起着关键作用 在成长过程中。骨膜骨形成具有不同于骨表面其他区域的机制， 如骨内膜、继发性松质骨和松质骨重塑等。 重要的是，骨膜往往被忽视，当涉及到发生在底层的过程， 皮质骨骨膜生物学仍然很少调查和了解不多。在结构上， 骨膜由两层组成;与骨膜骨表面相邻的是一层松散堆积的 对底层骨骼的生长和修复至关重要的细胞。再往外是一层密集的 骨膜来源的干细胞（PDSC），散布有血管、血管和神经末梢。的 外层的微环境充当维持PDSC的生态位，而内层提供 骨膜骨形成的成骨微环境。我们已经证明， 巨噬细胞和陷阱+单核细胞在CSF-1 op/op小鼠（CSF-1-/-），和有趣的是，没有明显的， 皮质骨形成单次注射rhM-CSF足以挽救破骨细胞募集， CSF-1-/-小鼠的存活率。这些结果表明，骨膜巨噬细胞是必不可少的维护 骨膜骨形成的微环境。此外，我们已经证明，陷阱+ 来源于野生型WT小鼠的单核细胞分泌PDGF-BB以诱导间充质细胞迁移 基质/干细胞。敲除Trap+细胞系中的PDGF-BB减少骨膜血管生成， 骨形成，但PDSC和基质蛋白仍然存在于骨膜中，表明骨膜 巨噬细胞在维持骨膜内环境稳定中起重要作用。另外我们有 发现机械应力诱导骨膜TRAP+单核细胞分泌PDGF-BB用于血管生成 和骨形成的初步数据因此，我们假设骨膜巨噬细胞维持 骨膜和TRAP+单核细胞的稳态从外层募集PDSC， 用于血管生成和骨形成的骨膜表面。在本提案中，我们将首先确定 骨膜巨噬细胞在骨膜稳态中的作用。然后我们将确定Trap+的功能 单核细胞，特别是PDSC被Trap+单核细胞募集的机制 用于骨膜骨形成。最后，我们将验证TRAP+单核细胞在机械性 应力诱导的骨膜骨形成。

Project Summary/ Abstract Periosteal bone growth and modeling take place in the periosteum at the outer surface of cortical bones. The perioseum, which covers the entire bone surface except the portion of bones that contains articular cartilage, is one of the most osteogenic tissues in the body and plays a critical role in cortical expansion during growth. Periosteal bone formation has different mechanisms from other areas of bone surface such as endosteum, secondary spongiosa and trabecular bone remodeling, etc. Despite its physiological significance, the periosteum is often overlooked when it comes to processes that occur in the underlying cortical bone. Periosteal biology remains little investigated and poorly understood. Structurally, the periosteum is composed of two layers; adjacent to the periosteal bone surface is a layer of loosely packed cells essential for growth and repair of the underlying bone. Further outward is a layer of densely packed periosteum derived stem cells (PDSCs) interspersed with lymphatics, blood vessels and nerve endings. The microenvironment of the outer layer serves as a niche to maintain the PDSCs whilst the inner layer provides an osteogenic microenvironment for periosteal bone formation. We have shown that there are no osteal macrophages and Trap+ mononuclear cells in CSF-1 op/op mice (CSF-1-/-), and interestingly, no obvious cortical bone formation. A single injection of rhM-CSF is sufficient for rescue of osteoclast recruitment and survival in CSF-1-/- mice. These results suggest that periosteal macrophages are essential in maintenance of periosteum microenvironment for periosteal bone formation. Moreover, we have shown that Trap+ mononuclear cells derived from wild WT mice secrete PDGF-BB to induce migration of mesenchymal stromal/stem cells. Knockout of PDGF-BB in the Trap+ cell lineage reduces periosteal angiogenesis and bone formation but PDSCs and matrix proteins are still present in the periosteum, suggesting periosteal macrophages play more important role in maintenance of periosteum homeostasis. In addition, we have found mechanical stress induces periosteal TRAP+ mononuclear cells to secrete PDGF-BB for angiogenesis and bone formation in our preliminary data. Thus, we hypothesize that periosteal macrophages maintain homeostasis of the periosteum and TRAP+ mononuclear cells recruit PDSCs from outward layer to the periosteal surface for angiogenesis and bone formation. In this proposal, we will first determine the role of periosteal macrophages in periosteum homeostasis. We will then determine the function of Trap+ mononuclear cells, specifically, the mechanisms by which PDSCs are recruited by Trap+ mononuclear cells for periosteal bone formation. Finally, we will validate the role of TRAP+ mononuclear cells in mechanical stress-induced periosteal bone formation.