The role of osteocytes in bone regeneration using a murine calvarial defect model

骨再生是自然界完美适应的过程之一，可以使骨折的骨骼无疤痕愈合。然而，当这种机制在病理上受损时，例如有严重缺陷，或由于潜在的疾病，就需要研究解决方案。虽然新型生物材料将在未来用于临床应用，但首先要了解细胞与骨再生的详细机制，这是非常重要的。目前，骨祖细胞、内皮细胞和免疫细胞在骨再生过程中的生化通讯正在进行中。我们假设，骨细胞作为矿化骨基质的居民，有助于愈合并在骨再生中具有重要的功能意义。骨细胞占骨细胞的绝大部分(90%-95%)，并通过其被称为树突的长细胞质突起形成一个连接的、机械感觉的细胞网络。在历史上，骨细胞的功能分析是具有挑战性的，因为它们被包裹在矿化的骨基质中，直到最近，骨细胞才被描述为具有内分泌作用的分泌细胞。由于其潜在的第二信使的高表达，骨细胞正在协调局部的骨重建，控制成骨细胞的新骨形成和破骨细胞对基质的吸收。另一方面，骨细胞死亡和树突状网络受损是几种骨病理的表现，如骨质疏松症，这种疾病由于骨密度降低和缺乏骨重建的生理平衡而增加了骨折风险。由于骨折导致骨细胞网络的破坏，而骨再生涉及到复杂的基质转换调节，骨细胞的调节作用似乎是可能的。然而，它们在复杂的骨修复过程中的作用还不是很清楚。我们的项目旨在利用小鼠颅骨缺损模型来研究骨细胞在骨愈合过程中的作用。我们的三个目标是：i)研究成活的骨细胞网络在雌性和雄性WT小鼠颅骨骨缺损修复中的作用；ii)利用绿色荧光新生血管转基因小鼠模型，确定骨细胞网络-血管通讯在颅骨修复中的作用；iii)使用老龄小鼠模型和机械感觉缺陷的Piezo1 fl/fl小鼠，剖析骨细胞网络受损对颅骨骨缺损修复的影响。我们相信，我们在骨细胞生物学、缺陷修复和成像方面的联合专业知识将使我们的项目蓬勃发展，并导致该领域的新发现，这些发现对普通骨生物学也具有重要意义。

Bone regeneration is one of nature’s perfectly adapted processes to allow for a scar-free healing of a fractured bone. Yet, when this mechanism is pathologically impaired e.g. with a critical defect, or due to underlying diseases, research solutions are required. Scaffolds bridging the defect and aiding the healing process are a promising avenue, and while new biomaterials will be useful for clinical applications in the future, it is of paramount importance to firstly understand the detailed mechanistic cellular interplay with bone regeneration. Already, the biochemical communication of osteoprogenitor cells, endothelial and immune cells during bone regeneration are subject to ongoing studies. We hypothesize that osteocytes, as inhabitants of the mineralized bone matrix, contribute to healing and possess a functional significance in bone regeneration. Osteocytes represent the vast majority of bone cells (90-95%) and form a connective, mechanosensory cellular network with their long cytoplasmic processes called dendrites. Historically the functional analysis of osteocytes was challenging because they are encased in the mineralized bone matrix, and only recently osteocytes were described as secretory cells of endocrine importance. With their potential high expression of second messengers, osteocytes are orchestrating the local bone remodeling, controlling new bone formation by osteoblasts and the resorption of matrix by osteoclasts. On the other hand, the death of osteocytes and the impaired dendritic network are seen with several bone pathologies i.e. osteoporosis, a disease in which the fracture risk is increased due to lower bone density and a lack of a physiological balance of bone remodeling. With the disruption of the osteocyte network due to a fractured bone, and bone regeneration involving an intricate regulation of matrix turnover, a regulatory role of osteocytes seems likely. However, their role in the complex process of bone repair is not well known. Our project aims to investigate the role of osteocytes in the healing process of bone, utilizing a murine calvarial defect model. Our three objectives are: i) to characterize the role of a viable osteocyte-network in the healing of calvarial bone defects in female and male WT mice, ii) to determine the role of osteocyte network-vessel communication during calvarial bone healing using a transgenic mouse model with green-fluorescent newly formed vessels, and iii) to dissect the effect of impaired osteocyte networks on the healing of calvarial bone defects, using an aged mouse model and the Piezo1 fl/fl mice with deficient mechanosensation. We believe that our joint expertise on osteocyte biology, defect healing and imaging will thrive our project and result in novel discoveries in the field that are also of importance for general bone biology.