Cadherin Mediated Cell-Cell Interactions in the Bone Microenvironment

描述(申请人提供)：骨重建缺陷是大多数代谢性骨病的病理生理学基础，包括绝经后和年龄相关性骨质疏松症。在以前的工作中，我们已经发现成骨细胞表达细胞黏附分子钙粘蛋白超家族成员，特别是钙粘蛋白-11(CAD11)和N-钙粘蛋白(Ncad)。钙粘蛋白介导细胞间的黏附，但它们也通过稳定细胞表面的β-连环蛋白而与Wnt信号通路相交。细胞间的黏附也是缝隙连接组装和细胞间通讯的先决条件。我们已经证明，在小鼠中，无论是钙粘蛋白功能的显性-负性中断，还是Ncad和/或CAD11基因(CDH2和Cadh11)的隐性零突变都会阻碍骨形成，导致峰值骨量降低和骨量减少。我们还发现，在体外，钙粘附素缺乏对Wnt/β-catenin系统产生负面影响，并降低细胞间连接(贴壁连接和缝隙连接)的丰度。这个项目的中心假设是，钙粘附素(Ncad和CAD11)通过调节骨髓微环境中细胞与细胞的相互作用，通过细胞-细胞黏附、通讯和信号转导来控制成骨分化。我们进一步假设Ncad和CAD11在成骨细胞分化过程中具有部分重叠但截然不同的作用。为了实现这一目标，我们建议确定：1)CDH2和CDH11在出生后骨骼中成骨细胞定位、分化和增殖中的相对作用；2)钙粘附素(Ncad和CAD11)与Wnt信号在成骨细胞分化和功能中的相互作用；3)细胞间连接(贴壁连接和缝隙连接)在成骨分化中依赖钙粘连蛋白的组织和功能。我们将采用体外、体外和体内多种方法，在我们建立的钙粘蛋白基因去除小鼠模型的基础上，研究钙粘素缺乏对骨发育、骨量和骨祖细胞募集和分化的影响。我们还将确定钙粘附素缺陷小鼠骨质减少的细胞和分子基础。这项建议阐述了在骨微环境中调节骨周转的基本机制。了解钙粘附素在骨生物学中的作用对于全面了解控制骨发育和动态平衡的分子网络是至关重要的。公共卫生相关性：骨质疏松症等骨质脱矿患者刺激骨形成的治疗选择有限。这项研究将研究两种分子，它们允许骨髓中的细胞和骨骼表面的细胞直接接触，从而影响彼此的功能和制造新骨的能力。研究结果将使我们更好地了解骨形成细胞在成年动物中是如何发育的，并将为我们提供新的工具，通过最大限度地发挥人们制造新骨的潜力来帮助骨量低和骨折的人。

DESCRIPTION (provided by applicant): Defective bone remodeling is the pathophysiologic basis of most metabolic bone diseases, including postmenopausal and age-dependent osteoporosis. In previous work, we have found that osteoblasts express members of the cadherin superfamily of cell adhesion molecules, in particular cadherin-11 (Cad11) and N-cadherin (Ncad). Cadherins mediate cell-cell adhesion, but they also intersect the Wnt signaling pathway by stabilizing ¿-catenin on the cell surface. Cell-cell adhesion is also a pre-requisite for assembly of gap junctions and intercellular communication. We have demonstrated that either dominant-negative disruption of cadherin function or recessive null mutations of the Ncad and/or Cad11 genes (Cdh2 and Cadh11) in mice hinders bone formation, leading to low peak bone mass and osteopenia. We also find that cadherin deficiency negatively affects the Wnt/¿-catenin system and reduces the abundance of intercellular junctions (adherens and gap junctions), in vitro. The central hypothesis of this project is that cadherins (Ncad and Cad11) control osteogenic differentiation by modulating cell-cell interactions in the bone marrow microenvironment, via cell-cell adhesion, communication and signaling. We further hypothesize that Ncad and Cad11 have partially overlapping, yet distinct roles in the osteoblast differentiation program. To achieve this goal, we propose to determine, 1) the relative roles of Cdh2 and Cdh11 in bone forming cell commitment and differentiation and proliferation in the post-natal skeleton; 2) the interactions between cadherins (Ncad and Cad11) and Wnt signaling in osteoblast differentiation and function and 3) cadherin dependent organization and function of intercellular junctions (adherens and gap junctions) in osteogenic differentiation. We will use multiple in vitro, ex vivo and in vivo approaches, based on cadherin gene ablation mouse models we have developed, to study the consequences of cadherin deficiency on bone development, bone mass and osteoprogenitor cell recruitment and differentiation. We will also determine the cellular and molecular bases of the osteopenia of cadherin deficient mice. This proposal addresses fundamental mechanisms by which bone turnover is modulated in the bone microenvironment. Understanding the role of cadherins in bone biology is essential to gain a full picture of the molecular network by which bone development and homeostasis are controlled. PUBLIC HEALTH RELEVANCE: Therapeutic options for stimulating bone formation in subjects with bone demineralization, such as osteoporosis, are limited. This research will study two molecules that allow cells in the bone marrow and on the bone surface to come in direct contact, thus influencing each others' function and ability to manufacture new bone. Results will allow us to better understand how bone forming cells develop in adult animals, and will give us new tools to help people with low bone mass and fractures, by maximizing their potential for making new bone.