Cadherin Mediated Cell-Cell Interactions in the Bone Microenvironment

描述（由申请人提供）：骨重塑缺陷是大多数代谢性骨疾病的病理生理基础，包括绝经后和年龄依赖性骨质疏松症。在之前的工作中，我们发现成骨细胞表达细胞粘附分子的cadherin超家族成员，特别是cadherin-11 （Cad11）和N-cadherin （Ncad）。钙粘蛋白介导细胞间的粘附，但它们也通过稳定细胞表面的¿-catenin与Wnt信号通路相交。细胞间的粘附也是细胞间隙连接和细胞间通讯的先决条件。我们已经证明，小鼠钙粘蛋白功能的显性阴性破坏或Ncad和/或Cad11基因（Cdh2和Cadh11）的隐性零突变都会阻碍骨形成，导致低峰值骨量和骨质减少。我们还发现，在体外，钙粘蛋白缺乏会对Wnt/¿-catenin系统产生负面影响，并减少细胞间连接（粘附和间隙连接）的丰度。该项目的中心假设是钙粘蛋白（Ncad和Cad11）通过调节骨髓微环境中的细胞间相互作用，通过细胞间粘附、通讯和信号传导来控制成骨分化。我们进一步假设Ncad和Cad11在成骨细胞分化程序中部分重叠，但具有不同的作用。为了实现这一目标，我们建议确定：1)Cdh2和Cdh11在出生后骨骼的骨形成细胞承诺和分化和增殖中的相对作用；2)钙粘蛋白（Ncad和Cad11）与Wnt信号在成骨细胞分化和功能中的相互作用；3)成骨分化中钙粘蛋白依赖的细胞间连接（粘附和间隙连接）的组织和功能。我们将使用多种体外、离体和体内方法，基于我们已经开发的钙粘蛋白基因消融小鼠模型，研究钙粘蛋白缺乏对骨发育、骨量和骨祖细胞募集和分化的影响。我们还将确定钙粘蛋白缺陷小鼠骨质减少的细胞和分子基础。这一建议解决了骨转换在骨微环境中被调节的基本机制。了解钙粘蛋白在骨生物学中的作用对于全面了解控制骨发育和体内平衡的分子网络至关重要。公共卫生相关性：骨脱矿（如骨质疏松）患者刺激骨形成的治疗选择是有限的。这项研究将研究两种分子，这两种分子允许骨髓细胞和骨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。结果将使我们更好地了解成骨细胞是如何在成年动物中发育的，并将为我们提供新的工具，通过最大化他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.