Mechanisms of Synovial Joint Formation

描述（由申请人提供）：滑膜关节对骨骼功能和生活质量至关重要，人们对其解剖组织、独特组织和常见疾病（包括年龄依赖性骨关节炎）的易感性了解甚多。相比之下，我们对它们的发育生物学知之甚少。如果这些信息可用，它可以直接或与生物工程工具结合使用，以创建新的关节修复和再生策略，如具有特定关节组织形成能力的工程干细胞。这个项目始于五年前，旨在填补这些明显的信息空白。在四肢，滑膜关节的形成开始于在软骨长骨软骨两侧的每个未来关节部位出现间充质细胞（统称为间区）。然而，长期以来，人们一直不知道带间细胞是如何获得其基本的间充质特性的，它们是否作为一个关键但短暂的关节分界点，以及/或者它们是否随着时间的推移实际上产生了关节组织。为了解决这些基本问题，我们对小鼠出生前和出生后的带间细胞进行了遗传追踪和跟踪。引人注目的是，我们发现这些细胞不是短暂的，而是产生关节组织，并且只产生关节组织，因此，构成了一个具有关节形成能力的多能祖细胞的特殊队列。我们发现，在早期阶段，细胞表现出强烈的Wnt/？连环蛋白信号。随着关节发育的进展，信号传导减少，但在关节软骨的表层区（对关节功能至关重要，并以独特的纤维-软骨表型为特征）保持强烈。是吗，有条件的？-catenin消融导致该区域几乎消失。额外的初步数据表明，Wnt/？-catenin途径不是单独作用，而是与类视黄酸途径和核视黄酸受体（RARs）协同维持和调节关节的形成。这些数据导致了这一竞争性更新应用的中心假设，即类维生素a和Wnt/？-连环蛋白信号通路建立早期带间细胞的多能间充质特性，然后进行地形调节以形成不同的关节组织。信号活动的维持将允许带间细胞产生纤维和纤维软骨关节组织，而信号的下降将允许关节软骨的形成。我们的目标是：(1)进一步表征类维甲酸信号在区间功能和关节形成中的作用；(2)确定两种信号通路相互作用调节带间细胞功能和关节形成的分子机制；(3)测定区间细胞的可塑性和分化潜能，并通过类维生素a和Wnt/？连环蛋白信号。本续提案中提出的工作将基本调控机制的实验系与区间细胞可塑性、可移植性和发育潜力的实验系结合起来。因此，它将继续产生对基础生物学知识具有基本价值的信息，并将对翻译医学和未来新型关节修复和再生疗法的创造具有重要意义。

DESCRIPTION (provided by applicant): Synovial joints are essential for skeletal function and quality of life and much is known about their anatomical organization, distinct tissues and susceptibility to common pathologies including age-dependent osteoarthritis. In contrast, very little is known about their developmental biology. Were such information available, it could be used directly or in combination with bioengineering tools to create new joint repair and regenerative strategies such as engineered stem cells with specific joint tissue-formation capacity. This project started five years ago to fill such glaring gaps in information. In the limbs, synovial joint formation initiates with the appearance of mesenchymal cells (collectively called the interzone) at each prospective joint site flanked by cartilaginous long bone anlaga. However, it had long remained unknown how the interzone cells acquire their essential mesenchymal character, whether they serve as a critical but transient joint demarcation point, and/or whether they actually produce joint tissues over time. To address these fundamental questions, we genetically traced and tracked the interzone cells prenatally and postnatally in mice. Strikingly, we found that the cells are not at all transient but produce joint tissues and only joint tissues and thus, constitute a specialized cohort of multipotent progenitor cells endowed with joint formation capacity. We showed that at early stages the cells exhibit strong Wnt/?-catenin signaling. As joint development progresses, signaling dwindled but remained strong in the superficial zone of articular cartilage (critical for joint function and characterized by a unique fibro-cartilaginous phenotype). Indeed, conditional ?-catenin ablation caused a near loss of that zone. Additional Preliminary Data now indicate that the Wnt/?-catenin pathway does not act alone, but cooperates with the retinoid pathway and nuclear retinoic acid receptors (RARs) to sustain and regulate joint formation. The data lead to the central hypothesis for this competitive renewal application that the retinoid and Wnt/?- catenin signaling pathways establish the multipotent mesenchymal character of early interzone cells and are then topographically modulated to permit formation of distinct joint tissues. Maintenance of signaling activity would allow interzone cells to produce fibrous and fibro-cartilaginous joint tissues, while a drop in signaling would allow formation of articular cartilage. Our Aims are: (1) to further characterize the roles of retinoid signaling in interzone function and joint formation; (2) to determine molecular mechanisms by which the two signaling pathways interact to regulate interzone cell function and joint formation; and (3) to determine interzone cells' plasticity and differentiation potentials and regulation by retinoid and Wnt/?-catenin signaling. The work proposed in this continuation proposal combines experimental lines on basic regulatory mechanisms with lines testing plasticity, transplantability and developmental potentials of interzone cells. It will thus continue to produce information of fundamental value to basic biologic knowledge and will also significant relevance for translation medicine and creation of future novel joint repair and regeneration therapies.