Mechanisms of Synovial Joint Formation

描述（由申请人提供）：滑膜关节对于骨骼功能和生活质量至关重要，并且对其解剖结构、不同组织和对常见病理（包括年龄依赖性骨关节炎）的易感性有很多了解。相反，人们对它们的发育生物学知之甚少。如果这些信息可用，它可以直接使用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，例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，旨在填补如此明显的信息空白。在四肢中，滑膜关节形成起始于软骨长骨anlaga两侧的每个预期关节部位处的间充质细胞（统称为间带）的出现。然而，长期以来，人们一直不知道间带细胞是如何获得其基本的间充质特征的，它们是否作为一个关键但短暂的关节分界点，和/或它们是否真的随着时间的推移产生关节组织。为了解决这些基本问题，我们从遗传学上追踪了小鼠出生前和出生后的区间细胞。引人注目的是，我们发现这些细胞根本不是瞬时的，而是产生关节组织并且仅产生关节组织，因此构成了具有关节形成能力的多能祖细胞的专门群体。我们发现，在早期阶段，细胞表现出强烈的Wnt/？连环蛋白信号传导。随着关节发育的进展，信号转导减少，但在关节软骨的浅表区（对关节功能至关重要，并以独特的纤维软骨表型为特征）保持强劲。是的，有条件的？连环蛋白消融导致该区域几乎丧失。额外的初步数据现在表明，Wnt/？-连环蛋白通路不是单独作用的，而是与类视色素通路和核视黄酸受体（RAR）合作来维持和调节关节形成。这些数据导致了这种竞争性更新应用的中心假设，即类维生素A和Wnt/？连环蛋白信号传导途径建立了早期间区细胞的多能间充质特征，然后被局部调节以允许形成不同的关节组织。维持信号传导活性将允许区间细胞产生纤维和纤维软骨关节组织，而信号传导的下降将允许关节软骨的形成。我们的目标是：（1）进一步表征类维生素A信号传导在带间功能和关节形成中的作用;（2）确定两种信号传导途径相互作用以调节带间细胞功能和关节形成的分子机制;和（3）确定带间细胞的可塑性和分化潜力以及类维生素A和Wnt/β的调节。连环蛋白信号传导。本延续计划中提出的工作将基本调控机制的实验品系与测试区间细胞可塑性、可移植性和发育潜力的品系相结合。因此，它将继续产生对基础生物学知识具有重要价值的信息，并将对翻译医学和创造未来新型关节修复和再生疗法具有重要意义。

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.