A Wnt/Shh signaling loop controls intervertebral disc growth and differentiation

项目描述（申请人提供）：本项目旨在确定出生后椎间盘生长和分化的分子机制，以及这些机制如何下调，导致椎间盘年龄相关的变化。每个IVD由一个中央半液体髓核（NP）组成，由多层纤维环（AF）包围，并通过软骨终板（EP）与相邻椎体相连。这些组成部分一起形成了一个坚固的关节，可以抵抗椎骨之间的张力和压缩力。椎间盘退行性疾病（DDD）是导致腰痛和其他神经系统症状的主要原因，导致生活质量下降。DDD非常普遍，影响多达七分之一的人。治疗费用很高，通常包括手术干预。然而，治疗基本上是姑息性的，因为它治疗椎间盘退变的影响而不是原因。该项目的长期目标是利用IVD正常生长和分化的相同途径，确定潜在的生物学治疗方法。我们已经建立了小鼠腰椎IVD模型，初步数据显示，它可以用来识别IVD中控制出生后生长和分化的信号通路。我们发现，在出生后的生长过程中，NP作为一个信号中心，控制生长和分化。NP细胞表达SHH，体外和体内研究表明，SHH信号的阻断对IVD细胞增殖和分化至关重要。NP细胞也表达几种Wnt配体，这些配体在IVD中维持Shh信号。这两种信号通路，以及Shh信号的下游目标，在生长期结束时被下调。然而，Shh信号和分化标记物的表达可以在生长期后被胎牛血清中的信号或Wnt激动剂重新激活，这表明生长和分化的下调并非不可逆转，并为未来的治疗提供了潜在的靶点。该项目的目的1检验了一个假设，即出生后生长期的持续时间是由活跃的Wnt信号决定的。目的2验证了一个假设，即Shh信号下游表达的Wnt抑制剂建立了Wnt和Shh信号之间的反馈回路。目的3验证循环信号通过作用于NP中的Wnt/Shh信号环控制所有ivd同步生长的假设。该项目的数据将为进一步探索IVD老化的本质、椎间盘损伤或退变的可能生物治疗的基础，以及在出生后生长过程中IVD生长和分化的控制方式提供新的科学见解。

DESCRIPTION (provided by applicant): This project aims to identify the molecular mechanisms of postnatal growth and differentiation of the intervertebral disc (IVD), and how these mechanisms are down-regulated, leading to age-related changes in the IVD. Each IVD consists of a central semi-liquid nucleus pulposus (NP), surrounded by a multi-layered annulus fibrosus (AF), and connected to the bodies of the adjacent vertebral bodies by cartilagenous end plates (EP). Together, these components form a strong joint that resists both tension and compression forces between vertebrae. Degenerative disc disease (DDD) is a major cause of lower back pain, and other neurological symptoms leading to a decreased quality of life. DDD is extremely common, affecting as many as one in seven people. The treatment costs are high, and often include surgical intervention. However, treatment is essentially palliative, since it treats the effects of disc degeneration rather than the causes. The long-term goal of this project is to identify potential biological approaches to therapy, using the same pathways by which the IVD normally grows and differentiates. We have developed the mouse lumbar IVD as a model, and preliminary data shows that it can be used to identify the signaling pathways in the IVD that control postnatal growth and differentiation. We have found that during postnatal growth, the NP acts as a signaling center that controls both growth and differentiation. NP cells express SHH, and blockade of Shh signaling both in vitro and in vivo shows that it is essential for cell proliferation and differentiation of the IVD. NP cells also express several Wnt ligands, which are required to maintain Shh signaling in the IVD. Both these signaling pathways, and the downstream targets of Shh signaling, are down-regulated by the end of the growth period. However, Shh signaling, and the expression of differentiation markers, can be re-activated after the growth period by signals present in fetal bovine serum, or by Wnt agonists, showing that down-regulation of growth and differentiation is not irreversible, and offers potential future targets for therapy. Aim 1 of the project tests the hypothesis that the duration of the postnatal growth period is determined by active Wnt signaling. Aim 2 tests the hypothesis that a feedback loop between Wnt and Shh signaling is established by Wnt inhibitors expressed downstream of Shh signaling. Aim 3 tests the hypothesis that circulating signals control the synchronous growth of all the IVDs by acting on Wnt/Shh signaling loop in the NP. The data from this project will provide the necessary information to explore further the nature of aging of the IVD, the basis of possible biological therapies for disc injury or degeneration, and novel scientific insights into te way growth and differentiation of the IVDs are controlled during postnatal growth.