Role of Shh/Brachyury axis in the maintenance of the postnatal intervertebral disc

项目总结/摘要 这项提案的目标是确定关键发育分子在生长和维持中的作用 出生后椎间盘（IVD或椎间盘）的分子，以及这些分子随年龄的损失如何导致 椎间盘的病理变化。椎间盘是存在于每个椎骨之间的软骨结构。盘 有三个组成部分：脊索衍生的中央髓核（NP），由正交层包围， 纤维环（AF）和邻近生长板的终板（EP）。随着年龄的增长或受伤，椎间盘 退行性变化导致慢性下背痛（cLBP），影响近80%的美国成年人 人口关于椎间盘生长分化的细胞和分子基础，还有很多需要了解的， 和衰老，这限制了有效疗法的发展。我们将使用条件遗传小鼠模型， 谱系追踪和椎间盘损伤模型，以确定关键发育调节因子Brachyury的功能 (Bra)在光盘中。我们的中心假设是NP细胞的Bra表达对于椎间盘的生长是必不可少的， 维持，并且其在老化期间的损失导致椎间盘中的病理变化。BRA是一个T-box 转录因子和脊索标记。以前，我们发现出生后的NP细胞表达Bra; 它的表达量随着年龄的增长而减少。我们还发现了一个重要的脊索信号， 由NP细胞分泌，调节出生后椎间盘生长和分化，并调节Bra表达。而 NP细胞的总数随着年龄的增长而减少，表达Bra的NP细胞也随着年龄的增长而减少， 被不表达Bra的“软骨细胞样细胞”（CLC）替代。CLC之间的谱系关系 他们所取代的表达Bra的细胞是未知的，也不知道Bra表达的丧失是如何（或是否）发生的。 导致椎间盘老化。我们的初步数据表明，所有的NP细胞在老年小鼠椎间盘中丢失。我们也 结果显示，成年小鼠Shh的条件性靶向加速椎间盘老化，沿着Bra的丢失， 表情我们进一步表明，Bra的单倍不足加速了椎间盘的衰老，这提供了合理的解释。 这个新项目的前提。目的1验证Bra是一个主要的转录调节因子的假设 SHH信号下游，并调节出生后椎间盘的生长和维持。目标2将测试 假设NP细胞分化成两个分子异质群体，其在以下方面不同： 嘘和胸罩表情。目的3将检验Bra控制NP细胞的存活，并阻止NP细胞的增殖的假设。 它们分化成“软骨细胞样”细胞。我们希望这项研究的结果将提供 深入了解发育分子在生长和衰老过程中维持出生后椎间盘的作用， 并将确定靶向这些分子的途径，以逆转衰老过程， 用于治疗椎间盘相关病症和LBP的治疗剂。

PROJECT SUMMARY/ ABSTRACT The goal of this proposal is to identify the role of critical developmental molecules in growth and maintenance of the postnatal intervertebral disc (IVD, or disc), and how the loss of these molecules with age results in pathological changes in the disc. The disc is a cartilaginous structure present between each vertebra. The disc has three components: notochord derived central nucleus pulposus (NP), surrounded by orthogonal layers of annulus fibrosus (AF), and endplate (EP) adjacent to the growth plate. With age or injury, the disc undergoes degenerative changes leading to chronic lower back pain (cLBP) affecting almost 80% of the adult US population. Much remains to be learned about the cellular and molecular basis of disc growth differentiation, and aging, that has limited development of effective therapies. We will use conditional genetic mouse models, lineage-tracing, and disc injury models to identify the function(s) of a crucial developmental regulator Brachyury (Bra) in the disc. Our central hypothesis is that Bra-expression by the NP cells is essential for disc growth and maintenance, and its loss during aging leads to the pathological changes in the disc. BRA is a T-box transcription factor and a notochordal marker. Previously, we showed that postnatal NP cells express Bra; but it’s expression decreases with age. We also found that sonic hedgehog (SHH), an important notochord signal secreted by NP cells, regulates postnatal disc growth and differentiation, and regulates Bra expression. While the total number of NP cells decreased with age, the Bra-expressing NP cells also decreased with age and were replaced by non-Bra-expressing "chondrocyte-like cells" (CLCs). The lineage relationship between CLCs and the Bra-expressing cells they replace is unknown, nor is it known how (or if) the loss of Bra expression leads to disc aging. Our preliminary data showed that all NP cells are lost in an aged mouse disc. We also showed that conditional targeting of Shh in adult mouse accelerates disc aging, along with the loss of Bra expression. We further showed that haploinsufficiency of Bra accelerates disc aging, providing the logical premise for this new project. Aim 1 tests the hypothesis that Bra is a primary transcriptional regulator downstream of SHH signaling, and regulates growth and maintenance of postnatal disc. Aim 2 will test the hypothesis that NP cells diverge into two molecularly heterogeneous populations, which differ with respect to Shh and Bra expression. Aim 3 will test the hypothesis that Bra controls the survival of NP cells, and prevents them from differentiating into "chondrocyte-like" cells. We expect that the findings from this study will provide insights into the role of developmental molecules in the maintenance of postnatal disc during growth and aging, and will identify avenues for targeting such molecules to reverse the aging process, aiding the development of therapeutics for the treatment of disc related disorders and LBP.