Constructing a growth-promoting pathway for functional regeneration after SCI

描述(由申请人提供)： 项目概述脊髓损伤(SCI)是影响美国军队伤员的最严重的致残疾病之一。例如，在阿富汗的持久自由行动(2001年至今)战争中，每五名受伤的军人中就有一人脊椎受伤。事实上，在全球反恐战争中(阿富汗和伊拉克)，脊柱损伤的发生率在美国军事医学史上是最高的。不幸的是，目前还没有针对脊髓损伤患者的有效治疗方法。因此，迫切需要开发新的修复策略来减轻脊髓损伤的破坏性，并将其临床转化为改善患有脊髓损伤的退伍军人的生活质量。脊髓损伤后，轴突在吻尾方向的再生对于显著的功能恢复至关重要。虽然大多数脊髓损伤后的再生研究都集中在从大脑投射到脊髓的长脊髓上通路[例如，皮质脊髓束(CST)和红核脊髓束(RST)]，但令人惊讶的是，对投射到脊髓内的固有脊髓通路的再生研究不足。在正常情况下，下行固有脊髓束(DPST)在调节包括反射、姿势和运动在内的多种脊髓功能中起着重要作用。DPST神经元主要位于中间灰质，接受强而汇聚的脊髓上神经支配，投射并作用于多个脊髓节段的脊髓运动神经元和中间神经元。在脊柱上通路中，CST在调节固有脊髓功能方面起着特殊的作用，其作用可能需要一个完整的固有脊髓回路。脊髓损伤后，CST轴突不能在损伤部位再生。因此，CST轴突在DPST神经元上的神经支配以及随后DPST轴突在损伤部位和以外的再生可能提供了另一种途径或“功能继电器”，将脊髓上的运动指令向下传递到脊髓，以促进运动和膀胱功能的恢复。本申请的目标是建立这样的功能继电器，并检查这种继电器是否有助于脊髓损伤后的功能恢复。我们将验证一个中心假说，即脊髓损伤后DPST轴突的成功再生和靶向神经支配为“功能继电器”提供了结构基础，该功能继而将脊髓上的命令向下传递到脊髓，并随后恢复运动和膀胱功能。为了验证这一创新假说，我们将构建一条由移植的高表达胶质细胞系衍生神经营养因子(GDNF)的雪旺细胞(SCs)形成的生长促进途径，从损伤部位到尾侧宿主脊髓，以促进成年大鼠在第10胸椎水平(T10)的完整脊髓横断后继续再生DPST轴突。利用这个模型，我们将确定：(1)脊髓损伤是否导致脊髓损伤后DPST神经元胞体和树突的变性变化，如果是，GDNF治疗可以逆转这种变化；(2)由高表达GDNF的移植干细胞形成的连续的促生长途径，促进DPST轴突再生到宿主脊髓远端，形成新的突触，促进功能恢复；(3)需要在DPST上对CST进行脊髓上神经支配，以引导“功能继发”。通过这项研究的完成，将产生新的知识，关于这一新构建的“功能继电器”是否以及如何有助于脊髓损伤后运动功能的恢复。如果这一策略被证明是有效的，它可能会转化为临床前和临床试验的发展，最终可能对我们遭受脊髓损伤的退伍军人患者有利。

DESCRIPTION (provided by applicant): Project Summary Spinal cord injury (SCI) is among the most disabling conditions affecting wounded members of the U.S. military. For example, in the Operation Enduring Freedom (2001-present) War in Afghanistan, one in five wounded service members that were evacuated suffered a spinal injury. In fact, the incidence of spinal injuries among combat casualties in the Global War on Terrorism (in both Afghanistan and Iraq) is among the highest in American military medical history. Unfortunately, there has been no effective treatment available for SCI patients. There is, therefore, an urgent need to develop novel repair strategies to mitigate the devastating nature of SCI and clinically translate them to improve quality of life of our veterans with SCI. After SCI, axonal regeneration in a rostrocaudal orientation is crucial for significant functional recovery. Whereas most regeneration studies after SCI have been focused on long supraspinal pathways that project from the brain to the spinal cord [e.g., the corticospinal (CST) and rubrospinal tracts (RST)], regeneration of propriospinal pathways projecting within the spinal cord has been surprisingly understudied. The descending propriospinal tract (DPST) plays an important role in mediating multiple spinal functions, including reflex, posture, and locomotion in normal conditions. Neurons of DPST are mainly located in the intermediate gray matter, receive strong and convergent supraspinal innervations, and project and act on spinal motoneurons and interneurons in multiple cord segments. Among supraspinal pathways, the CST plays a particular role in mediating propriospinal function and its action likely requires an intact propriospinal circuitry. Following SCI, the CST axons fail to regenerate through and beyond the lesion site. Therefore, the innervation of CST axons on DPST neurons and subsequent regeneration of the DPST axons through and beyond the lesion site may provide an alternative pathway or "functional relay" that transmits supraspinal motor command down to the spinal cord to promote recovery of motor and bladder function. The goal of this application is to establish such a functional relay and examine whether such a relay contributes to functional recovery after SCI. We will test a central hypothesis that successful regeneration and target innervation of DPST axons after SCI provides a structural foundation for a "functional relay" that mediates supraspinal commands down to the spinal cord and subsequent recovery of motor and bladder function. To test this innovative hypothesis, we will construct a growth-promoting pathway, formed by grafted Schwann cells (SCs) overexpressing glial cell line-derived neurotrophic factor (GDNF), from the lesion site to the caudal host spinal cord in order to promote continued regeneration of DPST axons through and beyond a complete spinal transection at the 10th thoracic level (T10) in adult rats. Using this model, we will determine whether (1) SCI induces degenerative changes of axotomized DPST neurons at their somas and dendrites, and if so, GDNF treatment can reverse such changes; (2) a continuous growth-promoting pathway, formed by grafted SCs overexpressing GDNF (SCs-GDNF), promotes regeneration of DPST axons into the distal host spinal cord, formation of new synapses, and enhancement of functional recovery; (3) supraspinal innervation of CST on DPST is required to direct the "functional relay. By completion of this research, new knowledge will be generated concerning whether and how this newly constructed "functional relay" contributes to recovery of motor function following SCI. If this strategy is proven to be effective, it may be translated to te development of preclinical and clinical trials that may eventually be beneficial for our veteran patients who suffer spinal cord injuries.