Constructing a growth-promoting pathway for functional regeneration after SCI

描述（由申请人提供）： 项目摘要 脊髓损伤 (SCI) 是影响美国军人受伤的最严重的疾病之一。例如，在阿富汗持久自由行动（2001 年至今）战争中，撤离的五分之一受伤军人遭受脊椎损伤。事实上，全球反恐战争（阿富汗和伊拉克）的战斗伤亡中脊柱损伤的发生率是美国军事医学史上最高的。不幸的是，目前尚无针对 SCI 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 SCI 的破坏性，并将其应用于临床，以提高 SCI 退伍军人的生活质量。 SCI 后，轴突再生对于显着的功能恢复至关重要。尽管 SCI 后的大多数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 (CST) 和红核脊髓束 (RST)]，但令人惊讶的是，对脊髓内投射的本体脊髓通路的再生研究不足。降固有脊髓束（DPST）在调节多种脊柱功能中发挥着重要作用，包括正常条件下的反射、姿势和运动。 DPST的神经元主要位于中间灰质，接受强而会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。在脊髓上通路中，CST 在介导本体脊髓​​功能中发挥着特殊作用，其作用可能需要完整的本体脊髓回路。 SCI 后，CST 轴突无法在损伤部位内外再生。因此，CST 轴突对 DPST 神经元的神经支配以及随后通过和超出病变部位的 DPST 轴突的再生可能提供替代途径或“功能中继”，将脊髓上运动命令向下传递到脊髓，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中继并检查这样的中继是否有助于 SCI 后的功能恢复。我们将测试一个中心假设，即 SCI 后 DPST 轴突的成功再生和目标神经支配为“功能中继”提供了结构基础，该“功能中继”将脊髓上命令向下传递至脊髓，并随后恢复运动和膀胱功能。为了测试这一创新假设，我们将构建一条由过表达胶质细胞系源性神经营养因子（GDNF）的移植雪旺细胞（SC）形成的生长促进通路，从病变部位到尾部宿主脊髓，以促进成年大鼠第10胸椎水平（T10）完全脊髓横断后DPST轴突的持续再生。使用该模型，我们将确定（1）SCI 是否会诱导轴突 DPST 神经元体细胞和树突的退行性变化，如果是这样，GDNF 治疗可以逆转这种变化； （2）过表达GDNF的移植SC（SCs-GDNF）形成连续的生长促进途径，促进DPST轴突再生到远端宿主脊髓，形成新突触，增强功能恢复； (3) 需要 CST 对 DPST 的脊髓上神经支配来指导“功能中继”。通过完成这项研究，将产生关于这种新构建的“功能中继”是否以及如何有助于 SCI 后运动功能恢复的新知识。如果该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老患者有益。

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.