Recovery of Respiratory Function After Spinal Cord Injury

描述（由申请人提供）：拟议的研究利用神经可塑性的令人兴奋的新发展，以促进颈脊髓损伤（SCI）后呼吸功能的恢复。美国每年约有12，000例新的SCI病例，近50万人受到影响。大多数SCI是不完全的，脊髓通路有一些保留。涉及颈脊髓的损伤的数量正在增加，从而导致节律性膈神经活动受损和膈肌麻痹。不能产生驱逐行为以及长期机械通气需要支持这样的SCI患者与感染率，发病率和死亡率升高。在该基金支持的最近研究中，我们发现神经营养蛋白脑源性神经营养因子（BDNF）通过全长高亲和力原肌球蛋白相关激酶受体亚型B（Trk B.FL）发挥作用，在神经可塑性和脊髓损伤后膈神经活动的恢复中起重要作用。该提议将利用多管齐下的方法来获得BDNF/TrkB.FL信号传导对以下作用的机制性洞察：1）加强对膈运动神经元的备用突触输入，以及2）增强SCI后运动神经元的存活。我们的工作假设是，增加BDNF/TrkB.FL信号在膈运动神经元增强功能恢复的节律性膈活动后，颈脊髓。三种不同影响呼吸功能的颈部SCI的互补模型将与靶向胸膜内AAV介导的TrkB.FL向膈运动神经元的递送组合使用，局部移植成人来源的间充质干细胞，工程化释放BDNF和化学遗传学方法，使用TrkB敲入小鼠，允许快速和选择性抑制TrkB激酶活性的功能获得/丧失，功能研究设计 膈运动神经元兴奋性谷氨酸和5-羟色胺受体的表达与SCI后功能恢复的时间进程相关，因此我们假设BDNF/TrkB.FL作用于膈运动神经元，通过表达特定的谷氨酸和5-羟色胺受体亚型来增强节律性膈活动的恢复。本研究的目的有三：1）确定是否通过靶向增加BDNF/TrkB.FL信号传导到膈运动神经元来增强SH后节律性Phenic活动的功能恢复：2）确定多巴胺能和多巴胺能神经传递在BDNF/TrkB.FL介导的SH后节律性Phenic活动恢复中的作用;（3）探讨膈神经运动神经元BDNF/TrkB.FL信号通路增强对颈中部钝挫伤后运动神经元存活和功能恢复的作用。我们将评估一系列运动行为的膈神经反应，以最大限度地提高与恢复相关的功能增益。我们的长期目标是开发一种有效的靶向疗法，以增加膈运动神经元中的BDNF/TrkB.FL信号传导，以加强对膈运动神经元的备用突触输入并促进运动神经元的存活，从而增强SCI后的功能恢复。

DESCRIPTION (provided by applicant): The proposed studies exploit exciting new developments in neuroplasticity to enhance recovery of respiratory function following cervical spinal cord injury (SCI). There are about 12,000 new cases of SCI in the United States each year, with nearly 500,000 people affected. Most SCI's are incomplete with some sparing of spinal cord pathways. The number of injuries involving the cervical spinal cord is increasing, with resulting impairments of rhythmic phrenic nerve activity and paralysis of the diaphragm muscle. Inability to generate expulsive behaviors as well as long-term mechanical ventilation needed to support such SCI patients is associated with elevated infectious, morbidity and mortality rates. In recent studies supported by this grant, we found that the neurotrophin brain-derived neurotrophic factor (BDNF) acting through the full-length high affinity tropomyosin related kinase receptor subtype B (TrkB.FL) plays an important role in neuroplasticity and recovery of phrenic activity following SCI. This proposal will exploit a multi-pronged approach to gain mechanistic insight into the effects of BDNF/TrkB.FL signaling on: 1) strengthening of spared synaptic inputs to phrenic motoneurons, and 2) enhancing motoneuron survival post-SCI. Our working hypothesis is that increasing BDNF/TrkB.FL signaling in phrenic motoneurons enhances functional recovery of rhythmic phrenic activity after cervical SCI. Three complementary models of cervical SCI that differentially impact respiratory function will be used in combination with targeted intrapleural AAV-mediated delivery of TrkB.FL to phrenic motoneurons, localized transplantation of adult-derived mesenchymal stem cells engineered to release BDNF and a chemical-genetic approach using a TrkB knock-in mouse that permits rapid and selective inhibition of TrkB kinase activity in gain-of-function/loss-of-function study design. Phrenic motoneuron expression of excitatory glutamate and serotonin receptors correlates with the time course of functional recovery after SCI, and thus we hypothesize that BDNF/TrkB.FL acts on phrenic motoneurons to enhance recovery of rhythmic phrenic activity via expression of specific glutamate and serotonin receptor subtypes. Three specific aims are proposed: 1) To determine whether functional recovery of rhythmic phenic activity after SH is enhanced by targeting increased BDNF/TrkB.FL signaling to phrenic motoneurons; 2) To determine the role of glutamatergic and serotonergic neurotransmission in the BDNF/TrkB.FL mediated recovery of rhythmic phrenic activity after SH; and 3) To determine the role of enhanced phrenic motoneuron BDNF/TrkB.FL signaling on motoneuron survival and functional recovery following mid-cervical contusion injury. We will assess phrenic responses across a range of motor behaviors to maximize functional gains associated with recovery. Our long-term goal is to develop an effective, targeted therapy to increase BDNF/TrkB.FL signaling in phrenic motoneurons to strengthen spared synaptic inputs to phrenic motoneurons and promote motoneuron survival, thereby enhancing functional recovery following SCI.