Recovery of Respiratory Function After Spinal Cord Injury

描述（由申请人提供）：拟进行的研究利用神经可塑性方面令人兴奋的新进展来促进颈脊髓损伤（SCI）后呼吸功能的恢复。美国每年大约有1.2万例脊髓损伤新病例，近50万人受到影响。大多数脊髓损伤是不完整的，有一些脊髓通路的保留。涉及颈脊髓的损伤数量正在增加，导致膈神经节律性活动受损和膈肌麻痹。不能产生排斥性行为以及支持这类脊髓损伤患者所需的长期机械通气与传染性、发病率和死亡率升高有关。在该基金支持的近期研究中，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 （TrkB.FL）发挥作用，在脊髓损伤后的神经可塑性和膈活动恢复中发挥重要作用。该提案将利用多管齐下的方法来深入了解BDNF/TrkB的作用机制。FL信号的作用：1)加强膈神经运动神经元的空闲突触输入，2)增强脊髓损伤后运动神经元的存活。我们的工作假设是增加BDNF/TrkB。膈运动神经元中的FL信号增强了脊髓损伤后膈节律性活动的功能恢复。三种不同程度影响呼吸功能的颈椎脊髓损伤互补模型将与靶向胸膜内aav介导的TrkB递送联合使用。在功能获得/功能丧失的研究设计中，利用TrkB敲入小鼠进行TrkB激酶活性的快速和选择性抑制的化学遗传学方法，将FL转移到膈运动神经元，改造成源间充质干细胞的局部移植以释放BDNF。

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.