Recovery of Respiratory Function After Spinal Cord Injury

描述(由申请人提供)：建议的研究利用神经可塑性方面令人兴奋的新发展，以促进颈髓损伤(SCI)后呼吸功能的恢复。美国每年约有12000例新的脊髓损伤病例，有近50万人受到影响。大多数脊髓损伤是不完整的，脊髓通路有一些保留。涉及颈髓的损伤数量正在增加，导致节律性膈神经活动受损和横隔肌瘫痪。不能产生排泄行为以及支持这类SCI患者所需的长期机械通气与感染、发病率和死亡率的升高有关。在最近的研究中，我们发现神经营养因子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受体B亚型(TrkB.FL)作用于脊髓损伤后的神经可塑性和膈神经活动的恢复。这一建议将利用多管齐下的方法来获得对BDNF/TrkB.FL信号在以下方面的作用的机械性洞察：1)加强对膈运动神经元的备用突触输入，2)提高脊髓损伤后运动神经元的存活。我们的工作假说是，在颈脊髓损伤后，增加膈运动神经元中的BDNF/TrkB.FL信号可促进节律性膈活动的功能恢复。三种对呼吸功能有不同影响的颈部脊髓损伤模型将被使用，结合靶向胸膜内AAV介导的TrkB.FL向膈运动神经元输送TrkB.FL、对成人来源的间充质干细胞进行局部移植以释放BDNF以及在功能获得/功能丧失研究设计中使用TrkB敲入鼠的化学遗传学方法允许快速和选择性地抑制TrkB激酶活性。 兴奋性谷氨酸和5-羟色胺受体的膈运动神经元的表达与脊髓损伤后功能恢复的时间进程有关，因此我们推测BDNF/TrkB.FL通过表达特定的谷氨酸和5-羟色胺受体亚型作用于膈运动神经元，促进节律性膈活动的恢复。我们提出了三个具体的目标：1)确定是否通过靶向增加的BDNF/TrkB.FL信号传导到膈运动神经元来促进SH后节律性神经活动的功能恢复；2)确定谷氨酸能和5-羟色胺能神经传递在BDNF/TrkB.FL介导的SH后节律性膈神经活动恢复中的作用；以及3)确定增强的膈运动神经元BDNF/TrkB.FL信号在颈中挫伤后运动神经元存活和功能恢复中的作用。我们将评估一系列运动行为的隔膜反应，以最大限度地增加与康复相关的功能收益。我们的长期目标是开发一种有效的、有针对性的治疗方法来增加膈运动神经元中的BDNF/TrkB.FL信号，以加强对膈运动神经元的备用突触输入，促进运动神经元的存活，从而促进脊髓损伤后的功能恢复。

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.