脊髓 V2a中间神经元在脊髓损伤修复运动神经环路重建中的作用

Spinal cord injury (SCI) is one of the most disabling conditions with high incidence and prevalence rates all around the world. In mammals, SCI results in permanent neurological damage below the level of lesion due to poor neuronal regenerative ability. The mechanisms behind post SCI repairation are mostly unknown, which lead to poor treatments after injury. SCI not only affect patients’ neurological and psychological functions but also bring heavy economic burdens to the family and society..Unlike mammals, adult zebrafish has a remarkable capacity to recover swimming around 4 weeks after SCI. Study the mechanisms underlying the zebrafish reestablishment of swimming ability after SCI is useful for us to compare and understand the poor recovery function in mammals. In this project, we have two main aims, first, we will focus on the role of excitatory interneurons V2a under reconstruction mechanisms of spinal locomotor circuit after SCI. Excitatory interneurons V2a are vital parts of spinal central pattern generator and are responsible for generating the locomotor rhythm. Our preliminary results showed that retrograded a single excitatory interneuron V2a 2 weeks after injury, the V2a interneuron axons were already regenerated through the lesion site and distributed in the caudle part of the spinal cord. Study the regenerative V2a axons distribution, reconnection of synapses and rewire mechanisms of spinal locomotor circuit in the adult zebrafish SCI modal are the key points to understand the recovery of swimming ability post injury. Second, we will focus on molecular single neuronal level. Based on the morphological and electrophysiological features of excitatory interneuron V2a during repair process, we will try to sub-class the V2a interneurons. Meanwhile, we will analyze the genetic characterizations of different V2a interneurons during recovery process, which may provide us useful information finding new targets to relief the SCI disabling conditions.

脊髓损伤作为全球高致残率疾患，好发于青壮年人群，目前尚缺乏有效治疗。与成年鼠等哺乳动物脊髓再生修复能力低相比，成年斑马鱼脊髓再生能力强，损伤后4-6周便可以恢复运动功能，是研究脊髓损伤后修复的好模型。研究表明兴奋性V2a中间神经元是脊髓CPG的关键部件，为脊髓运动提供节律性和驱动力。我们发现V2a神经元的轴突在成年斑马鱼脊髓损伤2周便由损伤头端再生至损伤部位并穿过愈合组织投射至尾端脊髓。斑马鱼V2a神经元轴突的再生与损伤2周左右开始的运动有强关联性，可能参与了损伤后神经环路的重建。该申请的目标是解析V2a神经元在脊髓损伤修复中的作用，探讨其轴突再生和参与环路重建的机制。通过形态学和电生理等方法细致地研究不同V2a神经元亚型在环路重建和损伤修复过程中的作用；并通过patch-seq和Crispr-Cas9等方法探索调控V2a神经元轴突再生和环路重建的分子机制。为脊髓损伤的治疗提供新思路。

脊髓损伤后针对脊髓内部神经环路的修复机制目前鲜有研究，成年斑马鱼脊髓再生能力强，损伤后4-6周便可以恢复运动功能，是研究脊髓损伤后环路重建机制的好模型。研究表明兴奋性V2a中间神经元作为脊髓CPG的关键部件，为脊髓运动提供节律性和驱动力。我们发现V2a中间神经元的轴突在成年斑马鱼脊髓损伤2周便由损伤头端再生至损伤部位并穿过愈合组织投射至尾端脊髓，这一群神经元的轴突再生与运动能力的恢复呈正相关。进一步研究发现V2a中间神经元的再生修复遵循一定的规律，该规律与脊髓神经环路发育过程具有相似性。首先完成轴突再生的为驱动快速运动神经元的快速V2a中间神经元，但是在损伤早期，快速V2a中间神经元不但驱动快速运动神经元还与慢速运动神经元形成联接，脊髓内无明显的快速和慢速运动模块之分；随着愈合过程的进展，慢速V2a中间神经元的轴突开始逐步再生，与慢速运动神经元建立联接，此时生理状态下的脊髓内模块化运动控制系统才逐步恢复。这一过程受到很多重要的基因调控，其中与快速肌肉，快速运动神经元等快速模块成分相关的Calb2b基因参与了快速V2a中间神经元轴突的再生过程。对其进行干预，敲除该基因，可以导致脊髓运动环路重建的受损。而通过运动训练是可以促进这一模块化运动控制的精准神经环路的修复。这一结果为我们更好的了解脊髓损伤后环路水平的病理生理变化提供了重要的知识。同时为再生能力差的哺乳动物和人脊髓损伤修复提供新的治疗思路。