凋亡神经元通过激活前体细胞中Wnt/beta-catenin信号诱导成年皮层局部神经元发生的研究

Adult cortex is normally regarded as a non-neurogenic region, which accounts for the hard-to-be-self-repaired brain disfunction in diseases such as ischemia. Activation of endogenous neural stem cells maybe crucial for triggering the endogenous regenerative programm. However, the underlying mechanisms are poorly understood. In the regeneration model animals, apoptotic cells stimulate the proliferation of resident stem/progenitor cells, thereby initiating regeneration. We have demonstrated that in the periphery nerve system, olfactory epithelial demage could activate the Wnt/beta-catenin signaling in the olfactory neural stem cells and mediate the corresponding neuronal regeneration (J Cell Sci. 2011 May 1; 124(Pt 9):1553-63). In the central nerve system, we further found that neuronal apoptosis could induce local neurogenesis in the cortex, and activate the Wnt signaling in the local progenitors. Based on these results, we hypothesize that apoptotic neurons might stimulate neurogenesis by activating the Wnt signaling in the local neural stem/progenitor cells.. To test our hypothesis, we propose here to investigate the following issues in detail using both in vitro and in vivo neuronal apoptosis and apoptosis defective models based on a Wnt signaling reporter transgenic mouse line TOPgal mice and Caspase 3 knockout mice: (1), the neuronal apoptosis induced cortical neurognesis; (2), the neuronal apoptosis induced Wnt activation; (3) the relationship between the apoptotic neuron induced neurogenesis and Wnt signaling; (4) and the possible mechanisms of the apoptotic neuron induced Wnt activation.. The carry-out of the proposed study will be helpful to understand the mechanisms of adult neural stem cell activation, and may provide insights for developing novel therapies for brain disorders such as ischemia.

成年大脑皮层缺乏神经元发生，是脑缺血等疾病导致功能丧失难以自发恢复的重要原因。内源性神经干细胞活化可能是激发中枢神经内源再生程序的关键，但至今机制不清。在再生模式动物，凋亡细胞可刺激干（前体）细胞的增殖而触发再生。在高等动物，目前仅有极少报道。我们发现：在外周，嗅神经损伤可激活嗅神经干细胞中的Wnt信号及相应嗅神经元再生（已发表）。在中枢，我们进一步发现，神经元凋亡可诱导皮层局部神经元发生，并激活局部神经前体细胞中的Wnt信号。因此，我们推测：凋亡神经元可能通过激活皮层局部神经前体细胞中的经典Wnt信号通路而诱导神经元发生。本项目拟采用Wnt信号报告基因TOPgal小鼠和Caspase3基因敲除小鼠，在体外、体内特异性神经元凋亡模型中，研究神经元凋亡诱导的皮层神经元发生与Wnt信号激活的关系，揭示凋亡神经元激活Wnt信号的机制，以期为理解神经干细胞活化的机制及脑缺血的治疗研究提供新思路

脑卒中是我国第一位的致死性疾病，其中80%以上为脑缺血。传统认为成年大脑皮层缺乏神经元发生，是脑缺血后难以自发修复的重要原因之一。近年研究发现脑缺血后皮质有少量来自侧脑室下区的神经干细胞的新生神经元。皮质原位可否有神经元发生一直存在争议。本课题围绕缺血后皮质原位的神经元发生，及其相关机制进行研究。. 利用光化学皮质缺血模型，我们发现，皮质缺血后有短暂的神经元发生。通过基于Cre和病毒的遗传学细胞命运追踪，我们确定了新生神经元主要来自皮质局部的Sox2阳性星形胶质细胞，少量来自侧脑室下区。进一步，我们发现缺血后凋亡神经元上调Wnt2，激活周围星形胶质细胞中的Wnt/beta-catenin信号。抑制Wnt2 /beta-catenin信号可显著减轻缺血诱导的神经元发生。在Caspase-3敲除小鼠，皮质缺血后，虽然神经元凋亡减轻，但Wnt2不能上调，神经元发生显著减少。在Caspase-3敲除小鼠的皮质过表达beta-catenin，可以挽救神经元发生。. 本课题的研究发现了皮质缺血后原位的神经元发生，并阐明了相关机制。论文投至国际知名期刊Nature Communications和EMBO J都在修回后被拒稿。经完善实验后，最近论文在Cell Research修回（附revision letter截图）。. 利用本项目的资助，我们还研究了脊髓损伤后星形胶质细胞和小胶质细胞死亡的机制，论文分别发表在Molecular Neurodegeneration（2016 Feb 3;11:14. doi: 10.1186/s13024-016-0081-8. IF: 6.55）和 Neuroscience（2015 Dec 17;311:362-73. IF：3.23)。发现Wnt信号活化的星形胶质细胞参与缺血后癫痫的发生，论文发表在Glia。（2016 Jun;64(6):1083-91. IF:5.99）。