Intrinsic and extrinsic regulation of injury-induced axonal growth in the CNS: a combinatorial approach with known pathways and exploring the unknown role of microRNAs

轴突的生长和再生是脊髓损伤后功能恢复的关键。已经确定了几种调节成年哺乳动物中枢神经系统（CNS）轴突生长和再生的机制和分子途径。PTEN（磷酸酶和紧张素同源物）负向调节神经元的内在生长能力，而髓磷脂衍生的轴突生长抑制剂调节空闲轴突的发芽。此外，硫酸软骨素蛋白多糖（CSPGs）抑制脊髓损伤后轴突的生长。尽管我们对轴突生长调节的理解有所进步，但迄今为止还没有治愈或有效的治疗方法来促进轴突的生长和功能恢复。进一步了解现有分子靶点之间的相互作用和识别新的分子靶点将有助于开发有效的治疗策略。在第一个项目中，我将研究外源因子介导的抑制与中枢神经系统损伤后轴突生长的神经元内在调节之间的功能相互作用。我将把NgR1（或Rtn4r； reticulon 4受体）和NgR3（或Rtn4rl1； reticulon 4受体样1）（CSPGs和髓鞘衍生轴突生长抑制剂的受体）的基因缺失与条件PTEN缺失结合起来，以评估对中枢神经系统损伤小鼠模型中轴突发芽和再生的影响。在第二个项目中，我的目标是鉴定调节损伤诱导的轴突生长的microRNAs （miRNAs）。mirna是一种小的非编码rna，长度约为22个核苷酸，通过与靶基因mRNA的相互作用转录后调节蛋白质合成。我将从评估靶向PTEN和其他轴突生长的神经元表达调节因子的候选mirna开始。体外神经突生长和轴突再生实验以及随后的体内中枢神经系统损伤模型将用于研究操纵miRNA表达后轴突的生长情况。第一个项目将让我学习该领域，并在CNS损伤和修复领域的现有知识基础上做出贡献，第二个项目将让我探索mirna在轴突生长和脊髓修复中的未知作用。

Axon growth and regeneration are of key importance for functional recovery after spinal cord injury. Several mechanisms and molecular pathways that regulate axon growth and regeneration in the adult mammalian central nervous system (CNS) have been identified. PTEN (phosphatase and tensin homolog) negatively regulates the neuron-intrinsic growth capacity while the myelin derived axon growth inhibitors modulate the sprouting of spared axons. Furthermore, chondroitin sulfate proteoglycans (CSPGs) inhibit axon growth after spinal cord injury. Despite the advancement in our understanding of axon growth regulation, there is no cure or effective treatment to promote axon growth and functional recovery to date. Further understanding the interaction between the existing molecular targets and identifying novel molecular targets will allow for the development of effective therapeutic strategies. In the first project I will investigate the functional interplay between extrinsic factor-mediated inhibition and neuron-intrinsic regulation of axon growth after CNS injury. I will combine gene deletion of NgR1 (or Rtn4r; reticulon 4 receptor) and NgR3 (or Rtn4rl1; reticulon 4 receptor-like 1) (receptors for CSPGs and myelin derived axon growth inhibitors) with conditional PTEN deletion in order to assess the consequence on axon sprouting and regeneration in mouse models of CNS injuries. In a second project I aim to identify microRNAs (miRNAs) that regulate injury-induced axonal growth. MiRNAs are small non-coding RNAs of about 22 nucleotides length which post-transcriptionally regulate protein synthesis via interaction with target gene mRNA. I will start by assessing candidate miRNAs that target PTEN and other neuronally expressed regulators of axon growth. In vitro neurite outgrowth and axon regeneration assays and subsequently in vivo CNS injury models will be applied to investigate axon growth after manipulation of miRNA expression. While the first project will allow me to learn the field and contribute to building on existing knowledge in the field of CNS injury and repair, the second project will allow me to explore the unknown role of miRNAs in axon growth and spinal cord repair.