The role of mitochondrial fission/fusion in CNS axon regeneration

描述（由申请人提供）：线粒体分裂/融合在CNS轴突再生中的作用中枢神经系统（CNS）疾病或损伤通常伴有进行性轴突变性，导致感觉、运动或认知能力丧失，几乎没有或没有再生反应。在寻找恢复退化的CNS轴突的信号传导因子中，我们鉴定了一组发育调节的转录因子，Kruppel样转录因子（KLF），其差异抑制或增强海马、皮质脊髓神经元和视网膜神经节细胞（RGC）轴突生长。然而，KLF调控轴突生长的下游机制尚不清楚。有证据表明，一个下游效应可能是线粒体（Mt）的裂变/融合动力学。我们最近发现，抑制分裂（增加融合）导致硫酸软骨素蛋白聚糖对轴突生长抑制作用的丧失， 支持CNS轴突生长和引导受Mt裂变-融合动力学调节的假设。这些数据还表明抑制Mt分裂是改善CNS创伤或疾病后轴突再生的潜在治疗策略。为了确定是否Mt分裂/融合机制也是KLF的轴突抑制/增强活性的基础，我们正在研究KLF临界调节Mt基因用于轴突生长的潜在能力。与我们先前的发现相关，我们发现轴突生长抑制KLF 9增加并且生长促进KLF 7减少线粒体分裂过程1.18 kDa（MTP 18）的基因表达，线粒体分裂过程1.18 kDa（MTP 18）是Mt分裂的正调节剂，支持增加的分裂抑制CNS神经元中轴突生长的假设。此外，我们最近分析家族性轴突病外显子组测序的数据也指出了与许多线粒体蛋白（包括MTP 18）作用于裂变/融合动力学的疾病相关性。因此，我们假设KLF 7/9介导的线粒体分裂增强子MTP 18的调节调节中枢神经系统神经元的内在轴突生长能力。为了解决这一假设，我们将在体外和体内表达/敲低MTP 18与KLF 7/9表达/敲低结合或独立于KLF 7/9表达/敲低，鉴定MTP 18在调节Mt分裂/融合动力学、CNS轴突生长和指导以及KLF 7/9介导的轴突再生中的神经元作用。总体目标是提高我们对Mt裂变/融合如何调节轴突再生的理解，并确定CNS损伤或疾病后恢复轴突生长的策略。

DESCRIPTION (provided by applicant): The role of mitochondrial fission/fusion in CNS axon regeneration Central nervous system (CNS) disease or injury is often accompanied by progressive axon degeneration, leading to lost sensory, motor, or cognitive abilities, with little o no regenerative response. In search of signaling factors to restore degenerated CNS axons, we identified a group of developmentally regulated transcription factors, the Kruppel-like transcription factors (KLFs), which differentially suppress or enhance hippocampal, corticospinal neuron, and retinal ganglion cell (RGC) axon growth. However, the downstream mechanisms by which KLFs regulate axon growth are unknown. Evidence suggests one downstream effector may be mitochondrial (Mt) fission/fusion dynamics. We recently showed that suppressing fission (increasing fusion) leads to a loss in axon growth inhibition by chondroitin sulfate proteoglycans, supporting a hypothesis in which CNS axon growth and guidance is regulated by Mt fission-fusion dynamics. These data also suggest suppressing Mt fission is a potential therapeutic strategy for improving axon regeneration after CNS trauma or disease. To identify whether Mt fission/fusion mechanisms also underlie the axon suppressing/enhancing activity of KLFs, we are investigating the potential ability for KLFs to critically regulate Mt genes for axon growth. Pertinent to our previous findings, we found that axon growth-suppressing KLF9 increased and growth- promoting KLF7 decreased the genetic expression of mitochondrial fission process 1,18 kDa (MTP18), a positive regulator of Mt fission, supporting the hypothesis that increased fission is inhibitory for axon growth in CNS neurons. Furthermore, our recent data analyzing exome sequencing of familial axonopathies also pointed to a disease association with a number of mitochondrial proteins thought to act on fission/fusion dynamics, including MTP18. Therefore, we hypothesize that KLF7/9-mediated regulation of the mitochondrial fission enhancer MTP18 regulates intrinsic axon growth ability in CNS neurons. To address this hypothesis, we will express/knockdown MTP18 in combination with or independent of KLF7/9 expression/knockdown in RGCs both in vitro and in vivo, identifying the neuronal role of MTP18 in regulating Mt fission/fusion dynamics, CNS axon growth and guidance, and KLF7/9-mediated axon regeneration. The overall goal is to improve our understanding of how Mt fission/fusion regulates axon regeneration and identify strategies for restoring axon growth after CNS injury or disease.