The role of mitochondrial fission/fusion in CNS axon regeneration

描述(申请人提供)：线粒体分裂/融合在中枢神经系统(CNS)轴突再生中的作用中枢神经系统(CNS)疾病或损伤通常伴随着进行性轴突变性，导致感觉、运动或认知能力丧失，几乎没有再生反应。为了寻找修复退化的中枢神经系统轴突的信号因子，我们发现了一组发育调节的转录因子，Kruppel样转录因子(KLFs)，它们分别抑制或促进海马、皮质脊髓神经元和视网膜神经节细胞(RGC)的轴突生长。然而，KLFS调节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)裂变/融合动力学。我们最近发现，抑制分裂(增加融合)会导致硫酸软骨素蛋白多糖对轴突生长的抑制作用减弱， 支持中枢神经系统轴突生长和引导受mt裂变-聚变动力学调控的假说。这些数据还表明，抑制线粒体分裂是改善中枢神经系统创伤或疾病后轴突再生的潜在治疗策略。为了确定线粒体分裂/融合机制是否也是轴突抑制/增强轴突活性的基础，我们正在研究KLFS对轴突生长的关键调控mt基因的潜在能力。与我们以前的研究结果相一致，我们发现抑制轴突生长的KLF9增加，而促进生长的KLF7减少线粒体分裂过程1，18 kDa(MTP18)的基因表达，MTP18是线粒体分裂的正向调节因子，支持了增加分裂对中枢神经系统神经元轴突生长的抑制的假说。此外，我们最近的数据分析了家族性轴索病变的外显子组序列，也指出了疾病与一些被认为作用于分裂/融合动力学的线粒体蛋白有关，包括MTP18。因此，我们假设KLF7/9介导的线粒体分裂增强子MTP18调节中枢神经系统神经元的内在轴突生长能力。为了解决这一假说，我们将在体外和体内的视网膜节细胞中表达/敲除MTP18，并联合或独立于KLF7/9的表达/击倒，以确定MTP18在调节MT分裂/融合动力学、CNS轴突生长和引导以及KLF7/9介导的轴突再生中的神经元作用。总体目标是提高我们对线粒体分裂/融合如何调节轴突再生的理解，并确定在中枢神经系统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.