Investigating coupling of metabolism with gene transcription to support the axonal regeneration programme for repair

脊髓损伤（SCI）是导致美国35万人和英国6万人永久严重残疾的原因。虽然神经康复方法取得了重要进展，但没有治疗方法可以显著改善许多神经功能障碍，包括感觉，运动，心血管，泌尿和性功能障碍。SCI后，由于中枢神经系统（CNS）轴突无法再生和重建丢失的回路，功能恢复失败。相反，外周神经系统（PNS）轴突能够部分再生并重新支配其靶，例如在坐骨神经受压后。直接比较支撑这种相反能力的机制可以识别SCI后再生的新靶点。我实验室最近的研究比较了这种相反的再生能力，发现了一种叫做戊糖磷酸途径（PPP）的代谢途径，它可以促进SCI后的再生和修复。PPP使用糖（葡萄糖）来产生NADPH，这对于减少核苷生物合成所需的自由基和核糖-5-磷酸（R5 P）很重要。这种途径不使用ATP形式的能量来产生其产物，因此非常适合损伤后的状态，其中受损的神经元对能量需求低的新代谢物有极端的需求。然而，关于PPP在损伤后轴突再生和可塑性中的作用还不清楚。我实验室的初步实验表明，虽然NADPH的PPP生产不影响再生生长，但DRG神经突生长需要PPP依赖的R5 P和下游核糖核苷生产。重要的是，我的实验室发现，过表达PPP酶转酮醇酶强烈增加了培养的DRG神经元中的轴突生长，并促进体内脊髓损伤后的轴突再生。总之，这使我们假设，通过增加核苷酸的可用性，提高PPP可以促进SCI后的轴突再生和修复，这些核苷酸是转录再生反应所需的元素。这项提议旨在为SCI后PPP的再生潜力提供证据，并揭示支持这种能力的分子机制。最后，它将利用PPP依赖的再生反应提出SCI后的治疗，以促进运动和感觉恢复，在临床上合适的具有翻译潜力的核苷的递送方式。具体目标将研究：（1）转酮醇酶过表达促进SCI后再生和突触可塑性的能力;（2）连接PPP激活与再生基因表达转录的分子机制;（3）在脊髓损伤小鼠模型中，体内核糖核苷递送作为增加SCI后可塑性、再生和恢复的治疗。该研究项目将通过研究PPP依赖的修复机制提供轴突再生能力的代谢控制的另一种观点，从而为损伤的再生反应提供全新的见解，这也将提供新的翻译机会。

Spinal cord injury (SCI) is a cause of permanent severe disability in 350,000 people in the US and 60,000 in the UK alone. While neurorehabilitation approaches have made important advances, no treatment is available to significantly improve the many neurological impairments spanning from sensory, motor, cardiovascular, urinary and sexual dysfunction. Following SCI, functional recovery fails due to the inability of central nervous system (CNS) axons to regenerate and re-establish lost circuits. Conversely, peripheral nervous system (PNS) axons are able to partially regenerate and reinnervate their targets such as after a compression of the sciatic nerve for example. A direct comparison of the mechanisms underpinning this opposite ability can lead to identify new targets for regeneration after SCI. Recent studies in my laboratory comparing this opposite regenerative ability led to the discovery of a metabolic pathway called Pentose Phosphate Pathway (PPP) that promotes regeneration and repair after SCI. The PPP uses sugar (glucose) to produce NADPH that is important to reduce free radicals and ribose-5-phosphate (R5P), needed for nucleoside biosynthesis. This pathway does not use energy in the form of ATP to generate its products and it is therefore ideally suited in a post-injury state where damaged neurons have an extreme need for new metabolites with a low energy demand. However, nothing is known about the role of the PPP in axonal regeneration and plasticity after injury. Initial experiments in my lab showed that while PPP production of NADPH does not affect regenerative growth, PPP-dependent R5P and downstream ribonucleoside production are needed for DRG neurite outgrowth. Importantly, my lab found that overexpressing the PPP enzyme transketolase strongly increases neurite outgrowth in cultured DRG neurons and it promotes axonal regeneration after a spinal cord injury in vivo. Altogether, this led us to hypothesise that boosting the PPP could promote axonal regeneration and repair after SCI by increasing the availability of nucleotides that are the elements needed for a transcriptional regenerative response. This proposal aims to provide evidence for the regenerative potential of the PPP after SCI and to unravel the molecular mechanisms underpinning this ability. Lastly, it will leverage upon the PPP-dependent regenerative response to propose treatment after SCI in order to promote locomotor and sensory recovery in a clinically suitable delivery modality of nucleosides with translational potential. The specific aims will investigate: (1) the ability of transketolase overexpression to promote regeneration and synaptic plasticity after SCI; (2) the molecular mechanisms linking PPP activation with transcription for regenerative gene expression; (3) in vivo ribonucleosides delivery as a treatment to increase plasticity, regeneration and recovery post-SCI in mouse models of spinal cord injuries. This research project will shed a completely new light on the regenerative response to injury by providing an alternative view of the metabolic control of the axonal regenerative ability by investigating PPP-dependent repair mechanisms that will also offer novel translational opportunities.