Role of Stress Granule Protein Aggregation in Axon Regeneration

周围神经自发再生，但轴突生长速度非常慢， 在人类中很少实现靶的完全功能性神经再支配。轴突再生 中枢神经系统甚至更糟，例如患有脊髓损伤（SCI）的个体 几乎总是在病变水平以下永久丧失感觉和运动功能。 迫切需要加速周围神经系统中的轴突再生， 增加中枢神经系统的轴突再生。我们的研究项目集中在轴突 再生的内在机制。轴突内合成的蛋白质支持轴突生长， 发育中的神经元我们已经证明，PNS神经元保留了合成蛋白质的能力， 它们的轴突和这些蛋白质支持受损轴突的生长。培养神经元的轴突含有 数以千计的mRNAs -和一些证据表明，复杂的群体的mRNAs在中枢神经系统 体内轴突和脊髓轴突在受到刺激时含有mRNA和翻译机制 用允许的底物再生。尽管 自2000年初以来取得了显着进展，决定何时何地的分子机制 在轴突中翻译的特定mRNA在很大程度上仍是未知的。这种监管水平是 对调节轴突生长能力至关重要。我们已经证明，mRNA储存在PNS轴突中， 含有应激颗粒蛋白G3 BP 1的RNA-蛋白质聚集体。G3 BP 1蛋白可以驱动 应激颗粒聚集和G3 BP 1磷酸化阻断应激颗粒组装。不像 经典定义的应激颗粒，轴突G3 PB 1蛋白在未损伤/功能性 PNS轴突。这些轴突G3 BP 1聚集体在轴突切断后迅速增加，但减少到低于 此后不久，在磷酸化的G3 BP 1中相应增加基础水平。G3 BP 1结合 轴突中的mRNA并减弱它们的翻译。我们已经发现了外源因子， 内源性信号触发轴突G3 BP 1聚集体的分解。述外源剂 特异性增加轴突蛋白质合成并加速轴突生长速率 vivo.这些观察使我们假设压力的生理聚集 轴突中的颗粒蛋白通过阻断翻译而减弱损伤的PNS和CNS中的轴突生长 一个轴突mRNA组群。我们将通过以下具体目标来检验这一假设： 目的1 -通过抑制G3 BP 1功能促进轴突生长。 目的2 -轴突G3 BP 1聚集体分解的内源性机制。 目的3 -轴突G3 BP 1聚集体分解后驱动轴突生长的机制。 轴突翻译的功能性作用现在已经显现出来，我们有坚实的体内证据 这一机制可以靶向加速急性周围神经损伤后轴突的生长。 完成拟议的研究将带来新的洞察机制的时间调节 轴突mRNA翻译在轴突损伤和再生中的作用，并发现新的治疗策略， 神经修复

Peripheral nerves spontaneously regenerate but the axon growth rate is abysmally slow, such that complete functional reinnervation of targets is rarely achieved in humans. Axon regeneration in the central nervous system is even worse, such that individuals with spinal cord injury (SCI) almost invariably have permanent lose of sensory and motor functions below the level of the lesion. There is a pressing need to accelerate axon regeneration in the peripheral nervous system and increase axon regeneration in the central nervous system. Our research program focuses on axon intrinsic mechanisms of regeneration. Intra-axonally synthesized proteins support axon growth in developing neurons. We have shown that PNS neurons retain the capacity to synthesize proteins in their axons and these proteins support growth of injured axons. Axons of cultured neurons contain thousands of mRNAs – and several lines of evidence point to complex populations of mRNAs in CNS axons in vivo and spinal cord axons contain mRNAs and translational machinery when encouraged to regenerate with permissive substrates. Despite remarkable advances since the early 2000’s, the molecular mechanisms that determine when and where a specific mRNA is translated in axons remain largely unknown. This level of regulation is critical for regulating axon growth capacity. We have shown that mRNAs are stored in PNS axons in RNA-protein aggregates that contain the stress granule protein G3BP1. G3BP1 protein can drive stress granule aggregation, and G3BP1 phosphorylation blocks stress granule assembly. Unlike the classically defined stress granule, axonal G3PB1 protein shows aggregation in uninjured/functioning PNS axons. These axonal G3BP1 aggregates rapidly increase after axotomy, but decrease to below basal levels shortly thereafter with a corresponding increase in phosphorylated G3BP1. G3BP1 binds to mRNAs in axons and attenuates their translation. We have discovered exogenous agents and endogenous signals that trigger disassembly of axonal G3BP1 aggregates. The exogenous agents specifically increase axonal protein synthesis and accelerate axon growth rates in vitro and in vivo. These observations have led us to hypothesize that physiological aggregation of stress granule proteins in axons attenuates axon growth in the injured PNS and CNS by blocking translation of an axonal mRNA cohort. We will test this hypothesis with the following specific aims: Aim 1 – Promotion of axon growth by inhibition of G3BP1 function. Aim 2 – Endogenous mechanisms for axonal G3BP1 aggregate disassembly. Aim 3 – Mechanisms driving axon growth upon disassembly of axonal G3BP1 aggregates. Functional roles for axonal translation have now come to light and we have solid in vivo evidence that this mechanism can be targeted to accelerate axon growth after acute peripheral nerve injury. Completion of the proposed research will bring new insight into mechanisms for temporal regulation of axonal mRNA translation in axon injury & regeneration and uncover new therapeutic strategies for neural repair.