The role of cGMP-GKI signalling in spinal cord axonal sprouting and regeneration following injury

脊髓损伤导致长期的神经损伤，这在很大程度上取决于受损的脊髓轴突不能发芽和再生，也不能重建适当的突触联系。损伤轴突的再生能力有限或缺失主要是由于其生长锥的塌陷。cmpp依赖性蛋白激酶I型（cGKI）具有多种功能，包括在感觉神经元的轴突生长和寻路中发挥作用，并抵消信号蛋白3A （Sema3A）诱导的生长锥塌陷，这也限制了脊髓损伤后的再生4。我们最近发现神经元的cGKI表达受转录因子p53的直接调控，这是生理轴突再生所必需的5,6。然而，cGMP-GKI通路在脊髓损伤后依赖p53和独立轴突生长和再生中的作用仍然难以捉摸。我们假设cGMP-GKI级联对于生理轴突发芽和轴突再生至关重要，cGMP-GKI功能实验的获得将导致脊髓损伤后轴突发芽和再生的增强，包括在缺乏神经元p53的小鼠中。我们将在T8时对小鼠进行脊髓背部半切，专门研究(1)在巢素阳性神经元（cGKI巢素-/-）缺乏cGKI的小鼠中轴突再生和发芽以及功能恢复；(2)在野生型和p53 loxP/巢素cre小鼠中，cGMP-cGKI信号增强（通过药理手段和病毒传递cGKI）促进轴突发芽和再生的能力。最终，该研究可能提供新的分子和药理学工具来增强脊髓损伤后的轴突再生，并可能阐明cGMP-cGKI以及p53依赖性的促再生途径。

Spinal cord injury leads to long term neurological impairment that largely depends upon the incapacity of lesioned spinal axons to sprout and regenerate and to re-establish appropriate synaptic contacts1-3. The limited or absent regenerative ability of injured axons is primarily due to the collapse of their growth cones. The cGMP-dependent protein kinase type I (cGKI) has multiple functions including a role in axonal growth and pathfinding of sensory neurons, and counteracts growth cone collapse induced by Semaphorin 3A (Sema3A), which also limits regeneration following spinal injuries4. We have recently shown that neuronal cGKI expression is directly regulated by the transcription factor p53, which is required for physiological axonal regeneration5,6. However, a role for cGMP-GKI pathways in p53 dependent and independent axonal outgrowth and regeneration following spinal injuries remains elusive. We hypothesize that cGMP-GKI cascade is essential for physiological axonal sprouting and for axonal regeneration and that cGMP-GKI gain of function experiments would lead to enhanced axonal sprouting and regeneration following spinal injury, including in mice lacking neuronal p53. We will employ a spinal dorsal overhemisection at T8 in mice to specifically investigate (1) axonal regeneration and sprouting as well as functional recovery in mice lacking cGKI in nestin positive neurons (cGKI nestin -/-) and (2) the capacity of enhanced cGMP-cGKI signaling (via pharmacological means and viral cGKI delivery) to promote axonal sprouting and regeneration in wild type as well as in p53 loxP/nestin cre mice.Ultimately, this study may provide novel molecular and pharmacological tools to enhance axonal regeneration following spinal lesions and may clarify the cGMP-cGKI as well as the p53-dependent pro-regeneration pathways.