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功能障碍，这在很大程度上取决于受损的脊髓轴突不能发芽和再生，并重新建立适当的突触接触1 -3。受损轴突的再生能力有限或缺失主要是由于其生长锥的崩溃。cGMP依赖性蛋白激酶I型（cGKI）具有多种功能，包括在轴突生长和感觉神经元的寻路中的作用，并抵消由脑信号蛋白3A（Sema 3A）诱导的生长锥塌陷，这也限制了脊髓损伤后的再生4。我们最近已经表明，神经元cGKI的表达是直接调节的转录因子p53，这是所需的生理轴突regeneration 5，6。然而，cGMP-GKI通路在p53依赖性和非依赖性轴突生长和脊髓损伤后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是必需的，并且cGMP-GKI功能实验的获得将导致脊髓损伤后轴突发芽和再生增强，包括在缺乏神经元p53的小鼠中。我们将在小鼠中采用T8的脊髓背侧过度半切来具体研究（1）巢蛋白阳性神经元中缺乏cGKI的小鼠中的轴突再生和发芽以及功能恢复（2）增强的cGMP-cGKI信号传导的能力（通过药理学手段和病毒cGKI递送）来促进野生型以及p53 loxP/nestin cre小鼠中的轴突发芽和再生。本研究可以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，并且可以阐明cGMP-cGKI以及p53依赖性促再生途径。

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.