Franssen Elske H P, Zhao Rong-Rong, Koseki Hiroaki, Kanamarlapudi Venkateswarlu, Hoogenraad Casper C, Eva Richard, Fawcett James W
Cambridge Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge CB2 OPY, United Kingdom.
Institute of Life Science 1, College of Medicine, Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom; and.
J Neurosci. 2015 May 27;35(21):8359-75. doi: 10.1523/JNEUROSCI.2850-14.2015.
Integrins are adhesion and survival molecules involved in axon growth during CNS development, as well as axon regeneration after injury in the peripheral nervous system (PNS). Adult CNS axons do not regenerate after injury, partly due to a low intrinsic growth capacity. We have previously studied the role of integrins in axon growth in PNS axons; in the present study, we investigate whether integrin mechanisms involved in PNS regeneration may be altered or lacking from mature CNS axons by studying maturing CNS neurons in vitro. In rat cortical neurons, we find that integrins are present in axons during initial growth but later become restricted to the somato-dendritic domain. We investigated how this occurs and whether it can be altered to enhance axonal growth potential. We find a developmental change in integrin trafficking; transport becomes predominantly retrograde throughout axons, but not dendrites, as neurons mature. The directionality of transport is controlled through the activation state of ARF6, with developmental upregulation of the ARF6 GEF ARNO enhancing retrograde transport. Lowering ARF6 activity in mature neurons restores anterograde integrin flow, allows transport into axons, and increases axon growth. In addition, we found that the axon initial segment is partly responsible for exclusion of integrins and removal of this structure allows integrins into axons. Changing posttranslational modifications of tubulin with taxol also allows integrins into the proximal axon. The experiments suggest that the developmental loss of regenerative ability in CNS axons is due to exclusion of growth-related molecules due to changes in trafficking.
整合素是在中枢神经系统（CNS）发育过程中参与轴突生长以及在周围神经系统（PNS）损伤后参与轴突再生的黏附分子和存活分子。成体CNS轴突损伤后不能再生，部分原因是其内在生长能力较低。我们之前研究了整合素在PNS轴突生长中的作用；在本研究中，我们通过体外研究成熟中的CNS神经元，来探究参与PNS再生的整合素机制在成熟CNS轴突中是否可能发生改变或缺失。在大鼠皮质神经元中，我们发现整合素在初始生长阶段存在于轴突中，但随后局限于胞体-树突区域。我们研究了这种情况是如何发生的，以及是否可以改变它以增强轴突生长潜力。我们发现整合素运输存在发育变化；随着神经元成熟，运输在整个轴突中主要变为逆行运输，但在树突中并非如此。运输的方向性通过ARF6的激活状态来控制，ARF6鸟嘌呤核苷酸交换因子ARNO的发育上调增强了逆行运输。降低成熟神经元中的ARF6活性可恢复整合素的顺行流动，使其能够运输到轴突中，并增加轴突生长。此外，我们发现轴突起始段部分负责整合素的排除，去除该结构可使整合素进入轴突。用紫杉醇改变微管蛋白的翻译后修饰也可使整合素进入近端轴突。这些实验表明，CNS轴突再生能力的发育性丧失是由于运输变化导致与生长相关分子的排除。
