Laboratory for Neuronal Growth Mechanisms, RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan; Division of Neuromedical Science, Institute of Natural Medicine, University of Toyama, Toyama, Toyama 930-0194, Japan.
Exp Neurol. 2013 Oct;248:157-69. doi: 10.1016/j.expneurol.2013.06.011. Epub 2013 Jun 21.
In the adult central nervous system, the tips of axons severed by injury are commonly transformed into dystrophic endballs and cease migration upon encountering a rising concentration gradient of inhibitory proteoglycans. However, intracellular signaling networks mediating endball migration failure remain largely unknown. Here we show that manipulation of protein kinase A (PKA) or its downstream adhesion component paxillin can reactivate the locomotive machinery of endballs in vitro and facilitate axon growth after injury in vivo. In dissociated cultures of adult rat dorsal root ganglion neurons, PKA is activated in endballs formed on gradients of the inhibitory proteoglycan aggrecan, and pharmacological inhibition of PKA promotes axon growth on aggrecan gradients most likely through phosphorylation of paxillin at serine 301. Remarkably, pre-formed endballs on aggrecan gradients resume forward migration in response to PKA inhibition. This resumption of endball migration is associated with increased turnover of adhesive point contacts dependent upon paxillin phosphorylation. Furthermore, expression of phosphomimetic paxillin overcomes aggrecan-mediated growth arrest of endballs, and facilitates axon growth after optic nerve crush in vivo. These results point to the importance of adhesion dynamics in restoring endball migration and suggest a potential therapeutic target for axon tract repair.
在成人中枢神经系统中，受伤切断的轴突末端通常会转化为退行性终球，并在遇到抑制性蛋白聚糖浓度梯度上升时停止迁移。然而，介导终球迁移失败的细胞内信号转导网络在很大程度上仍然未知。在这里，我们展示了蛋白激酶 A (PKA) 或其下游黏附成分桩蛋白的操纵可以在体外重新激活终球的运动机制，并促进体内损伤后的轴突生长。在成年大鼠背根神经节神经元的分离培养物中，PKA 在抑制性蛋白聚糖聚集素梯度上形成的终球中被激活，PKA 的药理学抑制通过桩蛋白丝氨酸 301 的磷酸化促进了在聚集素梯度上的轴突生长。值得注意的是，预先形成的在聚集素梯度上的终球对 PKA 抑制会恢复向前迁移。这种终球迁移的恢复与依赖于桩蛋白磷酸化的黏附点接触的周转率增加有关。此外，磷酸化模拟桩蛋白的表达克服了聚集素对终球生长的抑制作用，并促进了体内视神经挤压后的轴突生长。这些结果表明黏附动态在恢复终球迁移中的重要性，并为轴突束修复提供了一个潜在的治疗靶点。
