Jamsuwan Sataporn, Klimaschewski Lars, Hausott Barbara
Institute of Neuroanatomy, Medical University of Innsbruck, Innsbruck, Austria.
Front Cell Neurosci. 2020 Jan 21;13:583. doi: 10.3389/fncel.2019.00583. eCollection 2019.
Sprouty2 (Spry2) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) are both well-established regulators of receptor tyrosine kinase (RTK) signaling, and knockdown of Spry2 or PTEN enhances axon regeneration of dorsal root ganglia (DRG) neurons. The major role of Spry2 is the inhibition of the rat sarcoma RAS/extracellular signal-regulated kinase (ERK) pathway, whereas PTEN acts mainly as an inhibitor of the phosphoinositide 3-kinase (PI3K)/Akt pathway. In non-neuronal cells, Spry2 increases the expression and activity of PTEN, and PTEN enhances the amount of Spry2 by the inhibition of the microRNA-21 (miR-21) that downregulates Spry2. Applying dissociated DRG neuron cultures from wild-type (WT) or Spry2 deficient mice, we demonstrate that PTEN protein was reduced after 72 h during rapid axonal outgrowth on the laminin substrate. Furthermore, PTEN protein was decreased in DRG cultures obtained from homozygous Spry2-/- knockout mice. Vice versa, Spry2 protein was reduced by PTEN siRNA in WT and heterozygous Spry2+/- neurons. Knockdown of PTEN in DRG cultures obtained from homozygous Spry2-/- knockout mice promoted axon elongation without increasing axonal branching. Activation of Akt, but not ERK, was stronger in response to PTEN knockdown in homozygous Spry2-/- DRG neurons than in WT neurons. Together, our study confirms the important role of the signaling modulators Spry2 and PTEN in axon growth of adult DRG neurons. Both function as endogenous inhibitors of neuronal growth factor signaling and their simultaneous knockdown promotes axon elongation more efficiently than the single knockdown of each inhibitor. Furthermore, Spry2 and PTEN are reciprocally downregulated in adult DRG neuron cultures. Axon growth is influenced by multiple factors and our results demonstrate that the endogenous inhibitors of axon growth, Spry2 and PTEN, are co-regulated in adult DRG neuron cultures. Together, our data demonstrate that combined approaches may be more useful to improve nerve regeneration than targeting one single inhibitor of axon growth.
Sprouty2（Spry2）和10号染色体缺失的磷酸酶及张力蛋白同源物（PTEN）都是受体酪氨酸激酶（RTK）信号通路中公认的调节因子，敲低Spry2或PTEN可增强背根神经节（DRG）神经元的轴突再生。Spry2的主要作用是抑制大鼠肉瘤RAS/细胞外信号调节激酶（ERK）通路，而PTEN主要作为磷酸肌醇3激酶（PI3K）/Akt通路的抑制剂。在非神经元细胞中，Spry2可增加PTEN的表达和活性，而PTEN通过抑制下调Spry2的微小RNA-21（miR-21）来增加Spry2的量。应用来自野生型（WT）或Spry2缺陷小鼠的解离DRG神经元培养物，我们证明在层粘连蛋白底物上快速轴突生长的72小时内，PTEN蛋白减少。此外，从纯合Spry2-/-敲除小鼠获得的DRG培养物中PTEN蛋白减少。反之，在WT和杂合Spry2+/-神经元中，PTEN siRNA可降低Spry2蛋白水平。从纯合Spry2-/-敲除小鼠获得的DRG培养物中敲低PTEN可促进轴突伸长而不增加轴突分支。与WT神经元相比，纯合Spry2-/- DRG神经元中PTEN敲低后Akt的激活更强，但ERK的激活无明显变化。总之，我们的研究证实了信号调节因子Spry2和PTEN在成年DRG神经元轴突生长中的重要作用。二者均作为神经元生长因子信号的内源性抑制剂，同时敲低它们比单独敲低每种抑制剂更有效地促进轴突伸长。此外，在成年DRG神经元培养物中，Spry2和PTEN相互下调。轴突生长受多种因素影响，我们的结果表明轴突生长的内源性抑制剂Spry2和PTEN在成年DRG神经元培养物中共同调节。总之，我们的数据表明联合方法可能比靶向单一轴突生长抑制剂对改善神经再生更有用。
