Zhang Min, Zhou Qiang, Luo Yuncin, Nguyen Tara, Rosenblatt Mark I, Guaiquil Victor H
Department of Ophthalmology and Visual Sciences, University of Illinois-Chicago, Chicago, Illinois, United States of America.
PLoS One. 2018 Jan 25;13(1):e0191962. doi: 10.1371/journal.pone.0191962. eCollection 2018.
The peripheral sensory nerves that innervate the cornea can be easily damaged by trauma, surgery, infection or diabetes. Several growth factors and axon guidance molecules, such as Semaphorin3A (Sema3A) are upregulated upon cornea injury. Nerves can regenerate after injury but do not recover their original density and patterning. Sema3A is a well known axon guidance and growth cone repellent protein during development, however its role in adult cornea nerve regeneration remains undetermined. Here we investigated the neuro-regenerative potential of Sema3A on adult peripheral nervous system neurons such as those that innervate the cornea. First, we examined the gene expression profile of the Semaphorin class 3 family members and found that all are expressed in the cornea. However, upon cornea injury there is a fast increase in Sema3A expression. We then corroborated that Sema3A totally abolished the growth promoting effect of nerve growth factor (NGF) on embryonic neurons and observed signs of growth cone collapse and axonal retraction after 30 min of Sema3A addition. However, in adult isolated trigeminal ganglia or dorsal root ganglia neurons, Sema3A did not inhibited the NGF-induced neuronal growth. Furthermore, adult neurons treated with Sema3A alone produced similar neuronal growth to cells treated with NGF and the length of the neurites and branching was comparable between both treatments. These effects were replicated in vivo, where thy1-YFP neurofluorescent mice subjected to cornea epithelium debridement and receiving intrastromal pellet implantation containing Sema3A showed increased corneal nerve regeneration than those receiving pellets with vehicle. In adult PNS neurons, Sema3A is a potent inducer of neuronal growth in vitro and cornea nerve regeneration in vivo. Our data indicates a functional switch for the role of Sema3A in PNS neurons where the well-described repulsive role during development changes to a growth promoting effect during adulthood. The high expression of Sema3A in the normal and injured adult corneas could be related to its role as a growth factor.
支配角膜的外周感觉神经很容易因外伤、手术、感染或糖尿病而受损。几种生长因子和轴突导向分子，如信号素3A（Sema3A），在角膜损伤后会上调。神经损伤后能够再生，但无法恢复其原始密度和模式。Sema3A在发育过程中是一种众所周知的轴突导向和生长锥排斥蛋白，然而其在成年角膜神经再生中的作用仍未确定。在这里，我们研究了Sema3A对成年外周神经系统神经元（如支配角膜的神经元）的神经再生潜力。首先，我们检查了信号素3类家族成员的基因表达谱，发现它们都在角膜中表达。然而，角膜损伤后，Sema3A的表达迅速增加。然后我们证实，Sema3A完全消除了神经生长因子（NGF）对胚胎神经元的生长促进作用，并在添加Sema3A 30分钟后观察到生长锥塌陷和轴突回缩的迹象。然而，在成年分离的三叉神经节或背根神经节神经元中，Sema3A并未抑制NGF诱导的神经元生长。此外，单独用Sema3A处理的成年神经元产生的神经元生长与用NGF处理的细胞相似，两种处理之间神经突的长度和分支情况相当。这些效应在体内得到了重复，在那里，接受角膜上皮清创术并接受含有Sema3A的基质内微丸植入的thy1-YFP神经荧光小鼠比接受含有载体的微丸的小鼠显示出更多的角膜神经再生。在成年外周神经系统神经元中，Sema3A在体外是神经元生长的有效诱导剂，在体内是角膜神经再生的有效诱导剂。我们的数据表明Sema3A在周围神经系统神经元中的作用发生了功能转换，即在发育过程中众所周知的排斥作用在成年期转变为生长促进作用。Sema3A在正常和受伤的成年角膜中的高表达可能与其作为生长因子的作用有关。
