Jin Li-Qing, John Brittany H, Hu Jianli, Selzer Michael E
Shriners Hospitals Pediatric Research Center, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States.
Department of Neurology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, United States.
Front Neurosci. 2020 Nov 5;14:580692. doi: 10.3389/fnins.2020.580692. eCollection 2020.
We previously reported that spinal cord transection (TX) in the lamprey causes mRNA to accumulate in the injured tips of large reticulospinal (RS) axons. We sought to determine whether this mRNA accumulation results from phosphorylation and transport of retrograde signals, similar to what has been reported in mammalian peripheral nerve. Extracellular signal-regulated protein kinase (Erk), mediates the neurite outgrowth-promoting effects of many neurotrophic factors. To assess the role of Erk in retrograde signaling of RS axon injury, we used immunoblot and immunohistochemistry to determine the changes in phosphorylated Erk (p-Erk) in the spinal cord after spinal cord TX. Immunostaining for p-Erk increased within axons and local cell bodies, most heavily within the 1-2 mm closest to the TX site, at between 3 and 6 h post-TX. In axons, p-Erk was concentrated in 3-5 μm granules that became less numerous with distance from the TX. The retrograde molecular motor dynein colocalized with p-Erk, but vimentin, which in peripheral nerve was reported to participate with p-Erk as part of a retrograde signal complex, did not colocalize with p-Erk, even though vimentin levels were elevated post-TX. The results suggest that p-Erk, but not vimentin, may function as a retrograde axotomy signal in lamprey central nervous system neurons, and that this signal may induce transcription of mRNA, which is then transported down the axon to its injured tip.
我们之前报道过，七鳃鳗的脊髓横断（TX）会导致mRNA在大型网状脊髓（RS）轴突的损伤末端积累。我们试图确定这种mRNA积累是否源于逆行信号的磷酸化和运输，类似于在哺乳动物外周神经中所报道的情况。细胞外信号调节蛋白激酶（Erk）介导许多神经营养因子促进神经突生长的作用。为了评估Erk在RS轴突损伤逆行信号传导中的作用，我们使用免疫印迹和免疫组织化学来确定脊髓TX后脊髓中磷酸化Erk（p-Erk）的变化。TX后3至6小时，轴突和局部细胞体内的p-Erk免疫染色增加，在最靠近TX部位的1-2毫米范围内最为明显。在轴突中，p-Erk集中在3-5μm的颗粒中，这些颗粒随着与TX距离的增加而数量减少。逆行分子马达动力蛋白与p-Erk共定位，但波形蛋白（在周围神经中据报道作为逆行信号复合物的一部分与p-Erk一起参与）即使在TX后波形蛋白水平升高的情况下也不与p-Erk共定位。结果表明，p-Erk而非波形蛋白可能在七鳃鳗中枢神经系统神经元中作为逆行轴突切断信号起作用，并且该信号可能诱导mRNA转录，然后mRNA被运输到轴突向下至其损伤末端。
