神经营养因子3经受体切换促进大鼠脊髓损伤后神经功能的恢复

Neurotrophin-3 receptor switching promotes neural functional recovery in rats after spinal cord injury

背景:神经营养因子是治疗脊髓损伤的新方法,调控自噬是其发挥作用的机制之一,但具体的信号通路尚不明确。目的:探讨神经营养因子3如何通过P75NTR/Trk C受体切换来调节少突胶质细胞的自噬以及促进脊髓损伤后神经功能恢复的作用,进一步明确具体的分子机制。方法:将24只SD大鼠随机分为3组:假手术组、脊髓损伤组和神经营养因子3组,通过大鼠后肢神经功能评分来评估神经营养因子3对脊髓损伤大鼠的治疗效果,采用Western blot检测各组大鼠脊髓组织中神经营养因子3、Olig1、MBP蛋白以及自噬标记蛋白LC3B的表达水平。在细胞实验中,将少突胶质细胞接种在培养皿中,分为糖氧剥夺组、糖氧剥夺+神经营养因子3组、糖氧剥夺+神经营养因子3+P75NTR质粒组、糖氧剥夺+神经营养因子3+Trk C质粒组、糖氧剥夺+3-甲基腺嘌呤(自噬抑制剂)组及糖氧剥夺+雷帕霉素(自噬激活剂)组。光学显微镜观察少突胶质细胞形态变化,TUNEL染色观察细胞凋亡现象,Western blot检测Trk C受体、P75NTR、LC3B表达及PI3K/AKT/m TOR和AMPK/m TOR信号途径的磷酸化状态。结果与结论:(1)动物实验显示,与假手术组相比,脊髓损伤后神经营养因子3的表达显著增加(P<0.05);与脊髓损伤组相比,外源性神经营养因子3治疗能够加快大鼠神经功能的恢复(P<0.05),并增加Olig1和MBP蛋白的表达(P<0.05);(2)细胞实验发现,3 h是损伤早期与中后期的分界点,与糖氧剥夺组相比,糖氧剥夺+神经营养因子3组少突胶质细胞能够更长时间地维持其形态,Trk C受体在早期表达水平较低而中后期显著上调(P<0.05),P75NTR则在早期上调而中后期下调(P<0.05),自噬水平呈现出先升高后降低的趋势(P<0.05);(3)通过对比糖氧剥夺+神经营养因子3组、糖氧剥夺+雷帕霉素组和糖氧剥夺+3-甲基腺嘌呤组的细胞形态和TUNEL染色结果,发现单独促进或抑制自噬对少突胶质细胞的存活均有不利影响,而类似神经营养因子3这样调节自噬的方法则能最大限度地维持细胞存活;(4)神经营养因子3在早期通过P75NTR/AMPK/m TOR信号通路促进自噬,而在后期通过Trk C/PI3K/AKT/m TOR信号通路抑制自噬。根据上述结果,得到如下结论,即神经营养因子3可以通过P75NTR/Trk C受体的切换能够双向调控少突胶质细胞的自噬,从而维持细胞存活,有助于脊髓损伤后大鼠的神经功能恢复。

BACKGROUND:Neurotrophins represent a novel therapeutic approach for spinal cord injury,showing promising clinical applicability.Autophagy modulation is one of the mechanisms by which neurotrophins exert their effects,yet the specific signaling pathways involved remain unclear.OBJECTIVE:To explore how neurotrophin-3(NT-3)modulates autophagy in oligodendrocytes via switching between P75NTR and TrkC receptors and promotes neurological function recovery after spinal cord injury,aiming to further clarify the specific molecular mechanisms involved.METHODS:Twenty-four Sprague-Dawley rats were randomly divided into three groups:sham operation,spinal cord injury,and NT-3 groups.The therapeutic effect of NT-3 on spinal cord injury in rats was evaluated using the Basso,Beattie,and Bresnahan locomotor rating scale.The expression levels of NT-3,Olig1,myelin basic protein,and the autophagy marker LC3B in rat spinal cord tissue were detected by western blot.In a cellular experiment,oligodendrocytes were cultured in vitro and divided into six groups:oxygen-glucose deprivation(OGD),OGD+NT-3,OGD+NT-3+P75NTR plasmid,OGD+NT-3+TrkC plasmid,OGD+3-methyladenine(an autophagy inhibitor),and OGD+rapamycin(an autophagy activator).Oligodendrocyte morphology was observed under a light microscope,cell apoptosis was assessed by TUNEL staining,and the expression of TrkC receptor,P75NTR,LC3B,and the phosphorylation status of the PI3K/AKT/mTOR and AMPK/mTOR signaling pathways were evaluated by western blot.RESULTS AND CONCLUSION:Animal experiments demonstrated that compared with the sham operation group,NT-3 expression significantly increased after spinal cord injury(P<0.05);exogenous NT-3 treatment accelerated neurological function recovery in rats post spinal cord injury(P<0.05)and increased the expression of Olig1 and myelin basic proteins(P<0.05).Cellular experiments revealed that 3 hours marked the early to middle/late phase transition.Compared with the OGD group,oligodendrocytes in the OGD+NT-3 group could maintain their morphology for a longer period of time,TrkC receptor expression was lower in the early phase and significantly upregulated in the middle/late phase(P<0.05),whereas P75NTR protein expression was upregulated in the early phase and downregulated in the middle/late phase(P<0.05),and autophagy levels showed an initial increase followed by a decrease(P<0.05).By comparing the morphology and TUNEL staining results of cells in the OGD+NT-3,OGD+rapamycin,and OGD+3-methyladenine groups,we found that either promoting or inhibiting autophagy alone had adverse effects on oligodendrocyte survival,whereas modulating autophagy in a manner similar to NT-3 could maximally maintain cell survival.NT-3 could promote autophagy in the early phase via the P75NTR/AMPK/mTOR signaling pathway and inhibit autophagy in the later phase through the TrkC/PI3K/AKT/mTOR signaling pathway.Based on these findings,it is concluded that NT-3 can bidirectionally regulate autophagy in oligodendrocytes through the switching of P75NTR/TrkC receptors,thereby maintaining cell survival and facilitating the recovery of neurological functions in rats after spinal cord injury.