神经生长因子通过抑制内质网应激促进外周神经损伤后髓鞘碎片的清除

NGF Promotes Myelin Debris Clearance after Peripheral Nerve Injury by Inhibiting Endoplasmic Reticulum Stress

神经生长因子(never growth factor,NGF)可促进损伤外周神经的修复并加速轴突和髓鞘的再生,但对外周神经损伤前期作用的研究报道较少。本研究主要探究在损伤外周神经前期,NGF能否加速施旺细胞(Schwann cells,SCs)对髓鞘碎片的清除及其调控机制。将坐骨神经损伤的Wistar雄性大鼠连续5 d给予NGF治疗,并运用分子生物学检测手段分析损伤坐骨神经内部髓鞘碎片的清除,细胞的凋亡及内质网应激(endoplasmic reticulum stress,ERS)的表达和变化。免疫荧光分析结果显示,与模型组相比,NGF给药组显著加速髓鞘碎片的清除,并促进SCs的增殖(46.33±5.68 vs.66.69±8.76,P<0.05 for MPZ;47.58±4.52 vs.37.69±2.50,P<0.01for GFAP)。TUNEL免疫组化证实,NGF可有效抑制SCs的凋亡(25±4 vs.37±6,P<0.05),Western印迹结果显示,模型组坐骨神经内部内质网应激水平被过度激活,给予NGF治疗后,相关蛋白质表达被逆转(1.03±0.03 vs.1.24±0.07,P<0.01 for PDI;1.16±0.16 vs.1.48±0.10,P<0.05 for GRP-78;1.33±0.11 vs.1.76±0.17,P<0.01 for Caspase-12;1.01±0.05vs.1.39±0.16,P<0.01 for CHOP)。上述结果证实,NGF可通过抑制内质网应激减少神经组织内细胞的凋亡,并加速髓鞘碎片的清除,促进外周神经损伤的修复。

Nerve growth factor（ NGF） has been verified to facilitate neural repair and accelerate the regeneration of axon and myelin sheath. However,there are few studies regarding to the effects of NGF in regulating peripheral nerve injury（ PNI） at the early stage. This work mainly investigates whether NGF is able to recruit Schwann cells（ SCs） to accelerate myelin debris clearance and its molecular mechanisms at the early stage of PNI. Our study administrated NGF at the injured sciatic nerve for 5 consecutive days. The degree of myelin debris clearance,the rate of apoptosis cells and the expression of endoplasmic reticulum stress（ ERS） related proteins were detected by corresponding assays. Immunofluorescence staining analysis showed that NGF significantly accelerated the clearance of myelin debris and promoted the proliferation of SCs（ 46. 33 ± 5. 68 vs. 66. 69 ± 8. 76,P〈 0. 05 for MPZ and 47. 58 ± 4. 52 vs.37. 69 ± 2. 50,P〈 0. 01 for GFAP）. TUNEL immunohistochemistry confirmed that NGF could effectively inhibit SCs apoptosis（ 25 ± 4 vs. 37 ± 6,P〈 0. 05）. Western blotting result showed that the expression of ER stress associated proteins was significantly up-regulated in PNI group. These elevated levels were significantly reversed by administrating NGF for 5 days（ 1. 03 ± 0. 03 vs. 1. 24 ±0. 07,P〈 0. 01 for PDI; 1. 16 ± 0. 16 vs. 1. 48 ± 0. 10,P〈 0. 05 for GRP-78; 1. 33 ± 0. 11 vs.1. 76 ± 0. 17,P〈 0. 01 for Caspase-12; 1. 01 ± 0. 05 vs. 1. 39 ± 0. 16,P〈 0. 01 for CHOP）. The present study clearly demonstrated that treatment with exogenous NGF reduced the apoptosis of nerve tissue cells and accelerated the removal of myelin fragments via the inhibition of excessive ER stress,highlighting the protective role of NGF in ER stress and apoptosis of SCs,which may be a useful therapeutic strategy for PNI.