人脐血干细胞对大鼠部分性视神经损伤保护作用机制的研究

Neuroprotective mechanisms of human umbilical cord blood stem cells to retinal ganglion cells in a partial optic nerve crush rat model

背景视神经损伤后将导致视网膜神经节细胞（RGCs）的凋亡，而凋亡的重要机制是内质网应激（ERS），减弱ERS可能对RGCs起到保护作用。目的探讨ERS在大鼠视神经损伤中的机制及人脐血干细胞对大鼠部分性视神经损伤后RGCs的保护作用。方法采用40g自制夹钳夹持102只SD大鼠的左眼视神经制作部分性视神经钳夹伤动物模型，用随机数字表法将动物分为模型损伤组和人脐血干细胞组，每组51只，均取左眼为视神经损伤眼，右眼为正常对照眼。人脐血于细胞组大鼠左眼造模后立即将10川人脐血干细胞注入玻璃体腔。分别在造模后3、7、14、21、28d各处死3只大鼠，苏木精一伊红染色后光学显微镜下观察大鼠RGCs形态学的改变，并对存活的RGCs进行计数。在造模后3、12、24、48、72h及1周各处死6只大鼠，分别进行TUNEL法检测2组大鼠RGCs的凋亡率及逆转录聚合酶链反应（RT—PCR）法检测上述时间点GRP78 mRNA和CHOP mRNA在2组大鼠视网膜中的表达。结果模型损伤组和人脐血干细胞组随造模时间的延长，RGCs存活的数量明显下降，差异均有统计学意义（F目目=20．100，P=0．007），与模型损伤组相比，人脐血干细胞组RGCs存活的数量下降缓慢。各时间点间模型损伤组及人脐血干细胞组RGCs存活的数量明显低于正常对照组，差异均有统计学意义（P〈0．01），而人脐血干细胞组RGCs的数量明显高于正常对照组，差异有统计学意义（P〈0．01）。TUNEL检测表明，人脐血干细胞组在造模后24h内未见RGCs凋亡，而模型损伤组可见大量TUNEL阳性细胞出现，造模后48h～1周人脐血干细胞组RGCs凋亡率明显低于模型损伤组，差异有统计学意义（P〈0．01）。人脐血干细胞组视网膜GRP78 mRNA表达较强，CHOP mRNA表达微弱，与模型损伤组比较差异均有统计学意义（P〈0．01）。结论ERS参与了大鼠部分性视神经损伤后RGCs的凋亡机制，人脐血干细胞对大鼠部分性视神经损伤后RGCs起保护作用。

Background Optic nerve injury lead to apoptosis of retinal ganglion cells （RGCs）, and its mechanism of apoptosis is endoplasmic reticulum stress （ERS）. So, decreasing of ERS may protect the injury of RGCs. Objective The present study was to investigate the mechanisms of endoplasmic reticulum stress（ERS） and the protective effects of human umbilical cord blood stem cells on partial optic nerve crush injury. Methods The optical nerves were crushed with a 40 g clip by holding for 60 seconds to establish the partial optical nerve injury model in the left eyes of 102 SPF SD rats,and 10 μl of mRNA and 10 μl of nerve growth factor were injected into the vitreous immediately after the establishment of the model. The morphological changes of retinal ganglion cells（RGCs） were examined under the light microscope after 3,7,14,21 and 28 days and the RGCs number was calculated. The apoptosis rates of RGCs were detected by the TUNEL technique after 3,12,24,45,72 hours and 1 week. The expression levels of GRP78 mRNA and CHOP mRNA were detected by reverse transcription polymerase chain reation （ RT-PCR）. This procedure followed the Regulations for the Administration of Affair Concerning Experimental Animals by Hunan Provincial Science and Technology Committee. Results The number of RGCs was significantly decreased with the prolongation of time of optical nerve injury in the model injury group,whereas the number of RGCs in the human cord blood ceils group was reduced at a slower rate（Ftime = 20. 100 ,P = 0. 007 ）. At various time points after the injection of human cord blood ceils, the survival of RGCs was evidently increased in comparison with the model group（P〈0.01 ）. The apoptosis rate of RGCs was considerably elevated with injury time prolongation both in the model group and human cord blood cells group, but no apoptosis was seen from 3-24 hours after operation,and only a small amount of apoptotic ceils were found in the human cord blood cells group from 48 hours through 1 week than in the model group（P〈0.01 ）. In the human cord blood cells group, GRP78 mRNA level was significantly higher and the CHOP mRNA level was significantly lower than those in the injury group at identical time points（P〈0.01 ）. Conclusions In the rat optic nerve partial crush model,ERS induces the apoptosis of RGCs. Human umbilical cord blood stem cells can protect RGCs from ERS injury by inhibiting apoptosis.