β-APP和NF-L在评估弥漫性轴索损伤大鼠损伤程度中的价值

Value of β-APP and NF-L as markers in evaluation of rat diffuse axonal injury

目的利用自制装置建立轻、中、重度的弥漫性轴索损伤(diffuse axonal injury,DAI)大鼠模型,观察不同时间点β-淀粉样前体蛋白(β-amyloid precursor protein,β-APP)及神经丝蛋白轻链多肽(neurofilament light polypeptide,NF-L)的变化与恢复期的学习记忆能力的相关性。方法健康成年SD大鼠100只,随机分为正常对照组和A、B、C(轻、中、重型致伤)DAI组。伤后6、24、72 h及1、2周取脑组织切片行β-APP免疫组织化学染色;24 h时脑组织切片行HE染色和NF-L免疫组织化学染色;2周时行水迷宫测试。将损伤后24 h各组脑组织切片感兴趣区内测定的β-APP和NF-L累积光密度(IOD)值与损伤后恢复期大鼠的学习记忆能力做相关性分析。结果伤后24 h取脑组织肉眼观察致伤组大脑表面、蛛网膜下腔、脑室等区域未见出血,光镜下可见A、B、C组大鼠的胼胝体区神经束疏松、紊乱,血管淤滞,空泡形成,神经元肿胀变性,细胞核显示不清,突触结构模糊等经典DAI病理特征,NF-L免疫组化鉴定实验组均有典型中线部位轴索损伤改变。实验组伤后6、24、72 h及1、2周与对照组相比各时间点胼胝体β-APP均有升高(P<0.05),组内各时间点呈动态变化,于伤后24 h最高。伤后24 h,实验组NF-L免疫组化染色大脑水管水平脑干轴突和神经元胞体阳性染色较正常组增强,半定量分析A、B、C3组间差异有统计学意义(P<0.05)。水迷宫测试与正常对照组比较,A组大鼠学习记忆功能无明显下降;B、C两组下降明显(P<0.05)。损伤后24 h,A、B、C 3组脑组织切片感兴趣区内测定的β-APP和NF-L累积光密度(IOD)值与损伤后恢复期大鼠的学习记忆能力呈负相关(r分别为-0.937、-0.939)。结论β-APP和NF-L不仅可以反映DAI动物模型轴索损伤的程度,还可以早期预测损伤后大鼠的学习记忆恢复能力,可能成为DAI损伤的特异性分子探针。

Objective To observe the expression changes of β-amyloid precursor protein（ β-APP）and neurofilament light polypeptide（ NF-L） in rats with different degrees of diffuse axonal injury（ DAI） at different time points,and identify the correlation between the changes and the learning and memory abilities of the rats in the recovery period. Methods A total of 100 healthy adult SD rats were randomly divided into control group,and mild,moderate and severe injury groups,with 25 rats in each group. The brain tissue specimens were detected by immunohistochemistry using rabbit antibodies of β-APP at given time points（ 6,24 and 72 h,1 and 2 weeks after injury）,and at 24 h after injury,the brain tissue specimens were analyzed by HE staining and NF-L immunohistochemical staining. In 2 weeks later,the learning and memory ability of each group was tested by Morris water maze. Callosum and brainstem with cerebral aqueduct were selected as the interest region under a microscope. The correlation between the integral optical density（ IOD） of β-APP and NF-L in the interest region at 24 h after injury and the learning and memory abilities of the rats during the recovery period was analyzed. Results At 24 h after injury, the bleeding at the brain surface,subarachnoid,and cerebroventricular regions was not observed in all groups. However, typical DAI pathological features such as loosened and disordered nerve bundles,clogged blood vessels,cavitation,swelling and degenerative neurons,vague and unclear nucleus,and fuzzy synaptic structure were observed in the callosum and brainstem under the microscope. The immunohistochemical results showed that the immunoreactivity of β-APP at the callosum of the injury groups was significantly enhanced compared with the control group at the given time points,and semi-quantitative analysis further revealed that the IOD values had significant difference between the control group and the injury groups（ P 0. 05）. The IOD values at each time point were changed dynamically in the injury groups,and the immunoreactivity was strongest at 24 h.Compared with the control group,the immunoreactivity of NF-L in the axon and neuron cell body of the brainstem of the injury groups was significantly enhanced at 24 h after injury,and there was statistically significant difference（ P 0. 05）. Morris water maze test indicated that the learning and memory abilities had no statistically significant difference between the mild injury group and the control group,but there was statistically significant difference between the control group and the moderate and severe injury groups（ P 0. 05）. The correlation analysis showed that the learning and memory ability was negatively correlated with the IOD values of β-APP and NF-L at 24 h after injury（ r =-0. 937,r =-0. 939）. Conclusion The expression changes of β-APP and NF-L are significantly associated with the injury degree of DAI,and the learning and memory abilities in the recovery period can be predicted based on the expression changes ofβ-APP and NF-L at early time.