VEGF mRNA及蛋白在大鼠放射性脑损伤模型中的动态变化

Dynamic changes of VEGF mRNA and protein due to brain injury in irradiated rats

目的 研究VEGF mRNA及蛋白在大鼠放射性脑损伤模型中的动态改变.方法 健康SD大鼠114只,按随机数字表法分为假照组（麻醉后不照射,42只）和照射组[20 Gy电子线（6 MeV）单次全脑照射SD大鼠建立放射性脑损伤模型,72只],分别于照射后1、3、7、14、28、42、56 d被处死,取全部脑组织.通过HE染色光镜观察病理学变化,实时荧光定量反转录多聚酶链反应检测VEGF mRNA表达变化,Western blot检测全脑VEGF总蛋白含量改变,免疫组织化学结合计算机图像处理检测脑血管内皮细胞、胶质及神经细胞VEGF蛋白积分光密度值变化.结果 照射组脑组织在观察期主要历经了脑血管内膜细胞受损、血管源性水肿、血栓发生、血栓消融、血管再通及新生等病理变化过程.照射组VEGF mRNA在照后1～56 d出现下降,其中1、3、7、28和42 d降低与假照射组比较,差异有统计学意义（t=16.275～46.118,P＜0.05）.VEGF总蛋白在照后1和7d表达增高,3、14、28、42、56 d表达相对降低.照后1d起脑组织即出现VEGF染色阳性的血管内皮细胞、胶质及神经细胞.照后1、14、42、56 d胶质及神经细胞VEGF蛋白光密度值出现显著升高,与假照射组比较,差异有统计学意义（t=-8.394～-4.697,P＜0.05）,血管内皮细胞在照后1、14、42 d VEGF蛋白光密度值升高（t＝5.554 ～-4.159,P＜0.05）.结论 在放射性脑损伤模型中,大鼠脑组织中VEGF mRNA表达受到相对抑制;VEGF总蛋白仅在损伤急性期升高;脑血管内皮细胞、胶质及神经细胞表达的VEGF蛋白在观察期内持续上调,并参与了急性期内诱导水肿、形成血栓以及在早发延迟期内血管修复与再生、血栓消融等相关事件.

Objective To investigate the dynamic changes of VEGF mRNA and protein in the injured brain of rats irradiated by 20 Gy of electron beams.Methods A total of 114 Sprague-Dawley rats were randomly divided into two groups,42 rats in sham group with sham-irradiation,and the other 72 rats in irradiation group that the whole brains of rats were administered with a single dose of 20 Gy electron beam （6 MeV） to establish an animal model of radiation-induced brain injury.All rats were terminated at 1,3,7,14,28,42,56 d post-irradiation respectively.The pathological changes were observed with light microscopies.Real-time quantitative reverse transcriptase-PCR was used to measure the level of VEGF mRNA in the brain tissue.The expression of VEGF protein in whole brain tissue was detected with Western blot.The VEGF protein expression in brain endothelium,gliacyte and neuron were measured via immunohistoehemistry with computerized image processing.Results The pathological process of radiationinduced brain injury （RBI） included brain endothelial cell damage,brain edema,thrombosis formation and ablation,revascularization and angiogenesis.In the irradiation group,the expression of VEGF mRNA was declined significantly at 1,3,7,2g,42 d post-irradiation （t =16.275-46.118,P 〈 0.05）.The VEGF protein expression in whole brain tissue was up-regulated at 1 and 7 d after irradiation,but downregulated at 3,14,28,42,56 d post-irradiation.There were VEGF positive cells in the brain endothelium,gliacyte and neuron at 1 d after irradiation.The expression of VEGF protein in gliacyte and neuron significantly was increased at 1,14,42,56 d post-irradiation （t =-8.394--4.697,P 〈 0.05）,and increased significantly in brain endothelial cells at 1,14,and 42 d after irradiation （t =-5.554--4.159,P 〈 0.05）.Conclusions The expression of VEGF mRNA was relatively suppressed in RBI rats.The expression of VEGF protein in whole brain tissue was up-regulated only at the early stage of RBI.The expressions of VEGF protein in brain endothelium,gliacyte and neuron were increased in the observation period,which induced brain edema and the formation of thrombosis at the acute RBI stage,and participated in the progression of angiogenesis and thrombosis ablation at the early-delayed RBI stage.