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

Abstract

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. Key words: Vascular endothelial growth factor; Radiation-induced brain injury; Rat model