Objective: To investigate the effects of blocking the activation of ERK pathway on the expression of matrix metalloproteinase-9 (MMP-9) and the formation of cerebral edema in SD rats after brain injury.
Methods: Ninety SD rats were randomly divided into 3 equal groups, including a sham-operated group, modified Feeney's traumatic brain injury model group, and ERK inhibition group where the ERK inhibitor SCH772984 (500 μg/kg) was injected via the femoral vein 15 min before brain trauma. At 2 h and 2 days after brain trauma, the permeability of blood-brain barrier was assessed by Evans blue method, the water content of the brain tissue was determined, and the phosphorylation level of ERK and the expression level of MMP-9 mRNA and protein were measured by RT-PCR and Western blotting.
Results: Compared with the sham-operated group, the rats with brain trauma exhibited significantly increased level of ERK phosphorylation at 2 h and significantly increased expression of MMP-9 mRNA and protein 2 days after the injury (P < 0.01). Treatment with the ERK inhibitor significantly decreased the phosphorylation level of ERK after the injury (P < 0.01), suppressed over-expression of MMP-9 mRNA and protein 2 days after the injury (P < 0.01). The permeability of blood-brain barrier increased significantly 2 h after brain trauma (P < 0.05) and increased further at 2 days (P < 0.01); the water content of the brain did not change significantly at 2 h (P > 0.05) but increased significantly 2 d after the injury (P < 0.01). Treatment with the ERK inhibitor significantly lowered the permeability of blood-brain barrier and brain water content after brain trauma (P < 0.01).
Conclusions: Blocking the activation of ERK pathway significantly reduced the over-expression of MMP-9 and alleviates the damage of blood-brain barrier and traumatic brain edema, suggesting that ERK signaling pathway plays an important role in traumatic brain edema by regulating the expression of MMP-9.
目的: 观察并探讨阻断ERK通路激活对SD大鼠脑创伤后基质金属蛋白酶-9（MMP-9）表达变化及脑水肿形成的影响及意义。
方法: 取健康成年雄性SD大鼠90只，随机分为：对照组：只在颅骨上做一直径约为4 mm的骨窗，不作脑创伤；脑创伤组：制作改进式Feeney's创伤性脑损伤模型；ERK抑制组：脑创伤前15 min股静脉注射ERK抑制剂（SCH772984，500 μg/kg），每组30只/组大鼠。制作改进式Feeney's脑创伤模型后，分别在脑创伤后2 h、2 d时断头取脑，Evans Blue法测定血脑屏障通透性变化，干湿比重法测定脑组织含水量，RT-PCR法和Western blotting法检测各组大鼠脑组织ERK磷酸化的水平及MMP-9 mRNA及蛋白的表达水平。
结果: （1）与对照组比较，脑创伤组大鼠脑组织中ERK的磷酸化水平在伤后2 h和2 d均出现明显上升（P < 0.01），MMP-9 mRNA和蛋白的表达在脑创伤后2 d时表达也出现显著增高（均P < 0.01）；与脑创伤组比较，ERK抑制组大鼠脑组织中ERK的磷酸化水平在各时间点均明显下降（P < 0.01），MMP-9 mRNA和蛋白在伤后2 d的过表达水平也较脑创伤组出现明显降低（均P < 0.01）；（2）脑创伤组大鼠的血脑屏障通透性较对照组在伤后出现显著升高（P < 0.05），ERK抑制组大鼠的血脑屏障通透性则较脑创伤组出现明显降低（P < 0.05）；脑创伤组大鼠的脑含水量在伤后在2 d时出现显著增加（P < 0.01），ERK抑制组大鼠的脑含水量则较脑创伤组有明显降低（P < 0.01）。
结论: 阻断ERK通路过度的活化可显著降低大鼠脑创伤后MMP-9高表达，减轻大鼠血脑屏障破坏及创伤性脑水肿，提示ERK信号通路在脑创伤后的过度活化可通过调节MMP-9的表达在创伤性脑水肿中发挥重要作用。
Keywords: ERK; brain edema; matrix metalloproteinase-9; traumatic brain injury.