Abstract: 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). Conclusion 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.

Key words: ERK, matrix metalloproteinase-9, brain edema, traumatic brain injury