Abstract
BACKGROUND: Brain injury accompanied by hemorrhage, such as cerebral contusion or intracerebral hemorrhage, leads to the accumulation of activated microglia around the lesion. In addition, microglia at the site of injury can act either damagingly or protectively, depending on the time; for instance, it is damaging in the acute phase and protective in the chronic phase. Moreover, during brain injury, glutamate-induced excitotoxicity leads to secondary damage to neurons. However, the source of glutamate released from cells remains largely unknown. Our previous studies have revealed that cystine/glutamate antiporter system x(c) (-) (xc-) in microglia is an important source of glutamate release and that the induction of expression of xCT, a component molecule of xc-, is vital. METHODS: We investigated the effect of microglial xCT on traumatic brain injury using xCT-deficient mice. RESULTS: In cultured microglia supplemented with crude brain extract and the affected side of the brain injury model accompanied by hemorrhage, the expression level of xCT was increased on the affected side, and induction was observed mainly in microglia. In addition, EAAT2 levels on the affected side decreased. On the affected side, the number of CD80-positive microglia was significantly increased, and the xCT expression rate was elevated in CD80-positive cells. Assuming that xCT in microglia is important, we investigated xCT-deficient mice and microglia-specific xCT knockdown mice and found that the extent of brain damage was milder than in wildtype mice. The proportion of CD80-positive microglia was lower than that in wild-type mice. Assuming that microglial xCT could be a therapeutic target, we performed an experiment using the xCT inhibitor SSZ administered intraperitoneally. The extent of damage was narrowed, and the ratio of CD80-positive microglia was reduced, demonstrating a therapeutic effect. CONCLUSION: Thus, microglial xCT is important in the pathology of brain injury accompanied by bleeding and is considered a promising therapeutic target.