Complement component 3 (C3) expression in the hippocampus after excitotoxic injury: role of C/EBPβ

Background: The CCAAT/enhancer-binding protein beta (C/EBP beta) is a transcription factor implicated in the control of proliferation, differentiation, and inflammatory processes mainly in adipose tissue and liver; although more recent results have revealed an important role for this transcription factor in the brain. Previous studies from our laboratory indicated that CCAAT/enhancer-binding protein beta is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury. More recently, we have shown that the complement component 3 gene (C3) is a downstream target of CCAAT/enhancer-binding protein beta and it could be a mediator of the proinflammatory effects of this transcription factor in neural cells. Methods: Adult male Wistar rats (8-12 weeks old) were used throughout the study. C/EBP beta(+/+) and C/EBP beta(-/-) mice were generated from heterozygous breeding pairs. Animals were injected or not with kainic acid, brains removed, and brain slices containing the hippocampus analyzed for the expression of both CCAAT/enhancer-binding protein beta and C3. Results: In the present work, we have further extended these studies and show that CCAAT/enhancer-binding protein beta and C3 co-express in the CA1 and CA3 regions of the hippocampus after an excitotoxic injury. Studies using CCAAT/enhancer-binding protein beta knockout mice demonstrate a marked reduction in C3 expression after kainic acid injection in these animals, suggesting that indeed this protein is regulated by C/EBP beta in the hippocampus in vivo. Conclusions: Altogether these results suggest that CCAAT/enhancer-binding protein beta could regulate brain disorders, in which excitotoxic and inflammatory processes are involved, at least in part through the direct regulation of C3.