C/Ebpß regulates microglial ptges expression and pge2 production

Abstract

We have recently described that the transcription factor C/EBPß regulates pro-inflammatory gene expression in glial activation. Since the production of the inflammatory lipid mediator PGE2 is increased in activated glial cells, we have undertaken a study to analyze whether C/EBPß participates in the regulation of PGE2 synthesis enzymes in these cells. To this end gene expression and PGE2 production was compared between wild-type and C/EBPß -/- mice, both in vitro and in vivo. We have observed a robust effect of C/EBPß deficiency in the expression of PTGES (=mPGES1) in glial activation. Thus, PTGES expression and PGE2 production induced by LPS (100 ng/ml) +IFN?(0.1 ng/ml) in primary mixed glial cultures were abolished in the absence of C/EBPß. qChIP experiments revealed C/EBPß binding to the PTGES promoter after LPS+IFN? treatment and double immunofluorescence revealed that PTGES expression was of microglial origin. In line with this, marked LPS+IFN?-induced upregulation of PTGES expression was observed in microglial-enriched cultures and this was also abolished in the absence of C/EBPß. Systemic LPS injection (100 µg/mouse, i.p.) was used then to study neuroinflammation in vivo. This treatment upregulated PTGES mRNA levels in cerebral cortex and, as seen in vitro, the increase in PTGES expression was abolished in C/EBPß -/- mice. Interestingly, the expression of COX-2, another key enzyme in PGE2 synthesis, was also upregulated in glial activation in vitro and in vivo, but in contrast to PTGES, COX2 expression was barely affected by C/EBPß absence. Altogether these findings suggest that in microglial activation C/EBPß binds to the PTGES promoter, inducing its transcription. This leads to increased PTGES mRNA and protein levels and subsequent PGE2 accumulation. These findings strengthen the proposed role of C/EBPß as a key player in the orchestration of gene response in neuroinflammation.