KLF4 down-regulation resulting from TLR4 promotion of ERK1/2 phosphorylation underpins inflammatory response in sepsis

Sepsis is a systemic inflammatory response to invading pathogens, leading to high mortality rates in intensive care units worldwide. Krüppel-like factor 4 (KLF4) is an important anti-inflammatory transcription factor. In this study, we investigate the anti-inflammatory role of KLF4 in caecal ligation and puncture (CLP)-induced septic mice and lipopolysaccharide (LPS)-induced RAW264.7 cells and its potential mechanism. We found that KLF4 was down-regulated in CLP-induced septic mice and in LPS-induced RAW264.7 cells, and that its overexpression led to increased survival rates of septic mice along with inhibited inflammatory response in vivo and in vitro. ITGA2B was up-regulated in the setting of sepsis and was inhibited by KLF4 overexpression. ITGA2B knock-down mimicked the effects of KLF4 overexpression on septic mice and LPS-induced RAW264.7 cells. TLR4 promoted the phosphorylation of ERK1/2 and then up-regulated the ubiquitination and the degradation of KLF4, thereby elevating the expression of ITGA2B. Moreover, TLR4 knock-down or treatment with PD98059 (a MEK Inhibitor) inhibited inflammatory response in the setting of sepsis in vivo and in vitro. Furthermore, this effect of PD98059 treatment was lost upon KLF4 knock-down. Collectively, these results explain the down-regulation of KLF4 in sepsis, namely via TLR4 promotion of ERK1/2 phosphorylation, and identify ITGA2B as the downstream gene of KLF4, thus highlighting the anti-inflammatory role of KLF4 in sepsis.