MiR-155 promotes acute organ injury in LPS-induced endotoxemic mice by enhancing CCL-2 expression in macrophages.

ABSTRACT:Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Macrophages play important roles in the inflammatory process of sepsis by secreting chemokines. Chemokine (CC-motif) ligand 2 (CCL-2) is one of the main pro-inflammatory chemokines secreted by macrophages that plays a critical role in the recruitment of more monocytes and macrophages to the sites of injury in sepsis, but the mechanisms that regulate CCL-2 expression in macrophages during sepsis are still unknown. In the present study, by using the lipopolysaccharide (LPS)-induced endotoxemia model, we found that LPS induced the expression of microRNA (miR)-155 and CCL-2 in endotoxemic mice and RAW264.7 cells. MiR-155 mimics or miR-155 inhibitor treatment experiment suggested that miR-155 was sufficient to increase LPS-induced CCL-2 expression in macrophages, but miR-155 was not the only factor promoting CCL-2 expression. We further demonstrated that miR-155-induced increase of CCL-2 promoted chemotaxis of additional macrophages, which subsequently enhanced lung injury in endotoxemic mice. Serum/glucocorticoid regulated kinase family member 3 (SGK3), a potential target of miR-155, was identified by RNA sequencing and predicted by TargetScan and miRDB. We further confirmed miR-155 regulated SGK3 to increase LPS-induced CCL-2 by using miR-155 mimics and SGK3 overexpression. Thus, our study demonstrates that miR-155 targets SGK3 to increase LPS-induced CCL-2 expression in macrophages, which promotes macrophage chemotaxis and enhances organs injury during endotoxemia. Our study contributed to a better understanding of the mechanisms underlying the inflammatory response during sepsis.