Published online Dec 14, 2016. doi: 10.3748/wjg.v22.i46.10148
Peer-review started: August 3, 2016
First decision: August 19, 2016
Revised: September 8, 2016
Accepted: October 10, 2016
Article in press: October 10, 2016
Published online: December 14, 2016
Processing time: 132 Days and 12.7 Hours
To investigate the role of the complement 5a (C5a)/C5a receptor (C5aR) pathway in the pathogenesis of acute liver failure (ALF) in a mouse model.
BALB/c mice were randomly assigned to different groups, and intraperitoneal injections of lipopolysaccharide (LPS)/D-galactosamine (D-GalN) (600 mg/kg and 10 μg/kg) were used to induce ALF. The Kaplan-Meier method was used for survival analysis. Serum alanine aminotransferase (ALT) levels, at different time points within a 1-wk period, were detected with a biochemistry analyzer. Pathological examination of liver tissue was performed 36 h after ALF induction. Serum complement 5 (C5), C5a, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, high-mobility group protein B1 (HMGB1) and sphingosine-1-phosphate levels were detected by enzyme-linked immunosorbant assay. Hepatic morphological changes at 36 h after ALF induction were assessed by hematoxylin and eosin staining. Expression of C5aR, sphingosine kinase 1 (SphK1), p38-MAPK and p-p38-MAPK in liver tissue, peripheral blood mononuclear cells (PBMCs) and peritoneal exudative macrophages (PEMs) of mice or RAW 264.7 cells was analyzed by western blotting. C5aR mRNA levels were detected by quantitative real-time PCR.
Activation of C5 and up-regulation of C5aR were observed in liver tissue and PBMCs of mice with ALF. Blockade of C5aR with a C5aR antagonist (C5aRa C5aRa) significantly reduced the levels of serum ALT, inflammatory cytokines (TNF-α, IL-1β and IL-6) and HMGB1, as well as the liver tissue damage, but increased the survival rates (P < 0.01 for all). Blockade of C5aR decreased SphK1 expression in both liver tissue and PBMCs significantly at 0.5 h after ALF induction. C5aRa pretreatment significantly down-regulated the phosphorylation of p38-MAPK in liver tissues of ALF mice and C5a stimulated PEMs or RAW 264.7 cells. Moreover, inhibition of p38-MAPK activity with SB203580 reduced SphK1 protein production significantly in PEMs after C5a stimulation.
The C5a/C5aR pathway is essential for up-regulating SphK1 expression through p38 MAPK activation in ALF in mice, which provides a potential immunotherapeutic strategy for ALF in patients.
Core tip: Recent studies and our work show that SphK1 and complement activation play an important role in systemic inflammation in acute liver failure (ALF). It has been shown that C5a activates sphingosine kinase 1 (SphK1) in macrophages. However, the mechanism of C5a-induced SphK1 activation is unknown. In this study we found that excessive activation of C5 and up-regulation of C5aR in liver tissue, and the C5a/C5aR pathway is essential for potentiating SphK1 expression through p38 MAPK activation in ALF. To our knowledge, this is the first report of the mechanism of C5a-induced SphK1 activation, which provides a potential immunotherapeutic strategy for ALF in patients.