Activation of interleukin-6/STAT3 in rat cholangiocyte proliferation induced by lipopolysaccharide

Abstract

Background: Cholangiocytes are exposed to endotoxins (lipopolysaccharide, LPS) in a variety of biliary inflammations. It is known that LPS enhances the release of interleukin (IL)-6, a potent cholangiocyte mitogen. However, the role of LPS in cholangiocyte proliferation in vivo is unknown. Aims To investigate whether LPS stimulates cholangiocyte proliferation in vivo via the IL-6/STAT3 pathway.

Methods: Rats were randomized into four groups: the LPS group (injected intravenously with LPS 2.5 mg/kg), anti-IL-6 group (injected intravenously with anti-IL-6 0.5 mg/kg 1 h after LPS injection), RPM group (treated with RPM 0.4 mg/kg intraperitoneally 30 min before LPS injection), and control group. At 6, 12, 24, 48, and 72 h after LPS injection, LPS in plasma was detected by kinetic turbidimetric limulus test. IL-6 concentrations in liver homogenate and cholangiocyte proliferation were determined by ELISA or immunohistochemistry, respectively. Expression of IL-6 mRNA and phosphorylated-STAT3 (P-STAT3) protein in cholangiocytes was analyzed by real-time RT-PCR and western blotting.

Results: Cholangiocytes responded to LPS by a marked increase in cell proliferation, IL-6 secretion, and P-STAT3 expression. Anti-IL-6 neutralizing antibody inhibited LPS-induced proliferation of cholangiocytes and decreased levels of IL-6 and STAT3. Furthermore, after being treated with RPM, STAT3 activation was also depressed, which resulted a decreased proliferation of cholangiocytes.

Conclusions: LPS promotes cholangiocyte proliferation through the IL-6/STAT3 pathway, while RPM shows a depressive effect in this pathway.