HMGB1-mediated activation of TLR4 signaling in hepatic stellate cells

Abstract

To determine the potential of the high mobility group box-1 protein 1 (HMGB1) to activate Toll-like receptor 4 (TLR4) signaling in hepatic stellate cells (HSCs) and investigate the subsequent transition of HSC towards the inflammatory phenotype. Three immortalized mouse HSC cell lines, wild-type (JS1), TLR4-/- (JS2) and MyD88-/- (JS3), were subcultured in plates and divided into groups of normal control (untreated), postive control (lipopolysaccaride, LPS treatment), and experimental (HMGB1 treatment). All groups were transfected with luciferase reporter plasmids carrying responsive elements for either the nuclear factor-kappa B (NF-kB) or activator protein-1 AP-1 transcription factors. Following stimulation with normal saline, LPS (100 ng/mL) or HMGB1 (100 ng/mL), the activation of NF-kB or AP-1 was detected by a dual-luciferase reporter assay system. The induction of monocyte chemotactic protein-1 (MCP-1) transcription was determined by measuring the mRNA levels using real time quantitative reverse transcription PCR (qRT-PCR). The secreted protein levels of MCP-1 were determined by enzyme-linked immunosorbent assay (ELISA) of the culture supernatants. Activation of NF-kB- and AP-1-responsive reporters was significantly up-regulated in JS1 cells treated with HMGB1 or LPS, and the activation was coincident with markedly up-regulated transcription and secretion of MCP-1. However, HMGB1 and LPS treatment produced no responsive of the NF-kB and AP-1 reporters, and no increase in expression or secretion of MCP-1, in JS2 or JS3 cells. As an endogeous ligand of TLR4, HMGB1 may activate TLR4 signaling and the TLR4-mediated inflammatory response of HSC.