Role of toll-like receptors 2 and 4, and the receptor for advanced glycation end products in high-mobility group box 1-induced inflammation in vivo

Abstract

High-mobility group box 1 (HMGB-1) has been reported as a "late" proinflammatory mediator in sepsis. In vitro data have shown that HMGB-1 can induce activation of intracellular signaling pathways via interaction with at least three pattern recognition receptors: Toll-like receptor (TLR) 2, TLR-4, and the receptor for advanced glycation end products (RAGE). The objective of this study was to investigate the role of these receptors in the in vivo response to HMGB-1. Therefore, we first performed a time-series experiment with wild-type (Wt) mice. High-mobility group box 1 induced time-dependent elevations of TNF-alpha, IL-6, monocyte chemoattractant protein 1, and thrombin-antithrombin complex levels in peritoneal lavage fluid and plasma. This inflammatory reaction was accompanied by a prominent and sustained rise in neutrophil counts in the peritoneal cavity. We next administered HMGB-1 to Wt, TLR-2, TLR-4, and RAGE mice. All genotypes showed similar plasma levels of TNF-alpha, IL-6, IL-10, and thrombin-antithrombin complex at 2 h after intraperitoneal injection of HMGB-1. Compared with Wt mice, both TLR-4 and RAGE mice displayed lower TNF-alpha and IL-6 concentrations and lower neutrophil numbers in their peritoneal lavage fluid. In contrast, TLR-2 mice showed increased levels of TNF-alpha and IL-6 in their peritoneal cavity relative to Wt mice. These data indicate that HMGB-1 induces release of cytokines, activation of coagulation, and neutrophil recruitment in vivo via a mechanism that at least in part depends on TLR-4 and RAGE.

Fig. 1. High-mobility group box 1 induces inflammation in vivo

Wild-type mice received an intraperitoneal injection of HMGB-1 (500 µg) at t = 0. Left panels show plasma levels, and right panels show concentrations/numbers in PLF. Data are expressed as means ± SEM (n = 4 mice per time point). P values indicate overall differences in time.

Fig. 2. High-mobility group box 1–induced inflammation is partially dependent on TLR-4 and RAGE

Mice received an intraperitoneal injection of HMGB-1 (500 µg), and plasma and PLF were obtained 2 h later. Left panels show plasma levels, and right panels show concentrations/numbers in PLF. Baseline values of the measurements presented are given in Figure 1; there were no differences in these values between Wt and TLR-2^−/−, TLR-4^−/−, or RAGE^−/− mice. Data are expressed as means ± SEM (n = 8 mice per group). *P < 0.05 vs. Wt mice. **P < 0.05 vs. Wt mice.