Activated Protein C Inhibits High Mobility Group Box 1 Signaling in Endothelial Cells,

Abstract 3274

A pathogenic role for high mobility group box 1 (HMGB1) protein has been postulated in severe sepsis. Activated protein C (APC) is the only FDA-approved drug for severe sepsis, however, its effect on HMGB1 signaling has never been investigated. Here, we monitored the effect of APC on the LPS-mediated release of HMGB1 and the HMGB1-mediated modulation of pro-inflammatory signaling responses in human umbilical vein endothelial cells. APC potently inhibited the LPS-mediated release of HMGB1 and down-regulated the cell surface expression of VCAM-1, ICAM-1 and E-selectin as well as the adhesion of the monocytic cell line, THP-1, to HMGB1-activated endothelial cells. HMGB1 up-regulated pro-inflammatory responses by interacting with three pathogen-related pattern recognition receptors: toll-like receptors 2, 4 and the receptor for advanced glycation end products. APC not only inhibited the LPS-mediated HMGB1 release, but also down-regulated the cell surface expression of all three HMGB1 receptors on endothelial cells. The protective effects of APC were mediated through both EPCR and PAR-1, as evidenced by the function-blocking antibodies to either receptor abrogating the signaling function of APC. Interestingly, a thrombin derivative containing the Gla-domain of APC recapitulated all protective effects of APC with a 20–50-fold higher efficacy. These results suggest that the EPCR- and PAR-1-dependent protective effects of APC in severe sepsis may partially be mediated through the inhibition of HMGB1 signaling and that the chimeric thrombin mutant has potential therapeutic utility for severe sepsis.