Background and Purpose Microvascular barrier breakdown is a hallmark of sepsis that is associated with sepsis‐induced multiorgan failure. Histidine‐rich glycoprotein (HRG) is a 75‐kDa plasma protein that was demonstrated to improve the survival of septic mice through regulation of cell shape, spontaneous ROS production in neutrophils, and adhesion of neutrophils to vascular endothelial cells. We investigated HRG's role in the LPS/TNF‐α‐induced barrier dysfunction of endothelial cells in vitro and in vivo and the possible mechanism, to clarify the definitive roles of HRG in sepsis. Experimental Approach EA.hy 926 endothelial cells were pretreated with HRG or human serum albumin before stimulation with LPS/TNF‐α. A variety of biochemical assays were applied to explore the underlying molecular mechanisms on how HRG protected the barrier function of vascular endothelium. Key Results Immunostaining results showed that HRG maintains the endothelial monolayer integrity by inhibiting cytoskeleton reorganization, losses of VE‐cadherin and β‐catenin, focal adhesion kinase degradation, and cell detachment induced by LPS/TNF‐α. HRG also inhibited the cytokine secretion from endothelial cells induced by LPS/TNF‐α, which was associated with reduced NF‐κB activation. Moreover, HRG effectively prevented the LPS/TNF‐α‐induced increase in capillary permeability in vitro and in vivo. Finally, Western blot results demonstrated that HRG prevented the phosphorylation of MAPK family and RhoA activation, which are involved mainly in the regulation of cytoskeleton reorganization and barrier permeability. Conclusions and Implications Taken together, our results demonstrate that HRG has protective effects on vascular barrier function in vitro and in vivo, which may be due to the inhibition of MAPK family and Rho activation.

High-mobility group box-1 (HMGB1) protein has been postulated to play a pathogenic role in severe sepsis. Histidine-rich glycoprotein (HRG), a 75 kDa plasma protein, was demonstrated to improve the survival rate of septic mice through the regulation of neutrophils and endothelium barrier function. As the relationship of HRG and HMGB1 remains poorly understood, we investigated the effects of HRG on HMGB1-mediated pathway in endothelial cells, focusing on the involvement of specific receptors for HRG. HRG potently inhibited the HMGB1 mobilization and effectively suppressed rHMGB1-induced inflammatory responses and expression of all three HMGB1 receptors in endothelial cells. Moreover, we first clarified that these protective effects of HRG on endothelial cells were mediated through C-type lectin domain family 1 member A (CLEC-1A) receptor. Thus, current study elucidates protective effects of HRG on vascular endothelial cells through inhibition of HMGB1-mediated pathways may contribute to the therapeutic effects of HRG on severe sepsis.

Nishibori (2020): Histidine-rich glycoprotein possesses antioxidant activity through self-oxidation and inhibition of hydroxyl radical production via chelating divalent metal ions in Fenton's reaction, Free Radical Research,

No abstract

BackgroundSystemic allergic reaction is characterized by vasodilation and vascular leakage, which causes a rapid, precipitous and sustained decrease in arterial blood pressure with a concomitant decrease of cardiac output. Histamine is a major mediator released by mast cells in allergic inflammation and response. It causes a cascade of inflammation and strongly increases vascular permeability within minutes through its four G-protein-coupled receptors (GPCRs) on endothelial cells. High mobility group box-1 (HMGB1), a nonhistone chromatin-binding nuclear protein, can be actively secreted into the extracellular space by endothelial cells. HMGB1 has been reported to exert pro-inflammatory effects on endothelial cells and to increase vascular endothelial permeability. However, the relationship between histamine and HMGB1-mediated signaling in vascular endothelial cells and the role of HMGB1 in anaphylactic-induced hypotension have never been studied.Methods and resultsEA.hy 926 cells were treated with different concentrations of histamine for the indicated periods. The results showed that histamine induced HMGB1 translocation and release from the endothelial cells in a concentration- and time-dependent manner. These effects of histamine were concentration-dependently inhibited by d-chlorpheniramine, a specific H1 receptor antagonist, but not by H2 or H3/4 receptor antagonists. Moreover, an H1-specific agonist, 2-pyridylethylamine, mimicked the effects of histamine, whereas an H2-receptor agonist, 4-methylhistamine, did not. Adrenaline and noradrenaline, which are commonly used in the clinical treatment of anaphylactic shock, also inhibited the histamine-induced HMGB1 translocation in endothelial cells. We therefore established a rat model of allergic shock by i.v. injection of compound 48/80, a potent histamine-releasing agent. The plasma HMGB1 levels in compound 48/80-injected rats were higher than those in controls. Moreover, the treatment with anti-HMGB1 antibody successfully facilitated the recovery from compound 48/80-induced hypotension.ConclusionHistamine induces HMGB1 release from vascular endothelial cells solely through H1 receptor stimulation. Anti-HMGB1 therapy may provide a novel treatment for life-threatening systemic anaphylaxis.