Hemorrhagic Shock Induces NAD(P)H Oxidase Activation in Neutrophils: Role of HMGB1-TLR4 Signaling

Abstract

Hemorrhagic shock/resuscitation (HS/R)-induced generation of reactive oxygen species (ROS) plays an important role in posthemorrhage inflammation and tissue injury. We have recently reported that HS/R-activated neutrophils (PMN), through release of ROS, serve an important signaling function in mediating alveolar macrophage priming and lung inflammation. PMN NAD(P)H oxidase has been thought to be an important source of ROS following HS/R. TLR4 sits at the interface of microbial and sterile inflammation by mediating responses to both bacterial endotoxin and multiple endogenous ligands, including high-mobility group box 1 (HMGB1). Recent studies have implicated HMGB1 as an early mediator of inflammation after HS/R and organ ischemia/reperfusion. In the present study, we tested the hypothesis that HS/R activates NAD(P)H oxidase in PMN through HMGB1/TLR4 signaling. We demonstrated that HS/R induced PMN NAD(P)H oxidase activation, in the form of phosphorylation of p47phox subunit of NAD(P)H oxidase, in wild-type mice; this induction was significantly diminished in TLR4-mutant C3H/HeJ mice. HMGB1 levels in lungs, liver, and serum were increased as early as 2 h after HS/R. Neutralizing Ab to HMGB1 prevented HS/R-induced phosphorylation of p47phox in PMN. In addition, in vitro stimulation of PMN with recombinant HMGB1 caused TLR4-dependent activation of NAD(P)H oxidase as well as increased ROS production through both MyD88-IRAK4-p38 MAPK and MyD88-IRAK4-Akt signaling pathways. Thus, PMN NAD(P)H oxidase activation, induced by HS/R and as mediated by HMGB1/TLR4 signaling, is an important mechanism responsible for PMN-mediated inflammation and organ injury after hemorrhage.

Tissue damage negatively regulates LPS-induced macrophage necroptosis

“…Our previous studies and those of others have shown that trauma-induced release of DAMPs serves as a priming factor, which often enhances inflammatory responses to infection and bacterial products. [45][46][47][48][49][50] Those results, therefore, suggested that blocking DAMP-signaling may attenuate inflammatory responses to a secondary infection. In the current study, however, we demonstrate a novel finding that Part of the mechanism for upregulation of caveolin-1 is through RAGE-MyD88 signaling and downstream activation of Cdc42, leading to nuclear translocation of transcription factor Sp1 and alteration of caveolin-1 expression (Figure 7).…”

HMGB1 Develops Enhanced Proinflammatory Activity by Binding to Cytokines

“…Several studies indicated that HMGB1 could interact with multiple receptors, including TLR2, TLR4, the receptor for advanced glycation end products, and, most recently, TLR9 (10,17,19,20,26). Similarly, varying intracellular signaling pathways, involving p38 MAP, ERK, JNK, and other kinases, were reported to be activated in HMGB1-exposed cells (10, 11, 19 -22, 27-32).…”

Ethyl Pyruvate Rescues Nigrostriatal Dopaminergic Neurons by Regulating Glial Activation in a Mouse Model of Parkinson’s Disease

“…Upon stimulation, the oxidase complex is activated, a process that involves phosphorylation of p47 phox on serine residues and recruitment of the cytosolic components to the membrane-bound components, including gp91 phox , to assemble the active NADPH oxidase (44,45). Thus, both phosphorylation of p47 phox and binding of p47 phox and gp91 phox are thought to be important aspects of NADPH oxidase activation (46); the resulting activation leads to ROS generation (18). The generation of ROS by NADPH oxidase is increased in the SN of PD patients (7) and in the SN of MPTP-treated mice (15), and oxidants originating from microglia are thought to mediate the loss of DA neurons in the SN (47).…”