Despite recent advances in antibiotic therapy and intensive care, sepsis remains the most common cause of death in the intensive care units, claiming > 225,000 victims annually in the U.S. alone. The pathogenesis of sepsis remains obscure, but is partly attributable to dys-regulated inflammatory responses sustained by late pro-inflammatory mediators (e.g., HMGB1, CIRP, and NO). Our seminal discovery of HMGB1 as a late mediator of lethal systemic inflammation (LSI) (Science, 285: 248-51, 1999) has prompted an investigation of the intricate molecular mechanisms underlying the pharmacological modulation of HMGB1 secretion by traditional herbal medicine. Gancao (Radix glycyrrhizae, or licorice) has been traditionally used in the treatment of peptic ulcer, hepatic injury, and hepatitis, but its protective mechanisms remain elusive. Our preliminary data indicated that carbenoxolone (CBX), a derivative of the major Gancao component, glycyrrhizin (glycyrrhizic acid, GZA), dose-dependently abrogated LPS-induced PKR (double-stranded RNA-activated protein kinase R) phosphorylation and HMGB1 secretion, and rescued mice from lethal sepsis (induced by cecal ligation and puncture, CLP) even if given in a delayed fashion. Meanwhile, compelling evidence has emerged to support the critical roles of: i) STAT1 signaling in cytoplasmic HMGB1 translocation (PNAS, 111: 3068-73, 2014); and ii) PKR in inflammasome activation and HMGB1 secretion (Nature, 488: 670-4, 2012). In light of the possible role of Cx43 and Panx1 hemichannels in ATP efflux, as well as the requirement of ATP for ultrapure LPS-induced HMGB1 secretion, it is important to test a novel hypothesis that prolonged stimulation with crude LPS or other key HMGB1 secretion stimuli (such as SAA and CIRP) may lead to upregulation of Panx1 and/or Cx43 hemichannel proteins, which facilitate ATP-dependent PKR and STAT1 phosphorylation, thereby contributing to HMGB1 secretion and lethal systemic inflammation (LSI). Accordingly, we propose to test: 1) the novel hypothesis that crude LPS and other important inflammatory stimuli (e.g., SAA and CIRP) up-regulate Panx1 and Cx43 hemichannel expression, and trigger PKR phosphorylation and HMGB1 secretion (Aim 1); 2) the novel roles of Panx1 and Cx43 hemichannels in the pathogenesis of lethal systemic inflammation (LSI) (Aim 2); and 3) the novel mechanisms by which Panx1 or Cx43 hemichannel inhibitors (such as mimetic peptides antagonists, neutralizing antibodies, and herbal inhibitors such as GZA and CBX) affect the outcomes of LSI (Aim 3). Collectively, these proposed studies will improve our understanding of the mechanisms by which herbal medicine effectively inhibits exogenous PAMPs or endogenous proinflammatory mediators-induced HMGB1 secretion, and shed light on the development of novel hemichannel-targeting therapies for LSI.
Sepsis remains the most common cause of death in the intensive care units, claiming > 225,000 victims annually in the U.S. alone. Our seminal discovery of HMGB1 as a late mediator of lethal systemic inflammation (LSI) (Science, 285: 248-51, 1999) has prompted an investigation of the intricate molecular mechanisms underlying the pharmacological modulation of HMGB1 secretion and action by an important medicinal herb, Gancao (Radix glycyrrhizae, or licorice). The completion of these exciting studies will further improve our understanding of the mechanisms underlying herbal medicine-mediated innate immune modulation, and shed light on the development of novel hemichannel-targeting therapeutic strategies for sepsis and other inflammatory diseases.
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