The immunosuppression and immune dysregulation that follows severe injury includes type 2 immune responses manifested by elevations in interleukin (IL) 4, IL5, and IL13 early after injury. We ...hypothesized that IL33, an alarmin released early after tissue injury and a known regulator of type 2 immunity, contributes to the early type 2 immune responses after systemic injury.
Blunt trauma patients admitted to the trauma intensive care unit of a level I trauma center were enrolled in an observational study that included frequent blood sampling. Dynamic changes in IL33 and soluble suppression of tumorigenicity 2 (sST2) levels were measured in the plasma and correlated with levels of the type 2 cytokines and nosocomial infection. Based on the observations in humans, mechanistic experiments were designed in a mouse model of resuscitated hemorrhagic shock and tissue trauma (HS/T). These experiments utilized wild-type C57BL/6 mice, IL33-/- mice, B6.C3(Cg)-Rorasg/sg mice deficient in group 2 innate lymphoid cells (ILC2), and C57BL/6 wild-type mice treated with anti-IL5 antibody. Severely injured human blunt trauma patients (n = 472, average injury severity score ISS = 20.2) exhibited elevations in plasma IL33 levels upon admission and over time that correlated positively with increases in IL4, IL5, and IL13 (P < 0.0001). sST2 levels also increased after injury but in a delayed manner compared with IL33. The increases in IL33 and sST2 were significantly greater in patients that developed nosocomial infection and organ dysfunction than similarly injured patients that did not (P < 0.05). Mechanistic studies were carried out in a mouse model of HS/T that recapitulated the early increase in IL33 and delayed increase in sST2 in the plasma (P < 0.005). These studies identified a pathway where IL33 induces ILC2 activation in the lung within hours of HS/T. ILC2 IL5 up-regulation induces further IL5 expression by CXCR2+ lung neutrophils, culminating in early lung injury. The major limitations of this study are the descriptive nature of the human study component and the impact of the potential differences between human and mouse immune responses to polytrauma. Also, the studies performed did not permit us to make conclusions about the impact of IL33 on pulmonary function.
These results suggest that IL33 may initiate early detrimental type 2 immune responses after trauma through ILC2 regulation of neutrophil IL5 production. This IL33-ILC2-IL5-neutrophil axis defines a novel regulatory role for ILC2 in acute lung injury that could be targeted in trauma patients prone to early lung dysfunction.
High mobility group box 1 (HMGB1) is a multifunctional nuclear protein, probably known best as a prototypical alarmin or damage‐associated molecular pattern (DAMP) molecule when released from cells. ...However, HMGB1 has multiple functions that depend on its location in the nucleus, in the cytosol, or extracellularly after either active release from cells, or passive release upon lytic cell death. Movement of HMGB1 between cellular compartments is a dynamic process induced by a variety of cell stresses and disease processes, including sepsis, trauma, and hemorrhagic shock. Location of HMGB1 is intricately linked with its function and is regulated by a series of posttranslational modifications. HMGB1 function is also regulated by the redox status of critical cysteine residues within the protein, and is cell‐type dependent. This review highlights some of the mechanisms that contribute to location and functions of HMGB1, and focuses on some recent insights on important intracellular effects of HMGB1 during sepsis and trauma.
Review on location‐specific functions of HMGB1 in extracellular space, cytosol, and nucleus.
Sepsis is a life-threatening condition caused by pathogen infection and associated with pyroptosis. Pyroptosis occurs upon activation of proinflammatory caspases and their subsequent cleavage of ...gasdermin D (GSDMD), resulting in GSDMD N-terminal fragments that form membrane pores to induce cell lysis. Here, we show that antioxidant defense enzyme glutathione peroxidase 4 (GPX4) and its ability to decrease lipid peroxidation, negatively regulate macrophage pyroptosis, and septic lethality in mice. Conditional Gpx4 knockout in myeloid lineage cells increases lipid peroxidation-dependent caspase-11 activation and GSDMD cleavage. The resultant N-terminal GSDMD fragments then trigger macrophage pyroptotic cell death in a phospholipase C gamma 1 (PLCG1)-dependent fashion. Administration of the antioxidant vitamin E that reduces lipid peroxidation, chemical inhibition of PLCG1, or genetic Caspase-11 deletion or Gsdmd inactivation prevents polymicrobial sepsis in Gpx4−/− mice. Collectively, this study suggests that lipid peroxidation drives GSDMD-mediated pyroptosis and hence constitutes a potential therapeutic target for lethal infection.
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•Gpx4 deficiency in myeloid cells increases severity of polymicrobial sepsis in mice•Caspase-11-dependent pyroptosis mediates septic death in Gpx4Mye−/− mice•GPX4 decreases lipid peroxidation to block PLCG1-mediated GSDMD activity and pyroptosis•Antioxidant activity of vitamin E promotes survival during sepsis in Gpx4Mye−/− mice
Kang et al. demonstrate that glutathione peroxidase 4 (GPX4) serves a protective role in mice undergoing septic shock. Myeloid-specific deficiency of Gpx4 coordinates lipid peroxidation-dependent caspase-11 activation and gasdermin D-mediated pyroptosis during polymicrobial sepsis. Vitamin E administration reverses Gpx4Mye−/− susceptibility, thereby revealing a potential target for therapeutic intervention for lethal infection.
Excessive activation of the coagulation system leads to life-threatening disseminated intravascular coagulation (DIC). Here, we examined the mechanisms underlying the activation of coagulation by ...lipopolysaccharide (LPS), the major cell-wall component of Gram-negative bacteria. We found that caspase-11, a cytosolic LPS receptor, activated the coagulation cascade. Caspase-11 enhanced the activation of tissue factor (TF), an initiator of coagulation, through triggering the formation of gasdermin D (GSDMD) pores and subsequent phosphatidylserine exposure, in a manner independent of cell death. GSDMD pores mediated calcium influx, which induced phosphatidylserine exposure through transmembrane protein 16F, a calcium-dependent phospholipid scramblase. Deletion of Casp11, ablation of Gsdmd, or neutralization of phosphatidylserine or TF prevented LPS-induced DIC. In septic patients, plasma concentrations of interleukin (IL)-1α and IL-1β, biomarkers of GSDMD activation, correlated with phosphatidylserine exposure in peripheral leukocytes and DIC scores. Our findings mechanistically link immune recognition of LPS to coagulation, with implications for the treatment of DIC.
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•Deletion of caspase-11 prevents disseminated intravascular coagulation (DIC) in sepsis•Deletion of GSDMD prevents caspase-11- and TF-mediated DIC in endotoxemia•GSDMD deficiency inhibits endotoxin-induced TF activation by reducing PS exposure•Activation of GSDMD by caspase-11 triggers Ca2+-dependent PS exposure through TMEM16F
Excessive activation of the coagulation system by endotoxin leads to life-threatening disseminated intravascular coagulation (DIC). Yang, Cheng et al. reveal that caspase-11, a cytosolic LPS receptor, activates the coagulation cascade by enhancing the activation of tissue factor, an initiator of coagulation, through triggering the formation of gasdermin (GASMD) pores and subsequent phosphatidylserine exposure, in a manner independent of cell death.
Inflammation plays a significant role in protecting hosts against pathogens. Inflammation induced by non-infectious, endogenous agents can be detrimental, and if excessive can result in organ and ...tissue damage. The inflammasome is a major innate immune pathway that can be activated via both exogenous pathogen-associated molecular patterns (PAMPs) and endogenous damage-associated molecular patterns (DAMPs). Inflammasome activation involves formation and oligomerization of a protein complex including a NOD-like receptor (NLR), an adaptor protein (ASC) and procaspase-1. This then allows cleavage and activation of caspase-1, followed by downstream cleavage and release of proinflammatory cytokines, IL-1β and IL-18, from innate immune cells. Hyperinflammation caused by unrestrained inflammasome activation is linked with multiple inflammatory diseases, including inflammatory bowel disease, Alzheimer's disease and multiple sclerosis. So there is an understandable rush to understand mechanisms that regulate such potent inflammatory pathways. Autophagy has now been identified as a main regulator of inflammasomes. Autophagy is a vital intracellular process involved in cellular homeostasis, recycling and removal of damaged organelles (e.g. mitochondria) and intracellular pathogens. Autophagy is regulated by proteins that are important in endosomal/phagosomal pathways, as well as by specific autophagy proteins coded for by autophagy-related genes. Cytosolic components are surrounded and contained by a double-membraned vesicle, which then fuses with lysosomes to enable degradation of the contents. Autophagic removal of intracellular DAMPs, inflammasome components or cytokines can reduce inflammasome activation. Similarly, inflammasomes can regulate the autophagic process, allowing for a two-way, mutual regulation of inflammation that may hold the key for treatment of multiple diseases.
Sepsis, severe sepsis and septic shock are the main cause of mortality in non-cardiac intensive care units. Immunometabolism has been linked to sepsis; however, the precise mechanism by which ...metabolic reprogramming regulates the inflammatory response is unclear. Here we show that aerobic glycolysis contributes to sepsis by modulating inflammasome activation in macrophages. PKM2-mediated glycolysis promotes inflammasome activation by modulating EIF2AK2 phosphorylation in macrophages. Pharmacological and genetic inhibition of PKM2 or EIF2AK2 attenuates NLRP3 and AIM2 inflammasomes activation, and consequently suppresses the release of IL-1β, IL-18 and HMGB1 by macrophages. Pharmacological inhibition of the PKM2-EIF2AK2 pathway protects mice from lethal endotoxemia and polymicrobial sepsis. Moreover, conditional knockout of PKM2 in myeloid cells protects mice from septic death induced by NLRP3 and AIM2 inflammasome activation. These findings define an important role of PKM2 in immunometabolism and guide future development of therapeutic strategies to treat sepsis.
Sepsis and septic shock driven by microbial infections are still among the most challenging health problems, causing 11 million deaths worldwide every year. How does the host’s response to pathogen ...infections effectively restore homeostasis instead of precipitating pathogenic and potentially fatal feedforward reactions? Recently, there have been significant new advances in our understanding of the interface between mammalian immunity and coagulation (‘immunocoagulation’) and its impact on sepsis. In particular, the release and activation of F3 (the main initiator of coagulation) from and on myeloid or epithelial cells is facilitated by activating inflammasomes and consequent gasdermin D (GSDMD)-mediated pyroptosis, coupled to signaling via high mobility group box 1 (HMGB1), stimulator of interferon response CGAMP interactor 1 (STING1), or sequestosome 1 (SQSTM1). Pharmacological modulation of the immunocoagulation pathways emerge as novel and potential therapeutic strategies for sepsis.
Sepsis is a life-threatening organ dysfunction caused by the abnormal host response to infection, including to the new virus SARS-CoV-2 responsible for the COVID-19 ongoing pandemic in humans.The crosstalk between a mounting immune dysfunction and abnormal blood coagulation is the basic event favoring sepsis complications and multiple organ failure in humans and should be strategically targeted for therapeutic purposes.GSDMD is an effector of pyroptosis induced by canonical and non-canonical inflammasomes and plays an emerging role in the regulation of coagulation tissue factor F3 release and activation in human or mouse macrophages and monocytes.HMGB1-dependent LPS uptake by AGER or STING1-mediated cytosolic Ca2+ influx by ITPR1 promotes CASP1-, CASP11-, or CASP8-induced GSDMD activation and subsequent F3 release by human or mouse macrophages and monocytes.Extracellular SQSTM1 is a previously unrecognized mediator of septic death in mice that acts to activate the insulin receptor pathway in human or mouse macrophages and monocytes.Globally and/or conditionally deleting Casp1, Casp11, Gsdmd, Hmgb1, Ager, Sting1, Sqstm1, or Insr can prevent inflammation, coagulopathy, multiple organ failure, and lethality in mouse models of bacterial sepsis.
Background and Aims
Itaconate, a metabolite of the tricarboxylic acid cycle, plays anti‐inflammatory roles in macrophages during endotoxemia. The mechanisms underlying its anti‐inflammatory roles ...have been shown to be mediated by the modulation of oxidative stress, an important mechanism of hepatic ischemia–reperfusion (I/R) injury. However, the role of itaconate in liver I/R injury is unknown.
Approach and Results
We found that deletion of immune‐responsive gene 1 (IRG1), encoding for the enzyme producing itaconate, exacerbated liver injury and systemic inflammation. Furthermore, bone marrow adoptive transfer experiments indicated that deletion of IRG1 in both hematopoietic and nonhematopoietic compartments contributes to the protection mediated by IRG1 after I/R. Interestingly, the expression of IRG1 was up‐regulated in hepatocytes after I/R and hypoxia/reoxygenation‐induced oxidative stress. Modulation of the IRG1 expression levels in hepatocytes regulated hepatocyte cell death. Importantly, addition of 4‐octyl itaconate significantly improved liver injury and hepatocyte cell death after I/R. Furthermore, our data indicated that nuclear factor erythroid 2–related factor 2 (Nrf2) is required for the protective effect of IRG1 on mouse and human hepatocytes against oxidative stress–induced injury. Our studies document the important role of IRG1 in the acute setting of sterile injury induced by I/R. Specifically, we provide evidence that the IRG1/itaconate pathway activates Nrf2‐mediated antioxidative response in hepatocytes to protect liver from I/R injury.
Conclusions
Our data expand on the importance of IRG1/itaconate in nonimmune cells and identify itaconate as a potential therapeutic strategy for this unfavorable postsurgical complication.
Ferroptosis is a form of regulated cell death that may facilitate the selective elimination of tumor cells. The tumor suppressor p53 (TP53) has been demonstrated to promote ferroptosis via a ...transcription-dependent mechanism. Here, we show that TP53 limits erastin-induced ferroptosis by blocking dipeptidyl-peptidase-4 (DPP4) activity in a transcription-independent manner. Loss of TP53 prevents nuclear accumulation of DPP4 and thus facilitates plasma-membrane-associated DPP4-dependent lipid peroxidation, which finally results in ferroptosis. These findings reveal a direct molecular link between TP53 and DPP4 in the control of lipid metabolism and may provide a precision medicine strategy for the treatment of colorectal cancer by induction of ferroptosis.
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•TP53 inhibits ferroptosis in human colorectal cancer (CRC) cells•TP53 mediates SLC7A11C expression in human CRC cells•DPP4 mediates ferroptosis in TP53-deficient CRC cells•Loss of TP53 enhances the anticancer activity of erastin in vivo
Xie et al. find that TP53 antagonizes ferroptosis in colorectal cancer (CRC) cells by favoring the localization of DPP4 toward a nuclear, enzymatically inactive pool. This pathway is different from the previously identified function of TP53 as a positive regulator of ferroptosis in non-CRC cells.
Increasing evidence suggests the important role of metabolic reprogramming in the regulation of the innate inflammatory response, but the underlying mechanism remains unclear. Here we provide ...evidence to support a novel role for the pyruvate kinase M2 (PKM2)-mediated Warburg effect, namely aerobic glycolysis, in the regulation of high-mobility group box 1 (HMGB1) release. PKM2 interacts with hypoxia-inducible factor 1α (HIF1α) and activates the HIF-1α-dependent transcription of enzymes necessary for aerobic glycolysis in macrophages. Knockdown of PKM2, HIF1α and glycolysis-related genes uniformly decreases lactate production and HMGB1 release. Similarly, a potential PKM2 inhibitor, shikonin, reduces serum lactate and HMGB1 levels, and protects mice from lethal endotoxemia and sepsis. Collectively, these findings shed light on a novel mechanism for metabolic control of inflammation by regulating HMGB1 release and highlight the importance of targeting aerobic glycolysis in the treatment of sepsis and other inflammatory diseases.
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