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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.

Platelets have been shown to play an important immunomodulatory role in the pathogenesis of various diseases through their interactions with other immune and nonimmune cells. Sepsis is a major cause of death in the United States, and many of the mechanisms driving sepsis pathology are still unresolved. Monocytes have recently received increasing attention in sepsis pathogenesis, and multiple studies have associated increased levels of platelet-monocyte aggregates observed early in sepsis with clinical outcomes in sepsis patients. These findings suggest platelet-monocyte aggregates may be an important prognostic indicator. However, the mechanisms leading to platelet interaction and aggregation with monocytes, and the effects of aggregation during sepsis are still poorly defined. There are few studies that have really investigated functions of platelets and monocytes together, despite a large body of research showing separate functions of platelets and monocytes in inflammation and immune responses during sepsis. The goal of this review is to provide insights into what we do know about mechanisms and biological meanings of platelet-monocyte interactions, as well as some of the technical challenges and limitations involved in studying this important potential mechanism in sepsis pathogenesis. Improving our understanding of platelet and monocyte biology in sepsis may result in identification of novel targets that can be used to positively affect outcomes in sepsis.

Peritoneal resident macrophages (PRMs) have been a prominent topic in the research field of immunology due to their critical roles in immune surveillance in the peritoneal cavity. PRMs initially develop from embryonic progenitor cells and are replenished by bone marrow origin monocytes during inflammation and aging. Furthermore, PRMs have been shown to crosstalk with other cells in the peritoneal cavity to control the immune response during infection, injury, and tumorigenesis. With the advance in genetic studies, GATA-binding factor 6 (GATA6) has been identified as a lineage determining transcription factor of PRMs controlling the phenotypic and functional features of PRMs. Here, we review recent advances in the developmental origin, the phenotypic identity, and functions of PRMs, emphasizing the role of GATA6 in the pathobiology of PRMs in host defense, tissue repairing, and peritoneal tumorigenesis.

Hemorrhagic shock with tissue trauma (HS/T) leads to the activation of a system-wide immune-inflammatory response that involves all organs and body compartments. Recent advances in single-cell analysis permit the simultaneous assessment of transcriptomic patterns in a large number of cells making it feasible to survey the landscape of immune cell responses across numerous anatomic sites. Here, we used single-cell RNA sequencing of leukocytes from the blood, liver, and spleen to identify the major shifts in gene expression by cell type and compartment in a mouse HS/T model. At 6 h, dramatic changes in gene expression were observed across multiple-cell types and in all compartments in wild-type mice. Monocytes from circulation and liver exhibited a significant upregulation of genes associated with chemotaxis and migration and a simultaneous suppression of genes associated with interferon signaling and antigen presentation. In contrast, liver conventional DC exhibited a unique pattern compared with other myeloid cells that included a pronounced increase in major histocompatibility complex class II (MHCII) gene expression. The dominant pattern across all compartments for B and T cells was a suppression of genes associated with cell activation and signaling after HS/T. Using complement factor 3 (C3) knockout mice we unveiled a role for C3 in the suppression of monocyte Major Histocompatibility Complex class II expression and activation of gene expression associated with migration, phagocytosis and cytokine upregulation, and an unexpected role in promoting interferon-signaling in a subset of B and T cells across all three compartments after HS/T. This transcriptomic landscape study of immune cells provides new insights into the host immune response to trauma, as well as a rich resource for further investigation of trauma-induced immune responses and complement in driving interferon signaling.

Immune checkpoint inhibitors can improve the prognosis of patients with advanced malignancy, however, only a small subset of advanced colorectal cancer patients in microsatellite-instability-high or mismatch-repair-deficient colorectal cancer can benefit from immunotherapy. Unfortunately, the mechanism behind this ineffectiveness is unclear. The tumor microenvironment plays a critical role in cancer immunity, and may contribute to the inhibition of immune checkpoint inhibitors and other novel immunotherapies in patients with advanced cancer. Herein, we demonstrate that the DNase I enzyme plays a pivotal role in the degradation of NETs, significantly dampening the resistance to anti-PD-1 blockade in a mouse colorectal cancer model by attenuating tumor growth. Remarkably, DNase I decreases tumor-associated neutrophils and the formation of MC38 tumor cell-induced neutrophil extracellular trap formation in vivo. Mechanistically, the inhibition of neutrophil extracellular traps with DNase I results in the reversal of anti-PD-1 blockade resistance through increasing CD8+ T cell infiltration and cytotoxicity. These findings signify a novel approach to targeting the tumor microenvironment using DNase I alone or in combination with immune checkpoint inhibitors.

Pre-operative exercise therapy improves outcomes for many patients who undergo surgery. Despite the well-known effects on tolerance to systemic perturbation, the mechanisms by which pre-operative exercise protects the organ that is operated on from inflammatory injury are unclear. Here, we show that four-week aerobic pre-operative exercise significantly attenuates liver injury and inflammation from ischaemia and reperfusion in mice. Remarkably, these beneficial effects last for seven more days after completing pre-operative exercising. We find that exercise specifically drives Kupffer cells toward an anti-inflammatory phenotype with trained immunity via metabolic reprogramming. Mechanistically, exercise-induced HMGB1 release enhances itaconate metabolism in the tricarboxylic acid cycle that impacts Kupffer cells in an NRF2-dependent manner. Therefore, these metabolites and cellular/molecular targets can be investigated as potential exercise-mimicking pharmaceutical candidates to protect against liver injury during surgery. Zhang et al. show that pre-operative exercise protects against liver injury by driving Kupffer cells towards an anti-inflammatory phenotype via itaconate metabolism.

Group 2 innate lymphoid cells (ILC2), despite their scarcity, are the dominant innate lymphoid cell population in the lung, orchestrating innate immunity and adaptive immunity (Germain and Huang. Curr Opin Immunol 56:76-81, 2019; Krabbendam et al. Immunol Rev 286:74-85, 2018; Mindt et al. Front Immunol 9:840, 2018) . Recent studies reveal that ILC2 play critical roles in inflammation-associated lung injury during sepsis (Lai et al. Cell Death Dis 9:369, 2018; Xu et al. Immunol Cell Biol 96:935-947). Therefore, studies aiming to understand the pathobiology of ILC2 may reveal new therapeutic strategies for sepsis. However, the identification of ILC2 requires multiple surface and intracellular markers. This makes the detection of ILC2 in the lung challenging. Here we describe a method to detect ILC2 in the mouse lung using flow cytometry.

Introduction: Colorectal cancer (CRC) is a devastating disease, causing mortality worldwide, with the majority of the patients dying from hepatic metastasis. Resection of hepatic metastases improves overall disease-free survival. Unfortunately, not all patients have a successful surgical outcome. Pre-operative exercise therapy (PEx) have been demonstrated to be beneficial in the prevention of post-operative complications. Trained immunity in myeloid cells leads to an aggravated long-term inflammatory phenotype upon a secondary stimulation, a process that results from orchestrated metabolic-epigenetic changes. We hypothesize that PEx initially reverts pro-tumorigenic inflammatory responses following surgical stress and maintains an anti-tumor immune microenvironment through modulating Kupffer cells (KCs) with anti-tumor immunity. Methods: 8-week C57BL/6 mice were randomly divided into PEx and sedentary (Sed) groups, mice with PEx run on a motorized treadmill at a speed of 12.5 m/min for 60 min/day, 5 days/week for 4 weeks. 105 MC38 cells were injected directly through portal vein and surgical stress was subjected to a model of partial hepatic ischemia and reperfusion. The tumor progression was determined by bioluminescent imaging weekly. Both hepatic and tumor CD45+ cells from PEx or Sed mice 3 weeks after IR were submitted for single-cell RNA sequencing (scRNA-seq). Results: 4 weeks of PEx significantly reduces metastasis in the liver along 3 weeks after IR, compared with Sed controls. For the scRNA-seq, 11 cell lineages (KCs, monocytes, neutrophils, DCs, TAMs, TANs, B cells, CD4+ T cells, CD8+ T cells, NK cells, and NKT cells) were identified and annotated according to the transcriptomic profile of feature genes expression. Surprisingly, discontinued 4-week-PEx still led to a significant transcriptomic shift in the KCs. 3 clusters from the entire KCs population were unique in PEx mice. In contrast, 2 Clusters were derived from Sed mice. PEx-relevant KCs are enriched in gene expression related to the anti-tumor phenotype, whereas Sed-relevant KCs are enriched in gene expression related to pro-tumor or immunosuppressive phenotype, which suggests that PEx modulates transcriptomic changes in KCs towards an anti-tumor phenotype. Furthermore, with our established ex vivo trained immunity assay, we observe a clear induction of trained immunity in PEx-KCs when co-cultured with MC38 tumor cells, with noticeably higher levels of anti-tumor cytokines interferon (IFN)-γ and TNF-α compared to Sed-KCs. Summary: Our study is one of the first to show that PEx alters the hepatic immune microenvironment by shifting KC to a tumoricidal phenotype. This work offers a rationale for PEx for cancer patients undergoing liver surgery thereby decreasing post-operative metastases and morbidity. Citation Format: Hongji Zhang, Xiang Cheng, Chengli Shen, Meihong Deng, Allan Tsung, Hai Huang. Preoperative exercise therapy attenuates the progression of liver metastases following surgical stress by inducing Kupffer cells-mediated anti-tumor trained immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2109.

Additional file 1. Figure S1. In vitro toxicity profile of MaR1. Primary cultured mouse HCs and NPCs were exposed to escalating concentrations of Maresin 1 (MaR1), and cytotoxicity was evaluated using a CKK-8 assay. Figure S2. ALXR and LGR6 expression during hepatic I/Rinjury

Group 2 innate lymphoid cells (ILC2), despite their scarcity, are the dominant innate lymphoid cell population in the lung, orchestrating innate immunity and adaptive immunity (Germain and Huang. Curr Opin Immunol 56:76-81, 2019; Krabbendam et al. Immunol Rev 286:74-85, 2018; Mindt et al. Front Immunol 9:840, 2018) . Recent studies reveal that ILC2 play critical roles in inflammation-associated lung injury during sepsis (Lai et al. Cell Death Dis 9:369, 2018; Xu et al. Immunol Cell Biol 96:935-947). Therefore, studies aiming to understand the pathobiology of ILC2 may reveal new therapeutic strategies for sepsis. However, the identification of ILC2 requires multiple surface and intracellular markers. This makes the detection of ILC2 in the lung challenging. Here we describe a method to detect ILC2 in the mouse lung using flow cytometry.

IL-33 and WNT1-inducible secreted protein (WISP1) play central roles in acute lung injury (ALI) induced by mechanical ventilation with moderate tidal volume (MTV) in the setting of sepsis. Here, we sought to determine the inter-relationship between IL-33 and WISP1 and the associated signaling pathways in this process.We used a two-hit model of cecal ligation puncture (CLP) followed by MTV ventilation (4 h 10 mL/kg) in wild-type, IL-33-/- or ST2-/- mice or wild-type mice treated with intratracheal antibodies to WISP1. Macrophages (Raw 264.7 and alveolar macrophages from wild-type or ST2-/- mice) were used to identify specific signaling components.CLP + MTV resulted in ALI that was partially sensitive to genetic ablation of IL-33 or ST2 or antibody neutralization of WISP1. Genetic ablation of IL-33 or ST2 significantly prevented ALI after CLP + MTV and reduced levels of WISP1 in the circulation and bronchoalveolar lung fluid. rIL-33 increased WISP1 in alveolar macrophages in an ST2, PI3K/AKT, and ERK dependent manner. This WISP1 upregulation and WNT β-catenin activation were sensitive to inhibition of the β-catenin/TCF/CBP/P300 nuclear pathway.We show that IL-33 drives WISP1 upregulation and ALI during MTV in CLP sepsis. The identification of this relationship and the associated signaling pathways reveals a number of possible therapeutic targets to prevent ALI in ventilated sepsis patients.

Background: The mechanisms by which moderate tidal volume ventilation (MTV) may exacerbate preexisting lung injury remain unclear. We hypothesized that in two hit model (polyinosinic-polycytidylic acid (Poly(I:C)), a synthetic analog of dsRNA and MTV), systemic endotoxemia via gut-lung axis would lead to non-canonical (i.e. caspase-11 dependent) and canonical (caspase-1 dependent) inflammasome activation and programmed necrotic cell death (pyroptosis) contributing to acute lung injury (ALI) in intact mice.Methods: Anesthetized mice were administered Poly(I:C) intratracheally and then 6 h later, they were mechanically ventilated for 4 h with otherwise non-injurious MTV (10ml/kg). Changes in intestinal and alveolar capillary permeability were measured. Further documentation of ALI was assessed by evans blue albumin permeability, protein and IL-1 family concentration in bronchoalveolar lavage fluid (BALF) or plasma, and histopathology in cohorts of wildtype, whole body genetically ablated caspase-11 (caspase-11-/-), caspase-1/caspase-11 double knockout (caspase-1/11-/-), gasdermin D (GSDMD-/-), and NLRP3-/- mice. Results: Non-injurious MTV exacerbated mild Poly(I:C) lung injury including disruption of alveolar-capillary barrier and increased levels of IL-6, HMGB1, IL-1β in BALF and IL-18 in plasma. Combined (Poly(I:C)-MTV) injury was associated with increase in gastrointestinal permeability and endotoxin in plasma and BALF. Poly(I:C)-MTV injury was sensitive to caspase-11 deletion with no further contribution of caspase-1 except for maturation and release of IL-18 (that itself was sensitive to deletion of NLRP3). Combined injury led to large increases in pro-caspase-11 and its cleaved product as well as cleaved product of caspase-1. Genetic ablation of GSDMD attenuated alveolar-capillary disruption and maturation and release of cytokines in combined injury model.Conclusions: The previously noted TLR-4 independent exacerbation of mild Poly(I:C)-induced ALI by otherwise non-injurious MTV is associated with an increase in gut permeability resulting in systemic endotoxemia. The gut-lung axis resulted in activation of pulmonary non-canonical (cytosolic mediated caspase-11 activation) and canonical (caspase-1) inflammasome (NLRP3) mediated ALI in this two hit model resulting in GSDMD sensitive alveolar capillary barrier disruption, pyroptosis (in alveolar macrophages) and cytokine maturation and release (IL-1β; IL-18). Pharmacologic strategies at disrupting communication between gut and lung, inhibition of inflammasomes or effector molecule (GSDMD) in pyroptosis may be useful in ALI.

Immune dysfunction is an important factor driving mortality and adverse outcomes after trauma but remains poorly understood, especially at the cellular level. To deconvolute the trauma-induced immune response, we applied single-cell RNA sequencing to circulating and bone marrow mononuclear cells in injured mice and circulating mononuclear cells in trauma patients. In mice, the greatest changes in gene expression were seen in monocytes across both compartments. After systemic injury, the gene expression pattern of monocytes markedly deviated from steady state with corresponding changes in critical transcription factors, which can be traced back to myeloid progenitors. These changes were largely recapitulated in the human single-cell analysis. We generalized the major changes in human CD14+ monocytes into 6 signatures, which further defined 2 trauma patient subtypes (SG1 vs. SG2) identified in the whole-blood leukocyte transcriptome in the initial 12 hours after injury. Compared with SG2, SG1 patients exhibited delayed recovery, more severe organ dysfunction, and a higher incidence of infection and noninfectious complications. The 2 patient subtypes were also recapitulated in burn and sepsis patients, revealing a shared pattern of immune response across critical illness. Our data will be broadly useful to further explore the immune response to inflammatory diseases and critical illness.

Notch or STING, which is in charge of CD4 T cell fate?, Dysregulation of T cell apoptosis contributes to the pathogenesis of acute systemic inflammation–induced immunosuppression, as seen in sepsis and trauma. However, the regulatory mechanisms of T cell apoptosis are unclear. Activation of stimulator of interferon genes (STING) has been shown to induce T cell apoptosis. Notch was previously identified as the top negative regulator of STING in macrophages through a kinase inhibitor library screening. However, how Notch signaling regulates STING activation in T cells is unknown. Here, using a γ-secretase inhibitor to block Notch signaling, we found that Notch protected CD4 T cells from STING-mediated apoptosis during endotoxemia. Mechanistically, Notch intracellular domain (NICD) interacted with STING at the cyclic dinucleotide (CDN) binding domain and competed with CDN to inhibit STING activation. In conclusion, our data reveal a previously unidentified role of Notch in negative regulation of STING-mediated apoptosis in CD4 T cells.

Introduction Resection of colorectal cancer hepatic metastases improves overall disease-free survival. Unfortunately, not all patients have a successful surgical outcome. Pre-operative exercise therapy (PEx) have been demonstrated to be beneficial in the prevention of post-operative complications. We hypothesize that PEx initially reverts pro-tumorigenic inflammatory responses following surgical stress and maintains an anti-tumor immune microenvironment through modulating Kupffer cells (KCs) with anti-tumor immunity. Methods 8W C57BL/6 mice were randomly divided into PEx and sedentary (Sed) groups, mice with PEx run on a motorized treadmill at a speed of 12.5 m/min for 60 min/day, 5 days/W for 4 weeks. 105 MC38 cells were injected directly through portal vein and surgical stress was subjected to partial hepatic ischemia and reperfusion model. Both hepatic and tumor CD45+ cells from PEx or Sed mice 3 W after IR were submitted for single-cell RNA sequencing (scRNA-seq). Results 4 weeks of PEx significantly reduces metastasis in the liver along 3 weeks after IR, compared with Sed controls. For the scRNA-seq, 11 cell lineages were identified and annotated according to the transcriptomic profile of feature genes expression. Surprisingly, discontinued 4-week-PEx still led to a significant transcriptomic shift in the KCs. 3 clusters from the entire KCs population were unique in PEx mice. In contrast, 2 Clusters were derived from Sed mice. PEx-relevant KCs are enriched in gene expression related to the anti-tumor phenotype, whereas Sed-relevant KCs are enriched in gene expression related to pro-tumor or immunosuppressive phenotype, which suggests that PEx modulates transcriptomic changes in KCs towards an anti-tumor phenotype. Supported by National Institutes of Health R01-CA214865-01 and R01-GM95566-06 to AT, National Institutes of Health R01-AI152044 to MD, and National Institutes of Health R01-GM137203 and Joseph A. Patrick Research Fellowship in Transplantation to HH.

Immune checkpoint blockade (ICB) has been shown to improve the prognosis of patients with advanced malignancy; however, most patients do not respond to ICB therapy. Peritoneal resident macrophages (PRMs) are critical for peritoneal immunity in health and disease. A recent study has demonstrated that PRMs dampen the therapeutic efficacy of ICB via impairing anti-tumor CD8+ T cell immunity. Here we show that activation of TLR9, an endosomal DNA sensor, in fibroblastic reticular cells (FRCs) negatively regulates PRM retention. Mechanistically, TLR9 in FRCs suppresses retinol metabolism and thus suppresses GATA6 expression in PRMs. Notably, combined treatment of ODN1585, a TLR9 agonist, and anti-PD1 substantially improves the efficacy of anti-PD-1 immune checkpoint blockade therapies in MC-38 and CT26 colorectal carcinoma cell lines-induced peritoneal tumor in mice, evidenced by decreased tumor burden and mortality rate. The improvement is associated with an increase in the percent of CD8+ T cells and a decrease in the percent of CD39+ exhausted CD8+ T cells. Furthermore, global knockout of TLR9 or specific knockout of TLR9 in FRC diminished the beneficial effect of ODN1585 and anti-PD-1 combined treatment on tumor burden and survival. These data demonstrate the potential utility of the FRC-TLR9 signaling in modulating PRM retention to improve the therapeutic efficacy of ICB in peritoneal tumors. Supported by grants from NIH / startup fund

Liver ischemia-reperfusion (I/R) injury occurs through induction of oxidative stress and release of damage-associated molecular patterns (DAMPs), including cytosolic DNA released from dysfunctional mitochondria or from the nucleus. Cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) synthase (cGAS) is a cytosolic DNA sensor known to trigger stimulator of interferon genes (STING) and downstream type 1 interferon (IFN-I) pathways, which are pivotal innate immune system responses to pathogen. However, little is known about the role of cGAS/STING in liver I/R injury. We subjected C57BL/6 (WT), cGAS knockout (cGAS−/−), and STING-deficient (STINGgt/gt) mice to warm liver I/R injury and that found cGAS−/− mice had significantly increased liver injury compared with WT or STINGgt/gt mice, suggesting a protective effect of cGAS independent of STING. Liver I/R upregulated cGAS in vivo and also in vitro in hepatocytes subjected to anoxia/reoxygenation (A/R). We confirmed a previously published finding that hepatocytes do not express STING under normoxic conditions or after A/R. Hepatocytes and liver from cGAS−/− mice had increased cell death and reduced induction of autophagy under hypoxic conditions as well as increased apoptosis. Protection could be restored in cGAS−/− hepatocytes by overexpression of cGAS or by pretreatment of mice with autophagy inducer rapamycin. Our findings indicate a novel protective role for cGAS in the regulation of autophagy during liver I/R injury that occurs independently of STING. NEW & NOTEWORTHY Our studies are the first to document the important role of cGAS in the acute setting of sterile injury induced by I/R. Specifically, we provide evidence that cGAS protects liver from I/R injury in a STING-independent manner.

Additional file 1: Table S1. Composition of rodent special diets. Table S2. Primer sequence used for RT-PCR.

High-mobility group box-1 (HMGB1), a ubiquitous nuclear protein, acts as a late mediator of lethality when released extracellularly during sepsis. The major source of circulating HMGB1 in sepsis is hepatocytes. However, the mechanism of HMGB1 release of hepatocytes during sepsis is not very clear. We have previously shown that bacterial endotoxin [lipopolysaccharide (LPS)] sensing pathways, including Toll-like receptor (TLR)4 and caspase-11, regulate hepatocyte HMGB1 release in response to LPS. Here, we report the novel function of caspase-11 and gasdermin D (GsdmD) in LPS-induced active HMGB1 released from hepatocytes. HMGB1 release during endotoxemia was caspase-11/GsdmD dependent via an active way in vivo and in vitro. Caspase-11/GsdmD was responsible for HMGB1 translocation from nucleus to the cytoplasm via calcium changing-induced phosphorylation of calcium-calmodulin kinase kinase (camkk)β during endotoxemia. Cleaved GsdmD accumulated on the endoplasmic reticulum, suggesting this may lead to calcium leak and intracellular calcium increase. Furthermore, we investigated that exosome was an important pathway for HMGB1 release from hepatocytes; this process was dependent on TLR4, independent of caspase-11 and GsdmD in vivo and in vitro. These findings provide a novel mechanism that TLR4 signaling results in an increase in caspase-11 expression, as well as increased exosome release, while caspase-11/GsdmD activation/cleavage leads to accumulation of HMGB1 in the cytoplasm through a process associated with the release of calcium from the endoplasmic reticulum and camkkβ activation.

Thymic stromal lymphopoietin (TSLP) is a cytokine mainly released by epithelial cells that plays important roles in inflammation, autoimmune disease, and cancer. While TSLP is expressed in the liver at high levels, the role of TSLP in liver ischemia/reperfusion (I/R) injury remains unknown. Experiments were carried out to determine the role of TSLP in liver I/R injury. Wild-type (WT) and TSLP receptor–knockout (TSLPR(–/–)) mice were subjected to liver partial warm I/R injury. Liver injury was assessed by measuring serum alanine aminotransferase (ALT) level, necrotic areas by liver histology, hepatocyte death, and local hepatic inflammatory responses. Signal pathways were explored in vivo and in vitro to identify possible mechanisms for TSLP in I/R injury. TSLP and TSLPR protein expression increased during liver I/R in vivo and following hepatocyte hypoxia/reoxygenation in vitro. Deletion of TSLPR or neutralization of TSLP with anti-TSLP antibody exacerbated liver injury in terms of serum ALT levels as well as necrotic areas in liver histology. Administration of exogenous recombinant mouse TSLP to WT mice significantly reduced liver damage compared with controls, but failed to prevent I/R injury in TSLPR(–/–) mice. TSLP induced autophagy in hepatocytes during liver I/R injury. Mechanistically, Akt was activated in WT mice during liver I/R injury. The opposite results were observed in TSLPR(–/–) mice. In addition, TSLP could directly induce Akt activation in hepatocytes independent of nonparenchymal cells in vitro. Furthermore, the Akt agonist, insulin-like growth factor-1 (IGF-1), prevented I/R injury in TSLPR(–/–) mice and an Akt inhibitor, LY294002, blocked the protective effects of TSLP in WT mice subjected to I/R. Our data indicate that TSLP protects against liver I/R injury via activation of the PI3K/Akt pathway. Through this pathway, TSLP induces autophagy in hepatocytes. Thus, TSLP is a potent inhibitor of stress-induced hepatocyte necrosis.

Fibroblastic reticular cells (FRCs), a subpopulation of stromal cells in lymphoid organs and fat-associated lymphoid clusters (FALCs) in adipose tissue, play immune-regulatory roles in the host response to infection and may be useful as a form of cell therapy in sepsis. Here, we found an unexpected major role of TLR9 in controlling peritoneal immune cell recruitment and FALC formation at baseline and after sepsis induced by cecal ligation and puncture (CLP). TLR9 regulated peritoneal immunity via suppression of chemokine production by FRCs. Adoptive transfer of TLR9-deficient FRCs more effectively decreased mortality, bacterial load, and systemic inflammation after CLP than WT FRCs. Importantly, we found that activation of TLR9 signaling suppressed chemokine production by human adipose tissue-derived FRCs. Together, our results indicate that TLR9 plays critical roles in regulating peritoneal immunity via suppression of chemokine production by FRCs. These data form a knowledge basis upon which to design new therapeutic strategies to improve the therapeutic efficacy of FRC-based treatments for sepsis and immune dysregulation diseases.

Gasdermin D (GsdmD) was recently identified as the executioner of pyroptotic inflammatory cell death, and is a substrate for caspases-1 and 11. GsdmD is detrimental in lethal endotoxemia but protective in bacterial sepsis. However, little is known about its role during noninfectious/sterile injuries. In this study, we examined the contribution of GsdmD using WT and GsdmD−/− mice in two models of noninfectious liver injury: hemorrhagic shock with resuscitation (HS/R) and acetaminophen (APAP) overdose. GsdmD−/− mice had significantly increased liver damage at 6 h after HS/R or APAP vs WT, shown by significantly elevated ALT level and extended areas of cell death in liver. Caspase-8, a mediator of multiple cell death pathways, was highly elevated in GsdmD−/− mice after injury. Significantly increased cleavage of caspase-8 and subsequent high levels of apoptosis were found in livers of GsdmD−/− mice after HS/R, a relatively mild ROS-induced liver injury. However, during more severe APAP-mediated ROS-induced liver injury, caspase-8 cleavage in GsdmD−/− liver was inhibited compared with WT, resulting in accumulation of pro-caspase-8 and increased levels of necroptosis. Our findings indicate a novel hepatoprotective role for GsdmD in noninfectious inflammation models via regulation of caspase-8 expression and downstream cell death pathways. The effects of GsdmD protection are likely injury specific and may also depend on injury severity and levels of ROS produced. These data suggest modulation of GsdmD/caspase-8 may be a novel therapeutic option in ROS-mediated liver injury.

Kupffer cells and monocyte-derived macrophages are critical for liver repair after acetaminophen (APAP) overdose. These cells produce promitogenic cytokines and growth factors, and they phagocytose dead cell debris, a process that is critical for resolution of inflammation. The factors that regulate these dynamic functions of macrophages after APAP overdose, however, are not fully understood. We tested the hypothesis that the fibrinolytic enzyme, plasmin, is a key regulator of macrophage function after APAP-induced liver injury. In these studies, inhibition of plasmin in mice with tranexamic acid delayed up-regulation of proinflammatory cytokines after APAP overdose. In culture, plasmin directly, and in synergy with high-mobility group B1, stimulated Kupffer cells and bone marrow–derived macrophages to produce cytokines by a mechanism that required NF-κB. Inhibition of plasmin in vivo also prevented trafficking of monocyte-derived macrophages into necrotic lesions after APAP overdose. This prevented phagocytic removal of dead cells, prevented maturation of monocyte-derived macrophages into F4/80-expressing macrophages, and prevented termination of proinflammatory cytokine production. Our studies reveal further that phagocytosis is an important stimulus for cessation of proinflammatory cytokine production as treatment of proinflammatory, monocyte-derived macrophages, isolated from APAP-treated mice, with necrotic hepatocytes decreased expression of proinflammatory cytokines. Collectively, these studies demonstrate that plasmin is an important regulator of macrophage function after APAP overdose.

Fibroblastic reticular cells (FRC) are highly heterogeneous. Distinct FRC subsets play unique roles in the formation of secondary lymphoid organs and immune responses. We have previously shown that TLR9 signaling plays a critical role in regulating peritoneal immunity via suppressing chemokine production in FRC in the fat associated lymphoid clusters (FALC). However, the subset-specific roles of TLR9 in FRC of FALCs remain unknown. Using single-cell RNA-sequencing, we identified three distinct subsets of FRC (CD55hi, CD9hi and CD55loCD9lo) in mouse mesenteric FALCs at baseline. Based on the gene set enrichment analysis, the Cd55hi subset was enriched in gene expression related to cell differentiation. The CD9hi subset was enriched in gene expression related to immune response. The CD55loCD9lo subset was enriched in the gene expression related to extracellular matrix formation. Furthermore, we found that CD9hi FRC from Tlr9−/− mice increased gene expression associated with inflammation. Using flow cytometry and bulk-RNA seq, we successfully isolated and validated these three subsets in mouse FALCs. Interestingly, activation of TLR9 signaling using ODN1585 significantly decreased CD9 expression in FRC in vivo and in vitro. Furthermore, treatment of ODN1585 suppressed the proliferation of CD9hi FRC, evidenced by decreased expression of Ki67. These results indicate that CD9hi FRC in FALC are immunoregulatory. TLR9 signaling may modulate peritoneal immunity via regulation of the proliferation of CD9hi FRC. Understanding the mechanism of how TLR9 regulates CD9hi FRC may lead to discovering new therapies for inflammatory diseases.

Hemorrhagic shock (HS) is a life-threatening condition associated with tissue hypoperfusion, and often leads to injury of multiple organs including the liver. Pregnane X receptor (PXR) is a species-specific xenobiotic receptor that regulates the expression of drug-metabolizing enzymes (DMEs) such as the cytochrome P450 3A (CYP3A). Many clinical drugs, including those often prescribed to trauma patients, are known to activate PXR and induce CYP3A. The goal of this study is to determine whether PXR plays a role in the regulation of DMEs in the setting of HS, and whether activation of PXR is beneficial or detrimental to HS-induced hepatic injury. PXR transgenic, knockout, and humanized mice were subject to HS, and the liver injury was assessed histologically and biochemically. The expression and/or activity of PXR and CYP3A were manipulated genetically or pharmacologically in order to determine their effects on HS-induced liver injury. Our results showed that genetic or pharmacological activation of PXR sensitized wild-type and hPXR/CYP3A4 humanized mice to HS-induced hepatic injury, whereas knockout of PXR protected mice from HS-induced liver injury. Mechanistically, the sensitizing effect of PXR activation was accounted for by PXR-responsive induction of CYP3A and increased oxidative stress in the liver. The sensitizing effect of PXR was attenuated by ablation or pharmacological inhibition of CYP3A, treatment with the antioxidant N-acetylcysteine amide (NACA), or treatment with a PXR antagonist. CONCLUSIONS: We have uncovered a novel function of PXR in HS-induced hepatic injury. Our results suggest that the unavoidable use of PXR-activating drugs in trauma patients has the potential to exacerbate HS-induced hepatic injury, which can be mitigated by the co-administration of anti-oxidative agents, CYP3A inhibitors, or PXR antagonists.

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.

Significance CD24+CD133+ liver cancer stem cells (LCSCs) express higher levels of the inducible nitric oxide synthase (iNOS) and possess self-renewal and tumor growth properties. iNOS is associated with more aggressive hepatocellular carcinoma (HCC), leading to the upregulation of Notch1 signaling. The activation of Notch1 by iNOS/NO is dependent on cGMP/PKG-mediated activation of TACE and upregulation of iRhom-2. The expression of iNOS, CD24, and CD133 correlates with the expression of activated TACE and Notch signaling in more aggressive human HCC. These findings have implications for understanding how LCSCs are regulated in the setting of chronic inflammation, where signals to upregulate iNOS are often present. Targeting iNOS could have therapeutic benefit in HCC., The inducible nitric oxide synthase (iNOS) is associated with more aggressive solid tumors, including hepatocellular carcinoma (HCC). Notch signaling in cancer stem cells promotes cancer progression and requires Notch cleavage by ADAM (a disintegrin and metalloprotease) proteases. We hypothesized that iNOS/NO promotes Notch1 activation through TACE/ADAM17 activation in liver cancer stem cells (LCSCs), leading to a more aggressive cancer phenotype. Expression of the stem cell markers CD24 and CD133 in the tumors of patients with HCC was associated with greater iNOS expression and worse outcomes. The expression of iNOS in CD24+CD133+ LCSCs, but not CD24−CD133− LCSCs, promoted Notch1 signaling and stemness characteristics in vitro and in vivo, as well as accelerating HCC initiation and tumor formation in the mouse xenograft tumor model. iNOS/NO led to Notch1 signaling through a pathway involving the soluble guanylyl cyclase/cGMP/PKG-dependent activation of TACE/ADAM17 and up-regulation of iRhom2 in LCSCs. In patients with HCC, higher TACE/ADAM17 expression and Notch1 activation correlated with poor prognosis. These findings link iNOS to Notch1 signaling in CD24+CD133+ LCSCs through the activation of TACE/ADAM17 and identify a mechanism for how iNOS contributes to progression of CD24+CD133+ HCC.

The inducible nitric oxide synthase (iNOS) is associated with more aggressive solid tumors, including hepatocellular carcinoma (HCC). Notch signaling in cancer stem cells promotes cancer progression and requires Notch cleavage by ADAM (a disintegrin and metalloprotease) proteases. We hypothesized that iNOS/NO promotes Notch1 activation through TACE/ADAM17 activation in liver cancer stem cells (LCSCs), leading to a more aggressive cancer phenotype. Expression of the stem cell markers CD24 and CD133 in the tumors of patients with HCC was associated with greater iNOS expression and worse outcomes. The expression of iNOS in CD24+CD133+ LCSCs, but not CD24-CD133- LCSCs, promoted Notch1 signaling and stemness characteristics in vitro and in vivo, as well as accelerating HCC initiation and tumor formation in the mouse xenograft tumor model. iNOS/NO led to Notch1 signaling through a pathway involving the soluble guanylyl cyclase/cGMP/PKG-dependent activation of TACE/ADAM17 and up-regulation of iRhom2 in LCSCs. In patients with HCC, higher TACE/ADAM17 expression and Notch1 activation correlated with poor prognosis. These findings link iNOS to Notch1 signaling in CD24+CD133+ LCSCs through the activation of TACE/ADAM17 and identify a mechanism for how iNOS contributes to progression of CD24+CD133+ HCC.

Stearoyl lysophosphatidylcholine (LPC) exerts protective effect during endotoxemia and in experimental sepsis, but the underlying mechanism is unclear. Here, we demonstrated that stearoyl LPC could block caspase-11-mediated macrophage pyroptosis. In vitro, stearoyl LPC significantly decreased caspase-11 activation and pyroptosis induced by lipopolysaccharide (LPS) plus cholera toxin subunit B independent of the receptor G2A. Stearoyl LPC did not affect LPS uptake by mouse peritoneal macrophages but did significantly inhibit the interaction between LPS and caspase-11. Moreover, stearoyl LPC treatment conferred significant protection against lethal endotoxemia and significantly reduced the release of IL-1α and IL-1β. These findings identify stearoyl LPC as an inhibitor of LPS-mediated caspase-11 activation. This mechanism could explain the protective action of stearoyl LPC in experimental sepsis and endotoxemia.

Sepsis is defined as infection with organ dysfunction due to a dysregulated immune response. The lung is one of the most vulnerable organs at the onset of sepsis. Interleukin (IL)-33 can be released by injured epithelial and endothelial cells in the lung and regulate immune activation and infiltration. Therefore, we postulated that IL-33 would contribute to the immune response in the lung during sepsis. Using the cecal ligation and puncture (CLP) sepsis model, we show here that IL-33 contributes significantly to both sepsis-induced inflammation in the lung and systemic inflammatory response in the early phase of sepsis. Despite the higher intra-peritoneal bacterial burden, the absence of IL-33 resulted in less infiltration of neutrophils and monocytes into the lungs in association with lower circulating, lung and liver cytokine levels as well as reduced lung injury at 6 h after sepsis. IL-33 was required for the upregulation of IL-5 in type 2 Innate Lymphoid Cells (ILC2), while IL-5 neutralization suppressed neutrophil and monocyte infiltration in the lungs during CLP sepsis. This reduction in leukocyte infiltration in IL-33-deficient mice was reversed by administration of recombinant IL-5. These results indicate that IL-33 plays a major role in the local inflammatory changes in the lung, in part, by regulating IL-5 and this axis contributes to lung injury early after the onset of sepsis.

Thrombocytopenia impairs host defense and hemostasis in sepsis. However, the mechanisms of how platelets regulate host defense are not fully understood. High-mobility group box 1 (HMGB1), a danger-associated molecular pattern protein, is released during infection and contributes to the pathogenesis of sepsis. Platelets express HMGB1, which is released on activation and has been shown to play a critical role in thrombosis, monocyte recruitment, and neutrophil extracellular trap (NET) production. However, the contribution of platelet HMGB1 to host defense is unknown. To determine the role of platelet HMGB1 in polymicrobial sepsis, platelet-specific HMGB1 knockout (HMGB1 platelet factor 4 [PF4]) mice were generated and were subjected to cecal ligation and puncture (CLP), a clinically relevant intra-abdominal sepsis model. Compared with HMGB1 Flox mice and wild-type (WT) mice, HMGB1 PF4 mice showed significantly higher bacterial loads in the peritoneum and blood, an exaggerated systemic inflammation response, and significantly greater mortality after CLP. Deletion of HMGB1 in platelets was associated with lower platelet-derived chemokines (PF4 and RANTES) in the peritoneal cavity, and a decrease of platelet-neutrophil interaction in the lung after CLP. In vitro, neutrophils cocultured with activated HMGB1 knockout platelets showed fewer platelet-neutrophil aggregates, reduced reactive oxygen species (ROS) burst as compared with control. Taken together, these data reveal an unrecognized role of platelet HMGB1 in the regulation of neutrophil recruitment and activation via modulation of platelet activation during sepsis.