Cell death during sepsis: integration of disintegration in the inflammatory response to overwhelming infection

Engineered Extracellular Vesicles Driven by Erythrocytes Ameliorate Bacterial Sepsis by Iron Recycling, Toxin Clearing and Inflammation Regulation

Sepsis poses a significant challenge in clinical management. Effective strategies targeting iron restriction, toxin neutralization, and inflammation regulation are crucial in combating sepsis. However, a comprehensive approach simultaneously targeting these multiple processes has not been established. Here, an engineered apoptotic extracellular vesicles (apoEVs) derived from macrophages is developed and their potential as multifunctional agents for sepsis treatment is investigated. The extensive macrophage apoptosis in a Staphylococcus aureus-induced sepsis model is discovered, unexpectedly revealing a protective role for the host. Mechanistically, the protective effects are mediated by apoptotic macrophage-released apoEVs, which bound iron-containing proteins and neutralized α-toxin through interaction with membrane receptors (transferrin receptor and A disintegrin and metalloprotease 10). To further enhance therapeutic efficiency, apoEVs are engineered by incorporating mesoporous silica nanoparticles preloaded with anti-inflammatory agents (microRNA-146a). These engineered apoEVs can capture iron and neutralize α-toxin with their natural membrane while also regulating inflammation by releasing microRNA-146a in phagocytes. Moreover, to exploit the microcosmic movement and rotation capabilities, erythrocytes are utilized to drive the engineered apoEVs. The erythrocytes-driven engineered apoEVs demonstrate a high capacity for toxin and iron capture, ultimately providing protection against sepsis associated with high iron-loaded conditions. The findings establish a multifunctional agent that combines natural and engineered antibacterial strategies.

Transcriptome analysis of six tissues obtained post-mortem from sepsis patients

Septic shock is a life-threatening clinical condition characterized by a robust immune inflammatory response to disseminated infection. Little is known about its impact on the transcriptome of distinct human tissues. To address this, we performed RNA sequencing of samples from the prefrontal cortex, hippocampus, heart, lung, kidney and colon of seven individuals who succumbed to sepsis and seven uninfected controls. We identified that the lungs and colon were the most affected organs. While gene activation dominated, strong inhibitory signals were also detected, particularly in the lungs. We found that septic shock is an extremely heterogeneous disease, not only when different individuals are investigated, but also when comparing different tissues of the same patient. However, several pathways, such as respiratory electron transport and other metabolic functions, revealed distinctive alterations, providing evidence that tissue specificity is a hallmark of sepsis. Strikingly, we found evident signals of accelerated ageing in our sepsis population.

Mitochondria in health, disease, and aging

Mitochondria are well known as organelles responsible for the maintenance of cellular bioenergetics through the production of ATP. Although oxidative phosphorylation may be their most important function, mitochondria are also integral for the synthesis of metabolic precursors, calcium regulation, the production of reactive oxygen species, immune signaling, and apoptosis. Considering the breadth of their responsibilities, mitochondria are fundamental for cellular metabolism and homeostasis. Appreciating this significance, translational medicine has begun to investigate how mitochondrial dysfunction can represent a harbinger of disease. In this review, we provide a detailed overview of mitochondrial metabolism, cellular bioenergetics, mitochondrial dynamics, autophagy, mitochondrial damage-associated molecular patterns, mitochondria-mediated cell death pathways, and how mitochondrial dysfunction at any of these levels is associated with disease pathogenesis. Mitochondria-dependent pathways may thereby represent an attractive therapeutic target for ameliorating human disease.

Infection, Inflammation, and Immunity in Sepsis

Sepsis is triggered by microbial infection, injury, or even major surgery. Both innate and adaptive immune systems are involved in its pathogenesis. Cytoplasmic presence of DNA or RNA of the invading organisms or damaged nuclear material (in the form of micronucleus in the cytoplasm) in the host cell need to be eliminated by various nucleases; failure to do so leads to the triggering of inflammation by the cellular cGAS-STING system, which induces the release of IL-6, TNF-α, and IFNs. These cytokines activate phospholipase A2 (PLA2), leading to the release of polyunsaturated fatty acids (PUFAs), gamma-linolenic acid (GLA), arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), which form precursors to various pro- and anti-inflammatory eicosanoids. On the other hand, corticosteroids inhibit PLA2 activity and, thus, suppress the release of GLA, AA, EPA, and DHA. PUFAs and their metabolites have a negative regulatory action on the cGAS-STING pathway and, thus, suppress the inflammatory process and initiate inflammation resolution. Pro-inflammatory cytokines and corticosteroids (corticosteroids > IL-6, TNF-α) suppress desaturases, which results in decreased formation of GLA, AA, and other PUFAs from the dietary essential fatty acids (EFAs). A deficiency of GLA, AA, EPA, and DHA results in decreased production of anti-inflammatory eicosanoids and failure to suppress the cGAS-STING system. This results in the continuation of the inflammatory process. Thus, altered concentrations of PUFAs and their metabolites, and failure to suppress the cGAS-STING system at an appropriate time, leads to the onset of sepsis. Similar abnormalities are also seen in radiation-induced inflammation. These results imply that timely administration of GLA, AA, EPA, and DHA, in combination with corticosteroids and anti-IL-6 and anti-TNF-α antibodies, may be of benefit in mitigating radiation-induced damage and sepsis.

Protein arginine N-methyltransferase 4 (PRMT4) contributes to lymphopenia in experimental sepsis

BACKGROUND

One hallmark of sepsis is the reduced number of lymphocytes, termed lymphopenia, that occurs from decreased lymphocyte proliferation or increased cell death contributing to immune suppression. Histone modification enzymes regulate immunity by their epigenetic and non-epigenetic functions; however, the role of these enzymes in lymphopenia remains elusive.

METHODS

We used molecular biological approaches to investigate the high expression and function of a chromatin modulator protein arginine N-methyltransferase 4 (PRMT4)/coactivator-associated arginine methyltransferase 1 in human samples from septic patients and cellular and animal septic models.

RESULTS

We identified that PRMT4 is elevated systemically in septic patients and experimental sepsis. Gram-negative bacteria and their derived endotoxin lipopolysaccharide (LPS) increased PRMT4 in B and T lymphocytes and THP-1 monocytes. Single-cell RNA sequencing results indicate an increase of PRMT4 gene expression in activated T lymphocytes. Augmented PRMT4 is crucial for inducing lymphocyte apoptosis but not monocyte THP-1 cells. Ectopic expression of PRMT4 protein caused substantial lymphocyte death via caspase 3-mediated cell death signalling, and knockout of PRMT4 abolished LPS-mediated lymphocyte death. PRMT4 inhibition with a small molecule compound attenuated lymphocyte death in complementary models of sepsis.

CONCLUSIONS

These findings demonstrate a previously uncharacterised role of a key chromatin modulator in lymphocyte survival that may shed light on devising therapeutic modalities to lessen the severity of septic immunosuppression.

Melatonin: A potential adjuvant therapy for septic myopathy

Septic myopathy, also known as ICU acquired weakness (ICU-AW), is a characteristic clinical symptom of patients with sepsis, mainly manifested as skeletal muscle weakness and muscular atrophy, which affects the respiratory and motor systems of patients, reduces the quality of life, and even threatens the survival of patients. Melatonin is one of the hormones secreted by the pineal gland. Previous studies have found that melatonin has anti-inflammatory, free radical scavenging, antioxidant stress, autophagic lysosome regulation, mitochondrial protection, and other multiple biological functions and plays a protective role in sepsis-related multiple organ dysfunction. Given the results of previous studies, we believe that melatonin may play an excellent regulatory role in the repair and regeneration of skeletal muscle atrophy in septic myopathy. Melatonin, as an over-the-counter drug, has the potential to be an early, complementary treatment for clinical trials. Based on previous research results, this article aims to critically discuss and review the effects of melatonin on sepsis and skeletal muscle depletion.

Inhibition of HMGB1/RAGE Signaling Reduces the Incidence of Medication-Related Osteonecrosis of the Jaw (MRONJ) in Mice

Medication-related osteonecrosis of the jaw (MRONJ) is a severe complication of antiresorptive or antiangiogenic medications, used in the treatment of bone malignancy or osteoporosis. Bone necrosis, mainly represented by osteocytic death, is always present in MRONJ sites; however, the role of osteocyte death in MRONJ pathogenesis is unknown. High mobility group box 1 (HMGB1) is a non-histone nucleoprotein that in its acetylated form accumulates in the cytoplasm, whereas non-acetylated HMGB1 localizes in the nucleus. SIRT1 deacetylase regulates cellular localization of HMGB1. Interestingly, HMGB1 is released during cell necrosis and promotes inflammation through signaling cascades, including activation of the RAGE receptor. Here, we utilized a well-established mouse MRONJ model that utilizes ligature-induced experimental periodontitis (EP) and treatment with either vehicle or zolendronic acid (ZA). Initially, we evaluated HMGB1-SIRT1 expression in osteocytes at 1, 2, and 4 weeks of treatment. Significantly increased cytoplasmic and perilacunar HMGB1 expression was observed at EP sites of ZA versus vehicle (Veh) animals at all time points. SIRT1 colocalized with cytoplasmic HMGB1 and presented a statistically significant increased expression at the EP sites of ZA animals for all time points. RAGE expression was significantly higher in the submucosal tissues EP sites of ZA animals compared with those in vehicle group. To explore the significance of increased cytoplasmic and extracellular HMGB1 and increased RAGE expression in MRONJ pathogenesis, we used pharmacologic inhibitors of these molecules. Combined HMGB1/RAGE inhibition resulted in lower MRONJ incidence with statistically significant decrease in osteonecrotic areas and bone exposure versus non-inhibitor treated ZA animals. Together, our data point to the role of HMGB1 as a central alarmin, overexpressed at early phase of MRONJ pathogenesis during osteocytic death. Moreover, HMGB1-RAGE pathway may represent a new promising therapeutic target in patients at high risk of MRONJ. © 2022 American Society for Bone and Mineral Research (ASBMR).

Cardiomyocyte death in sepsis: Mechanisms and regulation (Review)

Sepsis‑induced cardiac dysfunction is one of the most common types of organ dysfunction in sepsis; its pathogenesis is highly complex and not yet fully understood. Cardiomyocytes serve a key role in the pathophysiology of cardiac function; due to the limited ability of cardiomyocytes to regenerate, their loss contributes to decreased cardiac function. The activation of inflammatory signalling pathways affects cardiomyocyte function and modes of cardiomyocyte death in sepsis. Prevention of cardiomyocyte death is an important therapeutic strategy for sepsis‑induced cardiac dysfunction. Thus, understanding the signalling pathways that activate cardiomyocyte death and cross‑regulation between death modes are key to finding therapeutic targets. The present review focused on advances in understanding of sepsis‑induced cardiomyocyte death pathways, including apoptosis, necroptosis, mitochondria‑mediated necrosis, pyroptosis, ferroptosis and autophagy. The present review summarizes the effect of inflammatory activation on cardiomyocyte death mechanisms, the diversity of regulatory mechanisms and cross‑regulation between death modes and the effect on cardiac function in sepsis to provide a theoretical basis for treatment of sepsis‑induced cardiac dysfunction.

The liver in sepsis: molecular mechanism of liver failure and their potential for clinical translation

Liver failure is a life-threatening complication of infections restricting the host's response to infection. The pivotal role of the liver in metabolic, synthetic, and immunological pathways enforces limits the host's ability to control the immune response appropriately, making it vulnerable to ineffective pathogen resistance and tissue damage. Deregulated networks of liver diseases are gradually uncovered by high-throughput, single-cell resolved OMICS technologies visualizing an astonishing diversity of cell types and regulatory interaction driving tolerogenic signaling in health and inflammation in disease. Therefore, this review elucidates the effects of the dysregulated host response on the liver, consequences for the immune response, and possible avenues for personalized therapeutics.

Regulated necrosis, a proinflammatory cell death, potentially counteracts pathogenic infections

Since the discovery of cell apoptosis, other gene-regulated cell deaths are gradually appreciated, including pyroptosis, ferroptosis, and necroptosis. Necroptosis is, so far, one of the best-characterized regulated necrosis. In response to diverse stimuli (death receptor or toll-like receptor stimulation, pathogenic infection, or other factors), necroptosis is initiated and precisely regulated by the receptor-interacting protein kinase 3 (RIPK3) with the involvement of its partners (RIPK1, TRIF, DAI, or others), ultimately leading to the activation of its downstream substrate, mixed lineage kinase domain-like (MLKL). Necroptosis plays a significant role in the host's defense against pathogenic infections. Although much has been recognized regarding modulatory mechanisms of necroptosis during pathogenic infection, the exact role of necroptosis at different stages of infectious diseases is still being unveiled, e.g., how and when pathogens utilize or evade necroptosis to facilitate their invasion and how hosts manipulate necroptosis to counteract these detrimental effects brought by pathogenic infections and further eliminate the encroaching pathogens. In this review, we summarize and discuss the recent progress in the role of necroptosis during a series of viral, bacterial, and parasitic infections with zoonotic potentials, aiming to provide references and directions for the prevention and control of infectious diseases of both human and animals.

The "Self-Sacrifice" of ImmuneCells in Sepsis

Sepsis is a life-threatening organ dysfunction caused by the host’s malfunctioning response to infection. Due to its high mortality rate and medical cost, sepsis remains one of the world’s most intractable diseases. In the early stage of sepsis, the over-activated immune system and a cascade of inflammation are usually accompanied by immunosuppression. The core pathogenesis of sepsis is the maladjustment of the host’s innate and adaptive immune response. Many immune cells are involved in this process, including neutrophils, mononuclear/macrophages and lymphocytes. The immune cells recognize pathogens, devour pathogens and release cytokines to recruit or activate other cells in direct or indirect manner. Pyroptosis, immune cell-extracellular traps formation and autophagy are several novel forms of cell death that are different from apoptosis, which play essential roles in the progress of sepsis. Immune cells can initiate “self-sacrifice” through the above three forms of cell death to protect or kill pathogens. However, the exact roles and mechanisms of the self-sacrifice in the immune cells in sepsis are not fully elucidated. This paper mainly analyzes the self-sacrifice of several representative immune cells in the forms of pyroptosis, immune cell-extracellular traps formation and autophagy to reveal the specific roles they play in the occurrence and progression of sepsis, also to provide inspiration and references for further investigation of the roles and mechanisms of self-sacrifice of immune cells in the sepsis in the future, meanwhile, through this work, we hope to bring inspiration to clinical work.

Electroacupuncture at ST36 (Zusanli) Prevents T-Cell Lymphopenia and Improves Survival in Septic Mice

Purpose

Sepsis is the main cause of death in intensive care unit. Maladaptive cytokine storm and T-cell lymphopenia are critical prognosis predictors of sepsis. Electroacupuncture (EA) is expected to be an effective intervention to prevent sepsis. This study aims to determine the potential of EA at ST36 (Zusanli) to prevent experimental septic mice.

Methods

Mice were randomly assigned into PBS, LPS, or EA+LPS group. EA (0.1 mA, continuous wave, 10 Hz) was performed stimulating the ST36 for 30 min, once a day for 3 days. After the third day, all mice were challenged with PBS or LPS (4 mg/kg) simultaneously. Mice were evaluated for survival, ear temperature, and other clinical symptoms. Lung and small intestine tissue injuries were analyzed by hematoxylin and eosin staining. Bio-Plex cytokine assay was used to analyze the concentration of cytokines. T lymphocytes were analyzed by flow cytometry and Western blot assays. The role of T cells in preventing sepsis by EA was analyzed by using nude mice lacking T lymphocytes.

Results

EA at ST36 improved survival, symptom scores, and ear temperature of endotoxemic mice. EA also improved dramatically pulmonary and intestinal injury by over 50% as compared to untreated mice. EA blunted the inflammatory cytokine storm by inducing a lasting inhibition of the production of major inflammatory factors (TNF-α, IL-1β, IL-5, IL-6, IL-10, IL-17A, eotaxin, IFN-γ, MIP-1β and KC). Flow cytometry and Western blot analyses showed EA significantly reduced T-lymphocyte apoptosis and pyroptosis. Furthermore, T lymphocytes were critical for the effects of EA at ST36 stimulation blunted serum TNF-α levels in wild-type but not in nude mice.

Conclusion

EA halted systemic inflammation and improved survival in endotoxemic mice. These effects are associated with the protective effect of EA on T lymphocytes, and T cells are required in the anti-inflammatory effects of EA in sepsis.

STING1 in sepsis: Mechanisms, functions, and implications

Sepsis is a life-threatening clinical syndrome and one of the most challenging health problems in the world. Pathologically, sepsis and septic shock are caused by a dysregulated host immune response to infection, which can eventually lead to multiple organ failure and even death. As an adaptor transporter between the endoplasmic reticulum and Golgi apparatus, stimulator of interferon response cGAMP interactor 1 (STING1, also known as STING or TMEM173) has been found to play a vital role at the intersection of innate immunity, inflammation, autophagy, and cell death in response to invading microbial pathogens or endogenous host damage. There is ample evidence that impaired STING1, through its immune and non-immune functions, is involved in the pathological process of sepsis. In this review, we discuss the regulation and function of the STING1 pathway in sepsis and highlight it as a suitable drug target for the treatment of lethal infection.

Association of Apoptosis-Mediated CD4+ T Lymphopenia With Poor Outcome After Type A Aortic Dissection Surgery

Background: Many patients with type A aortic dissection (AAD) show low lymphocyte counts pre-operatively. The present study investigated the prognostic values of lymphopenia and lymphocyte subsets for the postoperative major adverse events (MAEs) in AAD patients undergoing surgery, and explore mechanisms of lymphopenia.

Methods: We retrospectively analyzed pre-operative lymphocyte counts in 295 AAD patients treated at two hospitals, and evaluated their correlation with MAEs. We prospectively recruited 40 AAD patients and 20 sex- and age-matched healthy donors (HDs), and evaluated lymphocyte subsets, apoptosis, and pyroptosis by flow cytometry.

Results: Multivariable regression analysis of the retrospective cohort revealed pre-operative lymphopenia as a strong predictor of MAEs (odds ratio, 4.152; 95% CI, 2.434–7.081; p < 0.001). In the prospective cohort, lymphocyte depletion in the AAD group was mainly due to loss of CD4⁺ and CD8⁺ T cells as compared with HDs (CD4⁺ T cells: 346.7 ± 183.6 vs. 659.0 ± 214.6 cells/μl, p < 0.0001; CD8⁺ T cells: 219.5 ± 178.4 vs. 354.4 ± 121.8 cells/μl, p = 0.0036). The apoptosis rates of CD4⁺ and CD8⁺ T cells were significantly higher in AAD patients relative to HDs (both p < 0.0001). Furthermore, the pre-operative CD4⁺ T cells count at a cut-off value of 357.96 cells/μl was an effective and reliable predictor of MAEs (area under ROC curve = 0.817; 95% CI, 0.684-0.950; sensitivity, 74%; specificity, 81%; p < 0.005). Pre-operative lymphopenia, mainly due to CD4⁺ T cells exhaustion by apoptosis, correlates with poor prognosis in AAD patients undergoing surgery.

Conclusion: Pre-operative lymphopenia in particular CD4⁺ T lymphopenia via apoptosis correlates with poor prognosis in AAD patients undergoing surgery.

Interference on Cytosolic DNA Activation Attenuates Sepsis Severity: Experiments on Cyclic GMP-AMP Synthase (cGAS) Deficient Mice

Although the enhanced responses against serum cell-free DNA (cfDNA) in cases of sepsis—a life-threatening organ dysfunction due to systemic infection—are understood, the influence of the cytosolic DNA receptor cGAS (cyclic guanosine monophosphate–adenosine monophosphate (GMP–AMP) synthase) on sepsis is still unclear. Here, experiments on cGAS deficient (cGAS^-/-) mice were conducted using cecal ligation and puncture (CLP) and lipopolysaccharide (LPS) injection sepsis models and macrophages. Severity of CLP in cGAS^-/- mice was less severe than in wildtype (WT) mice, as indicated by mortality, serum LPS, cfDNA, leukopenia, cytokines (TNF-α, IL-6 and IL-10), organ histology (lung, liver and kidney) and spleen apoptosis. With the LPS injection model, serum cytokines in cGAS^-/- mice were lower than in WT mice, despite the similar serum cfDNA level. Likewise, in LPS-activated WT macrophages, the expression of several mitochondria-associated genes (as revealed by RNA sequencing analysis) and a profound reduction in mitochondrial parameters, including maximal respiration (determined by extracellular flux analysis), DNA (mtDNA) and mitochondrial abundance (revealed by fluorescent staining), were demonstrated. These data implied the impact of cfDNA resulting from LPS-induced cell injury. In parallel, an additive effect of bacterial DNA on LPS, seen in comparison with LPS alone, was demonstrated in WT macrophages, but not in cGAS^-/- cells, as indicated by supernatant cytokines (TNF-α and IL-6), M1 proinflammatory polarization (iNOS and IL-1β), cGAS, IFN-γ and supernatant cyclic GMP–AMP (cGAMP). In conclusion, cGAS activation by cfDNA from hosts (especially mtDNA) and bacteria was found to induce an additive proinflammatory effect on LPS-activated macrophages which was perhaps responsible for the more pronounced sepsis hyperinflammation observed in WT mice compared with the cGAS^-/- group.

Development and Validation of a Nomogram for the Prediction of Hospital Mortality of Patients With Encephalopathy Caused by Microbial Infection: A Retrospective Cohort Study

Background

Hospital mortality is high for patients with encephalopathy caused by microbial infection. Microbial infections often induce sepsis. The damage to the central nervous system (CNS) is defined as sepsis-associated encephalopathy (SAE). However, the relationship between pathogenic microorganisms and the prognosis of SAE patients is still unclear, especially gut microbiota, and there is no clinical tool to predict hospital mortality for SAE patients. The study aimed to explore the relationship between pathogenic microorganisms and the hospital mortality of SAE patients and develop a nomogram for the prediction of hospital mortality in SAE patients.

Methods

The study is a retrospective cohort study. The lasso regression model was used for data dimension reduction and feature selection. Model of hospital mortality of SAE patients was developed by multivariable Cox regression analysis. Calibration and discrimination were used to assess the performance of the nomogram. Decision curve analysis (DCA) to evaluate the clinical utility of the model.

Results

Unfortunately, the results of our study did not find intestinal infection and microorganisms of the gastrointestinal (such as: Escherichia coli) that are related to the prognosis of SAE. Lasso regression and multivariate Cox regression indicated that factors including respiratory failure, lactate, international normalized ratio (INR), albumin, SpO₂, temperature, and renal replacement therapy were significantly correlated with hospital mortality. The AUC of 0.812 under the nomogram was more than that of the Simplified Acute Physiology Score (0.745), indicating excellent discrimination. DCA demonstrated that using the nomogram or including the prognostic signature score status was better than without the nomogram or using the SAPS II at predicting hospital mortality.

Conclusion

The prognosis of SAE patients has nothing to do with intestinal and microbial infections. We developed a nomogram that predicts hospital mortality in patients with SAE according to clinical data. The nomogram exhibited excellent discrimination and calibration capacity, favoring its clinical utility.

Mesenchymal stem cell and endothelial progenitor cells coinjection improves LPS-induced lung injury via Tie2 activation and downregulation of the TLR4/MyD88 pathway

Sepsis is one of the most important complications of infection with a high mortality rate. Recently, cell therapy has been widely used to reduce the symptoms of sepsis. It has been previously reported that mesenchymal stem cell (MSC) and endothelial progenitor cells (EPC) therapy have beneficial effects in experimental models of sepsis. The effects of coculture of MSC and EPC have not yet been used to treat sepsis. Therefore, the aim of this study was to investigate the therapeutic potential of EPC + MSC coculture on the residual effects of sepsis in a lipopolysaccharide (LPS)-induced mice model. Coinjections of EPC + MSC significantly enhanced the survival rate of LPS-induced mice, decreased concentrations of pro-inflammatory cytokines, and increased the level of anti-inflammatory cytokine. The LPS-induced mice that were treated with EPC + MSC showed a notable reduction in pulmonary edema, hepatic enzymes, and C-reactive protein level compared with the control group. Our results showed that coinjection of EPC + MSC up and downregulates Tie2 and TLR4/MyD88 signaling pathways in LPS-induced mice, respectively. Also, in vitro study showed that viability, adhesion, and migration in coculture cells is significantly decreased after being induced with 10 μg/ml LPS. Our results showed that LPS impaired the functional activity of the cocultured EPC + MSC via upregulation of the TLR4/MyD88 signaling pathway, which may be associated with decreased pTie2/Tie2 expression. In conclusion, coinjection of EPC and MSC modulated the TLR4/MyD88 signaling pathway that leads to reduce the inflammatory response. This study may provide promising results for the introduction of cocultured cells to manage infectious diseases and balance the immune response through immune regulatory function.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Mechanism of Mitophagy and Its Role in Sepsis Induced Organ Dysfunction: A Review

Autophagy, an evolutionarily conserved process, plays an important role in maintaining cellular homeostasis under physiological and pathophysiological conditions. It is widely believed that mitochondria influence the development of disease by regulating cellular metabolism. When challenged by different stimuli, mitochondria may experience morphological disorders and functional abnormalities, leading to a selective form of autophagy-mitophagy, which can clear damaged mitochondria to promote mitochondrial quality control. Sepsis is a complex global problem with multiple organ dysfunction, often accompanied by manifold mitochondrial damage. Recent studies have shown that autophagy can regulate both innate and acquired immune processes to protect against organ dysfunction in sepsis. Sepsis-induced mitochondrial dysfunction may play a pathophysiological role in the initiation and progression of sepsis-induced organ failure. Mitophagy is reported to be beneficial for sepsis by eliminating disabled mitochondria and maintaining homeostasis to protect against organ failure. In this review, we summarize the recent findings and mechanisms of mitophagy and its involvement in septic organ dysfunction as a potential therapeutic target.

Lipopolysaccharide induces vascular endothelial cell pyroptosis via the SP1/RCN2/ROS signaling pathway

Endothelial cell pyroptosis is a novel cause of endothelial dysfunction in sepsis. Reticulocalbin-2 (RCN2) is involved in regulating vascular inflammation and plays an important role in the cardiovascular system. However, the role of RCN2 in inflammation-induced endothelial cell pyroptosis remains to be explored. Here, we found that RCN2 was upregulated after lipopolysaccharide (LPS) treatment in a concentration- and time-dependent manner. RCN2 knockdown resulted in a significant decrease in pyroptosis, reduced LDH and IL-1β release and ROS production and inhibited the expression of pyroptosis-related proteins (NLRP3, cleaved caspase-1, and cleaved GSDMD) (all p < 0.05). N-acetyl-L-cysteine (NAC) counteracted the effects of RCN2 on pyroptosis (all p < 0.01). The silencing of RCN2 antagonized the inhibitory effect of LPS on the phosphorylation of eNOS (p < 0.05). We predicted and confirmed that specificity protein-1(SP1) could directly bind to the RCN2 promoter and regulate RCN2. RCN2 overexpression rescued the inhibitory effect of SP1 inhibitor on HUVEC pyroptosis induced by LPS (all p < 0.05). These findings suggested that the activation of the SP1/RCN2/ROS signaling pathway could promote LPS-induced endothelial cell pyroptosis.

Systemic inflammation and protease profile of Afro-Caribbean patients with sepsis

Objectives:

Sepsis is one of the leading causes of morbidity and mortality within the healthcare system and remains a diagnostic and therapeutic challenge. A major issue in the diagnosis of sepsis is understanding the pathophysiologic mechanism, which revolves around host immune system activation and dysregulated responses. African Americans are more likely to experience severe sepsis with higher mortality rates compared to the general population. This pilot study characterized multiple inflammatory markers and proteases in plasma of primarily African American and Afro-Caribbean patients with mild sepsis.

Methods:

Plasma was collected from 16 healthy controls and 15 subjects presenting with sepsis, on admission, and again upon resolution of the signs of sepsis, defined as a resolution of sepsis criteria. Plasma samples were analyzed for cytokines, chemokines, and proteases using multiplex bead assays.

Results:

Elevated levels of granulocyte colony-stimulating factor, interleukin-10, interleukin-15, interleukin-1 receptor antagonist, interleukin-8, interferon gamma-induced protein 10, monocyte chemoattractant protein-1, matrix metallopeptidase 12, and cathepsin S were identified in plasma from sepsis patients on admission compared to control subjects. Interleukin-6, interleukin-8, granulocyte colony-stimulating factor, and cathepsin S were reduced in sepsis patients upon clinical resolution of sepsis.

Conclusion:

These findings profile the circulating inflammatory cytokines, chemokines, and proteases in African Americans and Afro-Caribbean patients during sepsis. The role of these targets in sepsis needs addressing in this patient population.

Survivin and caspases serum protein levels and survivin variants mRNA expression in sepsis

Sepsis is a dysregulated host response to infection related to devastating outcomes. Recently, interest has been shifted towards apoptotic and antiapoptotic pathobiology. Apoptosis is executed through the activation of caspases regulated by a number of antiapoptotic proteins, such as survivin. The survivin and caspases’ responses to sepsis have not yet been elucidated. This is a multicenter prospective observational study concerning patients with sepsis (n = 107) compared to patients with traumatic systemic inflammatory response syndrome (SIRS) (n = 75) and to healthy controls (n = 89). The expression of survivin was quantified through real-time quantitative polymerase chain reaction for the different survivin splice variants (wild type-WT, ΔEx3, 2B, 3B) in peripheral blood leukocytes. The apoptotic or antiapoptotic tendency was specified by measuring survivin-WT, caspase-3, and -9 serum protein concentrations through enzyme-linked immunosorbent assay. The survivin-WT, -2B, -ΔΕx3 mRNA, survivin protein, and caspases showed an escalated increase in SIRS and sepsis, whereas survivin-3B was repressed in sepsis (p < 0.05). Survivin correlated with IL-8 and caspase-9 (p < 0.01). For discriminating sepsis, caspase-9 achieved the best receiver operating characteristic curve (AUROC) of 0.95. In predicting mortality, caspase-9 and survivin protein achieved an AUROC of 0.70. In conclusion, specific apoptotic and antiapoptotic pathways might represent attractive targets for future research in sepsis.

The Central Role and Possible Mechanisms of Bacterial DNAs in Sepsis Development

The pathological roles of bacterial DNA have been documented many decades ago. Bacterial DNAs are different from mammalian DNAs; the latter are heavily methylated. Mammalian cells have sensors such as TLR-9 to sense the DNAs with nonmethylated CpGs and distinguish them from host DNAs with methylated CpGs. Further investigation has identified many other types of DNA sensors distributed in a variety of cellular compartments. These sensors not only sense foreign DNAs, including bacterial and viral DNAs, but also sense damaged DNAs from the host cells. The major downstream signalling pathways includeTLR-9-MyD88-IKKa-IRF-7/NF-κB pathways to increase IFN/proinflammatory cytokine production, STING-TBK1-IRF3 pathway to increase IFN-beta, and AIM2-ASC-caspas-1 pathway to release IL-1beta. The major outcome is to activate host immune response by inducing cytokine production. In this review, we focus on the roles and potential mechanisms of DNA sensors and downstream pathways in sepsis. Although bacterial DNAs play important roles in sepsis development, bacterial DNAs alone are unable to cause severe disease nor lead to death. Priming animals with bacterial DNAs facilitate other pathological factors, such as LPS and other virulent factors, to induce severe disease and lethality. We also discuss compartmental distribution of DNA sensors and pathological significance as well as the transport of extracellular DNAs into cells. Understanding the roles of DNA sensors and signal pathways will pave the way for novel therapeutic strategies in many diseases, particularly in sepsis.

Therapeutic Potential of Cathelicidin Peptide LL-37, an Antimicrobial Agent, in a Murine Sepsis Model

Among the mechanisms put-up by the host to defend against invading microorganisms, antimicrobial peptides represent the first line. In different species of mammals, the cathelicidin family of antimicrobial peptides AMPs has been identified, and in humans, LL-37 is the only type of cathelicidin identified. LL-37 has many different biological activities, such as regulation of responses to inflammation, besides its lipopolysaccharide (LPS)-neutralizing and antimicrobial and activities. Recently, employing a murine septic model that involves cecal ligation and puncture (CLP), we examined the effect of LL-37. The results indicated that LL-37 exhibits multiple protective actions on septic mice; firstly, the survival of CLP mice was found to be improved by LL-37 by the suppression of the macrophage pyroptosis that induces the release of pro-inflammatory cytokines (such as IL-1β) and augments inflammatory reactions in sepsis; secondly, the release of neutrophil extracellular traps (NETs), which have potent bactericidal activity, is enhanced by LL-37, and protects mice from CLP-induced sepsis; thirdly, LL-37 stimulates neutrophils to release antimicrobial microvesicles (ectosomes), which improve the pathological condition of sepsis. These findings indicate that LL-37 protects CLP septic mice through at least three mechanisms, i.e., the suppression of pro-inflammatory macrophage pyroptosis and the release of antimicrobial NETs (induction of NETosis) and ectosomes from neutrophils. Thus, LL-37 can be a potential therapeutic candidate for sepsis due to its multiple properties, including the modulation of cell death (pyroptosis and NETosis) and the release of antimicrobial NETs and ectosomes as well as its own bactericidal and LPS-neutralizing activities.

Antimicrobial peptide LL-37 ameliorates a murine sepsis model via the induction of microvesicle release from neutrophils

Sepsis is a life-threatening disease caused by systemic dys-regulated inflammatory response to infection. We previously revealed that LL-37, a human cathelicidin antimicrobial peptide, improves the survival of cecal ligation and puncture septic mice. Ectosomes, microvesicles released from neutrophils, are reported to be elevated in sepsis survivors; however, the functions of ectosomes in sepsis remain largely unknown. Therefore, we herein elucidated the protective action of LL-37 on sepsis, by focusing on LL-37-induced ectosome release in a cecal ligation and puncture model. The results demonstrated the enhancement of ectosome levels by LL-37 administration, accompanied by a reduction of bacterial load. Importantly, ectosomes isolated from LL-37-injected cecal ligation and puncture mice contained higher amounts of antimicrobial proteins/peptides and exhibited higher antibacterial activity, compared with those from PBS-injected cecal ligation and puncture mice, suggesting that LL-37 induces the release of ectosomes with antibacterial potential in vivo. Actually, LL-37 stimulated mouse bone-marrow neutrophils to release ectosomes ex vivo, and the LL-37-induced ectosomes possessed antibacterial potential. Furthermore, administration of LL-37-induced ectosomes reduced the bacterial load and improved the survival of cecal ligation and puncture mice. Together these observations suggest LL-37 induces the release of antimicrobial ectosomes in cecal ligation and puncture mice, thereby reducing the bacterial load and protecting mice from lethal septic conditions.

The effects of CLP-induced sepsis on proliferation and apoptosis of granulosa and theca cells in rat ovary: A histochemical and ultrastructural study

Sepsis is defined as a systemic inflammatory response to infection. This study is aimed to evaluate the effects of experimental sepsis on the proliferation and apoptosis of granulosa and theca cells in the rat ovary. 28-day-old immature Wistar-Albino female rats were treated with pregnant mare serum gonadotrophin to develop the first generation of preovulatory follicles. Sepsis was induced by cecal ligation and puncture (CLP). Following in vivo 5-Bromo-2-deoxyuridine (BrdU) labeling, animals were sacrificed and ovaries were embedded in paraffin and Epon. Besides electron microscopic evaluation, BrdU, cleaved caspase-3, p27 immunostaining, and TUNEL labeling were performed. In CLP-operated animals, cleaved caspase-3 immunoreactivity was significantly increased in Graafian follicles. TUNEL and BrdU labeling in the ovarian follicles were not statistically different between CLP and sham-operated rats. In septic animals, p27 immunoreactivity was increased significantly in the nuclei of oocytes and decreased in the cytoplasm of granulosa and theca cells in multilaminar primary follicles compared to the sham group. In ultrastructural evaluation, increased apoptosis was observed in theca interna and granulosa cells in both the early and late stages of follicles in the CLP group. In conclusion, experimentally-induced sepsis leads to apoptosis in ovarian follicles at advanced stages of development. Our data suggest that although sepsis may not cause a potential threat to developing follicles at least in the short term, more severe damage may occur during advanced stages of follicle development.

Mechanisms and treatment of organ failure in sepsis

Sepsis is a dysregulated immune response to an infection that leads to organ dysfunction. Knowledge of the pathophysiology of organ failure in sepsis is crucial for optimizing the management and treatment of patients and for the development of potential new therapies. In clinical practice, six major organ systems - the cardiovascular (including the microcirculation), respiratory, renal, neurological, haematological and hepatic systems - can be assessed and monitored, whereas others, such as the gut, are less accessible. Over the past 2 decades, considerable amounts of new data have helped improve our understanding of sepsis pathophysiology, including the regulation of inflammatory pathways and the role played by immune suppression during sepsis. The effects of impaired cellular function, including mitochondrial dysfunction and altered cell death mechanisms, on the development of organ dysfunction are also being unravelled. Insights have been gained into interactions between key organs (such as the kidneys and the gut) and organ-organ crosstalk during sepsis. The important role of the microcirculation in sepsis is increasingly apparent, and new techniques have been developed that make it possible to visualize the microcirculation at the bedside, although these techniques are only research tools at present.

Group A Streptococcus-Mediated Host Cell Signaling

In the past decade, the field of the cellular microbiology of group A Streptococcus (S. pyogenes) infection has made tremendous advances and touched upon several important aspects of pathogenesis, including receptor biology, invasive and evasive phenomena, inflammasome activation, strain-specific autophagic bacterial killing, and virulence factor-mediated programmed cell death. The noteworthy aspect of S. pyogenes-mediated cell signaling is the recognition of the role of M protein in a variety of signaling events, starting with the targeting of specific receptors on the cell surface and on through the induction and evasion of NETosis, inflammasome, and autophagy/xenophagy to pyroptosis and apoptosis. Variations in reports on S. pyogenes-mediated signaling events highlight the complex mechanism of pathogenesis and underscore the importance of the host cell and S. pyogenes strain specificity, as well as in vitro/in vivo experimental parameters. The severity of S. pyogenes infection is, therefore, dependent on the virulence gene expression repertoire in the host environment and on host-specific dynamic signaling events in response to infection. Commonly known as an extracellular pathogen, S. pyogenes finds host macrophages as safe havens wherein it survives and even multiplies. The fact that endothelial cells are inherently deficient in autophagic machinery compared to epithelial cells and macrophages underscores the invasive nature of S. pyogenes and its ability to cause severe systemic diseases. S. pyogenes is still one of the top 10 causes of infectious mortality. Understanding the orchestration of dynamic host signaling networks will provide a better understanding of the increasingly complex mechanism of S. pyogenes diseases and novel ways of therapeutically intervening to thwart severe and often fatal infections.

The emerging role of stimulator of interferons genes signaling in sepsis: Inflammation, autophagy, and cell death

Stimulator of interferons genes (STING) is an adaptor protein that plays a critical role in the secretion of type I interferons and pro-inflammatory cytokines in response to cytosolic nucleic acid. Recent research indicates the involvement of the STING pathway in uncontrolled inflammation, sepsis, and shock. STING signaling is significantly up-regulated in human sepsis, and STING agonists are suggested to contribute to the pathogenesis of sepsis and shock. Nevertheless, little is known about the consequences of activated STING-mediated signaling during sepsis. It has been shown that aberrant activation of the STING-dependent way can result in increased inflammation, type I interferons responses, and cell death (including apoptosis, necroptosis, and pyroptosis). In addition, autophagy modulation has been demonstrated to protect against multiple organs injuries in animal sepsis model. However, impaired autophagy may contribute to the aberrant activation of STING signaling, leading to uncontrolled inflammation and cell death. Here we present a comprehensive review of recent advances in the understanding of STING signaling, focusing on the regulatory mechanisms and the roles of this pathway in sepsis.

Pathophysiology of Acute Illness and Injury

The pathophysiology of acute illness and injury recognizes three main effectors: infection, trauma, and ischemia-reperfusion injury. Each of them can act by itself or in combination with the other two in developing a systemic inflammatory reaction syndrome (SIRS) that is a generalized reaction to the morbid event. The time course of SIRS is variable and influenced by the number and severity of subsequent insults (e.g., reparative surgery, acquired hospital infections). It occurs simultaneously with a complex of counter-regulatory mechanisms (compensatory anti-inflammatory response syndrome, CARS) that limit the aggressive effects of SIRS. In adjunct, a progressive dysfunction of the acquired (lymphocytes) immune system develops with increased risk for immunoparalysis and associated infectious complications. Both humoral and cellular effectors participate to the development of SIRS and CARS. The most important humoral mediators are pro-inflammatory (IL-1β, IL-6, IL-8, IL-12) and anti-inflammatory (IL-4, IL-10) cytokines and chemokines, complement, leukotrienes, and PAF. Effector cells include neutrophils, monocytes, macrophages, lymphocytes, and endothelial cells. The endothelium is a key factor for production of remote organ damage as it exerts potent chemo-attracting effects on inflammatory cells, allows for leukocyte trafficking into tissues and organs, and promotes further inflammation by cytokines release. Moreover, the loss of vasoregulatory properties and the increased permeability contribute to the development of hypotension and tissue edema. Finally, the disseminated activation of the coagulation cascade causes the widespread deposition of microthrombi with resulting maldistribution of capillary blood flow and ultimately hypoxic cellular damage. This mechanism together with increased vascular permeability and vasodilation is responsible for the development of the multiple organ dysfunction syndrome (MODS).

Understanding the Cellular Origin of the Mononuclear Phagocyte System Sheds Light on the Myeloid Postulate of Immune Paralysis in Sepsis

Sepsis, in essence, is a serious clinical condition that can subsequently result in death as a consequence of a systemic inflammatory response syndrome including febrile leukopenia, hypotension, and multiple organ failures. To date, such life-threatening organ dysfunction remains one of the leading causes of death in intensive care units, with an increasing incidence rate worldwide and particularly within the rapidly growing senior population. While most of the clinical trials are aimed at dampening the overwhelming immune response to infection that spreads through the bloodstream, based on several human immunological investigations, it is now widely accepted that susceptibility to nosocomial infections and long-term sepsis mortality involves an immunosuppressive phase that is characterized by a decrease in some subsets of dendritic cells (DCs). Only recently substantial advances have been made in terms of the origin of the mononuclear phagocyte system that is now likely to allow for a better understanding of how the paralysis of DCs leads to sepsis-related death. Indeed, the unifying view of each subset of DCs has already improved our understanding of the pivotal pathways that contribute to the shift in commitment of their progenitors that originate from the bone marrow. It is quite plausible that this anomaly in sepsis may occur at the single level of DC-committed precursors, and elucidating the immunological basis for such a derangement during the ontogeny of each subset of DCs is now of particular importance for restoring an adequate cell fate decision to their vulnerable progenitors. Last but not least, it provides a direct perspective on the development of sophisticated myelopoiesis-based strategies that are currently being considered for the treatment of immunosenescence within different tissue microenvironments, such as the kidney and the spleen.

PM2.5 induces autophagy-mediated cell death via NOS2 signaling in human bronchial epithelium cells

The biggest victim of ambient air pollution is the respiratory system. Mainly because of the harmful components, especially the particulate matters with an aerodynamic diameter of ≤ 2.5µm (PM2.5), can be directly inhaled and deeply penetrate into the lung alveoli, thus causing severe lung dysfunction, including chronic cough, bronchitis and asthma, even lung cancer. Unfortunately, the toxicological mechanisms of PM2.5 associations with these adverse respiratory outcomes have still not been clearly unveiled. Here, we found that PM2.5 rapidly induced inflammatory responses, oxidative injure and cell death in human bronchial epithelium cells through upregulation of IL-6 expression, ROS production and apoptosis. Furthermore, PM2.5 specifically induced nitric oxide synthase 2 (NOS2) expression and NO generation to elevate excessive autophagy. Finally, disruption of NOS2 signaling effectively blocked autophayosome formation and the subsequent cell death. Our novel findings systemically reveled the role of autophagy-mediated cell death in PM2.5-treated human bronchial epithelium cells and provided potential strategy for future clinic intervention.

Metabolic Inflammatory Complex in Sepsis: Septic Cachexia as a Novel Potential Therapeutic Target

Despite several decades of focused investigation, sepsis remains a major cause of mortality in critically ill patients. Advancements in intensive care have enabled more patients to survive the acute phase of sepsis than previously, but a growing number of them progress to chronic critical illness. The failure of previous randomized clinical trials of anti-inflammatory agents to show any pro-survival benefit in septic patients underscores current thought that simple anti-inflammatory strategies are ineffective because the inhibitory effect of anti-inflammatory agents undermines the immune response to pathogens. New strategies with the dual capability of ameliorating inflammation in organs while stimulating antimicrobial activity are eagerly awaited. On the other hand, the metabolic alterations associated with systemic inflammatory response, including mitochondrial dysfunction and metabolic shift, are closely linked through a nexus of signaling pathways and signaling molecules. Preventing these metabolic derangements may be an alternative way to control excessive inflammation, an intriguing possibility that has not been fully explored. New insight into the molecular pathogenesis of sepsis and sepsis-associated chronic critical illness has led to the recognition of septic cachexia, a life-threatening form of metabolic inflammatory complex associated with multiple organ dysfunction. The potential for septic cachexia to serve as a novel target disease state to improve the clinical outcome of septic patients is discussed in this review.

Transient Receptor Potential Melastatin 2 Negatively Regulates LPS-ATP-Induced Caspase-1-Dependent Pyroptosis of Bone Marrow-Derived Macrophage by Modulating ROS Production

Background

Pyroptosis, a new form of cell death, which has special morphological characteristics, depends on caspase-1 activation and occupies an important role in inflammatory immune diseases and ischemia-reperfusion injury. ROS is a common activator of NLR/caspase-1. Transient receptor potential melastatin 2 (TRPM2), a selective cation channel, is involved in inflammatory regulation. This study was designed to explore the role of TRPM2 in activating caspase-1 and caspase-1-dependent pyroptosis of mouse BMDMs.

Methods

BMDMs isolated from WT and TRPM2−/− mice were treated with LPS and ATP, along with ROS inhibitor (NAC and DPI), caspase-1 inhibitor (Z-YVAD), or not. The activation of caspase-1 was measured by western blot. EtBr and EthD-2 staining were used to assess the incidence of pyroptosis.

Results

Compared with WT, the activated caspase-1-P10 was higher and the percentage of EtBr positive cells was also increased in TRPM2−/− group, which were both inhibited by Z-YVAD, NAC, or DPI. ASC oligomerization was increased in TRPM2−/− group.

Conclusion

Deletion of TRPM2 can enhance the activation of caspase-1 and pyroptosis, which may be via modulating ROS production, suggesting that TRPM2 plays a critical role in immune adjustment.

Neutrophil extracellular traps induce IL-1β production by macrophages in combination with lipopolysaccharide

Upon exposure to invading microorganisms, neutrophils undergo NETosis, a recently identified type of programmed cell death, and release neutrophil extracellular traps (NETs). NETs are described as an antimicrobial mechanism, based on the fact that NETs can trap microorganisms and exhibit bactericidal activity through the action of NET‑associated components. In contrast, the components of NETs have been recognized as damage‑associated molecular pattern molecules (DAMPs), which trigger inflammatory signals to induce cell death, inflammation and organ failure. In the present study, to clarify the effect of NETs on cytokine production by macrophages, mouse macrophage‑like J774 cells were treated with NETs in combination with lipopolysaccharide (LPS) as a constituent of pathogen‑associated molecular patterns. The results revealed that NETs significantly induced the production of interleukin (IL)‑1β by J774 cells in the presence of LPS. Notably, the NET/LPS‑induced IL‑1β production was inhibited by both caspase‑1 and caspase‑8 inhibitors. Furthermore, nucleases and serine protease inhibitors but not anti‑histone antibodies significantly inhibited the NET/LPS‑induced IL‑1β production. Moreover, we confirmed that caspase‑1 and caspase‑8 were activated by NETs/LPS, and the combination of LPS, DNA and neutrophil elastase induced IL‑1β production in reconstitution experiments. These observations indicate that NETs induce the production of IL‑1β by J774 macrophages in combination with LPS via the caspase‑1 and caspase‑8 pathways, and NET‑associated DNA and serine proteases are involved in NET/LPS‑induced IL‑1β production as essential components.

Mincle activation enhances neutrophil migration and resistance to polymicrobial septic peritonitis

Sepsis is a systemic inflammatory response to bacterial infection. The therapeutic options for treating sepsis are limited. Impaired neutrophil recruitment into the infection site is directly associated with severe sepsis, but the precise mechanism is unclear. Here, we show that Mincle plays a key role in neutrophil migration and resistance during polymicrobial sepsis. Mincle-deficient mice exhibited lower survival rates in experimental sepsis from cecal ligation and puncture and Escherichia coli–induced peritonitis. Mincle deficiency led to higher serum inflammatory cytokine levels and reduced bacterial clearance and neutrophil recruitment. Transcriptome analyses revealed that trehalose dimycolate, a Mincle ligand, reduced the expression of G protein–coupled receptor kinase 2 (GRK2) in neutrophils. Indeed, GRK2 expression was upregulated, but surface expression of the chemokine receptor CXCR2 was downregulated in blood neutrophils from Mincle-deficient mice with septic injury. Moreover, CXCL2-mediated adhesion, chemotactic responses, and F-actin polymerization were reduced in Mincle-deficient neutrophils. Finally, we found that fewer Mincle-deficient neutrophils infiltrated from the blood circulation into the peritoneal fluid in bacterial septic peritonitis compared with wild-type cells. Thus, our results indicate that Mincle plays an important role in neutrophil infiltration and suggest that Mincle signaling may provide a therapeutic target for treating sepsis.

On the translocation of bacteria and their lipopolysaccharides between blood and peripheral locations in chronic, inflammatory diseases: the central roles of LPS and LPS-induced cell death

We have recently highlighted (and added to) the considerable evidence that blood can contain dormant bacteria. By definition, such bacteria may be resuscitated (and thus proliferate). This may occur under conditions that lead to or exacerbate chronic, inflammatory diseases that are normally considered to lack a microbial component. Bacterial cell wall components, such as the endotoxin lipopolysaccharide (LPS) of Gram-negative strains, are well known as potent inflammatory agents, but should normally be cleared. Thus, their continuing production and replenishment from dormant bacterial reservoirs provides an easy explanation for the continuing, low-grade inflammation (and inflammatory cytokine production) that is characteristic of many such diseases. Although experimental conditions and determinants have varied considerably between investigators, we summarise the evidence that in a great many circumstances LPS can play a central role in all of these processes, including in particular cell death processes that permit translocation between the gut, blood and other tissues. Such localised cell death processes might also contribute strongly to the specific diseases of interest. The bacterial requirement for free iron explains the strong co-existence in these diseases of iron dysregulation, LPS production, and inflammation. Overall this analysis provides an integrative picture, with significant predictive power, that is able to link these processes via the centrality of a dormant blood microbiome that can resuscitate and shed cell wall components.

Antimicrobial cathelicidin peptide LL-37 inhibits the pyroptosis of macrophages and improves the survival of polybacterial septic mice

LL-37 is the only known member of the cathelicidin family of antimicrobial peptides in humans. In addition to its broad spectrum of antimicrobial activities, LL-37 can modulate various inflammatory reactions. We previously revealed that LL-37 suppresses the LPS/ATP-induced pyroptosis of macrophages in vitro by both neutralizing the action of LPS and inhibiting the response of P2X7 (a nucleotide receptor) to ATP. Thus, in this study, we further evaluated the effect of LL-37 on pyroptosis in vivo using a cecal ligation and puncture (CLP) sepsis model. As a result, the intravenous administration of LL-37 improved the survival of the CLP septic mice. Interestingly, LL-37 inhibited the CLP-induced caspase-1 activation and pyroptosis of peritoneal macrophages. Moreover, LL-37 modulated the levels of inflammatory cytokines (IL-1β, IL-6 and TNF-α) in both peritoneal fluids and sera, and suppressed the activation of peritoneal macrophages (as evidenced by the increase in the intracellular levels of IL-1β, IL-6 and TNF-α). Finally, LL-37 reduced the bacterial burdens in both peritoneal fluids and blood samples. Together, these observations suggest that LL-37 improves the survival of CLP septic mice by possibly suppressing the pyroptosis of macrophages, and inflammatory cytokine production by activated macrophages and bacterial growth. Thus, the present findings imply that LL-37 can be a promising candidate for sepsis because of its many functions, such as the inhibition of pyroptosis, modulation of inflammatory cytokine production and antimicrobial activity.

Simvastatin inhibits apoptosis of endothelial cells induced by sepsis through upregulating the expression of Bcl-2 and downregulating Bax

BACKGROUND

Many studies have showed that apoptosis of endothelial cells plays a curial role in the progress of sepsis. But the role of simvastatin in apoptosis of endothelial cells induced by sepsis is not clear. The present study aimed to investigate the role of simvastatin in apoptosis of endothelial cells induced by sepsis and its mechanism.

METHODS

Human umbilical vein endothelial cells (HUVECs) were randomly divided into three groups: control group, sepsis serum intervention group (sepsis group) and simvastatin+sepsis serum intervention group (simvastatin group). After 24-hour incubation with corresponding culture medium, the relative growth rate of HUVECS in different groups was detected by MTT assay; the apoptosis of HUVECs was detected by Hoechst33258 assay and flow cytometry; and the expression of the Bcl-2 and Bax genes of HUVECs was detected by PCR.

RESULTS

Compared with the sepsis group, HUVECs in the simvastatin group had a higher relative growth rate. Apoptotic HUVECs decreased significantly in the simvastatin group in comparison with the sepsis group. Expression of the Bcl-2 gene in HUVECs decreased obviously, but the expression of the Bax gene increased obviously after 24-hour incubation with sepsis serum; however, the expression of the Bcl-2 and Bax genes was just the opposite in the simvastatin group.

CONCLUSIONS

Our study suggests that simvastatin can inhibit apoptosis of endothelial cells induced by sepsis through upregulating the expression of Bcl-2 and downregulating Bax. It may be one of the mechanisms for simvastatin to treat sepsis.

Receptor-interacting protein kinase 3 deficiency inhibits immune cell infiltration and attenuates organ injury in sepsis

INTRODUCTION

Sepsis is defined as a systemic hyper-inflammatory immune response, with a subsequent immune-suppressive phase, which leads to multiple organ dysfunction and late lethality. Receptor-interacting protein kinase 3 (RIPK3)-dependent necrosis is implicated in driving tumor necrosis factor alpha (TNF-α)- and sepsis-induced mortality in mice. However, it is unknown if RIPK3 deficiency has any impact on immune cell trafficking, which contributes to organ damage in sepsis.

METHODS

To study this, male wild-type (WT) and RIPK3-deficient (Ripk3-/-) mice on C57BL/6 background were subjected to sham operation or cecal ligation and puncture (CLP)-induced sepsis. Blood and tissue samples were collected 20 hours post-CLP for various measurements.

RESULTS

In our severe sepsis model, the mean survival time of Ripk3-/- mice was significantly extended to 68 hours compared to 41 hours for WT mice. Ripk3-/- mice had significantly decreased plasma levels of TNF-α and IL-6 and organ injury markers compared to WT mice post-CLP. In the lungs, Ripk3-/- mice preserved better integrity of microscopic structure with reduced apoptosis, and decreased levels of IL-6, macrophage inflammatory protein (MIP)-2 and keratinocyte-derived chemokine (KC), compared to WT. In the liver, the levels of MIP-1, MIP-2 and KC were also decreased in septic Ripk3-/- mice. Particularly, the total number of neutrophils in the lungs and liver of Ripk3-/- mice decreased by 59.9% and 66.7%, respectively, compared to WT mice post-CLP. In addition, the number of natural killer (NK) and CD8T cells in the liver decreased by 64.8% and 53.4%, respectively, in Ripk3-/- mice compared to WT mice post-sepsis.

CONCLUSIONS

Our data suggest that RIPK3 deficiency modestly protected from CLP-induced severe sepsis and altered the immune cell trafficking in an organ-specific manner attenuating organ injury. Thus, RIPK3 acts as a detrimental factor in contributing to the organ deterioration in sepsis.

Antimicrobial cathelicidin peptide LL-37 inhibits the LPS/ATP-induced pyroptosis of macrophages by dual mechanism

Pyroptosis is a caspase-1 dependent cell death, associated with proinflammatory cytokine production, and is considered to play a crucial role in sepsis. Pyroptosis is induced by the two distinct stimuli, microbial PAMPs (pathogen associated molecular patterns) and endogenous DAMPs (damage associated molecular patterns). Importantly, cathelicidin-related AMPs (antimicrobial peptides) have a role in innate immune defense. Notably, human cathelicidin LL-37 exhibits the protective effect on the septic animal models. Thus, in this study, to elucidate the mechanism for the protective action of LL-37 on sepsis, we utilized LPS (lipopolysaccharide) and ATP (adenosine triphosphate) as a PAMP and a DAMP, respectively, and examined the effect of LL-37 on the LPS/ATP-induced pyroptosis of macrophage-like J774 cells. The data indicated that the stimulation of J774 cells with LPS and ATP induces the features of pyroptosis, including the expression of IL-1β mRNA and protein, activation of caspase-1, inflammasome formation and cell death. Moreover, LL-37 inhibits the LPS/ATP-induced IL-1β expression, caspase-1 activation, inflammasome formation, as well as cell death. Notably, LL-37 suppressed the LPS binding to target cells and ATP-induced/P2X7-mediated caspase-1 activation. Together these observations suggest that LL-37 potently inhibits the LPS/ATP-induced pyroptosis by both neutralizing the action of LPS and inhibiting the response of P2X7 to ATP. Thus, the present finding may provide a novel insight into the modulation of sepsis utilizing LL-37 with a dual action on the LPS binding and P2X7 activation.