Caspase-1 regulates Escherichia coli sepsis and splenic B cell apoptosis independently of interleukin-1beta and interleukin-18

ROLE OF CASPASE-1/CASPASE-11-HMGB1-RAGE/TLR4 SIGNALING IN THE EXACERBATION OF EXTRAPULMONARY SEPSIS-INDUCED LUNG INJURY BY MECHANICAL VENTILATION

ABSTRACT

Background: Mechanical ventilation (MV) is a clinically important measure for respiratory support in critically ill patients. Although moderate tidal volume MV does not cause lung injury, it can further exacerbate lung injury in a pathological state such as sepsis. This pathological process is known as the "two-hit" theory, whereby an initial lung injury (e.g., infection, trauma, or sepsis) triggers an inflammatory response that activates immune cells, presenting the lung tissue in a fragile state and rendering it more susceptible to subsequent injury. The second hit occurs when MV is applied to lung tissue in a fragile state, and it is noteworthy that this MV is harmless to healthy lung tissue, further aggravating preexisting lung injury through unknown mechanisms. This interaction between initial injury and subsequent MV develops a malignant cycle significantly exacerbating lung injury and severely hampering patient prognosis. The two-hit theory is critical to understanding the complicated mechanisms of ventilator-associated lung injury and facilitates the subsequent development of targeted therapeutic strategies. Methods and Results: The cecum ligation and perforation mice model was used to mimic clinical sepsis patients. After 12 h, the mice were mechanically ventilated for 2 to 6 h. MV by itself did not lead to HMGB1 release, but significantly strengthened HMGB1 in plasma and cytoplasm of lung tissue in septic mice. Plasma and lung tissue activation of cytokines and chemokines, mitogen-activated protein kinase signaling pathway, neutrophil recruitment, and acute lung injury were progressively decreased in LysM HMGB1 -/- (Hmgb1 deletion in myeloid cells) and iHMGB1 -/- mice (inducible HMGB1 -/- mouse strain where the Hmgb1 gene was globally deleted after tamoxifen treatment). Compared with C57BL/6 mice, although EC-HMGB1 -/- (Hmgb1 deletion in endothelial cells) mice did not have lower levels of inflammation, neutrophil recruitment and lung injury were reduced. Compared with LysM HMGB1 -/- mice, EC-HMGB1 -/- mice had higher levels of inflammation but significantly lower neutrophil recruitment and lung injury. Overall, iHMGB1 -/- mice had the lowest levels of all the above indicators. The level of inflammation, neutrophil recruitment, and the degree of lung injury were decreased in RAGE -/- mice, and even the above indices were further decreased in TLR4/RAGE -/- mice. Levels of inflammation and neutrophil recruitment were decreased in caspase-11 -/- and caspase-1/11 -/- mice, but there was no statistical difference between these two gene knockout mice. Conclusions: These data show for the first time that the caspase-1/caspase-11-HMGB1-TLR4/RAGE signaling pathway plays a key role in mice model of sepsis-induced lung injury exacerbated by MV. Different species of HMGB1 knockout mice have different lung-protective mechanisms in the two-hit model, and location is the key to function. Specifically, LysM HMGB1 -/- mice due to the deletion of HMGB1 in myeloid cells resulted in a pulmonary-protective mechanism that was associated with a downregulation of the inflammatory response. EC-HMGB1 -/- mice are deficient in HMGB1 owing to endothelial cells, resulting in a distinct pulmonary-protective mechanism independent of the inflammatory response and more relevant to the improvement of alveolar-capillary permeability. iHMGB1 -/- mice, which are systemically HMGB1-deficient, share both of these lung-protective mechanisms.

Immunoadjuvant therapy in the regulation of cell death in sepsis: recent advances and future directions

Sepsis is characterized by a concomitant early pro-inflammatory response by immune cells to an infection, and an opposing anti-inflammatory response that results in protracted immunosuppression. The primary pathological event in sepsis is widespread programmed cell death, or cellular self-sacrifice, of innate and adaptive immune cells, leading to profound immunological suppression. This severe immune dysfunction hampers effective primary pathogen clearance, thereby increasing the risk of secondary opportunistic infections, latent viral reactivation, multiple organ dysfunction, and elevated mortality. The types of cell death include apoptosis (type I programmed cell death), autophagy (type II programmed cell death), NETosis (a program for formation of neutrophil extracellular traps (NETs)) and other programmed cell deaths like pyroptosis, ferroptosis, necroptosis, each contributing to immunosuppression in distinct ways during the later phases of sepsis. Extensive apoptosis of lymphocytes, such as CD4+, CD8+ T cells, and B cells, is strongly associated with immunosuppression. Apoptosis of dendritic cells further compromises T and B cell survival and can induce T cell anergy or promote regulatory Treg cell proliferation. Moreover, delayed apoptosis and impaired neutrophil function contribute to nosocomial infections and immune dysfunction in sepsis. Interestingly, aberrant NETosis and the subsequent depletion of mature neutrophils also trigger immunosuppression, and neutrophil pyroptosis can positively regulate NETosis. The interaction between programmed cell death 1 (PD-1) or programmed cell death 1 ligand (PD-L1) plays a key role in T cell modulation and neutrophil apoptosis in sepsis. The dendritic cell growth factor, Fms-like tyrosine kinase (FLTEL), increases DC numbers, enhances CD 28 expression, attenuates PD-L1, and improves survival in sepsis. Recently, immunoadjuvant therapies have attracted attention for their potential to restore host physiological immunity and homeostasis in patients with sepsis. This review focuses on several potential immunotherapeutic agents designed to bolster suppressed innate and adaptive immune responses in the management of sepsis.

Emerging trends and hotspots in intestinal microbiota research in sepsis: bibliometric analysis

Background

The association between the gut microbiota and sepsis has garnered attention in the field of intestinal research in sepsis. This study utilizes bibliometric methods to visualize and analyze the literature on gut microbiota research in sepsis from 2011 to 2024, providing a scientific foundation for research directions and key issues in this domain.

Methods

Original articles and reviews of gut microbiota research in sepsis, which published in English between 2011 and 2024, were obtained from the Web of Science Core Collection on June 21, 2024. Python, VOSviewer, and CiteSpace software were used for the visual analysis of the retrieved data.

Results

A total of 1,031 articles were analyzed, originating from 72 countries or regions, 1,614 research institutions, and 6,541 authors. The articles were published in 434 different journals, covering 89 different research fields. The number of publications and citations in this research area showed a significant growth trend from 2011 to 2024, with China, the United States, and the United Kingdom being the main research forces. Asada Leelahavanichkul from Thailand was identified as the most prolific author, making him the most authoritative expert in this field. "Nutrients" had the highest number of publications, while "Frontiers in Cellular and Infection Microbiology," "Frontiers in Immunology" and "the International Journal of Molecular Sciences" have shown increasing attention to this field in the past 2 years. Author keywords appearing more than 100 times included "gut microbiota (GM)," "sepsis" and "microbiota." Finally, this study identified "lipopolysaccharides (LPS)," "short-chain fatty acids (SCFAs)," "probiotics," "fecal microbiota transplantation (FMT)" and "gut-liver axis" as the research hotspots and potential frontier directions in this field.

Conclusion

This bibliometric study summarizes current important perspectives and offers comprehensive guidance between sepsis and intestinal microbiota, which may help researchers choose the most appropriate research directions.

Neutrophil pyroptosis regulates corneal wound healing and post-injury neovascularisation

RATIONALE

The cornea is a unique structure that maintains its clarity by remaining avascular. Corneal injuries can lead to neovascularisation (CNV) and fibrosis and are the third most common cause of blindness worldwide.

OBJECTIVE

Corneal injuries induce an immune cell infiltration to initiate reparative processes. However, inflammation caused by sustained immune cell infiltration is known to be detrimental and can delay the healing process. This study was designed to understand the potential role of neutrophil and epithelial cell crosstalk in post-injury CNV.

METHODS AND RESULTS

Western blotting and immunostaining assays demonstrated that neutrophils infiltrated corneas and underwent pyroptosis following acute alkali injury. In vivo studies showed that genetic ablation of Gasdermin D (GsdmD), a key effector of pyroptosis, enhanced corneal re-epithelialisation and suppressed post-injury CNV. In vitro co-culture experiments revealed that interleukin-1β (IL-1β) was released from pyroptotic neutrophils which suppressed migration of murine corneal epithelial cells. Real-time RT-PCR and immunostaining assays identified two factors, Wnt5a and soluble fms-like tyrosine kinase-1 (sflt-1), highly expressed in newly healed epithelial cells. sflt-1 is known to promote corneal avascularity. Bone marrow transplantation, antibody mediated neutrophil depletion, and pharmacological inhibition of pyroptosis promoted corneal wound healing and inhibited CNV in an in vivo murine corneal injury model.

CONCLUSION

Taken together, our study reveals the importance of neutrophil/epithelium crosstalk and neutrophil pyroptosis in response to corneal injuries. Inhibition of neutrophil pyroptosis may serve as a potential treatment to promote corneal healing without CNV.

KEY POINTS

Neutrophil pyroptosis delays re-epithelialization after corneal injury Compromised re-epithelialization promotes corneal neovascularization after injury Inhibition of post-injury pyroptosis could be an effective therapy to promote corneal wound healing.

Lymphopenia in sepsis: a narrative review

This narrative review provides an overview of the evolving significance of lymphopenia in sepsis, emphasizing its critical function in this complex and heterogeneous disease. We describe the causal relationship of lymphopenia with clinical outcomes, sustained immunosuppression, and its correlation with sepsis prediction markers and therapeutic targets. The primary mechanisms of septic lymphopenia are highlighted. In addition, the paper summarizes various attempts to treat lymphopenia and highlights the practical significance of promoting lymphocyte proliferation as the next research direction.

ASC-expressing pyroptotic extracellular vesicles alleviate sepsis by protecting B cells

Pyroptosis is an inflammatory programmed cell death process characterized by membrane rupture. Interestingly, pyroptotic cells can generate plenty of nanosized vesicles. Non-inflammatory apoptotic cell death-derived apoptotic vesicles (apoVs) were systemically characterized and displayed multiple physiological functions and therapeutic potentials. However, the characteristics of pyroptotic cell-generated extracellular vesicles (EVs) are largely unknown. Here, we identified a group of pyroptotic EVs (pyroEVs) from in vitro cultured pyroptotic mesenchymal stem cells (MSCs), as well as from septic mouse blood. Compared with apoVs, pyroEVs express similar levels of annexin V, calreticulin, and common EV markers, but express a decreased level of apoptotic marker cleave caspase-3. PyroEVs, but not apoVs and exosomes, specifically express pyroptotic maker apoptosis-associated speck-like protein containing CARD (ASC). More importantly, MSC-derived pyroEVs protect B cells in the spleen and bone marrow to relieve inflammatory responses and enhance the survival rate of the septic mice. Mechanistically, pyroEV membrane-expressed ASC binds to B cells to repress cell death by repressing Toll-like receptor 4. This study uncovered the characteristics of pyroEVs and their therapeutic role in sepsis and B cell-mediated immune response.

Cold atmospheric plasma induces the curing mechanism of diabetic wounds by regulating the oxidative stress mediators iNOS and NO, the pyroptotic mediators NLRP-3, Caspase-1 and IL-1β and the angiogenesis mediators VEGF and Ang-1

It has been demonstrated that cold atmospheric plasma (CAP) accelerates the wound healing process, however the underlying molecular pathways behind this effect remain unclear. Thus, the goal of the proposed investigation is to elucidate the therapeutic advantages of CAP on angiogenesis, pyroptotic, oxidative stress, and inflammatory mediators during the wound-healing mechanisms associated with diabetes. Intraperitoneal administration of streptozotocin (STZ, 60 mg/Kg) of body weight was used to induce type-1 diabetes. Seventy-five male mice were randomized into 3 groups: the control non-diabetic group, the diabetic group that was not treated, and the diabetic group that was treated with CAP. The key mediators of pyroptosis and its impact on the slow healing process of diabetic wounds were examined using histological investigations employing H&E staining, immunohistochemistry, ELISA, and Western blotting analysis. Angiogenesis proteins (VEGF, Ang-1, and HO-1) showed a significant decline in expression concentrations in the diabetic wounds, indicating that diabetic animals' wounds were less likely to heal. Furthermore, compared to the controls, the major mediators of pyroptosis (NLRP-3, IL-1β, and caspase-1), oxidative stress (iNOS and NO), and inflammation (TNF-α and IL-6) have higher expression levels in the diabetic wounds. These factors substantially impede the healing mechanism of diabetic wounds. Interestingly, our results disclosed the therapeutic impacts of CAP treatment in the healing process of diabetic wounds via significantly regulating the expression levels of angiogenesis, pyroptosis, oxidative stress and pro-inflammatory mediators. Our findings demonstrated the curative likelihood of CAP and the underlying mechanisms for enhancing the healing process of diabetic wounds.

Adenine model of chronic renal failure in rats to determine whether MCC950, an NLRP3 inflammasome inhibitor, is a renopreventive

BACKGROUND

Chronic renal failure (CRF) is defined by a significant decline in renal function that results in decreased salt filtration and inhibition of tubular reabsorption, which ultimately causes volume enlargement. This study evaluated the potential renopreventive effects of the NLRP3 inflammasome inhibitor MCC950 in adenine-induced CRF in rats due to conflicting evidence on the effects of MCC950 on the kidney.

METHODS

Since the majority of the kidney tubular abnormalities identified in people with chronic renal disease are comparable to those caused by adding 0.75 percent of adenine powder to a rat's diet each day for four weeks, this method has received broad approval as a model for evaluating kidney damage. Throughout the test, blood pressure was checked weekly and at the beginning. Additionally, oxidative stress factors, urine sample examination, histological modifications, and immunohistochemical adjustments of caspase-3 and interleukin-1 beta (IL-1) levels in renal tissues were carried out.

RESULTS

Results revealed that MCC950, an inhibitor of the NLRP3 inflammasome, had a renopreventive effect, which was demonstrated by a reduction in blood pressure readings and an improvement in urine, serum, and renal tissue indicators that indicate organ damage. This was also demonstrated by the decrease in neutrophil gelatinase-associated lipocalin tubular expression (NGAL). The NLRP3 inflammasome inhibitor MCC950 was found to significantly alleviate the worsening renal cellular alterations evidenced by increased expression of caspase-3 and IL-1, according to immunohistochemical tests.

CONCLUSION

The NLRP3 inflammasome inhibitor MCC950 demonstrated renopreventive effects in the CRF rat model, suggesting that it might be used as a treatment strategy to stop the progression of CRF.

INTRINSIC/EXTRINSIC APOPTOSIS AND PYROPTOSIS CONTRIBUTE TO THE SELECTIVE DEPLETION OF B CELL SUBSETS IN SEPTIC SHOCK PATIENTS

ABSTRACT

The depletion of peripheral blood B cells is associated with immunosuppression and poor prognosis during sepsis, and selective depletion occurs when B cell subsets are specifically targeted. In this study, we examined the mechanisms underlying the selective depletion of B cell subsets in the immunosuppressive phase of septic shock patients. Thirty-two septic shock patients were recruited as a septic shock group and 10 healthy volunteers as a control group. The expression of Bcl-2, CD95, cleaved caspase-9/8, and activated caspase-3/1 in the B cell subsets were measured by flow cytometry. Another 23 septic shock patients were recruited to test the remission of caspase-3 (Z-DEVD-FMK) and caspase-1 (VX-765) inhibitors on B cell subset depletion in vitro . In septic shock patients, the Bcl-2 levels in immature/transitional (IM) B cells decreased and the levels of cleaved caspase-9 in IM B cells increased; the levels of CD95 in IM, naive, resting memory (RM), and activated memory (AM) B cells and the levels of cleaved caspase-8 in IM, RM, and AM B cells increased; the levels of activated caspase-3 and caspase-1 in IM, RM, and AM B cells increased. Activated caspase-1 levels in IM B cells were higher compared with activated caspase-3 in septic shock patients, whereas the levels of activated caspase-1 in AM B cells were lower compared with activated caspase-3. Moreover, in vitro experiments showed that Z-DEVD-FMK and VX-765 could alleviate the depletion of IM, AM, and RM B cells. The selective reduction of circulating B cell subsets in septic shock patients could be attributed to intrinsic and extrinsic apoptosis as well as pyroptosis.

Circulating extracellular vesicles are associated with the clinical outcomes of sepsis

Introduction

Sepsis is associated with endothelial cell (EC) dysfunction, increased vascular permeability and organ injury, which may lead to mortality, acute respiratory distress syndrome (ARDS) and acute renal failure (ARF). There are no reliable biomarkers to predict these sepsis complications at present. Recent evidence suggests that circulating extracellular vesicles (EVs) and their content caspase-1 and miR-126 may play a critical role in modulating vascular injury in sepsis; however, the association between circulating EVs and sepsis outcomes remains largely unknown.

Methods

We obtained plasma samples from septic patients (n=96) within 24 hours of hospital admission and from healthy controls (n=45). Total, monocyte- or EC-derived EVs were isolated from the plasma samples. Transendothelial electrical resistance (TEER) was used as an indicator of EC dysfunction. Caspase-1 activity in EVs was detected and their association with sepsis outcomes including mortality, ARDS and ARF was analyzed. In another set of experiments, total EVs were isolated from plasma samples of 12 septic patients and 12 non-septic critical illness controls on days 1, and 3 after hospital admission. RNAs were isolated from these EVs and Next-generation sequencing was performed. The association between miR-126 levels and sepsis outcomes such as mortality, ARDS and ARF was analyzed.

Results

Septic patients with circulating EVs that induced EC injury (lower transendothelial electrical resistance) were more likely to experience ARDS (p<0.05). Higher caspase-1 activity in total EVs, monocyte- or EC-derived EVs was significantly associated with the development of ARDS (p<0.05). MiR-126-3p levels in EC EVs were significantly decreased in ARDS patients compared with healthy controls (p<0.05). Moreover, a decline in miR-126-5p levels from day 1 to day 3 was associated with increased mortality, ARDS and ARF; while decline in miR-126-3p levels from day 1 to day 3 was associated with ARDS development.

Conclusions

Enhanced caspase-1 activity and declining miR-126 levels in circulating EVs are associated with sepsis-related organ failure and mortality. Extracellular vesicular contents may serve as novel prognostic biomarkers and/or targets for future therapeutic approaches in sepsis.

Regulation of Mesenchymal Cell Fate by Transfer of Active Gasdermin-D via Monocyte-Derived Extracellular Vesicles

Fibrosis is characterized by inappropriately persistent myofibroblast accumulation and excessive extracellular matrix deposition with the disruption of tissue architecture and organ dysfunction. Regulated death of reparative mesenchymal cells is critical for normal wound repair, but profibrotic signaling promotes myofibroblast resistance to apoptotic stimuli. A complex interplay between immune cells and structural cells underlies lung fibrogenesis. However, there is a paucity of knowledge on how these cell populations interact to orchestrate physiologic and pathologic repair of the injured lung. In this context, gasdermin-D (GsdmD) is a cytoplasmic protein that is activated following cleavage by inflammatory caspases and induces regulated cell death by forming pores in cell membranes. This study was undertaken to evaluate the impact of human (Thp-1) monocyte-derived extracellular vesicles and GsdmD on human lung fibroblast death. Our data show that active GsdmD delivered by monocyte-derived extracellular vesicles induces caspase-independent fibroblast and myofibroblast death. This cell death was partly mediated by GsdmD-independent induction of cellular inhibitor of apoptosis 2 (cIAP-2) in the recipient fibroblast population. Our findings, to our knowledge, define a novel paradigm by which inflammatory monocytes may orchestrate the death of mesenchymal cells in physiologic wound healing, illustrating the potential to leverage this mechanism to eliminate mesenchymal cells and facilitate the resolution of fibrotic repair.

Insights into the Roles of B Cells in Patients with Sepsis

Sepsis is a life-threatening yet common disease, still posing high mortality worldwide. Sepsis-related deaths primarily occur during immunosuppression; the disease can hamper the numbers and function of B cells, which mediate innate and adaptive immune responses to maintain immune homeostasis. Dysfunction of B cells, along with aggravated immunosuppression, are closely related to poor prognosis. However, B cells in patients with sepsis have garnered little attention. This article focuses on the significance of B-cell subsets, including regulatory B cells, in sepsis and how the counts and function of circulating B cells are affected in patients with sepsis. Finally, potential B-cell-related immunotherapies for sepsis are explored.

Pyroptosis in development, inflammation and disease

In the early 2000s, caspase-1, an important molecule that has been shown to be involved in the regulation of inflammation, cell survival and diseases, was given a new function: regulating a new mode of cell death that was later defined as pyroptosis. Since then, the inflammasome, the inflammatory caspases (caspase-4/5/11) and their substrate gasdermins (gasdermin A, B, C, D, E and DFNB59) has also been reported to be involved in the pyroptotic pathway, and this pathway is closely related to the development of various diseases. In addition, important apoptotic effectors caspase-3/8 and granzymes have also been reported to b involved in the induction of pyroptosis. In our article, we summarize findings that help define the roles of inflammasomes, inflammatory caspases, gasdermins, and other mediators of pyroptosis, and how they determine cell fate and regulate disease progression.

Dysregulation of neutrophil death in sepsis

Sepsis is a prevalent disease that has alarmingly high mortality rates and, for several survivors, long-term morbidity. The modern definition of sepsis is an aberrant host response to infection followed by a life-threatening organ dysfunction. Sepsis has a complicated pathophysiology and involves multiple immune and non-immune mediators. It is now believed that in the initial stages of sepsis, excessive immune system activation and cascading inflammation are usually accompanied by immunosuppression. During the pathophysiology of severe sepsis, neutrophils are crucial. Recent researches have demonstrated a clear link between the process of neutrophil cell death and the emergence of organ dysfunction in sepsis. During sepsis, spontaneous apoptosis of neutrophils is inhibited and neutrophils may undergo some other types of cell death. In this review, we describe various types of neutrophil cell death, including necrosis, apoptosis, necroptosis, pyroptosis, NETosis, and autophagy, to reveal their known effects in the development and progression of sepsis. However, the exact role and mechanisms of neutrophil cell death in sepsis have not been fully elucidated, and this remains a major challenge for future neutrophil research. We hope that this review will provide hints for researches regarding neutrophil cell death in sepsis and provide insights for clinical practitioners.

Molecular mechanisms and functions of pyroptosis in sepsis and sepsis-associated organ dysfunction

Sepsis, a life-threatening organ dysfunction caused by a dysregulated host response to infection, is a leading cause of death in intensive care units. The development of sepsis-associated organ dysfunction (SAOD) poses a threat to the survival of patients with sepsis. Unfortunately, the pathogenesis of sepsis and SAOD is complicated, multifactorial, and has not been completely clarified. Recently, numerous studies have demonstrated that pyroptosis, which is characterized by inflammasome and caspase activation and cell membrane pore formation, is involved in sepsis. Unlike apoptosis, pyroptosis is a pro-inflammatory form of programmed cell death that participates in the regulation of immunity and inflammation. Related studies have shown that in sepsis, moderate pyroptosis promotes the clearance of pathogens, whereas the excessive activation of pyroptosis leads to host immune response disorders and SAOD. Additionally, transcription factors, non-coding RNAs, epigenetic modifications and post-translational modifications can directly or indirectly regulate pyroptosis-related molecules. Pyroptosis also interacts with autophagy, apoptosis, NETosis, and necroptosis. This review summarizes the roles and regulatory mechanisms of pyroptosis in sepsis and SAOD. As our understanding of the functions of pyroptosis improves, the development of new diagnostic biomarkers and targeted therapies associated with pyroptosis to improve clinical outcomes appears promising in the future.

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.

Serum IL-1, Pyroptosis and Intracranial Aneurysm Wall Enhancement: Analysis Integrating Radiology, Serum Cytokines and Histology

Background and Purpose

Aneurysm wall enhancement (AWE) is correlated with the rupture and growth risk of unruptured intracranial aneurysms (UIAs). Pyroptosis is a proinflammation mode of lytic cell death, mediated by pyroptosis-related proteins, i.e., gasdermin D and interleukin 1 β (IL-1β). Integrating serum cytokines and histology, this study aimed to investigate the correlation between AWE and pyroptosis in UIAs.

Methods

UIA patients receiving microsurgical clipping were prospectively enrolled from January 2017 and June 2020. UIA samples were collected, as well as the corresponding blood samples. In this study, high-resolution magnetic resonance was employed to identify the AWE. The serum 46-cytokines examination and the histological analysis were conducted to determine pyroptosis, CD68 and MMP2. The IL-1 ra/beta ratio was determined by complying with the serum IL-1β and IL-1.ra. A comparison was drawn in the differences between UIAs with and without AWE. Lastly, the correlation between inflammation in UIA samples and serums was investigated.

Results

This study included 34 UIA patients. The serum proinflammatory cytokines [IL-1β (P < 0.001) and TNF-α (P < 0.001)] were up-regulated, and serum anti-inflammatory cytokine (IL-1.ra, P = 0.042) were down-regulated in patients with AWE UIAs. The patients with AWE UIAs achieved a higher IL-1.ra/beta ratio (P < 0.001). The multivariate logistic analysis demonstrated IL-1β [odds ratio (OR), 1.15; 95% confidence interval (CI), 1.02–1.30; P = 0.028] and IL-1.ra (OR, 0.998; 95% CI, 0.997–1.000; P = 0.017) as the risk factors correlated with the AWE. IL-1.ra/beta ratio achieved the highest predictive accuracy [area under the curve (AUC), 0.96] for AWE, followed by IL-1.ra (AUC, 0.90), IL-1β (AUC, 0.88) and TNF-α (AUC, 0.85). As compared with the UIAs without AWE, the AWE UIAs were manifested as a severer wall remodeling, with higher relative levels of pyroptosis-related proteins, CD68 and MMP2. The serum IL-1β, IL-1.ra and IL-1.ra/beta ratio had a positive correlation with the relative levels of pyroptosis-related proteins, CD68 and MMP2 in UIA tissues.

Conclusion

The serum IL-1β and IL-1.ra were correlated with the AWE. More pyroptosis-related proteins were identified in UIAs with AWE. The serum IL-1β and IL-1.ra were correlated with the pyroptosis-related proteins in aneurysm tissues.

Sequential Changes of NLRP3 Inflammasome Activation in Sepsis and its Relationship With Death

INTRODUCTION

Inflammasomes are recognized as key components of the innate immune response in sepsis. We aimed to describe the transcriptional expression of nucleotide-binding domain, leucine-rich repeat-containing receptor, pyrin domain-containing-3 (NLRP3), and serum interleukin-1β (IL-1 β) in critically ill patients, their changes over the first week and their prognostic value in septic patients.

METHODS

Prospective study including patients with sepsis based on Sepsis-3 definitions and a control group of critically ill patients without sepsis. We measured the circulating levels of IL-1β as well as the transcriptional expression of NLRP3 at admission and on days 3 and 7. Caspase-1 and caspase-3 activation was analyzed in a matched cohort of patients with septic shock (four dead and four survivors).

RESULTS

Fifty-five septic patients and 11 non-septic patients were studied. Levels on day 0 and 3 of IL-1 β and NLRP3 inflammasome expression were significantly higher in patients with sepsis than in controls. NLRP3 was significantly higher in septic patients who survived at day 7 without significant difference between survivors and non-survivors at baseline and on day 3. In survivors, an increased caspase-1 protein expression with reduced expression caspase-3 was observed with the opposite pattern in those who died.

CONCLUSIONS

NLRP3 is activated in critically ill patients but this up-regulation is more intense in patients with sepsis. In sepsis, a sustained NLRP3 activation during the first week is protective and sepsis. An increased caspase-1 protein expression with reduced expression caspase-3 is the pattern observed in septic shock patients who survive.

Intracellular and Extracellular Lipopolysaccharide Signaling in Sepsis: Avenues for Novel Therapeutic Strategies

Sepsis is defined as organ dysfunction due to a dysregulated systemic host response to infection. During gram-negative bacterial infection and other acute illness such as absorption from the gut infection, lipopolysaccharide (LPS) is a major mediator in sepsis. LPS is able to trigger inflammation through both intracellular and extracellular pathways. Classical interactions between LPS and host cells first involve LPS binding to LPS binding protein (LBP), a carrier. The LPS-LBP complex then binds to a receptor complex including the CD14, MD2, and toll-like receptor 4 (TLR4) proteins, initiating a signal cascade which triggers the secretion of pro-inflammatory cytokines. However, it has been established that LPS is also internalized by macrophages and endothelial cells through TLR4-independent pathways. Once internalized, LPS is able to bind to the cytosolic receptors caspases-4/5 in humans and the homologous caspase-11 in mice. Bound caspases-4/5 oligomerize and trigger the assembly of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 inflammasome followed by the activation of inflammatory caspase-1 resulting in subsequent release of interleukin-1β. Caspases-4/5 also activate the perforin gasdermin D and purinergic receptor P2X7, inducing cell lysis and pyroptosis. Pyroptosis is a notable source of inflammation and damage to the lung endothelial barrier during sepsis. Thus, inhibition of caspases-4/5/1 or downstream effectors to block intracellular LPS signaling may be a promising therapeutic approach in adjunction with neutralizing extracellular LPS for treatment of sepsis.

Interaction between endogenous H2O2 and OsVPE3 in the GA-induced PCD of rice aleurone layers

Endogenous hydrogen peroxide (H₂O₂) is involved in regulating the gibberellic acid-induced programmed cell death (PCD) of the aleurone layers by cooperating with OsVPE3 during rice seed germination. Preliminary experiments revealed that H₂O₂ produced by the NOX pathway is the key factor affecting rice germination. Histochemical analysis indicated that H₂O₂ is located in the aleurone layer. Both the H₂O₂ scavenger DMTU and the NOX inhibitor DPI decreased H₂O₂ content and significantly slowed down vacuolation in a dose-dependent manner. Interestingly, DMTU down-regulated the OsNOX8 transcript or DMTU and DPI decreased the intracellular H₂O₂ level, resulting in a delay of PCD. In contrast, GA and H₂O₂ up-regulated the OsNOX8 transcript and intracellular H₂O₂ level, leading to premature PCD, and the effects of GA and H₂O₂ were reversed by DMTU and DPI, respectively. These results showed that the imbalance of intracellular H₂O₂ levels leads to the delayed or premature PCD. Further experiments indicated that GA up-regulated the OsVPE3 transcript and VPE activity, and the effect was reversed by DPI. Furthermore, Ac-YVAD-CMK significantly blocked H₂O₂ accumulation, and DPI + Ac-YVAD-CMK had a more significant inhibitory effect compared with DPI alone, resulting in the delayed PCD, suggesting that OsVPE3 regulates PCD by promoting H₂O₂ generation. Meanwhile, DPI significantly inhibited the OsVPE3 transcript and VPE activity, and in turn delayed PCD occurrence, suggesting that the H₂O₂ produced by the NOX pathway may regulate PCD by up-regulating the OsVPE3 transcript. Thus, the endogenous H₂O₂ produced by the NOX pathway mediates the GA-induced PCD of rice aleurone layers by interacting with OsVPE3.

The deubiquitinase STAMBP modulates cytokine secretion through the NLRP3 inflammasome

The NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome is a multimeric, cytoplasmic, protein complex that regulates maturation and secretion of interleukin (IL)-1β, a potent pro-inflammatory cytokine. Critical to host defense against pathogens, IL-1β amplifies early innate immune responses by activating transcription of numerous other cytokines and chemokines. Excessive IL-1β is associated with poor outcomes in inflammatory illnesses, such as sepsis and the acute respiratory distress syndrome (ARDS). Tight regulation of this signaling axis is vital, but little is known about mechanisms to limit excessive inflammasome activity. Here we identify the deubiquitinase STAM-binding protein (STAMBP) as a negative regulator of the NLRP3 inflammasome. In monocytes, knockout of STAMBP by CRISPR/Cas9 gene editing increased expression of numerous cytokines and chemokines in response to Toll-like receptor (TLR) agonists or bacterial lipopolysaccharide (LPS). This exaggerated inflammatory response was dependent on IL-1β signaling, and STAMBP knockout directly increased release of IL-1β with TLR ligation. While STAMBP does not modulate NLRP3 protein abundance, cellular depletion of the deubiquitinase increased NLRP3 K63 chain polyubiquitination resulting in increased NLRP3 inflammasome activation. These findings describe a unique mechanism of non-degradative ubiquitination of NLRP3 by STAMBP to limit excessive inflammasome activation and to reduce injurious IL-1β signaling.

Reactive Oxygen Species Interact With NLRP3 Inflammasomes and Are Involved in the Inflammation of Sepsis: From Mechanism to Treatment of Progression

Over the past 10 years, the crisis of sepsis has remained a great challenge. According to data from 2016, the sepsis-related mortality rate remains high. In addition, sepsis consumes extensive medical resources in intensive care units, and anti-inflammatory agents fail to improve sepsis-associated hyperinflammation and symptoms of immunosuppression. The specific immune mechanism of sepsis remains to be elucidated. Reactive oxygen species (ROS) are triggered by energy metabolism and respiratory dysfunction in sepsis, which not only cause oxidative damage to tissues and organelles, but also directly and indirectly promote NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation. NLRP3 inflammasomes enlarge the inflammatory response and trigger apoptosis of immune cells to exacerbate sepsis progression. Inhibiting the negative effects of ROS and NLRP3 inflammasomes therefore provides the possibility of reversing the excessive inflammation during sepsis. In this review, we describe the interaction of ROS and NLRP3 inflammasomes during sepsis, provide prevention strategies, and identify fields that need further study.

Sequential ubiquitination of NLRP3 by RNF125 and Cbl-b limits inflammasome activation and endotoxemia

Aberrant NLRP3 inflammasome activation contributes to the development of endotoxemia. The importance of negative regulation of NLRP3 inflammasomes remains poorly understood. Here, we show that the E3 ubiquitin ligase Cbl-b is essential for preventing endotoxemia induced by a sub-lethal dose of LPS via a caspase-11/NLRP3-dependent manner. Further studies show that NLRP3 undergoes both K63- and K48-linked polyubiquitination. Cbl-b binds to the K63-ubiquitin chains attached to the NLRP3 leucine-rich repeat domain (LRR) via its ubiquitin-associated region (UBA) and then targets NLRP3 at K496 for K48-linked ubiquitination and proteasome-mediated degradation. We also identify RNF125 as an additional E3 ubiquitin ligase that initiates K63-linked ubiquitination of the NLRP3 LRR domain. Therefore, NLRP3 is sequentially ubiquitinated by K63- and K48-linked ubiquitination, thus keeping the NLRP3 inflammasomes in check and restraining endotoxemia.

Gm614 Protects Germinal Center B Cells From Death by Suppressing Caspase-1 Transcription in Lupus-Prone Mice

Only a few signaling pathways have been reported in germinal center (GC) B-cell proliferation and death. In this study, we showed that a novel uncharacterized Gm614 protein is highly expressed in GC B cells from lupus-prone mice. Critically, ablation of this GC B-cell-specific Gm614 promoted GC B-cell death and mitigation of autoimmune symptoms, whereas overexpression protected GC B cells from death and exacerbated autoimmune symptoms. We demonstrated that mechanistically, nuclear-localized Gm614 reduced caspase-1 expression in GC B cells by binding with caspase-1 promoter to suppress its activation. Our results suggest that Gm614 protects GC B cells from death by suppressing caspase-1 transcription in autoimmune diseases. This may provide some hints for targeting the cell proliferation involved in autoimmune diseases.

The interaction between C/EBPβ and TFAM promotes acute kidney injury via regulating NLRP3 inflammasome-mediated pyroptosis

Sepsis-induced inflammatory damage is a crucial cause of acute kidney injury (AKI), and AKI is an ecumenical fearful complication in approximately half of patients with sepsis. CCAAT/enhancer-binding protein β (C/EBPβ) plays roles in regulating acute phase responses and inflammation. However, the role and mechanism of C/EBPβ in AKI are unclear. LPS combined with ATP-treated renal epithelial cells HK2 and cecal ligation-peferation (CLP)-mice were used as models of AKI in vitro and in vivo. Cell damage, the secretion of interleukin-1 beta (IL-1β), IL-18 and cysteinyl aspartate specific proteinase 1 (caspase-1) activity were tested by LDH, ELISA assay and flow cytometry analysis, respectively. The expression levels of TFAM, C/EBPβ, and pyroptosis-related molecules were tested by qRT-PCR and Western blotting. Chromatin immunoprecipitation (ChIP) assessed the interaction between C/EBPβ with TFAM. Hematoxylin-Eosin (H&E) staining detected pathological changes of kidney tissues, and immunohistochemistry measured TFAM and C/EBPβ in mice kidney tissues. C/EBPβ or TFAM were up-regulated in LPS combined with ATP -induced HK2 cells. Knockdown of C/EBPβ could suppress cell injury and the secretion of IL-1β and IL-18 induced by LPS combined with ATP. Furthermore, C/EBPβ up-regulated the expression levels of TFAM via directly binding to TFAM promoter. Overexpression of TFAM reversed the effects of C/EBPβ deficiency on pyroptosis. Knockdown of C/EBPβ could inhibit NLRP3 inflammasome-mediated caspase-1 signaling pathway by inactivating TFAM/RAGE pathway. It was further confirmed in the AKI mice that C/EBPβ and TFAM promoted AKI by activating NLRP3-mediated pyroptosis. The interaction of between C/EBPβ and TFAM facilitated pyroptosis by activating NLRP3/caspase-1 signal axis, thereby promoting the occurrence of AKI.

NLRP3 Inflammasome in Inflammation and Metabolism: Identifying Novel Roles in Postburn Adipose Dysfunction

Inflammasomes are multiprotein complexes that respond to pathogen or host associated damage markers, leading to caspase-1 maturation and processing of pro-inflammatory cytokines. Initially, inflammasomes were implicated primarily in inflammatory and infectious conditions. However, increasing evidence demonstrates broader roles beyond inflammation, including regulation of adipose tissue metabolism after burns. Here, we conducted a search for articles on PubMed, Web of Science, Embase, Scopus, and UpToDate with applied search strategies including a combination of "burns," "trauma," "(NLRP3) inflammasome," "metabolic conditions," "white adipose tissue," "macrophages," "browning," and "lipolysis" and included papers from 2000 to 2020. We discuss unexpected roles for NLRP3, the most characterized inflammasome to date, as a key metabolic driver in a variety of conditions. In particular, we highlight the function of NLRP3 inflammasome in burn trauma, which is characterized by both hyperinflammation and hypermetabolism. We identify a critical part for NLRP3 activation in macrophage dynamics and delineate a novel role in postburn white adipose tissue remodeling, a pathological response associated with hypermetabolism and poor clinical outcomes. Mechanistically, how inflammation and inflammasome activation is linked to postburn hypermetabolism is a novel concept to contemplate, and herein we provide evidence of an immunometabolic crosstalk between adipocytes and infiltrating macrophages.

The Critical Roles and Mechanisms of Immune Cell Death in Sepsis

Sepsis was first described by the ancient Greek physicians over 2000 years ago. The pathophysiology of the disease, however, is still not fully understood and hence the mortality rate is still unacceptably high due to lack of specific therapies. In the last decade, great progress has been made by shifting the focus of research from systemic inflammatory response syndrome (SIRS) to multiple organ dysfunction syndrome (MODS). Sepsis has been re-defined as infection-induced MODS in 2016. How infection leads to MODS is not clear, but what mediates MODS becomes the major topic in understanding the molecular mechanisms and developing specific therapies. Recently, the mechanism of infection-induced extensive immune cell death which releases a large quantity of damage-associated molecular patterns (DAMPs) and their roles in the development of MODS as well as immunosuppression during sepsis have attracted much attention. Growing evidence supports the hypothesis that DAMPs, including high-mobility group box 1 protein (HMGB1), cell-free DNA (cfDNA) and histones as well as neutrophil extracellular traps (NETs), may directly or indirectly contribute significantly to the development of MODS. Here, we provide an overview of the mechanisms and consequences of infection-induced extensive immune cell death during the development of sepsis. We also propose a pivotal pathway from a local infection to eventual sepsis and a potential combined therapeutic strategy for targeting sepsis.

Mechanistic insights into the role of pyroptosis in rheumatoid arthritis

Cell death is ascribed as an essential biological process that is fundamental for the development of an organism along with its survival. The procedure comprises of apoptosis and pyroptosis. Pyroptosis is a programmed procedure for cell death which is inflammatory in nature and this pathway gets activated via human caspase-4, human caspase-11 and human caspase-5. The activation of this process leads to release of pro-inflammatory mediators including cytokines, alarmins, IL-18 and IL-1β. The pro-inflammatory mediators released via interaction of intracellular kinases direct the development of Rheumatoid arthritis. Rheumatoid arthritis is characterized as disorder/disease that is auto-immune and chronic in nature. It involves erosions in marginal bone along with articular cartilage which is responsible for joint destruction. The cytokine along with its complex network is responsible for inflammation. The process of pyroptosis is linked with the destruction of plasma membrane, that releases these mediators and excessive release of these mediators is linked with rheumatoid arthritis.

[Molecular mechanism underlying the inhibitory effect of propofol on lipopolysaccharide-induced pyroptosis of mouse bone marrow-derived macrophages]

OBJECTIVE

To investigate the molecular mechanism underlying the inhibitory effect of propofol on pyroptosis of macrophages.

METHODS

Macrophages derived from bone marrow were extracted and divided into three groups: control group, LPS+ATP group and propofol+LPS+ATP group. The control group was not given any treatment; LPS+ATP group was given LPS 1 μg/mL stimulation for 4 h, then ATP 4 mM stimulation for 1 h; Propofol+LPS+ATP group was given propofol+LPS 1 μg/mL stimulation for 4 h, then ATP stimulation for 1 h. After treatment, the supernatant and cells of cell culture were collected. the cell activity was detected by CCK8 and flow cytometry. The inflammatory cytokines IL-1βand IL-18 were detected by Elisa. Western blot was used to detect the expression of caspase-1 protein and TLR4 on cell membran Immunohistochemical fluorescence was used to detect apoptosis of cells.

RESULTS

LPS+ATP significantly decreased the viability of the macrophages and increased the cellular production of IL-1β and IL-18, activation of caspase-1 protein and the expression of TLR-4 on the cell membrane (P &lt; 0.05). Treatment with propofol obviously reversed the changes induced by LPS+ATP.

CONCLUSIONS

LPS+ATP can induce pyroptosis of mouse bone marrow-derived macrophages, and propofol effectively inhibits such cell death, suggesting that propofol anesthesia is beneficial during operation and helps to regulate the immune function of in patients with sepsis.

The roles of NLRP3 inflammasome in bacterial infection

BACKGROUND

The NOD-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasomes are intracellular protein complexes that orchestrate immune responses through mediating caspase-1 activation, which leads to maturation of pro-interleukin (IL)-1β. Though it is known that both Gram-negative and Gram-positive bacteria could activate the NLRP3 inflammasome, the roles of NLRP3 inflammasome in bacterial sepsis is ill-defined.

METHODS

Sepsis was induced in C57BL/6, Nlrp3 KO, Asc KO and interleukin-1-receptor (Il1r) KO male mice. PBS or Escherichia coli were injected intravenously into mice. The number of days from cecal ligation and puncture (CLP) surgery or Escherichia coli injection to death in each group was documented for survival. After 16 h of CLP or Escherichia coli injection, livers, lungs and spleens were harvested and assessed for bacterial loads. Tissue sections of the liver and lung were done to show the infiltration of inflammatory cells and the serum and peritoneal lavage fluid were harvested and assessed by ELISA for pro-inflammatory cytokines (IL-6, IL-1β, IL-18), and by flow cytometric analysis for peritoneal neutrophil infiltration.

RESULTS

Using a murine CLP model, we found that the NLRP3 inflammasome is protective in polymicrobial abdominal infection. Genetic deletion of NLRP3 significantly inhibited the production of IL-1β and worsened the outcome after CLP. Loss of NLRP3 significantly inhibited neutrophil recruitment in peritoneal cavity and impaired the bacterial clearance after CLP. Genetic deletion of Il1r, the receptor of IL-1β, phenocopied NLRP3 deficiency in polymicrobial abdominal infection. However, NLRP3 deficiency conferred protection when Escherichia coli were directly injected into the blood stream.

CONCLUSION

Our results demonstrate that NLRP3 signaling confers protection against polymicrobial abdominal infection but promote lethality during disseminated bacterial infection.

Pyroptosis: The missing puzzle among innate and adaptive immunity crosstalk

Pyroptosis is a newly discovered programmed cell death with inflammasome formation. Pattern recognition receptors that identify repetitive motifs of prospective pathogens such as LPS of gram-negative bacteria are crucial to pyroptosis. Upon stimulation by pathogen-associated molecular patterns or damage-associated molecular patterns, proinflammatory cytokines, mainly IL-1 family members IL-1β and IL-18, are released through pyroptosis specific pore-forming protein, gasdermin D. Even though IL-1 family members are mainly involved in innate immunity, they can be factors in adaptive immunity. Given the importance of IL-1 family members in health and diseases, deciphering the role of pyroptosis in the regulation of innate and adaptive immunity is of great importance, especially with the recent progress in identifying the exact mechanism of such a pathway. In this review, we will focus on how the innate inflammatory mediators can regulate the adaptive immune system and vice versa via pyroptosis.

Immunotherapy in sepsis - brake or accelerate?

Sepsis, a life threating syndrome characterized by organ failure after infection, is the most common cause of death in hospitalized patients. The treatment of sepsis is generally supportive in nature, involving the administration of intravenous fluids, vasoactive substances and oxygen plus antibiotics to eliminate the pathogen. No drugs have been approved specifically for the treatment of sepsis, and clinical trials of potential therapies have failed to reduce mortality - suggesting that new approaches are needed. Abnormalities in the immune response elicited by the pathogen, ranging from excessive inflammation to immunosuppression, contribute to disease pathogenesis. Although hundreds of immunomodulatory agents are potentially available, it remains unclear which patient benefits from which immune therapy at a given time point. Results indicate the importance of personalized therapy, specifically the need to identify the type of intervention required by each individual patient at a given point in the disease process. To address this issue will require using biomarkers to stratify patients based on their individual immune status. This article reviews recent and ongoing clinical investigations using immunostimulatory or immunosuppressive therapies against sepsis including non-pharmacological and novel preclinical approaches.

6-Gingerol attenuates macrophages pyroptosis via the inhibition of MAPK signaling pathways and predicts a good prognosis in sepsis

BACKGROUND

Sepsis is a major cause of death for ICU patients. Sepsis development depends heavily on the presence of mature IL-1β cytokine. This study evaluates the potential therapeutic properties of a bioactive compound known as 6-gingerol on sepsis. This compound has previously been demonstrated to possess anti-inflammatory properties both in vivo and in vitro.

METHODS

C57BL/6 mice was used to establish models of sepsis by means of cecal ligation and puncture (CLP). Upon treatment with 6-gingerol, we assessed the survival rate of mice and measured the levels of key pro-inflammatory cytokines in serum and colon tissues. Sepsis pathogenesis was further explored using the RAW264.7 cell line and bone marrow-derived macrophages (BMDMs) treated with ATP and lipopolysaccharide (LPS). The impact of 6-gingerol on pyroptosis was also examined. In addition, we assessed the role of MAPK signaling in 6-gingerol-induced effects in BMDMs and RAW264.7 cells.

RESULTS

In CLP mice, 6-gingerol significantly ameliorated sepsis development, which was associated with the reduction of serum IL-1β. In BMDMs and RAW264.7 cells, 6-gingerol strongly attenuated pyroptosis as well as the release of caspase-1p20, HMGB1, mature IL-1β, IL-18 in response to ATP and LPS treatment. 6-Gingerol conferred these effects by blocking MAPK activation. Exposure to an ERK agonist (EGF) reversed effects of 6-gingerol, causing pyroptosis, LDH and caspase-1p20 release.

CONCLUSIONS

By targeting MAPK signaling, 6-gingerol significantly suppressed secretion of pro-inflammatory cytokines and inhibited macrophage cells pyroptosis resulting in overall inhibition of sepsis development.

Temporally Distinct Regulation of Pathways Contributing to Cardiac Proteostasis During the Acute and Recovery Phases of Sepsis

BACKGROUND

Cardiac dysfunction is a common manifestation of sepsis and is associated with early increases in inflammation and decreases in myocardial protein synthesis. However, little is known regarding the molecular mechanisms regulating protein homeostasis during the recovery phase after the removal of the septic nidus. Therefore, the purpose of this study was to investigate diverse signal transduction pathways that regulate myocardial protein synthesis and degradation.

METHODS

Adult male C57BL/6 mice were used to identify potential mechanisms mediating the acute (24 h) effect of cecal ligation and puncture as well as long-term changes that manifest during the chronic (10 days) recovery phase.

RESULTS

Sepsis acutely decreased cardiac protein synthesis that was associated with reduced phosphorylation of S6K1/S6 but not 4E-BP1. Sepsis also decreased proteasome activity, although with no change in MuRF1 and atrogin-1 mRNA expression. Sepsis acutely increased apoptosis (increased caspase-3 and PARP cleavage), autophagosome formation (increased LC3B-II), and canonical inflammasome activity (increased NLRP3, TMS1, cleaved caspase-1). In contrast, during the recovery phase, independent of a difference in food consumption, global protein synthesis was increased, the early repression in proteasome activity was restored to basal levels, whereas stimulation of apoptosis, autophagosome formation, and the canonical inflammasome pathway had abated. However, during recovery there was a selective stimulation of the noncanonical inflammasome pathway as evidenced by activation of caspase-11 with cleavage of Gasdermin D.

CONCLUSIONS

These data demonstrate a temporally distinct homeostatic shift in the cardiac proteostatic response to acute infection and recovery.

Neutrophil pyroptosis: new perspectives on sepsis

Pyroptosis is a caspase-1 or caspase-4/5/11-dependent programmed cell death associated with inflammation, which is initiated by inflammasomes or cytosolic LPS in innate immunity. Sepsis is a life-threatening organ dysfunction caused by an imbalance in the body's response to infection. It is a complex interaction between the pathogen and the host's immune system. Neutrophils play the role of a double-edged sword in sepsis, and a number of studies have previously shown that regulation of neutrophils is the most crucial part of sepsis treatment. Pyroptosis is one of the important forms for neutrophils to function, which is increasingly understood as a host active immune response. There is ample evidence that neutrophil pyroptosis may play an important role in sepsis. In recent years, a breakthrough in pyroptosis research has revealed the main mechanism of pyroptosis. However, the potential value of neutrophil pyroptosis in the treatment of sepsis did not draw enough attention. A literature review was performed on the main mechanism of pyroptosis in sepsis and the potential value of neutrophils pyroptosis in sepsis, which may be suitable targets for sepsis treatment in future.

Inner sensors of endotoxin - implications for sepsis research and therapy

Despite great efforts and numerous clinical trials, there is still a major need for effective therapies for sepsis. Neutralization or elimination of bacterial toxins remains a promising approach. The understanding of the interaction of the endotoxin (lipopolysaccharide, LPS) of Gram-negative bacteria with its cellular receptor, namely the CD14/TLR4/MD2 complex, was a major breakthrough. Unfortunately, clinical trials for sepsis on the neutralization of LPS or on the inhibition of TLR4 signaling failed whereas those on LPS removal remain controversial. Recent discoveries of another class of LPS receptors localized within the cytoplasm, namely caspase-11 in mice and caspases-4/5 in humans, have renewed interest in the field. These provide new potential targets for intervention in sepsis pathogenesis. Since cytoplasmic recognition of LPS induces non-canonical inflammasome pathway, a potentially harmful host response, it is conceivable to therapeutically target this mechanism. However, a great deal of care should be used in the translation of research on the non-canonical inflammasome inhibition due to multiple inter-species differences. In this review, we summarize the knowledge on endotoxin sensing in sepsis with special focus on the intracellular sensing. We also highlight the murine versus human differences and discuss potential therapeutic approaches addressing the newly discovered pathways.

Dexmedetomidine protects against high mobility group box 1-induced cellular injury by inhibiting pyroptosis

Dexmedetomidine (DEX) is a widely used clinical anesthetic with proven anti-inflammatory effects. Both high mobility group box 1 (HMGB1) and pyroptosis play an important role in the inflammatory response to infection and trauma. Thus far, there have been no studies published addressing the effect of DEX on HMGB1 and pyroptosis. In order to fill this gap in the literature, bone marrow-derived macrophages (BMDMs) were exposed to HMGB1 (4 µg/mL) with or without DEX (50 μM) pretreatment. The production of pro-inflammatory cytokines [such as tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-18], phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) and P38, and the activation of caspase-1 were measured by enzyme immunosorbent assay, western blot analysis, confocal microscope, and flow cytometry, respectively. We found that DEX protected against HMGB1-induced cell death of BMDMs. In addition, DEX suppressed the generation of TNF-α, IL-1β, and IL-18 as well as the phosphorylation of ERK1/2 and P38. Moreover, DEX inhibited caspase-1 activation and decreased pyroptosis. Taken together, these findings demonstrate the protective effect of DEX in mediating HMGB1-induced cellular injury, thus indicating that DEX may be a potential therapeutic candidate for the management of infection and trauma-derived inflammation.

Microparticulate Caspase 1 Regulates Gasdermin D and Pulmonary Vascular Endothelial Cell Injury

Lung endothelial cell apoptosis and injury occur throughout all stages of acute lung injury/acute respiratory distress syndrome and impact disease progression. Caspases 1, 4, and 5 are essential for completion of the apoptotic program known as pyroptosis that also involves proinflammatory cytokines. Because gasdermin D (GSDMD) mediates pyroptotic death and is essential for pore formation, we hypothesized that it might direct caspase 1-encapsulated microparticle (MP) release and mediate endothelial cell death. Our present work provides evidence that GSDMD is released by LPS-stimulated THP-1 monocytic cells, where it is packaged into microparticles together with active caspase 1. Furthermore, only MP released from stimulated monocytic cells that contain both cleaved GSDMD and active caspase 1 induce endothelial cell apoptosis. MPs pretreated with caspase 1 inhibitor Y-VAD or pan-caspase inhibitor Z-VAD do not contain cleaved GSDMD. MPs from caspase 1-knockout cells are also deficient in p30 active GSDMD, further confirming that caspase 1 regulates GSDMD function. Although control MPs contained cleaved GSDMD without caspase 1, these fractions were unable to induce cell death, suggesting that encapsulation of both caspase 1 and GSDMD is essential for cell death induction. Release of microparticulate active caspase 1 was abrogated in GSDMD knockout cells, although cytosolic caspase 1 activation was not impaired. Last, higher concentrations of microparticulate GSDMD were detected in the plasma of septic patients with acute respiratory distress syndrome than in that of healthy donors. Taken together, these findings suggest that GSDMD regulates the release of microparticulate active caspase 1 from monocytes essential for induction of cell death and thereby may play a critical role in sepsis-induced endothelial cell injury.

DNA-stimulated cell death: implications for host defence, inflammatory diseases and cancer

The immune system detects disturbances in homeostasis that occur during infection, sterile tissue damage and cancer. This initiates immune responses that seek to eliminate the trigger of immune activation and to re-establish homeostasis. At the same time, these mechanisms can also play a crucial role in the progression of disease. The occurrence of DNA in the cytosol constitutes a potent trigger for the innate immune system, governing the production of key inflammatory cytokines such as type I interferons and IL-1β. More recently, it has become clear that cytosolic DNA also triggers other biological responses, including various forms of programmed cell death. In this article, we review the emerging literature on the pathways governing DNA-stimulated cell death and the current knowledge on how these processes shape immune responses to exogenous and endogenous challenges.

Protective effects of rapamycin induced autophagy on CLP septic mice

Sepsis is a life-threatening condition that may develop to multiple organ failure and septic shock. Autophagy is considered to play an important role in the regulation of inflammation. The present study aims to investigate the protective role of mTORC1 inhibitor, rapamycin, on septic death using cecal ligation and puncture (CLP) mice model. Here, results showed that pretreatment with rapamycin reduced the pyroptosis of peritoneal macrophages stimulated by cecal contents and the release of inflammatory factors such as interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α); In septic mice, rapamycin treatment decreased the activation of inflammasome in lung, and alleviated the pathological injuries in lung, liver and spleen tissues during acute stage of sepsis. Treatment of rapamycin rescued animals from septic death significantly. Our results indicated that activation of autophagy is a potential strategy to regulate the excessive inflammation in acute stage of sepsis.

Cardiac gene expression and function in a mouse model of community-acquired methicillin-resistant Staphylococcus aureus sepsis: Role of inflammatory caspases 1 and 11

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is an important cause of invasive infections, including sepsis associated with myocardial dysfunction. Caspases 1 and 11, involved in activation of the inflammasome, have been shown to be critical in response to sepsis as well as myocardial dysfunction of numerous etiologies. We examined the survival, myocardial function, and production of inflammatory mediators in mice lacking caspases 1 and 11. Cas 1/11 KO mice demonstrated no significant difference in mortality or in cardiac shortening fraction relative to control mice. Cas 1/11 KO mice had significantly reduced upregulation of expression of tumor necrosis factor (TNF)-α and interleukin (IL)-6 in the heart relative to control mice after CA-MRSA infection, as well as reduced serum production of IL-1β, TNF-α, and IL-6, with no difference in IL-10 production. Other inflammatory mediators beyond IL-1β, TNF-α, and IL-6 may be involved in myocardial dysfunction in CA-MRSA sepsis.

Cytosolic Recognition of Microbes and Pathogens: Inflammasomes in Action

Infection is a dynamic biological process underpinned by a complex interplay between the pathogen and the host. Microbes from all domains of life, including bacteria, viruses, fungi, and protozoan parasites, have the capacity to cause infection. Infection is sensed by the host, which often leads to activation of the inflammasome, a cytosolic macromolecular signaling platform that mediates the release of the proinflammatory cytokines interleukin-1β (IL-1β) and IL-18 and cleavage of the pore-forming protein gasdermin D, leading to pyroptosis. Host-mediated sensing of the infection occurs when pathogens inject or carry pathogen-associated molecular patterns (PAMPs) into the cytoplasm or induce damage that causes cytosolic liberation of danger-associated molecular patterns (DAMPs) in the host cell. Recognition of PAMPs and DAMPs by inflammasome sensors, including NLRP1, NLRP3, NLRC4, NAIP, AIM2, and Pyrin, initiates a cascade of events that culminate in inflammation and cell death. However, pathogens can deploy virulence factors capable of minimizing or evading host detection. This review presents a comprehensive overview of the mechanisms of microbe-induced activation of the inflammasome and the functional consequences of inflammasome activation in infectious diseases. We also explore the microbial strategies used in the evasion of inflammasome sensing at the host-microbe interaction interface.

Dysregulated myelopoiesis and hematopoietic function following acute physiologic insult

PURPOSE OF REVIEW

The purpose of this review is to describe recent findings in the context of previous work regarding dysregulated myelopoiesis and hematopoietic function following an acute physiologic insult, focusing on the expansion and persistence of myeloid-deriver suppressor cells, the deterioration of lymphocyte number and function, and the inadequacy of stress erythropoiesis.

RECENT FINDINGS

Persistent myeloid-derived suppressor cell (MDSC) expansion among critically ill septic patients is associated with T-cell suppression, vulnerability to nosocomial infection, chronic critical illness, and poor long-term functional status. Multiple approaches targeting MDSC expansion and suppressor cell activity may serve as a primary or adjunctive therapeutic intervention. Traumatic injury and the neuroendocrine stress response suppress bone marrow erythropoietin receptor expression in a process that may be reversed by nonselective beta-adrenergic receptor blockade. Hepcidin-mediated iron-restricted anemia of critical illness requires further investigation of novel approaches involving erythropoiesis-stimulating agents, iron administration, and hepcidin modulation.

SUMMARY

Emergency myelopoiesis is a dynamic process with unique phenotypes for different physiologic insults and host factors. Following an acute physiologic insult, critically ill patients are subject to persistent MDSC expansion, deterioration of lymphocyte number and function, and inadequate stress erythropoiesis. Better strategies are required to identify patients who are most likely to benefit from targeted therapies.

Inflammasome function in monocyte subsets and a risk of late-onset sepsis in preterm very low birth weight neonates

BACKGROUND

Immature immune systems predispose very low birth weight (VLBW) neonates to systemic infections in early life. Defective inflammasome function may increase a neonate's susceptibility to late-onset sepsis (LOS).

METHODS

Blood samples were taken on the 5^th day of life (DOL) for all VLBW neonates (non-LOS and before-LOS groups; N.=76), and within 24 hours of sepsis onset (LOS group; N.=39). Monocyte (MO) subsets and intracellular interleukin-1β (IL-1β) expression were analyzed using flow cytometry. Inflammasome function, defined as level of IL-1β and interleukin-18 (IL-18) was measured with enzyme-linked immunosorbent assay. IRA B cells were reported as a fraction of all B cells.

RESULTS

Stimulation of classical MO in non-LOS cells demonstrated a higher expression of intracellular IL-1β in comparison to MO from before LOS group. Serum from the LOS group revealed a higher level of IL-18. Stimulation of mononuclear cultures from samples taken during LOS resulted in significantly increased supernatant level of IL-1β and IL-18 in comparison to samples taken on 5^th DOL. No changes in the levels of IRA B cells were detected with the onset of sepsis.

CONCLUSIONS

We did not observe a difference in the functioning of the inflammasome within monocytes taken on 5^th DOL from premature VLBW neonates. Furthermore, there was no observable change in the IRA B cells of the septic and non-septic groups. The decreased expression of intracellular IL-1β within classical MO of the before-LOS group may be an independent risk factor for LOS development.

Inflammasomes in the gastrointestinal tract: infection, cancer and gut microbiota homeostasis

Inflammasome signalling is an emerging pillar of innate immunity and has a central role in the regulation of gastrointestinal health and disease. Activation of the inflammasome complex mediates both the release of the pro-inflammatory cytokines IL-1β and IL-18 and the execution of a form of inflammatory cell death known as pyroptosis. In most cases, these mediators of inflammation provide protection against bacterial, viral and protozoal infections. However, unchecked inflammasome activities perpetuate chronic inflammation, which underpins the molecular and pathophysiological basis of gastritis, IBD, upper and lower gastrointestinal cancer, nonalcoholic fatty liver disease and obesity. Studies have also highlighted an inflammasome signature in the maintenance of gut microbiota and gut-brain homeostasis. Harnessing the immunomodulatory properties of the inflammasome could transform clinical practice in the treatment of acute and chronic gastrointestinal and extragastrointestinal diseases. This Review presents an overview of inflammasome biology in gastrointestinal health and disease and describes the value of experimental and pharmacological intervention in the treatment of inflammasome-associated clinical manifestations.

Adjuvant pretreatment with alum protects neonatal mice in sepsis through myeloid cell activation

The high mortality in neonatal sepsis has been related to both quantitative and qualitative differences in host protective immunity. Pretreatment strategies to prevent sepsis have received inadequate consideration, especially in the premature neonate, where outcomes from sepsis are so dismal. Aluminium salts-based adjuvants (alum) are used currently in many paediatric vaccines, but their use as an innate immune stimulant alone has not been well studied. We asked whether pretreatment with alum adjuvant alone could improve outcome and host innate immunity in neonatal mice given polymicrobial sepsis. Subcutaneous alum pretreatment improves survival to polymicrobial sepsis in both wild-type and T and B cell-deficient neonatal mice, but not in caspase-1/11 null mice. Moreover, alum increases peritoneal macrophage and neutrophil phagocytosis, and decreases bacterial colonization in the peritoneum. Bone marrow-derived neutrophils from alum-pretreated neonates produce more neutrophil extracellular traps (NETs) and exhibit increased expression of neutrophil elastase (NE) after in-vitro stimulation with phorbol esters. In addition, alum pretreatment increases bone marrow and splenic haematopoietic stem cell expansion following sepsis. Pretreatment of neonatal mice with an alum-based adjuvant can stimulate multiple innate immune cell functions and improve survival. These novel findings suggest a therapeutic pathway for the use of existing alum-based adjuvants for preventing sepsis in premature infants.

Emerging Insights into Noncanonical Inflammasome Recognition of Microbes

Inflammasomes are cytosolic multi-molecular complexes that sense intracellular microbial danger signals and metabolic perturbations. Inflammasome activation leads to the activation of caspase-1 and the release of pro-inflammatory cytokines IL-1β and IL-18 accompanied by cell death. An inflammasome-based surveillance machinery for Gram-negative bacterial infections has been recently discovered. This noncanonical inflammasome relies on sensing the cytosolic presence of lipopolysaccharide of Gram-negative bacteria via inflammatory caspases such as caspase-4, -5, and -11. This review discusses the recent findings related to the mechanism of activation of the noncanonical inflammasome and its biological functions.

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.

Deletion of Nlrp3 Augments Survival during Polymicrobial Sepsis by Decreasing Autophagy and Enhancing Phagocytosis

NLRP3 inflammasome is a critical player in innate immunity. Neutrophil recruitment to tissues and effective neutrophil function are critical innate immune mechanisms for bacterial clearance. However, the role of NLRP3 in neutrophil-dependent bacterial clearance in polymicrobial sepsis is unclear. In this study, we evaluated the role of NLRP3 in polymicrobial sepsis induced by cecal ligation and puncture (CLP). Our results showed protection from death in NLRP3-deficient (Nlrp3^-/-) and NLRP3 inhibitor-treated wild-type (C57BL/6) mice. Nlrp3^-/- and NLRP3 inhibitor-treated mice displayed lower bacterial load but no impairment in neutrophil recruitment to peritoneum. However, neutrophil depletion abrogated protection from death in Nlrp3^-/- mice in response to CLP. Intriguingly, following CLP, Nlrp3^-/- peritoneal cells (primarily neutrophils) demonstrate decreased autophagy, augmented phagocytosis, and enhanced scavenger receptor (macrophage receptor with collagenous structure) and mannose-binding leptin expression. These findings enhance our understanding of the critical role of NLRP3 in modulating autophagy and phagocytosis in neutrophils and suggest that therapies should be targeted to modulate autophagy and phagocytosis in neutrophils to control bacterial burden in tissues during CLP-induced polymicrobial sepsis.