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

The emerging role of adaptor proteins in regulating innate immunity of sepsis

Sepsis is a life-threatening syndrome caused by a dysregulated immune response. A large number of adaptor proteins have been found to play a pivotal role in sepsis via protein-protein interactions, thus participating in inflammatory cascades, leading to the generation of numerous inflammatory cytokines, as well as oxidative stress and regulated cell death. Although available strategies for the diagnosis and management of sepsis have improved, effective and specific treatments are lacking. This review focuses on the emerging role of adaptor proteins in regulating the innate immunity of sepsis and evaluates the potential value of adaptor protein-associated therapeutic strategy for sepsis.

Endogenous innate sensor NLRP3 is a key component in peritoneal macrophage dynamics required for cestode establishment

The NLRP3 receptor can assemble inflammasome platforms to trigger inflammatory responses; however, accumulating evidence suggests that it can also display anti-inflammatory properties. Here, we explored the role of nucleotide-binding oligomerization domain pyrin-containing protein 3 (NLRP3) in Taenia crassiceps experimental infection, which requires immune polarization into a Th2-type profile and peritoneal influx of suppressive macrophages for successful colonization. NLRP3 deficient mice (NLRP3-/-) were highly resistant against T. crassiceps, relative to wild-type (WT) mice. Resistance in NLRP3-/- mice was associated with a diminished IL-4 output, high levels of IL-15, growth factor for both innate and adaptive lymphocytes, and a dramatic decrease in peritoneum-infiltrating suppressive macrophages. Also, a transcriptional analysis on bone marrow-derived macrophages exposed to Taenia-secreted antigens and IL-4 revealed that NLRP3-/- macrophages express reduced transcripts of relm-α and PD-1 ligands, markers of alternative activation and suppressive ability, respectively. Finally, we found that the resistance displayed by NLRP3-/- mice is transferred through intestinal microbiota exchange, since WT mice co-housed with NLRP3-/- mice were significantly more resistant than WT animals preserving their native microbiota. Altogether, these data demonstrate that NLRP3 is a component of innate immunity required for T. crassiceps to establish, most likely contributing to macrophage recruitment, and controlling lymphocyte-stimulating cytokines such as IL-15.

Sepsis in elderly patients: the role of neutrophils in pathophysiology and therapy

Sepsis is among the most important causes of mortality, particularly within the elderly population. Sepsis prevalence is on the rise due to different factors, including increasing average population age and the concomitant rise in the prevalence of frailty and chronic morbidities. Recent investigations have unveiled a "trimodal" trajectory for sepsis-related mortality, with the ultimate zenith occurring from 60 to 90 days until several years after the original insult. This prolonged temporal course ostensibly emanates from the sustained perturbation of immune responses, persevering beyond the phase of clinical convalescence. This phenomenon is particularly associated with the aging immune system, characterized by a broad dysregulation commonly known as "inflammaging." Inflammaging associates with a chronic low-grade activation of the innate immune system preventing an appropriate response to infective agents. Notably, during the initial phases of sepsis, neutrophils-essential in combating pathogens-may exhibit compromised activity. Paradoxically, an overly zealous neutrophilic reaction has been observed to underlie multi-organ dysfunction during the later stages of sepsis. Given this scenario, discovering treatments that can enhance neutrophil activity during the early phases of sepsis while curbing their overactivity in the later phases could prove beneficial in fighting pathogens and reducing the detrimental effects caused by an overactive immune system. This narrative review delves into the potential key role of neutrophils in the pathological process of sepsis, focusing on how the aging process impacts their functions, and highlighting possible targets for developing immune-modulatory therapies. Additionally, the review includes tables that outline the principal potential targets for immunomodulating agents.

NLRP6 negatively regulates host defense against polymicrobial sepsis

Introduction

Sepsis remains a major cause of death in Intensive Care Units. Sepsis is a life-threatening multi-organ dysfunction caused by a dysregulated systemic inflammatory response. Pattern recognition receptors, such as TLRs and NLRs contribute to innate immune responses. Upon activation, some NLRs form multimeric protein complexes in the cytoplasm termed "inflammasomes" which induce gasdermin d-mediated pyroptotic cell death and the release of mature forms of IL-1β and IL-18. The NLRP6 inflammasome is documented to be both a positive and a negative regulator of host defense in distinct infectious diseases. However, the role of NLRP6 in polymicrobial sepsis remains elusive.

Methods

We have used NLRP6 KO mice and human septic spleen samples to examine the role of NLRP6 in host defense in sepsis.

Results

NLRP6 KO mice display enhanced survival, reduced bacterial burden in the organs, and reduced cytokine/chemokine production. Co-housed WT and KO mice following sepsis show decreased bacterial burden in the KO mice as observed in singly housed groups. NLRP6 is upregulated in CD3, CD4, and CD8 cells of septic patients and septic mice. The KO mice showed a higher number of CD3, CD4, and CD8 positive T cell subsets and reduced T cell death in the spleen following sepsis. Furthermore, administration of recombinant IL-18, but not IL-1β, elicited excessive inflammation and reversed the survival advantages observed in NLRP6 KO mice.

Conclusion

These results unveil NLRP6 as a negative regulator of host defense during sepsis and offer novel insights for the development of new treatment strategies for sepsis.

The NLRP3 inhibitor, OLT1177 attenuates brain injury in experimental intracerebral hemorrhage

BACKGROUND AND PURPOSE

It has been reported activation of NLRP3 inflammasome after intracerebral hemorrhage (ICH) ictus exacerbates neuroinflammation and brain injury. We hypothesized that inhibition of NLRP3 by OLT1177 (dapansutrile), a novel NLRP3 inflammasome inhibitor, could reduce brain edema and attenuate brain injury in experimental ICH.

METHODS

ICH was induced by injection of autologous blood into basal ganglia in mice models. Sixty-three C57Bl/6 male mice were randomly grouped into the sham, vehicle, OLT1177 (Dapansutrile, 200 mg/kg intraperitoneally) and treated for consecutive three days, starting from 1 h after ICH surgery. Behavioral test, brain edema, brain water content, blood-brain barrier integrity and vascular permeability, cell apoptosis, and NLRP3 and its downstream protein levels were measured.

RESULTS

OLT1177 significantly reduced cerebral edema after ICH and contributed to the attenuation of neurological deficits. OLT1177 could preserve blood-brain barrier integrity and lessen vascular leakage. In addition, OLT1177 preserved microglia morphological shift and significantly inhibited the activation of caspase-1 and release of IL-1β. We also found that OLT1177 can protect against neuronal loss in the affected hemisphere.

CONCLUSIONS

OLT1177 (dapansutrile) could significantly attenuate the brain edema after ICH and effectively alleviate the neurological deficit. This result suggests that the novel NLRP3 inhibitor, OLT1177, might serve as a promising candidate for the treatment of ICH.

NLRP3 knockout in mice provided protection against Serratia marcescens-induced acute pneumonia by decreasing PD-L1 and PD-1 expression in macrophages

Antibiotic-resistant Serratia marcescens (Sm) is known to cause bloodstream infections, pneumonia, etc. The nod-like receptor family, pyrin domain-containing 3 (NLRP3), has been implicated in various lung infections. Yet, its role in Sm-induced pneumonia was not well understood. In our study, we discovered that deletion of Nlrp3 in mice significantly improved Sm-induced survival rates, reduced bacterial loads in the lungs, bronchoalveolar lavage fluid (BALF), and bloodstream, and mitigated the severity of acute lung injury (ALI) compared to wild-type (WT) mice. Mechanistically, we observed that 24 h post-Sm infection, NLRP3 inflammasome activation occurred, leading to gasdermin D NH2-terminal (GSDMD-NT)-induced pyroptosis in macrophages and IL-1β secretion. The NLRP3 or NLRP3 inflammasome influenced the expression PD-L1 and PD-1, as well as the count of PD-L1 or PD-1-expressing macrophages, alveolar macrophages, interstitial macrophages, PD-L1-expressing neutrophils, and the count of macrophage receptors with collagenous structure (MARCO)-expressing macrophages, particularly MARCO+ alveolar macrophages. The frequency of MARCO+ alveolar macrophages, PD-1 expression, particularly PD-1+ interstitial macrophages were negatively or positively correlated with the Sm load, respectively. Additionally, IL-1β levels in BALF correlated with three features of acute lung injury: histologic score, protein concentration and neutrophil count in BALF. Consequently, our findings suggest that Nlrp3 deletion offers protection agaisnt acute Sm pneumonia in mice by inhibiting inflammasome activation and reducing Sm infection-induced PD-L1/PD-1 or MARCO expression, particularly in macrophages. This highlights potential therapeutic targets for Sm and other gram-negative bacteria-induced acute pneumonia.

PAMPs and DAMPs in Sepsis: A Review of Their Molecular Features and Potential Clinical Implications

Sepsis is a serious organ dysfunction caused by a dysregulated immune host reaction to a pathogen. The innate immunity is programmed to react immediately to conserved molecules, released by the pathogens (PAMPs), and the host (DAMPs). We aimed to review the molecular mechanisms of the early phases of sepsis, focusing on PAMPs, DAMPs, and their related pathways, to identify potential biomarkers. We included studies published in English and searched on PubMed® and Cochrane®. After a detailed discussion on the actual knowledge of PAMPs/DAMPs, we analyzed their role in the different organs affected by sepsis, trying to elucidate the molecular basis of some of the most-used prognostic scores for sepsis. Furthermore, we described a chronological trend for the release of PAMPs/DAMPs that may be useful to identify different subsets of septic patients, who may benefit from targeted therapies. These findings are preliminary since these pathways seem to be strongly influenced by the peculiar characteristics of different pathogens and host features. Due to these reasons, while initial findings are promising, additional studies are necessary to clarify the potential involvement of these molecular patterns in the natural evolution of sepsis and to facilitate their transition into the clinical setting.

Cell death proteins in sepsis: key players and modern therapeutic approaches

Cell death proteins play a central role in host immune signaling during sepsis. These interconnected mechanisms trigger cell demise via apoptosis, necroptosis, and pyroptosis while also driving inflammatory signaling. Targeting cell death mediators with novel therapies may correct the dysregulated inflammation seen during sepsis and improve outcomes for septic patients.

Current insight on the mechanisms of programmed cell death in sepsis-induced myocardial dysfunction

Sepsis is a clinical syndrome characterized by a dysregulated host response to infection, leading to life-threatening organ dysfunction. It is a high-fatality condition associated with a complex interplay of immune and inflammatory responses that can cause severe harm to vital organs. Sepsis-induced myocardial injury (SIMI), as a severe complication of sepsis, significantly affects the prognosis of septic patients and shortens their survival time. For the sake of better administrating hospitalized patients with sepsis, it is necessary to understand the specific mechanisms of SIMI. To date, multiple studies have shown that programmed cell death (PCD) may play an essential role in myocardial injury in sepsis, offering new strategies and insights for the therapeutic aspects of SIMI. This review aims to elucidate the role of cardiomyocyte's programmed death in the pathophysiological mechanisms of SIMI, with a particular focus on the classical pathways, key molecules, and signaling transduction of PCD. It will explore the role of the cross-interaction between different patterns of PCD in SIMI, providing a new theoretical basis for multi-target treatments for SIMI.

Restoring the infected powerhouse: Mitochondrial quality control in sepsis

Sepsis is a dysregulated host response to an infection, characterized by organ failure. The pathophysiology is complex and incompletely understood, but mitochondria appear to play a key role in the cascade of events that culminate in multiple organ failure and potentially death. In shaping immune responses, mitochondria fulfil dual roles: they not only supply energy and metabolic intermediates crucial for immune cell activation and function but also influence inflammatory and cell death pathways. Importantly, mitochondrial dysfunction has a dual impact, compromising both immune system efficiency and the metabolic stability of end organs. Dysfunctional mitochondria contribute to the development of a hyperinflammatory state and loss of cellular homeostasis, resulting in poor clinical outcomes. Already in early sepsis, signs of mitochondrial dysfunction are apparent and consequently, strategies to optimize mitochondrial function in sepsis should not only prevent the occurrence of mitochondrial dysfunction, but also cover the repair of the sustained mitochondrial damage. Here, we discuss mitochondrial quality control (mtQC) in the pathogenesis of sepsis and exemplify how mtQC could serve as therapeutic target to overcome mitochondrial dysfunction. Hence, replacing or repairing dysfunctional mitochondria may contribute to the recovery of organ function in sepsis. Mitochondrial biogenesis is a process that results in the formation of new mitochondria and is critical for maintaining a pool of healthy mitochondria. However, exacerbated biogenesis during early sepsis can result in accumulation of structurally aberrant mitochondria that fail to restore bioenergetics, produce excess reactive oxygen species (ROS) and exacerbate the disease course. Conversely, enhancing mitophagy can protect against organ damage by limiting the release of mitochondrial-derived damage-associated molecules (DAMPs). Furthermore, promoting mitophagy may facilitate the growth of healthy mitochondria by blocking the replication of damaged mitochondria and allow for post sepsis organ recovery through enabling mitophagy-coupled biogenesis. The remaining healthy mitochondria may provide an undamaged scaffold to reproduce functional mitochondria. However, the kinetics of mtQC in sepsis, specifically mitophagy, and the optimal timing for intervention remain poorly understood. This review emphasizes the importance of integrating mitophagy induction with mtQC mechanisms to prevent undesired effects associated with solely the induction of mitochondrial biogenesis.

Megakaryocyte NLRP3 hyperactivation induces mild anemia and potentiates inflammatory response in mice

Background

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome has been described in both immune cells and platelets, but its role in the megakaryocyte (MK) lineage remains elusive.

Objective

The aim of this study was to explore the role of NLRP3 inflammasome in megakaryocytes and platelets.

Methods

We generated Nlrp3 A350V/+/Gp1ba-CreKI/+ mice carrying a mutation genetically similar to the one observed in human Muckle-Wells syndrome, which leads to hyperactivity of NLRP3 specifically in MK and platelets.

Results

Platelets from the mutant mice expressed elevated levels of both precursor and active form of caspase-1, suggesting hyperactivity of NLRP3 inflammasome. Nlrp3 A350V/+/Gp1ba-CreKI/+ mice developed normally and had normal platelet counts. Expression of major platelet receptors, platelet aggregation, platelet deposition on collagen under shear, and deep vein thrombosis were unchanged. Nlrp3 A350V/+/Gp1ba-CreKI/+ mice had mild anemia, reduced Ter119+ cells in the bone marrow, and splenomegaly. A mild increase in MK TGF-β1 might be involved in the anemic phenotype. Intraperitoneal injection of zymosan in Nlrp3 A350V/+/Gp1ba-CreKI/+ mice induced increased neutrophil egression and elevated levels of a set of proinflammatory cytokines, alongside IL-10 and G-CSF, in the peritoneal fluid as compared with control animals.

Conclusion

MK/platelet NLRP3 inflammasome promotes the acute inflammatory response and its hyperactivation in mice leads to mild anemia and increased extramedullary erythropoiesis.

Lipid oxidation dysregulation: an emerging player in the pathophysiology of sepsis

Sepsis is a life-threatening organ dysfunction caused by abnormal host response to infection. Millions of people are affected annually worldwide. Derangement of the inflammatory response is crucial in sepsis pathogenesis. However, metabolic, coagulation, and thermoregulatory alterations also occur in patients with sepsis. Fatty acid mobilization and oxidation changes may assume the role of a protagonist in sepsis pathogenesis. Lipid oxidation and free fatty acids (FFAs) are potentially valuable markers for sepsis diagnosis and prognosis. Herein, we discuss inflammatory and metabolic dysfunction during sepsis, focusing on fatty acid oxidation (FAO) alterations in the liver and muscle (skeletal and cardiac) and their implications in sepsis development.

Autophagy-mediated immune system regulation in reproductive system and pregnancy-associated complications

Autophagy lysosomal degradation is the main cell mechanism in cellular, tissue and organismal homeostasis and is controlled by autophagy-related genes (ATG). Autophagy has important effects in cellular physiology, including adaptation to metabolic stress, removal of dangerous cargo (such as protein aggregates, damaged organelles, and intracellular pathogens), regeneration during differentiation and development, and prevention of genomic damage in general. Also, it has been found that autophagy is essential for pre-implantation, development, and maintaining embryo survival in mammals. Under certain conditions, autophagy may be detrimental through pro-survival effects such as cancer progression or through possible cell death-promoting effects. Hormonal changes and environmental stress can initiate autophagy in reproductive physiology. The activity of autophagy can be upregulated under conditions like a lack of nutrients, inflammation, hypoxia, and infections. In this regard the dysregulation of autophagy involved in some pregnancy complications such as preeclampsia (PE) and pregnancy loss, and has a major impact on reproductive outcomes. Therefore, we aimed to discuss the relationship between autophagy and the female reproductive system, with a special focus on the immune system, and its role in fetal and maternal health.

NLRP3 inflammasome-driven IL-1β and IL-18 contribute to lipopolysaccharide-induced septic cardiomyopathy

Sepsis is a life-threatening syndrome, and its associated mortality is increased when cardiac dysfunction and damage (septic cardiomyopathy [SCM]) occur. Although inflammation is involved in the pathophysiology of SCM, the mechanism of how inflammation induces SCM in vivo has remained obscure. NLRP3 inflammasome is a critical component of the innate immune system that activates caspase-1 (Casp1) and causes the maturation of IL-1β and IL-18 as well as the processing of gasdermin D (GSDMD). Here, we investigated the role of the NLRP3 inflammasome in a murine model of lipopolysaccharide (LPS)-induced SCM. LPS injection induced cardiac dysfunction, damage, and lethality, which was significantly prevented in NLRP3-/- mice, compared to wild-type (WT) mice. LPS injection upregulated mRNA levels of inflammatory cytokines (Il6, Tnfa, and Ifng) in the heart, liver, and spleen of WT mice, and this upregulation was prevented in NLRP3-/- mice. LPS injection increased plasma levels of inflammatory cytokines (IL-1β, IL-18, and TNF-α) in WT mice, and this increase was markedly inhibited in NLRP3-/- mice. LPS-induced SCM was also prevented in Casp1/11-/- mice, but not in Casp11mt, IL-1β-/-, IL-1α-/-, or GSDMD-/- mice. Notably, LPS-induced SCM was apparently prevented in IL-1β-/- mice transduced with adeno-associated virus vector expressing IL-18 binding protein (IL-18BP). Furthermore, splenectomy, irradiation, or macrophage depletion alleviated LPS-induced SCM. Our findings demonstrate that the cross-regulation of NLRP3 inflammasome-driven IL-1β and IL-18 contributes to the pathophysiology of SCM and provide new insights into the mechanism underlying the pathogenesis of SCM.

The CYP2E1 inhibitor Q11 ameliorates LPS-induced sepsis in mice by suppressing oxidative stress and NLRP3 activation

Sepsis is an infection-induced, multi-organ system failure with a pathophysiology related to inflammation and oxidative stress. Increasing evidence indicates that cytochrome P450 2E1 (CYP2E1) is involved in the incidence and development of inflammatory diseases. However, a role for CYP2E1 in lipopolysaccharide (LPS)-induced sepsis has not been completely explored. Here we use Cyp2e1 knockout (cyp2e1-/-) mice to determine if CYP2E1 could be a therapeutic target for sepsis. We also evaluated the ability of Q11, a new specific CYP2E1 inhibitor, to prevent and ameliorate LPS-induced sepsis in mice and in LPS-treated J774A.1 and RAW264.7 cells. Cyp2e1 deletion significantly reduced hypothermia, multi-organ dysfunction and histological abnormalities in LPS-treated mice; consistent with this finding, the CYP2E1 inhibitor Q11 significantly prolonged the survival time of septic mice and ameliorated multi-organ injury induced by LPS. CYP2E1 activity in liver correlated with indicators of multi-organ injury, such as the level of lactate dehydrogenase (LDH) and blood urea nitrogen (BUN) (P<0.05). Q11 significantly suppressed the expression of NLRP3 in tissues after LPS injection; in vitro studies revealed that activation of NLRP3 signaling and increase of ROS was attenuated by Q11 in LPS-stimulated macrophages, which was reflected by reduced expression of caspase-1 and formation of ASC specks. Overall, our results indicate that Q11 improves the survival of mice with LPS-induced sepsis and attenuates sepsis-induced multiple-organ injury, suggesting that CYP2E1 could be a therapeutic target for sepsis.

p120-Catenin suppresses NLRP3 inflammasome activation in macrophages

Inflammasome activation is of central importance for the process of generation of overwhelming inflammatory response and the pathogenesis of sepsis. The intrinsic molecular mechanism for controlling inflammasome activation is still poorly understood. Here we investigated the role of p120-catenin expression in macrophages in regulating nucleotide-binding oligomerization domain (NOD) and leucine-rich repeat (LRR)- and pyrin domain-containing proteins 3 (NLRP3) inflammasome activation. Depletion of p120-catenin in murine bone marrow-derived macrophages enhanced caspase-1 activation and secretion of active interleukin (IL)-1β in response to ATP stimulation following LPS priming. Coimmunoprecipitation analysis showed that p120-catenin deletion promoted NLRP3 inflammasome activation by accelerating the assembly of the inflammasome complex comprised of NLRP3, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and pro-caspase-1. Depletion of p120-catenin also increased the production of mitochondrial reactive oxygen species. Pharmacological inhibition of mitochondrial reactive oxygen species nearly completely abolished NLRP3 inflammasome activation, caspase-1 activation, and the production of IL-1β in p120-catenin-depleted macrophages. Furthermore, p120-catenin ablation significantly disrupted mitochondrial function, evidenced by decreased mitochondrial membrane potential and lower production of intracellular ATP. In alveolar macrophage-depleted mice challenged with cecal ligation and puncture, pulmonary transplantation of p120-catenin-deficient macrophages dramatically enhanced the accumulation of IL-1β and IL-18 in bronchoalveolar lavage fluid. These results demonstrate that p120-catenin prevents NLRP3 inflammasome activation in macrophages by maintaining mitochondrial homeostasis and reducing the production of mitochondrial reactive oxygen species in response to endotoxin insult. Thus, inhibition of NLRP3 inflammasome activation by stabilization of p120-catenin expression in macrophages may be a novel strategy to prevent an uncontrolled inflammatory response in sepsis.

Pyroptosis in platelets: Thrombocytopenia and inflammation

OBJECTIVE

The purpose of this manuscript was to conclude the role of platelets in immune inflammation and discuss the complex mechanisms of pyroptosis in platelets as well as their related diseases.

METHODS

This article reviewed the existing literature to see the development of pyroptosis in platelets.

RESULTS

Platelets have been shown to be capable of activating inflammasomes assembled from NOD-like receptor family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein containing a CARD (ASC) and caspase-1. Recently, they were also implicated in pyroptosis. Cleaved by caspase-1, N-terminal gasdermin D (N-GSDMD) could form pores in the cell membrane, inducing nonselective intracellular substance release. This programmed cell death induced thrombocytopenia and inflammatory cytokine release such as IL-1β and IL-18, promoting platelet aggregation, vaso-occlusion, endothelial permeability and cascaded inflammatory response.

CONCLUSION

Pyroptosis in platelets contributes to thrombocytopenia and inflammation.

The double sides of NLRP3 inflammasome activation in sepsis

Sepsis is defined as a life-threatening organ dysfunction induced by a dysregulated host immune response to infection. Immune response induced by sepsis is complex and dynamic. It is schematically described as an early dysregulated systemic inflammatory response leading to organ failures and early deaths, followed by the development of persistent immune alterations affecting both the innate and adaptive immune responses associated with increased risk of secondary infections, viral reactivations, and late mortality. In this review, we will focus on the role of NACHT, leucin-rich repeat and pyrin-containing protein 3 (NLRP3) inflammasome in the pathophysiology of sepsis. NLRP3 inflammasome is a multiproteic intracellular complex activated by infectious pathogens through a two-step process resulting in the release of the pro-inflammatory cytokines IL-1β and IL-18 and the formation of membrane pores by gasdermin D, inducing a pro-inflammatory form of cell death called pyroptosis. The role of NLRP3 inflammasome in the pathophysiology of sepsis can be ambivalent. Indeed, although it might protect against sepsis when moderately activated after initial infection, excessive NLRP3 inflammasome activation can induce dysregulated inflammation leading to multiple organ failure and death during the acute phase of the disease. Moreover, this activation might become exhausted and contribute to post-septic immunosuppression, driving impaired functions of innate and adaptive immune cells. Targeting the NLRP3 inflammasome could thus be an attractive option in sepsis either through IL-1β and IL-18 antagonists or through inhibition of NLRP3 inflammasome pathway downstream components. Available treatments and results of first clinical trials will be discussed.

Calcitonin gene-related peptide ameliorates sepsis-induced intestinal injury by suppressing NLRP3 inflammasome activation

Intestinal damage has long been viewed as the primary cause of sepsis-induced multiple organ dysfunction syndrome (MODS). Previous studies have demonstrated that calcitonin gene-related peptide (CGRP) exhibits anti-inflammatory and protective effects in mice exposed to endotoxin. This study investigated whether CGRP protects against sepsis-induced intestinal damage and its underlying mechanisms. Using a murine caecal ligation and puncture (CLP) model, we observed elevated serum and intestinal CGRP levels in septic mice. CGRP knockout (KO) mice showed more severe intestinal barrier damage, excessive NLRP3 inflammasome activation and higher levels of inflammation. In vitro, we used lipopolysaccharide (LPS) and adenosine triphosphate (ATP) to activate the NLRP3 inflammasome in MODE-K murine intestinal epithelial cells. CGRP inhibited NF-κB pathway activation; prevented ASC assembly and ROS accumulation; significantly decreased NLRP3, Caspase-1 p10, and IL-1β levels and LDH release; and increased cell viability. Treatment with an IL-1β inhibitor or CGRP suppressed p38 MAPK and ERK1/2 pathway activation and increased ZO-1 and Occludin protein levels in LPS+ATP-treated MODE-K cells. Finally, we used the CGRP upstream agonist drug rutaecarpine (RUT) to control endogenous CGRP release in mice, and this drug demonstrated good therapeutic effects on septic intestinal injury. In conclusion, our results suggest that CGRP ameliorates sepsis-induced intestinal damage, providing valuable insights for drug development.

Inhibition of sphingosine-1-phosphate receptor 3 suppresses ATP-induced NLRP3 inflammasome activation in macrophages via TWIK2-mediated potassium efflux

Background

Inhibition of sphingosine kinase 1 (SphK1), which catalyzes bioactive lipid sphingosine-1-phosphate (S1P), attenuates NLRP3 inflammasome activation. S1P exerts most of its function by binding to S1P receptors (S1PR1-5). The roles of S1P receptors in NLRP3 inflammasome activation remain unclear.

Materials and methods

The mRNA expressions of S1PRs in bone marrow-derived macrophages (BMDMs) were measured by real-time quantitative polymerase chain reaction (qPCR) assays. BMDMs were primed with LPS and stimulated with NLRP3 activators, including ATP, nigericin, and imiquimod. Interleukin-1β (IL-1β) in the cell culture supernatant was detected by enzyme-linked immunosorbent assay (ELISA). Intracellular potassium was labeled with a potassium indicator and was measured by confocal microscopy. Protein expression in whole-cell or plasma membrane fraction was measured by Western blot. Cecal ligation and puncture (CLP) was induced in C57BL/6J mice. Mortality, lung wet/dry ratio, NLRP3 activation, and bacterial loads were measured.

Results

Macrophages expressed all five S1PRs in the resting state. The mRNA expression of S1PR3 was upregulated after lipopolysaccharide (LPS) stimulation. Inhibition of S1PR3 suppressed NLRP3 and pro-IL-1β in macrophages primed with LPS. Inhibition of S1PR3 attenuated ATP-induced NLRP3 inflammasome activation, enhanced nigericin-induced NLRP3 activation, and did not affect imiquimod-induced NLRP3 inflammasome activation. In addition, inhibition of S1PR3 suppressed ATP-induced intracellular potassium efflux. Inhibition of S1PR3 did not affect the mRNA or protein expression of TWIK2 in LPS-primed BMDMs. ATP stimulation induced TWIK2 expression in the plasma membrane of LPS-primed BMDMs, and inhibition of S1PR3 impeded the membrane expression of TWIK2 induced by ATP. Compared with CLP mice treated with vehicle, CLP mice treated with the S1PR3 antagonist, TY52156, had aggravated pulmonary edema, increased bacterial loads in the lung, liver, spleen, and blood, and a higher seven-day mortality rate.

Conclusions

Inhibition of S1PR3 suppresses the expression of NLRP3 and pro-IL-1β during LPS priming, and attenuates ATP-induced NLRP3 inflammasome activation by impeding membrane trafficking of TWIK2 and potassium efflux. Although inhibition of S1PR3 decreases IL-1β maturation in the lungs, it leads to higher bacterial loads and mortality in CLP mice.

Prohibitin 1 regulates mtDNA release and downstream inflammatory responses

Exposure of mitochondrial DNA (mtDNA) to the cytosol activates innate immune responses. But the mechanisms by which mtDNA crosses the inner mitochondrial membrane are unknown. Here, we found that the inner mitochondrial membrane protein prohibitin 1 (PHB1) plays a critical role in mtDNA release by regulating permeability across the mitochondrial inner membrane. Loss of PHB1 results in alterations in mitochondrial integrity and function. PHB1-deficient macrophages, serum from myeloid-specific PHB1 KO (Phb1MyeKO) mice, and peripheral blood mononuclear cells from neonatal sepsis patients show increased interleukin-1β (IL-1β) levels. PHB1 KO mice are also intolerant of lipopolysaccharide shock. Phb1-depleted macrophages show increased cytoplasmic release of mtDNA and inflammatory responses. This process is suppressed by cyclosporine A and VBIT-4, which inhibit the mitochondrial permeability transition pore (mPTP) and VDAC oligomerization. Inflammatory stresses downregulate PHB1 expression levels in macrophages. Under normal physiological conditions, the inner mitochondrial membrane proteins, AFG3L2 and SPG7, are tethered to PHB1 to inhibit mPTP opening. Downregulation of PHB1 results in enhanced interaction between AFG3L2 and SPG7, mPTP opening, mtDNA release, and downstream inflammatory responses.

NLRP3 inflammasome activation in neutrophils directs early inflammatory response in murine peritonitis

NLR family pyrin domain containing 3 (NLRP3) inflammasome mediates caspase-1-dependent processing of inflammatory cytokines such as IL-1β, an essential endothelial activator, and contributes to the pathology of inflammatory diseases. To evaluate the role of NLRP3 in neutrophils in endothelial activation, which is still elusive, we used the thioglycollate-induced peritonitis model characterized by an early neutrophil influx, on Nlrp3-/- and Nlrp3+/+ mice. Nlrp3-/- mice recruited fewer neutrophils than Nlrp3+/+ into the peritoneum and showed lower IL-1β in peritoneal lavage fluid. The higher production of IL-1β in Nlrp3+/+ was neutrophil-dependent as neutrophil depletion prevented the IL-1β production. The Nlrp3+/+ neutrophils collected from the peritoneal fluid formed significantly more filaments (specks) than Nlrp3-/- neutrophils of ASC (apoptosis-associated speck-like protein containing a caspase activating and recruitment domain), a readout for inflammasome activation. Intravital microscopy revealed that leukocytes rolled significantly slower in Nlrp3+/+ venules than in Nlrp3-/-. Nlrp3-/- endothelial cells isolated from mesenteric vessels demonstrated a lower percentage of P-selectin-positive cells with lower intensity of surface P-selectin expression than the Nlrp3+/+ endothelial cells evaluated by flow cytometry. We conclude that neutrophils orchestrate acute thioglycollate-induced peritonitis by producing IL-1β in an NLRP3-dependent manner. This increases endothelial P-selectin expression and leukocyte transmigration.

NLRP3 inflammasome activation in cigarette smoke priming for Pseudomonas aeruginosa-induced acute lung injury

It is increasingly recognized that cigarette smoke (CS) exposure increases the incidence and severity of acute respiratory distress syndrome (ARDS) in critical ill humans and animals. However, the mechanism(s) is not well understood. This study aims to investigate mechanism underlying the priming effect of CS on Pseudomonas aeruginosa-triggered acute lung injury, by using pre-clinic animal models and genetically modified mice. We demonstrated that CS impaired P. aeruginosa-induced mitophagy flux, promoted p62 accumulation, and exacerbated P. aeruginosa-triggered mitochondrial damage and NLRP3 inflammasome activation in alveolar macrophages; an effect associated with increased acute lung injury and mortality. Pharmacological inhibition of caspase-1, a component of inflammasome, attenuated CS primed P. aeruginosa-triggered acute lung injury and improved animal survival. Global or myeloid-specific knockout of IL-1β, a downstream component of inflammasome activation, also attenuated CS primed P. aeruginosa-triggered acute lung injury. Our results suggest that NLRP3 inflammasome activation is an important mechanism for CS primed P. aeruginosa-triggered acute lung injury. (total words: 155).

CD6 deficiency impairs early immune response to bacterial sepsis

CD6 is a lymphocyte-specific scavenger receptor expressed on adaptive (T) and innate (B1a, NK) immune cells, which is involved in both fine-tuning of lymphocyte activation/differentiation and recognition of bacterial-associated molecular patterns (i.e., lipopolysaccharide). However, evidence on CD6’s role in the physiological response to bacterial infection was missing. Our results show that induction of monobacterial and polymicrobial sepsis in Cd6^−/− mice results in lower survival rates and increased bacterial loads and pro-inflammatory cytokine levels. Steady state analyses of Cd6^−/− mice show decreased levels of natural polyreactive antibodies, concomitant with decreased cell counts of spleen B1a and marginal zone B cells. Adoptive transfer of wild-type B cells and mouse serum, as well as a polyreactive monoclonal antibody improve Cd6^−/− mouse survival rates post-sepsis. These findings support a nonredundant role for CD6 in the early response against bacterial infection, through homeostatic expansion and functionality of innate-related immune cells.

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CD6 is a nonredundant receptor in early immune response to sepsis

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Cd6−/− mice show higher susceptibility to bacterial sepsis

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Cd6−/− mice show lower B1a and MZB cell and natural polyreactive antibody levels

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B cell and serum transfer restore susceptibility of Cd6−/− mice to bacterial sepsis

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.

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.

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.

NLRP6 Serves as a Negative Regulator of Neutrophil Recruitment and Function During Streptococcus pneumoniae Infection

Streptococcus pneumoniae is an invasive pathogen with high morbidity and mortality in the immunocompromised children and elderly. NOD-like receptor family pyrin domain containing 6 (NLRP6) plays an important role in the host innate immune response against pathogen infections. Our previous studies have shown that NLRP6 plays a negative regulatory role in host defense against S. pneumoniae, but the underlying mechanism is still unclear. The further negative regulatory role of NLRP6 in the host was investigated in this study. Our results showed that NLRP6^−/− mice in the lung had lower bacterial burdens after S. pneumoniae infection and expressed higher level of tight junction (TJ) protein occludin compared to WT mice, indicating the detrimental role of NLRP6 in the host defense against S. pneumoniae infection. Transcriptome analysis showed that genes related to leukocytes migration and recruitment were differentially expressed between wild-type (WT) and NLRP6 knockout (NLRP6^−/−) mice during S. pneumoniae infection. Also, NLRP6^−/− mice showed higher expression of chemokines including C-X-C motif chemokine ligand 1 (CXCL1) and 2 (CXCL2) and lower gene expression of complement C3a receptor 1 (C3aR1) and P-selectin glycoprotein ligand-1 (PSGL-1) which are the factors that inhibit the recruitment of neutrophils. Furthermore, NLRP6^−/− neutrophils showed increased intracellular bactericidal ability and the formation of neutrophil extracellular traps (NETs) during S. pneumoniae infection. Taken together, our study suggests that NLRP6 is a negative regulator of neutrophil recruitment and function during S. pneumoniae infection. Our study provides a new insight to develop novel strategies to treat invasive pneumococcal infection.

Autophagy-driven neutrophil extracellular traps: The dawn of sepsis

Sepsis is a systemic inflammatory syndrome caused by infection disorders. The core mechanism of sepsis is immune dysfunction. Neutrophils are the most abundant circulating white blood cells, which play a crucial role in mediating the innate immune response. Previous studies have shown that an effective way to treat sepsis is through the regulation of neutrophil functions. Autophagy, a highly conserved degradation process, is responsible for removing denatured proteins or damaged organelles within cells and protecting cells from external stimuli. It is a key homeostasis process that promotes neutrophil function and differentiation. Autophagy has been shown to be closely associated with inflammation and immunity. Neutrophils, the first line of innate immunity, migrate to inflammatory sites upon their activation. Neutrophil-mediated autophagy may participate in the clinical course of sepsis. In this review, we summarized and analyzed the latest research findings on the changes in neutrophil external traps during sepsis, the regulatory role of autophagy in neutrophil, and the potential application of autophagy-driven NETs in sepsis, so as to guide clinical treatment of sepsis.

Kakonein restores hyperglycemia‐induced macrophage digestion dysfunction through regulation of cathepsin B‐dependent NLRP3 inflammasome activation

In hyperglycemia‐induced complications, macrophages play important roles in disease progression, and altered digestion is a key feature that dictates macrophage function. Recent evidence indicates that kakonein (Ka) possesses anti‐inflammatory activities for hyperglycemia‐induced complication. In this study, we established a mouse model of Nlrp3^+/+ and Nlrp3^−/− hyperglycemia and administering Ka, primary culture macrophages were tested by engulfing and digesting microbes. The role of macrophages in the cathepsin B–NLRP3 pathway involved in the mechanism of Ka in restoring macrophage digestion function was investigated using biochemical analyses, molecular biotechnology, and microbiology. Ka restored the function of macrophage digestion, which were same characterized by Nlrp3^−/− mice. Meanwhile, kakonein could decrease NLRP3 inflammasome products expression and NLRP3/ASC or NLRP3/Casp1 colocalization in macrophage. Interestingly, Ka suppressed inflammasome response not by reducing NLRP3 and ASC expression but by reducing cathepsin B release and activation. And Ka restored macrophage digestion and inhibited NLRP3 inflammasome activation consistent with cathepsin B inhibitor. It is concluded that Ka reduced the release of lysosomal cathepsin B and consequently inhibited NLRP3 inflammasome activation to prevent macrophage digestion. Hence, Ka may contribute to new targets for treatment of hyperglycemia‐associated dysfunction of macrophage digestion and development of innovative drugs.

Evolutionary analyses of the gasdermin family suggest conserved roles in infection response despite loss of pore-forming functionality

BACKGROUND

Gasdermins are ancient (>500million-years-ago) proteins, constituting a family of pore-forming proteins that allow the release of intracellular content including proinflammatory cytokines. Despite their importance in the immune response, and although gasdermin and gasdermin-like genes have been identified across a wide range of animal and non-animal species, there is limited information about the evolutionary history of the gasdermin family, and their functional roles after infection. In this study, we assess the lytic functions of different gasdermins across Metazoa species, and use a mouse model of sepsis to evaluate the expression of the different gasdermins during infection.

RESULTS

We show that the majority of gasdermin family members from distantly related animal clades are pore-forming, in line with the function of the ancestral proto-gasdermin and gasdermin-like proteins of Bacteria. We demonstrate the first expansion of this family occurred through a duplication of the ancestral gasdermin gene which formed gasdermin E and pejvakin prior to the divergence of cartilaginous fish and bony fish ~475 mya. We show that pejvakin from cartilaginous fish and mammals lost the pore-forming functionality and thus its role in cell lysis. We describe that the pore-forming gasdermin A formed ~320 mya as a duplication of gasdermin E prior to the divergence of the Sauropsida clade (the ancestral lineage of reptiles, turtles, and birds) and the Synapsid clade (the ancestral lineage of mammals). We then demonstrate that the gasdermin A gene duplicated to form the rest of the gasdermin family including gasdermins B, C, and D: pore-forming proteins that present a high variation of the exons in the linker sequence, which in turn allows for diverse activation pathways. Finally, we describe expression of murine gasdermin family members in different tissues in a mouse sepsis model, indicating function during infection response.

CONCLUSIONS

In this study we explored the evolutionary history of the gasdermin proteins in animals and demonstrated that the pore-formation functionality has been conserved from the ancient proto-gasdermin protein. We also showed that one gasdermin family member, pejvakin, lost its pore-forming functionality, but that all gasdermin family members, including pejvakin, likely retained a role in inflammation and the physiological response to infection.

Activation of cannabinoid-2 receptor protects against Pseudomonas aeruginosa induced acute lung injury and inflammation

BACKGROUND

Bacterial pneumonia is a major risk factor for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Pseudomonas aeruginosa (PA), an opportunistic pathogen with an increasing resistance acquired against multiple drugs, is one of the main causative agents of ALI and ARDS in diverse clinical settings. Given the anti-inflammatory role of the cannabinoid-2 receptor (CB2R), the effect of CB2R activation in the regulation of PA-induced ALI and inflammation was tested in a mouse model as an alternative to conventional antibiotic therapy.

METHODS

In order to activate CB2R, a selective synthetic agonist, JWH133, was administered intraperitoneally (i.p.) to C57BL/6J mice. Furthermore, SR144528 (a selective CB2R antagonist) was administered in combination with JWH133 to test the specificity of the CB2R-mediated effect. PA was administered intratracheally (i.t.) for induction of pneumonia in mice. At 24 h after PA exposure, lung mechanics were measured using the FlexiVent system. The total cell number, protein content, and neutrophil population in the bronchoalveolar lavage fluid (BALF) were determined. The bacterial load in the whole lung was also measured. Lung injury was evaluated by histological examination and PA-induced inflammation was assessed by measuring the levels of BALF cytokines and chemokines. Neutrophil activation (examined by immunofluorescence and immunoblot) and PA-induced inflammatory signaling (analyzed by immunoblot) were also studied.

RESULTS

CB2R activation by JWH133 was found to significantly reduce PA-induced ALI and the bacterial burden. CB2R activation also suppressed the PA-induced increase in immune cell infiltration, neutrophil population, and inflammatory cytokines. These effects were abrogated by a CB2R antagonist, SR144528, further confirming the specificity of the CB2R-mediated effects. CB2R-knock out (CB2RKO) mice had a significantly higher level of PA-induced inflammation as compared to that in WT mice. CB2R activation diminished the excess activation of neutrophils, whereas mice lacking CB2R had elevated neutrophil activation. Pharmacological activation of CB2R significantly reduced the PA-induced NF-κB and NLRP3 inflammasome activation, whereas CB2KO mice had elevated NLRP3 inflammasome.

CONCLUSION

Our findings indicate that CB2R activation ameliorates PA-induced lung injury and inflammation, thus paving the path for new therapeutic avenues against PA pneumonia.

Bryodulcosigenin a natural cucurbitane-type triterpenoid attenuates dextran sulfate sodium (DSS)-induced colitis in mice

BACKGROUND

Bryodulcosigenin (BDG) a cucurbitane-type triterpenoid has been isolated from the roots of Bryonia dioca and possesses marked anti-inflammatory effects, although its beneficial effect against intestinal disorders remains unclear.

PURPOSE

To explore the underlying mechanism of BDG on the dysbiosis of chronic ulcerative colitis (UC) and its associated side-effects on lung tissues.

METHODS

A chronic UC model was established using 2.5% dextran sulfate sodium (DSS) in mice treated for 64 days and diagnostic assessments, western blot analysis and quantitative real time-PCR were employed to determine the protective mechanism of BDG.

RESULTS

Oral administration of BDG (10 mg/kg/day) significantly improved colon length, disease activity index, and alleviated colonic histopathological damage in the DSS-induced colitis  mice. BDG not only reversed the TNF-α-induced degradation of tight junction proteins (occludin and ZO-1) but also suppressed the elevated apoptosis seen in intestinal epithelial cells (NCM460). In addition, BDG significantly attenuated damage in alveolar epithelial cells (MLE-12) co-cultured with NCM460 cells under inflammatory conditions. Furthermore, BDG in vivo significantly prevented the symptoms of respiratory disorders and repressed alveolar inflammation by regulating DSS-induced chronic colitis in mice.

CONCLUSION

BDG effectively inhibited the apoptosis of intestinal epithelial cells and suppressed the activation of the NLRP3 inflammasome which resulted in the restoration of the intestinal barrier. Therefore, the enhanced integrity of intestinal epithelial cells produced by BDG intervention contributed to its anti-colitis effects, indicating its great potential as an inhibitor of UC and lung injury. Therefore, restoring intestinal integrity may represent a promising strategy in the prevention of pulmonary disease.

Inflammasome-mediated GSDMD activation facilitates escape of Candida albicans from macrophages

Candida albicans is the most common cause of fungal sepsis. Inhibition of inflammasome activity confers resistance to polymicrobial and LPS-induced sepsis; however, inflammasome signaling appears to protect against C. albicans infection, so inflammasome inhibitors are not clinically useful for candidiasis. Here we show disruption of GSDMD, a known inflammasome target and key pyroptotic cell death mediator, paradoxically alleviates candidiasis, improving outcomes and survival of Candida-infected mice. Mechanistically, C. albicans hijacked the canonical inflammasome-GSDMD axis-mediated pyroptosis to promote their escape from macrophages, deploying hyphae and candidalysin, a pore-forming toxin expressed by hyphae. GSDMD inhibition alleviated candidiasis by preventing C. albicans escape from macrophages while maintaining inflammasome-dependent but GSDMD-independent IL-1β production for anti-fungal host defenses. This study demonstrates key functions for GSDMD in Candida's escape from host immunity in vitro and in vivo and suggests that GSDMD may be a potential therapeutic target in C. albicans-induced sepsis.

Microglial NLRP3 Inflammasome Activation upon TLR2 and TLR5 Ligation by Distinct α-Synuclein Assemblies

Parkinson's disease (PD) is the second most common age-related neurodegenerative disorder and is characterized by the formation of cellular inclusions inside neurons that are rich in an abnormal form of the protein α-synuclein (α-syn). Microglia are the CNS resident immune cells that react to misfolded proteins through pattern recognition receptor ligation and activation of signaling transduction pathways. Here, we studied activation of primary microglia isolated from wild-type mouse by distinct α-syn forms and their clearance. Internalization of α-syn monomers and oligomers efficiently activated the NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome via TLR2 and TLR5 ligation, thereby acting on different signaling checkpoints. We found that primary microglia effectively engulf α-syn but hesitate in its degradation. NLRP3 inhibition by the selective inhibitor CRID3 sodium salt and NLRP3 deficiency improved the overall clearance of α-syn oligomers. Together, these data show that distinct α-syn forms exert different microglial NLRP3 inflammasome activation properties, thereby compromising its degradation, which can be prevented by NLRP3 inhibition.

Role of Neutrophils on the Ocular Surface

The ocular surface is a gateway that contacts the outside and receives stimulation from the outside. The corneal innate immune system is composed of many types of cells, including epithelial cells, fibroblasts, natural killer cells, macrophages, neutrophils, dendritic cells, mast cells, basophils, eosinophils, mucin, and lysozyme. Neutrophil infiltration and degranulation occur on the ocular surface. Degranulation, neutrophil extracellular traps formation, called NETosis, and autophagy in neutrophils are involved in the pathogenesis of ocular surface diseases. It is necessary to understand the role of neutrophils on the ocular surface. Furthermore, there is a need for research on therapeutic agents targeting neutrophils and neutrophil extracellular trap formation for ocular surface diseases.

Blockade of macrophage-associated programmed death 1 inhibits the pyroptosis signalling pathway in sepsis

OBJECTIVE

Programmed death 1 (PD-1) and macrophages are the most intriguing candidates in sepsis-induced inflammatory disorders. We aimed to investigate the association between monocyte PD-1 and sepsis severity and the mechanism by which blocking macrophage-associated PD-1 causes inflammatory disorders in sepsis.

MATERIALS AND METHODS

We first measured whether the expression of PD-1 on the monocyte subset is clinically associated with sepsis severity in an observational study. This study included 42 septic patients and 16 healthy controls (HCs) whose serum inflammatory factors were examined by Luminex MagPix. Then, we investigated the effect of PD-1 blockade on macrophages from septic mice (C57BL/6 mice) constructed by caecal ligation and puncture (CLP) via RNA sequencing. The positive genes screened by RNA-seq were verified in LPS-stimulated RAW264.7 cells by Western blot.

RESULTS

The results showed that the expression of PD-1 on CD14⁺CD16⁺ monocytes (intermediate monocytes, IM Mo) was significantly higher in both septic and septic shock patients than in HCs. Further analysis of serum cytokines in septic patients showed that the levels of IL-6 and TNF-α were significantly higher than those in HCs, while serum PD-1 levels were decreased in septic patients. More interestingly, blockade of PD-1 on macrophages from septic mice suppressed the gene expression levels of NLRP3/Caspase-4/AKT2/STAT3. The protein levels associated with pyroptosis including NLRP3, Caspase4, GSDMD and NT-GSDMD were significantly decreased in LPS-stimulated RAW264.7 cells treated with PD-1 antibody.

CONCLUSION

Our results suggested that intermediate monocytes with high expression of PD-1 may be involved in the progression of sepsis. PD-1 might play a critical role in regulating the pyroptosis signalling pathway in sepsis.

Altered Macrophage Function Associated with Crystalline Lung Inflammation in Acid Sphingomyelinase Deficiency

Deficiency of ASM (acid sphingomyelinase) causes the lysosomal storage Niemann-Pick disease (NPD). Patients with NPD type B may develop progressive interstitial lung disease with frequent respiratory infections. Although several investigations using the ASM-deficient (ASMKO) mouse NPD model revealed inflammation and foamy macrophages, there is little insight into the pathogenesis of NPD-associated lung disease. Using ASMKO mice, we report that ASM deficiency is associated with a complex inflammatory phenotype characterized by marked accumulation of monocyte-derived CD11b⁺ macrophages and expansion of airspace/alveolar CD11c⁺ CD11b^- macrophages, both with increased size, granularity, and foaminess. Both the alternative and classical pathways were activated, with decreased in situ phagocytosis of opsonized (Fc-coated) targets, preserved clearance of apoptotic cells (efferocytosis), secretion of Th2 cytokines, increased CD11c⁺/CD11b⁺ cells, and more than a twofold increase in lung and plasma proinflammatory cytokines. Macrophages, neutrophils, eosinophils, and noninflammatory lung cells of ASMKO lungs also exhibited marked accumulation of chitinase-like protein Ym1/2, which formed large eosinophilic polygonal Charcot-Leyden-like crystals. In addition to providing insight into novel features of lung inflammation that may be associated with NPD, our report provides a novel connection between ASM and the development of crystal-associated lung inflammation with alterations in macrophage biology.

A gain-of-function NLRP3 3'-UTR polymorphism causes miR-146a-mediated suppression of NLRP3 expression and confers protection against sepsis progression

Nucleotide-binding domain and leucine-rich repeat (LRR)-containing family protein 3 (NLRP3) regulated the maturation of inflammation-related cytokines by forming NLRP3 inflammasome, which plays pivotal roles in sepsis pathogenesis. In this study, we evaluated the genetic association of NLRP3 polymorphisms with sepsis (640 patients and 769 controls) and characterized the impact of NLRP3 polymorphisms on NLRP3 expression and inflammatory responses. No significant differences were observed in genotype/allelic frequencies of NLRP3 29940G>C between sepsis cases and controls. The G allele was significantly overrepresented in patients with septic shock than those in sepsis subgroup, and the GC/GG genetypes were related to the 28-day mortality of sepsis. Lipopolysaccharide challenge to peripheral blood mononuclear cells showed a significant suppression of NLRP3 mRNA expression and release of IL-1β and TNF-α in CC compared with the GC/GG genotype category. Functional experiments with luciferase reporter vectors containing the NLRP3 3′-UTR with the 29940 G-to-C variation in HUVECs and THP-1 cells showed a potential suppressive effect of miR-146a on NLRP3 transcription in the presence of the C allele. Taken together, these results demonstrated that the 29940 G-to-C mutation within the NLRP3 3′-UTR was a gain-of-function alteration that caused the suppression of NLRP3 expression and downstream inflammatory cytokine production via binding with miR-146a, which ultimately protected patients against susceptibility to sepsis progression and poor clinical outcome.

The Role of Melatonin on NLRP3 Inflammasome Activation in Diseases

NLRP3 inflammasome is a part of the innate immune system and responsible for the rapid identification and eradication of pathogenic microbes, metabolic stress products, reactive oxygen species, and other exogenous agents. NLRP3 inflammasome is overactivated in several neurodegenerative, cardiac, pulmonary, and metabolic diseases. Therefore, suppression of inflammasome activation is of utmost clinical importance. Melatonin is a ubiquitous hormone mainly produced in the pineal gland with circadian rhythm regulatory, antioxidant, and immunomodulatory functions. Melatonin is a natural product and safer than most chemicals to use for medicinal purposes. Many in vitro and in vivo studies have proved that melatonin alleviates NLRP3 inflammasome activity via various intracellular signaling pathways. In this review, the effect of melatonin on the NLRP3 inflammasome in the context of diseases will be discussed.

Autophagy Regulation on Pyroptosis: Mechanism and Medical Implication in Sepsis

Sepsis is defined as a life-threatening disease involving multiple organ dysfunction caused by dysregulated host responses to infection. To date, sepsis remains a dominant cause of death among critically ill patients. Pyroptosis is a unique form of programmed cell death mediated by the gasdermin family of proteins and causes lytic cell death and release of proinflammatory cytokines. Although there might be some positive aspects to pyroptosis, it is regarded as harmful during sepsis and needs to be restricted. Autophagy was originally characterized as a homeostasis-maintaining mechanism in living cells. In the past decade, its function in negatively modulating pyroptosis and inflammation during sepsis has attracted increased attention. Here, we present a comprehensive review of the regulatory effect of autophagy on pyroptosis during sepsis, including the latest advances in our understanding of the mechanism and signaling pathways involved, as well as the potential therapeutic application in sepsis.

Cord-Blood-Derived Professional Antigen-Presenting Cells: Functions and Applications in Current and Prospective Cell Therapies

Human umbilical cord blood (UCB) represents a valuable source of hematopoietic stem cells, particularly for patients lacking a matching donor. UCB provides practical advantages, including a lower risk of graft-versus-host-disease and permissive human leukocyte antigen mismatching. These advantageous properties have so far been applied for stem cell, mesenchymal stromal cell, and chimeric antigen receptor T cell therapies. However, UCB-derived professional antigen-presenting cells are increasingly being utilized in the context of immune tolerance and regenerative therapy. Here, we review the cell-specific characteristics as well as recent advancements in UCB-based cell therapies focusing on dendritic cells, monocytes, B lymphocytes, innate lymphoid cells, and macrophages.

NLRP6 modulates neutrophil homeostasis in bacterial pneumonia-derived sepsis

Bacterial pneumonia is a significant cause of morbidity, mortality, and health care expenditures. Optimum neutrophil recruitment and their function are critical defense mechanisms against respiratory pathogens. The nucleotide-binding oligomerization domain-like receptor (NLRP) 6 controls gut microbiota and immune response to systemic and enteric infections. However, the importance of NLRP6 in neutrophil homeostasis following lung infection remains elusive. To investigate the role of NLRs in neutrophil homeostasis, we used Nlrp6 gene-deficient (Nlrp6^-/-) mice in a model of Klebsiella pneumoniae-induced pneumonia-derived sepsis. We demonstrated that NLRP6 is critical for host survival, bacterial clearance, neutrophil influx, and CXC-chemokine production. Kp-infected Nlrp6^-/- mice have reduced numbers of hematopoietic stem cells and granulocyte-monocyte progenitors but increased retention of matured neutrophils in bone marrow. Neutrophil extracellular trap (NET) formation and NET-mediated bacterial killing were also impaired in Nlrp6^-/- neutrophils in vitro. Furthermore, recombinant CXCL1 rescued the impaired host defense, granulopoietic response, and NETosis in Kp-infected Nlrp6^-/- mice. Using A/J background mice and co-housing experiments, our findings revealed that the susceptible phenotype of Nlrp6^-/- mice is not strain-specific and gut microbiota-dependent. Taken together, these data unveil NLRP6 as a central regulator of neutrophil recruitment, generation, and function during bacterial pneumonia followed by sepsis.

The complex interplay between endoplasmic reticulum stress and the NLRP3 inflammasome: a potential therapeutic target for inflammatory disorders

Inflammation is the result of a complex network of cellular and molecular interactions and mechanisms that facilitate immune protection against intrinsic and extrinsic stimuli, particularly pathogens, to maintain homeostasis and promote tissue healing. However, dysregulation in the immune system elicits excess/abnormal inflammation resulting in unintended tissue damage and causes major inflammatory diseases including asthma, chronic obstructive pulmonary disease, atherosclerosis, inflammatory bowel diseases, sarcoidosis and rheumatoid arthritis. It is now widely accepted that both endoplasmic reticulum (ER) stress and inflammasomes play critical roles in activating inflammatory signalling cascades. Notably, evidence is mounting for the involvement of ER stress in exacerbating inflammasome-induced inflammatory cascades, which may provide a new axis for therapeutic targeting in a range of inflammatory disorders. Here, we comprehensively review the roles, mechanisms and interactions of both ER stress and inflammasomes, as well as their interconnected relationships in inflammatory signalling cascades. We also discuss novel therapeutic strategies that are being developed to treat ER stress- and inflammasome-related inflammatory disorders.

GYY4137 alleviates sepsis-induced acute lung injury in mice by inhibiting the PDGFRβ/Akt/NF-κB/NLRP3 pathway

AIMS

GYY4137 [GYY, morpholin-4-ium-4-methoxyphenyl (morpholino) phosphinodithioate] is a novel and perfect hydrogen sulfide (H₂S) donor that is stable in vivo and in vitro. H₂S, along with CO and NO, has been recognized as the third physiological gas signaling molecule that plays an active role in fighting various lung infections. However, the mechanism by which GYY4137 affects cecal ligation and puncture (CLP)-induced acute lung injury (ALI) is not understood. This study aimed to investigate whether GYY4137 inhibits the activation of the pyrin domain-containing protein 3 (NLRP3) inflammasome by inhibiting the PDGFRβ/Akt/NF-κB pathway.

MAIN METHODS

The model of CLP-induced ALI was established in vivo. The mice were subsequently treated with GYY4137 (25 μg/g and 50 μg/g) to simulate the realistic conditions of pathogenesis. Western blotting and immunohistochemical staining were used to examine protein expression, hematoxylin and eosin staining was used for the histopathological analysis, and the levels of inflammatory factors were determined using enzyme-linked immunosorbent assays (ELISAs).

KEY FINDINGS

GYY4137 significantly increased the 7-day survival of mice with septic peritonitis and protected against CLP-induced ALI, including decreasing neutrophil infiltration, improving sepsis-induced lung histopathological changes, diminishing lung tissue damage, and attenuating the severity of lung injury in mice. The protective effect of GYY4137 was undoubtedly dose-dependent. We discovered that GYY4137 reduced the levels of the p-PDGFRβ, p-NF-κB, ASC, NLRP3, caspase-1, and p-Akt proteins in septic mouse lung tissue. Akt regulates the generation of proinflammatory cytokines in endotoxemia-associated ALI by enhancing the nuclear translocation of NF-κB.

SIGNIFICANCE

These results indicate a new molecular mechanism explaining the effect of GYY4137 on the treatment of CLP-induced ALI in mice.

Cryptotanshinone specifically suppresses NLRP3 inflammasome activation and protects against inflammasome-mediated diseases

NLRP3 inflammasome activation is implicated in the pathogenesis of a wide range of inflammatory diseases, but medications targeting the NLRP3 inflammasome are not available for clinical use. Here, we demonstrate that cryptotanshinone (CTS), a major component derived from the traditional medicinal herb Salvia miltiorrhiza Bunge, is a specific inhibitor for the NLRP3 inflammasome. Cryptotanshinone inhibits NLRP3 inflammasome activation in macrophages, but has no effects on AIM2 or NLRC4 inflammasome activation. Mechanistically, cryptotanshinone blocks Ca2+ signaling and the induction of mitochondrial reactive oxygen species (mtROS), which are important upstream signals of NLRP3 inflammasome activation. In vivo, cryptotanshinone attenuates caspase-1 activation and IL-1β secretion in mouse models of NLRP3 inflammasome-mediated diseases such as endotoxemia syndrome and methionine- and choline-deficient-diet-induced nonalcoholic steatohepatitis (NASH). Our findings suggest that cryptotanshinone may be a promising therapeutic agent for the treatment of NLRP3 inflammasome-mediated diseases.

Ovarian hormones-autophagy-immunity axis in menstruation and endometriosis

Menstruation occurs in few species and involves a cyclic process of proliferation, breakdown and regeneration under the control of ovarian hormones. Knowledge of normal endometrial physiology, as it pertains to the regulation of menstruation, is essential to understand disorders of menstruation. Accumulating evidence indicates that autophagy in the endometrium, under the regulation of ovarian hormones, can result in the infiltration of immune cells, which plays an indispensable role in the endometrium shedding, tissue repair and prevention of infections during menstruation. In addition, abnormal autophagy levels, together with resulting dysregulated immune system function, are associated with the pathogenesis and progression of endometriosis. Considering its potential value of autophagy as a target for the treatment of menstrual-related and endometrium-related disorders, we review the activity and function of autophagy during menstrual cycles. The role of the estrogen/progesterone-autophagy-immunity axis in endometriosis are also discussed.

Preventing the development of severe COVID-19 by modifying immunothrombosis

BACKGROUND

COVID-19-associated acute respiratory distress syndrome (ARDS) is associated with significant morbidity and high levels of mortality. This paper describes the processes involved in the pathophysiology of COVID-19 from the initial infection and subsequent destruction of type II alveolar epithelial cells by SARS-CoV-2 and culminating in the development of ARDS.

MAIN BODY

The activation of alveolar cells and alveolar macrophages leads to the release of large quantities of proinflammatory cytokines and chemokines and their translocation into the pulmonary vasculature. The presence of these inflammatory mediators in the vascular compartment leads to the activation of vascular endothelial cells platelets and neutrophils and the subsequent formation of platelet neutrophil complexes. These complexes in concert with activated endothelial cells interact to create a state of immunothrombosis. The consequence of immunothrombosis include hypercoagulation, accelerating inflammation, fibrin deposition, migration of neutrophil extracellular traps (NETs) producing neutrophils into the alveolar apace, activation of the NLRP3 inflammazome, increased alveolar macrophage destruction and massive tissue damage by pyroptosis and necroptosis Therapeutic combinations aimed at ameliorating immunothrombosis and preventing the development of severe COVID-19 are discussed in detail.

An overview of disease models for NLRP3 inflammasome over-activation

Introduction: Inflammatory reactions, including those mediated by the NLRP3 inflammasome, maintain the body's homeostasis by removing pathogens, repairing damaged tissues, and adapting to stressed environments. However, uncontrolled activation of the NLRP3 inflammasome tends to cause various diseases using different mechanisms. Recently, many inhibitors of the NLRP3 inflammasome have been reported and many are being developed. In order to assess their efficacy, specificity, and mechanism of action, the screening process of inhibitors requires various types of cell and animal models of NLRP3-associated diseases.Areas covered: In the following review, the authors give an overview of the cell and animal models that have been used during the research and development of various inhibitors of the NLRP3 inflammasome.Expert opinion: There are many NLRP3 inflammasome inhibitors, but most of the inhibitors have poor specificity and often influence other inflammatory pathways. The potential risk for cross-reaction is high; therefore, the development of highly specific inhibitors is essential. The selection of appropriate cell and animal models, and combined use of different models for the evaluation of these inhibitors can help to clarify the target specificity and therapeutic effects, which is beneficial for the development and application of drugs targeting the NLRP3 inflammasome.