Caspase-11 Mediates Neutrophil Chemotaxis and Extracellular Trap Formation During Acute Gouty Arthritis Through Alteration of Cofilin Phosphorylation

Roles of the Caspase-11 Non-Canonical Inflammasome in Rheumatic Diseases

Inflammasomes are intracellular multiprotein complexes that activate inflammatory signaling pathways. Inflammasomes comprise two major classes: canonical inflammasomes, which were discovered first and are activated in response to a variety of pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs), and non-canonical inflammasomes, which were discovered recently and are only activated in response to intracellular lipopolysaccharide (LPS). Although a larger number of studies have successfully demonstrated that canonical inflammasomes, particularly the NLRP3 inflammasome, play roles in various rheumatic diseases, including rheumatoid arthritis (RA), infectious arthritis (IR), gouty arthritis (GA), osteoarthritis (OA), systemic lupus erythematosus (SLE), psoriatic arthritis (PA), ankylosing spondylitis (AS), and Sjögren's syndrome (SjS), the regulatory roles of non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 non-canonical inflammasomes, in these diseases are still largely unknown. Interestingly, an increasing number of studies have reported possible roles for non-canonical inflammasomes in the pathogenesis of various mouse models of rheumatic disease. This review comprehensively summarizes and discusses recent emerging studies demonstrating the regulatory roles of non-canonical inflammasomes, particularly focusing on the caspase-11 non-canonical inflammasome, in the pathogenesis and progression of various types of rheumatic diseases and provides new insights into strategies for developing potential therapeutics to prevent and treat rheumatic diseases as well as associated diseases by targeting non-canonical inflammasomes.

DNA hypomethylation promotes the expression of CASPASE-4 which exacerbates inflammation and amyloid-β deposition in Alzheimer's disease

Alzheimer's disease (AD) is the sixth leading cause of death in the USA. It is established that neuroinflammation contributes to the synaptic loss, neuronal death, and symptomatic decline of AD patients. Accumulating evidence suggests a critical role for microglia, innate immune phagocytes of the brain. For instance, microglia release pro-inflammatory products such as IL-1β which is highly implicated in AD pathobiology. The mechanisms underlying the transition of microglia to proinflammatory promoters of AD remain largely unknown. To address this gap, we performed reduced representation bisulfite sequencing (RRBS) to profile global DNA methylation changes in human AD brains compared to no disease controls. We identified differential DNA methylation of CASPASE-4 (CASP4), which when expressed promotes the generation of IL-1β and is predominantly expressed in immune cells. DNA upstream of the CASP4 transcription start site was hypomethylated in human AD brains, which was correlated with increased expression of CASP4. Furthermore, microglia from a mouse model of AD (5xFAD) express increased levels of CASP4 compared to wild-type (WT) mice. To study the role of CASP4 in AD, we developed a novel mouse model of AD lacking the mouse ortholog of CASP4 and CASP11, which is encoded by mouse Caspase-4 (5xFAD/Casp4-/-). The expression of CASP11 was associated with increased accumulation of pathologic protein aggregate amyloid-β (Aβ) and increased microglial production of IL-1β in 5xFAD mice. Utilizing RNA-sequencing, we determined that CASP11 promotes unique transcriptomic phenotypes in 5xFAD mouse brains, including alterations of neuroinflammatory and chemokine signaling pathways. Notably, in vitro, CASP11 promoted generation of IL-1β from macrophages in response to cytosolic Aβ through cleavage of downstream effector Gasdermin D (GSDMD). Therefore, here we unravel the role for CASP11 and GSDMD in the generation of IL-1β in response to Aβ and the progression of pathologic inflammation in AD. Overall, our results demonstrate that overexpression of CASP4 due to differential DNA methylation in AD microglia contributes to the progression of AD pathobiology. Thus, we identify CASP4 as a potential target for immunotherapies for the treatment and prevention of AD.

Dying to Defend: Neutrophil Death Pathways and their Implications in Immunity

Neutrophils, accounting for ≈70% of human peripheral leukocytes, are key cells countering bacterial and fungal infections. Neutrophil homeostasis involves a balance between cell maturation, migration, aging, and eventual death. Neutrophils undergo different death pathways depending on their interactions with microbes and external environmental cues. Neutrophil death has significant physiological implications and leads to distinct immunological outcomes. This review discusses the multifarious neutrophil death pathways, including apoptosis, NETosis, pyroptosis, necroptosis, and ferroptosis, and outlines their effects on immune responses and disease progression. Understanding the multifaceted aspects of neutrophil death, the intersections among signaling pathways and ramifications of immunity will help facilitate the development of novel therapeutic methods.

NLRP3-Induced NETosis: A Potential Therapeutic Target for Ischemic Thrombotic Diseases?

Ischemic thrombotic disease, characterized by the formation of obstructive blood clots within arteries or veins, is a condition associated with life-threatening events, such as stroke, myocardial infarction, deep vein thrombosis, and pulmonary embolism. The conventional therapeutic strategy relies on treatments with anticoagulants that unfortunately pose an inherent risk of bleeding complications. These anticoagulants primarily target clotting factors, often overlooking upstream events, including the release of neutrophil extracellular traps (NETs). Neutrophils are integral components of the innate immune system, traditionally known for their role in combating pathogens through NET formation. Emerging evidence has now revealed that NETs contribute to a prothrombotic milieu by promoting platelet activation, increasing thrombin generation, and providing a scaffold for clot formation. Additionally, NET components enhance clot stability and resistance to fibrinolysis. Clinical and preclinical studies have underscored the mechanistic involvement of NETs in the pathogenesis of thrombotic complications, since the clots obtained from patients and experimental models consistently exhibit the presence of NETs. Given these insights, the inhibition of NETs or NET formation is emerging as a promising therapeutic approach for ischemic thrombotic diseases. Recent investigations also implicate a role for the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome as a mediator of NETosis and thrombosis, suggesting that NLRP3 inhibition may also hold potential for mitigating thrombotic events. Therefore, future preclinical and clinical studies aimed at identifying and validating NLRP3 inhibition as a novel therapeutic intervention for thrombotic disorders are imperative.

The dysregulation of immune cells induced by uric acid: mechanisms of inflammation associated with hyperuricemia and its complications

Changes in lifestyle induce an increase in patients with hyperuricemia (HUA), leading to gout, gouty arthritis, renal damage, and cardiovascular injury. There is a strong inflammatory response in the process of HUA, while dysregulation of immune cells, including monocytes, macrophages, and T cells, plays a crucial role in the inflammatory response. Recent studies have indicated that urate has a direct impact on immune cell populations, changes in cytokine expression, modifications in chemotaxis and differentiation, and the provocation of immune cells by intrinsic cells to cause the aforementioned conditions. Here we conducted a detailed review of the relationship among uric acid, immune response, and inflammatory status in hyperuricemia and its complications, providing new therapeutic targets and strategies.

Inflammasome: structure, biological functions, and therapeutic targets

Inflammasomes are a group of protein complex located in cytoplasm and assemble in response to a wide variety of pathogen-associated molecule patterns, damage-associated molecule patterns, and cellular stress. Generally, the activation of inflammasomes will lead to maturation of proinflammatory cytokines and pyroptotic cell death, both associated with inflammatory cascade amplification. A sensor protein, an adaptor, and a procaspase protein interact through their functional domains and compose one subunit of inflammasome complex. Under physiological conditions, inflammasome functions against pathogen infection and endogenous dangers including mtROS, mtDNA, and so on, while dysregulation of its activation can lead to unwanted results. In recent years, advances have been made to clarify the mechanisms of inflammasome activation, the structural details of them and their functions (negative/positive) in multiple disease models in both animal models and human. The wide range of the stimuli makes the function of inflammasome diverse and complex. Here, we review the structure, biological functions, and therapeutic targets of inflammasomes, while highlight NLRP3, NLRC4, and AIM2 inflammasomes, which are the most well studied. In conclusion, this review focuses on the activation process, biological functions, and structure of the most well-studied inflammasomes, summarizing and predicting approaches for disease treatment and prevention with inflammasome as a target. We aim to provide fresh insight into new solutions to the challenges in this field.

Relief of gouty arthritis in rats by total saponins from Dioscorea nipponica Makino through suppression of neutrophil extracellular trap formation via the PI3K/AKT/mTOR axis

Gouty arthritis (GA) is an inflammatory disorder that is associated with elevated serum levels of uric acid. Total saponins from Dioscorea nipponica Makino (TSDN) are a natural component that ameliorates inflammation while also decreasing uric acid levels. The aim of the present study was to unravel the mechanism of TSDN in gouty rats in regard to regulation of the formation of neutrophil extracellular traps (NETs) via the PI3K/AKT/mTOR axis. A total of 40 Wistar rats were divided into 4 groups: normal, model, TSDN and rapamycin groups. Reverse-transcription-quantitative PCR (RT-qPCR) and western blot analysis were used to assess the mRNA and protein expression levels of the PI3K/AKT/mTOR axis. The formation of NETs was detected by immunohistochemical and immunofluorescent methods. ELISA was used to measure the levels of IL-1β and TNF-α. RT-qPCR and western blotting demonstrated that TSDN compromised the mRNA and protein expression levels of activated protein kinase (AMPK) and mTOR, as well as the mRNA expression levels of AKT and PTEN. Furthermore, it increased the protein expression levels of phosphorylated (p-) PI3K, p-AKT and p-AMPK. Immunohistochemical and immunofluorescent analyses revealed that TSDN decreased the protein expression levels of neutrophil elastase, proteinase 3, cathepsin G, lactoferrin and myeloperoxidase, as well as the number of citrullinated histone 3+ cells. TSDN also reduced the release of IL-1β and TNF-α. Overall, the anti-inflammatory action of TSDN in gouty rats may be realized by suppressing the formation of NETs by regulating the PI3K/AKT/mTOR axis.

DNA hypomethylation promotes the expression of CASPASE-4 which exacerbates neuroinflammation and amyloid-β deposition in Alzheimer's disease The Ohio State University College of Medicine

Alzheimer's Disease (AD) is the 6th leading cause of death in the US. It is established that neuroinflammation contributes to the synaptic loss, neuronal death, and symptomatic decline of AD patients. Accumulating evidence suggests a critical role for microglia, innate immune phagocytes of the brain. For instance, microglia release proinflammatory products such as IL-1β which is highly implicated in AD pathobiology. The mechanisms underlying the transition of microglia to proinflammatory promoters of AD remain largely unknown. To address this gap, we performed Reduced Representation Bisulfite Sequencing (RRBS) to profile global DNA methylation changes in human AD brains compared to no disease controls. We identified differential DNA methylation of CASPASE-4 (CASP4), which when expressed, can be involved in generation of IL-1β and is predominantly expressed in immune cells. DNA upstream of the CASP4 transcription start site was hypomethylated in human AD brains, which was correlated with increased expression of CASP4. Furthermore, microglia from a mouse model of AD (5xFAD) express increased levels of CASP4 compared to wild-type (WT) mice. To study the role of CASP4 in AD, we developed a novel mouse model of AD lacking the mouse ortholog of CASP4, CASP11, which is encoded by mouse Caspase-4 (5xFAD/Casp4-/-). The expression of CASP11 was associated with increased accumulation of pathologic protein aggregate amyloid-β (Aβ) and increased microglial production of IL-1β in 5xFAD mice. Utilizing RNA sequencing, we determined that CASP11 promotes unique transcriptomic phenotypes in 5xFAD mouse brains, including alterations of neuroinflammatory and chemokine signaling pathways. Notably, in vitro, CASP11 promoted generation of IL-1β from macrophages in response to cytosolic Aβ through cleavage of downstream effector Gasdermin D (G SDMD). We describe a role for CASP11 and GSDMD in the generation of IL-1β in response to Aβ and the progression of pathologic inflammation in AD. Overall, our results demonstrate that overexpression of CASP4 due to differential methylation in AD microglia contributes to the progression of AD pathobiology, thus identifying CASP4 as a potential target for immunotherapies for the treatment of AD.

Efficacy and safety of Danggui Niantong Decoction in patients with gout: a systematic review and meta-analysis

Background: This study aims to evaluate the efficacy and safety of Danggui Niantong Decoction (DGNT) systematically on gout treating. Methods: This study was registered in PROSPERO, and the registration number was CRD42021271607. By the end of December, 2022, literature research was conducted among eight electronic databases. Main results of this study were blood uric acid (BUA) and Creactive protein (CRP). Secondary outcomes were erythrocyte sedimentation rate (ESR), serum creatinine (Scr), urinary protein quantified at 24 h (Upro), and interleukin-8 (IL-8). Study screening, data collection, as well as quality assessment were performed by two reviewers independently, and analysis was completed using Stata (SE15.0) and Review Manager (5.4). Results: A total number of 13 studies were included in our meta-analysis (n = 1,094 participants). Results showed DGNT combined with conventional western medicine (CWM) was more effective than WM alone in BUA (weighted mean differences (WMD) = -3.49, 95% confidence interval (CI) [-50.36, -32.59], p = 0.000), CRP (WMD = -41.48, 95% CI [-4.32, -2.66], p = 0.017), ESR (WMD = -6.23, 95% CI [-9.28, -3.17], p = 0.019), Scr (WMD = -18.64, 95% CI [-23.09, -14.19], p = 0.001), Upro (WMD = -0.72, 95% CI [-0.91, -0.53], p = 0.000), and IL-8 (WMD = -4.77, 95% CI [-11.48, 1.94], p = 0.000). None of the adverse effects noted were severe, and no life-threatening event was reported. Conclusion: This study shows that DGNT combined with CWM seems to have an effective clinical therapeutic potential. In addition, it also provides a scientific basis for better clinical application of DGNT in the future. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021271607; Identifier: PROSPERO, CRD42021271607.

Regulatory Roles of Flavonoids in Caspase-11 Non-Canonical Inflammasome-Mediated Inflammatory Responses and Diseases

Inflammasomes are multiprotein complexes that activate inflammatory responses by inducing pyroptosis and secretion of pro-inflammatory cytokines. Along with many previous studies on inflammatory responses and diseases induced by canonical inflammasomes, an increasing number of studies have demonstrated that non-canonical inflammasomes, such as mouse caspase-11 and human caspase-4 inflammasomes, are emerging key players in inflammatory responses and various diseases. Flavonoids are natural bioactive compounds found in plants, fruits, vegetables, and teas and have pharmacological properties in a wide range of human diseases. Many studies have successfully demonstrated that flavonoids play an anti-inflammatory role and ameliorate many inflammatory diseases by inhibiting canonical inflammasomes. Others have demonstrated the anti-inflammatory roles of flavonoids in inflammatory responses and various diseases, with a new mechanism by which flavonoids inhibit non-canonical inflammasomes. This review discusses recent studies that have investigated the anti-inflammatory roles and pharmacological properties of flavonoids in inflammatory responses and diseases induced by non-canonical inflammasomes and further provides insight into developing flavonoid-based therapeutics as potential nutraceuticals against human inflammatory diseases.

Immune and inflammatory mechanisms and therapeutic targets of gout: An update

Gout is an autoimmune disease characterized by acute or chronic inflammation and damage to bone joints induced due to the precipitation of monosodium urate (MSU) crystals. In recent years, with the continuous development of animal models and ongoing clinical investigations, more immune cells and inflammatory factors have been found to play roles in gouty inflammation. The inflammatory network involved in gout has been discovered, providing a new perspective from which to develop targeted therapy for gouty inflammation. Studies have shown that neutrophil macrophages and T lymphocytes play important roles in the pathogenesis and resolution of gout, and some inflammatory cytokines, such as those in the interleukin-1 (IL-1) family, have been shown to play anti-inflammatory or proinflammatory roles in gouty inflammation, but the mechanisms underlying their roles are unclear. In this review, we explore the roles of inflammatory cytokines, inflammasomes and immune cells in the course of gout development and the research status of therapeutic drugs used for inflammation to provide insights into future targeted therapy for gouty inflammation and the direction of gout pathogenesis research.

Targeting pyroptosis as a preventive and therapeutic approach for stroke

Stroke has caused tremendous social stress worldwide, yet despite decades of research and development of new stroke drugs, most have failed and rt-PA (Recombinant tissue plasminogen activator) is still the accepted treatment for ischemic stroke. the complexity of the stroke mechanism has led to unsatisfactory efficacy of most drugs in clinical trials, indicating that there are still many gaps in our understanding of stroke. Pyroptosis is a programmed cell death (PCD) with inflammatory properties and are thought to be closely associated with stroke. Pyroptosis is regulated by the GSDMD of the gasdermin family, which when cleaved by Caspase-1/Caspase-11 into N-GSDMD with pore-forming activity can bind to the plasma membrane to form small 10-20 nm pores, which would allow the release of inflammatory factors IL-18 and IL-1β before cell rupture, greatly exacerbating the inflammatory response. The pyroptosis occurs mainly in the border zone of cerebral infarction, and glial cells, neuronal cells and brain microvascular endothelial cells (BMECs) all undergo pyroptosis after stroke, which largely exacerbates the breakdown of the blood-brain barrier (BBB) and thus aggravates brain injury. Therefore, pyroptosis may be a good direction for the treatment of stroke. In this review, we focus on the latest mechanisms of action of pyroptosis and the process by which pyroptosis regulates stroke development. We also suggest potential therapeutic stroke drugs that target the pyroptosis pathway, providing additional therapeutic strategies for the clinical management of stroke. The role of pyroptosis after stroke. After stroke, microglia first rush to the damaged area and polarize into M1 and M2 types. Under the influence of various stimuli, microglia undergo pyroptosis, release pro-inflammatory factors, and are converted to the M1 type; astrocytes and neuronal cells also undergo pyroptosis under the stimulation of various pro-inflammatory factors, leading to astrocyte death due to increased osmotic pressure in the membrane, resulting in water absorption and swelling until rupture. BMECs, the main structural component of the BBB, also undergo pyroptosis when stimulated by pro-inflammatory factors released from microglia and astrocytes, leading to the destruction of the structural integrity of the BBB, ultimately causing more severe brain damage. In addition, GSDMD in neutrophils mainly mediate the release of NETs rather than pyroptosis, which also aggravates brain injury. IL-10=interleukin-10; TGF-β = transforming growth factor-β; IL-18=interleukin-18; IL-1β = interleukin-1β; TNF-α = tumor necrosis factor-α; iNOS=induced nitrogen monoxide synthase; MMPs=Matrix metalloproteinases; GSDMD = gasdermin D; BMECs=brain microvascular endothelial cells; BBB = blood-brain barrier.

Anti-inflammatory role of Artemisia argyi methanol extract by targeting the caspase-11 non-canonical inflammasome in macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia argyi possesses pharmacological activities against various immunopathological conditions associated with inflammation.

AIM OF THE STUDY

This study explored the inhibitory role of Artemisia argyi methanol extract (Aa-ME) in inflammatory responses and the underlying mechanism in macrophages.

MATERIALS AND METHODS

Caspase-11 non-canonical inflammasome was activated in J774A.1 macrophage by Pam3CSK4 treatment and lipopolysaccharide (LPS) transfection. Aa-ME-mediated in vitro anti-inflammatory action was examined using MTT assay, lactate dehydrogenase (LDH) activity assay, enzyme-linked immunosorbent assay (ELISA), nitric oxide (NO) generation assay, and quantitative real-time polymerase chain reaction (qPCR). Aa-ME-mediated in vivo anti-inflammatory action was examined in LPS-stimulated lethal septic mice.

RESULTS

Aa-ME inhibited caspase-11 non-canonical inflammasome-stimulated pyroptosis and the secretion of IL-1β and IL-18 in J774A.1 macrophages. Aa-ME also inhibited NO generation by downregulating inducible NO synthase (iNOS) expression in LPS-primed and caspase-11 non-canonical inflammasome-triggered J774A.1 cells. The mechanism study revealed Aa-ME suppressed the auto-proteolytic activation of caspase-11 and gasdermin D (GSDMD) in J774A.1 cells and also interfered with caspase-11-mediated direct recognition of LPS. Moreover, Aa-ME alleviated LPS-induced lethal sepsis in mice by increasing their survival rate without significant toxicity.

CONCLUSION

These results suggest a novel mechanism by which Aa-ME alleviates inflammatory responses by deactivating caspase-11 non-canonical inflammasome in macrophages.

Genetic and Epigenetic Regulation of the Innate Immune Response to Gout

Gout is a disease caused by uric acid (UA) accumulation in the joints, causing inflammation. Two UA forms - monosodium urate (MSU) and soluble uric acid (sUA) have been shown to interact physically with inflammasomes, especially with the nod-like receptor (NLR) family pyrin domain containing 3 (NLRP3), albeit the role of the immune response to UA is poorly understood, given that asymptomatic hyperuricemia does also exist. Macrophage phagocytosis of UA activate NLRP3, lead to cytokines release, and ultimately, lead to chemoattract neutrophils and lymphocytes to the gout flare joint spot. Genetic variants of inflammasome genes and of genes encoding their molecular partners may influence hyperuricemia and gout susceptibility, while also influencing other comorbidities such as metabolic syndrome and cardiovascular diseases. In this review, we summarize the inflammatory responses in acute and chronic gout, specifically focusing on innate immune cell mechanisms and genetic and epigenetic characteristics of participating molecules. Unprecedently, a novel UA binding protein - the neuronal apoptosis inhibitor protein (NAIP) - is suggested as responsible for the asymptomatic hyperuricemia paradox.Abbreviation: β2-integrins: leukocyte-specific adhesion molecules; ABCG2: ATP-binding cassete family/breast cancer-resistant protein; ACR: American college of rheumatology; AIM2: absent in melanoma 2, type of pattern recognition receptor; ALPK1: alpha-protein kinase 1; ANGPTL2: angiopoietin-like protein 2; ASC: apoptosis-associated speck-like protein; BIR: baculovirus inhibitor of apoptosis protein repeat; BIRC1: baculovirus IAP repeat-containing protein 1; BIRC2: baculoviral IAP repeat-containing protein 2; C5a: complement anaphylatoxin; cAMP: cyclic adenosine monophosphate; CARD: caspase activation and recruitment domains; CARD8: caspase recruitment domain-containing protein 8; CASP1: caspase 1; CCL3: chemokine (C-C motif) ligand 3; CD14: cluster of differentiation 14; CD44: cluster of differentiation 44; Cg05102552: DNA-methylation site, usually cytosine followed by guanine nucleotides; contains arbitrary identification code; CIDEC: cell death-inducing DNA fragmentation factor-like effector family; CKD: chronic kidney disease; CNV: copy number variation; CPT1A: carnitine palmitoyl transferase - type 1a; CXCL1: chemokine (CXC motif) ligand 1; DAMPs: damage associated molecular patterns; DC: dendritic cells; DNMT(1): maintenance DNA methyltransferase; eQTL: expression quantitative trait loci; ERK1: extracellular signal-regulated kinase 1; ERK2: extracellular signal-regulated kinase 2; EULAR: European league against rheumatism; GMCSF: granulocyte-macrophage colony-stimulating factor; GWAS: global wide association studies; H3K27me3: tri-methylation at the 27th lysine residue of the histone h3 protein; H3K4me1: mono-methylation at the 4th lysine residue of the histone h3 protein; H3K4me3: tri-methylation at the 4th lysine residue of the histone h3 protein; HOTAIR: human gene located between hoxc11 and hoxc12 on chromosome 12; IκBα: cytoplasmatic protein/Nf-κb transcription inhibitor; IAP: inhibitory apoptosis protein; IFNγ: interferon gamma; IL-1β: interleukin 1 beta; IL-12: interleukin 12; IL-17: interleukin 17; IL18: interleukin 18; IL1R1: interleukin-1 receptor; IL-1Ra: interleukin-1 receptor antagonist; IL-22: interleukin 22; IL-23: interleukin 23; IL23R: interleukin 23 receptor; IL-33: interleukin 33; IL-6: interleukin 6; IMP: inosine monophosphate; INSIG1: insulin-induced gene 1; JNK1: c-jun n-terminal kinase 1; lncRNA: long non-coding ribonucleic acid; LRR: leucine-rich repeats; miR: mature non-coding microRNAs measuring from 20 to 24 nucleotides, animal origin; miR-1: miR followed by arbitrary identification code; miR-145: miR followed by arbitrary identification code; miR-146a: miR followed by arbitrary identification code, "a" stands for mir family; "a" family presents similar mir sequence to "b" family, but different precursors; miR-20b: miR followed by arbitrary identification code; "b" stands for mir family; "b" family presents similar mir sequence to "a" family, but different precursors; miR-221: miR - followed by arbitrary identification code; miR-221-5p: miR followed by arbitrary identification code; "5p" indicates different mature miRNAs generated from the 5' arm of the pre-miRNA hairpin; miR-223: miR followed by arbitrary identification code; miR-223-3p: mir followed by arbitrary identification code; "3p" indicates different mature miRNAs generated from the 3' arm of the pre-miRNA hairpin; miR-22-3p: miR followed by arbitrary identification code, "3p" indicates different mature miRNAs generated from the 3' arm of the pre-miRNA hairpin; MLKL: mixed lineage kinase domain-like pseudo kinase; MM2P: inductor of m2-macrophage polarization; MSU: monosodium urate; mTOR: mammalian target of rapamycin; MyD88: myeloid differentiation primary response 88; n-3-PUFAs: n-3-polyunsaturated fatty-acids; NACHT: acronym for NAIP (neuronal apoptosis inhibitor protein), C2TA (MHC class 2 transcription activator), HET-E (incompatibility locus protein from podospora anserina) and TP1 (telomerase-associated protein); NAIP: neuronal apoptosis inhibitory protein (human); Naip1: neuronal apoptosis inhibitory protein type 1 (murine); Naip5: neuronal apoptosis inhibitory protein type 5 (murine); Naip6: neuronal apoptosis inhibitory protein type 6 (murine); NBD: nucleotide-binding domain; Nek7: smallest NIMA-related kinase; NET: neutrophil extracellular traps; Nf-κB: nuclear factor kappa-light-chain-enhancer of activated b cells; NFIL3: nuclear-factor, interleukin 3 regulated protein; NIIMA: network of immunity in infection, malignancy, and autoimmunity; NLR: nod-like receptor; NLRA: nod-like receptor NLRA containing acidic domain; NLRB: nod-like receptor NLRA containing BIR domain; NLRC: nod-like receptor NLRA containing CARD domain; NLRC4: nod-like receptor family CARD domain containing 4; NLRP: nod-like receptor NLRA containing PYD domain; NLRP1: nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 1; NLRP12: nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain containing 12; NLRP3: nod-like receptor family pyrin domain containing 3; NOD2: nucleotide-binding oligomerization domain; NRBP1: nuclear receptor-binding protein; Nrf2: nuclear factor erythroid 2-related factor 2; OR: odds ratio; P2X: group of membrane ion channels activated by the binding of extracellular; P2X7: p2x purinoceptor 7 gene; p38: member of the mitogen-activated protein kinase family; PAMPs: pathogen associated molecular patters; PBMC: peripheral blood mononuclear cells; PGGT1B: geranylgeranyl transferase type-1 subunit beta; PHGDH: phosphoglycerate dehydrogenase; PI3-K: phospho-inositol; PPARγ: peroxisome proliferator-activated receptor gamma; PPARGC1B: peroxisome proliferative activated receptor, gamma, coactivator 1 beta; PR3: proteinase 3 antigen; Pro-CASP1: inactive precursor of caspase 1; Pro-IL1β: inactive precursor of interleukin 1 beta; PRR: pattern recognition receptors; PYD: pyrin domain; RAPTOR: regulatory associated protein of mTOR complex 1; RAS: renin-angiotensin system; REDD1: regulated in DNA damage and development 1; ROS: reactive oxygen species; rs000*G: single nuclear polymorphism, "*G" is related to snp where replaced nucleotide is guanine, usually preceded by an id number; SLC2A9: solute carrier family 2, member 9; SLC7A11: solute carrier family 7, member 11; SMA: smooth muscular atrophy; Smac: second mitochondrial-derived activator of caspases; SNP: single nuclear polymorphism; Sp3: specificity protein 3; ST2: serum stimulation-2; STK11: serine/threonine kinase 11; sUA: soluble uric acid; Syk: spleen tyrosine kinase; TAK1: transforming growth factor beta activated kinase; Th1: type 1 helper T cells; Th17: type 17 helper T cells; Th2: type 2 helper T cells; Th22: type 22 helper T cells; TLR: tool-like receptor; TLR2: toll-like receptor 2; TLR4: toll-like receptor 4; TNFα: tumor necrosis factor alpha; TNFR1: tumor necrosis factor receptor 1; TNFR2: tumor necrosis factor receptor 2; UA: uric acid; UBAP1: ubiquitin associated protein; ULT: urate-lowering therapy; URAT1: urate transporter 1; VDAC1: voltage-dependent anion-selective channel 1.

Effect of nanoparticles on gouty arthritis: a systematic review and meta-analysis

OBJECTIVE

The purpose of this study was to explore the effects of nanoparticles on gouty arthritis, and to provide evidence for the preclinical application of nanoparticles in gouty arthritis and ideas for nanomedicine improvement for nanoparticle researchers.

METHODS

Five databases including the Cochrane Library, PubMed, Scopus, Web of Science, and Embase were searched for eligible studies until April 2022. The quality of the selected studies was assessed by SYRCLE's risk of bias (RoB) tool, and the random-effects model was used to calculate the overall effect sizes of weighted mean differences (WMD).

RESULTS

Ten studies met the inclusion criteria. Results showed that nanoparticles were effective in reducing uric acid levels (WMD: -4.91; 95% confidence interval (CI): - 5.41 to - 4.41; p < 0.001), but were not better than allopurinol (WMD: -0.20; 95% CI: - 0.42 to 0.02; p = 0.099). It was worth noting that the nanoparticles were safer than allopurinol. Subgroup analyses indicated that nanoparticle encapsulated substance, animal species, nanoparticle dosage, animal quantity, and animal gender were all sources of heterogeneity.

CONCLUSION

The nanoparticles are safe medications for gouty arthritis which can effectively reduce uric acid levels in rodents. Although the results are still uncertain, it is expected to have certain clinical application value. The nanoparticles may be the preclinical medications for gouty arthritis in the future.

Novel perception of neutrophil extracellular traps in gouty inflammation

The self-limiting nature of the inflammatory flare is a feature of gout. The effects of neutrophil extracellular traps (NETs) on gout have remarkably attracted researchers' attention. Aggregated NETs promote the resolution of gouty inflammation by packing monosodium urate (MSU) crystals, degrading cytokines and chemokines, and blocking neutrophil recruitment and activation. Deficiency of NETs aggravates experimental gout. Thus, aggregated NETs are assumed to be a possible mechanism for the spontaneous resolution of gout. It is feasible to envisage therapeutic strategies for targeting NETosis (NET formation process) in gout. However, recent studies have demonstrated that levels of NETs are not associated with disease activity and inflammation in human gout. Moreover, the process of MSU crystal trapping is not affected in the absence of neutrophils. This review has concentrated on the mechanisms and associations between NETs and gout.

Tanshinone IIA Improves Acute Gouty Arthritis in Rats through Regulating Neutrophil Activation and the NLRP3 Inflammasome

Objectives

To investigate the prevention and treatment effect of tanshinone IIA (TIIA) on acute gouty arthritis (AGA) and its mechanism.

Methods

The anti-AGA effect of TIIA was observed in vivo and in vitro. Neutrophils were isolated from the abdominal cavity of mice, and the anti-AGA effect of TIIA was investigated in a rat model of MSU-induced AGA. The pathological changes of the ankle joint tissues were assessed by H&E. Cytokine and chemokine expression were determined by ELISA and RT-qPCR. The NLRP3 inflammasome pathway protein levels in the ankle joint tissues were evaluated via western blotting. Neutrophil migration was evaluated in air pouch and transwell assays. Immunohistochemistry and immunofluorescence analysis evaluate the release of myeloperoxidase (MPO), neutrophil elastase (NE), and citrullination of histone H3 (CitH3). Beclin-1 and LC3B expressions were determined using western blotting and immunofluorescence. Key Findings. Treatment with TIIA alleviated synovial hyperplasia and neutrophil infiltration, regulated cytokine and chemokine expressions, and inhibited NLRP3 activation in AGA rats, neutrophil migration, MPO, NE, and CitH3 expression, and LC3B and Beclin-1 protein expression.

Conclusions

These results demonstrate that TIIA can effectively enhance AGA by focusing on the neutrophils and NLRP3 inflammasome, demonstrating that TIIA may act as a potential helpful agent for AGA.

Neutrophils in autoimmunity: when the hero becomes the villain

Neutrophils were long considered to be a short-lived homogenous cell population, limited to their role as first responders in anti-bacterial and -fungal immunity. While it is true that neutrophils are first to infiltrate the site of infection to eliminate pathogens, growing evidence suggests their functions could extend beyond those of basic innate immune cells. Along with their well-established role in pathogen elimination, utilizing effector functions such as phagocytosis, degranulation, and the deployment of neutrophil extracellular traps (NETs), neutrophils have recently been shown to possess antigen-presenting capabilities. Moreover, the identification of different subtypes of neutrophils points to a multifactorial heterogeneous cell population with great plasticity in which some subsets have enhanced pro-inflammatory characteristics, while others seem to behave as immunosuppressors. Interestingly, the aberrant presence of activated neutrophils with a pro-inflammatory profile in several systemic and organ-specific autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), systemic sclerosis (SSc), multiple sclerosis (MS), and type 1 diabetes (T1D) could potentially be exploited in novel therapeutic strategies. The full extent of the involvement of neutrophils, and more specifically that of their various subtypes, in the pathophysiology of autoimmune diseases is yet to be elucidated.

Microglial pyroptosis: Therapeutic target in secondary brain injury following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a major cerebrovascular illness that causes substantial neurological sequelae and dysfunction caused by secondary brain injury (SBI), and there are no effective therapies to mitigate the disability. Microglia, the brain-resident macrophage, participates in the primary inflammatory response, and activation of microglia to an M1-like phenotype largely takes place in the acute phase following ICH. A growing body of research suggests that the pathophysiology of SBI after ICH is mediated by an inflammatory response mediated by microglial-pyroptotic inflammasomes, while inhibiting the activation of microglial pyroptosis could suppress the inflammatory cascade reaction, thus attenuating the brain injury after ICH. Pyroptosis is characterized by rapid plasma membrane disruption, followed by the release of cellular contents and pro-inflammatory mediators. In this review, we outline the molecular mechanism of microglial pyroptosis and summarize the up-to-date evidence of its involvement in the pathological process of ICH, and highlight microglial pyroptosis-targeted strategies that have the potential to cure intracerebral hemorrhage. This review contributes to a better understanding of the function of microglial pyroptosis in ICH and assesses it as a possible therapeutic target.

Environmental factors and risk of gout

Gout is a chronic disease with inflammatory arthritis caused by monosodium urate (MSU) crystals deposition, an elevated serum urate level (hyperuricaemia) is the critical factor leading to MSU crystals deposition and promoting the progression of gout. The onset and development of gout is generally the result of multiple factors, such as diet, heredity and environmental factors. Although genetics and diet are thought to play as major factors, a growing body of research evidence has highlighted that environmental factors also play a significant role in the onset and exacerbation of gout. Recent studies have shown that air pollutants such as particulate matter, sulfur dioxide (SO₂) and carbon monoxide (CO) may increase the risk of hospitalizations for gout, and that the changes in temperature and humidity may affect uric acid (UA) levels. There is also seasonal trend in gout. It has been demonstrated that environmental factors may induce or accelerate the production and release of pro-inflammatory mediators, causing an unbalance oxidative stress and systemic inflammation, and then participating in the overall process or a certain link of gout. Moreover, several environmental factors have shown the ability to induce the production urate and regulate the innate immune pathways, involving in the pathogenesis of gout. Nevertheless, the role of environmental factors in the etiology of gout remains unclear. In this review, we summarized the recent literatures and aimed to discuss the relationship between environmental factors (such as microclimate, season, ambient/indoor air pollution and extreme weather) and gout. We further discussed the inflammatory mechanisms of environmental factors and gout and the comprehensive effects of environmental factors on gout. We also made a prospect of the management and treatment of gout, with special consideration to environmental factors associated with gout.

Aberrant messenger RNA expression in peripheral blood mononuclear cells is associated with gouty arthritis

AIM

Gouty arthritis (GA) is a type of self-limiting inflammatory arthritis caused by deposition of monosodium urate (MSU). This study aimed to analyze the expression variation of messenger RNAs (mRNAs) in GA patients and investigated the role of mRNAs in GA pathogenesis.

METHODS

Five patients with acute GA (AGA), 5 with non-acute GA (NAGA), and 5 healthy controls (HC) were recruited to examine differential mRNA expression profiles in peripheral blood mononuclear cells (PBMCs) and explore whether mRNA is involved in the pathogenesis of AGA. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases were used to study the biological functions of differentially expressed mRNA and the relationship between genes and signal pathways.

RESULTS

Compared with HC, the AGA group had 1456 differentially expressed mRNAs, while the NAGA group had 437 differentially expressed mRNAs and compared with the NAGA group, 115 differentially expressed mRNAs were found in the AGA group. GO analysis showed that the differentially expressed mRNA in the AGA group was mainly enriched in processes related to leukocyte activation and immune response, while KEGG analysis showed that "Staphylococcus aureus infection" and "Cytokine-cytokine receptor interaction" are enriched in the up-regulated mRNAs in the AGA group.

CONCLUSION

This study identified genes and pathways that are differentially expressed during the onset of AGA, which might reveal part of the pathogenesis of the disease and provide clues to explaining the severe pain associated with disease onset and the rapid development of inflammatory response that subsides by itself.

Caspase-4 and -5 Biology in the Pathogenesis of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory disease of the gastrointestinal tract, associated with high levels of inflammatory cytokine production. Human caspases-4 and -5, and their murine ortholog caspase-11, are essential components of the innate immune pathway, capable of sensing and responding to intracellular lipopolysaccharide (LPS), a component of Gram-negative bacteria. Following their activation by LPS, these caspases initiate potent inflammation by causing pyroptosis, a lytic form of cell death. While this pathway is essential for host defence against bacterial infection, it is also negatively associated with inflammatory pathologies. Caspases-4/-5/-11 display increased intestinal expression during IBD and have been implicated in chronic IBD inflammation. This review discusses the current literature in this area, identifying links between inflammatory caspase activity and IBD in both human and murine models. Differences in the expression and functions of caspases-4, -5 and -11 are discussed, in addition to mechanisms of their activation, function and regulation, and how these mechanisms may contribute to the pathogenesis of IBD.

Caspase-4/11 exacerbates disease severity in SARS-CoV-2 infection by promoting inflammation and immunothrombosis

Severe acute respiratory syndrome coronavirus 2 (SARS–CoV-2) is a worldwide health concern, and new treatment strategies are needed. Targeting inflammatory innate immunity pathways holds therapeutic promise, but effective molecular targets remain elusive. Here, we show that human caspase-4 (CASP4) and its mouse homolog, caspase-11 (CASP11), are up-regulated in SARS–CoV-2 infections and that CASP4 expression correlates with severity of SARS–CoV-2 infection in humans. SARS–CoV-2–infected Casp11−/− mice were protected from severe weight loss and lung pathology, including blood vessel damage, compared to wild-type (WT) mice and mice lacking the caspase downstream effector gasdermin-D (Gsdmd−/−). Notably, viral titers were similar regardless of CASP11 knockout. Global transcriptomics of SARS–CoV-2–infected WT, Casp11−/−, and Gsdmd−/− lungs identified restrained expression of inflammatory molecules and altered neutrophil gene signatures in Casp11−/− mice. We confirmed that protein levels of inflammatory mediators interleukin (IL)-1β, IL-6, and CXCL1, as well as neutrophil functions, were reduced in Casp11−/− lungs. Additionally, Casp11−/− lungs accumulated less von Willebrand factor, a marker for endothelial damage, but expressed more Kruppel-Like Factor 2, a transcription factor that maintains vascular integrity. Overall, our results demonstrate that CASP4/11 promotes detrimental SARS–CoV-2–induced inflammation and coagulopathy, largely independently of GSDMD, identifying CASP4/11 as a promising drug target for treatment and prevention of severe COVID-19.

Regulatory Roles of Caspase-11 Non-Canonical Inflammasome in Inflammatory Liver Diseases

An inflammatory response consists of two consecutive steps: priming and triggering, to prepare and activate inflammatory responses, respectively. The cardinal feature of the triggering step is the activation of intracellular protein complexes called inflammasomes, which provide a platform for the activation of inflammatory signaling pathways. Despite many studies demonstrating the regulatory roles of canonical inflammasomes in inflammatory liver diseases, the roles of newly discovered non-canonical inflammasomes in inflammatory liver diseases are still largely unknown. Recent studies have reported the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing strong evidence that the caspase-11 non-canonical inflammasome may play key roles in the pathogenesis of inflammatory liver diseases. This review comprehensively discusses the emerging roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory liver diseases, focusing on non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and inflammatory liver injuries and its underlying mechanisms. This review highlights the current knowledge on the regulatory roles of the caspase-11 non-canonical inflammasome in inflammatory liver diseases, providing new insights into the development of potential therapeutics to prevent and treat inflammatory liver diseases by targeting the caspase-11 non-canonical inflammasome.

Inflammatory Response to Regulated Cell Death in Gout and Its Functional Implications

Gout, a chronic inflammatory arthritis disease, is characterized by hyperuricemia and caused by interactions between genetic, epigenetic, and metabolic factors. Acute gout symptoms are triggered by the inflammatory response to monosodium urate crystals, which is mediated by the innate immune system and immune cells (e.g., macrophages and neutrophils), the NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome activation, and pro-inflammatory cytokine (e.g., IL-1β) release. Recent studies have indicated that the multiple programmed cell death pathways involved in the inflammatory response include pyroptosis, NETosis, necroptosis, and apoptosis, which initiate inflammatory reactions. In this review, we explore the correlation and interactions among these factors and their roles in the pathogenesis of gout to provide future research directions and possibilities for identifying potential novel therapeutic targets and enhancing our understanding of gout pathogenesis.

(-)-Epicatechin Ameliorates Monosodium Urate-Induced Acute Gouty Arthritis Through Inhibiting NLRP3 Inflammasome and the NF-κB Signaling Pathway

Background: Gouty arthritis is a common and complex inflammatory disease that will reduce the life quality of human beings (-)-Epicatechin (EC) is famous for antioxidant and anti-inflammatory activities. Thus, the aim of this study was to investigate the therapeutic effect of EC on gouty arthritis and its mechanisms. Methods and results: EC was added into a monosodium urate (MSU)-stimulated THP-1 cell that was induced by phorbol 12-myristate 13-acetate and lipopolysaccharide (LPS) in advance to establish a gout model in vitro. The efficiency of EC on acute gouty arthritis mice induced by MSU was further investigated. The results showed that EC concentration-dependently improved the cell viability of LPS and MSU stimulated THP-1 cells, and significantly alleviated MSU-induced ankle edema in mice in a dose-dependent manner. In addition, EC inhibited the infiltration of inflammatory cells and local cascular congestion in ankle joint tissue. Furthermore, the secretion of inflammatory cytokines (IL-1β, IL-18, IL-6, and TNF-α) activation of NLRP3 inflammasome and NF-κB signaling pathway were markedly suppressed by EC in vitro and in vivo. Conclusion: These results indicated that EC could effectively improve MSU-induced acute gouty arthritis via inhibiting NLRP3 inflammasome and the NF-κB signaling pathway in vitro and in vivo, which suggested that EC might be a promising active ingredient for the prevention and treatment of gouty arthritis.

Dual roles of the caspase-11 non-canonical inflammasome in inflammatory bowel disease

Inflammation is a two-step process comprising the first priming step that prepares inflammatory responses and the second triggering step that activates inflammatory responses. The key feature of the triggering step is the activation of inflammasomes and intracellular inflammatory protein complexes that provide molecular platforms to activate inflammatory signal transduction cascades. Although canonical inflammasomes have been well demonstrated to be actively involved in numerous human diseases, the roles of the recently identified non-canonical inflammasomes are largely unknown. However, recent studies have demonstrated the emerging roles of the caspase-11 non-canonical inflammasome in various human inflammatory diseases, ultimately providing strong evidence that the caspase-11 non-canonical inflammasome is a key player in the pathogenesis of various human diseases. Here, we comprehensively reviewed the regulatory roles of the caspase-11 non-canonical inflammasome in the pathogenesis of inflammatory bowel disease (IBD) and its underlying mechanisms. Overall, this review highlights the current understanding of the regulatory roles of the caspase-11 non-canonical inflammasome in IBD and may provide insight into new strategies for preventing and treating IBD and caspase-11 non-canonical inflammasome-driven diseases.

Caspase-11 regulates lung inflammation in response to house dust mites

Asthma is an inflammatory lung disorder characterized by mucus hypersecretion, cellular infiltration, and bronchial hyper-responsiveness. House dust mites (HDM) are the most prevalent cause of allergic sensitization. Canonical and noncanonical inflammasomes are multiprotein complexes that assemble in response to pathogen or danger-associated molecular patterns (PAMPs or DAMPs). Murine caspase-11 engages the noncanonical inflammasome. We addressed the role of caspase-11 in mediating host responses to HDM and subsequent allergic inflammation using caspase-11-/- mice, which lack caspase-11 while express caspase-1. We found that HDM induce caspase-11 expression in vitro. The presence of IL-4 and IL-13 promote caspase-11 expression. Additionally, caspase-11-/- macrophages show reduced release of IL-6, IL-12, and KC, and express lower levels of costimulatory molecules (e.g., CD40, CD86 and MHCII) in response to HDM stimulation. Notably, HDM sensitization of caspase-11-/- mice resulted in similar levels of IgE responses and hypothermia in response to nasal HDM challenge compared to WT. However, analysis of cell numbers and cytokines in bronchiolar alveolar lavage fluid (BALF) and histopathology of representative lung segments demonstrate altered inflammatory responses and reduced neutrophilia in the airways of the caspase-11-/- mice. These findings indicate that caspase-11 regulates airway inflammation in response to HDM exposure.

Role of non-canonical pyroptosis in sepsis and other inflammatory diseases

As a form of new programmed cell death, pyroptosis is divided into a canonical pyroptosis pathway and a non-canonical pyroptosis pathway. In recent years, it is reported that non-canonical pyroptosis is closely related to inflammatory reactions, which directly affects the occurrence, development, and outcome of sepsis, inflammatory bowel disease, respiratory disease, nerve system inflammatory disease, and other inflammatory diseases. When the cells were infected with Gram-negative bacteria or lipopolysaccharide (LPS), it can induce the activation of cysteinyl aspartate specific proteinase(caspase)-4/5/11 and directly bind to the cells to cleave gasdermin D (GSDM-D) into the active amino-terminus of GSDM-D. The amino-terminus of GSDM-D with membrane punching activity migrates to the cell membrane, triggering the rupture of the cell membrane, and the cell contents discharge, leading to the occurrence of non-canonical pyroptosis. After activation of caspase-11, it also promotes the canonical pyroptosis, activates and releases interleukin-1β and interleukin-18, which aggravated inflammation. Caspase-4/5/11, GSDM-D, Toll-like receptor 4 and high mobility group protein B1 are the key molecules of the non-canonical pyroptosis. Exploring the mechanisms of non-canonical pyroptosis and the related research progresses in inflammatory diseases intensively is of great significance for clinical prevention and treatment of the relevant diseases.

Fumonisin B1 induces chicken heterophil extracellular traps mediated by PAD4 enzyme and P2 × 1 receptor

Fumonisin B₁ (FB₁) is a common mycotoxin contamination in agricultural commodities being considered as a significant risk to human and livestock health, while the mechanism of FB₁ immunotoxicity are less understood, especially in chicken. Given that extracellular traps as a novel defense mechanism of leukocytes play an important role against foreign matters, in this study we aimed to investigate the effects of FB₁ on chicken heterophil extracellular traps (HETs) formation. Our result showed that FB₁ induced HETs release in chicken heterophils observed via immunostaining, and it was concentration-dependent during 10 to 40 μM. Moreover, in 40 μM FB₁-exposed chicken heterophils, reactive oxygen species (ROS) level was increased, while catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activity and glutathione (GSH) content were decreased. Simultaneously, FB₁ (40 μM) activated ERK and p38 MAPK signaling pathways via increasing the phosphorylation level of ERK and p38 proteins. However, pretreatment of SB202190, U0126, and diphenyleneiodonium chloride (DPI) did not change FB₁-triggered ROS production and HETs formation, suggesting FB₁-induced HETs was a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, p38, and extracellular regulated protein kinases (ERK) signaling pathways-independent process. Inhibition of peptidyl arginine deiminase 4 (PAD4) enzyme and P2 × 1 receptor showed their vital role in 40 μM FB₁-triggered HETs. This study reported for the first time that 40 μM FB₁ induced the release of HETs in heterophils, and it was related to ROS production, PAD4, and P2 × 1, but was independent of NADPH oxidase, p38 and ERK signaling pathways, which might provide a whole novel perspective of perceiving and understanding the role of FB₁ in immunotoxicity.

Receptor-Mediated NETosis on Neutrophils

Neutrophil extracellular traps (NETs), a web-like structures containing chromatin, have a significant role in assisting the capture and killing of microorganisms by neutrophils during infection. The specific engagement of cell-surface receptors by extracellular signaling molecules activates diverse intracellular signaling cascades and regulates neutrophil effector functions, including phagocytosis, reactive oxygen species release, degranulation, and NET formation. However, overproduction of NETs is closely related to the occurrence of inflammation, autoimmune disorders, non-canonical thrombosis and tumor metastasis. Therefore, it is necessary to understand neutrophil activation signals and the subsequent formation of NETs, as well as the related immune regulation. In this review, we provide an overview of the immunoreceptor-mediated regulation of NETosis. The pathways involved in the release of NETs during infection or stimulation by noninfectious substances are discussed in detail. The mechanisms by which neutrophils undergo NETosis help to refine our views on the roles of NETs in immune protection and autoimmune diseases, providing a theoretical basis for research on the immune regulation of NETs.

Active Flavonoids From Lagotis brachystachya Attenuate Monosodium Urate-Induced Gouty Arthritis via Inhibiting TLR4/MyD88/NF-κB Pathway and NLRP3 Expression

Lagotis brachystachya Maxim is a characteristic herb commonly used in Tibetan medicine. Tibetan medicine records it as an important medicine for the clinical treatment of “Yellow Water Disease,” the symptoms of which are similar to that of arthritis. Our previous study showed that the flavonoid fraction extracted from L. brachystachya could attenuate hyperuricemia. However, the effects of the active flavonoids on gouty arthritis remain elusive, and the underlying mechanism is not understood. In the present study, the effects of the active flavonoids were evaluated in rats or Raw264.7 cells with gouty arthritis induced by monosodium urate (MSU) crystal, followed by the detection of TLR4, MyD88, pNF-κB, and NLR family pyrin domain-containing 3 (NLRP3) expression. The swelling of the ankle joint induced by MSU crystal began to be relieved 6 h post the administration with the active flavonoids. In addition, the active flavonoids not only alleviated MSU crystal-induced inflammation in synovial tissues by histopathological examination but also reduced tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) levels in the joint tissue fluid of MSU crystal-induced rats. Furthermore, Western blot analysis indicated that the active flavonoids reduced the production of these cytokines by inhibiting the TLR4/MyD88/NF-κB pathway and decreasing NLRP3 expression in synovial tissues of rats. More importantly, the inhibition of TLR4/MyD88/NF-κB pathway and NLRP3 expression was also confirmed in MSU-induced Raw264.7 cells. In conclusion, these results indicated that the active flavonoids from L. brachystachya could effectively attenuate gouty arthritis induced by MSU crystal through the TLR4/MyD88/NF-κB pathway and NLRP3 expression in vivo and in vitro, suggesting several potential candidates for the treatment of gouty arthritis.

Galectin-9 Regulates Monosodium Urate Crystal-Induced Gouty Inflammation Through the Modulation of Treg/Th17 Ratio

Gout is caused by depositing monosodium urate (MSU) crystals within the articular area. The infiltration of neutrophils and monocytes drives the initial inflammatory response followed by lymphocytes. Interestingly, emerging evidence supports the view that in situ imbalance of T helper 17 cells (Th17)/regulatory T cells (Treg) impacts the subsequent damage to target tissues. Galectin-9 (Gal-9) is a modulator of innate and adaptive immunity with both pro- and anti-inflammatory functions, dependent upon its expression and cellular location. However, the specific cellular and molecular mechanisms by which Gal-9 modulates the inflammatory response in the onset and progression of gouty arthritis has yet to be elucidated. In this study, we sought to comprehensively characterise the functional role of exogenous Gal-9 in an in vivo model of MSU crystal-induced gouty inflammation by monitoring in situ neutrophils, monocytes and Th17/Treg recruited phenotypes and related cyto-chemokines profile. Treatment with Gal-9 revealed a dose-dependent reduction in joint inflammation scores, knee joint oedema and expression of different pro-inflammatory cyto-chemokines. Furthermore, flow cytometry analysis highlighted a significant modulation of infiltrating inflammatory monocytes (CD11b⁺/CD115⁺/LY6-C^hi) and Th17 (CD4⁺/IL-17⁺)/Treg (CD4⁺/CD25⁺/FOXP-3⁺) cells following Gal-9 treatment. Collectively the results presented in this study indicate that the administration of Gal-9 could provide a new therapeutic strategy for preventing tissue damage in gouty arthritic inflammation and, possibly, in other inflammatory-based diseases.

MCC950, the NLRP3 Inhibitor, Protects against Cartilage Degradation in a Mouse Model of Osteoarthritis

Osteoarthritis (OA), characterized by chronic systemic low-level inflammation and cartilage degeneration, is a type of arthritis closely associated with aging. Inflammation and aging play a pivotal role in the occurrence and progression of OA. NLRP3 inflammasome is involved in many inflammatory and aging diseases, and NLRP3 inhibitor MCC950 has anti-inflammatory and antisenescence effects on some diseases such as Alzheimer's disease. In the present study, we found that NLRP3 protein was upregulated in human and mouse OA cartilage. Moreover, NLRP3 and Caspase1 expression induced by IL-1β in chondrocytes was blocked by MCC950. In addition, MCC950 inhibited the expression of inflammatory mediators, matrix-degrading enzymes, senescence marker protein P16 (INK4A), and β-galactosidase, as well as excessive production of ROS. Meanwhile, MCC950 promoted autophagy-related protein expression and autophagy flux under the inflammatory condition. However, autophagy inhibitor 3-MA reversed anti-inflammatory and anticatabolic effects of MCC950. In in vivo experiments, intra-articular administration of MCC950 further showed its protective effect on cartilage degeneration. Bioinformatic analysis and in vitro experimental results revealed that MCC950 might play a protective role in cartilage by regulating Nrf2/HO-1/NQO1, PI3k/Akt/mTOR, P38/MAPK, and JNK/MAPK pathways. In conclusion, our work demonstrated that NLRP3 inhibitor MCC950 might serve as a promising strategy for OA treatment.

An Epigenetic Insight into NLRP3 Inflammasome Activation in Inflammation-Related Processes

Aberrant NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) inflammasome activation in innate immune cells, triggered by diverse cellular danger signals, leads to the production of inflammatory cytokines (IL-1β and IL-18) and cell death by pyroptosis. These processes are involved in the pathogenesis of a wide range of diseases such as autoimmune, neurodegenerative, renal, metabolic, vascular diseases and cancer, and during physiological processes such as aging. Epigenetic dynamics mediated by changes in DNA methylation patterns, chromatin assembly and non-coding RNA expression are key regulators of the expression of inflammasome components and its further activation. Here, we review the role of the epigenome in the expression, assembly, and activation of the NLRP3 inflammasome, providing a critical overview of its involvement in the disease and discussing how targeting these mechanisms by epigenetic treatments could be a useful strategy for controlling NLRP3-related inflammatory diseases.

Approaching Neutrophil Pyroptosis

All cells must die at some point, and the dogma is that they do it either silently via apoptosis or via pro-inflammatory, lytic forms of death. Amongst these lytic cell death pathways, pyroptosis is one of the best characterized. Pyroptosis depends on inflammatory caspases which activate members of the gasdermin family of proteins, and it is associated with the release of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. Pyroptosis is an essential component of innate immunity, it initiates and amplifies inflammation and it removes the replication niche for intracellular pathogens. Most of the literature on pyroptosis focuses on monocytes and macrophages. However, the most abundant phagocytes in humans are neutrophils. This review addresses whether neutrophils undergo pyroptosis and the underlying mechanisms. Furthermore, I discuss how and why neutrophils might be able to resist pyroptosis.

Destructive Effects of Pyroptosis on Homeostasis of Neuron Survival Associated with the Dysfunctional BBB-Glymphatic System and Amyloid-Beta Accumulation after Cerebral Ischemia/Reperfusion in Rats

Neuroinflammation-related amyloid-beta peptide (Aβ) accumulation after cerebral ischemia/reperfusion (I/R) accounts for cerebral I/R injuries and poststroke dementia. Recently, pyroptosis, a proinflammatory cell death, has been identified as a crucial pathological link of cerebral I/R injuries. However, whether pyroptosis acts as a trigger of Aβ accumulation after cerebral I/R has not yet been demonstrated. Blood-brain barrier (BBB) and glymphatic system mediated by aquaporin-4 (AQP-4) on astrocytic endfeet are important pathways for the clearance of Aβ in the brain, and pyroptosis especially occurring in astrocytes after cerebral I/R potentially damages BBB integrity and glymphatic function and thus influences Aβ clearance and brain homeostasis. In present study, the method of middle cerebral artery occlusion/reperfusion (MCAO/R) was used for building models of focal cerebral I/R injuries in rats. Then, we used lipopolysaccharide and glycine as the agonist and inhibitor of pyroptosis, respectively, Western blotting for detections of pyroptosis, AQP-4, and Aβ_1-42 oligomers, laser confocal microscopy for observations of pyroptosis and Aβ locations, and immunohistochemical stainings of SMI 71 (a specific marker for BBB integrity)/AQP-4 and Nissl staining for evaluating, respectively, BBB-glymphatic system and neuronal damage. The results showed that pyroptosis obviously promoted the loss of BBB integrity and AQP-4 polarization, brain edema, Aβ accumulation, and the formation of Aβ_1-42 oligomers and thus increased neuronal damage after cerebral I/R. However, glycine could inhibit cerebral I/R-induced pyroptosis by alleviating cytomembrane damage and downregulating expression levels of cleaved caspase-11/1, N-terminal gasdermin D, NLRP3 (nucleotide-binding domain, leucine-rich repeat containing protein 3), interleukin-6 (IL-6) and IL-1β and markedly abate above pathological changes. Our study revealed that pyroptosis is a considerable factor causing toxic Aβ accumulation, dysfunctional BBB-glymphatic system, and neurological deficits after cerebral I/R, suggesting that targeting pyroptosis is a potential strategy for the prevention of ischemic stroke sequelae including dementia.

A unique death pathway keeps RIPK1 D325A mutant mice in check at embryonic day 10.5

Tumor necrosis factor receptor-1 (TNFR1) signaling, apart from its pleiotropic functions in inflammation, plays a role in embryogenesis as deficiency of varieties of its downstream molecules leads to embryonic lethality in mice. Caspase-8 noncleavable receptor interacting serine/threonine kinase 1 (RIPK1) mutations occur naturally in humans, and the corresponding D325A mutation in murine RIPK1 leads to death at early midgestation. It is known that both the demise of Ripk1D325A/D325A embryos and the death of Casp8-/- mice are initiated by TNFR1, but they are mediated by apoptosis and necroptosis, respectively. Here, we show that the defects in Ripk1D325A/D325A embryos occur at embryonic day 10.5 (E10.5), earlier than that caused by Casp8 knockout. By analyzing a series of genetically mutated mice, we elucidated a mechanism that leads to the lethality of Ripk1D325A/D325A embryos and compared it with that underlies Casp8 deletion-mediated lethality. We revealed that the apoptosis in Ripk1D325A/D325A embryos requires a scaffold function of RIPK3 and enzymatically active caspase-8. Unexpectedly, caspase-1 and caspase-11 are downstream of activated caspase-8, and concurrent depletion of Casp1 and Casp11 postpones the E10.5 lethality to embryonic day 13.5 (E13.5). Moreover, caspase-3 is an executioner of apoptosis at E10.5 in Ripk1D325A/D325A mice as its deletion extends life of Ripk1D325A/D325A mice to embryonic day 11.5 (E11.5). Hence, an unexpected death pathway of TNFR1 controls RIPK1 D325A mutation-induced lethality at E10.5.

How Aconiti Radix Cocta can Treat Gouty Arthritis Based on Systematic Pharmacology and UPLC-QTOF-MS/MS

Background: Gouty arthritis (GA) is a common metabolic disease caused by a long-term disorder of purine metabolism and increased serum levels of uric acid. The processed product of dried root of Aconitum carmichaeli Debeaux (Aconiti Radix cocta, ARC) is used often in traditional Chinese medicine (TCM) to treat GA, but its specific active components and mechanism of action are not clear.

Methods: First, we used ultra-performance liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry to identify the chemical spectrum of ARC. Based on this result, we explored the active components of ARC in GA treatment and their potential targets and pathways. Simultaneously, we used computer simulations, in vitro cell experiments and animal experiments to verify the prediction results of systems pharmacology. In vitro, we used aurantiamide acetate (AA) to treat monosodium urate (MSU)-stimulated THP-1 cells and demonstrated the reliability of the prediction by western blotting and real-time reverse transcription-quantitative polymerase chain reaction (RT-qPCR). ELISAs kit were used to measure changes in levels of proinflammatory factors in rats with GA induced by MSU to demonstrate the efficacy of ARC in GA treatment.

Results: Forty-three chemical constituents in ARC were identified. ARC could regulate 65 targets through 29 active components, and then treat GA, which involved 1427 Gene Ontology (GO) terms and 146 signaling pathways. Signaling pathways such as proteoglycans in cancer, C-type lectin receptor signaling pathway, and TNF signaling pathway may have an important role in GA treatment with ARC. In silico results showed that the active components songoramine and ignavine had high binding to mitogen-activated protein kinase p38 alpha (MAPK14) and matrix metallopeptidase (MMP)9, indicating that ARC treatment of GA was through multiple components and multiple targets. In vitro experiments showed that AA in ARC could effectively reduce expression of MAPK14, MMP9, and cyclooxygenase2 (PTGS2) in THP-1 cells stimulated by MSU, whereas it could significantly inhibit the mRNA expression of Caspase-1, spleen tyrosine kinase (SYK), and PTGS2. Animal experiments showed that a ARC aqueous extract could significantly reduce expression of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and intereleukin (IL)-18 in the serum of GA rats stimulated by MSU. Hence, ARC may inhibit inflammation by regulating the proteoglycans in cancer-associated signaling pathways.

Conclusion: ARC treatment of GA may have the following mechanisms, ARC can reduce MSU crystal-induced joint swelling, reduce synovial tissue damage, and reduce the expression of inflammatory factors in serum. AA in ARC may inhibit inflammation by regulating the protein expression of MAPK14, MMP9, and PTGS2 and the mRNA expression of caspase-1, SYK, and PTGS2.

Regulation, Activation and Function of Caspase-11 during Health and Disease

Caspase-11 is a pro-inflammatory enzyme that is stringently regulated during its expression and activation. As caspase-11 is not constitutively expressed in cells, it requires a priming step for its upregulation, which occurs following the stimulation of pathogen and cytokine receptors. Once expressed, caspase-11 activation is triggered by its interaction with lipopolysaccharide (LPS) from Gram-negative bacteria. Being an initiator caspase, activated caspase-11 functions primarily through its cleavage of key substrates. Gasdermin D (GSDMD) is the primary substrate of caspase-11, and the GSDMD cleavage fragment generated is responsible for the inflammatory form of cell death, pyroptosis, via its formation of pores in the plasma membrane. Thus, caspase-11 functions as an intracellular sensor for LPS and an immune effector. This review provides an overview of caspase-11—describing its structure and the transcriptional mechanisms that govern its expression, in addition to its activation, which is reported to be regulated by factors such as guanylate-binding proteins (GBPs), high mobility group box 1 (HMGB1) protein, and oxidized phospholipids. We also discuss the functional outcomes of caspase-11 activation, which include the non-canonical inflammasome, modulation of actin dynamics, and the initiation of blood coagulation, highlighting the importance of inflammatory caspase-11 during infection and disease.

Gasdermin D restricts Burkholderia cenocepacia infection in vitro and in vivo

Burkholderia cenocepacia (B. cenocepacia) is an opportunistic bacterium; causing severe life threatening systemic infections in immunocompromised individuals including cystic fibrosis patients. The lack of gasdermin D (GSDMD) protects mice against endotoxin lipopolysaccharide (LPS) shock. On the other hand, GSDMD promotes mice survival in response to certain bacterial infections. However, the role of GSDMD during B. cenocepacia infection is not yet determined. Our in vitro study shows that GSDMD restricts B. cenocepacia replication within macrophages independent of its role in cell death through promoting mitochondrial reactive oxygen species (mROS) production. mROS is known to stimulate autophagy, hence, the inhibition of mROS or the absence of GSDMD during B. cenocepacia infections reduces autophagy which plays a critical role in the restriction of the pathogen. GSDMD promotes inflammation in response to B. cenocepacia through mediating the release of inflammasome dependent cytokine (IL-1β) and an independent one (CXCL1) (KC). Additionally, different B. cenocepacia secretory systems (T3SS, T4SS, and T6SS) contribute to inflammasome activation together with bacterial survival within macrophages. In vivo study confirmed the in vitro findings and showed that GSDMD restricts B. cenocepacia infection and dissemination and stimulates autophagy in response to B. cenocepacia. Nevertheless, GSDMD promotes lung inflammation and necrosis in response to B. cenocepacia without altering mice survival. This study describes the double-edged functions of GSDMD in response to B. cenocepacia infection and shows the importance of GSDMD-mediated mROS in restriction of B. cenocepacia.

Pyroptosis by caspase-11 inflammasome-Gasdermin D pathway in autoimmune diseases

Inflammasomes are a group of supramolecular complexes primarily comprise a sensor, adaptor protein and an effector. Among them, canonical inflammasomes are assembled by one specific pattern recognition receptor, the adaptor protein apoptosis-associated speck-like protein containing a CARD and procaspase-1. Murine caspase-11 and its human ortholog caspase-4/5 are identified as cytosolic sensors which directly responds to LPS. Once gaining access to cytosol, LPS further trigger inflammasome activation in noncanonical way. Downstream pore-forming Gasdermin D is a pyroptosis executioner. Emerging evidence announced in recent years demonstrate the vital role played by caspase-11 non-canonical inflammasome in a range of autoimmune diseases. Pharmacological ablation of caspase-11 and its related effector results in potent therapeutic effects. Though recent advances have highlighted the potential of caspase-11 as a drug target, the understanding of caspase-11 molecular activation and regulation mechanism remains to be limited and thus hampered the discovery and progression of novel inhibitors. Here in this timeline review, we explored how caspase-11 get involved in the pathogenesis of autoimmune diseases, we also collected the reported small-molecular caspase-11 inhibitors. Moreover, the clinical implications and therapeutic potential of caspase-11 inhibitors are discussed. Targeting non-canonical inflammasomes is a promising strategy for autoimmune diseases treatment, while information about the toxicity and physiological disposition of the promising caspase-11 inhibitors need to be supplemented before they can be translated from bench to bedside.

Insights Into Mucosal Innate Immune Responses in House Dust Mite-Mediated Allergic Asthma

The prevalence of asthma has been rising steadily for several decades, and continues to be a major public health and global economic burden due to both direct and indirect costs. Asthma is defined as chronic heterogeneous inflammatory diseases characterized by airway obstruction, mucus production and bronchospasm. Different endotypes of asthma are being recognized based on the distinct pathophysiology, genetic predisposition, age, prognosis, and response to remedies. Mucosal innate response to environmental triggers such as pollen, cigarette smoke, fragrances, viral infection, and house dust mite (HDM) are now recognized to play an important role in allergic asthma. HDM are the most pervasive allergens that co-habitat with us, as they are ubiquitous in-house dusts, mattress and bedsheets, and feed on a diet of exfoliated human skin flakes. Dermatophagoides pteronyssinus, is one among several HDM identified up to date. During the last decade, extensive studies have been fundamental in elucidating the interactions between HDM allergens, the host immune systems and airways. Moreover, the paradigm in the field of HDM-mediated allergy has been shifted away from being solely a Th2-geared to a complex response orchestrated via extensive crosstalk between the epithelium, professional antigen presenting cells (APCs) and components of the adaptive immunity. In fact, HDM have several lessons to teach us about their allergenicity, the complex interactions that stimulate innate immunity in initiating and perpetuating the lung inflammation. Herein, we review main allergens of Dermatophagoides pteronyssinus and their interactions with immunological sentinels that promote allergic sensitization and activation of innate immunity, which is critical for the development of the Th2 biased adaptive immunity to HDM allergens and development of allergic asthma.

An overview of the non-canonical inflammasome

Inflammasomes are large cytosolic multiprotein complexes assembled in response to infection and cellular stress, and are crucial for the activation of inflammatory caspases and the subsequent processing and release of pro-inflammatory mediators. While caspase-1 is activated within the canonical inflammasome, the related caspase-4 (also known as caspase-11 in mice) and caspase-5 are activated within the non-canonical inflammasome upon sensing of cytosolic lipopolysaccharide (LPS) from Gram-negative bacteria. However, the consequences of canonical and non-canonical inflammasome activation are similar. Caspase-1 promotes the processing and release of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 and the release of danger signals, as well as a lytic form of cell death called pyroptosis, whereas caspase-4, caspase-5 and caspase-11 directly promote pyroptosis through cleavage of the pore-forming protein gasdermin D (GSDMD), and trigger a secondary activation of the canonical NLRP3 inflammasome for cytokine release. Since the presence of the non-canonical inflammasome activator LPS leads to endotoxemia and sepsis, non-canonical inflammasome activation and regulation has important clinical ramifications. Here we discuss the mechanism of non-canonical inflammasome activation, mechanisms regulating its activity and its contribution to health and disease.

Molecular Pathophysiology of Uric Acid Homeostasis

Uric acid, the end product of purine metabolism, plays a key role in the pathogenesis of gout and other disease processes. The circulating serum uric acid concentration is governed by the relative balance of hepatic production, intestinal secretion, and renal tubular reabsorption and secretion. An elegant synergy between genome-wide association studies and transport physiology has led to the identification and characterization of the major transporters involved with urate reabsorption and secretion, in both kidney and intestine. This development, combined with continued analysis of population-level genetic data, has yielded an increasingly refined mechanistic understanding of uric acid homeostasis as well as greater understanding of the genetic and acquired influences on serum uric acid concentration. The continued delineation of novel and established regulatory pathways that regulate uric acid homeostasis promises to lead to a more complete understanding of uric acid-associated diseases and to identify new targets for treatment.

Pyroptotic and non-pyroptotic effector functions of caspase-11

Innate immune cells, epithelial cells, and many other cell types are capable of detecting infection or tissue injury, thus mounting regulated immune response. Inflammasomes are highly sophisticated and effective orchestrators of innate immunity. These oligomerized multiprotein complexes are at the center of various innate immune pathways, including modulation of the cytoskeleton, production and maturation of cytokines, and control of bacterial growth and cell death. Inflammasome assembly often results in caspase‐1 activation, which is an inflammatory caspase that is involved in pyroptotic cell death and release of inflammatory cytokines in response to pathogen patterns and endogenous danger stimuli. However, the nature of stimuli and inflammasome components are diverse. Caspase‐1 activation mediated release of mature IL‐1β and IL‐18 in response to canonical stimuli initiated by NOD‐like receptor (NLR), and apoptosis‐associated speck‐like protein containing a caspase recruitment domain (ASC). On the other hand, caspase‐11 delineates a non‐canonical inflammasome that promotes pyroptotic cell death and non‐pyroptotic functions in response to non‐canonical stimuli. Caspase‐11 in mice and its homologues in humans (caspase‐4/5) belong to caspase‐1 family of cysteine proteases, and play a role in inflammation. Knockout mice provided new genetic tools to study inflammatory caspases and revealed the role of caspase‐11 in mediating septic shock in response to lethal doses of lipopolysaccharide (LPS). Recognition of LPS mediates caspase‐11 activation, which promotes a myriad of downstream effects that include pyroptotic and non‐pyroptotic effector functions. Therefore, the physiological functions of caspase‐11 are much broader than its previously established roles in apoptosis and cytokine maturation. Inflammation induced by exogenous or endogenous agents can be detrimental and, if excessive, can result in organ and tissue damage. Consequently, the existence of sophisticated mechanisms that tightly regulate the specificity and sensitivity of inflammasome pathways provides a fine‐tuning balance between adequate immune response and minimal tissue damage. In this review, we summarize effector functions of caspase‐11.

Caspase-11 contributes to pulmonary host defense against Klebsiella pneumoniae and local activation of coagulation

Klebsiella (K.) pneumoniae is a common cause of gram-negative pneumonia and sepsis. Caspase-11 is an intracellular receptor for lipopolysaccharide and regulates pyroptosis, a specific form of inflammatory cell death, which aids in host defense against intracellular gram-negative bacteria. Recently, caspase-11 has also been implicated in blood coagulation. Previously, we found that local fibrin formation contributes to protective immunity against Klebsiella infection of the lung. The aim of the present study was to determine the role of caspase-11 in host defense during K. pneumoniae-evoked pneumonia and sepsis. Therefore, we infected wild-type and caspase-11-deficient (Casp11^-/-) mice with a low-dose K. pneumoniae via the airways to induce a gradually evolving pneumosepsis. Casp11^-/- mice displayed increased bacterial numbers in the lung 12 h and 48 h after inoculation. Analysis of pulmonary IL-1α, IL-1β, and TNF levels showed reduced IL-1α levels in bronchoalveolar lavage fluid and increased TNF levels in the lung of Casp11^-/- mice at 48 h after inoculation. Lung γH2AX staining (marker for cell death), lung pathology and neutrophil influx in the lung, as well as bacterial dissemination and organ damage, however, were not altered in Casp11^-/- mice after Klebsiella infection. Strikingly, analysis of cross-linked fibrin and D-dimer (markers for coagulation) revealed significantly less fibrin formation in the lungs of Casp11^-/- mice at either time point after Klebsiella infection. These data reveal that caspase-11 contributes to protective immunity against K. pneumoniae possibly by activation of blood coagulation in the lung.