Reactive oxygen species regulate caspase-11 expression and activation of the non-canonical NLRP3 inflammasome during enteric pathogen infection

Mitochondrial P-JNK target, SAB (SH3BP5), in regulation of cell death

Cell death occurs in various circumstances, such as homeostasis, stress response, and defense, via specific pathways and mechanisms that are regulated by specific activator-induced signal transductions. Among them, Jun N-terminal kinases (JNKs) participate in various aspects, and the recent discovery of JNKs and mitochondrial protein SAB interaction in signal regulation of cell death completes our understanding of the mechanism of sustained activation of JNK (P-JNK), which leads to triggering of the machinery of cell death. This understanding will lead the investigators to discover the modulators facilitating or preventing cell death for therapeutic application in acute or chronic diseases and cancer. We discuss here the mechanism and modulators of the JNK-SAB-ROS activation loop, which is the core component of mitochondria-dependent cell death, specifically apoptosis and mitochondrial permeability transition (MPT)-driven necrosis, and which may also contribute to cell death mechanisms of ferroptosis and pyroptosis. The discussion here is based on the results and evidence discovered from liver disease models, but the JNK-SAB-ROS activation loop to sustain JNK activation is universally applicable to various disease models where mitochondria and reactive oxygen species contribute to the mechanism of disease.

Shenhuangdan decoction alleviates sepsis-induced lung injury through inhibition of GSDMD-mediated pyroptosis

ETHNOPHARMACOLOGICAL RELEVANCE

Sepsis-induced lung injury is closely associated with it remarkable morbidity and mortality. Shenhuangdan (SHD) decoction, a traditional Chinese medicine prescription, has been clinically proven to be an effective treatment for sepsis. However, the mechanism of SHD decoction in treating sepsis remains unclear.

AIM OF THE STUDY

This study aimed to evaluate the therapeutic effect of SHD decoction on sepsis-induced lung injury and its underlying mechanism.

MATERIALS AND METHODS

In this study, we established a mouse model of sepsis by cecum ligation and puncture (CLP) surgery. Firstly, seven-day survival analysis and histological staining of lung tissue were used to evaluate the therapeutic effect of SHD decoction on lung injury in septic mice. Multifactor microarray was used to detect cytokine expression changes in serum and bronchoalveolar lavage fluid (BALF). Subsequently, the main components in medicated serum of SHD decoction were inspected by Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The material basis of SHD decoction and potential interaction mechanisms were analysed by systemic pharmacology. To confirm the reliability of network pharmacology for predicting outcomes, we used molecular docking techniques to identify interactions between the core components and targets of SHD. Finally, TUNEL staining, immunofluorescence and western blotting were used to explore the mechanism of SHD decoction through the inhibition of GSDMD-mediated pyroptosis in septic mice.

RESULTS

SHD was found to be effective in reducing the mortality and alleviating lung pathological damage in septic mice. Multifactor microarray results showed that SHD can reduce the expression of inflammation factors (IL-18, IL-1β, IL-5, IL-6 and TNF-α) in serum and BALF of septic mice. There were 22 major blood-entry components detected by UPLC-MS/MS. Then, combined with the network pharmacological analysis, it is evident that the main components of SHD for sepsis are Renshen-ginsenoside Rh2, Danshen-tanshinone IIA and Dahuang-rhein. The main targets were IL-1β and caspase-1, which were related to GSDMD-mediated pyroptosis signalling pathway. Molecular docking exhibited that Renshen-ginsenoside Rh2, Danshen-tanshinone IIA and Dahuang-rhein can closely bind to GSDMD, IL-1β and caspase-1. In addition, TUNEL staining and immunohistochemistry demonstrated that SHD alleviated the expression of GSDMD protein. The western blotting showed that SHD significantly inhibited the protein expression levels of NLRP3, GSDMD, GSDMD-N, cleved caspase-1, caspase-1 and ASC in lung tissue.

CONCLUSIONS

Our study revealed that SHD improves CLP-induced lung injury by blocking the GSDMD-mediated pyroptosis signalling pathway in septic mice. This study provides evidence to support that SHD had a potential therapeutic effect on sepsis.

ECDD-S16 targets vacuolar ATPase: A potential inhibitor compound for pyroptosis-induced inflammation

BACKGROUND

Cleistanthin A (CA), extracted from Phyllanthus taxodiifolius Beille, was previously reported as a potential V-ATPase inhibitor relevant to cancer cell survival. In the present study, ECDD-S16, a derivative of cleistanthin A, was investigated and found to interfere with pyroptosis induction via V-ATPase inhibition.

OBJECTIVE

This study examined the ability of ECDD-S16 to inhibit endolysosome acidification leading to the attenuation of pyroptosis in Raw264.7 macrophages activated by both surface and endosomal TLR ligands.

METHODS

To elucidate the activity of ECDD-S16 on pyroptosis-induced inflammation, Raw264.7 cells were pretreated with the compound before stimulation with surface and endosomal TLR ligands. The release of lactate dehydrogenase (LDH) was determined by LDH assay. Additionally, the production of cytokines and the expression of pyroptosis markers were examined by ELISA and immunoblotting. Moreover, molecular docking was performed to demonstrate the binding of ECDD-S16 to the vacuolar (V-)ATPase.

RESULTS

This study showed that ECDD-S16 could inhibit pyroptosis in Raw264.7 cells activated with surface and endosomal TLR ligands. The attenuation of pyroptosis by ECDD-S16 was due to the impairment of endosome acidification, which also led to decreased Reactive Oxygen Species (ROS) production. Furthermore, molecular docking also showed the possibility of inhibiting endosome acidification by the binding of ECDD-S16 to the vacuolar (V-)ATPase in the region of V0.

CONCLUSION

Our findings indicate the potential of ECDD-S16 for inhibiting pyroptosis and prove that vacuolar H+ ATPase is essential for pyroptosis induced by TLR ligands.

Non-Canonical Inflammasome Pathway: The Role of Cell Death and Inflammation in Ehrlichiosis

Activating inflammatory caspases and releasing pro-inflammatory mediators are two essential functions of inflammasomes which are triggered in response to pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs). The canonical inflammasome pathway involves the activation of inflammasome and its downstream pathway via the adaptor ASC protein, which causes caspase 1 activation and, eventually, the cleavage of pro-IL-1b and pro-IL-18. The non-canonical inflammasome pathway is induced upon detecting cytosolic lipopolysaccharide (LPS) by NLRP3 inflammasome in Gram-negative bacteria. The activation of NLRP3 triggers the cleavage of murine caspase 11 (human caspase 4 or caspase 5), which results in the formation of pores (via gasdermin) to cause pyroptosis. Ehrlichia is an obligately intracellular bacterium which is responsible for causing human monocytic ehrlichiosis (HME), a potentially lethal disease similar to toxic shock syndrome and septic shock syndrome. Several studies have indicated that canonical and non-canonical inflammasome activation is a crucial pathogenic mechanism that induces dysregulated inflammation and host cellular death in the pathophysiology of HME. Mechanistically, the activation of canonical and non-canonical inflammasome pathways affected by virulent Ehrlichia infection is due to a block in autophagy. This review aims to explore the significance of non-canonical inflammasomes in ehrlichiosis, and how the pathways involving caspases (with the exception of caspase 1) contribute to the pathophysiology of severe and fatal ehrlichiosis. Improving our understanding of the non-canonical inflammatory pathway that cause cell death and inflammation in ehrlichiosis will help the advancement of innovative therapeutic, preventative, and diagnostic approaches to the treatment of ehrlichiosis.

The noncanonical inflammasome-induced pyroptosis and septic shock

Sepsis remains one of the most common and lethal conditions globally. Currently, no proposed target specific to sepsis improves survival in clinical trials. Thus, an in-depth understanding of the pathogenesis of sepsis is needed to propel the discovery of effective treatment. Recently attention to sepsis has intensified because of a growing recognition of a non-canonical inflammasome-triggered lytic mode of cell death termed pyroptosis upon sensing cytosolic lipopolysaccharide (LPS). Although the consequences of activation of the canonical and non-canonical inflammasome are similar, the non-canonical inflammasome formation requires caspase-4/5/11, which enzymatically cleave the pore-forming protein gasdermin D (GSDMD) and thereby cause pyroptosis. The non-canonical inflammasome assembly triggers such inflammatory cell death by itself; or leverages a secondary activation of the canonical NLRP3 inflammasome pathway. Excessive cell death induced by oligomerization of GSDMD and NINJ1 leads to cytokine release and massive tissue damage, facilitating devastating consequences and death. This review summarized the updated mechanisms that initiate and regulate non-canonical inflammasome activation and pyroptosis and highlighted various endogenous or synthetic molecules as potential therapeutic targets for treating sepsis.

PANoptosis: Mechanism and Role in Pulmonary Diseases

PANoptosis is a newly defined programmed cell death (PCD) triggered by a series of stimuli, and it engages three well-learned PCD forms (pyroptosis, apoptosis, necroptosis) concomitantly. Normally, cell death is recognized as a strategy to eliminate unnecessary cells, inhibit the proliferation of invaded pathogens and maintain homeostasis; however, vigorous cell death can cause excessive inflammation and tissue damage. Acute lung injury (ALI) and chronic obstructive pulmonary syndrome (COPD) exacerbation is related to several pathogens (e.g., influenza A virus, SARS-CoV-2) known to cause PANoptosis. An understanding of the mechanism and specific regulators may help to address the pathological systems of these diseases. This review presents our understanding of the potential mechanism of PANoptosis and the role of PANoptosis in different pulmonary diseases.

Cell type-specific roles of NLRP3, inflammasome-dependent and -independent, in host defense, sterile necroinflammation, tissue repair, and fibrosis

The NLRP3 inflammasome transforms a wide variety of infectious and non-infectious danger signals that activate pro-inflammatory caspases, which promote the secretion of IL-1β and IL-18, and pyroptosis, a pro-inflammatory form of cell necrosis. Most published evidence documents the presence and importance of the NLRP3 inflammasome in monocytes, macrophages, and neutrophils during host defense and sterile forms of inflammation. In contrast, in numerous unbiased data sets, NLRP3 inflammasome-related transcripts are absent in non-immune cells. However, an increasing number of studies report the presence and functionality of the NLRP3 inflammasome in almost every cell type. Here, we take a closer look at the reported cell type-specific expression of the NLRP3 inflammasome components, review the reported inflammasome-dependent and -independent functions, and discuss possible explanations for this discrepancy.

Paired protein kinases PRKCI-RIPK2 promote pancreatic cancer growth and metastasis via enhancing NF-κB/JNK/ERK phosphorylation

BACKGROUND

Protein kinases play a pivotal role in the malignant evolution of pancreatic cancer (PC) through mediating phosphorylation. Many kinase inhibitors have been developed and translated into clinical use, while the complex pathology of PC confounds their clinical efficacy and warrants the discovery of more effective therapeutic targets.

METHODS

Here, we used the Gene Expression Omnibus (GEO) database and protein kinase datasets to map the PC-related protein kinase-encoding genes. Then, applying Gene Expression and Profiling Interactive Analysis (GEPIA), GEO and Human Protein Atlas, we evaluated gene correlation, gene expression at protein and mRNA levels, as well as survival significance. In addition, we performed protein kinase RIPK2 knockout and overexpression to observe effects of its expression on PC cell proliferation, migration and invasion in vitro, as well as cell apoptosis, reactive oxygen species (ROS) production and autophagy. We established PC subcutaneous xenograft and liver metastasis models to investigate the effects of RIPK2 knockout on PC growth and metastasis. Co-immunoprecipitation and immunofluorescence were utilized to explore the interaction between protein kinases RIPK2 and PRKCI. Polymerase chain reaction and immunoblotting were used to evaluate gene expression and protein phosphorylation level.

RESULTS

We found fourteen kinases aberrantly expressed in human PC and nine kinases with prognosis significance. Among them, RIPK2 with both serine/threonine and tyrosine activities were validated to promote PC cells proliferation, migration and invasion. RIPK2 knockout could inhibit subcutaneous tumor growth and liver metastasis of PC. In addition, RIPK2 knockout suppressed autophagosome formation, increased ROS production and PC cell apoptosis. Importantly, another oncogenic kinase PRKCI could interact with RIPK2 to enhance the phosphorylation of downstream NF-κB, JNK and ERK.

CONCLUSION

Paired protein kinases PRKCI-RIPK2 with multiple phosphorylation activities represent a new pathological mechanism in PC and could provide potential targets for PC therapy.

Role of Tumor Necrosis Factor Receptor 1-Reactive Oxygen Species-Caspase 11 Pathway in Neuropathic Pain Mediated by HIV gp120 With Morphine in Rats

BACKGROUND

Recent clinical research suggests that repeated use of opioid pain medications can increase neuropathic pain in people living with human immunodeficiency virus (HIV; PLWH). Therefore, it is significant to elucidate the exact mechanisms of HIV-related chronic pain. HIV infection and chronic morphine induce proinflammatory factors, such as tumor necrosis factor (TNF)α acting through tumor necrosis factor receptor I (TNFRI). HIV coat proteins and/or chronic morphine increase mitochondrial superoxide in the spinal cord dorsal horn (SCDH). Recently, emerging cytoplasmic caspase-11 is defined as a noncanonical inflammasome and can be activated by reactive oxygen species (ROS). Here, we tested our hypothesis that HIV coat glycoprotein gp120 with chronic morphine activates a TNFRI-mtROS-caspase-11 pathway in rats, which increases neuroinflammation and neuropathic pain.

METHODS

Neuropathic pain was induced by repeated administration of recombinant gp120 with morphine (gp120/M) in rats. Mechanical allodynia was assessed using von Frey filaments, and thermal latency using hotplate test. Protein expression of spinal TNFRI and cleaved caspase-11 was examined using western blots. The image of spinal mitochondrial superoxide was examined using MitoSox Red (mitochondrial superoxide indicator) image assay. Immunohistochemistry was used to examine the location of TNFRI and caspase-11 in the SCDH. Intrathecal administration of antisense oligodeoxynucleotide (AS-ODN) against TNFRI, caspase-11 siRNA, or a scavenger of mitochondrial superoxide was given for antinociceptive effects. Statistical tests were done using analysis of variance (1- or 2-way), or 2-tailed t test.

RESULTS

Intrathecal gp120/M induced mechanical allodynia and thermal hyperalgesia lasting for 3 weeks ( P < .001). Gp120/M increased the expression of spinal TNFRI, mitochondrial superoxide, and cleaved caspase-11. Immunohistochemistry showed that TNFRI and caspase-11 were mainly expressed in the neurons of the SCDH. Intrathecal administration of antisense oligonucleotides against TNFRI, Mito-Tempol (a scavenger of mitochondrial superoxide), or caspase-11 siRNA reduced mechanical allodynia and thermal hyperalgesia in the gp120/M neuropathic pain model. Spinal knockdown of TNFRI reduced MitoSox profile cell number in the SCDH; intrathecal Mito-T decreased spinal caspase-11 expression in gp120/M rats. In the cultured B35 neurons treated with TNFα, pretreatment with Mito-Tempol reduced active caspase-11 in the neurons.

CONCLUSIONS

These results suggest that spinal TNFRI-mtROS-caspase 11 signal pathway plays a critical role in the HIV-associated neuropathic pain state, providing a novel approach to treating chronic pain in PLWH with opioids.

Novel Biomarkers for Inflammatory Bowel Disease and Colorectal Cancer: An Interplay between Metabolic Dysregulation and Excessive Inflammation

Persistent inflammation can trigger altered epigenetic, inflammatory, and bioenergetic states. Inflammatory bowel disease (IBD) is an idiopathic disease characterized by chronic inflammation of the gastrointestinal tract, with evidence of subsequent metabolic syndrome disorder. Studies have demonstrated that as many as 42% of patients with ulcerative colitis (UC) who are found to have high-grade dysplasia, either already had colorectal cancer (CRC) or develop it within a short time. The presence of low-grade dysplasia is also predictive of CRC. Many signaling pathways are shared among IBD and CRC, including cell survival, cell proliferation, angiogenesis, and inflammatory signaling pathways. Current IBD therapeutics target a small subset of molecular drivers of IBD, with many focused on the inflammatory aspect of the pathways. Thus, there is a great need to identify biomarkers of both IBD and CRC, that can be predictive of therapeutic efficacy, disease severity, and predisposition to CRC. In this study, we explored the changes in biomarkers specific for inflammatory, metabolic, and proliferative pathways, to help determine the relevance to both IBD and CRC. Our analysis demonstrated, for the first time in IBD, the loss of the tumor suppressor protein Ras associated family protein 1A (RASSF1A), via epigenetic changes, the hyperactivation of the obligate kinase of the NOD2 pathogen recognition receptor (receptor interacting protein kinase 2 [RIPK2]), the loss of activation of the metabolic kinase, AMP activated protein kinase (AMPKα1), and, lastly, the activation of the transcription factor and kinase Yes associated protein (YAP) kinase, that is involved in proliferation of cells. The expression and activation status of these four elements are mirrored in IBD, CRC, and IBD-CRC patients and, importantly, in matched blood and biopsy samples. The latter would suggest that biomarker analysis can be performed non-invasively, to understand IBD and CRC, without the need for invasive and costly endoscopic analysis. This study, for the first time, illustrates the need to understand IBD or CRC beyond an inflammatory perspective and the value of therapeutics directed to reset altered proliferative and metabolic states within the colon. The use of such therapeutics may truly drive patients into remission.

Non-canonical inflammasome activation mediates the adjuvanticity of nanoparticles

The non-canonical inflammasome sensor caspase-11 and gasdermin D (GSDMD) drive inflammation and pyroptosis, a type of immunogenic cell death that favors cell-mediated immunity (CMI) in cancer, infection, and autoimmunity. Here we show that caspase-11 and GSDMD are required for CD8⁺ and Th1 responses induced by nanoparticulate vaccine adjuvants. We demonstrate that nanoparticle-induced reactive oxygen species (ROS) are size dependent and essential for CMI, and we identify 50- to 60-nm nanoparticles as optimal inducers of ROS, GSDMD activation, and Th1 and CD8⁺ responses. We reveal a division of labor for IL-1 and IL-18, where IL-1 supports Th1 and IL-18 promotes CD8⁺ responses. Exploiting size as a key attribute, we demonstrate that biodegradable poly-lactic co-glycolic acid nanoparticles are potent CMI-inducing adjuvants. Our work implicates ROS and the non-canonical inflammasome in the mode of action of polymeric nanoparticulate adjuvants and establishes adjuvant size as a key design principle for vaccines against cancer and intracellular pathogens.

Circadian Control of Redox Reactions in the Macrophage Inflammatory Response

Significance: Macrophages are immune sentinels located throughout the body that function in both amplification and resolution of the inflammatory response. The circadian clock has emerged as a central regulator of macrophage inflammation. Reduction-oxidation (redox) reactions are central to both the circadian clock and macrophage function. Recent Advances: Circadian regulation of metabolism controls the macrophage inflammatory response, whereby disruption of the clock causes dysfunctional inflammation. Altering metabolism and reactive oxygen/nitrogen species (RONS) production rescues the inflammatory phenotype of clock-disrupted macrophages. Critical Issues: The circadian clock possesses many layers of regulation. Understanding how redox reactions coordinate clock function is critical to uncover the full extent of circadian regulation of macrophage inflammation. We provide insights into how circadian regulation of redox affects macrophage pattern recognition receptor signaling, immunometabolism, phagocytosis, and inflammasome activation. Future Directions: Many diseases associated with aberrant macrophage-derived inflammation exhibit time-of-day rhythms in disease symptoms and severity and are sensitive to circadian disruption. Macrophage function is highly dependent on redox reactions that signal through RONS. Future studies are needed to evaluate the extent of circadian control of macrophage inflammation, specifically in the context of redox signaling. Antioxid. Redox Signal. 37, 664-678.

BNTA alleviates inflammatory osteolysis by the SOD mediated anti-oxidation and anti-inflammation effect on inhibiting osteoclastogenesis

Abnormal activation and overproliferation of osteoclast in inflammatory bone diseases lead to osteolysis and bone mass loss. Although current pharmacological treatments have made extensive advances, limitations still exist. N-[2-bromo-4-(phenylsulfonyl)-3-thienyl]-2-chlorobenzamide (BNTA) is an artificially synthesized molecule compound that has antioxidant and anti-inflammatory properties. In this study, we presented that BNTA can suppress intracellular ROS levels through increasing ROS scavenging enzymes SOD1 and SOD2, subsequently attenuating the MARK signaling pathway and the transcription of NFATc1, leading to the inhibition of osteoclast formation and osteolytic resorption. Moreover, the results also showed an obvious restrained effect of BNTA on RANKL-stimulated proinflammatory cytokines, which indirectly mediated osteoclastogenesis. In line with the in vitro results, BNTA protected LPS-induced severe bone loss in vivo by enhancing scavenging enzymes, reducing proinflammatory cytokines, and decreasing osteoclast formation. Taken together, all of the results demonstrate that BNTA effectively represses oxidation, regulates inflammatory activity, and inhibits osteolytic bone resorption, and it may be a potential and exploitable drug to prevent inflammatory osteolytic bone diseases.

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.

Card9 protects sepsis by regulating Ripk2-mediated activation of NLRP3 inflammasome in macrophages

Sepsis is characterized by systemic inflammation, it's caused by primary infection of pathogenic microorganisms or secondary infection of damaged tissue. In this study, we focus on sepsis-induced intestine barrier functional disturbalice, presenting as increased permeability of intestinal epithelium. We observed that the phenotype of LPS-induced sepsis was exacerbated in Card9^-/- mice, especially displaying more serious intestinal inflammation and gut barrier dysfunction. Next, we found the hyperactivation of NLRP3 inflammasome in the intestinal macrophages of Card9^-/--sepsis mice. Moreover, Card9 over-expression decreased NLRP3 inflammasome activation in macrophages. Furthermore, we found that Card9 inhibited NLRP3 inflammasome activation by recruiting Ripk2. The competitive binding between Ripk2 with Caspase-1, instead of ASC with Caspase-1, inhibited the NLRP3 inflammasome activation. Over-expression of Ripk2 alleviated septic intestinal injury caused by Card9 deficiency. Taken together, we suggested Card9 acts as a negative regulation factor of NLRP3 inflammasome activation, which protects against intestinal damage during sepsis. Therefore, maintaining Card9-Ripk2 signaling homeostasis may provide a novel therapy of septic intestinal damage.

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.

Balancing reactive oxygen species generation by rebooting gut microbiota

Reactive oxygen species (ROS; free radical form O₂ ^•‾ , superoxide radical; OH^• , hydroxyl radical; ROO^• , peroxyl; RO^• , alkoxyl and non-radical form ¹ O₂ , singlet oxygen; H₂ O₂ , hydrogen peroxide) are inevitable companions of aerobic life with crucial role in gut health. But, overwhelming production of ROS can cause serious damage to biomolecules. In this review, we have discussed several sources of ROS production that can be beneficial or dangerous to the human gut. Microorganisms, organelles and enzymes play crucial role in ROS generation, where, NOX1 is the main intestinal enzyme, which produce ROS in the intestine epithelial cells. Previous studies have reported that probiotics play significant role in gut homeostasis by checking the ROS generation, maintaining the antioxidant level, immune system and barrier protection. With current knowledge, we have critically analyzed the available literature and presented the outcome in the form of bubble maps to suggest the probiotics that help in controlling the ROS-specific intestinal diseases, such as inflammatory bowel disease (IBD) and colon cancer. Finally, it has been concluded that rebooting of the gut microbiota with probiotics, postbiotics or fecal microbiota transplantation (FMT) can have crucial implications in the structuring of gut communities for the personalized management of the gastrointestinal (GI) diseases.

Autophagy, Pyroptosis, and Ferroptosis: New Regulatory Mechanisms for Atherosclerosis

Atherosclerosis is a chronic inflammatory disorder characterized by the gradual buildup of plaques within the vessel wall of middle-sized and large arteries. The occurrence and development of atherosclerosis and the rupture of plaques are related to the injury of vascular cells, including endothelial cells, smooth muscle cells, and macrophages. Autophagy is a subcellular process that plays an important role in the degradation of proteins and damaged organelles, and the autophagy disorder of vascular cells is closely related to atherosclerosis. Pyroptosis is a proinflammatory form of regulated cell death, while ferroptosis is a form of regulated nonapoptotic cell death involving overwhelming iron-dependent lipid peroxidation. Both of them exhibit distinct features from apoptosis, necrosis, and autophagy in morphology, biochemistry, and genetics. However, a growing body of evidence suggests that pyroptosis and ferroptosis interact with autophagy and participate in the development of cancers, degenerative brain diseases and cardiovascular diseases. This review updated the current understanding of autophagy, pyroptosis, and ferroptosis, finding potential links and their effects on atherogenesis and plaque stability, thus providing ways to develop new pharmacological strategies to address atherosclerosis and stabilize vulnerable, ruptured plaques.

"Driver-passenger" bacteria and their metabolites in the pathogenesis of colorectal cancer

Colorectal cancer (CRC) is a significant public health problem accounting for about 10% of all new cancer cases globally. Though genetic and epigenetic factors influence CRC, the gut microbiota acts as a significant component of the disease's etiology. Further research is still needed to clarify the specific roles and identify more bacteria related to CRC development. This review aims to provide an overview of the "driver-passenger" model of CRC. The colonization and active invasion of the "driver(s)" bacteria cause damages allowing other commensals, known as "passengers," or their by-products, i.e., metabolites, to pass through the epithelium . This review will not only focus on the species of bacteria implicated in this model but also on their biological functions implicated in the occurrence of CRC, such as forming biofilms, mucus, penetration and production of enterotoxins and genotoxins.

Role of Pyroptosis in Diabetes and Its Therapeutic Implications

Pyroptosis is mainly considered as a new pro-inflammatory mediated-programmed cell death. In addition, pyroptosis is described by gasdermin-induced pore formation on the membrane, cell swelling and rapid lysis, and several pro-inflammatory mediators interleukin-1β (IL-1β) and interleukin-18 (IL-18) release. Extensive studies have shown that pyroptosis is commonly involved by activating the caspase-1-dependent canonical pathway and caspase-4/5/11-dependent non-canonical pathway. However, pyroptosis facilitates local inflammation and inflammatory responses. Current researches have reported that pyroptosis promotes the progression of several diabetic complications. Emerging studies have suggested that some potential molecules targeting the pyroptosis and inflammasome signaling pathways could be a novel therapeutic avenue for managing and treating diabetes and its complications in the near future. Our narrative review concisely describes the possible mechanism of pyroptosis and its progressive understanding of the development of diabetic complications.

NLRP3 Inflammasome Blockade Reduces Cocaine-Induced Microglial Activation and Neuroinflammation

Cocaine use disorder is a major health crisis that is associated with increased oxidative stress and neuroinflammation. While the role of NLRP3 inflammasome in mediating neuroinflammation is well-recognized, whether cocaine induces this response remains unexplored. Based on the premise that cocaine induces both reactive oxygen species (ROS) as well as microglial activation, we hypothesized that cocaine-mediated microglial activation involves both ROS and NLRP3 signaling pathways. We examined activation of the NLRP3 pathway in microglia exposed to cocaine, followed by validation in mice administered either cocaine or saline for 7 days, with or without pretreatment with the NLRP3 inhibitor, MCC950, and in postmortem cortical brain tissues of chronic cocaine-dependent humans. We found that microglia exposed to cocaine exhibited significant induction of NLRP3 and mature IL-1β expression. Intriguingly, blockade of ROS (Tempol) attenuated cocaine-mediated priming of NLRP3 and microglial activation (CD11b). Blockade of NLRP3 by both pharmacological (MCC950) as well as gene silencing (siNLRP3) approaches underpinned the critical role of NLRP3 in cocaine-mediated activation of inflammasome and microglial activation. Pretreatment of mice with MCC950 followed by cocaine administration for 7 days mitigated cocaine-mediated upregulation of mature IL-1β and CD11b, in both the striatum and the cortical regions. Furthermore, cortical brain tissues of chronic cocaine-dependent humans also exhibited upregulated expression of the NLRP3 pathway mediators compared with non-cocaine dependent controls. Collectively, these findings suggest that cocaine activates microglia involving the NLRP3 inflammasome pathway, thereby contributing to neuroinflammation. NLRP3 can thus be considered as a potential therapeutic target for alleviating cocaine-mediated neuroinflammation.

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.

Pyruvate affects inflammatory responses of macrophages during influenza A virus infection

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Pyruvate is an essential metabolite but possesses anti-inflammatory properties.

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Pyruvate inhibits immune signaling but not influenza A virus replication.

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Decreased immune signaling caused by pyruvate is associated with altered metabolism.

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Pyruvate prevents mitochondrial damage in an infection specific manner.

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The anti-inflammatory effects of pyruvate are only observed during virus infection.

Pyruvate is the end product of glycolysis and transported into the mitochondria for use in the tricarboxylic acid (TCA) cycle. It is also a common additive in cell culture media. We discovered that inclusion of sodium pyruvate in culture media during infection of mouse bone marrow derived macrophages with influenza A virus impaired cytokine production (IL-6, IL-1β, and TNF-α). Sodium pyruvate did not inhibit viral RNA replication. Instead, the addition of sodium pyruvate alters cellular metabolism and diminished mitochondrial reactive oxygen species (ROS) production and lowered immune signaling. Overall, sodium pyruvate affects the immune response produced by macrophages but does not inhibit virus replication.

Caspase-11-mediated enteric neuronal pyroptosis underlies Western diet-induced colonic dysmotility

Enteric neuronal degeneration, as seen in inflammatory bowel disease, obesity, and diabetes, can lead to gastrointestinal dysmotility. Pyroptosis is a novel form of programmed cell death but little is known about its role in enteric neuronal degeneration. We observed higher levels of cleaved caspase-1, a marker of pyroptosis, in myenteric ganglia of overweight and obese human subjects compared with normal-weight subjects. Western diet-fed (WD-fed) mice exhibited increased myenteric neuronal pyroptosis, delayed colonic transit, and impaired electric field stimulation-induced colonic relaxation responses. WD increased TLR4 expression and cleaved caspase-1 in myenteric nitrergic neurons. Overactivation of nitrergic neuronal NF-κB signaling resulted in increased pyroptosis and delayed colonic motility. In caspase-11-deficient mice, WD did not induce nitrergic myenteric neuronal pyroptosis and colonic dysmotility. To understand the contributions of saturated fatty acids and bacterial products to the steps leading to enteric neurodegeneration, we performed in vitro experiments using mouse enteric neurons. Palmitate and lipopolysaccharide (LPS) increased nitrergic, but not cholinergic, enteric neuronal pyroptosis. LPS gained entry to the cytosol in the presence of palmitate, activating caspase-11 and gasdermin D, leading to pyroptosis. These results support a role of the caspase-11-mediated pyroptotic pathway in WD-induced myenteric nitrergic neuronal degeneration and colonic dysmotility, providing important therapeutic targets for enteric neuropathy.

Lipids, inflammasomes, metabolism, and disease

Inflammasomes are multi-protein complexes that regulate the cleavage of cysteine protease caspase-1, secretion of inflammatory cytokines, and induction of inflammatory cell death, pyroptosis. Several members of the nod-like receptor family assemble inflammasome in response to specific ligands. An exception to this is the NLRP3 inflammasome which is activated by structurally diverse entities. Recent studies have suggested that NLRP3 might be a sensor of cellular homeostasis, and any perturbation in distinct metabolic pathways results in the activation of this inflammasome. Lipid metabolism is exceedingly important in maintaining cellular homeostasis, and it is recognized that cells and tissues undergo extensive lipid remodeling during activation and disease. Some lipids are involved in instigating chronic inflammatory diseases, and new studies have highlighted critical upstream roles for lipids, particularly cholesterol, in regulating inflammasome activation implying key functions for inflammasomes in diseases with defective lipid metabolism. The focus of this review is to highlight how lipids regulate inflammasome activation and how this leads to the progression of inflammatory diseases. The key roles of cholesterol metabolism in the activation of inflammasomes have been comprehensively discussed. Besides, the roles of oxysterols, fatty acids, phospholipids, and lipid second messengers are also summarized in the context of inflammasomes. The overriding theme is that lipid metabolism has numerous but complex functions in inflammasome activation. A detailed understanding of this area will help us develop therapeutic interventions for diseases where dysregulated lipid metabolism is the underlying cause.

Reconciling protective and pathogenic roles of the NLRP3 inflammasome in leishmaniasis

Leishmaniasis is a global health problem that affects more than 2 billion people worldwide. Recent advances in research have demonstrated critical roles for cytoplasmic sensors and inflammasomes during Leishmania spp. infection and pathogenesis. Specifically, several studies have focused on the role of nod-like receptor family, pyrin domain-containing protein 3 (NLRP3) inflammasome and inflammasome-associated cytokines IL-1β and IL-18 in leishmaniasis. Despite these studies, our understanding of the priming and activation events that lead to NLRP3 inflammasome activation during Leishmania spp. infection is limited. Furthermore, whether NLRP3 plays a protective or pathogenic role during Leishmania spp. infection is far from resolved, with some studies showing a protective role and others showing a pathogenic role. In this review, we performed a critical review of the literature to provide a current update on priming and activating signals required for NLRP3 inflammasome activation during Leishmania spp. infection. Finally, we provide a thorough review of the literature to reconcile differences in the observed protective vs pathogenic roles of the NLRP3 inflammasome during Leishmania spp. infection.

Inflammasome activation and regulation: toward a better understanding of complex mechanisms

Inflammasomes are cytoplasmic multiprotein complexes comprising a sensor protein, inflammatory caspases, and in some but not all cases an adapter protein connecting the two. They can be activated by a repertoire of endogenous and exogenous stimuli, leading to enzymatic activation of canonical caspase-1, noncanonical caspase-11 (or the equivalent caspase-4 and caspase-5 in humans) or caspase-8, resulting in secretion of IL-1β and IL-18, as well as apoptotic and pyroptotic cell death. Appropriate inflammasome activation is vital for the host to cope with foreign pathogens or tissue damage, while aberrant inflammasome activation can cause uncontrolled tissue responses that may contribute to various diseases, including autoinflammatory disorders, cardiometabolic diseases, cancer and neurodegenerative diseases. Therefore, it is imperative to maintain a fine balance between inflammasome activation and inhibition, which requires a fine-tuned regulation of inflammasome assembly and effector function. Recently, a growing body of studies have been focusing on delineating the structural and molecular mechanisms underlying the regulation of inflammasome signaling. In the present review, we summarize the most recent advances and remaining challenges in understanding the ordered inflammasome assembly and activation upon sensing of diverse stimuli, as well as the tight regulations of these processes. Furthermore, we review recent progress and challenges in translating inflammasome research into therapeutic tools, aimed at modifying inflammasome-regulated human diseases.

A specific gene-microbe interaction drives the development of Crohn's disease-like colitis in mice

Bacterial dysbiosis is associated with Crohn's disease (CD), a chronic intestinal inflammatory disorder thought to result from an abnormal immune response against intestinal bacteria in genetically susceptible individuals. However, it is unclear whether dysbiosis is a cause or consequence of intestinal inflammation and whether overall dysbiosis or specific bacteria trigger the disease. Here, we show that the combined deficiency of NOD2 and phagocyte NADPH oxidase, two CD susceptibility genes, triggers early-onset spontaneous T_H1-type intestinal inflammation in mice with the pathological hallmarks of CD. Disease was induced by Mucispirillum schaedleri, a Gram-negative mucus-dwelling anaerobe. NOD2 and CYBB deficiencies led to marked accumulation of Mucispirillum, which was associated with impaired neutrophil recruitment and killing of the bacterium by luminal neutrophils. Maternal immunoglobulins against Mucispirillum protected mutant mice from disease during breastfeeding. Our results indicate that a specific intestinal microbe triggers CD-like disease in the presence of impaired clearance of the bacterium by innate immunity.

Functional crosstalk between non-canonical caspase-11 and canonical NLRP3 inflammasomes during infection-mediated inflammation

Inflammation is a part of the body's immune response for protection against pathogenic infections and other cellular damages; however, chronic inflammation is a major cause of various diseases. One key step in the inflammatory response is the activation of inflammasomes, intracellular protein complexes comprising pattern recognition receptors and other inflammatory molecules. The role of the NLRP3 inflammasome in inflammatory responses has been extensively investigated; however, the caspase-11 inflammasome has been recently identified and has been classified as a 'non-canonical' inflammasome, and emerging studies have highlighted its role in inflammatory responses. Because the ligands and the mechanisms for the activation of these two inflammasomes are different, studies to date have separately described their roles, although recent studies have reported the functional cooperation between these two inflammasomes during an inflammatory response. This review discusses the studies investigating the functional crosstalk between non-canonical caspase-11 and canonical NLRP3 inflammasomes in the context of inflammatory responses; moreover, it provides insight for the development of novel anti-inflammatory therapeutics to prevent and treat infectious and inflammatory diseases.

Glutathione peroxidase 8 negatively regulates caspase-4/11 to protect against colitis

Human caspase-4 and its mouse homolog caspase-11 are receptors for cytoplasmic lipopolysaccharide. Activation of the caspase-4/11-dependent NLRP3 inflammasome is required for innate defense and endotoxic shock, but how caspase-4/11 is modulated remains unclear. Here, we show that mice lacking the oxidative stress sensor glutathione peroxidase 8 (GPx8) are more susceptible to colitis and endotoxic shock, and exhibit reduced richness and diversity of the gut microbiome. C57BL/6 mice that underwent adoptive cell transfer of GPx8-deficient macrophages displayed a similar phenotype of enhanced colitis, indicating a critical role of GPx8 in macrophages. GPx8 binds covalently to caspase-4/11 via disulfide bonding between cysteine 79 of GPx8 and cysteine 118 of caspase-4 and thus restrains caspase-4/11 activation, while GPx8 deficiency leads to caspase-4/11-induced inflammation during colitis and septic shock. Inhibition of caspase-4/11 activation with small molecules reduces the severity of colitis in GPx8-deficient mice. Notably, colonic tissues from patients with ulcerative colitis display low levels of Gpx8 and high caspase-4 expression. In conclusion, these results suggest that GPx8 protects against colitis by negatively regulating caspase-4/11 activity.

Pyroptotic and apoptotic cell death in iNOS and nNOS overexpressing K562 cells: A mechanistic insight

Previous studies from this lab and others have demonstrated that nitric oxide (NO) in a concentration dependent manner, modulated neutrophil and leukemic cell survival. Subsequent studies delineated importance of iNOS in neutrophil differentiation and leukemic cell death. On the contrary, role of nNOS in survival of these cells remains least understood. Present study was therefore undertaken to assess and compare the role of iNOS and nNOS in the survival of NOS overexpressing myelocytic K562 cells. Cells with almost similar iNOS and nNOS activities displayed comparable cell cycle perturbation, Annexin V positivity, mitochondrial dysfunction, augmented DCF fluorescence, and also attenuated expression of antioxidants. Moreover, induction in cell death was also accompanied by the activation of pJNK/p38MAPK/Erk1/2 and reduction in PI3K/Akt/mTOR signaling. Treatment of NOS isoform overexpressing K562 cells with NAC, a potent free radical scavenger prevented cell death and also the modulations in the signaling proteins. In addition, enhanced expression of CASP1 and CASP4 genes, along with increased Caspase-1 cleavage and increased IL-1β release were significantly more in K562^iNOS cells, which indicate priming of these cells for pyroptotic cell death. On the other hand, K562^nNOS cells, displayed much enhanced CASP3 gene expression, Caspase-3 cleavage and Caspase-3 activity. Results obtained indicate that similar level of iNOS or nNOS activation in K562 cells, preferred pyroptotic and apoptotic cell death respectively.

A new research hot spot: The role of NLRP3 inflammasome activation, a key step in pyroptosis, in diabetes and diabetic complications

Pyroptosis is a form of cell death mediated by gasdermin D (GSDMD); it is characterised by NLRP3 inflammasome activation, caspase activation, cell membrane pore formation, and the release of interleukin-1β and interleukin-18. NLRP3 inflammasome activation plays a central role in pyroptosis. Recent research has suggested that NLRP3 inflammasome activation may be involved in the occurrence and development of diabetes mellitus and its associated complications. This finding provided the impetus for us to clarify the significance of pyroptosis in diabetes. In this review, we summarise the current understanding of the molecular mechanisms involved in pyroptosis, as well as recent advances in the role of NLRP3 inflammasome activation and pyroptosis in the development of diabetes and diabetic complications.

Citrobacter rodentium-host-microbiota interactions: immunity, bioenergetics and metabolism

Citrobacter rodentium is an extracellular enteric mouse-specific pathogen used to model infections with human pathogenic Escherichia coli and inflammatory bowel disease. C. rodentium injects type III secretion system effectors into intestinal epithelial cells (IECs) to target inflammatory, metabolic and cell survival pathways and establish infection. While the host responds to infection by activating innate and adaptive immune signalling, required for clearance, the IECs respond by rapidly shifting bioenergetics to aerobic glycolysis, which leads to oxygenation of the epithelium, an instant expansion of mucosal-associated commensal Enterobacteriaceae and a decline of obligate anaerobes. Moreover, infected IECs reprogramme intracellular metabolic pathways, characterized by simultaneous activation of cholesterol biogenesis, import and efflux, leading to increased serum and faecal cholesterol levels. In this Review we summarize recent advances highlighting the intimate relationship between C. rodentium pathogenesis, metabolism and the gut microbiota.

Non-canonical NLRP3 inflammasome activation and IL-1β signaling are necessary to L. amazonensis control mediated by P2X7 receptor and leukotriene B4

Leishmaniasis is a neglected tropical disease affecting millions of individuals worldwide. P2X7 receptor has been linked to the elimination of Leishmania amazonensis. Biological responses evoked by P2X7 receptor activation have been well-documented, including apoptosis, phagocytosis, cytokine release, such as IL-1β. It was demonstrated that NLRP3 inflammasome activation and IL-1β signaling participated in resistance against L. amazonensis. Furthermore, our group has shown that L. amazonensis elimination through P2X7 receptor activation depended on leukotriene B₄ (LTB₄) production and release. Therefore, we investigated whether L. amazonensis elimination by P2X7 receptor and LTB₄ involved NLRP3 inflammasome activation and IL-1β signaling. We showed that macrophages from NLRP3^-/-, ASC^-/-, Casp-1/11^-/-, gp91^{phox-/- ,} and IL-1R^-/- mice treated with ATP or LTB₄ did not decrease parasitic load as was observed in WT mice. When ASC^-/- macrophages were treated with exogenous IL-1β, parasite killing was noted, however, we did not see parasitic load reduction in IL-1R^-/- macrophages. Similarly, macrophages from P2X7 receptor-deficient mice treated with IL-1β also showed decreased parasitic load. In addition, when we infected Casp-11^-/- macrophages, neither ATP nor LTB₄ were able to reduce parasitic load, and Casp-11^-/- mice were more susceptible to L. amazonensis infection than were WT mice. Furthermore, P2X7^-/-L. amazonensis-infected mice locally treated with exogenous LTB₄ showed resistance to infection, characterized by lower parasite load and smaller lesions compared to untreated P2X7^-/- mice. A similar observation was noted when infected P2X7^-/- mice were treated with IL-1β, i.e., lower parasite load and smaller lesions compared to P2X7^-/- mice. These data suggested that L. amazonensis elimination mediated by P2X7 receptor and LTB₄ was dependent on non-canonical NLRP3 inflammasome activation, ROS production, and IL-1β signaling.

Leishmania spp. is a protozoan parasite that infects human and causes several diseases. Leishmania amazonensis causes cutaneous leishmaniasis (CL) and mucocutaneous leishmaniasis (MCL). Leishmania parasites preferentially infect macrophages. In macrophages, several mechanisms have been described as controlling L. amazonensis infection. Here, we showed that P2X7 receptor and LTB₄ eliminated L. amazonensis in macrophages by a pathway dependent on non-canonical NLRP3 inflammasome activation and IL-1β signaling.

Programmed necrotic cell death of macrophages: Focus on pyroptosis, necroptosis, and parthanatos

Macrophages are highly plastic cells of the innate immune system. Macrophages play central roles in immunity against microbes and contribute to a wide array of pathologies. The processes of macrophage activation and their functions have attracted considerable attention from life scientists. Although macrophages are highly resistant to many toxic stimuli, including oxidative stress, macrophage death has been reported in certain diseases, such as viral infections, tuberculosis, atherosclerotic plaque development, inflammation, and sepsis. While most studies on macrophage death focused on apoptosis, a significant body of data indicates that programmed necrotic cell death forms may be equally important modes of macrophage death. Three such regulated necrotic cell death modalities in macrophages contribute to different pathologies, including necroptosis, pyroptosis, and parthanatos. Various reactive oxygen and nitrogen species, such as superoxide, hydrogen peroxide, and peroxynitrite have been shown to act as triggers, mediators, or modulators in regulated necrotic cell death pathways. Here we discuss recent advances in necroptosis, pyroptosis, and parthanatos, with a strong focus on the role of redox homeostasis in the regulation of these events.

Right place, right time: localisation and assembly of the NLRP3 inflammasome

The NLRP3 inflammasome is a multimeric protein complex that cleaves caspase-1 and the pro-inflammatory cytokines interleukin 1 beta (IL-1β) and IL-18. Dysregulated NLRP3 inflammasome signalling is linked to several chronic inflammatory and autoimmune conditions; thus, understanding the activation mechanisms of the NLRP3 inflammasome is essential. Studies over the past few years have implicated vital roles for distinct intracellular organelles in both the localisation and assembly of the NLRP3 inflammasome. However, conflicting reports exist. Prior to its activation, NLRP3 has been shown to be resident in the endoplasmic reticulum (ER) and cytosol, although, upon activation, the NLRP3 inflammasome has been shown to assemble in the cytosol, mitochondria, and mitochondria-associated ER membranes by different reports. Finally, very recent work has suggested that NLRP3 may be localised on or adjacent to the Golgi apparatus and that release of mediators from this organelle may contribute to inflammasome assembly. Therefore, NLRP3 may be strategically placed on or in close proximity to these subcellular compartments to both sense danger signals originating from these organelles and use the compartment as a scaffold to assemble the complex. Understanding where and when NLRP3 inflammasome assembly occurs may help identify potential targets for treatment of NLRP3-related disorders.

Macrophage β2-Integrins Regulate IL-22 by ILC3s and Protect from Lethal Citrobacter rodentium-Induced Colitis

β2-integrins promote neutrophil recruitment to infected tissues and are crucial for host defense. Neutrophil recruitment is defective in leukocyte adhesion deficiency type-1 (LAD1), a condition caused by mutations in the CD18 (β2-integrin) gene. Using a model of Citrobacter rodentium (CR)-induced colitis, we show that CD18-/- mice display increased intestinal damage and systemic bacterial burden, compared to littermate controls, ultimately succumbing to infection. This phenotype is not attributed to defective neutrophil recruitment, as it is shared by CXCR2-/- mice that survive CR infection. CR-infected CD18-/- mice feature prominent upregulation of IL-17 and downregulation of IL-22. Exogenous IL-22 administration, but not endogenous IL-17 neutralization, protects CD18-/- mice from lethal colitis. β2-integrin expression on macrophages is mechanistically linked to Rac1/ROS-mediated induction of noncanonical-NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome-dependent IL-1β production, which promotes ILC3-derived IL-22. Therefore, β2-integrins are required for protective IL-1β-dependent IL-22 responses in colitis, and the identified mechanism may underlie the association of human LAD1 with colitis.

Regulation of the β-cell inflammasome and contribution to stress-induced cellular dysfunction and apoptosis

β-Cells may be a source of IL-1β that is produced as inactive pro-IL-1β and processed into biologically-active IL-1β by enzymatic cleavage mediated by the NLRP1-, NLRP3- and NLRC4-inflammasomes. Little is known about the β-cell inflammasomes. NLRP1-expression was upregulated in islet-cells from T2D-patients and by IL-1β+IFNγ in INS-1 cells in a histone-deacetylase dependent manner. NLRP3 was downregulated by cytokines in INS-1 cells. NLRC4 was barely expressed and not regulated by cytokines. High extracellular K⁺ reduced cytokine-induced apoptosis and NO production and restored cytokine-inhibited accumulated insulin-secretion. Basal inflammasome expression was JNK1-3 dependent. Knock-down of the ASC interaction domain common for NLRP1 and 3 improved insulin secretion and ameliorated IL-1β and/or glucolipotoxicity-induced cell death and reduced cytokine-induced NO-production. Broad inflammasome-inhibition, but not NLRP3-selective inhibition, protected against IL-1β-induced INS-1 cell-toxicity. We suggest that IL-1β causes β-cell toxicity in part by NLRP1 mediated caspase-1-activation and maturation of IL-1β leading to an autocrine potentiation loop.

Syk and JNK signaling pathways are involved in inflammasome activation in macrophages infected with Streptococcus pneumoniae

Streptococcus pneumoniae is a pathogen of significant clinical importance worldwide that can cause severe invasive diseases, such as pneumonia, otitis media and meningitis. Inflammsomes has been reported to participate in host defense against S. pneumoniae infection. S. pneumoniae could induce the assembly of the nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3)/absent in melanoma 2 (AIM2) inflammasome, which mediates the activation of caspase-1 and the subsequent maturation of Interleukin-1β (IL-1β). However, the precise signals that activate inflammasomes during pneumococcal infection remain to be fully elucidated. In the present study, primary mouse macrophages were selected as a cell model, and the effects of kinases on inflammasome activity induced by S. pneumoniae infection were examined by ELISA and western blotting after pretreatment with a kinase inhibitor. Here, we show that Syk and JNK signaling are required for S. pneumoniae-induced activation of the inflammasome. Inhibitors of Syk and JNK almost abolished the oligomerization of apoptosis-associated speck-like protein containing a caspase-activating and recruitment domain (ASC) and subsequent caspase-1 activation and IL-1β secretion. Moreover, pneumolysin (PLY) participated in this process and was critical for Syk/JNK activation. These results suggested that the Syk/JNK signaling pathway may play a vital role in the inflammasome activation and modulate host immune responses against S. pneumoniae.

Environmental Factors Modify the Severity of Acute DSS Colitis in Caspase-11-Deficient Mice

BACKGROUND

Human and mouse studies implicate the inflammasome in the pathogenesis of inflammatory bowel diseases, though the effects in mice are variable. The noncanonical inflammasome activator caspase-11 (Casp11) reportedly attenuates acute dextran sodium sulfate (DSS) colitis in mice. However, the effects of Casp11 on chronic experimental colitis and factors that influence the impact of Casp11 on acute DSS colitis are unknown.

METHODS

We studied the role of Casp11 in Il10-/- mice and acute and chronic DSS colitis mouse models. We quantified colonic Casp11 mRNA using quantative polymerase chain reaction and colitis using weight loss, blinded histological scoring, IL-12/23p40 secretion by colonic explants, and fecal lipocalin-2. We determined fecal microbial composition using 16S amplicon sequencing.

RESULTS

We detected increased colonic Casp11 mRNA in Il10-/- mice with chronic colitis, but not in mice with DSS colitis. The presence of Casp11 did not alter the severity of chronic colitis in DSS-treated or Il10-/- mice. Contrary to prior reports, we initially observed that Casp11 exacerbates acute DSS colitis. Subsequent experiments in the same animal facility revealed no effect of Casp11 on acute DSS colitis. There were pronounced stochastic changes in the fecal microbiome over this time. The majority of bacterial taxa that changed over time in wild-type vs Casp11-/- mice belong to the Clostridiales.

CONCLUSIONS

Casp11 does not impact chronic experimental colitis, and its effects on acute DSS colitis vary with environmental factors including the microbiota, particularly Clostridiales. Stochastic drifts in intestinal microbiota composition, even in mice in the same housing facility, should be considered when interpreting studies of acute DSS colitis models.

Role and mechanism of ROS scavengers in alleviating NLRP3-mediated inflammation

Inflammation, as a common immune response to various infections or injuries, can cause many dangerous and complicated diseases. Inflammasome is a protein complex playing a vital role in an inflammation process, and the nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome has been the most-widely studied one. Recent evidence suggests the reactive oxygen species (ROS)-NLRP3 signaling pathway to be a possible NLRP3 inflammasome regulation model. Numerous recent preclinical reports indicate that application of antioxidants could scavenge excessive ROS and attenuate inflammatory responses through suppressing NLRP3 inflammasome activation. This article, at first, briefly overviews how ROS may mediate the regulation of NLRP3 inflammasome activation. Then, preclinical researches of various ROS scavengers for treating NLRP3 inflammasome-associated diseases are focused on and critically analyzed. Finally, the potential of antioxidant treatment as a therapy for inflammation is to be discussed, and perspectives on future research directions will be shared.

Trafficking of cholesterol to the ER is required for NLRP3 inflammasome activation

Cellular lipid metabolism is being increasingly recognized to influence inflammatory responses. de la Roche et al. reveal that cellular sterol trafficking to the endoplasmic reticulum is required for the assembly and the activation of the NLRP3 inflammasome, thereby coupling lipid homeostasis to innate immune signaling.

Cellular lipids determine membrane integrity and fluidity and are being increasingly recognized to influence immune responses. Cellular cholesterol requirements are fulfilled through biosynthesis and uptake programs. In an intricate pathway involving the lysosomal cholesterol transporter NPC1, the sterol gets unequally distributed across intracellular compartments. By using pharmacological and genetic approaches targeting NPC1, we reveal that blockade of cholesterol trafficking through the late endosome–lysosome pathway blunts NLRP3 inflammasome activation. Altered cholesterol localization at the plasma membrane (PM) in Npc1^−/− cells abrogated AKT–mTOR signaling by TLR4. However, the inability to activate the NLRP3 inflammasome was traced to perturbed cholesterol trafficking to the ER but not the PM. Accordingly, acute cholesterol depletion in the ER membranes by statins abrogated casp-1 activation and IL-1β secretion and ablated NLRP3 inflammasome assembly. By contrast, assembly and activation of the AIM2 inflammasome progressed unrestricted. Together, this study reveals ER sterol levels as a metabolic rheostat for the activation of the NLRP3 inflammasome.

Inflammatory cell death in intestinal pathologies

The intestinal tract is a site of intense immune cell activity that is poised to mount an effective response against a pathogen and yet maintain tolerance toward commensal bacteria and innocuous dietary antigens. The role of cell death in gut pathologies is particularly important as the intestinal epithelium undergoes self-renewal every 4-7 days through a continuous process of cell death and cell division. Cell death is also required for removal of infected, damaged, and cancerous cells. Certain forms of cell death trigger inflammation through release of damage-associated molecular patterns. Further, molecules involved in cell death decisions also moonlight as critical nodes in immune signaling. The manner of cell death is, therefore, highly instructive of the immunological consequences that ensue. Perturbations in cell death pathways can impact the regulation of the immune system with deleterious consequences. In this review, we discuss the various forms of cell death with a special emphasis on lytic cell death pathways of pyroptosis and necroptosis and their implications in inflammation and cancer in the gut. Understanding the implications of distinct cell death pathways will help in the development of therapeutic interventions in intestinal pathologies.

Identification and Characterization of Novel Receptor-Interacting Serine/Threonine-Protein Kinase 2 Inhibitors Using Structural Similarity Analysis

Receptor-interacting protein kinase 2 (RIP2 or RICK, herein referred to as RIPK2) is linked to the pathogen pathway that activates nuclear factor κ-light-chain-enhancer of activated B cells (NFκB) and autophagic activation. Using molecular modeling (docking) and chemoinformatics analyses, we used the RIPK2/ponatinib crystal structure and searched in chemical databases for small molecules exerting binding interactions similar to those exerted by ponatinib. The identified RIPK2 inhibitors potently inhibited the proliferation of cancer cells by > 70% and also inhibited NFκB activity. More importantly, in vivo inhibition of intestinal and lung inflammation rodent models suggests effectiveness to resolve inflammation with low toxicity to the animals. Thus, our identified RIPK2 inhibitor may offer possible therapeutic control of inflammation in diseases such as inflammatory bowel disease, asthma, cystic fibrosis, primary sclerosing cholangitis, and pancreatitis.

Caspase-11 promotes cisplatin-induced renal tubular apoptosis through a caspase-3-dependent pathway

Renal tubular injury is the hallmark of cisplatin-induced nephrotoxicity. Caspase-11, a member of the caspase family, plays an important role in inflammation and cell death. However, its role in cisplatin-induced renal tubular injury remains unclear. In cisplatin-treated mice, caspase-11 expression was significantly elevated and the expression of caspase-11 was mainly located in renal tubule. Inhibition of caspase-11 by small-interference RNA or its inhibitor wedelolactone attenuated cisplatin-induced renal dysfunction and tubular injury. In cultured primary renal tubular epithelial cells, cisplatin significantly promoted the expression and activation of caspase-11. Inhibition of caspase-11 by small-interference RNA reduced cisplatin-induced cell apoptosis. Overexpression of caspase-11 promoted cell apoptosis by activating the caspase-3-related cell apoptosis. Furthermore, coimmunoprecipitation results showed there was a direct interaction between caspase-11 and caspase-3, and the interaction was enhanced by cisplatin. The fluorescence confocal microscopy results showed that caspase-11 and caspase-3 were colocalized in the cytoplasm of renal tubular epithelial cells. These results demonstrate that caspase-11 plays an important role in cisplatin-induced renal tubular injury. Caspase-11 promotes renal epithelial cell apoptosis by activating the caspase-3-dependent apoptotic pathway. Caspase-11 might be a potential target for therapeutic treatment against cisplatin-induced nephrotoxicity.

An update on cell intrinsic negative regulators of the NLRP3 inflammasome

Inflammasomes are multimeric protein complexes that promote inflammation (through specific cleavage and production of bioactive IL-1β and IL-18) and pyroptotic cell death. The central role of inflammasomes in combating infection and maintaining homeostasis has been studied extensively. Although inflammasome-mediated inflammation and cell death are vital to limit pathogenic insults and to promote wound healing/tissue regeneration, unchecked/uncontrolled inflammation, and cell death can cause cytokine storm, tissue damage, autoinflammatory and autoimmune diseases, and even death in the afflicted individuals. NLRP3 is one of the major cytosolic sensors that assemble an inflammasome. Given the adverse consequences of uncontrolled inflammasome activation, our immune system has developed tiered mechanisms to inhibit NLRP3 inflammasome activation. In this review, we highlight and discuss recent advances and our current understanding of mechanisms by which NLRP3 inflammasome can be negatively regulated.

Function and regulation of IL-1α in inflammatory diseases and cancer

The interleukin (IL)-1 family of cytokines is currently comprised of 11 members that have pleiotropic functions in inflammation and cancer. IL-1α and IL-1β were the first members of the IL-1 family to be described, and both signal via the same receptor, IL-1R. Over the last decade, much progress has been made in our understanding of biogenesis of IL-1β and its functions in human diseases. Studies from our laboratory and others have highlighted the critical role of nod-like receptors (NLRs) and multi-protein complexes known as inflammasomes in the regulation of IL-1β maturation. Recent studies have increased our appreciation of the role played by IL-1α in inflammatory diseases and cancer. However, the mechanisms that regulate the production of IL-1α and its bioavailability are relatively understudied. In this review, we summarize the distinctive roles played by IL-1α in inflammatory diseases and cancer. We also discuss our current knowledge about the mechanisms that control IL-1α biogenesis and activity, and the major unanswered questions in its biology.