Monocyte Caspase-1 Is Released in a Stable, Active High Molecular Weight Complex Distinct from the Unstable Cell Lysate-Activated Caspase-1

Interrogating direct NLRP3 engagement and functional inflammasome inhibition using cellular assays

As a key regulator of the innate immune system, the NLRP3 inflammasome responds to a variety of environmental insults through activation of caspase-1 and release of the proinflammatory cytokines IL-1β and IL-18. Aberrant NLRP3 inflammasome function is implicated in numerous inflammatory diseases, spurring drug discovery efforts at NLRP3 as a therapeutic target. A diverse array of small molecules is undergoing preclinical/clinical evaluation with a reported mode of action involving direct modulation of the NLRP3 pathway. However, for a subset of these ligands the functional link between live-cell target engagement and pathway inhibition has yet to be fully established. Herein we present a cohort of mechanistic assays to both query direct NLRP3 engagement in cells, and functionally interrogate different nodes of NLRP3 pathway activity. This system enabled the stratification of potency for five confirmed NLRP3 inhibitors, and identification of two reported NLRP3 inhibitors that failed to demonstrate direct pathway antagonism.

The PI3K-Akt pathway is a multifaceted regulator of the macrophage response to diverse group B Streptococcus isolates

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a common member of the microbial flora in healthy individuals. However, problems may arise when GBS-colonized mothers become pregnant. GBS may be transferred from a colonized mother to her newborn or developing fetus, which may result in complications such as miscarriage, pre-term birth, meningitis, pneumonia, or sepsis. Macrophages play an especially important role in the fetal and newborn response to GBS due to the limited development of the adaptive immune system early in life. The goal of this study was to expand what is currently known about how GBS manipulates macrophage cell signaling to evade the immune system and cause disease. To this end, we investigated whether the PI3K-Akt pathway was involved in several key aspects of the macrophage response to GBS. We explored whether certain GBS strains, such as sequence type (ST)-17 strains, rely on this pathway for the more rapid macrophage uptake they induce compared to other GBS strains. Our findings suggest that this pathway is, indeed, important for macrophage uptake of GBS. Consistent with these findings, we used immunofluorescence microscopy to demonstrate that more virulent strains of GBS induce more actin projections in macrophages than less virulent strains. Additionally, we explored whether PI3K-Akt signaling impacted the ability of GBS to survive within macrophages after phagocytosis and whether this pathway influenced the survival rate of macrophages themselves following GBS infection. The PI3K-Akt pathway was found to promote the survival of both macrophages and intracellular GBS following infection. We also observed that inhibition of the PI3K-Akt pathway significantly reduced GBS-mediated activation of NFκB, which is a key regulator of cell survival and inflammatory responses. Overall, these insights into strain-dependent GBS-mediated manipulation of the PI3K-Akt pathway and its downstream targets in infected macrophages may provide new insights for the development of diagnostic and therapeutic tools to combat severe GBS disease.

Increased serum interleukin-6 and lactate dehydrogenase levels among nonsurvival severe COVID-19 patients when compared to survival ones

BACKGROUND

Accurate and rapid laboratory diagnosis of COVID-19 infection and its deterioration is one of the milestones of pandemic control. Therefore, this study aimed to compare the diagnostic and prognostic accuracy of the mainly used laboratory biomarkers (WBCS, neutrophil and lymphocyte percentages, CRP, ferritin, IL-6, D-dimer, procalcitonin, and LDH) in the sera of severe COVID-19 Egyptian patients to assess the most appropriate biomarker used in severe COVID-19 patients.

METHODS

A total of 180 unvaccinated severe COVID-19 patients were enrolled in our study. Demographic data, hospitalization time, medical history, oxygen saturation, respiratory rate, oxygen supply, laboratory findings, and thorax tomography of the patients were obtained retrospectively from the hospital's electronic information system.

RESULTS

Our results revealed that the levels of neutrophil percentage, CRP, IL-6, PCT, and LDH were significantly increased while lymphocyte percentage was significantly decreased among nonsurvival severe COVID-19 patients when compared with survival ones. By using ROC curve analysis, IL-6, and LDH are the most sensitive and specific markers for the prediction of bad prognosis and mortality among severe COVID-19 patients with 100% and 93% sensitivity and 93.7% specificity; respectively. IL-6 and LDH showed significant correlations with the other parameters, which suggested their association with the severity of COVID-19.

CONCLUSION

By using survival severe COVID-19 patients as a control group, our results showed that blood neutrophil percentage, serum CRP, IL-6, PCT, and LDH were significantly increased in non-survivors as compared to survivors. As biomarkers, our results revealed that IL-6 and LDH are good predictors of mortality among severe COVID-19 patients.

Oligomeric states of ASC specks regulate inflammatory responses by inflammasome in the extracellular space

Inflammasomes are multi-protein complexes and play a crucial role in host defense against pathogens. Downstream inflammatory responses through inflammasomes are known to be related to the oligomerization degree of ASC specks, but the detailed mechanism still remains unexplored. Here, we demonstrate that oligomerization degrees of ASC specks regulate the caspase-1 activation in the extracellular space. A protein binder specific for a pyrin domain (PYD) of ASC (ASC^PYD) was developed, and structural analysis revealed that the protein binder effectively inhibits the interaction between PYDs, disassembling ASC specks into low oligomeric states. ASC specks with a low oligomerization degree were shown to enhance the activation of caspase-1 by recruiting and processing more premature caspase-1 through interactions between CARD of caspase-1 (caspase-1^CARD) and CARD of ASC (ASC^CARD). These findings can provide insight into controlling the inflammasome-mediated inflammatory process as well as the development of inflammasome-targeting drugs.

Uncoupled pyroptosis and IL-1β secretion downstream of inflammasome signaling

Inflammasomes are supramolecular platforms that organize in response to various damage-associated molecular patterns and pathogen-associated molecular patterns. Upon activation, inflammasome sensors (with or without the help of ASC) activate caspase-1 and other inflammatory caspases that cleave gasdermin D and pro-IL-1β/pro-IL-18, leading to pyroptosis and mature cytokine secretion. Pyroptosis enables intracellular pathogen niche disruption and intracellular content release at the cost of cell death, inducing pro-inflammatory responses in the neighboring cells. IL-1β is a potent pro-inflammatory regulator for neutrophil recruitment, macrophage activation, and T-cell expansion. Thus, pyroptosis and cytokine secretion are the two main mechanisms that occur downstream of inflammasome signaling; they maintain homeostasis, drive the innate immune response, and shape adaptive immunity. This review aims to discuss the possible mechanisms, timing, consequences, and significance of the two uncoupling preferences downstream of inflammasome signaling. While pyroptosis and cytokine secretion may be usually coupled, pyroptosis-predominant and cytokine-predominant uncoupling are also observed in a stimulus-, cell type-, or context-dependent manner, contributing to the pathogenesis and development of numerous pathological conditions such as cryopyrin-associated periodic syndromes, LPS-induced sepsis, and Salmonella enterica serovar Typhimurium infection. Hyperactive cells consistently release IL-1β without LDH leakage and pyroptotic death, thereby leading to prolonged inflammation, expanding the lifespans of pyroptosis-resistant neutrophils, and hyperactivating stimuli-challenged macrophages, dendritic cells, monocytes, and specific nonimmune cells. Death inflammasome activation also induces GSDMD-mediated pyroptosis with no IL-1β secretion, which may increase lethality in vivo. The sublytic GSDMD pore formation associated with lower expressions of pyroptotic components, GSDMD-mediated extracellular vesicles, or other GSDMD-independent pathways that involve unconventional secretion could contribute to the cytokine-predominant uncoupling; the regulation of caspase-1 dynamics, which may generate various active species with different activities in terms of GSDMD or pro-IL-1β, could lead to pyroptosis-predominant uncoupling. These uncoupling preferences enable precise reactions to different stimuli of different intensities under specific conditions at the single-cell level, promoting cooperative cell and host fate decisions and participating in the pathogen "game". Appropriate decisions in terms of coupling and uncoupling are required to heal tissues and eliminate threats, and further studies exploring the inflammasome tilt toward pyroptosis or cytokine secretion may be helpful.

Resting time after phorbol 12-myristate 13-acetate in THP-1 derived macrophages provides a non-biased model for the study of NLRP3 inflammasome

Background

The activation of NLRP3 inflammasome in macrophages has been proven to play a crucial role in the development of cardiovascular diseases. THP-1 monocytes can be differentiated to macrophages by incubation with phorbol-12-myristate 13-acetate (PMA), providing a suitable model for in vitro studies. However, PMA has been shown to have effects on the levels of IL-1β, the main mediator of NLRP3 inflammasome, while the effects on the other mediators of the inflammasome have not been reported before.

Methods

THP-1 monocytes were incubated without (THP-1), with 5ng/ml PMA for 48h (PMA48h) or with 5ng/ml PMA for 48h plus 24h in fresh medium (PMArest). Morphological changes and the expression of macrophage surface markers (CD14, CD11b, CD36 and CD204) were evaluated by flow cytometry. Changes in intracellular levels of inflammasome components (NLRP3, ASC, pro-caspase-1, pro-IL1β) were analyzed by western blot and release of mature IL-1β in cell supernatant was analyzed by ELISA. ASC speck formation was determined by immunofluorescence.

Results

After 48h incubation with PMA or subsequent rest in fresh medium, cells became adherent, and the differential expression of CD36, CD11b, CD14 and CD204 compared to THP-1 cells confirmed that PMArest resemble macrophages from a molecular point of view. Changes in the levels were detected in PMA48h group for all the NLRP3-related proteins, with increase of NLRP3 and pro-IL-1β and secretion of mature IL-1β. In PMArest, no pro-IL-1β and lower amounts of mature IL-1β were detected. No ASC speck was found in PMA treated groups, but the addition of a second stimulus to PMArest resulted in ASC speck formation, together with IL-1β production, confirming the responsiveness of the model.

Conclusion

Differentiation of THP-1 with 5ng/ml PMA followed by 24h resting period provides a model that morphologically and molecularly resembles macrophages. However, even at low concentrations, PMA induces production of IL-1β. The 24h rest period provides for down-regulation of pro-IL-1β in PMArest group, without affecting its ability to respond to a second stimulus through activation of inflammasome.

Interactions between the NLRP3-Dependent IL-1β and the Type I Interferon Pathways in Human Plasmacytoid Dendritic Cells

Generally, a reciprocal antagonistic interaction exists between the antiviral type I interferon (IFN) and the antibacterial nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain containing 3 (NLRP3)-dependent IL-1β pathways that can significantly shape immune responses. Plasmacytoid dendritic cells (pDCs), as professional type I IFN-producing cells, are the major coordinators of antiviral immunity; however, their NLRP3-dependent IL-1β secretory pathway is poorly studied. Our aim was to determine the functional activity of the IL-1β pathway and its possible interaction with the type I IFN pathway in pDCs. We found that potent nuclear factor-kappa B (NF-κB) inducers promote higher levels of pro-IL-1β during priming compared to those activation signals, which mainly trigger interferon regulatory factor (IRF)-mediated type I IFN production. The generation of cleaved IL-1β requires certain secondary signals in pDCs and IFN-α or type I IFN-inducing viruses inhibit IL-1β production of pDCs, presumably by promoting the expression of various NLRP3 pathway inhibitors. In line with that, we detected significantly lower IL-1β production in pDCs of psoriasis patients with elevated IFN-α levels. Collectively, our results show that the NLRP3-dependent IL-1β secretory pathway is inducible in pDCs; however, it may only prevail under inflammatory conditions, in which the type I IFN pathway is not dominant.

Promiscuous Inflammasomes: The False Dichotomy of RNA/DNA Virus-Induced Inflammasome Activation and Pyroptosis

It is well-known that viruses activate various inflammasomes, which can initiate the programmed cell death pathway known as pyroptosis, subsequently leading to cell lysis and release of inflammatory cytokines IL-1β and IL-18. This pathway can be triggered by various sensors, including, but not limited to, NLRP3, AIM2, IFI16, RIG-I, and NLRC4. Many viruses are known either to activate or inhibit inflammasomes as a part of the innate immune response or as a mechanism of pathogenesis. Early research in the field of virus-induced pyroptosis suggested a dichotomy, with RNA viruses activating the NLRP3 inflammasome and DNA viruses activating the AIM2 inflammasome. More recent research has shown that this dichotomy may not be as distinct as once thought. It seems many viruses activate multiple inflammasome sensors. Here, we detail which viruses fit the dichotomy as well as many that appear to defy this clearly false dichotomy. It seems likely that most, if not all, viruses activate multiple inflammasome sensors, and future research should focus on expanding our understanding of inflammasome activation in a variety of tissue types as well as virus activation of multiple inflammasomes, challenging biases that stemmed from early literature in this field. Here, we review primarily research performed on human viruses but also include details regarding animal viruses whenever possible.

Insights into inflammasome regulation: cellular, molecular, and pathogenic control of inflammasome activation

Maintenance of immune homeostasis is an intricate process wherein inflammasomes play a pivotal role by contributing to innate and adaptive immune responses. Inflammasomes are ensembles of adaptor proteins that can trigger a signal following innate sensing of pathogens or non-pathogens eventuating in the inductions of IL-1β and IL-18. These inflammatory cytokines substantially influence the antigen-presenting cell's costimulatory functions and T helper cell differentiation, contributing to adaptive immunity. As acute and chronic disease conditions may accompany parallel tissue damage, we analyze the critical role of extracellular factors such as cytokines, amyloids, cholesterol crystals, etc., intracellular metabolites, and signaling molecules regulating inflammasome activation/inhibition. We develop an operative framework for inflammasome function and regulation by host cell factors and pathogens. While inflammasomes influence the innate and adaptive immune components' interplay modulating the anti-pathogen adaptive immune response, pathogens may target inflammasome inhibition as a survival strategy. As trapped between health and diseases, inflammasomes serve as promising therapeutic targets and their modus operandi serves as a scientific rationale for devising better therapeutic strategies.

The central inflammasome adaptor protein ASC activates the inflammasome after transition from a soluble to an insoluble state

Apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC) is a 22 kDa protein that functions as the central adaptor for inflammasome assembly. ASC forms insoluble specks in monocytes undergoing pyroptosis, and the polymerization of ASC provides a template of CARDs that leads to proximity-mediated autoactivation of caspase-1 in canonical inflammasomes. However, specks are insoluble protein complexes, and solubility is typically important for protein function. Therefore, we sought to define whether ASC specks comprise active inflammasome complexes or are simply the end stage of exhausted ASC polymers. Using a THP-1 cell–lysing model of caspase-1 activation that is ASC dependent, we compared caspase-1 activation induced by preassembled insoluble ASC specks and soluble monomeric forms of ASC. Unexpectedly, after controlling for the concentration dependence of ASC oligomerization, we found that only insoluble forms of ASC promoted caspase-1 autocatalysis. This link to insolubility was recapitulated with recombinant ASC. We show that purified recombinant ASC spontaneously precipitated and was functional, whereas the maltose-binding protein–ASC fusion to ASC (promoting enhanced solubility) was inactive until induced to insolubility by binding to amylose beads. This functional link to insolubility also held true for the Y146A mutation of the CARD of ASC, which avoids insolubility and caspase-1 activation. Thus, we conclude that the role of ASC insolubility in inflammasome function is inextricably linked to its pyrin domain–mediated and CARD-mediated polymerizations. These findings will support future studies into the molecular mechanisms controlling ASC solubility.

Non-Apoptotic Caspase Activity Preferentially Targets a Novel Consensus Sequence Associated With Cytoskeletal Proteins in the Developing Auditory Brainstem

The auditory brainstem relies on precise circuitry to facilitate sound source localization. In the chick, the development of this specialized circuitry requires non-apoptotic activity of caspase-3, for which we previously identified several hundred proteolytic substrates. Here we tested whether the sequence of the caspase cleavage site differentially encodes proteolytic preference in apoptotic and non-apoptotic contexts. We constructed a consensus sequence for caspase activity in the non-apoptotic chick auditory brainstem comprising the four residues N-terminal to the cleavage site: IX(G/R)D↓ where X represents no significant enrichment and ↓ represents the cleavage site. We identified GO terms significantly enriched among caspase substrates containing motifs found in the above consensus sequence. (G/R)D↓ was associated with the term “Structural Constituent of Cytoskeleton” (SCoC), suggesting that SCoC proteins may be specifically targeted by caspase activity during non-apoptotic developmental processes. To ascertain whether this consensus sequence was specific to the non-apoptotic auditory brainstem at embryonic day (E) 10, we used protein mass spectrometry of brainstems harvested at a time when auditory brainstem neurons undergo apoptotic cell death (E13). The apoptotic motif VD was significantly enriched among E13 cleavage sites, indicating that motif preference at the P2 subsite had shifted toward the canonical caspase consensus sequence. Additionally, Monte Carlo simulations revealed that only the GD motif was associated with SCoC substrates in the apoptotic auditory brainstem, indicating that GD encodes specificity for SCoC proteins in both non-apoptotic and apoptotic contexts, despite not being preferred in the latter. Finally, to identify candidate human non-apoptotic consensus sequences, we used Monte Carlo analyses to determine motifs and motif pairs associated with SCoC caspase substrates in the Degrabase, a database of cleavage sites in human apoptotic cell lines. We found 11 motifs significantly associated with SCoC proteolysis, including IXXD and GD. We employed a stepwise method to select motif pairs that optimized SCoC specificity for a given coverage of SCoC cleavage events, yielding 11 motif pairs likely to be preferred in SCoC-directed human non-apoptotic caspase consensus sequences. GD + IXXD was among these motif pairs, suggesting a conservation of non-apoptotic consensus sites among vertebrates.

Pyroptosis-inducing active caspase-1 as a genetic adjuvant in anti-cancer DNA vaccination

Pyroptosis is a recently discovered form of inflammatory programmed necrosis characterized by caspase-1-mediated and gasdermin D-dependent cell death leading to the release of pro-inflammatory cytokines such as Interleukin-1 beta (IL-1β). Here, we evaluated whether pyroptosis could be exploited in DNA vaccination by incorporating a constitutively active variant of caspase-1 to the antigen-expressing DNA. In vitro, transfection with constitutively active caspase-1 DNA induced pro-IL-1β maturation and IL-1β release as well as gasdermin D-dependent cell death. To test active caspase-1 as a genetic adjuvant for the induction of antigen-specific T cell responses, mice were vaccinated intradermally with a DNA vaccine consisting of the active caspase-1 plasmid together with a plasmid encoding an ovalbumin-derived CD8 T cell epitope. Active caspase-1 accelerated and amplified antigen-specific CD8 T cell responses when administered simultaneously with the DNA vaccine at an equimolar dose. Moreover, upon challenge with melanoma cells expressing ovalbumin, mice vaccinated with the antigen vaccine adjuvanted with active caspase-1 showed significantly better survival compared to the non-adjuvanted group. In conclusion, we have developed a novel genetic adjuvant that for the first time employs the pyroptosis pathway to improve DNA vaccination against cancer.

Upregulated Proteasome Subunits in COVID-19 Patients: A Link with Hypoxemia, Lymphopenia and Inflammation

Severe COVID-19 disease leads to hypoxemia, inflammation and lymphopenia. Viral infection induces cellular stress and causes the activation of the innate immune response. The ubiquitin-proteasome system (UPS) is highly implicated in viral immune response regulation. The main function of the proteasome is protein degradation in its active form, which recognises and binds to ubiquitylated proteins. Some proteasome subunits have been reported to be upregulated under hypoxic and hyperinflammatory conditions. Here, we conducted a prospective cohort study of COVID-19 patients (n = 44) and age-and sex-matched controls (n = 20). In this study, we suggested that hypoxia could induce the overexpression of certain genes encoding for subunits from the α and β core of the 20S proteasome and from regulatory particles (19S and 11S) in COVID-19 patients. Furthermore, the gene expression of proteasome subunits was associated with lymphocyte count reduction and positively correlated with inflammatory molecular and clinical markers. Given the importance of the proteasome in maintaining cellular homeostasis, including the regulation of the apoptotic and pyroptotic pathways, these results provide a potential link between COVID-19 complications and proteasome gene expression.

Inflammasome signaling in human placental trophoblasts regulates immune defense against Listeria monocytogenes infection

The human placenta is a dynamic organ that modulates physiological adaptations to pregnancy. To define the immunological signature of the human placenta, we performed unbiased profiling of secreted immune factors from human chorionic villi isolated from placentas at mid and late stages of pregnancy. We show that placental trophoblasts constitutively secrete the inflammasome-associated cytokines IL-1β and IL-18, which is blocked by NLRP3 inflammasome inhibitors and occurs without detectable gasdermin D cleavage. We further show that placenta-derived IL-1β primes monocytes for inflammasome induction to protect against Listeria monocytogenes infection. Last, we show that the human placenta responds to L. monocytogenes infection through additional inflammasome activation and that inhibition of this pathway sensitizes villi to infection. Our results thus identify the inflammasome as an important mechanism by which the human placenta regulates systemic and local immunity during pregnancy to defend against L. monocytogenes infection.

NLRP3 Ubiquitination-A New Approach to Target NLRP3 Inflammasome Activation

In response to diverse pathogenic and danger signals, the cytosolic activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing (3)) inflammasome complex is a critical event in the maturation and release of some inflammatory cytokines in the state of an inflammatory response. After activation of the NLRP3 inflammasome, a series of cellular events occurs, including caspase 1-mediated proteolytic cleavage and maturation of the IL-1β and IL-18, followed by pyroptotic cell death. Therefore, the NLRP3 inflammasome has become a prime target for the resolution of many inflammatory disorders. Since NLRP3 inflammasome activation can be triggered by a wide range of stimuli and the activation process occurs in a complex, it is difficult to target the NLRP3 inflammasome. During the activation process, various post-translational modifications (PTM) of the NLRP3 protein are required to form a complex with other components. The regulation of ubiquitination and deubiquitination of NLRP3 has emerged as a potential therapeutic target for NLRP3 inflammasome-associated inflammatory disorders. In this review, we discuss the ubiquitination and deubiquitination system for NLRP3 inflammasome activation and the inhibitors that can be used as potential therapeutic agents to modulate the activation of the NLRP3 inflammasome.

Immunohistochemical Study of ASC Expression and Distribution in the Hippocampus of an Aged Murine Model of Alzheimer's Disease

Neuroinflammation is involved in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease (AD), and is notably dependent on age. One important inflammatory pathway exerted by innate immune cells of the nervous system in response to danger signals is mediated by inflammasomes (IF) and leads to the generation of potent pro-inflammatory cytokines. The protein “apoptosis-associated speck-like protein containing a caspase recruitment domain” (ASC) modulates IF activation but has also other functions which are crucial in AD. We intended to characterize immunohistochemically ASC and pattern recognition receptors (PRR) of IF in the hippocampus (HP) of the transgenic mouse model Tg2576 (APP), in which amyloid-beta (Aβ) pathology is directly dependent on age. We show in old-aged APP a significant amount of ASC in microglia and astrocytes associated withAβ plaques, in the absence of PRR described by others in glial cells. In addition, APP developed foci with clusters of extracellular ASC granules not spatiallyrelated to Aβ plaques, which density correlated with the advanced age of mice and AD development. Clusters were associated withspecific astrocytes characterized by their enlarged ring-shaped process terminals, ASC content, and frequent perivascular location. Their possible implication in ASC clearance and propagation of inflammation is discussed.

Dapagliflozin, an SGLT2 inhibitor, ameliorates acetic acid-induced colitis in rats by targeting NFκB/AMPK/NLRP3 axis

The development of effective treatment strategies has been hindered by the complex pathogenesis of ulcerative colitis (UC). UC patients treated with current therapeutic approaches experienced either treatment failure or suffered excessive adverse reactions. Overactivity of NLRP3 inflammasome enhances inflammation, resulting in aggravation of colonic damage. We were interested in exploring, for the first time, the potential coloprotective effect of dapagliflozin (DPZ) on acetic acid-induced UC in rats in comparison with 5-ASA. DPZ improved histologic and macroscopic features of colon tissues and prolonged survival of UC rats. DPZ also prevented colon shortening and declined disease activity. Additionally, DPZ lessened colon tissue neutrophil content and improved antioxidant defense machinery. Further, DPZ specifically declined the colonic inflammatory marker IL-6 and upregulated the anti-inflammatory cytokine IL-10. The pyroptosis process is constrained in consequence of the repressed caspase-1 activity and caspase-1-dependent release of the bioactive cytokines IL-1β and IL-18. These protective effects might be attributed to that DPZ on the one hand, prevented the priming step (signal 1) of NLRP3 inflammasome activation as revealed by modulating NFκB/AMPK interplay and on the other hand, inhibited the activation step (signal 2) as indicated by interrupting NLRP3/caspase-1 signaling. Since DPZ was found to be safe and well tolerated by healthy volunteers with no evidence of hypoglycemia, it might show promise in the future management of UC. However, further investigations are warranted to confirm the reversal of injury and that the coloprotective effect is substantial.

Cold-inducible RNA-binding protein (CIRP) potentiates uric acid-induced IL-1β production

Background

Gout is an autoinflammatory disease driven by interleukin-1 (IL-1) induction in response to uric acid crystals. IL-1β production is dependent on inflammasome activation, which requires a priming signal, followed by an activating signal. The cold-inducible RNA-binding protein (CIRP) has been recently identified as a damage-associated molecular pattern (DAMP). In this study, we evaluated the roles of CIRP in monosodium urate (MSU)-mediated IL-1β secretion using human neutrophils.

Methods

Human neutrophils were stimulated by MSU in the presence or absence of CIRP priming to determine NLRP3 inflammasome activation and subsequent caspase-1 activation and IL-1β production. Cellular supernatants were analyzed by enzyme-linked immunosorbent assay (ELISA) to determine the presence of IL-1β or caspase-1 (p20). The cellular supernatants and lysates were also analyzed by immunoblotting using anti-cleaved IL-1β or anti-cleaved caspase-1 antibodies.

Results

Neither CIRP nor MSU stimulation alone induced sufficient IL-1β secretion from neutrophils. However, MSU stimulation induced IL-1β secretion from CIRP-primed neutrophils in a dose-dependent manner. This MSU-induced IL-1β secretion from CIRP-primed neutrophils was accompanied by the induction of cleaved IL-1β (p17), which was inhibited by the pretreatment of MCC950, a specific inhibitor for NLRP3. Furthermore, cleaved caspase-1 was induced in the cellular lysates of CIRP/MSU-treated neutrophils. Additionally, CIRP stimulation induced the protein expression of pro-IL-1β in neutrophils.

Conclusions

Our data indicate that CIRP, an endogenous stress molecule, triggers uric acid-induced mature IL-1β induction as a priming stimulus for NLRP3 inflammasome in human neutrophils. We propose that CIRP acts as an important proinflammatory stimulant that primes and activates inflammasome and pro-IL-1β processing in response to uric acid in innate immune cells.

MDM2 inhibition improves cisplatin-induced renal injury in mice via inactivation of Notch/hes1 signaling pathway

OBJECTIVE

To explore the potential function of MDM2-mediated Notch/hes1 signaling pathway in cisplatin-induced renal injury.

METHODS

The acute renal injury models of mice after intraperitoneal injection of cisplatin in vivo, and the apoptotic models of human renal tubular epithelial (HK-2) cells induced by cisplatin in vitro, were conducted respectively. The renal function-related parameters were measured. The renal tissue pathological changes and apoptosis were observed by PAS staining and TUNEL staining, respectively. Cell viability and apoptosis were detected by MTT and flow cytometry. Notch/hes1 pathway-related proteins were tested by Western blotting.

RESULTS

After mice injected by cisplatin, the levels of Cr, BUN, urine cystatin C, urine NGAL and urine ACR were increased and GFR was decreased with the elevation of renal tubular injury scores, the upregulation of the expressions of MDM2, N1ICD, Hes1 and Cleaved caspase-3, as well as the enhancement of cell apoptosis accompanying decreased ratio of Bcl-2/Bax. However, these cisplatin-induced renal injuries of mice have been improved by MDM2 inhibition. Besides, the declined viability, increased cytotoxicity, and enhanced apoptosis were observed in cisplatin-induced HK-2 cells, with the activated Notch/hes1 pathway. Notably, the phenomenon was alleviated in cisplatin-induced HK-2 cells transfected with MDM2 shRNA, but was severer in those co-treated with AdMDM2. Moreover, Notch1 siRNA can reverse the injury of AdMDM2 on HK-2 cells.

CONCLUSION

Inhibiting MDM2 could reduce cell apoptosis through blocking Notch/hes1 signaling pathway, thus alleviating the acute renal injury caused by cisplatin.

The intricate biophysical puzzle of caspase-1 activation

This review takes a closer look at the structural components of the molecules involved in the processes leading to caspase-1 activation. Interleukins 1β and 18 (IL-1β, IL-18) are well-known proinflammatory cytokines that are produced following cleavage of their respective precursor proteins by the cysteine protease caspase-1. Active caspase-1 is the final step of the NLRP3 inflammasome, a three-protein intracellular complex involved in inflammation and induction of pyroptosis (a proinflammatory cell-death process). NLRP3 activators facilitate assembly of the inflammasome complex and subsequent activation of caspase-1 by autoproteolysis. However, the definitive structural components of active caspase-1 are still unclear and new data add to the complexity of this process. This review outlines the historical and recent findings that provide supporting evidence for the structural aspects of caspase-1 autoproteolysis and activation.

Differences in immune components of blood, spleen and head kidney between diploid and auto- and allotriploid Salmonidae

Immune components were investigated in peripheral blood and in spleen and head kidney of autotriploid Salmo trutta f. lacustris, Salvelinus fontinalis, and Salvelinus umbla, and of allotriploid hybrids of S. trutta f. lacustris x Onchorynchus mykiss and S. fontinalis x O. mykiss in comparison to their diploid parents. In peripheral blood the number of lymphocytes was reduced in all investigated autotriploids and in the allotriploid S. trutta f. lacustris x O.mykiss, and the numbers of thrombocytes in autotriploid S. trutta f. lacustris and in both allotriploids. Alternative pathway of complement activity and immunoglobulin concentration were significantly decreased in all investigated auto- and allotriploids, lysozyme activity in autotriploid S. fontinalis and in both allotriploids. In the spleen of the 3 autotriploids the number of erythrocytes was increased, while the number of lymphoid precursor cells was decreased. In their head kidney the erythrocytes numbers were decreased and the numbers of erythropoietic precursor cells and the melanomacrophage centers were increased. Contrary, cytology of spleen and head kidney of the two allotriploid hybrids was similar to diploid controls. Caspase 1, caspase 6, lysozyme, and acid phosphatase activity and immunoglobulin concentration of spleen and head kidney showed specific changes which were related to cytological results. These data indicate alterations in immune system and in lymphoid organs of auto- and allotriploid Salmonidae.

Omega-3 Docosahexaenoic Acid (DHA) Impedes Silica-Induced Macrophage Corpse Accumulation by Attenuating Cell Death and Potentiating Efferocytosis

Airway exposure of lupus-prone NZBWF1 mice to crystalline silica (cSiO₂), a known trigger of human autoimmune disease, elicits sterile inflammation and alveolar macrophage death in the lung that, in turn, induces early autoimmune onset and accelerates lupus progression to fatal glomerulonephritis. Dietary supplementation with docosahexaenoic acid (DHA), a marine ω-3 polyunsaturated fatty acid (PUFA), markedly ameliorates cSiO₂-triggered pulmonary, systemic, and renal manifestations of lupus. Here, we tested the hypothesis that DHA influences both cSiO₂-induced death and efferocytotic clearance of resultant cell corpses using three murine macrophage models: (i) primary alveolar macrophages (AM) isolated from NZBWF1 mice; (ii) self-renewing AM-like Max Planck Institute (MPI) cells isolated from fetuses of C57BL/6 mice, and (iii) RAW 264.7 murine macrophages, a virus-transformed cell line derived from BALB/c mice stably transfected with the inflammasome adaptor protein ASC (RAW-ASC). Incubation with cSiO₂ at 25 and 50 μg/ml for 6 h was found to dose-dependently induce cell death (p < 0.05) in all three models as determined by both acridine orange/propidium iodide staining and release of lactate dehydrogenase into cell culture supernatant. Pre-incubation with DHA at a physiologically relevant concentration (25 μM) significantly reduced cSiO₂-induced death (p < 0.05) in all three models. Cell death induction by cSiO₂ alone and its suppression by DHA were primarily associated with caspase-3/7 activation, suggestive of apoptosis, in AM, MPI, and RAW-ASC cells. Fluorescence microscopy revealed that all three macrophage models were similarly capable of efferocytosing RAW-ASC target cell corpses. Furthermore, MPI effector cells could likewise engulf RAW-ASC target cell corpses elicited by treatment with staurosporine (apoptosis), LPS, and nigericin (pyroptosis), or cSiO₂. Pre-incubation of RAW-ASC target cells with 25 μM DHA prior to death induced by these agents significantly enhanced their efferocytosis (p < 0.05) by MPI effector cells. In contrast, pre-incubating MPI effector cells with DHA did not affect engulfment of RAW-ASC target cells pre-incubated with vehicle. Taken together, these findings indicate that DHA at a physiologically relevant concentration was capable of attenuating macrophage death and could potentiate efferocytosis, with the net effect of reducing accumulation of cell corpses capable of eliciting autoimmunity.

Heat-Killed Fusobacterium nucleatum Triggers Varying Heme-Related Inflammatory and Stress Responses Depending on Primary Human Respiratory Epithelial Cell Type

Fusobacterium nucleatum (Fn) is generally an opportunistic oral pathogen that adheres to mammalian mucosal sites, triggering a host inflammatory response. In general, Fn is normally found within the human oral cavity; however, it was previously reported that Fn is a risk factor for certain respiratory diseases. Surprisingly, this was never fully elucidated. Here, we investigated the virulence potential of heat-killed Fn on primary human tracheal, bronchial, and alveolar epithelial cells. In this study, we measured the secretion of inflammatory- (IL-8 and IL-6), stress- (total heme and hydrogen peroxide), and cell death-related (caspase-1 and caspase-3) signals. We established that the inflammatory response mechanism varies in each epithelial cell type: (1) along tracheal cells, possible Fn adherence would trigger increased heme secretion and regulated inflammatory response; (2) along bronchial cells, potential Fn adherence would simultaneously initiate an increase in secreted H₂O₂ and inflammatory response (ascribable to decreased secreted heme amounts); and (3) along alveolar cells, putative Fn adherence would instigate the increased secretion of inflammatory responses attributable to a decrease in secreted heme levels. Moreover, regardless of the epithelial cell-specific inflammatory mechanism, we believe these are putative, not harmful. Taken together, we propose that any potential Fn-driven inflammation along the respiratory tract would be initiated by differing epithelial cell-specific inflammatory mechanisms that are collectively dependent on secreted heme.

Peripheral innate immune and bacterial signals relate to clinical heterogeneity in Parkinson's disease

The innate immune system is implicated in Parkinson's disease (PD), but peripheral in-vivo clinical evidence of the components and driving mechanisms involved and their relationship with clinical heterogeneity and progression to dementia remain poorly explored. We examined changes in peripheral innate immune-related markers in PD cases (n = 41) stratified according to risk of developing early dementia. 'Higher Risk'(HR) (n = 23) and 'Lower Risk' (LR) (n = 18) groups were defined according to neuropsychological predictors and MAPT H1/H2 genotype, and compared to age, gender and genotype-matched controls. Monocyte subsets and expression of key surface markers were measured using flow cytometry. Serum markers including alpha-synuclein, inflammasome-related caspase-1 and bacterial translocation-related endotoxin were measured using quantitative immuno-based assays. Specific markers were further investigated using monocyte assays and validated in plasma samples from a larger incident PD cohort (n = 95). We found that classical monocyte frequency was elevated in PD cases compared to controls, driven predominantly by the HR group, in whom Toll-Like Receptor (TLR)4+ monocytes and monocyte Triggering Receptor Expressed on Myeloid cells-2 (TREM2) expression were also increased. Monocyte Human Leukocyte Antigen (HLA)-DR expression correlated with clinical variables, with lower levels associated with worse cognitive/motor performance. Notably, monocyte changes were accompanied by elevated serum bacterial endotoxin, again predominantly in the HR group. Serum alpha-synuclein and inflammasome-related caspase-1 were decreased in PD cases compared to controls regardless of group, with decreased monocyte alpha-synuclein secretion in HR cases. Further, alpha-synuclein and caspase-1 correlated positively in serum and monocyte lysates, and in plasma from the larger cohort, though no associations were seen with baseline or 36-month longitudinal clinical data. Principal Components Analysis of all monocyte and significant serum markers indicated 3 major components. Component 1 (alpha-synuclein, caspase-1, TLR2+ monocytes) differentiated PD cases and controls in both groups, while Component 2 (endotoxin, monocyte TREM2, alpha-synuclein) did so predominantly in the HR group. Component 3 (classical monocytes, alpha-synuclein) also differentiated cases and controls overall in both groups. These findings demonstrate that systemic innate immune changes are present in PD and are greatest in those at higher risk of rapid progression to dementia. Markers associated with PD per-se (alpha-synuclein, caspase-1), differ from those related to cognitive progression and clinical heterogeneity (endotoxin, TREM2, TLR4, classical monocytes, HLA-DR), with mechanistic and therapeutic implications. Alpha-synuclein and caspase-1 are associated, suggesting inflammasome involvement common to all PD, while bacterial translocation associated changes may contribute towards progression to Parkinson's dementia. Additionally, HLA-DR-associated variations in antigen presentation/clearance may modulate existing clinical disease.

Uric acid-mediated inflammasome activation in IL-6 primed innate immune cells is regulated by baricitinib

OBJECTIVES

Gout is an inflammatory arthropathy caused by the deposition of monosodium urate (MSU). The synthesis and release of IL-1β is crucial for MSU-induced synovial inflammation. The aim of the present study was to investigate the mechanism of MSU crystal-induced autoinflammatory processes.

METHODS

In vitro studies were used to evaluate the role of IL-6 in inflammasome activation in human neutrophils cultured with MSU crystals. Human neutrophils were stimulated with MSU in the presence or absence of IL-6 priming to determine NLRP3 inflammasome activation and subsequent cleaved caspase-1 induction or IL-1β production.

RESULTS

IL-6 or MSU stimulation alone did not result in the efficient IL-1β production from human neutrophils. However, MSU stimulation induced marked IL-1β production from IL-6-primed neutrophils. Pretreatment with baricitinib, which blocks IL-6 receptor signaling, prevented MSU-induced cleaved caspase-1 or IL-1β induction in IL-6-primed neutrophils. Tocilizumab pretreatment also inhibited MSU-mediated IL-1β production from IL-6-primed neutrophils.

CONCLUSION

Priming of human neutrophils with IL-6 promotes uric acid-mediated IL-1β secretion in the absence of microbial stimulation. These results suggest that an endogenous cytokine, IL-6, is involved in MSU-mediated NLRP3 inflammasome activation and subsequent IL-1β production from innate immune cells and has a crucial role in MSU crystal-induced synovial inflammation. These findings provide insights into uric acid-mediated autoinflammation in the innate immune system.

Inflammasome Adaptor ASC Is Highly Elevated in Lung Over Plasma and Relates to Inflammation and Lung Diffusion in the Absence of Speck Formation

Rationale: Caspase-1 is a zymogen whose activation predominantly depends upon the assembly of ASC monomers into insoluble prion-like polymers (specks). ASC polymers support caspase-1 dimer formation inducing a proximity mediated auto-activation of caspase-1. Therefore, the amount and nature of ASC monomers and polymers in lung bronchoalveolar lavage fluid (BALF) might serve as a marker of lung inflammasome activity.

Objectives: To determine whether lung ASC concentrations or oligomerization status predicts lung function or activity of lung inflammation.

Methods: BALF ASC amount and oligomerization status was studied in three distinct cohorts: (1) young healthy non-smokers, vapers and smokers; (2) healthy HIV+ smokers who underwent detailed lung function studies; and (3) hospitalized patients with suspected pneumonia. We quantified cell free BALF ASC levels by ELISA and immunoblot. Oligomers (i.e., ASC specks) were identified by chemical crosslinking and ability to sediment with centrifugation.

Measurement and Main Results: ASC levels are significantly higher in lung lining fluid than in plasma as well as higher in smoker lungs compared to non-smoker lungs. In this context, ASC levels correlate with macrophage numbers, smoking intensity and loss of lung diffusion capacity in a well-characterized cohort of healthy HIV+ smokers. However, only monomeric ASC was found in our BALF samples from all subjects, including patients with lung infections.

Conclusions: Even though, most, if not all, extracellular ASC in BALF exists in the soluble, monomeric form, monomeric ASC concentrations still reflect the inflammatory status of the lung microenvironment and correlate with loss of lung function.

Dopamine activates NF-κB and primes the NLRP3 inflammasome in primary human macrophages

Induction of innate immune genes in the brain is thought to be a major factor in the development of addiction to substances of abuse. As the major component of the innate immune system in the brain, aberrant activation of myeloid cells such as macrophages and microglia due to substance use may mediate neuroinflammation and contribute to the development of addiction. All addictive drugs modulate the dopaminergic system and our previous studies have identified dopamine as a pro-inflammatory modulator of macrophage function. However, the mechanism that mediates this effect is currently unknown. Inflammatory activation of macrophages and induction of cytokine production is often mediated by the transcription factor NF-κB, and prior studies have shown that dopamine can modulate NF-κB activity in T-cells and other non-immune cell lines. Here we demonstrated that dopamine can activate NF-κB in primary human macrophages, resulting in the induction of its downstream targets including the NLRP3 inflammasome and the inflammatory cytokine IL-1β. These data also indicate that dopamine primes but does not activate the NLRP3 inflammasome in human macrophages. Activation of NF-κB was required for dopamine-mediated increases in IL-1β, as an inhibitor of NF-κB was able to abrogate the effects of dopamine on production of these cytokines. Connecting an increase in extracellular dopamine to NF-κB activation and inflammation suggests specific intracellular targets that could be used to ameliorate the inflammatory impact of dopamine in neuroinflammatory conditions associated with myeloid cell activation such as addiction.

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Dopamine exposure primes, but does not activate the NLRP3 inflammasome.

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Inflammasome priming can be mediated, at least partially, by a dopamine-induced increase in the activation and nuclear translocation of NF-κB in primary human macrophages.

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Dopamine additively increases the impact of cytomegalovirus on NF-κB activation in macrophages.

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Dopamine priming increases IL-1β release in response to inflammasome activation.

Adenovirus VA RNAI Blocks ASC Oligomerization and Inhibits NLRP3 Inflammasome Activation

Virus infected immune cells can rapidly respond to the invader by activating the inflammasome and as a consequence release proinflammatory cytokines and eventually die by pyroptosis. In human adenovirus-5 (Ad5) infected THP-1 cells, inhibition of NLRP3 inflammasome activation was demonstrated by a decreased secretion of HMGB1 and matured forms of caspase-1and IL-1ß. An Ad5 mutant virus defective in expression of the non-coding VA RNAI failed to inhibit the NLRP3 inflammasome and in addition displayed formation of ASC specks and increased cell lysis. Importantly, in vitro synthesized VA RNAI was able to inhibit the NLRP3 inflammasome activity in THP-1 cells in the absence of an Ad5 infection, suggesting that VA RNAI binding to PKR and blocking its function is sufficient for inhibition of the NLRP3 inflammasome. Although the inhibition of NLRP3 inflammasome activation required the phylogenetically conserved base paired tetranucleotide sequence in the central stem of VA RNAI, we demonstrate that PKR binding to VA RNAI primarily protected the apical stem, but not the tetranucleotide sequence itself. VA RNAI did not influence the interaction between PKR and NLRP3. In contrast, we describe a novel interaction between PKR and ASC and further show that VA RNAI inhibited ASC phosphorylation and oligomerization. Collectively, our results indicate a novel role for Ad5 VA RNAI as an inhibitor of NLRP3 inflammasome activation by targeting the cellular pro-inflammatory protein PKR.

Hydroxychloroquine inhibits IL-1β production from amyloid-stimulated human neutrophils

BACKGROUND

Hydroxychloroquine (HCQ) is used for the treatment of patients with rheumatic diseases. We tested the hypothesis that HCQ affects the NLRP3 inflammasome, which is involved in autoinflammation.

METHODS

Human neutrophils were stimulated with serum amyloid A (SAA) in vitro and measured for IL-1β and caspase-1 (p20) secretion by ELISA. Pro-IL-1β mRNA expression in human neutrophils was quantified by real-time RT-PCR.

RESULTS

SAA stimulation induced significant production of IL-1β in human neutrophils. SAA stimulation also induced NF-κB activation, pro-IL-1β mRNA expression, and NLRP3 protein expression in human neutrophils. HCQ pretreatment significantly inhibited the SAA-induced IL-1β production in human neutrophils, but did not affect the SAA-induced NF-κB activation, pro-IL-1β mRNA expression, and NLRP3 protein expression. Furthermore, SAA stimulation induced cleaved caspase-1 (p20) secretion from human neutrophils, and this release was suppressed by HCQ pretreatment.

CONCLUSIONS

Treatment with HCQ was associated with impaired production of IL-1β in SAA-stimulated human neutrophils without affecting the priming process of the NLRP3 inflammasome such as pro-IL-1β or NLRP3 induction. These findings suggest that HCQ affects the NLRP3 activation process, resulting in the impaired IL-1β production in human neutrophils, as representative innate immune cells.

The in vitro Mycobacterium bovis BCG Moreau infection of human monocytes that induces Caspase-1 expression, release and dependent cell death is mostly reliant upon cell integrity

Background

Caused by Mycobacterium tuberculosis, tuberculosis (TB) is an extremely contagious disease predominantly affecting the lungs. TB is found worldwide and has a major impact on public health safety primarily due to its high mortality rate. Applied for over a hundred years as a preventive measure, Mycobacterium bovis BCG remains the only available TB vaccine. Only one seminal study about the apoptotic pathways induced by this vaccine in the monocytic lineage of the host cell has found the effects of BCG on regulation of apoptosis. The aim of this study was to explore beyond that pioneer study the pathway related to the in vitro cell-death pattern and the inflammatory response to the BCG vaccine in human monocytes.

Methods

Cohorts of HIV-negative volunteers were enrolled: adult Healthy Donors (HD) and neonates’ Umbilical Cord Blood (UCB) individuals. Host mononuclear cells were infected with the M. bovis Moreau strain of BCG vaccine at 16, 24, 48, and 72 h. The Real-Time RT-PCR for TRADD, Bcl-2, and Caspases-1 and -3 were performed, and supernatants were assayed in parallel for Caspase-1, NLRP3, HO-1, and IL-1β levels whereas caspases were assessed intracellularly. The effect of a BCG infection in monocytes was characterized via a metabolic activity assay by LDH release profiles.

Results

Overall, the BCG vaccine induced significantly higher Caspase-1 and Bcl-2 mRNA levels in both the HD and UCB groups (p-value ≤0.05). In addition, a significant increase solely in Caspase-1 protein levels was also noted in both HD and UCB (p-value ≤0.05) notwithstanding the absence of any damaged cell membranes.

Conclusions

Our data directly corroborate other findings showing that BCG Moreau led to an increased secretion of IL-1β but not IL-18, two Caspase-1-activated cytokines, and are also in support of the model that the BCG Moreau infection of human mononuclear cells may induce a cell-death pattern involving Caspase-1 activation.

Electronic supplementary material

The online version of this article (10.1186/s12950-019-0223-1) contains supplementary material, which is available to authorized users.

Francisella induced microparticulate caspase-1/gasdermin-D activation is regulated by NLRP3 independent of Pyrin

Although the study of pathogen sensing by host defense systems continues to uncover a role for inflammasome components specific to particular pathogens, gaps remain in our knowledge. After internalization, Francisella escapes from the phagosome in mononuclear cells and is thought to be detected by intracellular pathogen-response-receptors pyrin and Aim2 in human and murine models, respectively. However, it remains controversial as to the role of pyrin in detecting Francisella. Our current work aims to study the contribution of inflammasome sensor, Pyrin in regulating microparticulate caspase-1/GSDM-D activation by Francisella. Our findings suggest that NLRP3 is central to the activation/release of active caspase-1/GSDM-D encapsulated in microparticles (MP) by Francisella. We also provide evidence that this regulation is independent of pyrin, implicated in sensing cytosolic Francisella in NLRP3-/- conditions where endogenous Pyrin is present. Absence of NLRP3 completely abrogated Francisella mediated MP caspase-1/GSDM-D activation and release both before and after internalization of the pathogen. However, deletion of pyrin not only enhanced both LPS and Francisella mediated MP active caspase-1/GSDM-D release, but pyrin overexpression resulted in a reduction of inflammasome activation and release; suggesting an inhibitory role of pyrin in LPS and Francisella mediated MP responses. This NLRP3 dependence and inhibitory effect of pyrin correlated with cytokine release as well. These observations also correlated with MPs ability to induce cell death; as LPS and Francisella-induced MPs from pyrin-deficient cells were more potent than wild-type monocytes whereas, NLRP3-/- MPs failed to induce cell death. Taken together, we report that NLPR3 not only mediates Francisella induced cytokine responses, but is also critical for cytokine-independent microparticle-induced inflammasome activation and endothelial cell injury independent of pyrin.

Surface modification of polymer nanoparticles with native albumin for enhancing drug delivery to solid tumors

Albumin is a promising surface modifier of nanoparticulate drug delivery systems. Serving as a dysopsonin, albumin can protect circulating nanoparticles (NPs) from the recognition and clearance by the mononuclear phagocytic system (MPS). Albumin may also help transport the NPs to solid tumors based on the increased consumption by cancer cells and interactions with the tumor microenvironment. Several studies have explored the benefits of surface-bound albumin to enhance NP delivery to tumors. However, it remains unknown how the surface modification process affects the conformation of albumin and the performance of the albumin-modified NPs. We use three different surface modification methods including two prevalent approaches (physisorption and interfacial embedding) and a new method based on dopamine polymerization to modify the surface of poly(lactic-co-glycolic acid) NPs with albumin and compare the extent of albumin binding, conformation of the surface-bound albumin, and biological performances of the albumin-coated NPs. We find that the dopamine polymerization method preserves the albumin structure, forming a surface layer that facilitates NP transport and drug delivery into tumors via the interaction with albumin-binding proteins. In contrast, the interfacial embedding method creates NPs with denatured albumin that offers no particular benefit to the interaction with cancer cells but rather promotes the MPS uptake via direct and indirect interactions with scavenger receptor A. This study demonstrates that the surface-bound albumin can bring distinct effects according to the way they interact with NP surface and thus needs to be controlled in order to achieve favorable therapeutic outcomes.

Tofacitinib inhibits granulocyte-macrophage colony-stimulating factor-induced NLRP3 inflammasome activation in human neutrophils

Background

Granulocyte–macrophage colony-stimulating factor (GM-CSF) has emerged as a crucial cytokine that activates myeloid cells to initiate tissue inflammation. However, the molecular actions of GM-CSF against innate immunity are still poorly characterized. Here, we investigated the in vitro effects of GM-CSF on the activation of human myeloid lineages, neutrophils, and the underlying intracellular signaling mechanism, including inflammasome activation.

Methods

Human neutrophils were stimulated with GM-CSF in the presence or absence of tofacitinib. The cellular supernatants were analyzed for interleukin-1 beta (IL-1β) and caspase-1 by enzyme-linked immunosorbent assay (ELISA) methods. Pro-IL-1β mRNA expressions in human neutrophils were analyzed by real-time polymerase chain reaction. Protein phosphorylation of neutrophils was assessed by Western blot using phospho-specific antibodies.

Results

Stimulation with GM-CSF alone, but not tumor necrosis factor-alpha, was shown to increase the release of IL-1β and cleaved caspase-1 (p20) from human neutrophils. Tofacitinib, which inhibits GM-CSF–induced Janus kinase 2 (Jak2)-mediated signal transduction, completely abrogated GM-CSF–induced IL-1β and caspase-1 (p20) secretion from neutrophils. GM-CSF stimulation also induced pro-IL-1β mRNA expression in neutrophils and induced NLR family pyrin domain-containing 3 (NLRP3) protein expression. Although tofacitinib pretreatment marginally inhibited GM-CSF–induced pro-IL-1β mRNA expression, tofacitinib completely abrogated NLRP3 protein expression in neutrophils.

Conclusions

These results indicate that GM-CSF signaling induces NLRP3 expression and subsequent IL-1β production by affecting neutrophils, which may cause the activation of innate immunity. Therefore, GM-CSF is a key regulator of the NLRP3 inflammasome and IL-1β production by activating innate immune cells. This process can be blocked by tofacitinib, which interferes with JAK/STAT signaling pathways.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1685-x) contains supplementary material, which is available to authorized users.

Effects of metal ions on caspase-1 activation and interleukin-1β release in murine bone marrow-derived macrophages

Ions released from metal implants have been associated with adverse tissue reactions and are therefore a major concern. Studies with macrophages have shown that cobalt, chromium, and nickel ions can activate the NLRP3 inflammasome, a multiprotein complex responsible for the activation of caspase-1 (a proteolytic enzyme converting pro-interleukin [IL]-1β to mature IL-1β). However, the mechanism(s) of inflammasome activation by metal ions remain largely unknown. The objectives of the present study were to determine if, in macrophages: 1. caspase-1 activation and IL-1β release induced by metal ions are oxidative stress-dependent; and 2. IL-1β release induced by metal ions is NF-κB signaling pathway-dependent. Lipopolysaccharide (LPS)-primed murine bone marrow-derived macrophages (BMDM) were exposed to Co2+ (6-48 ppm), Cr3+ (100-500 ppm), or Ni2+ (12-96 ppm), in the presence or absence of a caspase-1 inhibitor (Z-WEHD-FMK), an antioxidant (L-ascorbic acid [L-AA]), or an NF-κB inhibitor (JSH-23). Culture supernatants were analyzed for caspase-1 by western blotting and/or IL-1β release by ELISA. Immunoblotting revealed the presence of caspase-1 (p20 subunit) in supernatants of BMDM incubated with Cr3+, but not with Ni2+ or Co2+. When L-AA (2 mM) was present with Cr3+, the caspase-1 p20 subunit was undetectable and IL-1β release decreased down to the level of the negative control, thereby demonstrating that caspase-1 activation and IL-1β release induced by Cr3+ was oxidative stress-dependent. ELISA demonstrated that Cr3+ induced the highest release of IL-1β, while Co2+ had no or limited effects. In the presence of Ni2+, the addition of L-AA (2 mM) also decreased IL-1β release, below the level of the negative control, suggesting that IL-1β release induced by Ni2+ was also oxidative stress-dependent. Finally, when present during both priming with LPS and activation with Cr3+, JSH-23 blocked IL-1β release, demonstrating NF-κB involvement. Overall, this study showed that while both Cr3+ and Ni2+ may be inducing inflammasome activation, Cr3+ is likely a more potent activator, acting through oxidative stress and the NF-κB signaling pathway.

Caspase-1-associated immune activation in an accelerated SIV-infected rhesus macaque model

In the antiretroviral therapy (ART) era, chronic HIV infection is primarily associated with chronic inflammation driving comorbidities such as cardiovascular disease and neurocognitive impairment. Caspase-1 activation in leukocytes has been documented in HIV infection; however, whether caspase-1 activation and the downstream pro-inflammatory cytokines interleukin-1beta (IL-1β) and interleukin-18 (IL-18) contribute to chronic inflammation in HIV comorbidities remains undetermined. The relationship between the caspase-1 cascade and persistent inflammation in HIV has not been investigated. Here, we used an accelerated simian immunodeficiency virus (SIV)-infected rhesus macaque model with or without ART to investigate the dynamics of caspase-1 and immune cell activation before infection, 21 days post infection (dpi), and necropsy. Caspase-1, IL-18, IL-1β, and immune markers were measured both in the circulation and lymphoid tissues. We found a significant increase in caspase-1 and IL-18 in SIV infection that positively correlated with inflammatory monocytes and negatively correlated with CD4⁺ T cell counts. ART attenuated these effects at necropsy in the circulation. Further, lymph nodes from SIV+ or SIV+ART animals had increased activation of caspase-1 and potential upstream priming of the NF-κB pathway, indicating that tissue-specific immune activation persists with ART. Together, these results shed light on the interconnectedness of the caspase-1 pathway and peripheral immune activation and further indicate that ART is not sufficient for suppressing inflammation. The caspase-1 pathway may provide novel therapeutic targets to improve HIV-associated comorbidities and health outcomes in the context of viral suppression.

Complement Receptor 3-Mediated Inhibition of Inflammasome Priming by Ras GTPase-Activating Protein During Francisella tularensis Phagocytosis by Human Mononuclear Phagocytes

Francisella tularensis is a remarkably infectious facultative intracellular bacterium of macrophages that causes tularemia. Early evasion of host immune responses contributes to the success of F. tularensis as a pathogen. F. tularensis entry into human monocytes and macrophages is mediated by the major phagocytic receptor, complement receptor 3 (CR3, CD11b/CD18). We recently determined that despite a significant increase in macrophage uptake following C3 opsonization of the virulent Type A F. tularensis spp. tularensis Schu S4, this phagocytic pathway results in limited pro-inflammatory cytokine production. Notably, MAP kinase/ERK activation is suppressed immediately during C3-opsonized Schu S4-CR3 phagocytosis. A mathematical model of CR3-TLR2 crosstalk predicted early involvement of Ras GTPase-activating protein (RasGAP) in immune suppression by CR3. Here, we link CR3-mediated uptake of opsonized Schu S4 by human monocytes and macrophages with inhibition of early signal 1 inflammasome activation, evidenced by limited caspase-1 cleavage and IL-18 release. This inhibition is due to increased RasGAP activity, leading to a reduction in the Ras-ERK signaling cascade upstream of the early inflammasome activation event. Thus, our data uncover a novel signaling pathway mediated by CR3 following engagement of opsonized virulent F. tularensis to limit inflammasome activation in human phagocytic cells, thereby contributing to evasion of the host innate immune system.

Calcium phosphate particles stimulate interleukin-1β release from human vascular smooth muscle cells: A role for spleen tyrosine kinase and exosome release

AIMS

Calcium phosphate (CaP) particle deposits are found in several inflammatory diseases including atherosclerosis and osteoarthritis. CaP, and other forms of crystals and particles, can promote inflammasome formation in macrophages leading to caspase-1 activation and secretion of mature interleukin-1β (IL-1β). Given the close association of small CaP particles with vascular smooth muscle cells (VSMCs) in atherosclerotic fibrous caps, we aimed to determine if CaP particles affected pro-inflammatory signalling in human VSMCs.

METHODS AND RESULTS

Using ELISA to measure IL-1β release from VSMCs, we demonstrated that CaP particles stimulated IL-1β release from proliferating and senescent human VSMCs, but with substantially greater IL-1β release from senescent cells; this required caspase-1 activity but not LPS-priming of cells. Potential inflammasome agonists including ATP, nigericin and monosodium urate crystals did not stimulate IL-1β release from VSMCs. Western blot analysis demonstrated that CaP particles induced rapid activation of spleen tyrosine kinase (SYK) (increased phospho-Y525/526). The SYK inhibitor R406 reduced IL-1β release and caspase-1 activation in CaP particle-treated VSMCs, indicating that SYK activation occurs upstream of and is required for caspase-1 activation. In addition, IL-1β and caspase-1 colocalised in intracellular endosome-like vesicles and we detected IL-1β in exosomes isolated from VSMC media. Furthermore, CaP particle treatment stimulated exosome secretion by VSMCs in a SYK-dependent manner, while the exosome-release inhibitor spiroepoxide reduced IL-1β release.

CONCLUSIONS

CaP particles stimulate SYK and caspase-1 activation in VSMCs, leading to the release of IL-1β, at least in part via exosomes. These novel findings in human VSMCs highlight the pro-inflammatory and pro-calcific potential of microcalcification.

Identification of an Evolutionarily Conserved Ankyrin Domain-Containing Protein, Caiap, Which Regulates Inflammasome-Dependent Resistance to Bacterial Infection

Many proteins contain tandemly repeated modules of several amino acids, which act as the building blocks that form the underlying architecture of a specific protein-binding interface. Among these motifs and one of the most frequently observed is ankyrin repeats (ANK), which consist of 33 amino acid residues that are highly conserved. ANK domains span a wide range of functions, including protein–protein interactions, such as the recruitment of substrate to the catalytic domain of an enzyme, or the assembly of stable multiprotein complexes. Here, we report the identification of an evolutionarily conserved protein, that we term Caiap (from CARD- and ANK-containing Inflammasome Adaptor Protein), which has an N-terminal CARD domain and 16 C-terminal ANK domains and is required for the inflammasome-dependent resistance to Salmonella Typhimurium in zebrafish. Intriguingly, Caiap is highly conserved from cartilaginous fish to marsupials but is absent in placental mammals. Mechanistically, Caiap acts downstream flagellin and interacts with catalytic active Caspa, the functional homolog of mammalian caspase-1, through its ANK domain, while its CARD domain promotes its self-oligomerization. Our results therefore point to ANK domain-containing proteins as key inflammasome adaptors required for the stabilization of active caspase-1 in functionally stable, high molecular weight complexes.

A bioluminescent caspase-1 activity assay rapidly monitors inflammasome activation in cells

Inflammasomes are protein complexes induced by diverse inflammatory stimuli that activate caspase-1, resulting in the processing and release of cytokines, IL-1β and IL-18, and pyroptosis, an immunogenic form of cell death. To provide a homogeneous method for detecting caspase-1 activity, we developed a bioluminescent, plate-based assay that combines a substrate, Z-WEHD-aminoluciferin, with a thermostable luciferase in an optimized lytic reagent added directly to cultured cells. Assay specificity for caspase-1 is conferred by inclusion of a proteasome inhibitor in the lytic reagent and by use of a caspase-1 inhibitor to confirm activity. This approach enables a specific and rapid determination of caspase-1 activation. Caspase-1 activity is stable in the reagent thereby providing assay convenience and flexibility. Using this assay system, caspase-1 activation has been determined in THP-1 cells following treatment with α-hemolysin, LPS, nigericin, gramicidin, MSU, R848, Pam3CSK4, and flagellin. Caspase-1 activation has also been demonstrated in treated J774A.1 mouse macrophages, bone marrow-derived macrophages (BMDMs) from mice, as well as in human primary monocytes. Caspase-1 activity was not detected in treated BMDMs derived from Casp1^-/- mice, further confirming the specificity of the assay. Caspase-1 activity can be measured directly in cultured cells using the lytic reagent, or caspase-1 activity released into medium can be monitored by assay of transferred supernatant. The caspase-1 assay can be multiplexed with other assays to monitor additional parameters from the same cells, such as IL-1β release or cell death. The caspase-1 assay in combination with a sensitive real-time monitor of cell death allows one to accurately establish pyroptosis. This assay system provides a rapid, convenient, and flexible method to specifically and quantitatively monitor caspase-1 activation in cells in a plate-based format. This will allow a more efficient and effective assessment of inflammasome activation as well as enable high-throughput screening for inflammasome modulators.