IL-1 receptor antagonist ameliorates inflammasome-dependent inflammation in murine and human cystic fibrosis

Cutaneous manifestations of cystic fibrosis

Cystic fibrosis (CF) is caused by a mutation in the Cystic fibrosis transmembrane conductance regulator (CFTR) gene, and features recurrent sinus and pulmonary infections, steatorrhea, and malnutrition. CF is associated with diverse cutaneous manifestations, including transient reactive papulotranslucent acrokeratoderma of the palms, nutrient deficiency dermatoses, and vasculitis. Rarely these are presenting symptoms of CF, prior to pulmonary or gastrointestinal sequelae. Cutaneous drug eruptions are also highly common in patients with CF (PwCF) given frequent antibiotic exposure. Finally, CFTR modulating therapy, which has revolutionized CF management, is associated with cutaneous side effects ranging from acute urticaria to toxic epidermal necrolysis. Recognition of dermatologic clinical manifestations of CF is important to appropriately care for PwCF. Dermatologists may play a significant role in the diagnosis and management of CF and associated skin complications.

MICT ameliorates hypertensive nephropathy by inhibiting TLR4/NF-κB pathway and down-regulating NLRC4 inflammasome

BACKGROUND

Hypertensive nephropathy (HN) is one of the main causes of end-stage renal disease (ESRD), leading to serious morbidity and mortality in hypertensive patients. However, existing treatment for hypertensive nephropathy are still very limited. It has been demonstrated that aerobic exercise has beneficial effects on the treatment of hypertension. However, the underlying mechanisms of exercise in HN remain unclear.

METHODS

The spontaneously hypertensive rats (SHR) were trained for 8 weeks on a treadmill with different exercise prescriptions. We detected the effects of moderate intensity continuous training (MICT) and high intensity interval training (HIIT) on inflammatory response, renal function, and renal fibrosis in SHR. We further investigated the relationship between TLR4 and the NLRC4 inflammasome in vitro HN model.

RESULTS

MICT improved renal fibrosis and renal injury, attenuating the inflammatory response by inhibiting TLR4/NF-κB pathway and the activation of NLRC4 inflammasome. However, these changes were not observed in the HIIT group. Additionally, repression of TLR4/NF-κB pathway by TAK-242 inhibited activation of NLRC4 inflammasome and alleviated the fibrosis in Ang II-induced HK-2 cells.

CONCLUSION

MICT ameliorated renal damage, inflammatory response, and renal fibrosis via repressing TLR4/NF-κB pathway and the activation of NLRC4 inflammasome. This study might provide new references for exercise prescriptions of hypertension.

Pseudomonas aeruginosa in chronic lung disease: untangling the dysregulated host immune response

Pseudomonas aeruginosa is a highly adaptable opportunistic pathogen capable of exploiting barriers and immune defects to cause chronic lung infections in conditions such as cystic fibrosis. In these contexts, host immune responses are ineffective at clearing persistent bacterial infection, instead driving a cycle of inflammatory lung damage. This review outlines key components of the host immune response to chronic P. aeruginosa infection within the lung, beginning with initial pathogen recognition, followed by a robust yet maladaptive innate immune response, and an ineffective adaptive immune response that propagates lung damage while permitting bacterial persistence. Untangling the interplay between host immunity and chronic P. aeruginosa infection will allow for the development and refinement of strategies to modulate immune-associated lung damage and potentiate the immune system to combat chronic infection more effectively.

Integrating genetic and immune factors to uncover pathogenetic mechanisms of viral-associated pulmonary aspergillosis

Invasive pulmonary aspergillosis is a severe fungal infection primarily affecting immunocompromised patients. Individuals with severe viral infections have recently been identified as vulnerable to developing invasive fungal infections. Both influenza-associated pulmonary aspergillosis (IAPA) and COVID-19-associated pulmonary aspergillosis (CAPA) are linked to high mortality rates, emphasizing the urgent need for an improved understanding of disease pathogenesis to unveil new molecular targets with diagnostic and therapeutic potential. The recent establishment of animal models replicating the co-infection context has offered crucial insights into the mechanisms that underlie susceptibility to disease. However, the development and progression of human viral-fungal co-infections exhibit a significant degree of interindividual variability, even among patients with similar clinical conditions. This observation implies a significant role for host genetics, but information regarding the genetic basis for viral-fungal co-infections is currently limited. In this review, we discuss how genetic factors known to affect either antiviral or antifungal immunity could potentially reveal pathogenetic mechanisms that predispose to IAPA or CAPA and influence the overall disease course. These insights are anticipated to foster further research in both pre-clinical models and human patients, aiming to elucidate the complex pathophysiology of viral-associated pulmonary aspergillosis and contributing to the identification of new diagnostic and therapeutic targets to improve the management of these co-infections.

The XPO1 inhibitor selinexor ameliorates bleomycin-induced pulmonary fibrosis in mice via GBP5/NLRP3 inflammasome signaling

Pulmonary fibrosis is an irreversible and progressive lung disease with limited treatments available. Selinexor (Sel), an orally available, small-molecule, selective inhibitor of XPO1, exhibits notable antitumor, anti-inflammatory and antiviral activities. However, its potential role in treating pulmonary fibrosis is unknown. C57BL/6J mice were used to establish a pulmonary fibrosis model by intratracheal administration of bleomycin (BLM). Subsequently, Sel was administered intraperitoneally. Our data demonstrated that Sel administration ameliorated BLM-induced pulmonary fibrosis by increasing mouse body weights; reducing H&E staining, Masson staining scores, and shadows in mouse lung computed tomography (CT) images, decreasing the total cell and neutrophil counts in the lung and bronchoalveolar lavage fluid (BALF); and decreasing the levels of TGF-β1. We next confirmed that Sel reduced the deposition of extracellular matrix (ECM) components in the lungs of BLM-induced pulmonary fibrosis mice. We showed that collagen I, alpha-smooth muscle actin (α-SMA), and hydroxyproline levels and the mRNA levels of Col1a1, Eln, Fn1, Ctgf, and Fgf2 were reduced. Mechanistically, tandem mass tags (TMT)- based quantitative proteomics analysis revealed a significant increase in GBP5 in the lungs of BLM mice but a decrease in that of BLM + Sel mice; this phenomenon was confirmed by western blotting and RT-qPCR. NLRP3 inflammasome signaling was significantly enriched in both the BLM group and BLM + Sel group based on GO and KEGG analyses of differentially expressed proteins between the groups. Furthermore, Sel reduced the expression of NLRP3, cleaved caspase 1, and ASC in vivo and in vitro, and decreased the levels of IL-1β, IL-18, and IFN-r in lung tissue and BALF. SiRNA-GBP5 inhibited NLRP3 signaling in vitro, and overexpression of GBP5 inhibited the protective effect of Sel against BLM-induced cellular injury. Taken together, our findings indicate that Sel ameliorates BLM-induced pulmonary fibrosis by targeting GBP5 via NLRP3 inflammasome signaling. Thus, the XPO1 inhibitor - Sel might be a potential therapeutic agent for pulmonary fibrosis.

Anti-Angiogenic and Anti-Scarring Dual Effect of Galectin-3 Inhibition in Mouse Models of Corneal Wound Healing

Corneal scarring is the third leading cause of global blindness. Neovascularization of ocular tissues is a major predisposing factor in scar development. Although corneal transplantation is effective in restoring vision, some patients are at high risk for graft rejection due to the presence of blood vessels in the injured cornea. Current treatment options for controlling corneal scarring are limited, and outcomes are typically poor. In this study, topical application of a small-molecule inhibitor of galectin-3, GB1265, in mouse models of corneal wound healing, led to the reduction of the following in injured corneas: i) corneal angiogenesis; ii) corneal fibrosis; iii) infiltration of immune cells; and iv) expression of the proinflammatory cytokine IL-1β. Four independent techniques (RNA sequencing, NanoString, real-time quantitative RT-PCR, and Western blot analysis) determined that decreased corneal opacity in the galectin-3 inhibitor-treated corneas was associated with decreases in the numbers of genes and signaling pathways known to promote fibrosis. These findings allowed for a high level of confidence in the conclusion that galectin-3 inhibition by the small-molecule inhibitor GB1265 has dual anti-angiogenic and anti-scarring effects. Targeting galectin-3 by GB1265 is, thus, attractive for the development of innovative therapies for a myriad of ocular and nonocular diseases characterized by pathologic angiogenesis and fibrosis.

Immunometabolic Regulation of Bacterial Infection, Biofilms, and Antibiotic Susceptibility

BACKGROUND

Upon infection, mucosal tissues activate a brisk inflammatory response to clear the pathogen, i.e., resistance to disease. Resistance to disease is orchestrated by tissue-resident macrophages, which undergo profound metabolic reprogramming after sensing the pathogen. These metabolically activated macrophages release many inflammatory factors, which promote their bactericidal function. However, in immunocompetent individuals, pathogens like Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella evade this type of immunity, generating communities that thrive for the long term.

SUMMARY

These organisms develop features that render them less susceptible to eradication, such as biofilms and increased tolerance to antibiotics. Furthermore, after antibiotic therapy withdrawal, "persister" cells rapidly upsurge, triggering inflammatory relapses that worsen host health. How these pathogens persisted in inflamed tissues replete with activated macrophages remains poorly understood.

KEY MESSAGES

In this review, we discuss recent findings indicating that the ability of P. aeruginosa, S. aureus, and Salmonella to evolve biofilms and antibiotic tolerance is promoted by the similar metabolic routes that regulate macrophage metabolic reprogramming.

Regulation and functions of the NLRP3 inflammasome in RNA virus infection

Virus infection is one of the greatest threats to human life and health. In response to viral infection, the host's innate immune system triggers an antiviral immune response mostly mediated by inflammatory processes. Among the many pathways involved, the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome has received wide attention in the context of viral infection. The NLRP3 inflammasome is an intracellular sensor composed of three components, including the innate immune receptor NLRP3, adaptor apoptosis-associated speck-like protein containing CARD (ASC), and the cysteine protease caspase-1. After being assembled, the NLRP3 inflammasome can trigger caspase-1 to induce gasdermin D (GSDMD)-dependent pyroptosis, promoting the maturation and secretion of proinflammatory cytokines such as interleukin-1 (IL-1β) and interleukin-18 (IL-18). Recent studies have revealed that a variety of viruses activate or inhibit the NLRP3 inflammasome via viral particles, proteins, and nucleic acids. In this review, we present a variety of regulatory mechanisms and functions of the NLRP3 inflammasome upon RNA viral infection and demonstrate multiple therapeutic strategies that target the NLRP3 inflammasome for anti-inflammatory effects in viral infection.

Therapeutic Effects of IL-1RA against Acute Bacterial Infections, including Antibiotic-Resistant Strains

Innate immunity is essential for the anti-microbial defense, but excessive immune activation may cause severe disease. In this study, immunotherapy was shown to prevent excessive innate immune activation and restore the anti-bacterial defense. E. coli-infected Asc-/- mice develop severe acute cystitis, defined by IL-1 hyper-activation, high bacterial counts, and extensive tissue pathology. Here, the interleukin-1 receptor antagonist (IL-1RA), which inhibits IL-1 hyper-activation in acute cystitis, was identified as a more potent inhibitor of inflammation and NK1R- and substance P-dependent pain than cefotaxime. Furthermore, IL-1RA treatment inhibited the excessive innate immune activation in the kidneys of infected Irf3-/- mice and restored tissue integrity. Unexpectedly, IL-1RA also accelerated bacterial clearance from infected bladders and kidneys, including antibiotic-resistant E. coli, where cefotaxime treatment was inefficient. The results suggest that by targeting the IL-1 response, control of the innate immune response to infection may be regained, with highly favorable treatment outcomes, including infections caused by antibiotic-resistant strains.

Recent advances in pyroptosis, liver disease, and traditional Chinese medicine: A review

In recent years, the incidence of liver disease has increased, becoming a major cause of death. Various liver diseases are intricately linked to pyroptosis, which is one of the most common forms of programmed cell death. As a powerful weapon in the fight against liver diseases, traditional Chinese medicine (TCM) can affect pyroptosis via a number of routes, including the classical, nucleotide oligomerization domain-like receptors protein 3/caspase-1/gasdermin D (GSDMD) pathway, the nonclassical lipopolysaccharide/caspase-11/GSDMD pathway, the ROS/caspase-3/gasdermin E pathway, the caspase-9/caspase-3/GSDMD pathway, and the Apaf-1/caspase-11/caspase-3 pathway. In this review, we provide an overview of pyroptosis, the interplay between pyroptosis and liver diseases, and the mechanisms through which TCM regulates pyroptosis in liver diseases. The information used in the text was collected and compiled from the databases of PubMed, Web of Science, Scopus, CNKI, and Wanfang Data up to June 2023. The search was not limited with regard to the language and country of the articles. Research and review articles were included, and papers with duplicate results or unrelated content were excluded. We examined the current understanding of the relationship between pyroptosis and liver diseases as well as the advances in TCM interventions to provide a resource for the identification of potential targets for TCM in the treatment of liver diseases.

NLRP3 and cancer: Pathogenesis and therapeutic opportunities

More than a decade ago IL-1 blockade was suggested as an add-on therapy for the treatment of cancer. This proposal was based on the overall safety record of anti-IL-1 biologics and the anti-tumor properties of IL-1 blockade in animal models of cancer. Today, a new frontier in IL-1 activity regulation has developed with several orally active NLRP3 inhibitors currently in clinical trials, including cancer. Despite an increasing body of evidence suggesting a role of NLRP3 and IL-1-mediated inflammation driving cancer initiation, immunosuppression, growth, and metastasis, NLRP3 activation in cancer remains controversial. In this review, we discuss the recent advances in the understanding of NLRP3 activation in cancer. Further, we discuss the current opportunities for NLRP3 inhibition in cancer intervention with novel small molecules.

Lung Inflammatory Genes in Cystic Fibrosis and Their Relevance to Cystic Fibrosis Transmembrane Conductance Regulator Modulator Therapies

Cystic fibrosis (CF) is a monogenic syndrome determined by over 2000 mutations in the CF Transmembrane Conductance Regulator (CFTR) gene harbored on chromosome 7. In people with CF (PWCF), lung disease is the major determinant of morbidity and mortality and is characterized by a clinical phenotype which differs in the presence of equal mutational assets, indicating that genetic and environmental modifiers play an important role in this variability. Airway inflammation determines the pathophysiology of CF lung disease (CFLD) both at its onset and progression. In this narrative review, we aim to depict the inflammatory process in CF lung, with a particular emphasis on those genetic polymorphisms that could modify the clinical outcome of the respiratory disease in PWCF. The natural history of CF has been changed since the introduction of CFTR modulator therapies in the clinical arena. However, also in this case, there is a patient-to-patient variable response. We provide an overview on inflammatory/immunity gene variants that affect CFLD severity and an appraisal of the effects of CFTR modulator therapies on the inflammatory process in lung disease and how this knowledge may advance the optimization of the management of PWCF.

Bridging of host-microbiota tryptophan partitioning by the serotonin pathway in fungal pneumonia

The aromatic amino acid L-tryptophan (Trp) is essentially metabolized along the host and microbial pathways. While much is known about the role played by downstream metabolites of each pathways in intestinal homeostasis, their role in lung immune homeostasis is underappreciated. Here we have examined the role played by the Trp hydroxylase/5-hydroxytryptamine (5-HT) pathway in calibrating host and microbial Trp metabolism during Aspergillus fumigatus pneumonia. We found that 5-HT produced by mast cells essentially contributed to pathogen clearance and immune homeostasis in infection by promoting the host protective indoleamine-2,3-dioxygenase 1/kynurenine pathway and limiting the microbial activation of the indole/aryl hydrocarbon receptor pathway. This occurred via regulation of lung and intestinal microbiota and signaling pathways. 5-HT was deficient in the sputa of patients with Cystic fibrosis, while 5-HT supplementation restored the dysregulated Trp partitioning in murine disease. These findings suggest that 5-HT, by bridging host-microbiota Trp partitioning, may have clinical effects beyond its mood regulatory function in respiratory pathologies with an inflammatory component.

Pseudomonas-dominant microbiome elicits sustained IL-1β upregulation in alveolar macrophages from lung transplant recipients

BACKGROUND

Isolation of Pseudomonas aeruginosa (PsA) is associated with increased BAL (bronchoalveolar lavage) inflammation and lung allograft injury in lung transplant recipients (LTR). However, the effect of PsA on macrophage responses in this population is incompletely understood. We examined human alveolar macrophage (AMΦ) responses to PsA and Pseudomonas dominant microbiome in healthy LTR.

METHODS

We stimulated THP-1 derived macrophages (THP-1MΦ) and human AMΦ from LTR with different bacteria and LTR BAL derived microbiome characterized as Pseudomonas-dominant. Macrophage responses were assessed by high dimensional flow cytometry, including their intracellular production of cytokines (TNF-α, IL-6, IL-8, IL-1β, IL-10, IL-1RA, and TGF-β). Pharmacological inhibitors were utilized to evaluate the role of the inflammasome in PsA-macrophage interaction.

RESULTS

We observed upregulation of pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-1β) following stimulation by PsA compared to other bacteria (Staphylococcus aureus (S.Aur), Prevotella melaninogenica, Streptococcus pneumoniae) in both THP-1MΦ and LTR AMΦ, predominated by IL-1β. IL-1β production from THP-1MΦ was sustained after PsA stimulation for up to 96 hours and 48 hours in LTR AMΦ. Treatment with the inflammasome inhibitor BAY11-7082 abrogated THP-1MΦ IL-1β production after PsA exposure. BAL Pseudomonas-dominant microbiota elicited an increased IL-1β, similar to PsA, an effect abrogated by the addition of antibiotics.

CONCLUSION

PsA and PsA-dominant lung microbiota induce sustained IL-1β production in LTR AMΦ. Pharmacological targeting of the inflammasome reduces PsA-macrophage-IL-1β responses, underscoring their use in lung transplant recipients.

Role of toll-like receptors and nod-like receptors in acute lung infection

The respiratory system exposed to microorganisms continuously, and the pathogenicity of these microbes not only contingent on their virulence factors, but also the host's immunity. A multifaceted innate immune mechanism exists in the respiratory tract to cope with microbial infections and to decrease tissue damage. The key cell types of the innate immune response are macrophages, neutrophils, dendritic cells, epithelial cells, and endothelial cells. Both the myeloid and structural cells of the respiratory system sense invading microorganisms through binding or activation of pathogen-associated molecular patterns (PAMPs) to pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and NOD-like receptors (NLRs). The recognition of microbes and subsequent activation of PRRs triggers a signaling cascade that leads to the activation of transcription factors, induction of cytokines/5chemokines, upregulation of cell adhesion molecules, recruitment of immune cells, and subsequent microbe clearance. Since numerous microbes resist antimicrobial agents and escape innate immune defenses, in the future, a comprehensive strategy consisting of newer vaccines and novel antimicrobials will be required to control microbial infections. This review summarizes key findings in the area of innate immune defense in response to acute microbial infections in the lung. Understanding the innate immune mechanisms is critical to design host-targeted immunotherapies to mitigate excessive inflammation while controlling microbial burden in tissues following lung infection.

TLR7 activation at epithelial barriers promotes emergency myelopoiesis and lung antiviral immunity

Monocytes are heterogeneous innate effector leukocytes generated in the bone marrow and released into circulation in a CCR2-dependent manner. During infection or inflammation, myelopoiesis is modulated to rapidly meet the demand for more effector cells. Danger signals from peripheral tissues can influence this process. Herein we demonstrate that repetitive TLR7 stimulation via the epithelial barriers drove a potent emergency bone marrow monocyte response in mice. This process was unique to TLR7 activation and occurred independently of the canonical CCR2 and CX3CR1 axes or prototypical cytokines. The monocytes egressing the bone marrow had an immature Ly6C-high profile and differentiated into vascular Ly6C-low monocytes and tissue macrophages in multiple organs. They displayed a blunted cytokine response to further TLR7 stimulation and reduced lung viral load after RSV and influenza virus infection. These data provide insights into the emergency myelopoiesis likely to occur in response to the encounter of single-stranded RNA viruses at barrier sites.

The influence of pyroptosis-related genes on the development of chronic obstructive pulmonary disease

Increasing evidences have demonstrated that pyroptosis exerts key roles in the occurrence, development of chronic obstructive pulmonary disease. However, the mechanisms of pyroptosis in COPD remain largely unknown. In our research, Statistics were performed using R software and related packages in this study. Series matrix files of small airway epithelium samples were downloaded from the GEO database. Differential expression analysis with FDR < 0.05 was performed to identify COPD-associated pyroptosis-related genes. 8 up-regulated genes (CASP4, CASP5, CHMP7, GZMB, IL1B, AIM2, CASP6, GSDMC) and 1 down-regulated genes (PLCG1) was identified as COPD-associated pyroptosis-related genes. Twenty-six COPD key genes was identified by WGCNA analysis. PPI analysis and gene correlation analysis showed their relationship clearly. KEGG and GO analysis have revealed the main pyroptosis-related mechanism of COPD. The expression of 9 COPD-associated pyroptosis-related genes in different grades was also depicted. The immune environment of COPD was also explored. Furthermore, the relationship of pyroptosis-related genes and the expression of immune cells was also be shown in the end. In the end, we concluded that pyroptosis influences the development of COPD. This study may provide new insight into the novel therapeutic targets for COPD clinical treatment.

Emerging Non-Antibiotic Options Targeting Uropathogenic Mechanisms for Recurrent Uncomplicated Urinary Tract Infection

Urinary tract infections (UTIs) are the most frequent bacterial infections in the clinical setting. Even without underlying anatomic or functional abnormalities, more than 40% of women experience at least one UTI in their lifetime, of which 30% develop recurrent UTIs (rUTIs) within 6 months. Conventional management with antibiotics for rUTIs may eventually lead to the development of multidrug-resistant uropathogens. Targeting of the pathogenicity of rUTIs, the evolution of uropathogenic Escherichia coli (UPEC), and inadequate host defenses by immune responses should be explored to provide non-antibiotic solutions for the management of rUTIs. The adaptive evolution of UPEC has been observed in several aspects, including colonization, attachment, invasion, and intracellular replication to invade the urothelium and survive intracellularly. Focusing on the antivirulence of UPEC and modulating the immunity of susceptible persons, researchers have provided potential alternative solutions in four categories: antiadhesive treatments (i.e., cranberries and D-mannose), immunomodulation therapies, vaccines, and prophylaxis with topical estrogen therapy and probiotics (e.g., Lactobacillus species). Combination therapies targeting multiple pathogenic mechanisms are expected to be a future trend in UTI management, although some of these treatment options have not been well established in terms of their long-term efficacy. Additional clinical trials are warranted to validate the therapeutic efficacy and durability of these techniques.

Control of mitochondrial functions by Pseudomonas aeruginosa in cystic fibrosis

Cystic fibrosis (CF) is a genetic disease characterized by mutations of cystic fibrosis transmembrane conductance regulator (CFTR) gene, which lead to a dysfunctional chloride and bicarbonate channel. Abnormal mucus viscosity, persistent infections and hyperinflammation that preferentially affect the airways, referred to the pathogenesis of CF lung disease. It has largely demonstrated that Pseudomonas aeruginosa (P. aeruginosa) represents the most important pathogen that affect CF patients, leading to worsen inflammation by stimulating pro-inflammatory mediators release and tissue destruction. The conversion to mucoid phenotype and formation of biofilms, together with the increased frequency of mutations, are only few changes that characterize the P. aeruginosa's evolution during CF lung chronic infection. Recently, mitochondria received increasing attention due to their involvement in inflammatory-related diseases, including in CF. Alteration of mitochondrial homeostasis is sufficient to stimulate immune response. Exogenous or endogenous stimuli that perturb mitochondrial activity are used by cells, which, through the mitochondrial stress, potentiate immunity programs. Studies show the relationship between mitochondria and CF, supporting the idea that mitochondrial dysfunction endorses the exacerbation of inflammatory responses in CF lung. In particular, evidences suggest that mitochondria in CF airway cells are more susceptible to P. aeruginosa infection, with consequent detrimental effects that lead to amplify the inflammatory signals. This review discusses the evolution of P. aeruginosa in relationship with the pathogenesis of CF, a fundamental step to establish chronic infection in CF lung disease. Specifically, we focus on the role of P. aeruginosa in the exacerbation of inflammatory response, by triggering mitochondria in CF.

An emerging role of inflammasomes in spinal cord injury and spinal cord tumor

Spinal cord injury (SCI) and spinal cord tumor are devastating events causing structural and functional impairment of the spinal cord and resulting in high morbidity and mortality; these lead to a psychological burden and financial pressure on the patient. These spinal cord damages likely disrupt sensory, motor, and autonomic functions. Unfortunately, the optimal treatment of and spinal cord tumors is limited, and the molecular mechanisms underlying these disorders are unclear. The role of the inflammasome in neuroinflammation in diverse diseases is becoming increasingly important. The inflammasome is an intracellular multiprotein complex and participates in the activation of caspase-1 and the secretion of pro-inflammatory cytokines such as interleukin (IL)-1β and IL-18. The inflammasome in the spinal cord is involved in the stimulation of immune-inflammatory responses through the release of pro-inflammatory cytokines, thereby mediating further spinal cord damage. In this review, we highlight the role of inflammasomes in SCI and spinal cord tumors. Targeting inflammasomes is a promising therapeutic strategy for the treatment of SCI and spinal cord tumors.

The circadian control of tryptophan metabolism regulates the host response to pulmonary fungal infections

The environmental light/dark cycle has left its mark on the body's physiological functions to condition not only our inner biology, but also the interaction with external cues. In this scenario, the circadian regulation of the immune response has emerged as a critical factor in defining the host-pathogen interaction and the identification of the underlying circuitry represents a prerequisite for the development of circadian-based therapeutic strategies. The possibility to track down the circadian regulation of the immune response to a metabolic pathway would represent a unique opportunity in this direction. Herein, we show that the metabolism of the essential amino acid tryptophan, involved in the regulation of fundamental processes in mammals, is regulated in a circadian manner in both murine and human cells and in mouse tissues. By resorting to a murine model of pulmonary infection with the opportunistic fungus Aspergillus fumigatus, we showed that the circadian oscillation in the lung of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO)1, generating the immunoregulatory kynurenine, resulted in diurnal changes in the immune response and the outcome of fungal infection. In addition, the circadian regulation of IDO1 drives such diurnal changes in a pre-clinical model of cystic fibrosis (CF), an autosomal recessive disease characterized by progressive lung function decline and recurrent infections, thus acquiring considerable clinical relevance. Our results demonstrate that the circadian rhythm at the intersection between metabolism and immune response underlies the diurnal changes in host-fungal interaction, thus paving the way for a circadian-based antimicrobial therapy.

Single-cell transcriptomic dissection of the cellular and molecular events underlying the triclosan-induced liver fibrosis in mice

BACKGROUND

Triclosan [5-chloro-2-(2,4-dichlorophenoxy) phenol, TCS], a common antimicrobial additive in many personal care and health care products, is frequently detected in human blood and urine. Therefore, it has been considered an emerging and potentially toxic pollutant in recent years. Long-term exposure to TCS has been suggested to exert endocrine disruption effects, and promote liver fibrogenesis and tumorigenesis. This study was aimed at clarifying the underlying cellular and molecular mechanisms of hepatotoxicity effect of TCS at the initiation stage.

METHODS

C57BL/6 mice were exposed to different dosages of TCS for 2 weeks and the organ toxicity was evaluated by various measurements including complete blood count, histological analysis and TCS quantification. Single cell RNA sequencing (scRNA-seq) was then carried out on TCS- or mock-treated mouse livers to delineate the TCS-induced hepatotoxicity. The acquired single-cell transcriptomic data were analyzed from different aspects including differential gene expression, transcription factor (TF) regulatory network, pseudotime trajectory, and cellular communication, to systematically dissect the molecular and cellular events after TCS exposure. To verify the TCS-induced liver fibrosis, the expression levels of key fibrogenic proteins were examined by Western blotting, immunofluorescence, Masson's trichrome and Sirius red staining. In addition, normal hepatocyte cell MIHA and hepatic stellate cell LX-2 were used as in vitro cell models to experimentally validate the effects of TCS by immunological, proteomic and metabolomic technologies.

RESULTS

We established a relatively short term TCS exposure murine model and found the TCS mainly accumulated in the liver. The scRNA-seq performed on the livers of the TCS-treated and control group profiled the gene expressions of > 76,000 cells belonging to 13 major cell types. Among these types, hepatocytes and hepatic stellate cells (HSCs) were significantly increased in TCS-treated group. We found that TCS promoted fibrosis-associated proliferation of hepatocytes, in which Gata2 and Mef2c are the key driving TFs. Our data also suggested that TCS induced the proliferation and activation of HSCs, which was experimentally verified in both liver tissue and cell model. In addition, other changes including the dysfunction and capillarization of endothelial cells, an increase of fibrotic characteristics in B plasma cells, and M2 phenotype-skewing of macrophage cells, were also deduced from the scRNA-seq analysis, and these changes are likely to contribute to the progression of liver fibrosis. Lastly, the key differential ligand-receptor pairs involved in cellular communications were identified and we confirmed the role of GAS6_AXL interaction-mediated cellular communication in promoting liver fibrosis.

CONCLUSIONS

TCS modulates the cellular activities and fates of several specific cell types (including hepatocytes, HSCs, endothelial cells, B cells, Kupffer cells and liver capsular macrophages) in the liver, and regulates the ligand-receptor interactions between these cells, thereby promoting the proliferation and activation of HSCs, leading to liver fibrosis. Overall, we provide the first comprehensive single-cell atlas of mouse livers in response to TCS and delineate the key cellular and molecular processes involved in TCS-induced hepatotoxicity and fibrosis.

Turning Microbial AhR Agonists into Therapeutic Agents via Drug Delivery Systems

Developing therapeutics for inflammatory diseases is challenging due to physiological mucosal barriers, systemic side effects, and the local microbiota. In the search for novel methods to overcome some of these problems, drug delivery systems that improve tissue-targeted drug delivery and modulate the microbiota are highly desirable. Microbial metabolites are known to regulate immune responses, an observation that has resulted in important conceptual advances in areas such as metabolite pharmacology and metabolite therapeutics. Indeed, the doctrine of "one molecule, one target, one disease" that has dominated the pharmaceutical industry in the 20th century is being replaced by developing therapeutics which simultaneously manipulate multiple targets through novel formulation approaches, including the multitarget-directed ligands. Thus, metabolites may not only represent biomarkers for disease development, but also, being causally linked to human diseases, an unexploited source of therapeutics. We have shown the successful exploitation of this approach: by deciphering how signaling molecules, such as the microbial metabolite, indole-3-aldehyde, and the repurposed drug anakinra, interact with the aryl hydrocarbon receptor may pave the way for novel therapeutics in inflammatory human diseases, for the realization of which drug delivery platforms are instrumental.

C-type lectin receptors in antifungal immunity: Current knowledge and future developments

C-type lectin receptors (CLRs) constitute a category of innate immune receptors that play an essential role in the antifungal immune response. For over two decades, scientists have uncovered what are the fungal ligands recognized by CLRs and how these receptors initiate the immune response. Such studies have allowed the identification of genetic polymorphisms in genes encoding for CLRs or for proteins involved in the signalisation cascade they trigger. Nevertheless, our understanding of how these receptors functions and the full extent of their function during the antifungal immune response is still at its infancy. In this review, we summarize some of the main findings about CLRs in antifungal immunity and discuss what the future might hold for the field.

The RIPK3 Scaffold Regulates Lung Inflammation During Pseudomonas Aeruginosa Pneumonia

RIPK3 (receptor-interacting protein kinase 3) activity triggers cell death via necroptosis, whereas scaffold function supports protein binding and cytokine production. To determine if RIPK3 kinase or scaffold domains mediate pathology during Pseudomonas aeruginosa infection, control mice and those with deletion or mutation of RIPK3 and associated signaling partners were subjected to Pseudomonas pneumonia and followed for survival or killed for biologic assays. Murine immune cells were studied in vitro for Pseudomonas-induced cytokine production and cell death, and RIPK3 binding interactions were blocked with the viral inhibitor M45. Human tissue effects were assayed by infecting airway epithelial cells with Pseudomonas and measuring cytokine production after siRNA inhibition of RIPK3. Deletion of RIPK3 reduced inflammation and decreased animal mortality after Pseudomonas pneumonia. RIPK3 kinase inactivation did neither. In cell culture, RIPK3 was dispensable for cell killing by Pseudomonas and instead drove cytokine production that required the RIPK3 scaffold domain but not kinase activity. Blocking the RIP homotypic interaction motif (RHIM) with M45 reduced the inflammatory response to infection in vitro. Similarly, siRNA knockdown of RIPK3 decreased infection-triggered inflammation in human airway epithelial cells. Thus, the RIPK3 scaffold drives deleterious pulmonary inflammation and mortality in a relevant clinical model of Pseudomonas pneumonia. This process is distinct from kinase-mediated necroptosis, requiring only the RIPK3 RHIM. Inhibition of RHIM signaling is a potential strategy to reduce lung inflammation during infection.

Pseudomonas quinolone signal induces organelle stress and dysregulates inflammation in human macrophages

Pseudomonas quinolone signal (PQS) is a quorum-sensing molecule associated with Pseudomonas aeruginosa that regulates quorum sensing, extracellular vesicle biogenesis, iron acquisition, and the secretion of virulence factors. PQS has been shown to have immunomodulatory effects on the host. It induces oxidative stress, modulates cytokine levels, and activates regulated cell death in the host. In this study, we investigated the effects of PQS (10 μM) on host organelle dynamics and dysfunction in human macrophages at the interphase of endoplasmic reticulum (ER), mitochondria, and lysosome. This study showed that PQS increases cytosolic Ca⁺² levels and elevates ER stress, as evidenced by increased expression of BiP and activation of the PERK-CHOP axis of unfolded protein response (UPR). Moreover, PQS also negatively affects mitochondria by disrupting mitochondrial membrane potential and increasing mitochondrial ROS generation (mROS). Additionally, PQS stimulation decreased the number of acridine orange-positive lysosomes, indicating lysosomal destabilization. Furthermore, PQS-induced lysosomal destabilization also induces overexpression of the lysosomal stress-responsive gene TFEB. Besides organelle dysfunction, PQS dysregulates inflammation-related genes by upregulating NLRC4, TMS1, and Caspase 1 while downregulating NLRP3 and IL-1β. Also, PQS increases gene expression of pro-inflammatory cytokines (IL-6, TNF-α, and IFN-γ). In conclusion, our findings suggest that PQS negatively affects human macrophages by interfering with organelle function and dysregulating inflammatory response. Consequently, this study provides crucial insight into PQS-driven macrophage dysfunction and may contribute to a better understanding of Pseudomonas aeruginosa-associated infections.

Pseudomonas aeruginosa Cytotoxins: Mechanisms of Cytotoxicity and Impact on Inflammatory Responses

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells. In this review, we provide an in-depth review of P. aeruginosa cytotoxins based on their mechanisms of cytotoxicity and the possible consequences of their cytotoxicity on host immune responses.

ABC transporters affects tumor immune microenvironment to regulate cancer immunotherapy and multidrug resistance

Multidrug resistance (MDR) is the phenomenon in which cancer cells simultaneously develop resistance to a broad spectrum of structurally and mechanistically unrelated drugs. MDR severely hinders the effective treatment of cancer and is the major cause of chemotherapy failure. ATP-binding cassette (ABC) transporters are extensively expressed in various body tissues, and actively transport endogenous and exogenous substrates through biological membranes. Overexpression of ABC transporters is frequently observed in MDR cancer cells, which promotes efflux of chemotherapeutic drugs and reduces their intracellular accumulation. Increasing evidence suggests that ABC transporters regulate tumor immune microenvironment (TIME) by transporting various cytokines, thus controlling anti-tumor immunity and sensitivity to anticancer drugs. On the other hand, the expression of various ABC transporters is regulated by cytokines and other immune signaling molecules. Targeted inhibition of ABC transporter expression or function can enhance the efficacy of immune checkpoint inhibitors by promoting anticancer immune microenvironment. This review provides an update on the recent research progress in this field.

Pulmonary drug delivery technology enables anakinra repurposing in cystic fibrosis

Inflammation is a key pathological driver in cystic fibrosis (CF). Current therapies are ineffective in treating and preventing the escalation of inflammatory events often exacerbated by superimposed infection. In this work, we propose a novel treatment based on the pulmonary administration of anakinra, a non-glycosylated recombinant form of IL-1Ra. An inhalable dry powder of anakinra was successfully developed to meet the specific needs of lung drug delivery. The new formulation was investigated in vitro for aerodynamic performances and activity and in vivo for its pharmacological profile, including the pharmacokinetics, treatment schedule, antimicrobial and anti-inflammatory activity and systemic toxicity. The protein was structurally preserved inside the formulation and retained its pharmacological activity in vitro immediately after preparation and over time when stored at ambient conditions. Anakinra when delivered to the lungs showed an improved and extended therapeutic efficacy in CF models in vivo as well as higher potency compared to systemic delivery. Peripheral side effects were significantly reduced and correlated with lower serum levels compared to systemic treatment. These findings provide proof-of-concept demonstration for anakinra repurposing in CF through the pulmonary route.

Update on Innate and Adaptive Immunity in Cystic Fibrosis

Cystic fibrosis (CF) pathophysiology is hallmarked by excessive inflammation and the inability to resolve lung infections, contributing to morbidity and eventually mortality. Paradoxically, despite a robust inflammatory response, CF lungs fail to clear bacteria and are susceptible to chronic infections. Impaired mucociliary transport plays a critical role in chronic infection but the immune mechanisms contributing to the adaptation of bacteria to the lung microenvironment is not clear. CFTR modulator therapy has advanced CF life expectancy opening up the need to understand changes in immunity as CF patients age. Here, we have summarized the current understanding of immune dysregulation in CF.

The Impact of Highly Effective Modulator Therapy on Cystic Fibrosis Microbiology and Inflammation

Highly effective cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapy (HEMT) corrects the underlying molecular defect causing CF disease. HEMT decreases symptom burden and improves clinical metrics and quality of life for most people with CF (PwCF) and eligible cftr mutations. Improvements in measures of pulmonary health suggest that restoration of function of defective CFTR anion channels by HEMT not only enhances airway mucociliary clearance, but also reduces chronic pulmonary infection and inflammation. This article reviews the evidence for how HEMT influences the dynamic and interdependent processes of infection and inflammation in the CF airway, and what questions remain unanswered.

TREM2/β-catenin attenuates NLRP3 inflammasome-mediated macrophage pyroptosis to promote bacterial clearance of pyogenic bacteria

Triggering receptors expressed on myeloid cells 2 (TREM2) is considered a protective factor to protect host from bacterial infection, while how it elicits this role is unclear. In the present study, we demonstrate that deficiency of triggering receptors expressed on myeloid cells 2 (TREM2) significantly enhanced macrophage pyroptosis induced by four common pyogenic bacteria including Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, and Escherichia coli. TREM2 deficiency also decreased bacterial killing ratio of macrophage, while Caspase-1 or GSDMD inhibition promoted macrophage-mediated clearance to these bacteria. Further study demonstrated that the effect of TREM2 on macrophage pyroptosis and bacterial eradication mainly dependents on the activated status of NLRP3 inflammasome. Moreover, as the key downstream of TREM2, β-catenin phosphorylated at Ser675 by TREM2 signal and accumulated in nucleus and cytoplasm. β-catenin mediated the effect of TREM2 on NLRP3 inflammasome and macrophage pyroptosis by reducing NLRP3 expression, and inhibiting inflammasome complex assembly by interacting with ASC. Collectively, TREM2/β-catenin inhibits NLRP3 inflammasome to regulate macrophage pyroptosis, and enhances macrophage-mediated pyogenic bacterial clearance.

Pilot study of inflammatory biomarkers in matched induced sputum and bronchoalveolar lavage of 2-year-olds with cystic fibrosis

BACKGROUND

In this pilot study, we investigated whether induced sputum (IS) could serve as a viable alternative to bronchoalveolar lavage (BAL) and yield robust inflammatory biomarkers in toddlers with cystic fibrosis (CF) featuring minimal structural lung disease.

METHODS

We collected IS, BAL (right middle lobe and lingula), and blood, and performed chest computed tomography (CT) scans from 2-year-olds with CF (N = 11), all within a single visit. Inflammatory biomarkers included 20 soluble immune mediators and neutrophil elastase (NE), as well as frequency and phenotype of T cells, monocytes/macrophages, and neutrophils.

RESULTS

At the molecular level, nine mediators showed similar levels in IS and BAL (CXCL1, CXCL8, IL-1α, IL-1RA, IL-6, CCL2, CXCL10, M-CSF, VEGF-A), four were higher in IS than in BAL (CXCL5, IL-1β, CXCL11, TNFSF10), and two were present in IS, but undetectable in BAL (IL-10, IFN-γ). Meanwhile, soluble NE had lower activity in IS than in BAL. At the cellular level, T-cell frequency was lower in IS than in BAL. Monocytes/macrophages were dominant in IS and BAL with similar frequencies, but differing expression of CD16 (lower in IS), CD115, and surface-associated NE (higher in IS). Neutrophil frequency and phenotype did not differ between IS and BAL. Finally, neutrophil frequency in IS correlated positively with air trapping.

CONCLUSIONS

IS collected from 2-year-olds with CF yields biomarkers of early airway inflammation with good agreement with BAL, notably with regard to molecular and cellular outcomes related to neutrophils and monocytes/macrophages.

Examination of the role of necroptotic damage-associated molecular patterns in tissue fibrosis

Fibrosis is defined as the abnormal and excessive deposition of extracellular matrix (ECM) components, which leads to tissue or organ dysfunction and failure. However, the pathological mechanisms underlying fibrosis remain unclear. The inflammatory response induced by tissue injury is closely associated with tissue fibrosis. Recently, an increasing number of studies have linked necroptosis to inflammation and fibrosis. Necroptosis is a type of preprogrammed death caused by death receptors, interferons, Toll-like receptors, intracellular RNA and DNA sensors, and other mediators. These activate receptor-interacting protein kinase (RIPK) 1, which recruits and phosphorylates RIPK3. RIPK3 then phosphorylates a mixed lineage kinase domain-like protein and causes its oligomerization, leading to rapid plasma membrane permeabilization, the release of cellular contents, and exposure of damage-associated molecular patterns (DAMPs). DAMPs, as inflammatory mediators, are involved in the loss of balance between extensive inflammation and tissue regeneration, leading to remodeling, the hallmark of fibrosis. In this review, we discuss the role of necroptotic DAMPs in tissue fibrosis and highlight the inflammatory responses induced by DAMPs in tissue ECM remodeling. By summarizing the existing literature on this topic, we underscore the gaps in the current research, providing a framework for future investigations into the relationship among necroptosis, DAMPs, and fibrosis, as well as a reference for later transformation into clinical treatment.

COVID-19-associated fungal infections

Coronavirus disease 2019 (COVID-19)-associated invasive fungal infections are an important complication in a substantial number of critically ill, hospitalized patients with COVID-19. Three groups of fungal pathogens cause co-infections in COVID-19: Aspergillus, Mucorales and Candida species, including Candida auris. Here we review the incidence of COVID-19-associated invasive fungal infections caused by these fungi in low-, middle- and high-income countries. By evaluating the epidemiology, clinical risk factors, predisposing features of the host environment and immunological mechanisms that underlie the pathogenesis of these co-infections, we set the scene for future research and development of clinical guidance.

Hoenigl and colleagues review the epidemiology, immunology and clinical risk factors contributing to COVID-19-associated fungal infections.

Emerging Concepts in Defective Macrophage Phagocytosis in Cystic Fibrosis

Cystic fibrosis (CF) is caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Chronic inflammation and decline in lung function are major reasons for morbidity in CF. Mutant CFTR expressed in phagocytic cells such as macrophages contributes to persistent infection, inflammation, and lung disease in CF. Macrophages play a central role in innate immunity by eliminating pathogenic microbes by a process called phagocytosis. Phagocytosis is required for tissue homeostasis, balancing inflammation, and crosstalk with the adaptive immune system for antigen presentation. This review focused on (1) current understandings of the signaling underlying phagocytic mechanisms; (2) existing evidence for phagocytic dysregulation in CF; and (3) the emerging role of CFTR modulators in influencing CF phagocytic function. Alterations in CF macrophages from receptor initiation to phagosome formation are linked to disease progression in CF. A deeper understanding of macrophages in the context of CFTR and phagocytosis proteins at each step of phagosome formation might contribute to the new therapeutic development of dysregulated innate immunity in CF. Therefore, the review also indicates future areas of research in the context of CFTR and macrophages.

Immunomodulation therapy offers new molecular strategies to treat UTI

Innovative solutions are needed for the treatment of bacterial infections, and a range of antibacterial molecules have been explored as alternatives to antibiotics. A different approach is to investigate the immune system of the host for new ways of making the antibacterial defence more efficient. However, the immune system has a dual role as protector and cause of disease: in addition to being protective, increasing evidence shows that innate immune responses can become excessive and cause acute symptoms and tissue pathology during infection. This role of innate immunity in disease suggests that the immune system should be targeted therapeutically, to inhibit over-reactivity. The ultimate goal is to develop therapies that selectively attenuate destructive immune response cascades, while augmenting the protective antimicrobial defence but such treatment options have remained underexplored, owing to the molecular proximity of the protective and destructive effects of the immune response. The concept of innate immunomodulation therapy has been developed successfully in urinary tract infections, based on detailed studies of innate immune activation and disease pathogenesis. Effective, disease-specific, immunomodulatory strategies have been developed by targeting specific immune response regulators including key transcription factors. In acute pyelonephritis, targeting interferon regulatory factor 7 using small interfering RNA or treatment with antimicrobial peptide cathelicidin was protective and, in acute cystitis, targeting overactive effector molecules such as IL-1β, MMP7, COX2, cAMP and the pain-sensing receptor NK1R has been successful in vivo. Furthermore, other UTI treatment strategies, such as inhibiting bacterial adhesion and vaccination, have also shown promise.

Hyperactivation of innate immunity is a disease determinant in urinary tract infections (UTIs). Modulation of innate immunity has promise as a therapy for UTIs. In this Review, the authors discuss potential mechanisms and immunomodulatory therapeutic strategies in UTIs.

Excessive innate immune responses to infection cause symptoms and pathology in acute pyelonephritis and acute cystitis.

Innate immunomodulation therapy is, therefore, a realistic option for treating these conditions.

Targeting excessive innate immune responses at the level of transcription has been successful in animal models.

Innate immunomodulation therapy reduces excessive inflammation and tissue pathology and accelerates bacterial clearance from infected kidneys and bladders in mice.

Innate immunomodulation therapy also accelerates the clearance of antibiotic-resistant bacterial strains.

Effects of Drugs Formerly Suggested for COVID-19 Repurposing on Pannexin1 Channels

Although many efforts have been made to elucidate the pathogenesis of COVID-19, the underlying mechanisms are yet to be fully uncovered. However, it is known that a dysfunctional immune response and the accompanying uncontrollable inflammation lead to troublesome outcomes in COVID-19 patients. Pannexin1 channels are put forward as interesting drug targets for the treatment of COVID-19 due to their key role in inflammation and their link to other viral infections. In the present study, we selected a panel of drugs previously tested in clinical trials as potential candidates for the treatment of COVID-19 early on in the pandemic, including hydroxychloroquine, chloroquine, azithromycin, dexamethasone, ribavirin, remdesivir, favipiravir, lopinavir, and ritonavir. The effect of the drugs on pannexin1 channels was assessed at a functional level by means of measurement of extracellular ATP release. Immunoblot analysis and real-time quantitative reversetranscription polymerase chain reaction analysis were used to study the potential of the drugs to alter pannexin1 protein and mRNA expression levels, respectively. Favipiravir, hydroxychloroquine, lopinavir, and the combination of lopinavir with ritonavir were found to inhibit pannexin1 channel activity without affecting pannexin1 protein or mRNA levels. Thusthree new inhibitors of pannexin1 channels were identified that, though currently not being used anymore for the treatment of COVID-19 patients, could be potential drug candidates for other pannexin1-related diseases.

NLRP3 Inflammasome-Mediated Pyroptosis Pathway Contributes to the Pathogenesis of Candida albicans Keratitis

Purpose

Fungal keratitis is a sight-threatening corneal infection caused by fungal pathogens, and the pathogenic mechanisms have not been fully elucidated. The aim of this study was to determine whether NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated pyroptosis contributes to Candida albicans (C. albicans) keratitis and explore the underlying mechanism.

Methods

An in vivo mouse model of C. albicans keratitis and an in vitro culture model of human corneal epithelial cells (HCECs) challenged with heat-killed C. albicans (HKCA) were established in this study. The degree of corneal infection was evaluated by clinical scoring. Gene expression was assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis or immunofluorescence staining was performed to evaluate protein expression. TdT-mediated dUTP nick end labeling (TUNEL) staining was performed to examine the pyroptotic cell death. A lactate dehydrogenase (LDH) release assay was performed to assess cytotoxicity.

Results

Compared with the mock-infected group, we observed that the mRNA levels of NLRP3, caspase-1 (CASP1), interleukin (IL)−1β and gasdermin-D (GSDMD) in C. albicans-infected mice cornea was significantly increased. Our data also demonstrated that the protein expression of NLRP3 and the pyroptosis-related markers apoptosis-associated speck-like protein containing a CARD (ASC), cleaved CASP1, N-GSDMD, cleaved IL-1β and cleaved IL-18 as well as pyroptotic cell death were dramatically elevated in the mouse model of C. albicans keratitis. More importantly, NLRP3 knockdown markedly alleviated pyroptosis and consequently reduced corneal inflammatory reaction in C. albicans keratitis. In vitro, the presence of activated NLRP3 inflammasome and pyroptotic cell death were validated in HCECs exposed to HKCA. Furthermore, the potassium (K⁺) channel inhibitor glyburide decreased LDH release and suppressed NLRP3 inflammasome activation and pyroptosis in HCECs exposed to HKCA.

Conclusion

In conclusion, the current study revealed for the first time that NLRP3 inflammasome activation and pyroptosis occur in C. albicans-infected mouse corneas and HCECs. Moreover, NLRP3 inflammasome-mediated pyroptosis signaling is involved in the disease severity of C. albicans keratitis. Therefore, This NLRP3 inflammasome-dependent pathway may be an attractive target for the treatment of fungal keratitis.

The Mechanism and Regulation of the NLRP3 Inflammasome during Fibrosis

Fibrosis is often the end result of chronic inflammation. It is characterized by the excessive deposition of extracellular matrix. This leads to structural alterations in the tissue, causing permanent damage and organ dysfunction. Depending on the organ it effects, fibrosis can be a serious threat to human life. The molecular mechanism of fibrosis is still not fully understood, but the NLRP3 (NOD-, LRR- and pyrin–domain–containing protein 3) inflammasome appears to play a significant role in the pathogenesis of fibrotic disease. The NLRP3 inflammasome has been the most extensively studied inflammatory pathway to date. It is a crucial component of the innate immune system, and its activation mediates the secretion of interleukin (IL)-1β and IL-18. NLRP3 activation has been strongly linked with fibrosis and drives the differentiation of fibroblasts into myofibroblasts by the chronic upregulation of IL-1β and IL-18 and subsequent autocrine signaling that maintains an activated inflammasome. Both IL-1β and IL-18 are profibrotic, however IL-1β can have antifibrotic capabilities. NLRP3 responds to a plethora of different signals that have a common but unidentified unifying trigger. Even after 20 years of extensive investigation, regulation of the NLRP3 inflammasome is still not completely understood. However, what is known about NLRP3 is that its regulation and activation is complex and not only driven by various activators but controlled by numerous post-translational modifications. More recently, there has been an intensive attempt to discover NLRP3 inhibitors to treat chronic diseases. This review addresses the role of the NLRP3 inflammasome in fibrotic disorders across many different tissues. It discusses the relationships of various NLRP3 activators to fibrosis and covers different therapeutics that have been developed, or are currently in development, that directly target NLRP3 or its downstream products as treatments for fibrotic disorders.

NLRP3, NLRC4 and NLRC5 Gene Polymorphisms Associate with Susceptibility of Pulmonary Aspergillosis in Non-Neutropenic Patients

Background: Non-neutropenic pulmonary aspergillosis is one of the most common and serious fungal infections. Previous studies have shown that single nucleotide polymorphisms (SNPs) of pattern recognition receptors genes are associated with susceptibility to aspergillosis. NOD-like receptors (NLRs) play an important role in the immunological response against fungal infection. In this study, we investigated the relationship between polymorphisms of three NLRs and susceptibility to pulmonary aspergillosis disease in non-neutropenic patients. Methods: We included 73 patients with proven pulmonary aspergillosis and 103 healthy controls. A total of sixteen SNPs in the NLRP3, NLRC4, and NLRC5 genes were detected by PCR-direct sequencing. Then, we evaluated the association between these polymorphisms and susceptibility to aspergillosis. Results: Fifteen SNPs were consistent with Hardy–Weinberg equilibrium except for NLRP3 rs7525979. A total of eight SNPs (NLRP3 rs3806265, NLRC4 rs212704 and NLRC5 rs1684579, rs12598522, rs3995817, rs3995818, rs34531240, rs28438857) were observed an association with susceptibility of pulmonary aspergillosis. The CC homozygote of NLRP3 rs3806265, TT homozygote of NLRC5 rs1684579 and T allele of NLRC5 rs12598522 were associated with a higher risk of aspergillosis while TT homozygote of NLRC4 rs212704 was associated with a lower risk of aspergillosis. Especially in the invasive pulmonary aspergillosis subgroup, the TT homozygote of NLRC5 rs1684579 and rs3995817, the CC homozygote of NLRC5 rs34531240 and rs28438857, GG homozygote of NLRC5 rs3995818, the C allele and CC homozygote of NLRP3 rs3806265 were associated with higher susceptibility. Conclusions: This study showed an association between polymorphisms of NLRP3, NLRC4, and NLRC5 and susceptibility to pulmonary aspergillosis for the first time. Further investigations in larger populations are needed, and functional studies are also required to investigate the function of these NLRs in aspergillosis, as well as other fungal infection diseases.

CrkII/Abl phosphorylation cascade is critical for NLRC4 inflammasome activity and is blocked by Pseudomonas aeruginosa ExoT

Type 3 Secretion System (T3SS) is a highly conserved virulence structure that plays an essential role in the pathogenesis of many Gram-negative pathogenic bacteria, including Pseudomonas aeruginosa. Exotoxin T (ExoT) is the only T3SS effector protein that is expressed in all T3SS-expressing P. aeruginosa strains. Here we show that T3SS recognition leads to a rapid phosphorylation cascade involving Abl / PKCδ / NLRC4, which results in NLRC4 inflammasome activation, culminating in inflammatory responses that limit P. aeruginosa infection in wounds. We further show that ExoT functions as the main anti-inflammatory agent for P. aeruginosa in that it blocks the phosphorylation cascade through Abl / PKCδ / NLRC4 by targeting CrkII, which we further demonstrate to be important for Abl transactivation and NLRC4 inflammasome activation in response to T3SS and P. aeruginosa infection.

Pseudomonas aeruginosa secretes the toxin ExoT, which is important for pathogenesis. Here, the authors show that ExoT inhibits NLRC4-dependent inflammatory responses during wound infection.

Epithelial Pyroptosis in Host Defense

Pyroptosis is a lytic form of cell death that is executed by a family of pore-forming proteins called gasdermins (GSDMs). GSDMs are activated upon proteolysis by host proteases including the proinflammatory caspases downstream of inflammasome activation. In myeloid cells, GSDM pore formation serves two primary functions in host defense: the selective release of processed cytokines to initiate inflammatory responses, and cell death, which eliminates a replicative niche of the pathogen. Barrier epithelia also undergo pyroptosis. However, unique mechanisms are required for the removal of pyroptotic epithelial cells to maintain epithelial barrier integrity. In the following review, we discuss the role of epithelial inflammasomes and pyroptosis in host defense against pathogens. We use the well-established role of inflammasomes in intestinal epithelia to highlight principles of epithelial pyroptosis in host defense of barrier tissues, and discuss how these principles might be shared or distinctive across other epithelial sites.

Neutrophil-derived extracellular vesicles promote feed-forward inflammasome signaling in cystic fibrosis airways

Cystic fibrosis (CF) airways feature high extracellular levels of the IL-1 family of proinflammatory mediators. These mediators are cleavage products of caspase-1, the final protease in the inflammasome cascade. Due to the proven chronic presence of reprogrammed neutrophils in the CF airway lumen, understanding inflammasome signaling in these cells is of great importance to understand how disease is perpetuated in this milieu. Here, we hypothesized that CF airway neutrophils contribute to chronic inflammation, in part, via the packaging of inflammasome-inducing signals in extracellular vesicles (EVs). We confirmed that CF airway fluid is enriched in IL-1α, IL-1β, and IL-18, and that CF airway neutrophils up-regulate the activating receptor IL-1R1. Meanwhile, down-modulatory signals such as IL-1R2 and IL-1RA are unchanged. Active caspase-1 itself is present in CF airway fluid EVs, with neutrophil-derived EVs being most enriched. Using a transmigration model of CF airway inflammation, we show that CF airway fluid EVs are necessary and sufficient to induce primary granule exocytosis by naïve neutrophils (hallmark of reprogramming) and concomitantly activate caspase-1 and IL-1β production by these cells and that the addition of triple-combination highly effective CFTR modulator therapy does not abrogate these effects. Finally, EVs from activated neutrophils can deliver active caspase-1 to primary tracheal epithelial cells and induce their release of IL-1α. These findings support the existence of a feed-forward inflammatory process by which reprogrammed CF airway neutrophils bypass 2-step control of inflammasome activation in neighboring cells (naïve neutrophils and epithelial cells) via the transfer of bioactive EVs.

Inflammasome Activation in Pulmonary Arterial Hypertension

Inflammasomes are multi-protein complexes that sense both infectious and sterile inflammatory stimuli, launching a cascade of responses to propagate danger signaling throughout an affected tissue. Recent studies have implicated inflammasome activation in a variety of pulmonary diseases, including pulmonary arterial hypertension (PAH). Indeed, the end-products of inflammasome activation, including interleukin (IL)-1β, IL-18, and lytic cell death (“pyroptosis”) are all key biomarkers of PAH, and are potentially therapeutic targets for human disease. This review summarizes current knowledge of inflammasome activation in immune and vascular cells of the lung, with a focus on the role of these pathways in the pathogenesis of PAH. Special emphasis is placed on areas of potential drug development focused on inhibition of inflammasomes and their downstream effectors.

The Effect of PGC-1alpha-SIRT3 Pathway Activation on Pseudomonas aeruginosa Infection

The innate immune response to P. aeruginosa pulmonary infections relies on a network of pattern recognition receptors, including intracellular inflammasome complexes, which can recognize both pathogen- and host-derived signals and subsequently promote downstream inflammatory signaling. Current evidence suggests that the inflammasome does not contribute to bacterial clearance and, in fact, that dysregulated inflammasome activation is harmful in acute and chronic P. aeruginosa lung infection. Given the role of mitochondrial damage signals in recruiting inflammasome signaling, we investigated whether mitochondrial-targeted therapies could attenuate inflammasome signaling in response to P. aeruginosa and decrease pathogenicity of infection. In particular, we investigated the small molecule, ZLN005, which transcriptionally activates peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, antioxidant defense, and cellular respiration. We demonstrate that P. aeruginosa infection promotes the expression of inflammasome components and attenuates several components of mitochondrial repair pathways in vitro in lung epithelial cells and in vivo in an acute pneumonia model. ZLN005 activates PGC-1α and its downstream effector, Sirtuin 3 (SIRT3), a mitochondrial-localized deacetylase important for cellular metabolic processes and for reactive oxygen species homeostasis. ZLN005 also attenuates inflammasome signaling induced by P. aeruginosa in bronchial epithelial cells and this action is dependent on ZLN005 activation of SIRT3. ZLN005 treatment reduces epithelial-barrier dysfunction caused by P. aeruginosa and decreases pathogenicity in an in vivo pneumonia model. Therapies that activate the PGC-1α—SIRT3 axis may provide a complementary approach in the treatment of P. aeruginosa infection.

Pathogenesis of Respiratory Viral and Fungal Coinfections

Individuals suffering from severe viral respiratory tract infections have recently emerged as "at risk" groups for developing invasive fungal infections. Influenza virus is one of the most common causes of acute lower respiratory tract infections worldwide. Fungal infections complicating influenza pneumonia are associated with increased disease severity and mortality, with invasive pulmonary aspergillosis being the most common manifestation. Strikingly, similar observations have been made during the current coronavirus disease 2019 (COVID-19) pandemic. The copathogenesis of respiratory viral and fungal coinfections is complex and involves a dynamic interplay between the host immune defenses and the virulence of the microbes involved that often results in failure to return to homeostasis. In this review, we discuss the main mechanisms underlying susceptibility to invasive fungal disease following respiratory viral infections. A comprehensive understanding of these interactions will aid the development of therapeutic modalities against newly identified targets to prevent and treat these emerging coinfections.

P. aeruginosa biofilm activates the NLRP3 inflammasomes in vitro

The ability of P.aeruginosa to form biofilms renders common treatments inefficient, thereby promoting chronic infection. Inflammasomes activate caspase-1, which is important for the maturation of IL-1β and IL-18 and evoke an inflammatory response. We aimed to investigate the activation of inflammasomes induced by P.aeruginosa biofilm. THP-1 cells were mock-infected or infected with PAO1 biofilms. Protein levels of caspase-1 p20, pro-caspase-1, caspase-4 p20, and pro-caspase-4 in THP-1 macrophages were determined by Western blotting. The expression of NLRC4 and NLRP3 was measured by RT-PCR. The production of IL-1β and IL-18 was monitored using ELISA. P. aeruginosa biofilm significantly elevated caspase-1 levels, and decreased NLRC4 levels. Additionally, caspase-4 and NLRP3 levels were significantly increased. P.aeruginosa biofilm significantly enhanced IL-1β and IL-18 production. We concluded that P. aeruginosa biofilm induced the production of IL-1β and IL-18, possibly via NLRP3 inflammasomes, rather than NLRC4 inflammasomes.

Aspergillus-related lung disease in people with cystic fibrosis: can imaging help us to diagnose disease?

In people with cystic fibrosis (PwCF), viscous sputum and dysfunction of the mucociliary escalator leads to early and chronic infections. The prevalence of Aspergillus fumigatus in sputum is high in PwCF and the contribution of A. fumigatus to the progression of structural lung disease has been reported. However, overall, relatively little is known about the contribution of A. fumigatus to CF lung disease. More knowledge is needed to aid clinical decisions on whether to start antifungal treatment. In this review, we give an overview of A. fumigatus colonisation and infection in PwCF and the different types of pulmonary disease caused by it. Furthermore, we discuss the current evidence for structural lung damage associated with A. fumigatus in PwCF on chest computed tomography and magnetic resonance imaging. We conclude that radiological outcomes to identify disease caused by A. fumigatus can be important for clinical studies and management.