Candida albicans triggers NLRP3-mediated pyroptosis in macrophages

Alpha1-antitrypsin impacts innate host-pathogen interactions with Candida albicans by stimulating fungal filamentation

Our immune system possesses sophisticated mechanisms to cope with invading microorganisms, while pathogens evolve strategies to deal with threats imposed by host immunity. Human plasma protein α1-antitrypsin (AAT) exhibits pleiotropic immune-modulating properties by both preventing immunopathology and improving antimicrobial host defence. Genetic associations suggested a role for AAT in candidemia, the most frequent fungal blood stream infection in intensive care units, yet little is known about how AAT influences interactions between Candida albicans and the immune system. Here, we show that AAT differentially impacts fungal killing by innate phagocytes. We observed that AAT induces fungal transcriptional reprogramming, associated with cell wall remodelling and downregulation of filamentation repressors. At low concentrations, the cell-wall remodelling induced by AAT increased immunogenic β-glucan exposure and consequently improved fungal clearance by monocytes. Contrastingly, higher AAT concentrations led to excessive C. albicans filamentation and thus promoted fungal immune escape from monocytes and macrophages. This underscores that fungal adaptations to the host protein AAT can differentially define the outcome of encounters with innate immune cells, either contributing to improved immune recognition or fungal immune escape.

Candida albicans and Candida glabrata: global priority pathogens

SUMMARYA significant increase in the incidence of Candida-mediated infections has been observed in the last decade, mainly due to rising numbers of susceptible individuals. Recently, the World Health Organization published its first fungal pathogen priority list, with Candida species listed in medium, high, and critical priority categories. This review is a synthesis of information and recent advances in our understanding of two of these species-Candida albicans and Candida glabrata. Of these, C. albicans is the most common cause of candidemia around the world and is categorized as a critical priority pathogen. C. glabrata is considered a high-priority pathogen and has become an increasingly important cause of candidemia in recent years. It is now the second most common causative agent of candidemia in many geographical regions. Despite their differences and phylogenetic divergence, they are successful as pathogens and commensals of humans. Both species can cause a broad variety of infections, ranging from superficial to potentially lethal systemic infections. While they share similarities in certain infection strategies, including tissue adhesion and invasion, they differ significantly in key aspects of their biology, interaction with immune cells, host damage strategies, and metabolic adaptations. Here we provide insights on key aspects of their biology, epidemiology, commensal and pathogenic lifestyles, interactions with the immune system, and antifungal resistance.

Modeling of intravenous caspofungin administration using an intestine-on-chip reveals altered Candida albicans microcolonies and pathogenicity

Candida albicans is a commensal yeast of the human intestinal microbiota that, under predisposing conditions, can become pathogenic and cause life-threatening systemic infections (candidiasis). Fungal-host interactions during candidiasis are commonly studied using conventional 2D in vitro models, which have provided critical insights into the pathogenicity. However, microphysiological models with a higher biological complexity may be more suitable to mimic in vivo-like infection processes and antifungal drug efficacy. Therefore, a 3D intestine-on-chip model was used to investigate fungal-host interactions during the onset of invasive candidiasis and evaluate antifungal treatment under clinically relevant conditions. By combining microbiological and image-based analyses we quantified infection processes such as invasiveness and fungal translocation across the epithelial barrier. Additionally, we obtained novel insights into fungal microcolony morphology and association with the tissue. Our results demonstrate that C. albicans microcolonies induce injury to the epithelial tissue by disrupting apical cell-cell contacts and causing inflammation. Caspofungin treatment effectively reduced the fungal biomass and induced substantial alterations in microcolony morphology during infection with a wild-type strain. However, caspofungin showed limited effects after infection with an echinocandin-resistant clinical isolate. Collectively, this organ-on-chip model can be leveraged for in-depth characterization of pathogen-host interactions and alterations due to antimicrobial treatment.

Non-canonical activation of IRE1α during Candida albicans infection enhances macrophage fungicidal activity

While the canonical function of IRE1α is to detect misfolded proteins and activate the unfolded protein response (UPR) to maintain cellular homeostasis, microbial pathogens can also activate IRE1α, which modulates innate immunity and infection outcomes. However, how infection activates IRE1α and its associated inflammatory functions have not been fully elucidated. Recognition of microbe-associated molecular patterns can activate IRE1α, but it is unclear whether this depends on protein misfolding. Here, we report that a common and deadly fungal pathogen, Candida albicans, activates macrophage IRE1α through C-type lectin receptor signaling, reinforcing a role for IRE1α as a central regulator of host responses to infection by a broad range of pathogens. This activation did not depend on protein misfolding in response to C. albicans infection. Moreover, lipopolysaccharide treatment was also able to activate IRE1α prior to protein misfolding, suggesting that pathogen-mediated activation of IRE1α occurs through non-canonical mechanisms. During C. albicans infection, we observed that IRE1α activity promotes phagolysosomal fusion that supports the fungicidal activity of macrophages. Consequently, macrophages lacking IRE1α activity displayed inefficient phagosome maturation, enabling C. albicans to lyse the phagosome, evade fungal killing, and drive aberrant inflammatory cytokine production. Mechanistically, we show that IRE1α activity supports phagosomal calcium flux after phagocytosis of C. albicans, which is crucial for phagosome maturation. Importantly, deletion of IRE1α activity decreased the fungicidal activity of phagocytes in vivo during systemic C. albicans infection. Together, these data provide mechanistic insight for the non-canonical activation of IRE1α during infection, and reveal central roles for IRE1α in macrophage antifungal responses.

"We've got to get out"-Strategies of human pathogenic fungi to escape from phagocytes

Human fungal pathogens are a deadly and underappreciated risk to global health that most severely affect immunocompromised individuals. A virulence attribute shared by some of the most clinically relevant fungal species is their ability to survive inside macrophages and escape from these immune cells. In this review, we discuss the mechanisms behind intracellular survival and elaborate how escape is mediated by lytic and non-lytic pathways as well as strategies to induce programmed host cell death. We also discuss persistence as an alternative to rapid host cell exit. In the end, we address the consequences of fungal escape for the host immune response and provide future perspectives for research and development of targeted therapies.

Macrophage pyroptosis induced by Candida albicans

Candida albicans (C. albicans) is a prevalent opportunistic pathogen that causes mucocutaneous and systemic infections, particularly in immunocompromised individuals. Macrophages play a crucial role in eliminating C. albicans in local and bloodstream contexts, while also regulating antifungal immune responses. However, C. albicans can induce macrophage lysis through pyroptosis, a type of regulated cell death. This process can enable C. albicans to escape from immune cells and trigger the release of IL-1β and IL-18, which can impact both the host and the pathogen. Nevertheless, the mechanisms by which C. albicans triggers pyroptosis in macrophages and the key factors involved in this process remain unclear. In this review, we will explore various factors that may influence or trigger pyroptosis in macrophages induced by C. albicans, such as hypha, ergosterol, cell wall remodeling, and other virulence factors. We will also examine the possible immune response following macrophage pyroptosis.

MDA5 Enhances Invasive Candida albicans Infection by Regulating Macrophage Apoptosis and Phagocytosis/Killing Functions

Candida albicans is a common opportunistic pathogenic fungus. The innate immune system provides the first-line host defense against fungal infection. Innate immune receptors and downstream molecules have been shown to play various roles during fungal infection. The innate immune receptor MDA5, encoded by the gene Ifih1, enhances host resistance against viral and Aspergillus fumigatus infection by inducing the production of interferons (IFNs). However, the role of MDA5 in C. albicans infection is still unclear. Here, we found that the gene expression levels of IFIH1 were significantly increased in innate immune cells after C. albicans stimulation through human bioinformatics analysis or mouse experiments. Through in vivo study, MDA5 was shown to enhance host susceptibility to C. albicans infection independent of IFN production. Instead, MDA5 exerted its influence on macrophages and kidneys by modulating the expression of Noxa, Bcl2, and Bax, thereby promoting apoptosis. Additionally, MDA5 compromised killing capabilities of macrophage by inhibition iNOS expression. The introduction of the apoptosis inducer PAC1 further impaired macrophage functions, mimicking the enhancing effect of MDA5 on C. albicans infection. Furthermore, the administration of macrophage scavengers increased the susceptibility of Ifih1-/- mice to C. albicans. The founding suggests that MDA5 promote host susceptibility to invasive C. albicans by enhancing cell apoptosis and compromising macrophage functions, making MDA5 a target to treat candidiasis.

Pyroptosis in microbial infectious diseases

Pyroptosis is a gasdermins-mediated programmed cell death that plays an essential role in immune regulation, and its role in autoimmune disease and cancer has been studied extensively. Increasing evidence shows that various microbial infections can lead to pyroptosis, associated with the occurrence and development of microbial infectious diseases. This study reviews the recent advances in pyroptosis in microbial infection, including bacterial, viral, and fungal infections. We also explore potential therapeutic strategies for treating microbial infection-related diseases by targeting pyroptosis.

The short-chain fatty acid crotonate reduces invasive growth and immune escape of Candida albicans by regulating hyphal gene expression

IMPORTANCE

Macrophages curtail the proliferation of the pathogen Candida albicans within human body niches. Within macrophages, C. albicans adapts its metabolism and switches to invasive hyphal morphology. These adaptations enable fungal growth and immune escape by triggering macrophage lysis. Transcriptional programs regulate these metabolic and morphogenetic adaptations. Here we studied the roles of chromatin in these processes and implicate lysine crotonylation, a histone mark regulated by metabolism, in hyphal morphogenesis and macrophage interactions by C. albicans. We show that the short-chain fatty acid crotonate increases histone crotonylation, reduces hyphal formation within macrophages, and slows macrophage lysis and immune escape of C. albicans. Crotonate represses hyphal gene expression, and we propose that C. albicans uses diverse acylation marks to regulate its cell morphology in host environments. Hyphal formation is a virulence property of C. albicans. Therefore, a further importance of our study stems from identifying crotonate as a hyphal inhibitor.

Respiration supports intraphagosomal filamentation and escape of Candida albicans from macrophages

IMPORTANCE

Candida albicans is a leading human fungal pathogen that often causes life-threatening infections in immunocompromised individuals. The ability of C. albicans to transition between yeast and filamentous forms is key to its virulence, and this occurs in response to many host-relevant cues, including engulfment by host macrophages. While previous efforts identified C. albicans genes required for filamentation in other conditions, the genes important for this morphological transition upon internalization by macrophages remained largely enigmatic. Here, we employed a functional genomic approach to identify genes that enable C. albicans filamentation within macrophages and uncovered a role for the mitochondrial ribosome, respiration, and the SNF1 AMP-activated kinase complex. Additionally, we showed that glucose uptake and glycolysis by macrophages support C. albicans filamentation. This work provides insights into the metabolic dueling that occurs during the interaction of C. albicans with macrophages and identifies vulnerabilities in C. albicans that could serve as promising therapeutic targets.

Modulatory immune responses in fungal infection associated with organ transplant - advancements, management, and challenges

Organ transplantation stands as a pivotal achievement in modern medicine, offering hope to individuals with end-stage organ diseases. Advancements in immunology led to improved organ transplant survival through the development of immunosuppressants, but this heightened susceptibility to fungal infections with nonspecific symptoms in recipients. This review aims to establish an intricate balance between immune responses and fungal infections in organ transplant recipients. It explores the fundamental immune mechanisms, recent advances in immune response dynamics, and strategies for immune modulation, encompassing responses to fungal infections, immunomodulatory approaches, diagnostics, treatment challenges, and management. Early diagnosis of fungal infections in transplant patients is emphasized with the understanding that innate immune responses could potentially reduce immunosuppression and promise efficient and safe immuno-modulating treatments. Advances in fungal research and genetic influences on immune-fungal interactions are underscored, as well as the potential of single-cell technologies integrated with machine learning for biomarker discovery. This review provides a snapshot of the complex interplay between immune responses and fungal infections in organ transplantation and underscores key research directions.

Targeting Microglia/Macrophages Notch1 Protects Neurons from Pyroptosis in Ischemic Stroke

BACKGROUND AND AIMS

The immune-inflammatory cascade and pyroptosis play an important role in the pathogenesis of cerebral ischemia-reperfusion injury (CIRI). The maintenance of immune homeostasis is inextricably linked to the Notch signaling pathway, but whether myeloid Notch1 affects microglia polarization as well as neuronal pyroptosis in CIRI is not fully understood. This study was designed to clarify the role of myeloid Notch1 in CIRI, providing new therapeutic strategies for ischemic stroke.

METHODS AND RESULTS

Myeloid-specific Notch1 knockout (Notch1M-KO) mice and the floxed Notch1 (Notch1FL/FL) mice were subjected to middle cerebral artery occlusion (MCAO). After 3 days of CIRI, we evaluated the neurological deficit score and cerebral infarction volume. Immunofluorescence staining was used to detect the expression of Notch1 and microglial subtype markers. Cerebral infiltrating macrophages were detected by flow cytometry. RT-qPCR was used to detect pro-inflammatory cytokines. Western blot was used to detect the expression of pyroptosis related proteins. The Notch1-siRNA transfected BV2 cells were co-cultured with HT22 cells to investigate the potential mechanisms by which microglial Notch1 affects neuronal pyroptosis induced by anoxia/reoxygenation in vitro. We found that Notch1 was activated in cerebral microglia/macrophages after CIRI. Myeloid Notch1 deficiency decreased the cerebral infarct volume (24.17 ± 3.29 vs. 36.17 ± 2.27, p < 0.001), neurological function scores (2.33 ± 0.47 vs. 3.17 ± 0.37, p < 0.001) and the infiltration of peripheral monocytes/macrophages (3.26 ± 0.53 vs. 5.67 ± 0.57, p < 0.01). Strikingly, myeloid-specific Notch1 knockout alleviated pyroptosis. Compared with microglia M1, increased microglia M2 were detected in the ischemic penumbra. In parallel in vitro co-culture experiments, we found that Notch1 knockdown in microglial BV2 cells inhibited anoxia/reoxygenation-induced JAK2/STAT3 activation and pyroptosis in hippocampal neuron HT22 cells.

CONCLUSIONS

Our findings elucidate the underlying mechanism of the myeloid Notch1 signaling pathway in regulating neuronal pyroptosis in CIRI, suggesting that targeting myeloid-specific Notch1 is an effective strategy for the treatment of ischemic stroke.

Candida auris-macrophage cellular interactions and transcriptional response

The pathogenic yeast Candida auris represents a global threat of the utmost clinical relevance. This emerging fungal species is remarkable in its resistance to commonly used antifungal agents and its persistence in the nosocomial settings. The innate immune system is one the first lines of defense preventing the dissemination of pathogens in the host. C. auris is susceptible to circulating phagocytes, and understanding the molecular details of these interactions may suggest routes to improved therapies. In this work, we examined the interactions of this yeast with macrophages. We found that macrophages avidly phagocytose C. auris; however, intracellular replication is not inhibited, indicating that C. auris resists the killing mechanisms imposed by the phagocyte. Unlike Candida albicans, phagocytosis of C. auris does not induce macrophage lysis. The transcriptional response of C. auris to macrophage phagocytosis is very similar to other members of the CUG clade (C. albicans, C. tropicalis, C. parapsilosis, C. lusitaniae), i.e., downregulation of transcription/translation and upregulation of alternative carbon metabolism pathways, transporters, and induction of oxidative stress response and proteolysis. Gene family expansions are common in this yeast, and we found that many of these genes are induced in response to macrophage co-incubation. Among these, amino acid and oligopeptide transporters, as well as lipases and proteases, are upregulated. Thus, C. auris shares key transcriptional signatures shared with other fungal pathogens and capitalizes on the expansion of gene families coding for potential virulence attributes that allow its survival, persistence, and evasion of the innate immune system.

Differential Transcriptional Responses of Human Granulocytes to Fungal Infection with Candida albicans and Aspergillus fumigatus

Neutrophils are critical phagocytic cells in innate immunity, playing a significant role in defending against invasive fungal pathogens. This study aimed to explore the transcriptional activation of human neutrophils in response to different fungal pathogens, including Candida albicans and Aspergillus fumigatus, compared to the bacterial pathogen Escherichia coli. We identified distinct transcriptional profiles and stress-related pathways in neutrophils during fungal infections, highlighting their functional diversity and adaptability. The transcriptional response was largely redundant across all pathogens in immune-relevant categories and cytokine pathway activation. However, differences in the magnitude of differentially expressed genes (DEGs) were observed, with A. fumigatus inducing a lower transcriptional effect compared to C. albicans and E. coli. Notably, specific gene signatures associated with cell death were differentially regulated by fungal pathogens, potentially increasing neutrophil susceptibility to autophagy, pyroptosis, and neutrophil extracellular trap (NET) formation. These findings provide valuable insights into the complex immunological responses of neutrophils during fungal infections, offering new avenues for diagnostic and therapeutic strategies, particularly in the management of invasive fungal diseases.

C5a-licensed phagocytes drive sterilizing immunity during systemic fungal infection

Systemic candidiasis is a common, high-mortality, nosocomial fungal infection. Unexpectedly, it has emerged as a complication of anti-complement C5-targeted monoclonal antibody treatment, indicating a critical niche for C5 in antifungal immunity. We identified transcription of complement system genes as the top biological pathway induced in candidemic patients and as predictive of candidemia. Mechanistically, C5a-C5aR1 promoted fungal clearance and host survival in a mouse model of systemic candidiasis by stimulating phagocyte effector function and ERK- and AKT-dependent survival in infected tissues. C5ar1 ablation rewired macrophage metabolism downstream of mTOR, promoting their apoptosis and enhancing mortality through kidney injury. Besides hepatocyte-derived C5, local C5 produced intrinsically by phagocytes provided a key substrate for antifungal protection. Lower serum C5a concentrations or a C5 polymorphism that decreases leukocyte C5 expression correlated independently with poor patient outcomes. Thus, local, phagocyte-derived C5 production licenses phagocyte antimicrobial function and confers innate protection during systemic fungal infection.

A positive feedback cycle between the alarmin S100A8/A9 and NLRP3 inflammasome-GSDMD signalling reinforces the innate immune response in Candida albicans keratitis

OBJECTIVE

Fungal keratitis is a severe sight-threatening ocular infection, without effective treatment strategies available now. Calprotectin S100A8/A9 has recently attracted great attention as a critical alarmin modulating the innate immune response against microbial challenges. However, the unique role of S100A8/A9 in fungal keratitis is poorly understood.

METHODS

Experimental fungal keratitis was established in wild-type and gene knockout (TLR4^-/- and GSDMD^-/-) mice by infecting mouse corneas with Candida albicans. The degree of mouse cornea injuries was evaluated by clinical scoring. To interrogate the molecular mechanism in vitro, macrophage RAW264.7 cell line was challenged with Candida albicans or recombinant S100A8/A9 protein. Label-free quantitative proteomics, quantitative real-time PCR, Western blotting, and immunohistochemistry were conducted in this research.

RESULTS

Herein, we characterized the proteome of mouse corneas infected with Candida albicans and found that S100A8/A9 was robustly expressed at the early stage of the disease. S100A8/A9 significantly enhanced disease progression by promoting NLRP3 inflammasome activation and Caspase-1 maturation, accompanied by increased accumulation of macrophages in infected corneas. In response to Candida albicans infection, toll-like receptor 4 (TLR4) sensed extracellular S100A8/A9 and acted as a bridge between S100A8/A9 and NLRP3 inflammasome activation in mouse corneas. Furthermore, the deletion of TLR4 resulted in noticeable improvement in fungal keratitis. Remarkably, NLRP3/GSDMD-mediated macrophage pyroptosis in turn facilitates S100A8/A9 secretion during Candida albicans keratitis, thus forming a positive feedback cycle that amplifies the proinflammatory response in corneas.

CONCLUSIONS

The present study is the first to reveal the critical roles of the alarmin S100A8/A9 in the immunopathology of Candida albicans keratitis, highlighting a promising approach for therapeutic intervention in the future.

Thalidomide promotes NLRP3/caspase-1-mediated pyroptosis of macrophages in Talaromyces marneffei infection

Macrophage-derived inflammatory cytokines are critical for host defense against Talaromyces marneffei (T. marneffei) infection among HIV/AIDS patients, and excessive inflammatory cytokines are associated with poor outcomes of AIDS-associated talaromycosis. However, the underlying mechanisms of macrophage-caused pyroptosis and cytokine storm are poorly understood. Here, in the T. marneffei-infected mice and macrophages, we show that T. marneffei induced pyroptosis in macrophages through the NLRP3/caspase-1 pathway. The immunomodulatory drug thalidomide could promote the pyroptosis of macrophages infected T. marneffei. In T. marneffei-infected mice, the splenic macrophages underwent increasing pyroptosis as talaromycosis deteriorated. Thalidomide ameliorated inflammation of mice, while amphotericin B (AmB) in combination with thalidomide did not improve overall survival compared with AmB alone. Taken together, our findings suggest that thalidomide promotes NLRP3/caspase-1-mediated pyroptosis of macrophages in T. marneffei infection.

Candida albicans Hyphal Morphogenesis within Macrophages Does Not Require Carbon Dioxide or pH-Sensing Pathways

The opportunistic fungal pathogen Candida albicans has evolved a variety of mechanisms for surviving inside and escaping macrophages, including the initiation of filamentous growth. Although several distinct models have been proposed to explain this process at the molecular level, the signals driving hyphal morphogenesis in this context have yet to be clarified. Here, we evaluate the following three molecular signals as potential hyphal inducers within macrophage phagosomes: CO2, intracellular pH, and extracellular pH. Additionally, we revisit previous work suggesting that the intracellular pH of C. albicans fluctuates in tandem with morphological changes in vitro. Using time-lapse microscopy, we observed that C. albicans mutants lacking components of the CO2-sensing pathway were able to undergo hyphal morphogenesis within macrophages. Similarly, a rim101Δ strain was competent in hyphal induction, suggesting that neutral/alkaline pH sensing is not necessary for the initiation of morphogenesis within phagosomes either. Contrary to previous findings, single-cell pH-tracking experiments revealed that the cytosolic pH of C. albicans remains tightly regulated both within macrophage phagosomes and under a variety of in vitro conditions throughout the process of morphogenesis. This finding suggests that intracellular pH is not a signal contributing to morphological changes.

The Interplay between Candida albicans, Vaginal Mucosa, Host Immunity and Resident Microbiota in Health and Disease: An Overview and Future Perspectives

Vulvovaginal candidiasis (VVC), which is primarily caused by Candida albicans, is an infection that affects up to 75% of all reproductive-age women worldwide. Recurrent VVC (RVVC) is defined as >3 episodes per year and affects nearly 8% of women globally. At mucosal sites of the vagina, a delicate and complex balance exists between Candida spp., host immunity and local microbial communities. In fact, both immune response and microbiota composition play a central role in counteracting overgrowth of the fungus and maintaining homeostasis in the host. If this balance is perturbed, the conditions may favor C. albicans overgrowth and the yeast-to-hyphal transition, predisposing the host to VVC. To date, the factors that affect the equilibrium between Candida spp. and the host and drive the transition from C. albicans commensalism to pathogenicity are not yet fully understood. Understanding the host- and fungus-related factors that drive VVC pathogenesis is of paramount importance for the development of adequate therapeutic interventions to combat this common genital infection. This review focuses on the latest advances in the pathogenic mechanisms implicated in the onset of VVC and also discusses novel potential strategies, with a special focus on the use of probiotics and vaginal microbiota transplantation in the treatment and/or prevention of recurrent VVC.

Advanced Glycation End-Products (AGEs) Promote Endothelial Cell Pyroptosis Under Cerebral Ischemia and Hypoxia via HIF-1α-RAGE-NLRP3

This work mainly aimed to explore the role and mechanism of advanced glycation end-products (AGEs) in inducing cerebrovascular endothelial cell pyroptosis under oxygen glucose deprivation (OGD) condition. The mouse cerebral microvascular endothelial cells (BMECs and bEnd.3) were used as the objects to construct the OGD model in vitro. Then, cells were pretreated with AGE-modified human serum albumin (AGE-HSA). Thereafter, CCK-8 assay was conducted to detect cell viability, and flow cytometry (FCM) was performed to measure cell pyroptosis level. Meanwhile, the expression of inflammatory factors was detected by enzyme-linked immunosorbent assay (ELISA). The expression of HIF-α, NLRP3, and RAGE was detected by fluorescence staining. The opening status of cell membrane pore was observed under the electron microscope, and the expression levels of FL-GSDMD, NT-GSDMD, and caspase-1 were measured through Western Blot (WB) assay. Moreover, bEnd.3 cells were treated with siRAN-silenced NLRP3 and HIF-α inhibitor, so as to observe the effect of AGEs on cell pyroptosis level. In the mouse model, the middle cerebral artery occlusion (MCAO) model was constructed by the suture-occluded method. After intraperitoneal injection of AGEs, the pathological changes in mouse brain tissues were detected; the expression levels of NLRP3, ZO-1, and CD31 were determined by histochemical staining, and the levels of inflammatory factors and pyroptosis-related proteins were also detected. Under OGD condition, AGEs induced the pyroptosis of bEnd.3 cells, and the cell pyroptosis rate increased, higher than that of the OGD group. Meanwhile, the levels of inflammatory factors were up-regulated; the expression of HIF-α, NLRP3, and RAGE in cells increased; and the levels of NT-GSDMD and caspase-1 were markedly higher than those of the control and OGD groups. siRNA-NLRP3 or HIF-α inhibitor treatment suppressed pyroptosis and reduced the inflammatory factor levels. In mouse experiments, AGE injection aggravated brain injury in the MCAO mouse model, decreased the expression of ZO-1 and CD31, and elevated the levels of NLRP3 and inflammatory factors. Under cerebral ischemia condition, AGEs can induce endothelial cell pyroptosis via HIF-α-RAGE-NLRP3, thereby further aggravating brain injury.

Fungal infections: Immune defense, immunotherapies and vaccines

Invasive fungal infection is an under recognized and emerging global health threat. Recently, the World Health Organization (WHO) released the first ever list of health-threatening fungi to guide research and public health interventions to strengthen global response to fungi infections and antifungal resistance. Currently, antifungal drugs only demonstrate partial success in improving prognosis of infected patients, and this is compounded by the rapid evolution of drug resistance among fungi species. The increased prevalence of fungal infections in individuals with underlying immunological deficiencies reflects the importance of an intact host immune system in controlling mycoses, and further highlights immunomodulation as a potential new avenue for the treatment of disseminated fungal diseases. In this review, we will summarize how host innate immune cells sense invading fungi through their pattern recognition receptors, and subsequently initiate a series of effector mechanisms and adaptive immune responses to mediate fungal clearance. In addition, we will discuss emerging preclinical and clinical data on antifungal immunotherapies and fungal vaccines which can potentially expand our antifungal armamentarium in future.

"Under Pressure" - How fungi evade, exploit, and modulate cells of the innate immune system

The human immune system uses an arsenal of effector mechanisms to prevent and counteract infections. Yet, some fungal species are extremely successful as human pathogens, which can be attributed to a wide variety of strategies by which these fungi evade, exploit, and modulate the immune system. These fungal pathogens normally are either harmless commensals or environmental fungi. In this review we discuss how commensalism, but also life in an environmental niche without human contact, can drive the evolution of diverse and specialized immune evasion mechanisms. Correspondingly, we discuss the mechanisms contributing to the ability of these fungi to cause superficial to life-threatening infections.

Fungal resilience and host-pathogen interactions: Future perspectives and opportunities

We are constantly exposed to the threat of fungal infection. The outcome-clearance, commensalism or infection-depends largely on the ability of our innate immune defences to clear infecting fungal cells versus the success of the fungus in mounting compensatory adaptive responses. As each seeks to gain advantage during these skirmishes, the interactions between host and fungal pathogen are complex and dynamic. Nevertheless, simply compromising the physiological robustness of fungal pathogens reduces their ability to evade antifungal immunity, their virulence, and their tolerance against antifungal therapy. In this article I argue that this physiological robustness is based on a 'Resilience Network' which mechanistically links and controls fungal growth, metabolism, stress resistance and drug tolerance. The elasticity of this network probably underlies the phenotypic variability of fungal isolates and the heterogeneity of individual cells within clonal populations. Consequently, I suggest that the definition of the fungal Resilience Network represents an important goal for the future which offers the clear potential to reveal drug targets that compromise drug tolerance and synergise with current antifungal therapies.

Nature of β-1,3-Glucan-Exposing Features on Candida albicans Cell Wall and Their Modulation

Candida albicans exists as a commensal of mucosal surfaces and the gastrointestinal tract without causing pathology. However, this fungus is also a common cause of mucosal and systemic infections when antifungal immune defenses become compromised. The activation of antifungal host defenses depends on the recognition of fungal pathogen-associated molecular patterns (PAMPs), such as β-1,3-glucan. In C. albicans, most β-1,3-glucan is present in the inner cell wall, concealed by the outer mannan layer, but some β-1,3-glucan becomes exposed at the cell surface. In response to host signals, such as lactate, C. albicans induces the Xog1 exoglucanase, which shaves exposed β-1,3-glucan from the cell surface, thereby reducing phagocytic recognition. We show here that β-1,3-glucan is exposed at bud scars and punctate foci on the lateral wall of yeast cells, that this exposed β-1,3-glucan is targeted during phagocytic attack, and that lactate-induced masking reduces β-1,3-glucan exposure at bud scars and at punctate foci. β-1,3-Glucan masking depends upon protein kinase A (PKA) signaling. We reveal that inactivating PKA, or its conserved downstream effectors, Sin3 and Mig1/Mig2, affects the amounts of the Xog1 and Eng1 glucanases in the C. albicans secretome and modulates β-1,3-glucan exposure. Furthermore, perturbing PKA, Sin3, or Mig1/Mig2 attenuates the virulence of lactate-exposed C. albicans cells in Galleria. Taken together, the data are consistent with the idea that β-1,3-glucan masking contributes to Candida pathogenicity. IMPORTANCE Microbes that coexist with humans have evolved ways of avoiding or evading our immunological defenses. These include the masking by these microbes of their "pathogen-associated molecular patterns" (PAMPs), which are recognized as "foreign" and used to activate protective immunity. The commensal fungus Candida albicans masks the proinflammatory PAMP β-1,3-glucan, which is an essential component of its cell wall. Most of this β-1,3-glucan is hidden beneath an outer layer of the cell wall on these microbes, but some can become exposed at the fungal cell surface. Using high-resolution confocal microscopy, we examine the nature of the exposed β-1,3-glucan at C. albicans bud scars and at punctate foci on the lateral cell wall, and we show that these features are targeted by innate immune cells. We also reveal that downstream effectors of protein kinase A (Mig1/Mig2, Sin3) regulate the secretion of major glucanases, modulate the levels of β-1,3-glucan exposure, and influence the virulence of C. albicans in an invertebrate model of systemic infection. Our data support the view that β-1,3-glucan masking contributes to immune evasion and the virulence of a major fungal pathogen of humans.

A Novel Defined Pyroptosis-Related Gene Signature for Predicting the Prognosis of Endometrial Cancer

Endometrial carcinoma (EC) is the second major female genital malignancy. Genetic signatures may be an improved choice to predict the prognosis of EC patients. The relationship between pyroptosis and tumours has attracted much attention in recent years. Here, we constructed a new pyroptosis-related gene (PRG) signature for predicting the prognosis of EC. In this study, gene data and clinical information of EC patients were obtained from The Cancer Genome Atlas (TCGA). Following the identification of PRGs correlated with EC prognosis, we further investigate the bioinformatics functions of these PRGs by univariate Cox regression analysis and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. Then, we used the least absolute contraction and selection operator (LASSO) regression and multiple Cox regression analysis to construct a new PRG signature that contains seven PRGs (NFKB1, EEF2K, CTSV, MDM2, GZMB, PANX1, and PTEN) and performed the Kaplan-Meier (K-M) analysis, receiver operating characteristic curve (ROC) analysis, and principal component analysis (PCA) to evaluate the prognostic value of our novel PRG signature. Finally, we assessed the correlations between pyroptosis and immune cells/checkpoints through the CIBERSORT tool and single-sample gene set enrichment analysis (ssGSEA). The result suggested that our signature was powerful in predicting EC prognosis and may play a part in assessing response to immunotherapy in EC patients. In conclusion, our study established a novel PRG signature for EC, which can be used as an effective prognostic marker in clinical practice in the future.

Inflammasome and Inflammatory Programmed Cell Death in Chromoblastomycosis

Chromoblastomycosis (CBM) is a chronic, progressive fungal disease of the skin and subcutaneous tissue caused by a group of dematiaceous fungi. Verrucous lesions present parasite-rich granulomas and predominance of a Th2 patterns of cytokines. The inflammasome constitutes a macromolecular protein complex that play a role in the activation of caspase 1 that cleaves pro-IL1β and pro-IL18, essential mediators of inflammation, and also activates pyroptosis. We intended to explore the presence and a possible role of inflammasome elements in cutaneous human lesions in CBM, considering the expression of IL1β, IL18, caspase 1, NLRP1, and also RIPK3, a key downstream component of necroptosis signaling. 35 skin biopsies of cutaneous lesions of verrucous form of CBM and 10 biopsies from normal skin were selected. The diagnosis was based on histological and clinical analysis. An immunohistochemical protocol was performed. The histopathological analysis evidenced epidermis with hyperkeratosis, irregular acanthosis, and micro abscesses. The dermis presented suppurative granulomas and inflammatory infiltrate composed by giant cells, macrophages, epithelioid cells, lymphocytes, and some eosinophils. Positive cells were distributed in the inflammatory infiltrate, with an increased number of cells expressing caspase 1, IL1β and IL18. Cells expressing RIPK3 and NLRP1 were less frequent. The intense presence of caspase 1, IL1β and IL18, allied to NLRP1 expression, suggest that inflammasome and pyroptosis could play a role in the immune response against fungal agents of CBM. Our results, allied to data from literature, could suggest that inflammasome-mediated response and pyroptosis could be a target to be explored to decrease CBM lesions.

IL-23 signaling prevents ferroptosis-driven renal immunopathology during candidiasis

During infection the host relies on pattern-recognition receptors to sense invading fungal pathogens to launch immune defense mechanisms. While fungal recognition and immune effector responses are organ and cell type specific, during disseminated candidiasis myeloid cells exacerbate collateral tissue damage. The β-glucan receptor ephrin type-A 2 receptor (EphA2) is required to initiate mucosal inflammatory responses during oral Candida infection. Here we report that EphA2 promotes renal immunopathology during disseminated candidiasis. EphA2 deficiency leads to reduced renal inflammation and injury. Comprehensive analyses reveal that EphA2 restrains IL-23 secretion from and migration of dendritic cells. IL-23 signaling prevents ferroptotic host cell death during infection to limit inflammation and immunopathology. Further, host cell ferroptosis limits antifungal effector functions via releasing the lipid peroxidation product 4-hydroxynonenal to induce various forms of cell death. Thus, we identify ferroptotic cell death as a critical pathway of Candida-mediated renal immunopathology that opens a new avenue to tackle Candida infection and inflammation.

The escape of Candida albicans from macrophages is enabled by the fungal toxin candidalysin and two host cell death pathways

The egress of Candida hyphae from macrophages facilitates immune evasion, but it also alerts macrophages to infection and triggers inflammation. To better define the mechanisms, here we develop an imaging assay to directly and dynamically quantify hyphal escape and correlate it to macrophage responses. The assay reveals that Candida escapes by using two pore-forming proteins to permeabilize macrophage membranes: the fungal toxin candidalysin and Nlrp3 inflammasome-activated Gasdermin D. Candidalysin plays a major role in escape, with Nlrp3 and Gasdermin D-dependent and -independent contributions. The inactivation of Nlrp3 does not reduce hyphal escape, and we identify ETosis via macrophage extracellular trap formation as an additional pathway facilitating hyphal escape. Suppressing hyphal escape does not reduce fungal loads, but it does reduce inflammatory activation. Our findings explain how Candida escapes from macrophages by using three strategies: permeabilizing macrophage membranes via candidalysin and engaging two host cell death pathways, Gasdermin D-mediated pyroptosis and ETosis.

Immunomodulatory responses of differentially polarized macrophages to fungal infections

Macrophages, the first line of defense against invasive fungi in the innate immune system, are widely distributed in the blood and tissues of the body. In response to various internal and external stimulators, macrophages can polarize into classically activated macrophages (M1) and alternatively activated macrophages (M2). These two types of polarized macrophages play different roles in antifungal activity and in maintaining the steady-state balance between inflammation and tissue repair. However, the antifungal mechanisms of M1- and M2-type macrophages have not been fully described. In this review, the immune regulatory mechanisms against pathogenic fungi of these two classical types of macrophages in various tissues are summarized. The effects of antifungal factors on macrophage differentiation are also highlighted. The description of these data, on the one hand provides valuable insight for future investigations and also highlights new strategies for the treatment of pathogenic fungal infections.

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.

Mechanism of Electroacupuncture Against Cerebral Ischemia–Reperfusion Injury: Reducing Inflammatory Response and Cell Pyroptosis by Inhibiting NLRP3 and Caspase-1

Cell pyroptosis is one of the main forms of neuronal injury after cerebral ischemia–reperfusion. It is accompanied by an inflammatory reaction and regulated by the caspase gene family. Electroacupuncture (EA) can reduce neuronal injury caused by cerebral ischemia–reperfusion, and we speculated that EA can prevent neuronal pyroptosis after cerebral ischemia–reperfusion by regulating the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3)/caspase-1 pathway. The cerebral ischemia–reperfusion injury model of C57 and caspase-1 gene knockout (Cas-1 ko) mice was established by Longa's method. EA was conducted at acupoints Chize (LU5), Hegu (LI4), Sanyinjiao (SP6), and Zusanli (ST36) for 1.5 h after cerebral ischemia–reperfusion injury for 20 min, and observation was carried out after 24 h. Neurological deficit scores evaluated the neurological function, cerebral infarction volume was observed by triphenyl tetrazolium chloride (TTC) staining, hematoxylin and eosin (H&E) staining, TUNEL and caspase-1 double-labeled fluorescence staining, and NLRP3 and caspase-1 double-labeled immunofluorescence staining that were used to observe the morphology of neurons in hippocampus, and the protein expression of NLRP3, pro-caspase-1, cleaved caspase-1 p20, pro-interleukin-1β (IL-1β), cleaved IL-1β, and GSDMD was detected by Western blot assay. Results showed that EA could reduce the score of neurological deficit, reduce the volume of cerebral infarction and improve the degree of nerve cell injury, and inhibit NLRP3, pro-caspase-1, cleaved caspase-1 p20, pro-IL-1β, cleaved IL-1β, and GSDMD protein expression. In summary, EA plays a neuroprotective role by reducing the pyroptotic neurons that were caspase 1-mediated and inflammatory response after cerebral ischemia–reperfusion.

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.

Genetic Screening of Candida albicans Inactivation Mutants Identifies New Genes Involved in Macrophage-Fungal Cell Interactions

Candida albicans, an important fungal pathogen of humans, displays different morphologies, such as yeast, pseudo-hyphae and hyphae, which are recognized unequally by phagocytic cells of the innate immune response. Once C. albicans cells invade host tissues, immune cells such as macrophages are attracted to the site of infection and activated to recognize, engulf and kill the pathogen. We have investigated this fungal cell-macrophage interface by using high-throughput screening of the C. albicans GRACE library to identify genes that can influence this interaction and modify the kinetics of engulfment. Compared with the wild-type (WT) strain, we identified generally faster rates of engulfment for those fungal strains with constitutive pseudo-hyphal and hyphal phenotypes, whereas yeast-form-locked strains showed a reduced and delayed recognition and internalization by macrophages. We identified a number of GRACE strains that showed normal morphological development but exhibited different recognition and engulfment kinetics by cultured macrophages and characterized two mutants that modified interactions with the murine and human-derived macrophages. One mutant inactivated an uncharacterized C. albicans open reading frame that is the ortholog of S. cerevisiae OPY1, the other inactivated CaKRE1. The modified interaction was monitored during a 4 h co-culture. Early in the interaction, both opy1 and kre1 mutant strains showed reduced recognition and engulfment rates by macrophages when compared with WT cells. At fungal germ tube initiation, the engulfment kinetics increased for both mutants and WT cells, however the WT cells still showed a higher internalization by macrophages up to 2 h of interaction. Subsequently, between 2 and 4 h of the interaction, when most macrophages contain engulfed fungal cells, the engulfment kinetics increased for the opy1 mutant and further decreased for the kre1 mutant compared with Ca-WT. It appears that fungal morphology influences macrophage association with C. albicans cells and that both OPY1 and KRE1 play roles in the interaction of the fungal cells with phagocytes.

Voluven treatment could induce NLRP3 inflammasome mediated pyroptosis of bone marrow derived macrophages

AIM

To investigate the influence of voluven on the NLRP3 inflammasome mediated pyroptosis in bone marrow derived macrophage (BMDM).

METHODS

Separated BMDMs were cultured and treated with different concentration of voluven (0, 0.1, 0.5 µg) dissolving in 10 µL 0.9% Nacl solution for 24 h. Both wildtype and NLRP3-/- C57BL/6J mice (n=18) were intravenously injected with 0.2 mL 0, 5%, 10 % voluven through femoral vein, respectively. Pyroptosis were inspected with flow cytometry. The mRNA levels of NLRP3 and caspase-1 were detected with qRT-PCR. The levels of NLRP3, pro-caspase-1 and cleaved-caspase-1 (p10) in serum were determined with western blot. The expression of IL-17A in peripheral blood CD4+ T cells were analyzed with flow cytometry. The expression of cleaved-caspase-1 (p10) in mice spleens were inspected with immunofluorescence.

RESULTS

Compared with control group, the ratio of pyroptosis in voluven treated groups were all significantly risen. The levels of NLRP3 and caspase-1 were increased after voluven treatment. The expression of IL-17A in voluven treated CD4+ T cells was also increased, exhibiting a dose-dependent pattern. In wildtype mice, voluven treated mice had higher levels of IL-17A, NLRP3 and cleaved-caspase-1 (p10) in a dose-dependent manner. The effects of voluven were diminished in NLRP3-/- mice.

Immune regulation by fungal strain diversity in inflammatory bowel disease

The fungal microbiota (mycobiota) is an integral part of the complex multikingdom microbial community colonizing the mammalian gastrointestinal tract and has an important role in immune regulation1-6. Although aberrant changes in the mycobiota have been linked to several diseases, including inflammatory bowel disease3-9, it is currently unknown whether fungal species captured by deep sequencing represent living organisms and whether specific fungi have functional consequences for disease development in affected individuals. Here we developed a translational platform for the functional analysis of the mycobiome at the fungal-strain- and patient-specific level. Combining high-resolution mycobiota sequencing, fungal culturomics and genomics, a CRISPR-Cas9-based fungal strain editing system, in vitro functional immunoreactivity assays and in vivo models, this platform enables the examination of host-fungal crosstalk in the human gut. We discovered a rich genetic diversity of opportunistic Candida albicans strains that dominate the colonic mucosa of patients with inflammatory bowel disease. Among these human-gut-derived isolates, strains with high immune-cell-damaging capacity (HD strains) reflect the disease features of individual patients with ulcerative colitis and aggravated intestinal inflammation in vivo through IL-1β-dependent mechanisms. Niche-specific inflammatory immunity and interleukin-17A-producing T helper cell (TH17 cell) antifungal responses by HD strains in the gut were dependent on the C. albicans-secreted peptide toxin candidalysin during the transition from a benign commensal to a pathobiont state. These findings reveal the strain-specific nature of host-fungal interactions in the human gut and highlight new diagnostic and therapeutic targets for diseases of inflammatory origin.

Nrf2 in the Field of Dentistry with Special Attention to NLRP3

The aim of this review article was to summarize the functional implications of the nuclear factor E2-related factor or nuclear factor (erythroid-derived 2)-like 2 (Nrf2), with special attention to the NACHT (nucleotide-binding oligomerization), LRR (leucine-rich repeat), and PYD (pyrin domain) domains-containing protein 3 (NLRP3) inflammasome in the field of dentistry. NLRP3 plays a crucial role in the progression of inflammatory and adaptive immune responses throughout the body. It is already known that this inflammasome is a key regulator of several systemic diseases. The initiation and activation of NLRP3 starts with the oral microbiome and its association with the pathogenesis and progression of several oral diseases, including periodontitis, periapical periodontitis, and oral squamous cell carcinoma (OSCC). The possible role of the inflammasome in oral disease conditions may involve the aberrant regulation of various response mechanisms, not only in the mouth but in the whole body. Understanding the cellular and molecular biology of the NLRP3 inflammasome and its relationship to Nrf2 is necessary for the rationale when suggesting it as a potential therapeutic target for treatment and prevention of oral inflammatory and immunological disorders. In this review, we highlighted the current knowledge about NLRP3, its likely role in the pathogenesis of various inflammatory oral processes, and its crosstalk with Nrf2, which might offer future possibilities for disease prevention and targeted therapy in the field of dentistry and oral health.

Control of β-glucan exposure by the endo-1,3-glucanase Eng1 in Candida albicans modulates virulence

Candida albicans is a major opportunistic pathogen of humans. It can grow as morphologically distinct yeast, pseudohyphae and hyphae, and the ability to switch reversibly among different forms is critical for its virulence. The relationship between morphogenesis and innate immune recognition is not quite clear. Dectin-1 is a major C-type lectin receptor that recognizes β-glucan in the fungal cell wall. C. albicans β-glucan is usually masked by the outer mannan layer of the cell wall. Whether and how β-glucan masking is differentially regulated during hyphal morphogenesis is not fully understood. Here we show that the endo-1,3-glucanase Eng1 is differentially expressed in yeast, and together with Yeast Wall Protein 1 (Ywp1), regulates β-glucan exposure and Dectin-1-dependent immune activation of macrophage by yeast cells. ENG1 deletion results in enhanced Dectin-1 binding at the septa of yeast cells; while eng1 ywp1 yeast cells show strong overall Dectin-1 binding similar to hyphae of wild-type and eng1 mutants. Correlatively, hyphae of wild-type and eng1 induced similar levels of cytokines in macrophage. ENG1 expression and Eng1-mediated β-glucan trimming are also regulated by antifungal drugs, lactate and N-acetylglucosamine. Deletion of ENG1 modulates virulence in the mouse model of hematogenously disseminated candidiasis in a Dectin-1-dependent manner. The eng1 mutant exhibited attenuated lethality in male mice, but enhanced lethality in female mice, which was associated with a stronger renal immune response and lower fungal burden. Thus, Eng1-regulated β-glucan exposure in yeast cells modulates the balance between immune protection and immunopathogenesis during disseminated candidiasis.

Pathogenesis and virulence of Candida albicans

Candida albicans is a commensal yeast fungus of the human oral, gastrointestinal, and genital mucosal surfaces, and skin. Antibiotic-induced dysbiosis, iatrogenic immunosuppression, and/or medical interventions that impair the integrity of the mucocutaneous barrier and/or perturb protective host defense mechanisms enable C. albicans to become an opportunistic pathogen and cause debilitating mucocutaneous disease and/or life-threatening systemic infections. In this review, we synthesize our current knowledge of the tissue-specific determinants of C. albicans pathogenicity and host immune defense mechanisms.

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

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

Functionalized niosomes as a smart delivery device in cancer and fungal infection

Various diseases remain untreated due to lack of suitable therapeutic moiety or a suitable drug delivery device, especially where toxicities and side effects are the primary reason for concern. Cancer and fungal infections are diseases where treatment schedules are not completed due to severe side effects or lengthy treatment protocols. Advanced treatment approaches such as active targeting and inhibition of angiogenesis may be preferred method for the treatment for malignancy over the conventional method. Niosomes may be a better alternative drug delivery carrier for various therapeutic moieties (either hydrophilic or hydrophobic) and also due to ease of surface modification, non-immunogenicity and economical. Active targeting approach may be done by targeting the receptors through coupling of suitable ligand on niosomal surface. Moreover, various receptors (CD44, folate, epidermal growth factor receptor (EGFR) & Vascular growth factor receptor (VGFR)) expressed by malignant cells have also been reviewed. The preparation of suitable niosomal formulation also requires considerable attention, and its formulation depends upon various factors such as selection of non-ionic surfactant, method of fabrication, and fabrication parameters. A combination therapy (dual drug and immunotherapy) has been proposed for the treatment of fungal infection with special consideration for surface modification with suitable ligand on niosomal surface to sensitize the receptors (C-type lectin receptors, Toll-like receptors & Nucleotide-binding oligomerization domain-like receptors) present on immune cells involved in fungal immunity. Certain gene silencing concept has also been discussed as an advanced alternative treatment for cancer by silencing the mRNA at molecular level using short interfering RNA (si-RNA).

GRIM19 downregulation-induced pyroptosis of macrophages through NLRP3 pathway in adenomyosis

RESEARCH QUESTION

Does the absence of GRIM19 affect pyroptosis of macrophages? Is the release of IL-1β caused by pyroptosis a relevant factor in the regulation of adenomyosis progression?

DESIGN

Endometrial tissues were collected from patients with (n = 12) and without (n = 12) adenomyosis. GRIM19 expression of adenomyosis tissues was analysed by western blot and real-time polymerase chain reaction (RT-PCR). In GRIM19 knockdown macrophages, pyroptosis-related factors expressions were also measured by western blot and RT-PCR. The human endometrial stromal cells (HESC) were co-cultured with GRIM19-depleted macrophages and IL-1β neutralizing antibody to detect the effects of pyroptosis of macrophages on apoptosis, proliferation and migration of HESC.

RESULTS

The expression of GRIM19 was significantly lower in adenomyosis (P = 0.0002). In THP-1-derived macrophages, the expression of NLRP3 (P < 0.0001), ASC (P = 0.0176), caspase-1 (P = 0.0368), GSDMD (P = 0.0453) and IL-1β (P = 0.0208) are increased after downregulation of GRIM19. GRIM19 knockdown induced the release of IL-1β (P = 0.0195) in THP-1-derived macrophages. The apoptosis of HESC co-cultured with GRIM19 knockdown macrophages was significantly inhibited (P < 0.0001), the proliferation (P = 0.0254) and migration (P < 0.0001) were markedly promoted. Existence of IL-1β neutralizing antibody in supernatants recovered the effects (P < 0.0001) of GRIM19 knockdown macrophages on HESC.

CONCLUSIONS

GRIM19 downregulation induces pyroptosis of macrophages through NLRP3 pathway, increases the secretion of IL-1β and promotes adenomyosis progression.

Pre-existing mycobacterial infection modulates Candida albicans-driven pyroptosis

Active tuberculosis patients are at high risk of coinfection with opportunistic fungal pathogen Candida albicans. However, the molecular mechanisms that orchestrate pathogenesis of Mycobacterium tuberculosis (Mtb)-C. albicans coinfection remain elusive. In the current study, we utilize a mouse model to demonstrate that Mtb promotes a macrophage environment that is conducive for C. albicans survival. Mtb-dependent protein kinase Cζ-WNT signalling axis induces expression of an E3 ubiquitin ligase, constitutive photomorphogenesis protein 1 (COP1). A secondary infection of C. albicans in such Mtb-infected macrophages causes COP1 to mediate the proteasomal degradation of interferon regulatory factor 9 (IRF9), a cardinal factor that we identified to arbitrate an inflammatory programmed cell death, pyroptosis. In vivo experiments mimicking a pre-existing Mtb infection demonstrate that inhibition of pyroptosis in mice results in increased C. albicans burden and aberrant lung tissue architecture, leading to increased host mortality. Together, our study reveals the crucial role of pyroptosis regulation for manifesting a successful C. albicans-Mtb coinfection.

The δ subunit of F1Fo-ATP synthase is required for pathogenicity of Candida albicans

Fungal infections, especially candidiasis and aspergillosis, claim a high fatality rate. Fungal cell growth and function requires ATP, which is synthesized mainly through oxidative phosphorylation, with the key enzyme being F₁F_o-ATP synthase. Here, we show that deletion of the Candida albicans gene encoding the δ subunit of the F₁F_o-ATP synthase (ATP16) abrogates lethal infection in a mouse model of systemic candidiasis. The deletion does not substantially affect in vitro fungal growth or intracellular ATP concentrations, because the decrease in oxidative phosphorylation-derived ATP synthesis is compensated by enhanced glycolysis. However, the ATP16-deleted mutant displays decreased phosphofructokinase activity, leading to low fructose 1,6-bisphosphate levels, reduced activity of Ras1-dependent and -independent cAMP-PKA pathways, downregulation of virulence factors, and reduced pathogenicity. A structure-based virtual screening of small molecules leads to identification of a compound potentially targeting the δ subunit of fungal F₁F_o-ATP synthases. The compound induces in vitro phenotypes similar to those observed in the ATP16-deleted mutant, and protects mice from succumbing to invasive candidiasis. Our findings indicate that F₁F_o-ATP synthase δ subunit is required for C. albicans lethal infection and represents a potential therapeutic target.

Fungal diseases: Oral dysbiosis in susceptible hosts

The oral cavity is colonized by a large number of microorganisms that are referred to collectively as the oral microbiota. These indigenous microorganisms have evolved in symbiotic relationships with the oral mucosal immune system and are involved in maintaining homeostasis in the oral cavity. Although Candida species are commonly found in the healthy oral cavity without causing infection, these fungi can become pathogenic. Recents advances indicate that the development of oral candidiasis is driven both by Candida albicans overgrowth in a dysbiotic microbiome and by disturbances in the host's immune system. Perturbation of the oral microbiota triggered by host-extrinsic (ie, medications), host-intrinsic (ie, host genetics), and microbiome-intrinsic (ie, microbial interactions) factors may increase the risk of oral candidiasis. In this review, we provide an overview of the oral mycobiome, with a particular focus on the interactions of Candida albicans with some of the most common oral bacteria and the oral mucosal immune system. Also, we present a summary of our current knowledge of the host-intrinsic and host-extrinsic factors that can predispose to oral candidiasis.

Monitoring Inflammasome Priming and Activation in Response to Candida albicans

Candida albicans is a common mucosal colonizer, as well as a cause of lethal invasive fungal infections. The major predisposing factor for invasive fungal disease is a compromised immune system. One component of the host immune response to fungal infection is the activation of the inflammasome, a multimeric protein complex that is critical for regulating host pro-inflammatory responses. Here, we describe methods for investigating the interactions between C. albicans and host macrophages, with a focus on the inflammasome. C. albicans isolates differ in the degree to which they activate the inflammasome due to differences in internalization, morphogenic switching, and inflammasome priming. Therefore, we include protocols for identifying these factors. This simple in vitro model can be used to elucidate the contributions of specific C. albicans strains or mutants to different aspects of interactions with macrophages. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Measuring inflammasome priming in response to Candida albicans Basic Protocol 2: Measuring inflammasome activation in response to Candida albicans Support Protocol: Controlling for phagocytosis.

Candidalysin triggers epithelial cellular stresses that induce necrotic death

Candida albicans is a common opportunistic fungal pathogen that causes a wide range of infections from superficial mucosal to hematogenously disseminated candidiasis. The hyphal form plays an important role in the pathogenic process by invading epithelial cells and causing tissue damage. Notably, the secretion of the hyphal toxin candidalysin is essential for both epithelial cell damage and activation of mucosal immune responses. However, the mechanism of candidalysin-induced cell death remains unclear. Here, we examined the induction of cell death by candidalysin in oral epithelial cells. Fluorescent imaging using healthy/apoptotic/necrotic cell markers revealed that candidalysin causes a rapid and marked increase in the population of necrotic rather than apoptotic cells in a concentration dependent manner. Activation of a necrosis-like pathway was confirmed since C. albicans and candidalysin failed to activate caspase-8 and -3, or the cleavage of poly (ADP-ribose) polymerase. Furthermore, oral epithelial cells treated with candidalysin showed rapid production of reactive oxygen species, disruption of mitochondria activity and mitochondrial membrane potential, ATP depletion and cytochrome c release. Collectively, these data demonstrate that oral epithelial cells respond to the secreted fungal toxin candidalysin by triggering numerous cellular stress responses that induce necrotic death. TAKE AWAYS: Candidalysin secreted from Candida albicans causes epithelial cell stress. Candidalysin induces calcium influx and oxidative stress in host cells. Candidalysin induces mitochondrial dysfunction, ATP depletion and epithelial necrosis. The toxicity of candidalysin is mediated from the epithelial cell surface.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

Antifungal activity of polymethyl methacrylate/Si3N4 composites against Candida albicans

Previous studies using gram-positive and -negative bacteria demonstrated that hydrolysis of silicon nitride (Si₃N₄) in aqueous suspensions elutes nitrogen and produces gaseous ammonia while buffering pH. According to immunochemistry assays, fluorescence imaging, and in situ Raman spectroscopy, we demonstrate here that the antipathogenic surface chemistry of Si₃N₄ can be extended to polymethylmethacrylate (PMMA) by compounding it with a minor fraction (~8 vol.%) of Si₃N₄ particles without any tangible loss in bulk properties. The hydrolytic products, which were eluted from partly exposed Si₃N₄ particles at the composite surface, exhibited fungicidal action against Candida albicans. Using a specific nitrative stress sensing dye and highly resolved fluorescence micrographs, we observed in situ congestion of peroxynitrite (ONOO^-) radicals in the mitochondria of the Candida cells exposed to the PMMA/Si₃N₄ composite, while these radicals were absent in the mitochondria of identical cells exposed to monolithic PMMA. These in situ observations suggest that the surface chemistry of Si₃N₄ mimics the antifungal activity of macrophages, which concurrently produce NO radicals and superoxide anions (O₂•^-) resulting in the formation of candidacidal ONOO^-. The fungicidal properties of PMMA/Si₃N₄ composites could be used in dental appliances to inhibit the uncontrolled growth of Candida albicans and ensuing candidiasis while being synergic with chemoprophylaxis. STATEMENT OF SIGNIFICANCE: In a follow-up of previous studies of gram-positive and gram-negative bacteria, we demonstrate here that the antipathogenic surface chemistry of Si₃N₄ could be extended to polymethylmethacrylate (PMMA) containing a minor fraction (~8 vol.%) of Si₃N₄ particles without tangible loss in bulk properties. Hydrolytic products eluted from Si₃N₄ particles at the composite surface exhibited fungicidal action against Candida albicans. Highly resolved fluorescence microscopy revealed congestion of peroxynitrite (ONOO^-) radicals in the mitochondria of the Candida cells exposed to the PMMA/Si₃N₄ composite, while radicals were absent in the mitochondria of identical cells exposed to monolithic PMMA. The fungicidal properties of PMMA/Si₃N₄ composites could be used in dental appliances to inhibit uncontrolled growth of Candida albicans and ensuing candidiasis in synergy with chemoprophylaxis.

Anticipatory Stress Responses and Immune Evasion in Fungal Pathogens

In certain niches, microbes encounter environmental challenges that are temporally linked. In such cases, microbial fitness is enhanced by the evolution of anticipatory responses where the initial challenge simultaneously activates pre-emptive protection against the second impending challenge. The accumulation of anticipatory responses in domesticated yeasts, which have been termed 'adaptive prediction', has led to the emergence of 'core stress responses' that provide stress cross-protection. Protective anticipatory responses also seem to be common in fungal pathogens of humans. These responses reflect the selective pressures that these fungi have faced relatively recently in their evolutionary history. Consequently, some pathogens have evolved 'core environmental responses' which exploit host signals to trigger immune evasion strategies that protect them against imminent immune attack.