AIM2 enhances Candida albicans infection through promoting macrophage apoptosis via AKT signaling.

Candida albicans is among the most prevalent invasive fungal pathogens for immunocompromised individuals and novel therapeutic approaches that involve immune response modulation are imperative. Absent in melanoma 2 (AIM2), a pattern recognition receptor for DNA sensing, is well recognized for its involvement in inflammasome formation and its crucial role in safeguarding the host against various pathogenic infections. However, the role of AIM2 in host defense against C. albicans infection remains uncertain. This study reveals that the gene expression of AIM2 is induced in human and mouse innate immune cells or tissues after C. albicans infection. Furthermore, compared to their wild-type (WT) counterparts, Aim2-/- mice surprisingly exhibit resistance to C. albicans infection, along with reduced inflammation in the kidneys post-infection. The resistance of Aim2-/- mice to C. albicans infection is not reliant on inflammasome or type I interferon production. Instead, Aim2-/- mice display lower levels of apoptosis in kidney tissues following infection than WT mice. The deficiency of AIM2 in macrophages, but not in dendritic cells, results in a phenocopy of the resistance observed in Aim2-/- mice against C. albican infection. The treatment of Clodronate Liposome, a reagent that depletes macrophages, also shows the critical role of macrophages in host defense against C. albican infection in Aim2-/- mice. Furthermore, the reduction in apoptosis is observed in Aim2-/- mouse macrophages following infection or treatment of DNA from C. albicans in comparison with controls. Additionally, higher levels of AKT activation are observed in Aim2-/- mice, and treatment with an AKT inhibitor reverses the host resistance to C. albicans infection. The findings collectively demonstrate that AIM2 exerts a negative regulatory effect on AKT activation and enhances macrophage apoptosis, ultimately compromising host defense against C. albicans infection. This suggests that AIM2 and AKT may represent promising therapeutic targets for the management of fungal infections.

A pathological study on the efficacy of Syk inhibitors in a Candida albicans-induced aortic root vasculitis murine model.

BACKGROUND: The activation of innate immunity may be involved in the development of Candida albicans-induced murine vasculitis, which resembles Kawasaki disease (KD) vasculitis. This study aimed to histologically clarify the time course of the development of vasculitis in this model in detail and to estimate the potential role of spleen tyrosine kinase (Syk) inhibitors in KD vasculitis. METHODS AND RESULTS: DBA/2 male mice were intraperitoneally injected with a vasculitis-inducing substance and treated with a Syk inhibitor (R788 or GS-9973). Systemic vasculitis, especially in the aortic annulus area, was histologically evaluated. Regarding lesions in the aortic annulus area, some mice in the untreated control group already showed initiation of vasculitis 1 day after the final injection of a vasculitis-inducing substance. The vasculitis expanded over time. Inflammation occurred more frequently at the aortic root than at the coronary artery. The distribution of inflammatory cells was limited to the intima, intima plus adventitia, or all layers. In the Syk inhibitor-treated groups, only one mouse had vasculitis at all observation periods. The severity and area of the vasculitis were reduced by both Syk inhibitors. CONCLUSION: Candida albicans-induced murine vasculitis may occur within 1 day after the injection of a vasculitis-inducing substance. Additionally, Syk inhibitors suppress murine vasculitis.

The modern face of esophageal candidiasis in an oncology center: Correlating clinical manifestations, endoscopic grade, and pathological data in 323 contemporary cancer patients.

OBJECTIVES: Clinical presentation and outcomes of esophageal candidiasis (EC) in cancer patients are scarcely studied in the azole era, as is the correlation between clinical, endoscopic, and histopathological EC manifestations. METHODS: We retrospectively reviewed the risk factors, clinical features, and outcomes of pathology-documented EC cases at MD Anderson Cancer Center. We further assessed associations between presence of symptoms, standardized 4-stage endoscopic grade (Kodsi classification), histopathological data, and fluconazole treatment failure. RESULTS: Among 323 cancer patients with EC, 89% had solid tumors, most commonly esophageal cancer (29%). Thirty-three percent of EC patients were asymptomatic. The proportion of symptomatic EC patients significantly increased with endoscopic grade (P = 0.005). Among 202 patients receiving oral fluconazole, 27 (13%) had treatment failure. Underlying esophageal disease was the only independent predictor of fluconazole treatment failure (odds ratio: 3.88, P = 0.005). Endoscopic grade correlated significantly with Candida organism burden (Correlation coefficient [ρ] = 0.21, P < 0.01) and neutrophilic inflammation (ρ = 0.18, P < 0.01). Candida invasion of the squamous mucosal layer was associated with treatment failure (P = 0.049). CONCLUSIONS: EC was predominantly encountered in patients with solid tumors. One-third of EC patients were asymptomatic, challenging traditional symptom-based diagnosis. The development of integrated clinicopathological scoring systems could further guide the therapeutic management of cancer patients with EC.

Clinicopathological and diagnostic imaging findings in a dog with neurocandidiasis.

Neurocandidiasis is systemic candidiasis with central nervous system involvement. This case report describes the clinical presentation, diagnostic test results, and histopathology of a dog with neurocandidiasis. A 3-year-old German shepherd dog was presented for a 3-day history of abnormal mentation, neck pain, and ataxia. Magnetic resonance imaging (MRI) scan of the brain revealed multifocal, small, round, intra-axial lesions within the forebrain. Examination of the cerebrospinal fluid revealed severe neutrophilic inflammation. Extensive testing for infectious diseases was negative. The dog was administered immunosuppressive doses of corticosteroids. The dog's clinical signs improved transiently but got worse 12 days after starting the treatment. Repeat MRI scan revealed multiple, intra-axial, target-like nodular lesions scattered throughout the brain parenchyma. In the temporal muscles, nodules were seen. Cytology of the fine needle aspirates of the nodules in the temporal muscles revealed a neutrophilic inflammation with hyalohyphomycosis. Postmortem examination was compatible with a severe systemic fungal infection. Candida albicans was isolated from the brain, kidney, and heart.

Gastrointestinal colonization by Diutina (Candida) rugosa in a 6-year-old Siberian Husky.

A 6-year-old 21.5 kg castrated male Siberian Husky was presented for acute onset of lethargy, vomiting, hemorrhagic diarrhea, and inappetence. Physical examination revealed marked discomfort upon abdominal palpation and 5%-7% dehydration. The CBC and biochemical profile revealed changes consistent with mild to moderate inflammation, dehydration, and gastrointestinal (GI) disease. Despite aggressive gastrointestinal support, anorexia persisted, and an upper GI endoscopy was performed in conjunction with esophagostomy tube placement. Endoscopy revealed abnormal gastric mucosa characterized by moderately well-demarcated areas of blue-black discoloration. Impression smears of a gastric biopsy revealed abundant extracellular yeasts with morphology most consistent with Candida spp. and frequent extracellular cocci. Similar yeast and bacteria, in lower numbers, were observed on cytologic analysis of a direct smear of the rectal mucosa. A rectal swab submitted for fungal culture yielded pure growth of fungal yeasts identified as Diutina (formerly Candida) rugosa by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry. The dog's clinical signs improved with fluconazole, and he was discharged. Follow-up fungal culture of a rectal swab showed no growth of D. rugosa. To the authors' knowledge, this is the first case report that describes the clinical, hematologic, cytologic, and gross findings of enteric colonization by D. rugosa in a dog.

Candida albicans extracellular vesicles trigger type I IFN signalling via cGAS and STING.

The host type I interferon (IFN) pathway is a major signature of inflammation induced by the human fungal pathogen, Candida albicans. However, the molecular mechanism for activating this pathway in the host defence against C. albicans remains unknown. Here we reveal that mice lacking cyclic GMP-AMP synthase (cGAS)-stimulator of IFN genes (STING) pathway components had improved survival following an intravenous challenge by C. albicans. Biofilm-associated C. albicans DNA packaged in extracellular vesicles triggers the cGAS-STING pathway as determined by induction of interferon-stimulated genes, IFNß production, and phosphorylation of IFN regulatory factor 3 and TANK-binding kinase 1. Extracellular vesicle-induced activation of type I IFNs was independent of the Dectin-1/Card9 pathway and did not require toll-like receptor 9. Single nucleotide polymorphisms in cGAS and STING potently altered inflammatory cytokine production in human monocytes challenged by C. albicans. These studies provide insights into the early innate immune response induced by a clinically significant fungal pathogen.

An insight into the role of protein kinases as virulent factors, regulating pathogenic attributes in Candida albicans.

Candida albicans is a polymorphic, opportunistic pathogen, member of normal human microbiome causing candidiasis. It causes wide range of infections from superficial skin infections to life-threatening systemic infections. The pathogenicity in C. albicans attributes through several morphological characteristics and virulence factors. These morphological features are regulated by various molecules among which kinases are the most important. Several kinases and kinase signaling cascades play a well established role in Candidiasis. In this review we present an update on our current understanding of the pathogenicity attributes which is regulated by kinases as virulence factors.

Acute disseminated candidiasis due to Candida tropicalis with skin and muscular lesions in a patient with Tcell acute lymphocytic leukemia (T-ALL).

Candida tropicalis is the Candida species that is mostly involved in case of acute disseminated candidiasis. We report here a case with whole body dissemination (pulmonary, cutaneous, muscular, hepatic, spinal and cerebral) highlighted by impressive imagery obtained by positron emission tomography scanner in a patient treated for T cell acute lymphocytic leukemia.

Calcium-dependent ESCRT recruitment and lysosome exocytosis maintain epithelial integrity during Candida albicans invasion.

Candida albicans is both a commensal and an opportunistic fungal pathogen. Invading hyphae of C. albicans secrete candidalysin, a pore-forming peptide toxin. To prevent cell death, epithelial cells must protect themselves from direct damage induced by candidalysin and by the mechanical forces exerted by expanding hyphae. We identify two key Ca2+-dependent repair mechanisms employed by epithelial cells to withstand candidalysin-producing hyphae. Using camelid nanobodies, we demonstrate candidalysin secretion directly into the invasion pockets induced by elongating C. albicans hyphae. The toxin induces oscillatory increases in cytosolic [Ca2+], which cause hydrolysis of PtdIns(4,5)P2 and loss of cortical actin. Epithelial cells dispose of damaged membrane regions containing candidalysin by an Alg-2/Alix/ESCRT-III-dependent blebbing process. At later stages, plasmalemmal tears induced mechanically by invading hyphae are repaired by exocytic insertion of lysosomal membranes. These two repair mechanisms maintain epithelial integrity and prevent mucosal damage during both commensal growth and infection by C. albicans.

Missing the blind spot in a HeartMate 3 LVAD outflow graft obstruction caused by fungal infection.

A patient was admitted in cardiogenic shock and a constant decrease of pump flow requiring combined inotropic support. To evaluate the cause, echocardiography and a ramp test were performed. The results suggested a LVAD related problem - particularly a suspected outflow graft obstruction. Wether CT scan nor angiography confirmed the assumption. However, a post-mortem LVAD examination revealed an outflow obstruction caused by a fungal thrombus formation invisible for standard imaging procedures.

Evaluation of bisphenylthiazoles as a promising class for combating multidrug-resistant fungal infections.

To minimize the intrinsic toxicity of the antibacterial agent hydrazinyloxadiazole 1, the hydrazine moiety was replaced with ethylenediamine (compound 7). This replacement generated a potent antifungal agent with no antibacterial activity. Notably, use of a 1,2-diaminocyclohexane moiety, as a conformationally-restricted isostere for ethylenediamine, potentiated the antifungal activity in both the cis and trans forms of N-(5-(2-([1,1'-biphenyl]-4-yl)-4-methylthiazol-5-yl)-1,3,4-oxadiazol-2-yl)cyclohexane-1,2-diamine (compounds 16 and 17). Both compounds 16 and 17 were void of any antibacterial activity; nonetheless, they showed equipotent antifungal activity in vitro to that of the most potent approved antifungal agent, amphotericin B. The promising antifungal effects of compounds 16 and 17 were maintained when assessed against an additional panel of 26 yeast and mold clinical isolates, including the Candida auris and C. krusei. Furthermore, compound 17 showed superior activity to amphotericin B in vitro against Candida glabrata and Cryptococcus gattii. Additionally, neither compound inhibited the normal human microbiota, and both possessed excellent safety profiles and were 16 times more tolerable than amphotericin B.

Proteinous Components of Neutrophil Extracellular Traps Are Arrested by the Cell Wall Proteins of Candida albicans during Fungal Infection, and Can Be Used in the Host Invasion.

One of defense mechanisms of the human immune system to counteract infection by the opportunistic fungal pathogen Candida albicans is the recruitment of neutrophils to the site of invasion, and the subsequent production of neutrophil extracellular traps (NETs) that efficiently capture and kill the invader cells. In the current study, we demonstrate that within these structures composed of chromatin and proteins, the latter play a pivotal role in the entrapment of the fungal pathogen. The proteinous components of NETs, such as the granular enzymes elastase, myeloperoxidase and lactotransferrin, as well as histones and cathelicidin-derived peptide LL-37, are involved in contact with the surface of C. albicans cells. The fungal partners in these interactions are a typical adhesin of the agglutinin-like sequence protein family Als3, and several atypical surface-exposed proteins of cytoplasmic origin, including enolase, triosephosphate isomerase and phosphoglycerate mutase. Importantly, the adhesion of both the elastase itself and the mixture of proteins originating from NETs on the C. albicans cell surface considerably increased the pathogen potency of human epithelial cell destruction compared with fungal cells without human proteins attached. Such an implementation of adsorbed NET-derived proteins by invading C. albicans cells might alter the effectiveness of the fungal pathogen entrapment and affect the further host colonization.

Crystal structure of histone chaperone Vps75 from Candida albicans.

Vps75 is a histone chaperone that interacts with the fungal-specific histone acetyltransferase Rtt109 and stimulates its acetylation activity on histone H3. Here we report the crystal structure of Vps75 of Candida albicans, one of the most common fungal pathogens. CaVps75 exists as a headphone-like dimer that forms a large negatively charged region on its concave side, showing the potential to bind positively charged regions of histones. The distal ends of the concave side of the CaVps75 dimer are positively charged and each has one more α helix than yeast Vps75. CaVps75 exhibits ionic strength- and concentration-dependent higher oligomerization in solution. In the crystal, two dimers are bound through electrostatic interactions between charged regions on the concave side of their earmuff domains, and this inter-dimer interaction differs from the currently known inter-dimer interactions of Vps75s. Our results will help to understand the role of Vps75 in C. albicans.

The histone chaperone HIR maintains chromatin states to control nitrogen assimilation and fungal virulence.

Adaptation to changing environments and immune evasion is pivotal for fitness of pathogens. Yet, the underlying mechanisms remain largely unknown. Adaptation is governed by dynamic transcriptional re-programming, which is tightly connected to chromatin architecture. Here, we report a pivotal role for the HIR histone chaperone complex in modulating virulence of the human fungal pathogen Candida albicans. Genetic ablation of HIR function alters chromatin accessibility linked to aberrant transcriptional responses to protein as nitrogen source. This accelerates metabolic adaptation and increases the release of extracellular proteases, which enables scavenging of alternative nitrogen sources. Furthermore, HIR controls fungal virulence, as HIR1 deletion leads to differential recognition by immune cells and hypervirulence in a mouse model of systemic infection. This work provides mechanistic insights into chromatin-coupled regulatory mechanisms that fine-tune pathogen gene expression and virulence. Furthermore, the data point toward the requirement of refined screening approaches to exploit chromatin modifications as antifungal strategies.

Smoking increases oral mucosa susceptibility to Candida albicans infection via the Nrf2 pathway: In vitro and animal studies.

Smoking and Candida albicans (C. albicans) infection are risk factors for many oral diseases. Several studies have reported a close relationship between smoking and the occurrence of C. albicans infection. However, the exact underlying mechanism of this relationship remains unclear. We established a rat infection model and a C. albicans-Leuk1 epithelial cell co-culture model with and without smoke exposure to investigate the mechanism by which smoking contributes to C. albicans infection. Oral mucosa samples from healthy individuals and patients with oral leucoplakia were also analysed according to their smoking status. Our results indicated that smoking induced oxidative stress and redox dysfunction in the oral mucosa. Smoking-induced Nrf2 negatively regulated the NLRP3 inflammasome, impaired the oral mucosal defence response and increased the oral mucosa susceptibility to C. albicans. The results suggest that the Nrf2 pathway could be involved in the pathogenesis of oral diseases by mediating an antioxidative response to cigarette smoke exposure and suppressing host immunity against C. albicans.

Cdc42 regulates reactive oxygen species production in the pathogenic yeast Candida albicans.

Across eukaryotes, Rho GTPases such as Rac and Cdc42 play important roles in establishing cell polarity, which is a key feature of cell growth. In mammals and filamentous fungi, Rac targets large protein complexes containing NADPH oxidases (NOX) that produce reactive oxygen species (ROS). In comparison, Rho GTPases of unicellular eukaryotes were believed to signal cell polarity without ROS, and it was unclear whether Rho GTPases were required for ROS production in these organisms. We document here the first example of Rho GTPase-mediated post-transcriptional control of ROS in a unicellular microbe. Specifically, Cdc42 is required for ROS production by the NOX Fre8 of the opportunistic fungal pathogen Candida albicans. During morphogenesis to a hyphal form, a filamentous growth state, C. albicans FRE8 mRNA is induced, which leads to a burst in ROS. Fre8-ROS is also induced during morphogenesis when FRE8 is driven by an ectopic promoter; hence, Fre8 ROS production is in addition controlled at the post-transcriptional level. Using fluorescently tagged Fre8, we observe that the majority of the protein is associated with the vacuolar system. Interestingly, much of Fre8 in the vacuolar system appears inactive, and Fre8-induced ROS is only produced at sites near the hyphal tip, where Cdc42 is also localized during morphogenesis. We observe that Cdc42 is necessary to activate Fre8-mediated ROS production during morphogenesis. Cdc42 regulation of Fre8 occurs without the large NOX protein complexes typical of higher eukaryotes and therefore represents a novel form of ROS control by Rho GTPases.

Whole transcriptome analysis of schinifoline treatment in Caenorhabditis elegans infected with Candida albicans.

Candida albicans is an opportunistic fungal human pathogen that has been causing an increasing number of deaths each year. Due to the widespread use of broad-spectrum antibiotics and immunosuppressants, C. albicans resistance to these therapies has increased. Thus, natural plant inhibitors are being investigated for treating C. albicans infections. Schinifoline is a 4-quinolinone alkaloid with antibacterial, insecticidal, antitumor, and other biological activities. Here, we explored the effects of schinifoline on C. albicans in C. elegans and extracted RNA from uninfected C. elegans, C. elegans infected with C. albicans, and C. elegans infected with C. albicans and treated with 100 mg/l schinifoline. Our results showed that there were significant differences among the three groups. The GO and KEGG pathway analysis suggested that the pathogenicity of C. albicans to C. elegans was caused by abnormal protein function. Schinifoline regulates lysosomal pathway related genes that accelerate the metabolism and degradation of abnormal proteins, thereby inhibiting the negative effects of C. albicans in vivo. These findings advance our understanding of the molecular mechanisms underlying schinifoline inhibition of C. albicans.

A peptidoglycan storm caused by ß-lactam antibiotic's action on host microbiota drives Candida albicans infection.

The commensal fungus Candida albicans often causes life-threatening infections in patients who are immunocompromised with high mortality. A prominent but poorly understood risk factor for the C. albicans commensal‒pathogen transition is the use of broad-spectrum antibiotics. Here, we report that ß-lactam antibiotics cause bacteria to release significant quantities of peptidoglycan fragments that potently induce the invasive hyphal growth of C. albicans. We identify several active peptidoglycan subunits, including tracheal cytotoxin, a molecule produced by many Gram-negative bacteria, and fragments purified from the cell wall of Gram-positive Staphylococcus aureus. Feeding mice with ß-lactam antibiotics causes a peptidoglycan storm that transforms the gut from a niche usually restraining C. albicans in the commensal state to promoting invasive growth, leading to systemic dissemination. Our findings reveal a mechanism underlying a significant risk factor for C. albicans infection, which could inform clinicians regarding future antibiotic selection to minimize this deadly disease incidence.

Comparative assessment of immune evasion mechanisms in human whole-blood infection assays by a systems biology approach.

Computer simulations of mathematical models open up the possibility of assessing hypotheses generated by experiments on pathogen immune evasion in human whole-blood infection assays. We apply an interdisciplinary systems biology approach in which virtual infection models implemented for the dissection of specific immune mechanisms are combined with experimental studies to validate or falsify the respective hypotheses. Focusing on the assessment of mechanisms that enable pathogens to evade the immune response in the early time course of a whole-blood infection, the least-square error (LSE) as a measure for the quantitative agreement between the theoretical and experimental kinetics is combined with the Akaike information criterion (AIC) as a measure for the model quality depending on its complexity. In particular, we compare mathematical models with three different types of pathogen immune evasion as well as all their combinations: (i) spontaneous immune evasion, (ii) evasion mediated by immune cells, and (iii) pre-existence of an immune-evasive pathogen subpopulation. For example, by testing theoretical predictions in subsequent imaging experiments, we demonstrate that the simple hypothesis of having a subpopulation of pre-existing immune-evasive pathogens can be ruled out. Furthermore, in this study we extend our previous whole-blood infection assays for the two fungal pathogens Candida albicans and C. glabrata by the bacterial pathogen Staphylococcus aureus and calibrated the model predictions to the time-resolved experimental data for each pathogen. Our quantitative assessment generally reveals that models with a lower number of parameters are not only scored with better AIC values, but also exhibit lower values for the LSE. Furthermore, we describe in detail model-specific and pathogen-specific patterns in the kinetics of cell populations that may be measured in future experiments to distinguish and pinpoint the underlying immune mechanisms.

Lead optimization generates selenium-containing miconazole CYP51 inhibitors with improved pharmacological profile for the treatment of fungal infections.

A series of selenium-containing miconazole derivatives were identified as potent antifungal drugs in our previous study. Representative compound A03 (MIC = 0.01 µg/mL against C.alb. 5314) proved efficacious in inhibiting the growth of fungal pathogens. However, further study showed lead compound A03 exhibited potential hemolysis, significant cytotoxic effect and unfavorable metabolic stability and was therefore modified to overcome these drawbacks. In this article, the further optimization of selenium-containing miconazole derivatives resulted in the discovery of similarly potent compound B17 (MIC = 0.02 µg/mL against C.alb. 5314), exhibiting a superior pharmacological profile with decreased rate of metabolism, cytotoxic effect and hemolysis. Furthermore, compound B17 showed fungicidal activity against Candida albicans and significant effects on the treatment of resistant Candida albicans infections. Meanwhile, compound B17 not only could reduce the ergosterol biosynthesis pathway by inhibiting CYP51, but also inhibited biofilm formation. More importantly, compound B17 also shows promising in vivo efficacy after intraperitoneal injection and the PK study of compound B17 was evaluated. In addition, molecular docking studies provide a model for the interaction between the compound B17 and the CYP51 protein. Overall, we believe that these selenium-containing miconazole compounds can be further developed for the potential treatment of fungal infections.