Size Matters: Measurement of Capsule Diameter in Cryptococcus neoformans

Deciphering antifungal and antibiofilm mechanisms of isobavachalcone against Cryptococcus neoformans through RNA-seq and functional analyses

Cryptococcus neoformans has been designated as critical fungal pathogens by the World Health Organization, mainly due to limited treatment options and the prevalence of antifungal resistance. Consequently, the utilization of novel antifungal agents is crucial for the effective treatment of C. neoformans infections. This study exposed that the minimum inhibitory concentration (MIC) of isobavachalcone (IBC) against C. neoformans H99 was 8 µg/mL, and IBC dispersed 48-h mature biofilms by affecting cell viability at 16 µg/mL. The antifungal efficacy of IBC was further validated through microscopic observations using specific dyes and in vitro assays, which confirmed the disruption of cell wall/membrane integrity. RNA-Seq analysis was employed to decipher the effect of IBC on the C. neoformans H99 transcriptomic profiles. Real-time quantitative reverse transcription PCR (RT-qPCR) analysis was performed to validate the transcriptomic data and identify the differentially expressed genes. The results showed that IBC exhibited various mechanisms to impede the growth, biofilm formation, and virulence of C. neoformans H99 by modulating multiple dysregulated pathways related to cell wall/membrane, drug resistance, apoptosis, and mitochondrial homeostasis. The transcriptomic findings were corroborated by the antioxidant analyses, antifungal drug sensitivity, molecular docking, capsule, and melanin assays. In vivo antifungal activity analysis demonstrated that IBC extended the lifespan of C. neoformans-infected Caenorhabditis elegans. Overall, the current study unveiled that IBC targeted multiple pathways simultaneously to inhibit growth significantly, biofilm formation, and virulence, as well as to disperse mature biofilms of C. neoformans H99 and induce cell death.

Murine Models of Cryptococcus Infection

Cryptococcus is recognized as one of the emerging fungal pathogens that have major impact on diverse populations worldwide. Because of the high mortality rate and limited antifungal therapy options, there is an urgent need to understand the impact of dynamic processes between fungal pathogens and hosts that influence cryptococcal pathogenesis and disease outcomes. With known common limitations in human studies, experimental murine cryptococcosis models that can recapitulate human disease provide a valuable tool for studying fungal virulence and the host interaction, leading to development of better treatment strategies. Infection with Cryptococcus in mice via intranasal inhalation is mostly used because it is noninvasive and considered to be the most common mode of infection, strongly correlating with cryptococcal disease in humans. The protocols described in this article provide the procedures of establishing a murine model of Cryptococcus infection by intranasal inhalation and assessing the host immune response and disease progression during Cryptococcus infection. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Murine model of pulmonary cryptococcal infection via intranasal inhalation Basic Protocol 2: Assessment of the pulmonary immune response during Cryptococcus infection Support Protocol: Evaluation of pulmonary gene expression by real-time PCR Basic Protocol 3: Enumeration of survival rate and organ fungal burden.

Chelation of Mitochondrial Iron as an Antiparasitic Strategy

Iron, as an essential micronutrient, plays a crucial role in host-pathogen interactions. In order to limit the growth of the pathogen, a common strategy of innate immunity includes withdrawing available iron to interfere with the cellular processes of the microorganism. Against that, unicellular parasites have developed powerful strategies to scavenge iron, despite the effort of the host. Iron-sequestering compounds, such as the approved and potent chelator deferoxamine (DFO), are considered a viable option for therapeutic intervention. Since iron is heavily utilized in the mitochondrion, targeting iron chelators in this organelle could constitute an effective therapeutic strategy. This work presents mitochondrially targeted DFO, mitoDFO, as a candidate against a range of unicellular parasites with promising in vitro efficiency. Intracellular Leishmania infection can be cleared by this compound, and experimentation with Trypanosoma brucei 427 elucidates its possible mode of action. The compound not only affects iron homeostasis but also alters the physiochemical properties of the inner mitochondrial membrane, resulting in a loss of function. Furthermore, investigating the virulence factors of pathogenic yeasts confirms that mitoDFO is a viable candidate for therapeutic intervention against a wide spectrum of microbe-associated diseases.

Quantification of C. neoformans Capsule Diameter

The polysaccharide capsule of Cryptococcus neoformans is the primary virulence factor and one of the most commonly studied aspects of this pathogenic yeast. Capsule size varies widely between strains, has the ability to grow rapidly when introduced to stressful or low-nutrient conditions, and has been positively correlated with strain virulence. For these reasons, the size of the capsule is of great interest to C. neoformans researchers. Inducing the growth of the C. neoformans capsule is used during phenotypic testing to help understand the effects of different treatments on the yeast or size differences between strains. Here, we describe one of the standard methods of capsule induction and detail two accepted methods of staining: (i) India ink, a negative stain, used in conjunction with conventional light microscopy and (ii) co-staining with fluorescent dyes of both the cell wall and capsule followed by confocal microscopy. Finally, we outline how to measure capsule diameter manually and offer a protocol for automated diameter measurement of India ink-stained samples using computational image analysis.

Regulation of symbiotic interactions and primitive lichen differentiation by UMP1 MAP kinase in Umbilicaria muhlenbergii

Lichens are of great ecological importance but mechanisms regulating lichen symbiosis are not clear. Umbilicaria muhlenbergii is a lichen-forming fungus amenable to molecular manipulations and dimorphic. Here, we established conditions conducive to symbiotic interactions and lichen differentiation and showed the importance of UMP1 MAP kinase in lichen development. In the initial biofilm-like symbiotic complexes, algal cells were interwoven with pseudohyphae covered with extracellular matrix. After longer incubation, fungal-algal complexes further differentiated into primitive lichen thalli with a melanized cortex-like and pseudoparenchyma-like tissues containing photoactive algal cells. Mutants deleted of UMP1 were blocked in pseudohyphal growth and development of biofilm-like complexes and primitive lichens. Invasion of dividing mother cells that contributes to algal layer organization in lichens was not observed in the ump1 mutant. Overall, these results showed regulatory roles of UMP1 in symbiotic interactions and lichen development and suitability of U. muhlenbergii as a model for studying lichen symbiosis.

In vivo assessment of differences in fungal cell density in cerebral cryptococcomas of mice infected with Cryptococcus neoformans or Cryptococcus gattii

In cerebral cryptococcomas caused by Cryptococcus neoformans or Cryptococcus gattii, the density of fungal cells within lesions can contribute to the overall brain fungal burden. In cultures, cell density is inversely related to the size of the cryptococcal capsule, a dynamic polysaccharide layer surrounding the cell. Methods to investigate cell density or related capsule size within fungal lesions of a living host are currently unavailable, precluding in vivo studies on longitudinal changes. Here, we assessed whether intravital microscopy and quantitative magnetic resonance imaging techniques (diffusion MRI and MR relaxometry) would enable non-invasive investigation of fungal cell density in cerebral cryptococcomas in mice. We compared lesions caused by type strains C. neoformans H99 and C. gattii R265 and evaluated potential relations between observed imaging properties, fungal cell density, total cell and capsule size. The observed inverse correlation between apparent diffusion coefficient and cell density permitted longitudinal investigation of cell density changes. Using these imaging methods, we were able to study the multicellular organization and cell density within brain cryptococcomas in the intact host environment of living mice. Since the MRI techniques are also clinically available, the same approach could be used to assess fungal cell density in brain lesions of patients.

Influence of Pathogen Carbon Metabolism on Interactions With Host Immunity

Cryptococcus neoformans is a ubiquitous opportunistic fungal pathogen typically causing disease in immunocompromised individuals and is globally responsible for about 15% of AIDS-related deaths annually. C. neoformans first causes pulmonary infection in the host and then disseminates to the brain, causing meningoencephalitis. The yeast must obtain and metabolize carbon within the host in order to survive in the central nervous system and cause disease. Communication between pathogen and host involves recognition of multiple carbon-containing compounds on the yeast surface: polysaccharide capsule, fungal cell wall, and glycosylated proteins comprising the major immune modulators. The structure and function of polysaccharide capsule has been studied for the past 70 years, emphasizing its role in virulence. While protected by the capsule, fungal cell wall has likewise been a focus of study for several decades for its role in cell integrity and host recognition. Associated with both of these major structures are glycosylated proteins, which exhibit known immunomodulatory effects. While many studies have investigated the role of carbon metabolism on virulence and survival within the host, the precise mechanism(s) affecting host-pathogen communication remain ill-defined. This review summarizes the current knowledge on mutants in carbon metabolism and their effect on the host immune response that leads to changes in pathogen recognition and virulence. Understanding these critical interactions will provide fresh perspectives on potential treatments and the natural history of cryptococcal disease.

X-linked immunodeficient (XID) mice exhibit high susceptibility to Cryptococcus gattii infection

Cryptococcosis is an opportunistic disease caused by the fungus Cryptococcus neoformans and Cryptococcus gattii. It starts as a pulmonary infection that can spread to other organs, such as the brain, leading to the most serious occurrence of the disease, meningoencephalitis. The humoral response has already been described in limiting the progression of cryptococcosis where the B-1 cell seems to be responsible for producing natural IgM antibodies, crucial for combating fungal infections. The role of the B-1 cell in C. neoformans infection has been initially described, however the role of the humoral response of B-1 cells has not yet been evaluated during C. gattii infections. In the present study we tried to unravel this issue using XID mice, a murine model deficient in the Btk protein which compromises the development of B-1 lymphocytes. We use the XID mice compared to BALB/c mice that are sufficient for the B-1 population during C. gattii infection. Our model of chronic lung infection revealed that XID mice, unlike the sufficient group of B-1, had early mortality with significant weight loss, in addition to reduced levels of IgM and IgG specific to GXM isolated from the capsule of C. neoformans. In addition to this, we observed an increased fungal load in the blood and in the brain. We described an increase in the capsular size of C. gattii and the predominant presence of cytokines with a Th2 profile was also observed in these animals. Thus, the present study strongly points to a higher susceptibility of the XID mouse to C. gattii, which suggests that the presence of B-1 cells and anti-GXM antibodies is fundamental during the control of infection by C. gattii.

Anticapsular and Antifungal Activity of α-Cyperone

Fungal infections affect 300 million people and cause 1.5 million deaths globally per year. With the number of immunosuppressed patients increasing steadily, there is an increasing number of patients infected with opportunistic fungal infections such as infections caused by the species of Candida and Cryptococcus. In fact, the drug-resistant Can. krusei and the emerging pan-antifungal resistant Can. auris pose a serious threat to human health as the existing limited antifungals are futile. To further complicate therapy, fungi produce capsules and spores that are resistant to most antifungal drugs/host defenses. Novel antifungal drugs are urgently needed to fill unmet medical needs. From screening a collection of medicinal plant sources for antifungal activity, we have identified an active fraction from the rhizome of Cyperus rotundus, the nut grass plant. The fraction contained α-Cyperone, an essential oil that showed fungicidal activity against different species of Candida. Interestingly, the minimal inhibitory concentration of α-Cyperone was reduced 8-fold when combined with a clinical antifungal drug, fluconazole, indicating its antifungal synergistic potential and could be useful for combination therapy. Furthermore, α-Cyperone affected the synthesis of the capsule in Cryp. neoformans, a causative agent of fungal meningitis in humans. Further work on mechanistic understanding of α-Cyperone against fungal virulence could help develop a novel antifungal agent for drug-resistant fungal pathogens.

Visualization and Documentation of Capsule and Melanin Production in Cryptococcus neoformans

Cryptococcus neoformans is an opportunistic fungal pathogen primarily targeting immunosuppressed populations in both resource-rich and resource-limited nations. Successful treatment is limited to a few antifungals that have become compromised by cryptococcal resistance, leading to intensive research seeking new drug candidates. Two distinguishing hallmarks of this species are the ability to develop a polysaccharide capsule and melanization of the fungal cells. These also act as virulence factors, protecting this pathogen in the host as well as in the environment. Here we describe two classic methods to document capsule and melanin. Although initially described and documented several decades ago, these methods remain relevant in spite of the advent of more sophisticated methodology, due in part to their simplicity and cost efficiency. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Capsule visualization by India ink counterstaining Basic Protocol 2: Assessment of melanin on solid media Alternative Protocol: Quantification of melanin production in liquid medium.

Scanning electron microscopy and machine learning reveal heterogeneity in capsular morphotypes of the human pathogen Cryptococcus spp

Phenotypic heterogeneity is an important trait for the development and survival of many microorganisms including the yeast Cryptococcus spp., a deadly pathogen spread worldwide. Here, we have applied scanning electron microscopy (SEM) to define four Cryptococcus spp. capsule morphotypes, namely Regular, Spiky, Bald, and Phantom. These morphotypes were persistently observed in varying proportions among yeast isolates. To assess the distribution of such morphotypes we implemented an automated pipeline capable of (1) identifying potentially cell-associated objects in the SEM-derived images; (2) computing object-level features; and (3) classifying these objects into their corresponding classes. The machine learning approach used a Random Forest (RF) classifier whose overall accuracy reached 85% on the test dataset, with per-class specificity above 90%, and sensitivity between 66 and 94%. Additionally, the RF model indicates that structural and texture features, e.g., object area, eccentricity, and contrast, are most relevant for classification. The RF results agree with the observed variation in these features, consistently also with visual inspection of SEM images. Finally, our work introduces morphological variants of Cryptococcus spp. capsule. These can be promptly identified and characterized using computational models so that future work may unveil morphological associations with yeast virulence.

TNF-α-Producing Cryptococcus neoformans Exerts Protective Effects on Host Defenses in Murine Pulmonary Cryptococcosis

Tumor necrosis factor alpha (TNF-α) plays a critical role in the control of cryptococcal infection, and its insufficiency promotes cryptococcal persistence. To explore the therapeutic potential of TNF-α supplementation as a booster of host anti-cryptococcal responses, we engineered a C. neoformans strain expressing murine TNF-α. Using a murine model of pulmonary cryptococcosis, we demonstrated that TNF-α-producing C. neoformans strain enhances protective elements of host response including preferential T-cell accumulation and improved Th1/Th2 cytokine balance, diminished pulmonary eosinophilia and alternative activation of lung macrophages at the adaptive phase of infection compared to wild type strain-infected mice. Furthermore, TNF-α expression by C. neoformans enhanced the fungicidal activity of macrophages in vitro. Finally, mice infected with the TNF-α-producing C. neoformans strain showed improved fungal control and considerably prolonged survival compared to wild type strain-infected mice, but could not induce sterilizing immunity. Taken together, our results support that TNF-α expression by an engineered C. neoformans strain while insufficient to drive complete immune protection, strongly enhanced protective responses during primary cryptococcal infection.