Host Defenses to Fungal Pathogens

Circulating redox status in sheep naturally infected with Trichophyton verrucosum

Trichophyton verrucosum is a zoophilic dermatophyte that causes skin inflammation. The present study aimed to evaluate the redox status in the blood of sheep clinically infected with T. verrucosum. According to clinical and mycological investigations, 48 juvenile male Balady sheep were selected in their natural habitat and divided into four groups depending on the lesion size: mild (MID), moderate (MOD), severe (SEV) T. verrucosum infection, and healthy control groups. Compared to the controls, plasma superoxide anion increased (P < 0.05) in both MOD and SEV but total peroxides (TPx) gradually increased (P < 0.05) in MID followed by MOD and SEV. Superoxide dismutase and total antioxidant capacity (TAC) were higher (P < 0.05) in MID and lower (P < 0.05) in MOD and SEV than in controls, but SEV showed lower TAC than MOD. Malondialdehyde (MDA, a lipid peroxide marker) increased (P < 0.05) in SEV than in controls, but protein carbonyl (PC, a protein peroxidation marker) was augmented (P < 0.05) as lesions progressed from mild to severe. The oxidative stress index (TPx/TAC ratio) progressively increased (P < 0.05) in MOD and SEV. The correlation of PC was positive with TPx and negative with TAC (P < 0.01). In conclusion, sheep infection with T. verrucosum is characterized by increased TPx and decreased TAC in plasma depending on the lesion area. The redox status is shifted towards the oxidizing state, particularly in MOD and SEV cases. This results in a condition of OS, which may contribute to the pathogenesis of the disease.

Screening the pandemic response box identified benzimidazole carbamates, Olorofim and ravuconazole as promising drug candidates for the treatment of eumycetoma

Eumycetoma is a chronic subcutaneous neglected tropical disease that can be caused by more than 40 different fungal causative agents. The most common causative agents produce black grains and belong to the fungal orders Sordariales and Pleosporales. The current antifungal agents used to treat eumycetoma are itraconazole or terbinafine, however, their cure rates are low. To find novel drugs for eumycetoma, we screened 400 diverse drug-like molecules from the Pandemic Response Box against common eumycetoma causative agents as part of the Open Source Mycetoma initiative (MycetOS). 26 compounds were able to inhibit the growth of Madurella mycetomatis, Madurella pseudomycetomatis and Madurella tropicana, 26 compounds inhibited Falciformispora senegalensis and seven inhibited growth of Medicopsis romeroi in vitro. Four compounds were able to inhibit the growth of all five species of fungi tested. They are the benzimidazole carbamates fenbendazole and carbendazim, the 8-aminoquinolone derivative tafenoquine and MMV1578570. Minimal inhibitory concentrations were then determined for the compounds active against M. mycetomatis. Compounds showing potent activity in vitro were further tested in vivo. Fenbendazole, MMV1782387, ravuconazole and olorofim were able to significantly prolong Galleria mellonella larvae survival and are promising candidates to explore in mycetoma treatment and to also serve as scaffolds for medicinal chemistry optimisation in the search for novel antifungals to treat eumycetoma.

Epidemiology and risk of invasive fungal infections in systemic lupus erythematosus: a nationwide population-based cohort study

Introduction

Infections are a leading cause of mortality in patients with systemic lupus erythematosus (SLE). Among various infections, invasive fungal infections (IFIs) have a particularly high mortality rate; however, studies examining IFIs in patients with SLE are limited.

Methods

Patients diagnosed as having SLE between 1997 and 2012 were enrolled from Taiwan's National Health Insurance Research Database along with age- and sex-matched non-SLE controls at a ratio of 1:10. IFIs were identified based on International Classification of Diseases, Ninth Revision, Clinical Modification codes and validated by the prescriptions of systemic antifungal agents. The incidence rate (IR), incidence rate ratio (IRR), and all-cause mortality rate of IFIs and its subtypes were analyzed. A Cox multivariate regression model with time-dependent covariates was applied to analyze independent risk factors for IFIs.

Results

A total of 24,541 patients with SLE and 245,410 non-SLE controls were included. We observed 445 IFI episodes in the SLE cohort, with an all-cause mortality rate of 26.7%. Candida spp. (52.8%) was the most common pathogen, followed by Cryptococcus spp. (18.2%) and Aspergillus spp. (18.2%). The IR of IFIs in the SLE cohort was 20.83 per 10,000 person-years, with an IRR of 11.1 [95% confidence interval (CI): 9.8-12.6] relative to the non-SLE controls. Juvenile patients with SLE aged ⩽18 years had the highest IRR of 47.2 (95% CI: 26.9-86.8). Intravenous steroid therapy administered within 60 days (hazard ratio: 29.11, 95% CI: 23.30-36.37) was the most critical risk factor for overall IFIs and each of the three major fungal pathogens. Distinct risk factors were found among different IFI subtypes.

Conclusion

Patients with SLE had a higher risk of IFIs, especially juvenile patients. Intravenous steroid therapy is the most critical risk factor for IFIs. This study provides crucial information for the risk stratification of IFIs in SLE.

Plain Language Summaries

Patients with systemic lupus erythematosus and physicians treating this patient group should be aware of the risk of invasive fungal infections.Invasive fungal infections (IFIs) are a severe complication with a high mortality rate among patients with systemic lupus erythematosus (SLE); however, studies on this topic are scant. We performed a nationwide population-based study in Taiwan to estimate the incidence and mortality of and risk factors for IFIs. We found an incidence rate of 20.83 per 10,000 person-years for IFIs, with a mortality rate of 26.7%. Juvenile patients aged ⩽18 years had the highest relative risk of IFIs. Although candidiasis was the most common IFI, cryptococcosis and aspergillosis should be concerned in juvenile patients as well. Intravenous steroid therapy was the most critical risk factor for all IFIs, and different immunosuppressive agents posed different risks in patients for acquiring certain fungal pathogens.Our findings provide pivotal epidemiological information and indicate risk factors for IFIs in patients with SLE. Age and exposure to specific immunosuppressants and steroids might help predict the risk of IFIs. Because the manifestation of these infections is sometimes indistinguishable from a lupus flare, physicians should be aware of this fatal complication, especially when patients are not responsive to immunosuppressive therapy. Early recognition, implication of diagnostic tools, and empirical antimicrobial agents can be the key to treating patients with IFIs. Additional studies are required to develop a risk management program for patients with SLE.

Interrogation of the cell wall integrity pathway in Aspergillus niger identifies a putative negative regulator of transcription involved in chitin deposition

Post-fermentation fungal biomass waste provides a viable source for chitin. Cell wall chitin of filamentous fungi, and in particular its de-N-acetylated derivative chitosan, has a wide range of commercial applications. Although the cell wall of filamentous fungi comprises 10–30% chitin, these yields are too low for cost-effective production. Therefore, we aimed to identify the genes involved in increased chitin deposition by screening a collection of UV-derived cell wall mutants in Aspergillus niger. This screen revealed a mutant strain (RD15.4#55) that showed a 30–40% increase in cell wall chitin compared to the wild type. In addition to the cell wall chitin phenotype, this strain also exhibited sensitivity to SDS and produces an unknown yellow pigment. Genome sequencing combined with classical genetic linkage analysis identified two mutated genes on chromosome VII that were linked with the mutant phenotype. Single gene knockouts and subsequent complementation analysis revealed that an 8 bp deletion in NRRL3_09595 is solely responsible for the associated phenotypes of RD15.4#55. The mutated gene, which was named cwcA (cell wall chitin A), encodes an orthologue of Saccharomyces cerevisiae Bypass of ESS1 (BYE1), a negative regulator of transcription elongation. We propose that this conserved fungal protein is involved in preventing cell wall integrity signaling under non-inducing conditions, where loss of function results in constitutive activation of the cell wall stress response pathway, and consequently leads to increased chitin content in the mutant cell wall.

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An Aspergillus niger UV-mutant with increased cell wall chitin was characterized.

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Causative mutation was identified in a single gene, named cell wall chitin A (cwcA).

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CwcA is orthologous to yeast Bye1p and exists as a single copy gene.

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Three relevant domains are found in both CwcA and Bye1p: PHD, TFIIS and SPOC.

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CwcA acts as negative regulator of CWI signaling.

A seven-membered cell wall related transglycosylase gene family in Aspergillus niger is relevant for cell wall integrity in cell wall mutants with reduced α-glucan or galactomannan

Chitin is an important fungal cell wall component that is cross-linked to β-glucan for structural integrity. Acquisition of chitin to glucan cross-links has previously been shown to be performed by transglycosylation enzymes in Saccharomyces cerevisiae, called Congo Red hypersensitive (Crh) enzymes. Here, we characterized the impact of deleting all seven members of the crh gene family (crhA-G) in Aspergillus niger on cell wall integrity, cell wall composition and genome-wide gene expression. In this study, we show that the seven-fold crh knockout strain shows slightly compact growth on plates, but no increased sensitivity to cell wall perturbing compounds. Additionally, we found that the cell wall composition of this knockout strain was virtually identical to that of the wild type. In congruence with these data, genome-wide expression analysis revealed very limited changes in gene expression and no signs of activation of the cell wall integrity response pathway. However, deleting the entire crh gene family in cell wall mutants that are deficient in either galactofuranose or α-glucan, mainly α-1,3-glucan, resulted in a synthetic growth defect and an increased sensitivity towards Congo Red compared to the parental strains, respectively. Altogether, these results indicate that loss of the crh gene family in A. niger does not trigger the cell wall integrity response, but does play an important role in ensuring cell wall integrity in mutant strains with reduced galactofuranose or α-glucan.

Rab GDP-dissociation inhibitor gdiA is an essential gene required for cell wall chitin deposition in Aspergillus niger

The cell wall is a distinctive feature of filamentous fungi, providing them with structural integrity and protection from both biotic and abiotic factors. Unlike plant cell walls, fungi rely on structurally strong hydrophobic chitin core for mechanical strength together with alpha- and beta-glucans, galactomannans and glycoproteins. Cell wall stress conditions are known to alter the cell wall through the signaling cascade of the cell wall integrity (CWI) pathway and can result in increased cell wall chitin deposition. A previously isolated set of Aspergillus niger cell wall mutants was screened for increased cell wall chitin deposition. UV-mutant RD15.8#16 was found to contain approximately 60% more cell wall chitin than the wild type. In addition to the chitin phenotype, RD15.8#16 exhibits a compact colony morphology and increased sensitivity towards SDS. RD15.8#16 was subjected to classical genetic approach for identification of the underlying causative mutation, using co-segregation analysis and SNP genotyping. Genome sequencing of RD15.8#16 revealed eight SNPs in open reading frames (ORF) which were individually checked for co-segregation with the associated phenotypes, and showed the potential relevance of two genes located on chromosome IV. In situ re-creation of these ORF-located SNPs in a wild type background, using CRISPR/Cas9 genome editing, showed the importance Rab GTPase dissociation inhibitor A (gdiA) for the phenotypes of RD15.8#16. An alteration in the 5' donor splice site of gdiA reduced pre-mRNA splicing efficiency, causing aberrant cell wall assembly and increased chitin levels, whereas gene disruption attempts showed that a full gene deletion of gdiA is lethal.

Activity and Cell-Death Pathway in Leishmania infantum Induced by Sugiol: Vectorization Using Yeast Cell Wall Particles Obtained From Saccharomyces cerevisiae

Visceral leishmaniasis, caused by Leishmania infantum, is a neglected tropical disease, to which efforts in the innovation of effective and affordable treatments remain limited, despite the rising incidence in several regions of the world. In this work, the antileishmanial effects of sugiol were investigated in vitro. This compound was isolated from the bark of Cupressus lusitanica and showed promising activity against L. infantum. In spite of the positive results, it is known that the compound is a poorly water-soluble diterpene molecule, which hinders further investigation, especially in preclinical animal studies. Thus, in an alternative delivery method, sugiol was entrapped in glucan-rich particles obtained from Saccharomyces cerevisiae yeast cell walls (YCWPs). To evaluate the activity of sugiol, the experiments were divided into two parts: (i) the in vitro investigation of antileishmanial activity of free sugiol against L. infantum promastigotes after 24, 48, and 72 h of treatment and (ii) the evaluation of antileishmanial activity of sugiol entrapped in glucan-rich particles against intracellular L. infantum amastigotes. Free sugiol induced the cell-death process in promastigotes, which was triggered by enhancing cytosolic calcium level and promoting the autophagy up to the first 24 h. Over time, the presence of autophagic vacuoles became rarer, especially after treatment with lower concentrations of sugiol, but other cellular events intensified, like ROS production, cell shrinkage, and phosphatidylserine exposure. Hyperpolarization of mitochondrial membrane potential was found at 72 h, induced by the mitochondria calcium uptake, causing an increase in ROS production and lipid peroxidation as a consequence. These events resulted in the cell death of promastigotes by secondary necrosis. Sugiol entrapped in glucan-rich particles was specifically recognized by dectin-1 receptor on the plasma membrane of macrophages, the main host cell of Leishmania spp. Electron micrographs revealed particles containing sugiol within the infected macrophages and these particles were active against the intracellular L. infantum amastigotes without affecting the host cell. Therefore, the YCWPs act like a Trojan horse to successfully deliver sugiol into the macrophage, presenting an interesting strategy to deliver water-insoluble drugs to parasitized cells.