SDH2 is involved in proper hypha formation and virulence in Candida albicans

The deletion of ppr2 interferes iron sensing and leads to oxidative stress response in Schizosaccharomyces pombe

Pentatricopeptide repeat proteins are involved in mitochondrial both transcriptional and posttranscriptional regulation. Schizosaccharomyces pombe Ppr2 is a general mitochondrial translation factor that plays a critical role in the synthesis of all mitochondrial DNA-encoded oxidative phosphorylation subunits, which are essential for mitochondrial respiration. Our previous analysis showed that ppr2 deletion resulted in increased expression of iron uptake genes and caused ferroptosis-like cell death in S. pombe. In the present work, we showed that deletion of ppr2 reduced viability on glycerol- and galactose-containing media.Php4 is a transcription repressor that regulates iron homeostasis in fission yeast. We found that in the ppr2 deletion strain, Php4 was constitutively active and accumulated in the nucleus in the stationary phase. We also found that deletion of ppr2 decreased the ferroptosis-related protein Gpx1 in the mitochondria. Overexpression of Gpx1 improves the viability of Δppr2 cells. We showed that the deletion of ppr2 increased the production of ROS, downregulated heme synthesis and iron-sulfur cluster proteins, and induced stress proteins. Finally, we observed the nuclear accumulation of Pap1-GFP and Sty1-GFP, suggesting that Sty1 and Pap1 in response to cellular stress in the ppr2 deletion strain. These results suggest thatppr2 deletion may cause mitochondrial dysfunction, which is likely to lead to iron-sensing defect and iron starvation response, resulting in perturbation of iron homeostasis and increased hydroxyl radical production. The increased hydroxyl radical production triggers cellular responses in theppr2 deletion strain.

Synergy and Mechanism of Leflunomide Plus Fluconazole Against Resistant Candida albicans: An in vitro Study

Objective

The global rise in the resistance of Candida albicans to conventional antifungals makes Candida albicans infections harder to treat. The main objective of this study was to investigate the antifungal effects and underlying mechanisms of leflunomide in combination with triazoles against resistant Candida albicans.

Methods

In this study, the microdilution method was used to determine the antifungal effects of leflunomide in combination with three triazoles on planktonic cells in vitro. The morphological transition from yeast to hyphae was observed under a microscope. The effects on ROS, metacaspase, efflux pumps, and intracellular calcium concentration were investigated, respectively.

Results

Our findings suggested that leflunomide + triazoles showed a synergistic effect against resistant Candida albicans in vitro. Further study concluded that the synergistic mechanisms were resulted from multiple factors, including the inhibited efflux of triazoles, the inhibition of yeast-to-hyphae transition, ROS increasing, metacaspase activation, and [Ca²⁺]_i disturbance.

Discussion

Leflunomide appears to be a potential enhancer of current antifungal agents for treating candidiasis caused by resistant Candida albicans. This study can also serve as an example to inspire the exploration of new approaches to treating resistant Candida albicans.

Combined Transcriptome and Metabolome Analysis Reveals That the Potent Antifungal Pyrylium Salt Inhibits Mitochondrial Complex I in Candida albicans

Based on the structural modification of SM21, xy12, a new pyrylium salt derivative with enhanced antifungal activities, was synthesized. The MICs (MIC90) of xy12 against Candida albicans ranged from 0.125 to 0.25 μg/mL, about 2-fold lower than those of SM21. In addition, xy12 inhibited hypha and biofilm formation in C. albicans in a dose-dependent manner. A total of 3,454 differentially expressed genes and 260 differential metabolites were identified in the xy12-treated C. albicans by RNA-seq and non-targeted metabolomics. By integrating KEGG pathway enrichment analysis, we found that inhibition of oxidative phosphorylation was the important antifungal mechanism of action of xy12. Electron transport through mitochondrial respiratory complexes I to IV is the common process of oxidative phosphorylation. Compared with the sensitivity of the wild-type SC5314 to xy12, decreased sensitivities in mitochondrial complex I (CI)-deficient mutants and increased sensitivities in mitochondrial complex III- and IV-deficient mutants suggested that the antifungal effects of xy12 were dependent on CI. Consistently, xy12 exhibited antagonism with rotenone, an inhibitor of CI, and significantly inhibited the expression and activity of CI. Meanwhile, the phenotypes in the xy12-treated C. albicans were similar to those in the CI-deficient mutants, such as decreased ATP production, reduced mitochondrial membrane potential, loss of mitochondrial DNA, inability to utilize nonfermentative carbon sources, and decreased cell wall N-linked mannoproteins. Collectively, our results revealed that the pyrylium salt xy12 could constrain oxidative phosphorylation by inhibiting mitochondrial complex I in C. albicans, providing a novel lead compound for the development of mitochondria-targeted antifungal drugs. IMPORTANCE The development of new antifungal drugs is critical for solving the problem of antifungal resistance and expanding the limited variety of clinical antifungal drugs. Based on the modification of the pyrylium salt SM21, a new lead compound, xy12, was synthesized which was effective against Candida species both in vitro and in vivo. In this study, conjoined analysis of the transcriptome and metabolome elucidated the antifungal mechanism of action of xy12, which inhibited the activity of mitochondrial complex I in C. albicans. Targeting fungi-specific mitochondrial complex proteins has been reported as a promising antifungal strategy. Our study provided a new lead compound for targeting C. albicans mitochondrial complex I, which could be beneficial for discovering novel antifungal drugs.

Juxtaposing Caenorhabditis elegans-Pathogenic Mould Model with Other Models; How Reliable Is This Nematode Model? A Mini Review

The application of Caenorhabditis elegans as a pathogenic model has spanned decades. Its use for pathogenic mould modeling has been attracting some attention lately, though not without some reservations. Several studies have shown C. elegans to be a reliable model for evaluating moulds' virulence factors and patterns as well as for screening the pathogenicity of mutant strains alongside their parental/wild type and revertant/complementary strains. There is a very high degree of reported similarities between the virulence patterns demonstrated in C. elegans and those of other invertebrate and vertebrate models. We have here presented several works in which this nematode model was adopted for virulence evaluation, and other comparative research in which virulence in C. elegans model were juxtaposed with other models. We have further presented possible reasons why there might have been variations of virulence in a few cases, thereby validating C. elegans to be an effective and reliable tool in the study of pathogenic moulds.

iTRAQ-based proteomics revealed baicalein enhanced oxidative stress of Candida albicans by up-regulating CPD2 expression

Baicalein could inhibit the growth and biofilm formation of Candida albicans, the most common clinical fungal pathogen. However, the antifungal mechanism of baicalein has not been elucidated. In this study, isobaric tags for relative and absolute quantification (iTRAQ) was used to verify the mechanism of antifungal fluconazole and baicalein. A total of 58 common proteins were detected in cells treated with fluconazole. These proteins encompassed fluconazole-targeted sterol synthesis pathway, including Erg11p, Erg6p, Erg3p, Erg25p, Erg5p, Erg10p and Ncp1p. Next, iTRAQ was applied to the comparison of baicalein-treated C. albicans proteins, which detected 16 common proteins. The putative NADH dehydrogenase Cpd2p and the ATP-binding cassette transporter Snq2p were the most up-regulated proteins with the treatment of baicalein. Our results showed that CPD2 disruption elevated C. albicans resistance to baicalein significantly both in vitro and in vivo. Further in-depth studies revealed that CPD2 disruption reduced the activation of C. albicans metacaspase and partially restored the mitochondrial membrane potential reduction caused by the treatment of baicalein, which indicated that CPD2 was involved in the apoptosis induced by baicalein. Consistently, under the treatment of baicalein, CPD2Δ/Δ mutant produced lower reactive oxygen species (ROS) that was critical in causing oxidative damage and apoptosis in C. albicans. These results indicated that baicalein could increase intracellular oxidative damage by up-regulating the expression of Cpd2p so as to inhibit the growth of C. albicans, which provides new insights for investigating the antifungal target of baicalein.

Evaluation of Anti-Candida Potential of Piper nigrum Extract in Inhibiting Growth, Yeast-Hyphal Transition, Virulent Enzymes, and Biofilm Formation

Due to the increased incidence of fungal infections and the emergence of antifungal resistance mainly by Candida species, the need for safe and effective novel therapies is imperative. Consequently, plants and herbs are a powerful source to combat infections. Here, we evaluated the anti-Candida potential of an ethanolic extract from Piper nigrum. The phytochemical analysis of P. nigrum revealed bioactive compounds such as alkaloids, terpenoids, and tannis. Our results showed that P. nigrum extract suppressed the virulence factors of C. albicans strains, including hyphae formation in both liquid and solid media, reduced secretion of phospholipases/proteinases, and affected biofilm formation. Furthermore, the P. nigrum extract showed no hemolytic effect in vitro and exhibited reduced cytotoxicity on Vero cells and G. mellonella larvae at concentrations that inhibited hyphae and biofilm in C. albicans. Moreover, the extract demonstrated antifungal activity against C. auris strains. In conclusion, the P. nigrum extract affected the growth and morphogenesis of Candida (even in resistant strains), demonstrating that this plant has an anti-candida activity and represents a promising resource for discovering novel antifungal compounds.

Mining the Flavoproteome of Brucella ovis, the Brucellosis Causing Agent in Ovis aries

Flavoproteins are a diverse class of proteins that are mostly enzymes and contain as cofactors flavin mononucleotide (FMN) and/or flavin adenine dinucleotide (FAD), which enable them to participate in a wide range of physiological reactions. We have compiled 78 potential proteins building the flavoproteome of Brucella ovis (B. ovis), the causative agent of ovine brucellosis. The curated list of flavoproteins here reported is based on (i) the analysis of sequence, structure and function of homologous proteins, and their classification according to their structural domains, clans, and expected enzymatic functions; (ii) the constructed phylogenetic trees of enzyme functional classes using 19 Brucella strains and 26 pathogenic and/or biotechnological relevant alphaproteobacteria together with B. ovis; and (iii) the evaluation of the genetic context for each entry. Candidates account for ∼2.7% of the B. ovis proteome, and 75% of them use FAD as cofactor. Only 55% of these flavoproteins belong to the core proteome of Brucella and contribute to B. ovis processes involved in maintenance activities, survival and response to stress, virulence, and/or infectivity. Several of the predicted flavoproteins are highly divergent in Brucella genus from revised proteins and for them it is difficult to envisage a clear function. This might indicate modified catalytic activities or even divergent processes and mechanisms still not identified. We have also detected the lack of some functional flavoenzymes in B. ovis, which might contribute to it being nonzoonotic. Finally, potentiality of B. ovis flavoproteome as the source of antimicrobial targets or biocatalyst is discussed. IMPORTANCE Some microorganisms depend heavily on flavin-dependent activities, but others maintain them at a minimum. Knowledge about flavoprotein content and functions in different microorganisms will help to identify their metabolic requirements, as well as to benefit either industry or health. Currently, most flavoproteins from the sheep pathogen Brucella ovis are only automatically annotated in databases, and only two have been experimentally studied. Indeed, certain homologues with unknown function are not characterized, and they might relate to still not identified mechanisms or processes. Our research has identified 78 members that comprise its flavoproteome, 76 of them flavoenzymes, which mainly relate to bacteria survival, virulence, and/or infectivity. The list of flavoproteins here presented allows us to better understand the peculiarities of Brucella ovis and can be applied as a tool to search for candidates as new biocatalyst or antimicrobial targets.

Transcriptional Control of Hypoxic Hyphal Growth in the Fungal Pathogen Candida albicans

The ability of Candida albicans, an important human fungal pathogen, to develop filamentous forms is a crucial determinant for host invasion and virulence. While hypoxia is one of the predominant host cues that promote C. albicans filamentous growth, the regulatory circuits that link oxygen availability to filamentation remain poorly characterized. We have undertaken a genetic screen and identified the two transcription factors Ahr1 and Tye7 as central regulators of the hypoxic filamentation. Both ahr1 and tye7 mutants exhibited a hyperfilamentous phenotype specifically under an oxygen-depleted environment suggesting that these transcription factors act as negative regulators of hypoxic filamentation. By combining microarray and ChIP-chip analyses, we have characterized the set of genes that are directly modulated by Ahr1 and Tye7. We found that both Ahr1 and Tye7 modulate a distinct set of genes and biological processes. Our genetic epistasis analysis supports our genomic finding and suggests that Ahr1 and Tye7 act independently to modulate hyphal growth in response to hypoxia. Furthermore, our genetic interaction experiments uncovered that Ahr1 and Tye7 repress the hypoxic filamentation via the Efg1 and Ras1/Cyr1 pathways, respectively. This study yielded a new and an unprecedented insight into the oxygen-sensitive regulatory circuit that control morphogenesis in a fungal pathogen.

Caenorhabditis elegans as an Infection Model for Pathogenic Mold and Dimorphic Fungi: Applications and Challenges

The threat burden from pathogenic fungi is universal and increasing with alarming high mortality and morbidity rates from invasive fungal infections. Understanding the virulence factors of these fungi, screening effective antifungal agents and exploring appropriate treatment approaches in in vivo modeling organisms are vital research projects for controlling mycoses. Caenorhabditis elegans has been proven to be a valuable tool in studies of most clinically relevant dimorphic fungi, helping to identify a number of virulence factors and immune-regulators and screen effective antifungal agents without cytotoxic effects. However, little has been achieved and reported with regard to pathogenic filamentous fungi (molds) in the nematode model. In this review, we have summarized the enormous breakthrough of applying a C. elegans infection model for dimorphic fungi studies and the very few reports for filamentous fungi. We have also identified and discussed the challenges in C. elegans-mold modeling applications as well as the possible approaches to conquer these challenges from our practical knowledge in C. elegans-Aspergillus fumigatus model.

Impact of serial systemic infection on Candida albicans virulence factors

Aim: To evaluate changes in virulence and pathogenicity approaches from Candida albicans after successive passages in a murine model of systemic candidiasis. Materials & methods: Phenotypic assays were performed using colonies recovered from animals infected serially, totalizing five passages. Results: A progressive infection was observed along the passages, with increased fungal burden and the presence of greater inflammatory areas in the histopathological findings. Recovered strains exhibited increased filamentation and biofilm abilities, along with modulation of phospholipase and proteinase activities. Conclusion: Repeated contact between yeast and host increased the expression of virulence factors. Furthermore, a correspondence between phenotypic profile and proteomic data obtained previously was observed.

A New Antifungal Agent (4-phenyl-1, 3-thiazol-2-yl) Hydrazine Induces Oxidative Damage in Candida albicans

A gradual rise in immunocompromised patients over past years has led to the increasing incidence of invasive fungal infections. Development of effective fungicides can not only provide new means for clinical treatment, but also reduce the occurrence of fungal resistance. We identified a new antifungal agent (4-phenyl-1, 3-thiazol-2-yl), hydrazine (numbered as 31C) which showed high-efficiency, broad-spectrum and specific activities. The minimum inhibitory concentration of 31C against pathogenic fungi was between 0.0625-4 μg/ml in vitro, while 31C had no obvious cytotoxicity to human umbilical vein endothelial cells with the concentration of 4 μg/ml. In addition, 31C of 0.5 μg/ml could exhibit significant fungicidal activity and inhibit the biofilm formation of C. albicans. In vivo fungal infection model showed that 31C of 10 mg/kg significantly increased the survival rate of Galleria mellonella. Further study revealed that 31C-treatment increased the reactive oxygen species (ROS) in C. albicans and elevated the expression of some genes related to anti-oxidative stress response, including CAP1, CTA1, TRR1, and SODs. Consistently, 31C-induced high levels of intracellular ROS resulted in considerable DNA damage, which played a critical role in antifungal-induced cellular death. The addition of ROS scavengers, such as glutathione (GSH), N-Acetyl-L-cysteine (NAC) or oligomeric proanthocyanidins (OPC), dramatically reduced the antifungal activities of 31C and rescued the 31C-induced filamentation defect. Collectively, these results showed that 31C exhibited strong antifungal activity and induced obvious oxidative damage, which indicated that compounds with a structure similar to 31C may provide new sight for antifungal drug development.