Nanoscopic cell-wall architecture of an immunogenic ligand in Candida albicans during antifungal drug treatment

The cell wall of Candida albicans is composed largely of polysaccharides. Here we focus on β-glucan, an immunogenic cell-wall polysaccharide whose surface exposure is often restricted, or “masked,” from immune recognition by Dectin-1 on dendritic cells (DCs) and other innate immune cells. Previous research suggested that the physical presentation geometry of β-glucan might determine whether it can be recognized by Dectin-1. We used direct stochastic optical reconstruction microscopy to explore the fine structure of β-glucan exposed on C. albicans cell walls before and after treatment with the antimycotic drug caspofungin, which alters glucan exposure. Most surface-accessible glucan on C. albicans yeast and hyphae is limited to isolated Dectin-1–binding sites. Caspofungin-induced unmasking caused approximately fourfold to sevenfold increase in total glucan exposure, accompanied by increased phagocytosis efficiency of DCs for unmasked yeasts. Nanoscopic imaging of caspofungin-unmasked C. albicans cell walls revealed that the increase in glucan exposure is due to increased density of glucan exposures and increased multiglucan exposure sizes. These findings reveal that glucan exhibits significant nanostructure, which is a previously unknown physical component of the host– Candida interaction that might change during antifungal chemotherapy and affect innate immune activation.

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Recognition and Blocking of Innate Immunity Cells by Candida albicans Chitin

Infection and Immunity ◽

10.1128/iai.01282-10 ◽

2011 ◽

Vol 79 (5) ◽

pp. 1961-1970 ◽

Cited By ~ 111

Author(s):

Héctor M. Mora-Montes ◽

Mihai G. Netea ◽

Gerben Ferwerda ◽

Megan D. Lenardon ◽

Gordon D. Brown ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Cell Walls ◽

Mononuclear Cells ◽

Cytokine Production ◽

Immune Cell ◽

Human Peripheral Blood ◽

Immune Recognition ◽

Cell Wall Polysaccharide ◽

Content Type

ABSTRACTChitin is a skeletal cell wall polysaccharide of the inner cell wall of fungal pathogens. As yet, little about its role during fungus-host immune cell interactions is known. We show here that ultrapurified chitin fromCandida albicanscell walls did not stimulate cytokine production directly but blocked the recognition ofC. albicansby human peripheral blood mononuclear cells (PBMCs) and murine macrophages, leading to significant reductions in cytokine production. Chitin did not affect the induction of cytokines stimulated by bacterial cells or lipopolysaccharide (LPS), indicating that blocking was not due to steric masking of specific receptors. Toll-like receptor 2 (TLR2), TLR4, and Mincle (the macrophage-inducible C-type lectin) were not required for interactions with chitin. Dectin-1 was required for immune blocking but did not bind chitin directly. Cytokine stimulation was significantly reduced upon stimulation of PBMCs with heat-killed chitin-deficientC. albicanscells but not with live cells. Therefore, chitin is normally not exposed to cells of the innate immune system but is capable of influencing immune recognition by blocking dectin-1-mediated engagement with fungal cell walls.

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Remasking of Candida albicans β-Glucan in Response to Environmental pH Is Regulated by Quorum Sensing

mBio ◽

10.1128/mbio.02347-19 ◽

2019 ◽

Vol 10 (5) ◽

Cited By ~ 7

Author(s):

Fabien Cottier ◽

Sarah Sherrington ◽

Sarah Cockerill ◽

Valentina del Olmo Toledo ◽

Stephen Kissane ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Quorum Sensing ◽

Immune Responses ◽

Female Reproductive Tract ◽

Innate Immune ◽

Immune Recognition ◽

Innate Immune Responses ◽

Content Type ◽

Cell Wall Remodeling

ABSTRACT Candida albicans is a commensal yeast of the human gut which is tolerated by the immune system but has the potential to become an opportunistic pathogen. One way in which C. albicans achieves this duality is through concealing or exposing cell wall pathogen-associated molecular patterns (PAMPs) in response to host-derived environment cues (pH, hypoxia, and lactate). This cell wall remodeling allows C. albicans to evade or hyperactivate the host’s innate immune responses, leading to disease. Previously, we showed that adaptation of C. albicans to acidic environments, conditions encountered during colonization of the female reproductive tract, induces significant cell wall remodeling resulting in the exposure of two key fungal PAMPs (β-glucan and chitin). Here, we report that this pH-dependent cell wall remodeling is time dependent, with the initial change in pH driving cell wall unmasking, which is then remasked at later time points. Remasking of β-glucan was mediated via the cell density-dependent fungal quorum sensing molecule farnesol, while chitin remasking was mediated via a small, heat-stable, nonproteinaceous secreted molecule(s). Transcript profiling identified a core set of 42 genes significantly regulated by pH over time and identified the transcription factor Efg1 as a regulator of chitin exposure through regulation of CHT2. This dynamic cell wall remodeling influenced innate immune recognition of C. albicans, suggesting that during infection, C. albicans can manipulate the host innate immune responses. IMPORTANCE Candida albicans is part of the microbiota of the skin and gastrointestinal and reproductive tracts of humans and has coevolved with us for millennia. During that period, C. albicans has developed strategies to modulate the host’s innate immune responses, by regulating the exposure of key epitopes on the fungal cell surface. Here, we report that exposing C. albicans to an acidic environment, similar to the one of the stomach or vagina, increases the detection of the yeast by macrophages. However, this effect is transitory, as C. albicans is able to remask these epitopes (glucan and chitin). We found that glucan remasking is controlled by the production of farnesol, a molecule secreted by C. albicans in response to high cell densities. However, chitin-remasking mechanisms remain to be identified. By understanding the relationship between environmental sensing and modulation of the host-pathogen interaction, new opportunities for the development of innovative antifungal strategies are possible.

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Adaptation of Candida albicans to environmental pH induces cell wall remodelling and enhances innate immune recognition

PLoS Pathogens ◽

10.1371/journal.ppat.1006403 ◽

2017 ◽

Vol 13 (5) ◽

pp. e1006403 ◽

Cited By ~ 69

Author(s):

Sarah L. Sherrington ◽

Eleanor Sorsby ◽

Nabeel Mahtey ◽

Pizga Kumwenda ◽

Megan D. Lenardon ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Innate Immune ◽

Immune Recognition

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Chemical and enzymatic changes in the cell walls of Candida albicans and Saccharomyces cerevisiae by scanning electron microscopy

Canadian Journal of Microbiology ◽

10.1139/m80-164 ◽

1980 ◽

Vol 26 (8) ◽

pp. 965-970 ◽

Cited By ~ 22

Author(s):

Yvonne Koch ◽

K. H. Rademacher

Keyword(s):

Electron Microscopy ◽

Saccharomyces Cerevisiae ◽

Scanning Electron Microscopy ◽

Cell Wall ◽

Candida Albicans ◽

Cell Walls ◽

Wall Structure ◽

Before And After ◽

Enzymatic Changes ◽

Scanning Electron

Candida albicans and Saccharomyces cerevisiae cells were examined by scanning electron microscopy before and after extraction of the mannans of the cell wall. The surfaces of control cells were smooth; after mannan extraction they were rough and showed erosions which were particularly striking within the area of the scars. Helicase digested irregular holes through the cell wall within 20 min; these increased in size during an additional 40 min of digestion. These holes were not localized in or on the bud scars, which remained intact even after the long digestion period. The results were used to construct a model for yeast cell wall structure.

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Masking of β(1-3)-Glucan in the Cell Wall of Candida albicans from Detection by Innate Immune Cells Depends on Phosphatidylserine

Infection and Immunity ◽

10.1128/iai.01612-14 ◽

2014 ◽

Vol 82 (10) ◽

pp. 4405-4413 ◽

Cited By ~ 32

Author(s):

Sarah E. Davis ◽

Alex Hopke ◽

Steven C. Minkin ◽

Anthony E. Montedonico ◽

Robert T. Wheeler ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

De Novo ◽

Invasive Disease ◽

Innate Immune ◽

Dependent Manner ◽

Content Type ◽

Immune Effector ◽

Host Interactions ◽

Innate Immune Effector

ABSTRACTThe virulence ofCandida albicansin a mouse model of invasive candidiasis is dependent on the phospholipids phosphatidylserine (PS) and phosphatidylethanolamine (PE). Disruption of the PS synthase geneCHO1(i.e.,cho1Δ/Δ) eliminates PS and blocks thede novopathway for PE biosynthesis. In addition, thecho1Δ/Δ mutant's ability to cause invasive disease is severely compromised. Thecho1Δ/Δ mutant also exhibits cell wall defects, and in this study, it was determined that loss of PS results in decreased masking of cell wall β(1-3)-glucan from the immune system. In wild-typeC. albicans, the outer mannan layer of the wall masks the inner layer of β(1-3)-glucan from exposure and detection by innate immune effector molecules like the C-type signaling lectin Dectin-1, which is found on macrophages, neutrophils, and dendritic cells. Thecho1Δ/Δ mutant exhibits increases in exposure of β(1-3)-glucan, which leads to greater binding by Dectin-1 in both yeast and hyphal forms. The unmasking of β(1-3)-glucan also results in increased elicitation of TNF-α from macrophages in a Dectin-1-dependent manner. The role of phospholipids in fungal pathogenesis is an emerging field, and this is the first study showing that loss of PS inC. albicansresults in decreased masking of β(1-3)-glucan, which may contribute to our understanding of fungus-host interactions.

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Spatial Distribution of a Porphyrin-Based Photosensitizer Reveals Mechanism of Photodynamic Inactivation of Candida albicans

Frontiers in Medicine ◽

10.3389/fmed.2021.641244 ◽

2021 ◽

Vol 8 ◽

Author(s):

Thomas Voit ◽

Fabian Cieplik ◽

Johannes Regensburger ◽

Karl-Anton Hiller ◽

Anita Gollmer ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Fungal Infections ◽

Cell Envelope ◽

Antimicrobial Photodynamic Therapy ◽

Fungal Cell ◽

Before And After ◽

Antifungal Action ◽

Complete Cell ◽

Further Development

The antimicrobial photodynamic therapy (aPDT) is a promising approach for the control of microbial and especially fungal infections such as mucosal mycosis. TMPyP [5,10,15, 20-tetrakis(1-methylpyridinium-4-yl)-porphyrin tetra p-toluenesulfonate] is an effective photosensitizer (PS) that is commonly used in aPDT. The aim of this study was to examine the localization of TMPyP in Candida albicans before and after irradiation with visible light to get information about the cellular mechanism of antifungal action of the photodynamic process using this PS. Immediately after incubation of C. albicans with TMPyP, fluorescence microscopy revealed an accumulation of the PS in the cell envelope. After irradiation with blue light the complete cell showed red fluorescence, which indicates, that aPDT is leading to a damage in the cell wall with following influx of PS into the cytosol. Incubation of C. albicans with Wheat Germ Agglutinin (WGA) could confirm the cell wall as primary binding site of TMPyP. The finding that the porphyrin accumulates in the fungal cell wall and does not enter the interior of the cell before irradiation makes it unlikely that resistances can emerge upon aPDT. The results of this study may help in further development and modification of PS in order to increase efficacy against fungal infections such as those caused by C. albicans.

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Melanin Externalization in Candida albicans Depends on Cell Wall Chitin Structures

Eukaryotic Cell ◽

10.1128/ec.00051-10 ◽

2010 ◽

Vol 9 (9) ◽

pp. 1329-1342 ◽

Cited By ~ 55

Author(s):

Claire A. Walker ◽

Beatriz L. Gómez ◽

Héctor M. Mora-Montes ◽

Kevin S. Mackenzie ◽

Carol A. Munro ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Fungal Pathogen ◽

Cell Walls ◽

Chitin Synthesis ◽

Melanin Production ◽

Content Type ◽

Encoding Gene ◽

Chitinase Genes

ABSTRACT The fungal pathogen Candida albicans produces dark-pigmented melanin after 3 to 4 days of incubation in medium containing l-3,4-dihydroxyphenylalanine (l-DOPA) as a substrate. Expression profiling of C. albicans revealed very few genes significantly up- or downregulated by growth in l-DOPA. We were unable to determine a possible role for melanin in the virulence of C. albicans. However, we showed that melanin was externalized from the fungal cells in the form of electron-dense melanosomes that were free or often loosely bound to the cell wall exterior. Melanin production was boosted by the addition of N-acetylglucosamine to the medium, indicating a possible association between melanin production and chitin synthesis. Melanin externalization was blocked in a mutant specifically disrupted in the chitin synthase-encoding gene CHS2. Melanosomes remained within the outermost cell wall layers in chs3Δ and chs2Δ chs3Δ mutants but were fully externalized in chs8Δ and chs2Δ chs8Δ mutants. All the CHS mutants synthesized dark pigment at equivalent rates from mixed membrane fractions in vitro, suggesting it was the form of chitin structure produced by the enzymes, not the enzymes themselves, that was involved in the melanin externalization process. Mutants with single and double disruptions of the chitinase genes CHT2 and CHT3 and the chitin pathway regulator ECM33 also showed impaired melanin externalization. We hypothesize that the chitin product of Chs3 forms a scaffold essential for normal externalization of melanosomes, while the Chs8 chitin product, probably produced in cell walls in greater quantity in the absence of CHS2, impedes externalization.

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Screening and Antifungal Activity of a β-Carboline Derivative against Cryptococcus neoformans and C. gattii

International Journal of Microbiology ◽

10.1155/2019/7157845 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Kátia Santana Cruz ◽

Emerson Silva Lima ◽

Marcia de Jesus Amazonas da Silva ◽

Erica Simplício de Souza ◽

Andreia Montoia ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Antifungal Activity ◽

Cryptococcus Neoformans ◽

Active Compound ◽

Cell Walls ◽

Human Fibroblasts ◽

Lead Compound ◽

Fungal Cell ◽

Fungal Cell Walls

Background. Cryptococcosis is a fungal disease of bad prognosis due to its pathogenicity and the toxicity of the drugs used for its treatment. The aim of this study was to investigate the medicinal potential of carbazole and β-carboline alkaloids and derivatives against Cryptococcus neoformans and C. gattii. Methods. MICs were established in accordance with the recommendations of the Clinical and Laboratory Standards Institute for alkaloids and derivatives against C. neoformans and C. gattii genotypes VNI and VGI, respectively. A single active compound was further evaluated against C. neoformans genotypes VNII, VNIII, and VNIV, C. gattii genotypes VGI, VGIII, and VGIV, Candida albicans ATCC 36232, for cytotoxicity against the MRC-5 lineage of human fibroblasts and for effects on fungal cells (cell wall, ergosterol, and leakage of nucleic acids). Results. Screening of 11 compounds revealed 8-nitroharmane as a significant inhibitor (MIC 40 μg/mL) of several C. neoformans and C. gattii genotypes. It was not toxic to fibroblasts (IC50 > 50 µg/mL) nor did it alter fungal cell walls or the concentration of ergosterol in C. albicans or C. neoformans. It increased leakage of substances that absorb at 260 nm. Conclusions. The synthetic β-carboline 8-nitroharmane significantly inhibits pathogenic Cryptococcus species and is interesting as a lead compound towards new therapy for Cryptococcus infections.

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Étude cytochimique ultrastructurale de la dégradation des lignines dans les résidus pariétaux de bois d'épicéa et de peuplier par le Reticulitermes lucifugus var. santonensis (Rhinotermitidae, Isoptera)

Canadian Journal of Botany ◽

10.1139/b92-117 ◽

1992 ◽

Vol 70 (5) ◽

pp. 933-941 ◽

Cited By ~ 2

Author(s):

E. Garnier-Sillam ◽

I. Grech ◽

Y. Czaninski ◽

M.-T. Tollier ◽

B. Monties

Keyword(s):

Cell Wall ◽

Cell Walls ◽

Periodic Acid ◽

Mechanical Action ◽

Free Cell ◽

Uranyl Acetate ◽

Picea Sitchensis ◽

Wall Material ◽

Before And After ◽

Acetate Lead

Free cell-wall residues were prepared by extracting wood samples of spruce (Populus euramericana cv. Fidzi Pauley) and poplar (Picea sitchensis). These species were chosen for their lignin types: guaiacyl in spruce and guaiacyl–syringyl in poplar. The parietal residues obtained were used as the sole food for the xylophagous termite Reticulitermes lucifugus var. santonensis and were compared before and after ingestion and transit in the digestive tracts. Differences due to the mechanical action of the gizzard were found in association with chemical changes. Polysaccharides were unmasked after digestion and could clearly be observed after reaction with periodic acid – thiocarbohydrazide – silver proteinate. A fibrillary meshwork was also observed inside the lignified cell walls. Biodegradation of cell wall material was particularly clear in poplar where granules formed an electron-dense plasma when uranyl acetate – lead citrate or periodic acid – thiocarbohydrazide – silver proteinate was used as a contrast medium. A selective biodegradation of syringyl monomers in poplar parietal residues was indicated by thioacidolysis but requires confirmation. Breakdown of lignified cell walls begins with a biodegradation of the lignin network associated with or followed by the digestion of polysaccharides. Syringyl-rich lignin fractions seemed to break down faster. Whether the enzymic pathway leading to ligninolysis originates from the termite digestive cells or from the endosymbionts present in their digestive tract lumen remains to be defined. Key words: Isoptera, Reticulitermes lucifugus var. santonensis, wood, lignin, spruce, poplar.

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