Candida glabrata: A Lot More Than Meets the Eye (original) (raw)
Related papers
2014
Candida glabrata is both a human fungal commensal and an opportunistic pathogen which can withstand activities of the immune system. For example, C. glabrata can survive phagocytosis and replicates within macrophages. However, the mechanisms underlying intracellular survival remain unclear. In this work, we used a functional genomic approach to identify C. glabrata determinants necessary for survival within human monocyte-derived macrophages by screening a set of 433 deletion mutants. We identified 23 genes which are required to resist killing by macrophages. Based on homologies to Saccharomyces cerevisiae orthologs, these genes are putatively involved in cell wall biosynthesis, calcium homeostasis, nutritional and stress response, protein glycosylation, or iron homeostasis. Mutants were further characterized using a series of in vitro assays to elucidate the genes' functions in survival. We investigated different parameters of C. glabrata-phagocyte interactions: uptake by macrophages, replication within macrophages, phagosomal pH, and recognition of mutant cells by macrophages as indicated by production of reactive oxygen species and tumor necrosis factor alpha (TNF-␣). We further studied the cell surface integrity of mutant cells, their ability to grow under nutrient-limited conditions, and their susceptibility to stress conditions mirroring the harsh environment inside a phagosome. Additionally, resistance to killing by neutrophils was analyzed. Our data support the view that immune evasion is a key aspect of C. glabrata virulence and that increased immune recognition causes increased antifungal activities by macrophages. Furthermore, stress resistance and efficient nutrient acquisition, in particular, iron uptake, are crucial for intraphagosomal survival of C. glabrata.
The Journal of Immunology, 2011
Although Candida glabrata is an important human pathogenic yeast, its pathogenicity mechanisms are largely unknown. Immune evasion strategies seem to play key roles during infection, since very little inflammation is observed in mouse models. Furthermore, C. glabrata multiplies intracellularly after engulfment by macrophages. In this study, we sought to identify the strategies that enable C. glabrata to survive phagosome biogenesis and antimicrobial activities within human monocyte-derived macrophages. We show that, despite significant intracellular proliferation, macrophage damage or apoptosis was not apparent, and production of reactive oxygen species was inhibited. Additionally, with the exception of GM-CSF, levels of pro-and antiinflammatory cytokines were only marginally increased. We demonstrate that adhesion to and internalization by macrophages occur within minutes, and recruitment of endosomal early endosomal Ag 1 and lysosomal-associated membrane protein 1 indicates phagosome maturation. However, phagosomes containing viable C. glabrata, but not heat-killed yeasts, failed to recruit cathepsin D and were only weakly acidified. This inhibition of acidification did not require fungal viability, but it had a heatsensitive surface attribute. Therefore, C. glabrata modifies the phagosome into a nonacidified environment and multiplies until the host cells finally lyse and release the fungi. Our results suggest persistence of C. glabrata within macrophages as a possible immune evasion strategy.
The fungal pathogen Candida glabrata has risen from an innocuous commensal to a major human pathogen that causes life-threatening infections with an associated mortality rate of up to 50%. The dramatic rise in the number of immunocompromised individuals from HIV infection, tuberculosis, and as a result of immunosuppressive regimens in cancer treatment and transplant interventions have created a new and hitherto unchartered niche for the proliferation of C. glabrata. Iron acquisition is a known microbial virulence determinant and human diseases of iron overload have been found to correlate with increased bacterial burden. Given that over 2 billion people worldwide suffer from iron deficiency and that iron overload is one of the most common single-gene inherited diseases, it is important to understand whether host iron status may influences C. glabrata infectious disease progression. Here we identify Sit1 as the sole siderophore-iron transporter in C. glabrata and demonstrate that siderophore-mediated iron acquisition is critical for enhancing C. glabrata survival to the microbicidal activities of macrophages. Within the Sit1 transporter, we identify a conserved extracellular SIderophore Transporter Domain (SITD) that is critical for siderophore-mediated ability of C. glabrata to resist macrophage killing. Using macrophage models of human iron overload disease, we demonstrate that C. glabrata senses altered iron levels within the phagosomal compartment. Moreover, Sit1 functions as a determinant for C. glabrata to survive macrophage killing in a manner that is dependent on macrophage iron status. These studies suggest that host iron status is a modifier of infectious disease that modulates the dependence on distinct mechanisms of microbial Fe acquisition.
Endothelial Cell Injury Caused by Candida albicans Is Dependent on Iron
1998
Although it is known that Candida albicans causes endothelial cell injury, in vitro and in vivo, the mechanism by which this process occurs remains unknown. Iron is critical for the induction of injury in many types of host cells. Therefore, we investigated the role of iron in Candida-induced endothelial cell injury. We found that pretreatment of endothelial cells with the
A family of 11 cell surface-associated aspartyl proteases (CgYps1–11), also referred as yapsins, is a key virulence factor in the pathogenic yeast Candida glabrata. However, the mechanism by which CgYapsins modulate immune response and facilitate survival in the mammalian host remains to be identified. Here, using RNA-Seq analysis, we report that genes involved in cell wall metabolism are differentially regulated in the Cgyps1– 11 mutant. Consistently, the mutant contained lower-glucan and mannan levels and exhibited increased chitin content in the cell wall. As cell wall components are known to regulate the innate immune response, we next determined the macrophage transcriptional response to C. glabrata infection and observed differential expression of genes implicated in inflammation, chemotaxis, ion transport, and the tumor necrosis factor signal-ing cascade. Importantly, the Cgyps1–11 mutant evoked a different immune response, resulting in an enhanced release of the pro-inflammatory cytokine IL-1 in THP-1 macrophages. Further, Cgyps1–11–induced IL-1 production adversely affected intracellular proliferation of co-infected WT cells and depended on activation of spleen tyrosine kinase (Syk) sig-naling in the host cells. Accordingly, the Syk inhibitor R406 augmented intracellular survival of the Cgyps1–11 mutant. Finally, we demonstrate that C. glabrata infection triggers elevated IL-1 production in mouse organs and that the CgYPS genes are required for organ colonization and dissemination in the murine model of systemic infection. Altogether, our results uncover the basis for macrophage-mediated killing of Cgyps1– 11 cells and provide the first evidence that aspartyl proteases in C. glabrata are required for suppression of IL-1 production in macrophages.
PLoS Pathogens, 2010
Candida albicans in the immunocompetent host is a benign member of the human microbiota. Though, when host physiology is disrupted, this commensal-host interaction can degenerate and lead to an opportunistic infection. Relatively little is known regarding the dynamics of C. albicans colonization and pathogenesis. We developed a C. albicans cell surface protein microarray to profile the immunoglobulin G response during commensal colonization and candidemia. The antibody response from the sera of patients with candidemia and our negative control groups indicate that the immunocompetent host exists in permanent host-pathogen interplay with commensal C. albicans. This report also identifies cell surface antigens that are specific to different phases (i.e. acute, early and mid convalescence) of candidemia. We identified a set of thirteen cell surface antigens capable of distinguishing acute candidemia from healthy individuals and uninfected hospital patients with commensal colonization. Interestingly, a large proportion of these cell surface antigens are involved in either oxidative stress or drug resistance. In addition, we identified 33 antigenic proteins that are enriched in convalescent sera of the candidemia patients. Intriguingly, we found within this subset an increase in antigens associated with heme-associated iron acquisition. These findings have important implications for the mechanisms of C. albicans colonization as well as the development of systemic infection.
Plasma and extracellular matrix proteins mediate in the fate of Candida albicans in the human host
Medical hypotheses, 1994
The fungus, Candida albicans, causes trivial to life-threatening diseases in man when normal host defenses are compromised. The fungus appears to have evolved receptors (hereinafter referred to as adhesins) for human fluid phase glycoproteins such as fibronectin and immobilized basement membrane glycoproteins in order to establish and maintain a niche in the mucus-lined cavities of man. The hypothesis advanced is that the fate of the fungus may be determined by interactions with these same glycoproteins. For example, Candida may adhere to fibronectin on the surface of epithelial cells in order to maintain its residency in mucus-lined cavities, whereas when the fungus has escaped its normal niche and become bloodborne, yeast cells may be opsonized by fluid phase fibronectin and hence phagocytosed and killed more rapidly than uncoated fungi. On the other hand, bloodborne yeast cells may preferentially adhere to immobilized fibronectin exposed in the interstitial space or contained wit...
The FEBS journal, 2015
Candida glabrata has emerged as a major fungal pathogen over the last two decades, but our understanding of its survival strategies inside the mammalian host remains rudimentary. An important requirement for survival in vivo is the ability to acquire critical nutrients such as iron from host niches of varied iron content. Here, we demonstrate for the first time that C. glabrata cells respond to high external iron levels via activation of two stress-responsive mitogen-activated protein kinases (MAPKs), CgHog1 and CgSlt2, and lack of either kinase result in sensitivity to the high-iron medium. Further, we show that CgHOG1 deletion led to perturbed iron homeostasis (elevated intracellular iron content and high mitochondrial aconitase activity), reduced survival in macrophages and attenuated virulence in a murine model of disseminated candidiasis. Consistently, several genes implicated in iron acquisition and storage displayed deregulated expression in the Cghog1∆ mutant. Genome-wide tr...
PLoS Pathogens, 2013
Nutritional immunity -the withholding of nutrients by the host -has long been recognised as an important factor that shapes bacterial-host interactions. However, the dynamics of nutrient availability within local host niches during fungal infection are poorly defined. We have combined laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS), MALDI imaging and immunohistochemistry with microtranscriptomics to examine iron homeostasis in the host and pathogen in the murine model of systemic candidiasis. Dramatic changes in the renal iron landscape occur during disease progression. The infection perturbs global iron homeostasis in the host leading to iron accumulation in the renal medulla. Paradoxically, this is accompanied by nutritional immunity in the renal cortex as iron exclusion zones emerge locally around fungal lesions. These exclusion zones correlate with immune infiltrates and haem oxygenase 1-expressing host cells. This local nutritional immunity decreases iron availability, leading to a switch in iron acquisition mechanisms within mature fungal lesions, as revealed by laser capture microdissection and qRT-PCR analyses. Therefore, a complex interplay of systemic and local events influences iron homeostasis and pathogen-host dynamics during disease progression. Citation: Potrykus J, Stead D, MacCallum DM, Urgast DS, Raab A, et al. (2013) Fungal Iron Availability during Deep Seated Candidiasis Is Defined by a Complex Interplay Involving Systemic and Local Events. PLoS Pathog 9(10): e1003676.
Candida innate immunity at the mucosa
Seminars in cell & developmental biology, 2018
The tremendous diversity in microbial species that colonise the mucosal surfaces of the human body is only now beginning to be fully appreciated. Distinguishing between the behaviour of commensal microbes and harmful pathogens that reside at mucosal sites in the body is a complex, and exquisitely fine-tuned process central to mucosal health. The fungal pathobiont Candida albicans is frequently isolated from mucosal surfaces with an asymptomatic carriage rate of approximately 60% in the human population. While normally a benign member of the microbiota, overgrowth of C. albicans often results in localised mucosal infection causing morbidity in otherwise healthy individuals, and invasive infection that often causes death in the absence of effective immune defence. C. albicans triggers numerous innate immune responses at mucosal surfaces, and detection of C. albicans hyphae in particular, stimulates the production of antimicrobial peptides, danger-associated molecular patterns and cyto...