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Metabolic competition between host and pathogen dictates inflammasome responses to fungal infection.

ABSTRACT: The NLRP3 inflammasome has emerged as a central immune regulator that senses virulence factors expressed by microbial pathogens for triggering inflammation. Inflammation can be harmful and therefore this response must be tightly controlled. The mechanisms by which immune cells, such as macrophages, discriminate benign from pathogenic microbes to control the NLRP3 inflammasome remain poorly defined. Here we used live cell imaging coupled with a compendium of diverse clinical isolates to define how macrophages respond and activate NLRP3 when faced with the human yeast commensal and pathogen Candida albicans. We show that metabolic competition by C. albicans, rather than virulence traits such as hyphal formation, activates NLRP3 in macrophages. Inflammasome activation is triggered by glucose starvation in macrophages, which occurs when fungal load increases sufficiently to outcompete macrophages for glucose. Consistently, reducing Candida's ability to compete for glucose and increasing glucose availability for macrophages tames inflammatory responses. We define the mechanistic requirements for glucose starvation-dependent inflammasome activation by Candida and show that it leads to inflammatory cytokine production, but it does not trigger pyroptotic macrophage death. Pyroptosis occurs only with some Candida isolates and only under specific experimental conditions, whereas inflammasome activation by glucose starvation is broadly relevant. In conclusion, macrophages use their metabolic status, specifically glucose metabolism, to sense fungal metabolic activity and activate NLRP3 when microbial load increases. Therefore, a major consequence of Candida-induced glucose starvation in macrophages is activation of inflammatory responses, with implications for understanding how metabolism modulates inflammation in fungal infections.

SUBMITTER: Tucey TM

PROVIDER: S-EPMC7433900 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The success of plant pathogenic fungi mostly relies on their arsenal of virulence factors that are expressed and delivered into the host tissue during colonization. The biotrophic fungal pathogen Ustilago hordei causes covered smut disease on both barley and oat. The biotrophic interaction of the fungus with its host plant starts with formation of appressorium and subsequent penetration of invasive hyphae into the plant cell, in which the plasma membrane of the infected cell gets invaginated and encases the penetrating hypha. After penetration, the fungus grows towards and in later stages along the vascular bundles, which contain assimilates and metabolites, representing a source of nutrients for the fungus. In this study, we combined cytological, genomics and molecular biological methods to achieve a better understanding of the molecular interactions in the U. hordei-barley pathosystem. This study focuses on the genome-wide Agilent Microarray-based transcriptome analysis of U. hordei during early stages (20 hpi, 40 hpi, 3 dpi, 6 dpi) of the biotrophic interaction in comparison to axenic culture growth. This should give insights into the molecular processes during these stages by the identification of regulated genes. Furthermore, the regulation of putative secreted enzymes and effector proteins can be studied. Transcriptome analysis of U. hordei at different stages of host infection revealed 273 effector gene candidates with differentially expressed transcript levels. Furthermore, U. hordei transcriptionally activates core-effector genes that may suppress even non-host early defense responses. It could be shown that about one half of the U. hordei open reading frames are differentially regulated during at least one of the analyzed stages. Based on the transcriptome data, some of them were identified to be involved in stage-specific processes, e.g. in the nutrient acquisition by the induction of carbohydrate transporters during the later stages of infection. Furthermore, a set of strongly induced genes was identified, which encode for secreted proteins. The acquired datasets show a strong induction of stage-specific secreted effector proteins, whose functions remain unclear. Based on the expression values, a group of 16 promising candidates was chosen for functional characterization. The success of plant pathogenic fungi mostly relies on their arsenal of virulence factors that are expressed and delivered into the host tissue during colonization. The biotrophic fungal pathogen Ustilago hordei causes covered smut disease on both barley and oat. The biotrophic interaction of the fungus with its host plant starts with formation of appressorium and subsequent penetration of invasive hyphae into the plant cell, in which the plasma membrane of the infected cell gets invaginated and encases the penetrating hypha. After penetration, the fungus grows towards and in later stages along the vascular bundles, which contain assimilates and metabolites, representing a source of nutrients for the fungus. In this study, we combined cytological, genomics and molecular biological methods to achieve a better understanding of the molecular interactions in the U. hordei-barley pathosystem. This study focuses on the genome-wide Agilent Microarray-based transcriptome analysis of U. hordei during early stages (20 hpi, 40 hpi, 3 dpi, 6 dpi) of the biotrophic interaction in comparison to axenic culture growth. This should give insights into the molecular processes during these stages by the identification of regulated genes. Furthermore, the regulation of putative secreted enzymes and effector proteins can be studied. Transcriptome analysis of U. hordei at different stages of host infection revealed 273 effector gene candidates with differentially expressed transcript levels. Furthermore, U. hordei transcriptionally activates core-effector genes that may suppress even non-host early defense responses. It could be shown that about one half of the U. hordei open reading frames are differentially regulated during at least one of the analyzed stages. Based on the transcriptome data, some of them were identified to be involved in stage-specific processes, e.g. in the nutrient acquisition by the induction of carbohydrate transporters during the later stages of infection. Furthermore, a set of strongly induced genes was identified, which encode for secreted proteins.The acquired datasets show a strong induction of stage-specific secreted effector proteins, whose functions remain unclear. Based on the expression values, a group of 16 promising candidates was chosen for functional characterization.

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Metabolic competition between host and pathogen dictates inflammasome responses to fungal infection.

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