Project

Candida, antifungal resistance, virulence

Lead
Les infections fongiques causées les espèces de Candida (C. albicans, C. glabrata) restent une menace pour la santé humaine, même avec l'utilisation d'antifongiques. Suite aux traitements antifongiques, la résistance se développe et compromet le succès de la thérapie. La résistance antifongique est médiée par de multiples mécanismes. Ils permettent aux champignons de survivre sous la pression de la drogue chez l'hôte, mais ont aussi des coûts pour le pathogène en compromettant sa virulence.
Lay summary
Chez C. glabrata, le mécanisme de résistance principal est la surexpression du gène CDR1 (un transporteur multidrogue). CDR1 est impliqué dans la résistance aux antifongiques azolés, qui sont encore largement utilisés en médecine. La surexpression de CDR1 est due à des mutations du facteur de transcription PDR1, un régulateur majeur de CDR1. Une idée répandue est que la résistance est couplée avec des coûts importants pour les microbes en terme de virulence. Cependant les mutations PDR1 confèrent un potentiel de virulence plus élevée chez C. glabrata dans des modèles animaux. Nos travaux ont révélé que PDR1 pourrait diminuer l’adhésion de C. glabrata aux macrophages de l'hôte. Cette adhésion altérée constitue un mécanisme d'évitement des défenses immunitaires et expliquent du moins en partie la virulence accrue due à la résistance. Dans cette étude, nous allons examiner si cet effet d’adhérence modifiée est conservée parmi les différents types de cellules de l'hôte, y compris les cellules épithéliales et endothéliales. Ensuite, nous allons identifier des gènes spécifiques  qui participent à ce phénomène. Pour ce faire, plusieurs approches seront utilisées (méthodes protéomiques, transcriptomiques et génomiques). En conclusion, nos résultats pourront mettre en évidence le rôle de gènes spécifiques à Candida qui associent résistance antifongique avec des interactions à des cellules hôtes et qui contribuent à la pathogenèse de ces champignons.

Direct link to Lay Summary

Last update: 12.09.2013

Lead
Infections in humans caused by fungal pathogens belonging to Candida species (such as C. albicans and C. glabrata) remain a threat to human health, even with the use of available antifungal agents. As a consequence of antifungal treatments, resistance can develop and compromise the success of therapy. Antifungal resistance is mediated by multiple mechanisms and, while they enable fungi survival under drug pressure in the host, they also have costs for the pathogen compromising its virulence.
Lay summary
In C. glabrata, one major resistance mechanism is the overexpression of the multidrug transporter CDR1. CDR1 is involved in resistance to azole antifungals, which are widely used in medicine. CDR1 overexpression is due to mutations in the transcription factor PDR1, a major regulator of CDR1.  In opposite to the belief that resistance is coupled with significant costs in microbes, PDR1 mutations confer higher virulence potential to C. glabrata in animal models. Our work revealed that PDR1 could decrease C. glabrata adherence to host macrophages. This altered adherence constitutes an escape mechanism to host defenses explaining increased virulence. In this proposal, we will address whether altered adherence is conserved among different host cell types including epithelial and endothelial cells. Next, we will identity specific genes participating to the decreased adherence of C. glabrata to these cell types. For this purpose, several approaches will be used (proteomic, transcriptomic and genomic methods).  In conclusion, our results are expected to highlight the role of specific Candida genes, which intriguingly associate antifungal resistance with interactions to host cells and which contribute to pathogenesis of these fungi.

Direct link to Lay Summary

Last update: 12.09.2013

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

Infections caused by fungal pathogens belonging to Candida spp. (C. albicans and C. glabrata) are still a challenge to the medical practice. Despite available antifungal fungal diseases remains a threat to human health and especially in the population of immuno-compromised patients. As a consequence of antifungal treatment in patients and exposure of the pathogens to antifungals, resistance can develop and compromise the success of the therapy. Antifungal resistance is mediated by multiple mechanisms and, while they enable fungal survival under drug pressure in the host, can lead to fitness costs. In C. glabrata, mutations in the transcription factor CgPDR1 (so called GOF mutations for gain-of-function) are participating to the upregulation of the ABC transporter CDR1 which is involved in azole resistance. The occurrence of the same mutations results in enhanced virulence and fitness in animal models. In C. albicans, mutations in factors involved in drug resistance have on the opposite neutral of even negative impact on virulence, however compensation mechanisms can operate to correct negative effects. We have shown in C. glabrata that two CgPDR1-regulated genes including CDR1 and a mitochondrial gene (PUP1) could be made partially responsible for this virulence attribute. Our recent work has revealed that CgPDR1 could also mediate a decreased adherence of C. glabrata to specific cells of the immune system (mice bone marrow derived macrophages, BMDMs) but without altering C. glabrata survival within BMDMs after phagocytosis. Altered adherence step could constitute an escape mechanism by which increased virulence in mice can be further established. Interestingly, the CgPDR1-dependent decreased adherence is not observed in all C. glabrata clinical isolates, thus highlighting that specific CgPDR1 target genes, most likely encoding cell wall proteins, are absent (or mutated) in specific C. glabrata genomes. In the first part of this research proposal, we will address whether the adherence phenotype is conserved among different host cell types including cells of the innate immune system, epithelial and endothelial cells. Next, we will address the identity of specific genes that are participating to the decreased adherence of C. glabrata to specific cell types. For this purpose, several approaches will be used, including proteomic, transcriptomic and genomic methods. We will then establish a panel of C. glabrata isolates taken from our clinical collection with a CgPDR1-dependent adherence phenotype. Two groups will be created: one with low and the other with high adherence to host cells. These isolates will be then systematically investigated in order to identify the genetic basis for the differences between the two yeast groups. Transcriptional and genomic data will be matched in these analyses, however the group of cell wall genes will be more specifically targeted. Candidate genes would be then systematically investigated and a tetracycline-regulatable system will be used to assess their role in host cell adherence. In a second part of this research proposal, we will address by transcriptomic and genomic approaches how C. albicans can compensate for the decreased virulence caused by mutation in mediators of antifungal resistance. We will here use a clinical isolate with a known mutation in a gene involved in sterol biosynthesis (ERG3) but exhibiting no fitness costs as opposed to laboratory isolates with the same mutation.In conclusion, our results are expected to highlight the role of specific Candida genes, which intriguingly associate antifungal resistance with interactions to host cells and which contribute to pathogenesis of these fungi which are still the cause of a majority of fungal diseases in human.