Dominique Sanglard Lab

Dominique Sanglard, PhD,  Associate Professor
++41 (0)21 314 4083
++41 (0)79 556 2691
dominique.sanglard@chuv.ch

Research topics (D. Sanglard)

Molecular mechanisms of antifungal drug resistance in yeast pathogens
Infections caused by fungal pathogens are common in patients with defects in their immune system. For example, patients with acquired immuno-deficiency syndrome (AIDS) can suffer from oropharyngeal candidiasis (OPC) and others undergoing organ transplantation or anti-cancer drug treatments can be affected by fungal invasive diseases. The major yeast species involved in these diseases belong to Candida albicans but also to other Candida species such as C. glabrata or C. tropicalis. Azole antifungals, especially fluconazole, have been used widely to treat theses fungal diseases. However, an increasing number of cases of clinical resistance against this antifungal correlating with in vitro resistance has been reported. The goal of our research is to investigate the mechanisms of resistance to azole antifungal agents at the molecular level in clinical yeast isolates acquiring azole resistance. Mutations in the target of azoles (ERG11) and upregulation of multidrug transporters genes were found as major madiators of azole resistance.

Regulation of multidrug transporters in Candida species
We found that ABC (ATP binding Cassette) transporters CDR1/CDR2 and the Major Facilitator MDR1 were mediators of azole resistance in C. albicans. The genes encoding these proteins are upregulated in azole-resistant strains. Regulatory cis-acting regions in the promoter of these genes have been identified. A trans-acting regulatory factor, TAC1, has been isolated as regulator of the C. albicans ABC transporter genes CDR1 and CDR2. Mutations in TAC1 confer hyperactivity to Tac1p and therefore upregulation of CDR1/CDR2 and azole resistance. In C. glabrata, PDR1 is a transcription factor controlling the expression of the ABC transporters CgCDR1, CgCDR2, and CgSNQ2 that are upregulated in azole-resistant isolates. PDR1 mutations have been identified and are responsible for hyperactivity of this transcription factor.  The mutations identified in the genes encoding these transcription factors will help to design tools for the diagnosis of antifungal resistance among yeast pathogens.

Molecular mechanisms of antifungal drug tolerance in Candida albicans
Current antifungals for the treatment of C. albicans infections in humans are mainly belonging to the class of azole antifungals and, among those, fluconazole is extensively used. C. albicans is tolerant to fluconazole (fluconazole has only fungistatic activity in C. albicans) and resistance to this agent (the decrease of drug susceptibility) can occur in clinical isolates by different mechanisms. We found that the combination of the immuno-suppressive drug cyclosporin A with fluconazole was rendering fluconazole fungicidal therefore making C. abicans not tolerant to fluconazole.. We are interested to investigate the molecular basis of this interaction. Cyclosporin A binds to cyclophilin A and this complex inhibits the activity of calcineurin, a protein phosphatase activated by a calcium signaling pathway. We found that calcineurin was essential for fluconazole tolerance in C. albicans. The exact mechanisms by which fluconazole is becoming fungicidal in the calcineurin mutant remain to be established. To answer this question, identification of calcineurin targets in C,albicans  has been initiated in our laboratory. We found a transcription factor, CRZ1, as major target of calcineurin in C. albicans, This gene being not essential for azole tolerance, other calcineurin targets are being identified.

Impact of antifungal drug resistance on virulence and fitness of fungal pathogens
Antifungal drug resistance develops by several mechanisms, however one of the common mechanism is based on altered transcriptional activities. Both in Candida albicans and Candida glabrata, mutations in transcriptional activators including TAC1, MRR1, UPC2 (C. albicans) and CgPDR1 (C. glabrata) are responsible for enhanced expression of target genes crucial for resistance, including multidrug transporters and targets of antifungal agents.
It has been recognized in several pathogens that antimicrobial resistance is associated with decreased virulence or altered fitness during infections. This dogma was addressed with azole-resistant isolates from C. glabrata in animal models of infection and surprisingly, these isolates showed enhanced virulence and fitness as compared to wild type parent isolates. Our current investigations interrogate the molecular basis of this unexpected phenotype in the perspective of host-pathogen interactions. Our experimental approaches include genome-wide transcriptional methods, in vivo assays and mammalian culture based assays.
Moreover, the effect of drug resistance development on C. albicans fitness and virulence is also addressed with fungal cells engineered to contain specific mutations in the transcriptional activators TAC1, MRR1 and UPC2.

Research topics (A. Coste)

Alix Coste, PhD, Research associate
++41 (0)21-314 4061
alix.coste@chuv.ch

Virulence factors in pathogenic fungi

Candida albicans is an opportunistic pathogen causing oral, vaginal or systemic infections in immuno-compromized patients. Such patients, like HIV+, transplanted patients and those receiving chemotherapy, are in constant augmentation. In up to 30% of the patients with C. albicans systemic infections, the issue is fatal. Control of C. albicans infections is essentially achieved using treatments inhibiting microbial growth, such as treatment with azoles. For HIV+ and transplanted patients, long-time prophylactic and therapeutic antifungal treatment are needed. C. albicans exposed for a long time to these antifungals adapts to this stress, and develops resistance leading to treatment failure. Therefore, alternative treatment strategies are needed.
Host-pathogen interaction is a key component of any infectious process. Treatment modifying this relationship can be designed. Transcription factors (TF) are potentially important for C. albicans virulence since they integrate several signals from host environment and participate in an adapted microbial response.
In this project, we develop an original approach to analyze a collection of C. albicans transcription factor mutant strains in vivo. A collection of TF mutant strains are screened in a mice model of systemic infection in order to identify those factors crucial for virulence. Additional analysis is performed on the selected TF to understand at which steps of the infection they are involved and which element of the host defense they target.
Genes under the control of those TF will then be identified in order to determine which metabolic pathways of the fungus are involved in the infection.
This analysis is important for C. albicans infection but will constitute a model for other pathogenic fungi. A mid-term outcome of this project will be a better understanding of the global host-fungus interactions, which may lead to the development of new drugs and treatment strategies.

Currently funded research topics

1. Regulatory genes of antifungal resistance and their impact on fitness and virulence of pathogenic Candida species.
FNRS 31003A_127378 (2010-2013).
Involved personnel: Luis Vale Silva, Post-doc; Andrea Lohberger, PhD student

2. Strategies to combat MultiDrug Resistance (MDR) in human pathogenic Candida species.
Indo Swiss Research Program grant No. 122 917 (2009-2012).
Involved personnel: Patrick Vandepute, Post-doc; Nitesh Khandelwal, PhD student

3. Investigations of molecular resistance mechanisms from a Tunisian yeast collection.
Bourse de la confédération, Secrétariat d'Etat à l'éducation et à la recherche (SER) (2010-2012).
Involved personnel: J. Eddouzi, PhD student

4. Genome wide analysis of the role of transcription factors in the virulence of Candida albicans
Bourse Pro-femme, UNIL and intra-muros funding (2008-2012)
Involved personnel: A. Coste, Research associate

Full publication list (2012-01-09 147 Ko)

Selected publications