Department of Microbiology and Parasitology, IRYCIS
Facultad de Farmacia. Universidad Complutense de Madrid (Madrid)
Daniel Prieto, Susana Hidalgo, Elvira Román, Rebeca Alonso and Jesús Pla
Our group has been working for many years on (and with) an opportunistic pathogenic yeast of humans, Candida albicans. It is a fungus that is part of our intestinal (and vaginal) microbiota without apparently causing us harm in healthy individuals. When immunological alterations occur in the host, broad-spectrum antibiotics are used, diabetes is suffered or there are certain genetic alterations, the appearance of so-called candidiasis is favored, which are usually superficial, mucocutaneous or, in the most serious cases, systemic. In women, they cause vulvovaginitis, which can be recurrent and are a serious problem. Although infections caused by this fungus are not as common as other viral or bacterial infections, they are very serious and almost always require antifungal therapy. This therapy is scarce in number, antifungals may have pharmacokinetic, spectrum or economic limitations and this may be aggravated in the coming years with the appearance of resistance to some used in the clinic. C. albicans it is the fungus most frequently isolated in systemic nosocomial infections.
Although the reasons for our interest in this fungus are largely fortuitous, in our group we have always tried to use this fascinating microorganism to ask ourselves (and try to answer) increasingly complex questions. In that sense, we can be happy with the organism with which we have been working for decades, since this yeast does not stop supplying us with them. The question of raising answers also excites us, of course, although this entails dealing with a multitude of variable parameters (and not only of a biological nature).
Experimenting with this fungus means living with its apparent contradictions. It is a microbe that grows well in the laboratory, but it alternates different morphologies in the course of the infection and each one contributes in a different way to the infectious process, although it is not known in full detail. It is a diploid organism without a complete sexual cycle, which makes it difficult to produce mutants in the laboratory, and much effort has been devoted by our group and others to implement improvements in its genetic manipulation strategies. Although this fungus at some point in its evolution lost the ability to carry out meiosis, it presents very interesting and complex alternative mechanisms for generating genetic variability.
The axis of our group's work for years has been the study of signaling pathways mediated by MAP-type kinases (MAPKs) in this fungus. These types of pathways mediate responses to certain stimuli such as various types of stress, alterations in the fungal cell wall, quorum sensing molecules, etc. After activation by sequential phosphorylation of different elements of the pathways (sometimes interconnected), MAPK can be translocated to the nucleus, triggering transcriptional activation/repression in specific genes that allows the cell to specifically compensate or adapt to the changes that gave rise to it. to the initial stimulus. However, overactivation often implies toxicity, so signaling is tightly regulated. Its relative evolutionary closeness to Saccharomyces cerevisiae has allowed us to identify and study most of the components of these routes. We have revealed the role of some of these kinases in the response to oxidative damage, in the construction of the cell wall, in the morphological changes that occur during infection and in the interaction with the immune system. It is not surprising, therefore, that these routes are important factors of pathogenicity (if this concept makes any sense in an opportunistic pathogen) and are therapeutic targets on which to base the design of new antifungals.
Part of our initial effort consisted in the development of genetic manipulation systems (isolation of replicons, deletion schemes, expression systems) that would allow us to work with this fungus. More recently, we have used the CRISPR methodology as a gene expression regulation system in this yeast. Although the genetic manipulation of C. albicans It has been a constant and necessary occupation in our group, we have always been oriented towards the study of interaction with the host. This has meant using cell models, mainly of innate immunity (barriers, macrophages, neutrophils) and with animal models (mouse) whose fine-tuning and analysis have occupied much of our scientific capacity in recent years. We have delved not only into the infectious process (cellular models and systemic virulence in mice), but we have also implemented commensalism models, such as gastrointestinal colonization. This last approach seems especially relevant to us for several reasons: for many years it has been little studied, it is a stage of interaction with higher prevalence and longer in time, it allows us to analyze the role of the microbiota and uses minimally invasive animal models without generating suffering. Thanks to this, we are beginning to know which genes are responsible for intestinal colonization, what role certain factors (oxygen, bile salts, adhesion) play in colonization. As two do not argue if one does not want to, we have also addressed the study of host factors that intervene in the pathogenicity of this fungus, of the host and we have contributed to knowing the role of some immune populations (intestinal CX3CR1+) and receptors (TLR2/ MyD88 , Gal3, Dectin 1) in the control of fungal infection.
The questions that we currently ask ourselves in the group are very diverse and complex despite their apparent simplicity. Does adhesion influence the ability of this yeast to colonize the gastrointestinal tract? And the ability to filament? In what processes are MAPKs involved during the course of infection? Is mating in vivo (i.e., during infection or during colonization) possible? If so, under what conditions and what advantages would it have? for yeast? Can we develop strains with greater or lesser colonization capacity? Could we use those strains of C. albicans as a carrier of antigens for the prevention of human diseases? And finally, why are we colonized by this yeast? If in the course of co-evolution between human and C. albicans for thousands of years we continue to be colonized, what advantages does it bring us?
Our line consists of 5 permanent professors (D.P, E.R., R.A. and J.P), 2 predoctoral researchers (S.H. and Isabel Cortés) and 1 technician (Ioana Comán), in addition to 3-4 master's or final degree students that we welcome punctually every course.
CONTRIBUTIONS AND SELECTED PUBLICATIONS
- Román E, Coman I, Prieto D, Alonso-Monge R, Pla J. Implementation of a CRISPR-Based System for Gene Regulation in Candida albicans. mSphere. 2019;4(1).
- Leonardi I, Li X, Semon A, Li D, Doron I, Putzel G, et al. CX3CR1(+) mononuclear phagocytes control immunity to intestinal fungi. Science. 2018;359(6372):232-6.
- Prieto D, Román E, Alonso-Monge R, Pla J. Overexpression of the Transcriptional Regulator WOR1 Increases Susceptibility to Bile Salts and Adhesion to the Mouse Gut Mucosa in Candida albicans. Front Cell Infect Microbiol. 2017;7:389.
- Román E, Correia I, Salazin A, Fradin C, Jouault T, Poulain D, et al. The Cek1-mediated MAP kinase pathway regulates exposure of a-(1,2) and b-(1,2)-mannosides in the cell wall of Candida albicans modulating immune recognition. Virulence. 2016;7(5):558-77.
- Correia I, Alonso-Monge R, Pla J. The Hog1 MAP Kinase Promotes the Recovery from Cell Cycle Arrest Induced by Hydrogen Peroxide in Candida albicans. Front Microbiol. 2016;7:2133.