Transcriptome profiling of Paracoccidioides brasiliensis yeast-phase cells recovered from infected mice brings new insights into fungal response upon host interaction

Preferential transcription of Paracoccidioides brasiliensis genes: host niche and time-dependent expression

Paracoccidioides brasiliensis causes infection through inhalation by the host of airborne propagules from the mycelium phase of the fungus. This fungus reaches the lungs, differentiates into the yeast form and is then disseminated to virtually all parts of the body. Here we review the identification of differentially-expressed genes in host-interaction conditions. These genes were identified by analyzing expressed sequence tags (ESTs) from P. brasiliensis cDNA libraries. The P. brasiliensis was recovered from infected mouse liver as well as from fungal yeast cells incubated in human blood and plasma, mimicking fungal dissemination to organs and tissues and sites of infection with inflammation, respectively. In addition, ESTs from a cDNA library of P. brasiliensis mycelium undergoing the transition to yeast were previously analyzed. Together, these studies reveal significant changes in the expression of a number of genes of potential importance in the host-fungus interaction. In addition, the unique and divergent representation of transcripts when the cDNA libraries are compared suggests differential gene expression in response to specific niches in the host. This analysis of gene expression patterns provides details about host-pathogen interactions and peculiarities of sites within the host.

Identification and characterization of antigenic proteins potentially expressed during the infectious process of Paracoccidioides brasiliensis

Paracoccidioides brasiliensis causes paracoccidioidomycosis (PCM), a systemic mycosis presenting clinical manifestations ranging from mild to severe forms. A P. brasiliensis cDNA expression library was produced and screened with pooled sera from PCM patients adsorbed against antigens derived from in vitro-grown P. brasiliensis yeast cells. Sequencing DNA inserts from clones reactive with PCM patients sera indicated 35 open reading frames presenting homology to genes involved in metabolic pathways, transport, among other predicted functions. The complete cDNAs encoding aromatic-l-amino-acid decarboxylase (Pbddc), lumazine synthase (Pbls) and a homologue of the high affinity copper transporter (Pbctr3) were obtained. Recombinant proteins PbDDC and PbLS were obtained; a peptide was synthesized for PbCTR3. The proteins and the synthetic peptide were recognized by sera of patients with confirmed PCM and not by sera of healthy patients. Using the in vivo-induced antigen technology (IVIAT), we identified immunogenic proteins expressed at high levels during infection. Quantitative real time RT-PCR demonstrated high transcript levels of Pbddc, Pbls and Pbctr3 in yeast cells infecting macrophages. Transcripts in yeast cells derived from spleen and liver of infected mice were also measured by qRT-PCR. Our results suggest a putative role for the immunogenic proteins in the infectious process of P. brasiliensis.

The catalases of Paracoccidioides brasiliensis are differentially regulated: protein activity and transcript analysis

Paracoccidioides brasiliensis is a fungal pathogen of humans. The P. brasiliensis response to oxidative stress is largely unexplored. We report the analysis of three catalases, PbCatA, PbCatP and PbCatC. The former are monofunctional catalases and the latter is a catalase-peroxidase. Differential expression of catalases as measured by activity and by quantitative analysis of transcripts was observed in the morphological conversion and in response to different stress conditions. PbCatA manifested higher activity in the mycelial phase, showed increased activity during transition from mycelium to yeast and during conditions of endogenous oxidative stress. Consistent with our previous studies, PbCatP manifested higher activity in yeast cells since it is putatively involved in the control of exogenous reactive oxygen species. P. brasiliensis displays an oxidative stress response following phagocytosis by macrophages, inducing the expression of catalase A and P transcripts. PbCatC displayed a relatively constant pattern of expression, being modestly induced in cells exposed to osmotic and heat stress.

Characterization of Paracoccidioides brasiliensis COX9, COX12, and COX16 respiratory genes

Paracoccidioides brasiliensis is a thermo-dimorphic fungus that is the causative agent of paracoccidioidomyicosis (PCM), a human systemic granulomatous mycosis found in Latin America. Dimorphic transition from mycelium to yeast is required for establishing pathogenicity. Dimorphism is marked by changes in mitochondrial physiology, including modulation of respiration rate. In this work, we present the identification of three P. brasiliensis nuclear genes PbCOX9, PbCOX12, and PbCOX16 that code for structural subunits and a putative assembly facilitator (PbCOX16) of the mitochondrial cytochrome c oxidase (COX), the terminal enzyme complex of the respiratory chain. We measured their expression pattern during the dimorphic transition from mycelium to yeast and back by real-time reverse transcription quantitative polymerase chain reaction (real-time RT-qPCR). Our results show that messages from these genes increase during the mycelium to yeast transition and decrease during the opposite conversion. This result supports active mitochondrial participation in the transition. Heterologous complementation of the corresponding Saccharomyces cerevisiae null mutant with the PbCOX9 gene was successfully obtained.

Fungal killing by mammalian phagocytic cells

Phagocytes are considered the most important effector cells in the immune response against fungal infections. To exert their role, they must recognize the invading fungi, internalise, and kill them within the phagosome. Major advances in the field have elucidated the roles of pattern-recognition receptors in the innate immunity sensing and the importance of reactive oxygen and nitrogen species in intracellular killing of fungi. Surprising exit mechanisms for intracellular pathogens and extracellular traps have also been discovered. These and several other recent breakthroughs in our understanding of the mechanisms used by phagocytes to kill fungal pathogens are reviewed in this work.