Characterization of the Paracoccidioides Hypoxia Response Reveals New Insights into Pathogenesis Mechanisms of This Important Human Pathogenic Fungus

Abstract

Background

Hypoxic microenvironments are generated during fungal infection. It has been described that to survive in the human host, fungi must also tolerate and overcome in vivo microenvironmental stress conditions including low oxygen tension; however nothing is known how Paracoccidioides species respond to hypoxia. The genus Paracoccidioides comprises human thermal dimorphic fungi and are causative agents of paracoccidioidomycosis (PCM), an important mycosis in Latin America.

Methodology/Principal Findings

In this work, a detailed hypoxia characterization was performed in Paracoccidioides. Using NanoUPLC-MS ^E proteomic approach, we obtained a total of 288 proteins differentially regulated in 12 and 24 h of hypoxia, providing a global view of metabolic changes during this stress. In addition, a functional characterization of the homologue to the most important molecule involved in hypoxia responses in other fungi, the SREBP (sterol regulatory element binding protein) was performed. We observed that Paracoccidioides species have a functional homologue of SREBP, named here as SrbA, detected by using a heterologous genetic approach in the srbA null mutant in Aspergillus fumigatus. Paracoccidioides srbA ( PbsrbA), in addition to involvement in hypoxia, is probable involved in iron adaptation and azole drug resistance responses.

Conclusions/Significance

In this study, the hypoxia was characterized in Paracoccidioides. The first results can be important for a better understanding of the fungal adaptation to the host and improve the arsenal of molecules for the development of alternative treatment options in future, since molecules related to fungal adaptation to low oxygen levels are important to virulence and pathogenesis in human pathogenic fungi.

Author Summary

The genus Paracoccidioides is composed of species that are causative agents of paracoccidioidomycosis (PCM), a neglected human granulomatous mycosis, endemic in Latin America. To survive in the human host, fungi must tolerate and overcome in vivo micro environmental stress conditions, including low oxygen levels. Paracoccidioides spp. depicts differential responses to several stresses such as iron/zinc deprivation, oxidative and nitrosative stresses and carbon starvation. In addition, Paracoccidioides yeast cells recovered from liver of infected mice demonstrated adaptability to the host conditions. Mechanisms by which fungi sense oxygen levels have been characterized, although this is the first description in Paracoccidioides spp. Little is known about hypoxia in thermally dimorphic fungi and nothing has been studied in Paracoccidioides genus, one of the representatives of this group of pathogens. A detailed characterization of the hypoxia responses was performed using proteomic and heterologous genetics approaches. Paracoccidioides genus have a functional homologue of the key regulator of hypoxia adaptation in fungi, SrbA, a SREBP (sterol regulatory element binding protein) orthologue. The proteome during hypoxia provided a global view of metabolic changes during this stress and species of the Paracoccidioides genus have a functional SrbA. Our study provides a better understanding of the fungal adaptation to the host and it can improve the arsenal of molecules for the development of alternative treatment options to paracoccidioidomycosis, since molecules related to fungal adaptation to low oxygen levels are important to virulence and pathogenesis in human pathogenic fungi.