Lack of an atypical PDR transporter generates an immunogenicCryptococcus neoformansstrain that drives a dysregulated and lethal immune response in murine lungs

Abstract

Cryptococcus neoformansis an opportunistic fungal pathogen responsible for >150,000 deaths every year with a mortality rate as high as 81%. This high medical burden is due, in part, to an incomplete understanding of its pathogenesis. In a previous study, we identified a cryptococcal atypical pleiotropic drug resistance (PDR) transporter,PDR6, that regulated antifungal resistance and host interactions. Here, we follow-up on the role ofPDR6in cryptococcal virulence.In vivo, mice infected with thepdr6Δ strain display altered symptomatology and disease progression. Specifically, we observed a significant increase in the innate immune cell populations in thepdr6Δ-infected mice when compared to their WT-infected littermates. Furthermore, quantification of pulmonary cytokines/chemokines revealed a robust increase of pro-inflammatory cytokines in mice infected with thepdr6Δ mutant strain. Whereas antifungal treatment ofpdr6Δ-infected animals did not affect survival, treatment with a corticosteroid significantly extended survival, highlighting the importance of a balanced/controlled host immune response. We determined that the hyper-inflammatory immune response occurs, in part, because the loss of the Pdr6 transporter indirectly alters the cryptococcal cell wall architecture and results in the increased exposure of chitin, β-glucan, and other cryptococcal-specific pathogen associated molecular patterns. Taken together, this study provides clinical insights regarding cryptococcal pathogenesis while also providing additional functions of PDR-type ATP-binding cassette (ABC) transporters in pathogenic fungi.IMPORTANCEYeasts of theCryptococcusgenus, especiallyC. neoformans, can cause disease with unacceptably high mortality. This is due to delays in diagnostics, ineffective treatments, and an incomplete understanding of the interactions between this fungus and our immune system. In this study, we expand our knowledge of the biological function of thePDR6gene, particularly its effect on modulating the host’s immune response. Normally,C. neoformans’s infections are characterized by an anti-inflammatory response that is unable to control the yeast. In the absence ofPDR6, the response to the infection is a dysregulated pro-inflammatory response that initially controls the fungi but eventually results in death of the host due to too much tissue damage. This is due, in part, to an altered fungal surface. Given the dual role ofPDR6in modulating antifungal sensitivity and immune responses, this work provides important insights that may lead to new or improved therapeutics.