Polyphosphate mobilization influences the ability ofCryptococcus neoformansto cause disease in a murine model of cryptococcosis

Abstract

Cryptococcus neoformans, an invasive basidiomycete fungal pathogen, causes one of the most prevalent, life-threatening diseases in immunocompromised individuals and accounts for ∼15% of AIDS-associated deaths. A dire need for the development of novel antifungal drugs, vaccines, and improved diagnostics has emerged with the increased frequency of fungal infections. Therefore, understanding the pathogenesis ofC. neoformansand its interactions with the host immune system is critical for the development of therapeutics against cryptococcosis. Previous research demonstrated thatC. neoformanscells lacking polyphosphate (polyP), an immunomodulatory polyanionic storage molecule, display altered cell surface architecture. However, the relevance of surface changes and the role of polyP in the virulence ofC. neoformansremain unclear. Here we show that mutants lacking the polyphosphatases (Xpp1 and Epp1) are attenuated for virulence in a murine inhalational model of cryptococcosis, demonstrate reduced proliferation in host tissue, and provoke an altered immune response. An analysis of mutants lacking the polyphosphatases and the Vtc4 protein for polyP synthesis indicated that the Xpp1 and Epp1 contribute to the organization of the cell surface, virulence factor production, the response to stress, and mitochondrial function. Overall, we conclude that polyP mobilization plays a multifaceted role in the pathogenesis ofC. neoformans.Author SummaryCryptococcus neoformanscauses one of the most prevalent fungal diseases in people with compromised immune systems and accounts for 15-20% of AIDS-associated deaths worldwide. The continual increase in the incidence of fungal infections and limited treatment options necessitate the development of new antifungal drugs and improved diagnostics. Polyphosphate (polyP), an under-explored biopolymer, functions as a storage molecule, modulates the host immune response, and contributes to the ability of many fungal and bacterial pathogens to cause disease. However, the role of polyP in cryptococcal disease remains unclear. In this study, we report that the enzymes that regulate polyP synthesis and turnover contribute to the virulence ofC. neoformansin a mouse model of cryptococcosis. The polyphosphatases, Xpp1 and Epp1, influenced the survival ofC. neoformansin macrophages and altered the host immune response. The loss of Xpp1 and Epp1 led to changes in cell surface architecture, cell size, impaired growth, and defects in both mitochondrial function and the stress response ofC. neoformans.Thus, our work establishes polyP as a key factor in the disease caused byC. neoformans, and identifies polyP mobilization as a novel target to support new therapeutic approaches.