Maturation, Germination, and Pathogenesis of Cryptococcus Spores

PROJECT SUMMARY/ABSTRACT Worldwide, over a billion people each year experience high morbidity and/or mortality from the effects of human fungal pathogens. People with AIDS, chemotherapy patients, and transplant recipients are at highest risk of acquiring life-threatening infections, but many fungi also cause disease in apparently healthy individuals.

Among these is the spore-forming yeast, Cryptococcus, which is ubiquitous in the environment. Like many pathogenic fungi, Cryptococcus causes disease when it is inhaled into the lung. From the lung Cryptococcus can disseminate to the central nervous system (CNS) and cause fungal meningoencephalitis that is fatal ~25%

of the time, even with state-of-the-art treatments. In the United States the case mortality rate overall from invasive fungal diseases is ~50%, indicating the dire need for improved therapeutic strategies. To develop new antifungal therapeutics, we need to identify novel fungal-specific molecules or pathways. Thus, it is imperative

that we gain a better understanding of the fundamental biology of pathogenic fungi, especially the development and growth of spores. Our long-term research goal is to understand how infectious spores survive in new environments, including the mammalian lung, and use that information to identify fungal-specific targets for

therapeutic interventions. To accomplish this goal, we have developed the Cryptococcus system as a model for the study of infectious spores. The objective of this proposed project is to determine the molecular processes by which infectious spores transition into vegetatively growing yeast (germinate) and how this

process influences disease. Our overarching hypothesis is that determining the molecular mechanisms of germination will identify key pathways in spore-mediated infections that can be targeted for inhibition. To test this hypothesis, we will carry out three Specific Aims: 1) Determine the molecular pathways and processes

required for spore germination, 2) identify the molecular processes and events that promote germination competence of spores, and 3) determine the effects of spore germination kinetics on host-pathogen interactions and disease progression. We will combine molecular and classical genetics, gene expression

analyses, chemical genetics, protein composition analyses, and quantitative germination assays to reveal the developmental and regulatory mechanisms that facilitate spore survival in diverse environments. At the same time, we will use in vitro tissue culture models and a mouse intranasal model of infection to determine how

spores infect and escape the mammalian lung. These innovative experiments will result in an in-depth map of spore pathways and insights into how spores invade the host. Understanding pathways and processes associated with spore germination makes significant contributions to the long-term objective of this work to

identify new and diverse molecular targets that can be exploited for novel antifungal therapeutics and strategies to prevent and/or treat cryptococcosis and other fatal human fungal diseases.