The Cryptococcus spore surface and its role in host invasion

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Abstract Invasive fungal pathogens cause 1.5 million deaths a year and Cryptococcus neoformans is the primary cause of fungal meningitis worldwide. Cryptococcus is a ubiquitous fungus that is inhaled from the environment and, through mechanisms that we still don’t understand, disseminates out of the lung and subsequently enters the brain. The Cryptococcus yeast morphotype has been widely studied, and the study of its anti-phagocytic capsule has been critical to combating this pathogen; however, the yeast cell type is not the only morphotype to consider in cryptococcal disease. Cryptococcus produces dormant and stress resistant basidiospores (sexual spores) that are smaller and better aerosolized than yeast and thus more likely to reach the lower airways. Importantly these spores have a distinct surface to yeast, lacking the anti-phagocytic capsule. Spores are the presumed infectious morphotype, yet due to difficulties associated in working with spores, the Cryptococcus spore surface remains undefined and relatively few studies exist evaluating spore-host interactions. Critically, Cryptococcus spores can can disseminate out of the host lung better than yeast which translates to spores of otherwise avirulent yeast causing disease in intranasal murine models of cryptococcosis. This preferential dissemination and disease are likely a result of spores being able to invade host lung cells better than yeast. As spores germinate into yeast, and become more yeast-like, this preferential internalization diminishes probably due to surface epitopes being masked as the yeast capsule is formed. The spore surface components that drive host cell invasion, dissemination and disease remain a mystery. This research, conducted in the Casadevall lab, will be centered on defining the distinct surface components of spores, determining which components drive preferential host cells invasion, and identifying the molecular mechanisms enabling Cryptococcus dissemination and disease. Previous work has shown that cell surface hydrophobicity plays a role in yeast phagocytosis. Additionally, spores have distinct surface sugar epitopes to yeast, suggesting a unique surface glycoproteome. In specific aim 1, the cell surface hydrophobicity of spores will be systematically perturbed and evaluated, and the spore surface proteome will be defined. These surface components will subsequently be probed for roles in host cell invasion. Once surface properties that drive host-cell invasion have been identified, the molecular mechanisms driving dissemination and disease can be identified. In specific aim 2, the role of spore internalization by specific host cell types in disease kinetics will be determined by identifying fungal surface components and host receptors that drive uptake by different resident lung cells. Next, the role of these interactions in murine models will be probed for changes in in vivo host cell invasion, dissemination and disease. This work will identify novel mechanisms of host cell invasion that drive dissemination and disease, which can subsequently be used in the development of novel diagnostic tools and treatments for invasive fungal diseases.