Mechanism of cryptococcal fitness, innate defense subversion, and the adaptive immune skewing in lungs

Veterans Health Administration, Decatur PA

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Abstract

Cryptococcus neoformans (C. neo), is one of the most significant fungal pathogens worldwide. However, much is still unknown on how it interacts with the host to evade and subvert the immune response. Here we propose to study the biological effects of intercepting the trehalose sugar biosynthetic pathway, which our data suggest affects interactions of cryptococcus with multiple lines of host defenses and could serve as an “Achilles heel” for the fungus. Trehalose-6-phosphate synthase (TPS1) catalyzes the first step in the biosynthetic pathway to generate trehalose, a disaccharide that canonically protects C. neo (and other microbes) against stress, which is not synthesized or required by mammalian cells. TPS1 has been described as a virulence factor for C. neo in multiple animal infection models, but the mechanistic underpinnings are undefined. We propose to mechanistically uncover how TPS1-deletion alters fungal-host interactions to drive this increased fungal control. Our preliminary data show that in murine models of pulmonary infection, trehalose-deficient C. neo (tps1Δ) is very rapidly cleared due to improved immune protection. As such, we hypothesize that cryptococcal TPS1 is required to protect the fungus against all 3 lines of pulmonary host defenses via (1) interference with the local resident defenses; (2) the recruitment/activation of the innate immune cells for early fungal control, and (3) modulation of the adaptive memory responses. We propose that trehalose is required to protect C. neo against innate factors in the alveolar space, such as surfactants. Our preliminary data support a role for the surfactant proteins A and D in trehalose-deficient C. neo control (Aim 1). We also propose that the loss of trehalose facilitates rapid fungal clearance by resident innate immune cells, specifically neutrophils (Aim2). Further, our preliminary data suggest that the loss of Tps1-function by Cryptococcus results in an immunostimulation that supports the development of protective skewing and an adaptive immune memory response (Aim 3). This improved the level of immunoprotection supports that targeting the TPS pathway, apart from directly aiding the fungal removal, can induce long-term protective immune memory effects. Eventually, understanding how trehalose alters cryptococcal interactions with host defenses could support the development of a future class of broad antifungal inhibitors that could aid the treatment of multiple types of fungal infections. In summary, this work will provide novel context for how C. neo avoids pulmonary host defenses and how these interactions can be exploited. The studies proposed above make up the scientific basis for the VA CDA-2 program that will provide training and career development for Dr. Kristie Goughenour into an independent VA investigator. Dr. Goughenour completes the third year of her postdoctoral training in the Multidisciplinary T32 Research Training Program in Lung Disease. Her primary research focus is on host-pathogen interactions of pathogenic fungi in pulmonary infections. Her training has provided her with both the technical ability and theoretical framework to dissect both the human host factors and the microbial virulence mechanisms that interact to determine the outcomes of infections. This proposal builds upon her skills in molecular mechanisms of fungal pathogenesis and host responses to fungal pathogens to combine into unique expertise in host immune control of pulmonary fungal pathogens and novel mechanisms of fungal immune evasion. Dr. Goughenour will strengthen her expertise in different aspects of immune processes and learn several new technologies. Her mentoring team of 5 top experts in their respective fields has been carefully developed to provide expertise and career support while she transitions towards independence and to provide aid on the proposed studies.