Defining the fungal-host interactions between the pathogenic yeast Cryptococcus neoformans and human microglia

About This Grant

PROJECT SUMMARY Cryptococcus neoformans, the etiological agent of cryptococcal meningitis (CM), is a globally distributed environmental yeast that mainly causes infections in immunocompromised individuals. Particularly in low- resource countries, the mortality rate of CM can reach 81% and accounts for 19% of HIV/AIDS-related deaths each year. Despite this high burden, CM treatment options are suboptimal, largely due to an incomplete understanding of the fungal biology and host-pathogen interactions. In immunocompromised individuals, once inhaled, C. neoformans escapes from the lungs and disseminates with special predilection for the central nervous system (CNS). Once in the brain, C. neoformans interacts with microglia, the tissue-resident macrophages of the CNS. Previous studies indirectly showed that microglia are ineffective at controlling this fungal infection. It has also been shown that many phagocytosed yeasts can survive, replicate, and avoid killing in the microglial phagosome, and this can be influenced by prior yeast opsonization. The mechanisms underlying this fungal survival and proliferation within the CNS, however, remain unclear. My preliminary studies have expanded on these previous findings, showing that immortalized and primary human microglia have decreased phagocytic and killing activity that is specific to C. neoformans. This has led to my central hypothesis that C. neoformans survives in the CNS by using both novel, capsule-independent, antiphagocytic mechanisms and phagosome maturation disruption within microglia, and that these mechanisms vary based on yeast opsonization. To test this, I will use an immortalized human microglia cell line to study the interactions between these immune cells and C. neoformans. This model is advantageous as it is more translational that rodent-derived cell lines, and it is easier to culture and obtain than primary human microglia. Experiments in Aim #1 will define the process of phagosome maturation in microglia after engulfment of wild-type C. neoformans. I will look at phagosome development, acidification, damage, and subsequent function. Experiments in Aim #2 will identify antiphagocytic cryptococcal proteins and determine their impact on microglia killing efficiency and phagosome maturation. Experiments in Aim #3 will define if yeast opsonization leads to differential receptor engagement and how this impacts the outcome of the infection. Specifically, I will study how opsonization impacts microglial phagosome maturation and killing efficiency, as well as study the receptors necessary for cryptococcal recognition and engulfment. Overall, my project takes advantage of the expertise in cryptococcal-phagocyte interactions and glia biology and function of my sponsor and co-sponsor laboratories, respectively, and will yield a better understanding of the interactions between C. neoformans and microglia, ultimately contributing to the knowledge of fungal biology and CM pathogenesis, making it more likely that effective therapeutics to treat CM will be developed.