The pathogenic fungus, Histoplasma capsulatum, is endemic to the Midwestern and Southeastern US and is the most frequent cause of respiratory fungal infection. The organism thrives within the intracellular environ- ment of monocytes (Mo) and macrophages (M?) and has the capacity to establish a latent state. Employing a multidisciplinary approach including metallomics, immunology, cell biology and bioinformatics, our studies have identified novel functions of granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 that help to explain their disparate effects on the growth of the fungus with Mo/M?. GM-CSF deprives the organism of zinc intracellularly while concurrently boosting production of reactive oxygen species. The end result is killing of yeast cells. On the other hand, IL-4 promotes intracellular survival by fortifying the amount of zinc available to Histoplasma. Crucial to the activities of GM-CSF and IL-4 are metallothioneins (MTs), which store and donate zinc, and zinc transporters. They are a central node mediating the link between cytokine activation and effector function. For GM-CSF, MTs1 & 2 are essential whereas for IL-4, it is MT3. In this proposal, we will build on our work conducted during the last funding cycle and explore in depth how the MT- zinc axis regulates the activity of GM-CSF and IL-4 on human and mouse Mo/M?. We have collected exciting data that glycolysis governs the expression of MTs1&2 in infected GM-CSF-stimulated Mo/M?. On the other hand, MT3 tempers the glycolytic response in IL-4 activated in these cells.
Aim 1 will decipher how glycolysis molds MT1&2 expression and intracellular Zn2+ distribution to bolster Mo/M? effector function.
Aim 2 will define the intracellular alterations in GM-CSF-activated Mo/M? that deny the fungus access to zinc and the in vivo effect of MTs1&2 on host defenses exerted by these phagocytes.
Aim 3 will elucidate the intersection of glycolysis and MT3 in shaping the physiology of IL-4 on Histoplasma-infected Mo/M?. These studies will provide new insights into cytokine regulation of metabolism and metallobiology in Histoplasma-infected Mo/M?.
The fungus, Histoplasma capsulatum, multiplies in macrophages and requires zinc for growth. Two cytokines exert disparate effects on fungal survival in macrophages by limiting or adding zinc. Our work will decipher how these cytokines regulate zinc homeostasis and provide new data on phagocyte biology.
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