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Histoplasma circumvents nutrition limitations to proliferate within macrophages

Shen, Qian
http://orcid.org/0000-0002-9001-7636
http://rave.ohiolink.edu/etdc/view?acc_num=osu1563371073816792

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Microbiology.
Histoplasma capsulatum is a dimorphic fungal organism that switches between mycelium and yeast phase upon sensing environmental temperature changes. Histoplasma lives in the soil as avirulent mycelium. Upon encountering elevated temperature in the mammalian host during infection, Histoplasma differentiates into pathogenic yeast phase. Histoplasma yeasts survive and proliferate in the host phagocytes, especially within the macrophage phagosome. However, the phagosome is a nutrient-depleted environment, yet it does not prevent the growth of Histoplasma yeasts. The goal of this dissertation is to advance the understandings of molecular mechanisms by which Histoplasma yeasts rely on to proliferate in the nutrient-depleted phagosomal environment. Through a genetic screen, we isolated a mutant that had a disruption in the CTR3 gene encoding a high affinity copper transporter. Loss of Ctr3 function prevented Histoplasma growth under copper limited conditions. Depletion of Ctr3 did not impair intracellular growth in non-activated macrophages but resulted in growth defect in IFN-γ activated macrophages. Ctr3-deficient yeasts were fully virulent during innate immunity but attenuated after the onset of adaptive immunity. This indicates that the phagosomal environment switches from high copper to lower copper upon IFN-γ mediated macrophage activation, which subsequently forces Histoplasma to rely on Ctr3 to acquire sufficient copper. In order to proliferate within macrophages, Histoplasma must be able to assimilate carbon substrates in the phagosomal environment to meet its nutritional needs. We isolated a mutant containing a lesion in the PCK1 gene, which encodes the phosphoenolpyruvate carboxykinase, an enzyme catalyzing the first committed step of gluconeogenesis. Transcriptional analysis showed that Histoplasma yeasts down-regulated glycolysis and fatty acid utilization but up-regulated gluconeogenesis within macrophages. Depletion of glycolysis or fatty acid utilization pathway neither prevented Histoplasma growth within macrophages, nor impaired virulence in vivo. However, loss of function in Pck1 resulted in intramacrophage growth defect and severely attenuated virulence in vivo, indicating that Histoplasma yeasts rely on catabolizing gluconeogenic substrates to proliferate within macrophages. Furthermore, Histoplasma yeasts lacking the GDH2 gene, which encodes a glutamate dehydrogenase involved in glutamate catabolism, showed impaired intramacrophage growth and severely attenuated virulence in vivo. Taken together, glutamate catabolism in Histoplasma produces α-ketoglutarate, which further is utilized to produce all key precursor metabolites to support its cellular biosynthesis through gluconeogenesis. In addition, we isolated mutants that had disruption in genes encoding proteins involved in peroxisome biogenesis. Loss of Pex10 or Pex33 function prevented Histoplasma growth within macrophages and resulted in complete loss of virulence in vivo. Compared to wild type, peroxisome-deficient yeasts showed increased susceptibility to iron restricted conditions, suggesting that peroxisomes are required for siderophore production for iron acquisition. However, depletion of siderophore biosynthetic pathway did not impair Histoplasma’s virulence in vivo, indicating that peroxisomes do not contribute to Histoplasma pathogenesis through siderophore production.
Chad Rappleye (Advisor)
Birgit Alber (Committee Member)
John Gunn (Committee Member)
Ruiz Natividad (Committee Member)
214 p.
Microbiology
Histoplasma, Nutritional immunity, Host-pathogen interaction, Carbon metabolism

Recommended Citations

Citations

  • Shen, Q. (2019). Histoplasma circumvents nutrition limitations to proliferate within macrophages [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563371073816792

    APA Style (7th edition)

  • Shen, Qian. Histoplasma circumvents nutrition limitations to proliferate within macrophages. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1563371073816792.

    MLA Style (8th edition)

  • Shen, Qian. "Histoplasma circumvents nutrition limitations to proliferate within macrophages." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563371073816792

    Chicago Manual of Style (17th edition)

osu1563371073816792
319
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This open access ETD is published by The Ohio State University and OhioLINK.