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Impact of macrophage zinc metabolism on host defense against Mycobacterium tuberculosis

Pyle, Charlie Jacob

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Pharmacy.
Tuberculosis (TB) is a global epidemic caused by infection of human macrophages with the world’s most deadly single bacterial pathogen Mycobacterium tuberculosis (M.tb). Manipulation of dietary micronutrients is a critical mechanism of host defense against infection and is referred to as nutritional immunity. In particular the essential trace element zinc functions as a critical modulator in inflammation through the human zinc transporter ZIP8. We hypothesize that zinc metabolism modulates macrophage host defense through ZIP8 during infection with Mycobacterium tuberculosis which is critical to the host response to TB. We began our investigation by establishing a physiologically relevant, in vitro model for the evaluation of zinc metabolism in human macrophage host defense. We then used the model to investigate the relationship between zinc, ZIP8 and NF-kappaB. ZIP8 is constitutively present in human macrophages, and induced through NF-kappaB as well as in response to LPS. Cellular zinc deprivation of macrophages increases LPS-induced macrophage zinc uptake, however ZIP8 knockdown in macrophages does not impact zinc accumulation prior to the arrival of the induced protein. Zinc supplementation increases NF-kappaB activity, independently of ZIP8. However, in response to LPS, ZIP8 inhibits NF-kappaB in the absence of zinc supplementation. Based upon these observations, we next identified the impact of ZIP8- dependent zinc on the balance of macrophage pro- and anti-inflammatory cytokine production. Zinc uptake within hours of LPS stimulation results in reduced IL-10 production and an increase in pro-inflammatory cytokine production in macrophages. ZIP8 knockdown partially reverses zinc-dependent reduction of IL-10 release but does not impact pro-inflammatory cytokine production. Localization of NF-kappaB subunits to binding sites on the IL-10 promoter is independent of zinc and ZIP8. However zinc supplementation of LPS-exposed macrophages reduces activity of the IL-10 inducing transcription factor C/EBPbeta revealing a potential mechanism for the IL-10 effect. Finally we identified the impact of zinc and ZIP8 on macrophage inflammation and host defense during M.tb infection. We began by critically evaluating published epidemiologic studies and discovered that TB disease correlates with inadequate nutritional zinc intake and reduced circulating zinc levels. We also determined in vitro that M.tb infection uniquely induces ZIP8 expression in comparison to the other 23 known zinc transporters. M.tb infection during zinc supplementation results in redistribution and increase of cytosolic zinc. Importantly, supplementation of zinc during macrophage infection reduces both IL-10 production and M.tb growth, which is independent of ZIP8. Using a novel, in vivo myeloid specific ZIP8 knockout mouse we determined that during M.tb infection, ZIP8 induces expression of pro-inflammatory cytokines and immune modulators in alveolar macrophages. Finally we revealed that the absence of ZIP8 is associated with decreased M.tb growth in the lung in vivo. This work establishes a framework demonstrating that macrophage zinc metabolism modulates the antimicrobial response to M.tb through alterations in zinc metabolism. The impact of zinc metabolism on M.tb infection is both ZIP8- dependent- and –independent, further revealing that the impact of zinc is complex, involving multiple factors. These critical observations will facilitate investigation of the impact of macrophage zinc metabolism on the intracellular lifestyle of M.tb. Future studies determining the relative cellular distributions of ZIP8 and zinc throughout infection and the mechanisms underlying their impact on critical host defense functions have the potential to improve our understanding of TB pathogenesis.
Knoell Daren, PharmD (Advisor)
Schlesinger Larry, MD (Advisor)
Amer Amal, MD, PhD (Committee Member)
Werbovetz Karl, PhD (Committee Member)
234 p.

Recommended Citations

Citations

  • Pyle, C. J. (2016). Impact of macrophage zinc metabolism on host defense against Mycobacterium tuberculosis [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469135576

    APA Style (7th edition)

  • Pyle, Charlie. Impact of macrophage zinc metabolism on host defense against Mycobacterium tuberculosis. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1469135576.

    MLA Style (8th edition)

  • Pyle, Charlie. "Impact of macrophage zinc metabolism on host defense against Mycobacterium tuberculosis." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469135576

    Chicago Manual of Style (17th edition)