Granulocyte Macrophage-Colony Stimulating Factor Induced Zn Sequestration Enhances Macrophage Superoxide and Limits Intracellular Pathogen Survival

Abstract

SUMMARY Macrophages possess numerous mechanisms to combat microbial invasion, including sequestration of essential nutrients, like Zn. The pleiotropic cytokine granulocyte macrophage-colony stimulating factor (GM-CSF) enhances antimicrobial defenses against intracellular pathogens such as Histoplasma capsulatum, but its mode of action remains elusive. We have found that GM-CSF activated infected macrophages sequestered labile Zn by inducing binding to metallothioneins (MTs) in a STAT3 and STAT5 transcription factor-dependent manner. GM-CSF upregulated expression of Zn exporters, Slc30a4 and Slc30a7 and the metal was shuttled away from phagosomes and into the Golgi apparatus. This distinctive Zn sequestration strategy elevated phagosomal H+ channel function and triggered reactive oxygen species (ROS) generation by NADPH oxidase. Consequently, H. capsulatum was selectively deprived of Zn, thereby halting replication and fostering fungal clearance. GM-CSF mediated Zn sequestration via MTs in vitro and in vivo in mice and in human macrophages. These findings illuminate a GM-CSF-induced Zn-sequestration network that drives phagocyte antimicrobial effector function.

Differential impact of zinc deficiency on phagocytosis, oxidative burst, and production of pro-inflammatory cytokines by human monocytes

“…8 Furthermore, zinc deprivation of Histoplasma capsulatum has been shown to lead to increased susceptibility of the pathogen against ROS, whereas at the same time zinc accumulation improves ROS-tolerance of the host cell. 30,31 Oxidative burst is increased by zinc deficiency during macrophage differentiation. 11 Accordingly, in the present study zinc deficiency promotes the oxidative burst of human monocytes, but seemingly only in response to GFP-S. aureus, thereby excluding a general effect.…”

The Role of Copper and Zinc Toxicity in Innate Immune Defense against Bacterial Pathogens

“…Metal analysis demonstrated that total Zn content was increased within activated macrophages infected with the fungal pathogen Histoplasma capsulatum (78). This was the result of increased Zn import via the ZIP2 importer, but the Zn ion was then distributed to intracellular Decreased survival [70] organelles such as the Golgi apparatus via Zn transporters ZnT4 and ZnT7 or bound to metallothionein (78). By contrast, LPS binding to the TLR4 receptor does not trigger Zn import into the macrophage.…”

The Physiological, Biochemical, and Molecular Roles of Zinc Transporters in Zinc Homeostasis and Metabolism

“…In the villus of the small intestine, ZnT4 expression is dramatically increased during differentiation (16). Upregulation of ZnT4 mRNA expression, along with ZnT7 mRNA by GM-CSF in macrophages, may contribute to the phagocyte antimicrobial effector function by shuttling zinc away from phagosomes through the mobilization of zinc into the Golgi apparatus (388). ZnT4 expression decreases in the progression from benign to invasive prostate cancer (153).…”