ZIP8 is a transmembrane importer of divalent metals into the cytosolic space through the cell membrane and from subcellular compartments. Although GWAS data implicate hypofunctional ZIP8 mutations in a myriad of serious pathologies, there is a paucity of mechanistic studies investigating its functions during homeostasis or pathologic conditions. We have created two novel ZIP8 knockout (KO) mouse models in order to study this transporter, an inducible whole-body KO and a lung epithelium-specific KO, and our preliminary data indicate significant roles of ZIP8 in lung host immunity, splenic iron recycling, and placental nutrient transport. Specific Aim 1. Define the functions of ZIP8 as a metal transporter in the immune response to lung infections. ZIP8 expression is higher in the lung than in any other organ system, but its biological function is unknown. Our preliminary data show that lung ZIP8 is located primarily in the alveolar epithelium, where it imports iron from the alveolar space, is upregulated with both inflammatory stimuli and gram-negative bacterial infection, and is important for induction of the antioxidant enzyme manganese superoxide dismutase by lipopolysaccharide (LPS). We will characterize ZIP8-mediated transport of Fe, Zn, and Mn during both homeostasis and LPS lung injury using radioactive metal tracers, and study the effects of ZIP8 on the outcomes of gram-negative bacterial and fungal lung infections. Specific Aim 2. Define the role of ZIP8 in splenic macrophage erythrophagocytosis and iron recycling. Our preliminary data show that spleen ZIP8 is primarily expressed in macrophages, ZIP8 deletion induces splenic iron sequestration within red pulp macrophages and serum iron restriction, and spleen ZIP8 expression is regulated by splenic iron levels. We will identify the location, activity, and regulation of ZIP8 within splenic macrophages. Using mouse models of altered iron handling with iron overload, iron deficiency, and hemolysis, we will also characterize the function of ZIP8 in iron recycling during both baseline homeostasis and stress. Specific Aim 3. Define the contribution of ZIP8 to maternal-fetal nutrient transport in the placenta. The placenta is the second highest ZIP8-expressing tissue type in humans, and global ZIP8 ablation in mice is embryonic lethal. Our preliminary data show that placental ZIP8 is expressed in syncytiotrophoblasts, indicating a key role of ZIP8 in the transport of nutrient metals from maternal circulation to the embryo. We will use a novel trophoblast specific ZIP8 KO mouse to define the role of ZIP8 in placental transport of Fe, Zn, and Mn, perform confirmatory studies using primary human trophoblasts, and investigate ZIP8 regulation by maternal iron status. Our proposal will answer fundamental questions about the pathophysiologic functions of this critical metal transporter in metal-mediated lung host immunity, splenic iron recycling, and placental transport of nutrient metals. The findings will inform our clinical approaches in diagnosing and managing the many pathologies associated with disrupted metal homeostasis.

ZIP8 is a poorly understood transmembrane metal importer of iron, zinc, and manganese that appears to be important in multiple organ systems, including the lung, spleen, and placenta. We propose to study the functions of ZIP8 during bacterial and fungal lung infection, red blood cell recycling and iron processing by the spleen, and delivery of essential micronutrients to the developing fetus. Our findings will inform the clinical management of important public health issues, including infectious pneumonias, blood disorders, and pregnancy.