| The anemia of chronic disease is driven by inflammatory cytokines. These cytokines also regulate genes that produce hypozincemia and hepatic zinc accumulation. In the sterile abscess model of inflammation, up-regulation of the zinc transporter, Zip14, by IL-6 is the mechanism responsible for the hypozincemia. However, experiments with IL-6 knockout mice show that LPS regulates Zip14 expression by a mechanism that is partially independent of IL-6. The LPS-induced model of sepsis may occur by a mechanism signaled by nitric oxide (NO) as a secondary messenger. Therefore, it was hypothesized that NO can modulate Zip14 expression during LPS-induced inflammation. To address this hypothesis, primary hepatocytes from wild-type mice were treated with the nitric oxide donor s-nitroso n-acetyl penicillamine (SNAP). After treatment with SNAP, Zip14 steady-state mRNA levels displayed a biphasic response with a maximal increase after 8 h, and a concomitant increase in the transcriptional activity of the gene. ChIP analysis documented the kinetics of AP-1 and Pol II association with the Zip14 promoter after NO exposure, indicating a role of AP-1 in transcription of Zip14. A more physiologic approach was then taken to investigate NO regulation by stimulating primary murine hepatocytes with IL-1beta, an LPS-induced proinflammatory cytokine. IL-1beta is a potent activator of inducible nitric oxide synthase (iNOS) and NO production. In support of our hypothesis, IL-1beta treatment led to a three-fold increase in Zip14 mRNA and enhanced zinc transport as measured by FluoZin3-AM fluorescence in wild-type, but not iNOS-/- hepatocytes. These data suggest that signaling pathways activated by NO are factors in the up-regulation of Zip14 that in turn mediates hepatic zinc accumulation and hypozincemia during inflammation and sepsis.;On the other hand, NO causes a decrease in hepatic Zip10 expression. Recently, Zip10 expression was shown to increase in vivo in the absence of metal-responsive transcription factor-1 (MTF-1). Therefore, a goal was set to determine if zinc and/or NO could regulate hepatic Zip10, and if this regulation occurs via MTF-1. To answer these questions, both in vivo and in vitro methods were used. First, primary mouse hepatocytes were incubated with increasing amounts of zinc. A dose-dependent decrease in Zip10 mRNA expression was observed, with an apparent 10-fold decrease within 3 h after zinc addition. Similar results were observed with NO. Mice were fed a zinc-deficient diet (<1ppm) for 21 d. Interestingly, hepatic Zip10 mRNA increased five fold, and a concomitant increase in ZIP10 protein expression was also observed. The mechanism of Zip10 down-regulation by zinc and/or NO was elucidated by using siRNA to knockdown MTF-1 expression in AML12 cells. Neither zinc nor NO could suppress Zip10 expression in the absence of MTF-1. Therefore, under these conditions MTF-1 is acting as a transcriptional repressor. These results suggest that hepatic Zip10 expression is negatively regulated by zinc through MTF-1, and Zip10 may be important for hepatic zinc uptake during deficiency.;In summary, the data presented here show that the liver controls zinc uptake under stress by either up- or down-regulating certain Zip transporters. |
