Regulation of murine Zip14 during hepatic inflammation

Abstract

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 Zip14 zinc transporter 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 as a secondary messenger. IL-1β, an LPS-induced proinflammatory cytokine, is a potent activator of inducible nitric oxide synthase (iNOS), and nitric oxide production. Therefore, we hypothesized that nitric oxide can regulate Zip14 expression during LPS-induced inflammation. To address this hypothesis, we treated primary hepatocytes from wild-type mice with the nitric oxide donor s-nitroso n-acetyl penicillamine (SNAP). After treatment with 50 μM SNAP for 8 hr, Zip14 mRNA increased two-fold. We then took a more physiological approach by treating primary murine hepatocytes with IL-1β. As expected, IL-1β treatment increased iNOS mRNA as well as nitric oxide, as measured by nitrite concentration. In support of our hypothesis, IL-1β treatment also led to a six-fold increase in Zip14 mRNA and enhanced zinc transport as measured by the Zn2+-specific fluorophore, FluoZin-3 AM. Experiments utilizing siRNA to knockdown Zip14 expression and those using hepatocytes from iNOS knockout mice also support our hypothesis. These data suggest that signaling pathways activated by nitric oxide are factors in the up-regulation of Zip14 that in turn mediates hepatic zinc accumulation and reduction of serum zinc concentrations during inflammation and sepsis. Supported by NIH Grant DK 31127.