Inflammatory Cytokine IL-1β Upregulates Hepcidin Expression in Human Hepatoma Cell Lines.

Abstract

The anemia of chronic disease (ACD) is commonly observed in patients with inflammatory disorders, malignancies, and chronic infections. ACD is characterized by low serum iron concentration and elevated serum ferritin concentration. A number of previous findings suggest that impaired mobilization of iron from the reticuloendotherial system (RES), such as macrophages, and an inhibition of iron absorption from intestine contribute to ACD. However, the precise mechanisms for generating the conditions of ACD have long been unclear despite extensive investigations until hepcidin was recently found. Hepcidin was found as one of antimicrobial peptides, but hepcidin is now thought to be a key regulator in iron metabolism. Hepcidin inhibits iron absorption from enterocytes and iron efflux from RES, which have suggested that hepcidin could account for the pathogenesis of ACD. Some cytokines have also been shown to modulate iron metabolism in the condition of inflammation. Interleukin-6 (IL-6), one of inflammatory cytokines, has been reported to induce hepcidin production not only in vitro but also in vivo. However, it is not clear whether other cytokines have such effect or not. We, therefore, investigated the possibility that other inflammatory cytokines might have a regulatory effect on hepcidin expression. Because hepcidin is produced mainly by hepatocytes, we used human hepatoma-derived cell line HuH-7 cells and hepatoblastoma-derived cell line HepG2 cells. Cells are incubated with or without inflammatory cytokines, such as IL-1β, IL-6, tumor necrosis factor α (TNFα), and then total RNA was extracted. Quantitative RT-PCR was then performed, revealing that IL-1β upregulate hepcidin mRNA expression as well as IL-6, although TNFα down regulates hepcidin expression in both cell lines. We next investigated the dose-response effect of IL-1β and IL-6 on hepcidin mRNA expression. Strong induction of hepcidin mRNA by IL-1β was observed when cells were incubated with low concentrations of IL-1β (0.2 ng/ml), although much higher concentrations of IL-6 were needed for hepcidin mRNA upregulation. It was likely that the concentrations of IL-1β that needed for hepcidin upregulation were more physiological than those of IL-6. Since it has been reported that IL-1β induce IL-6 production in hepatocytes, there was a possibility that the effect of IL-1β on hepcidin mRNA expression was not direct but come from IL-6 induced by IL-1β. However, the manners of IL-6 mRNA induction and hepcidin mRNA induction by IL-1β stimulation were quite different when cells were incubated with IL-1β at the concentrations ranging from 0.1 to 10 ng/ml. Moreover, antibody against IL-6 did not inhibit the induction of hepcidin mRNA by IL-1β stimulation. Therefore, it is likely that the effect of IL-1β on hepcidin mRNA expression is independent from that of IL-6. We conclude that inflammatory cytokine IL-1β can induce hepcidin expression and might be a key cytokine in the condition of ACD as well as IL-6, and IL-1β might be more important than IL-6 in physiological situations.