Effect of hepcidin on intracellular calcium in human osteoblasts.

Hepcidin is known to increase intracellular iron through binding to and degrading ferroportin, which is a transmembrane protein that transports iron from the intracellular to the outside. However, it is not clear whether hepcidin has a similar effect on intracellular calcium. Here, we investigated the influence of hepcidin on intracellular calcium in human osteoblasts, with or without high environmental iron concentrations. Our data showed that hepcidin (<100 nmol/L) could increase intracellular calcium, and this effect was more significant when cells were exposed to high environmental iron concentrations. To further explore its underlying mechanisms, we pretreated human osteoblasts with Nimodipine, a L-type calcium channel blocker, and Dantrolene, a ryanodine receptor antagonist to inhibit abnormal calcium release from the sarco-endoplasmic reticulum. These treatments had not resulted in any alteration of intracellular calcium in human osteoblasts. Thus, these findings indicate that the increase of intracellular calcium induced by hepcidin is probably due to calcium release from endoplasmic reticulum, which is triggered by calcium influx.

Increased intracellular iron and mineralization of cultured hFOB 1.19 cells following hepcidin activation through ferroportin-1.

OBJECTIVE: To address whether hepcidin functions in bone metabolism. METHODS: This study was carried out in the Laboratory of Radiation Medicine and Public Health of Soochow University, and the Laboratory of the Second Affiliated Hospital of Soochow University, Suzhou, China, from September 2009 to July 2010. The positive expression of ferroportin-1 (Fpn-1) was detected by reverse transcriptase-polymerase chain reaction. After the treatment with distilled water (control group) and hepcidin (25noml/L, 50noml/L, 100noml/L), the fluorescence intensity related to intracellular iron concentration of a human fetal osteoblast cell line (hFOB 1.19) was measured by a confocal laser scanning microscope. A 3-(4,5- dimethylthiazol-2-yl) -2-5-diphenyltetrazolium bromide assay, and Von Kossa staining was performed to evaluate cell proliferation and mineralization in cultured hFOB 1.19 cells. RESULTS: This study revealed a high level expression of Fpn-1 in hFOB 1.19. On the basis of which, it was found that 25noml/L, 50noml/L, 100noml/L hepcidin could promote the fluorescence intensity related to intracellular iron concentration and mineralization in hFOB 1.19 in a dose-dependent manner (p<0.05), but hepcidin had no effect on FOB 1.19 proliferation (p>0.05). CONCLUSION: The hepcidin-ferroportin signal pathway may function in the osteoblast cell line of hFOB 1.19 cells. It is also suggested that cross-talk between iron and calcium homeostasis may play a role in bone metabolism in responding to hepcidin activation.