Homocysteine upregulates hepcidin expression through BMP6/SMAD signaling pathway in hepatocytes

Subjects with severe hyperhomocysteinemia have hypoferric anemia and excessive iron deposition in the liver. Hepcidin, the central regulator of iron homeostasis, plays a key role in iron metabolism. However, the regulation of homocysteine (Hcy) on hepcidin is largely unclear. We conducted experiments in HepG2 cells to identify the mechanisms with which Hcy modulates hepcidin expression. We found that treatment with Hcy dose-dependently increased both hepcidin transcript levels and protein levels, as assessed by quantitative real-time reverse-transcriptase polymerase chain reaction and western blotting, respectively. Hcy also activated BMP6 signaling and increased the phosphorylation of SMAD1/5/8 in HepG2 cells. We found that Hcy's effect on hepcidin expression was impaired by the knockdown of BMP6 and its receptors ALK2/3/6 with siRNAs. These results demonstrated that Hcy up-regulated hepcidin expression through the BMP6/SMAD pathway, suggesting a novel mechanism underlying the hyperhomocysteinemia-associated perturbation of iron homeostasis.