Mechanism of Ferroportin Ubiquitination and its Therapeutic Potential in Anemia of Chronic Disease

点击翻译按钮获取中文摘要

The hepcidin-ferroportin signaling pathway has an important role in many disorders of iron metabolism, including iron overload syndromes (hemochromatosis) and anemia. Anemia of chronic disease is the second most common form of anemia and is present in conditions associated with infection, malignancy and inflammation. Anemia of chronic disease is characterized by low plasma iron concentrations despite sufficient stores of iron in the bone marrow, liver and spleen. In patients with these conditions, inflammatory cytokines induce expression of the hepatic hormone hepcidin. Hepcidin post-translationally regulates the cell surface expression of the iron exporter ferroportin. Ferroportin is the only membrane channel that is able to export iron from inside cells and thereby regulates the amount of circulating iron. Hepcidin binds to ferroportin and induces its ubiquitination, internalization and lysosomal degradation. As a result, the amount of iron that is available to developing red blood cells decreases. The objectives of the proposed research are to identify the enzymes involved in hepcidin- induced ferroportin ubiquitination and to determine whether inhibition of ferroportin ubiquitination is a potential novel therapy for the treatment of anemia of chronic disease. A cell line that inducible expresses ferroportin fused to green fluorescent protein (GFP) will be used to screen a commercially-available siRNA library that targets individual enzymes that are potentially involved in the transfer of ubiquitin to ferroportin. After identifying the ubiquitin conjugating and ligating enzymes that are involved in the degradation of ferroportin, the effect of siRNA-mediated knockdown of these enzymes on the development of turpentine-induced anemia of chronic disease in mice will be investigated. The host laboratory has established a cell line that expresses inducible ferroportin-GFP and is able to induce the expression of hepcidin by BMP treatment. This allows the analysis of ferroportin degradation under more physiological conditions. In addition, the chief of the host laboratory, Dr. Bloch, has extensive experience in the field of iron homeostasis and the use of murine models of chronic disease. The proposed research program will increase our understanding of iron homeostasis by elucidating the mechanism of ferroportin ubiquitination and degradation. It is anticipated that the results of these studies will permit the development of novel approaches to treat patients with iron-restrictive disorders.