Iron is essential to the cell. Both
iron deficiency and overload impinge negatively on cardiac health. Thus, effective
iron homeostasis is important for cardiac function.
Ferroportin (FPN), the only known mammalian
iron-exporting
protein, plays an essential role in
iron homeostasis at the systemic level. It increases systemic
iron availability by releasing
iron from the cells of the duodenum, spleen, and liver, the sites of
iron absorption, recycling, and storage respectively. However, FPN is also found in tissues with no known role in systemic
iron handling, such as the heart, where its function remains unknown. To explore this function, we generated mice with a cardiomyocyte-specific deletion of Fpn. We show that these animals have severely impaired cardiac function, with a median survival of 22 wk, despite otherwise unaltered systemic
iron status. We then compared their phenotype with that of ubiquitous
hepcidin knockouts, a recognized model of the
iron-loading disease
hemochromatosis. The phenotype of the
hepcidin knockouts was far milder, with normal survival up to 12 mo, despite far greater
iron loading in the hearts. Histological examination demonstrated that, although cardiac
iron accumulates within the cardiomyocytes of Fpn knockouts, it accumulates predominantly in other cell types in the
hepcidin knockouts. We conclude, first, that cardiomyocyte FPN is essential for intracellular
iron homeostasis and, second, that the site of deposition of
iron within the heart determines the severity with which it affects cardiac function. Both findings have significant implications for the assessment and treatment of cardiac complications of
iron dysregulation.