Non-Transferrin-Mediated Iron Delivery

In iron overload conditions such as thalassemia major and hereditary hemochromatosis, the iron-carrying capacity of plasma transferrin is exceeded, giving rise to non-transferrin-bound iron (NTBI). NTBI is taken up preferentially by the liver, and to a lesser extent, the kidney, pancreas, and heart. How NTBI is taken up by various tissues has been elusive. We recently demonstrated that the plasma membrane metal-ion transporter SLC39A14 (ZIP14) mediates NTBI uptake and iron loading of the liver and pancreas, but not the kidney, heart or most other tissues¹ Given that the heart is particularly susceptible to iron-related toxicity, we are currently investigating the contribution of other iron transporters to iron loading of this organ. Possible alternative cardiac iron importers include L-type and T-type calcium channels, divalent metal transporter 1 (DMT1), and SLC39A8 (ZIP8). To examine the role of DMT1 and ZIP8 in cardiac iron metabolism, we generated mice with cardiomyocyte-specific disruption of DMT1 (Dmt1^heart/heart) or ZIP8 (Zip8^heart/heart). The mice were then crossed with hemojuvelin knockout (Hjv^-/-) mice, a model of juvenile hemochromatosis characterized by high circulating levels of NTBI. Dmt1^heart/heart mice were found to have cardiac non-heme iron concentrations that were 30% lower (P<0.01) than those of wild-type littermate controls at 6 weeks of age. Interestingly, however, double mutant Hjv^-/-; Dmt1^heart/heart mice accumulated more cardiac non-heme iron (3.9X control) than did single-mutant Hjv^-/- mice (2.3X control) at 6 weeks of age. Cardiac-specific disruption of Zip8 did not affect cardiac non-heme iron concentrations under basal conditions or when mice were crossed with Hjv^-/- mice. Collectively, these data indicate that DMT1 and ZIP8 are dispensable for iron loading of the heart in a mouse model of hemochromatosis. Our data additionally suggest that DMT1 may play a role in normal cardiac iron metabolism.

Reference:

1. Jenkitkasemwong S, Wang C, Coffey R, et al. SLC39A14 is required for the development of hepatocellular iron overload in murine models of hereditary hemochromatosis.Cell Metabolism.2015; 22(1):138-150.