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Sporadic iron overload in rats has been reported, but whether it is due to genetic or environmental causes is unknown. In the current study, phenotypic analysis of Hsd:HHCL Wistar rats revealed a low incidence of histologically detected liver iron overload. Here we characterized the pathophysiology of the iron overload and showed that the phenotype is heritable and due to a mutation in a single gene. We identified a single male rat among the 132 screened animals that exhibited predominantly periportal, hepatocellular iron accumulation. This rat expressed low RNA levels of the iron regulatory hormone hepcidin and low protein levels of transferrin receptor 2 (Tfr2), a membrane protein essential for hepcidin expression in humans and mice and mutated in forms of hereditary hemochromatosis. Sequencing of Tfr2 in the iron-overloaded rat revealed a novel Ala679Gly polymorphism in a highly conserved residue. Quantitative trait locus mapping indicated that this polymorphism correlated strongly with serum iron and transferrin saturations in male rats. Expression of the Gly679 variant in tissue culture cell lines revealed decreased steady-state levels of Tfr2. Characterization of iron metabolism in the progeny of polymorphic rats suggested that homozygosity for the Ala679Gly allele leads to a hemochromatosis phenotype. However, we currently cannot exclude the possibility that a polymorphism or mutation in the noncoding region of Tfr2 contributes to the iron-overload phenotype. Hsd:HHCL rats are the first genetic rat model of hereditary hemochromatosis and may prove useful for understanding the molecular mechanisms underlying the regulation of iron metabolism.

Abstract 612 Sporadic iron overload has been reported previously in rats but the underlying cause has not been ascertained. In this study, phenotypic analysis of a subpopulation of Wistar rats designated Hsd:HHCL revealed a low incidence of histologically detected liver iron overload. One rat out of 132 screened animals exhibited liver iron accumulation in a predominantly periportal, hepatocellular distribution; this male rat expressed low RNA levels of the iron regulatory hormone hepcidin and low protein levels of transferrin receptor 2, a membrane protein essential for hepcidin expression in humans and mice and mutated in forms of hereditary hemochromatosis, a disease of excessive intestinal iron absorption and progressive tissue iron overload. Sequencing of the transferrin receptor 2 gene in the iron-overloaded rat revealed a novel Ala679Gly polymorphism affecting a highly conserved residue. Quantitative trait locus mapping revealed that a transferrin receptor 2 polymorphism correlated strongly with serum iron and transferrin saturations in male rats. Transfection of Tfr2 expression constructs into tissue culture cell lines revealed that the Gly679 Tfr2 variant is expressed at a lower level than the Ala679 variant. Selective breeding of rats carrying this polymorphism and characterization of iron metabolism in the resulting progeny indicated that homozygosity for the Ala679Gly allele leads to a hemochromatosis phenotype. The Hsd:HHCL rat is the first genetic rat model of hereditary hemochromatosis and may prove useful for understanding the molecular mechanisms underlying the regulation of iron metabolism and the pathogenesis of hereditary hemochromatosis. Disclosures: No relevant conflicts of interest to declare.