Increased duodenal DMT-1 expression and unchanged HFE mRNA levels in HFE-associated hereditary hemochromatosis and iron deficiency

Abstract

HFE-associated hereditary hemochromatosis is characterized by imbalances of iron homeostasis and alterations in intestinal iron absorption. The identification of the HFE gene and the apical iron transporter divalent metal transporter-1, DMT-1, provide a direct method to address the mechanisms of iron overload in this disease. The aim of this study was to evaluate the regulation of duodenal HFE and DMT-1 gene expression in HFE-associated hereditary hemochromatosis. Small bowel biopsies and serum iron indices were obtained from a total of 33 patients. The study population comprised 13 patients with hereditary hemochromatosis (C282Y homozygous), 10 patients with iron deficiency anemia, and 10 apparently healthy controls, all of whom were genotyped for the two common mutations in the HFE gene (C282Y and H63D). Total RNA was isolated from tissue and amplified via RT-PCR for HFE, DMT-1, and the internal control GAPDH. DMT-1 protein expression was additionally assessed by immunohistochemistry. Levels of HFE mRNA did not differ significantly between patient groups (P = 0.09), specifically between C282Y homozygotes and iron deficiency anemic patients, when compared to controls (P = 0.09, P = 0.9, respectively). In contrast, DMT-1 mRNA levels were at least twofold greater in patients with hereditary hemochromatosis and iron deficiency anemia when compared to controls (P = 0.02, P = 0.01, respectively). Heightened DMT-1 protein expression correlated with mRNA levels in all patients. Loss of HFE function in hereditary hemochromatosis is not derived from inhibition of its gene expression. DMT-1 expression in C282Y homozygote subjects is consistent with the hypothesis of a "paradoxical" duodenal iron deficiency in hereditary hemochromatosis. The observed twofold upregulation of the DMT-1 is consistent with the slow but steady increase in body iron stores observed in those presenting with clinical features of hereditary hemochromatosis.