Lack of intestinal divalent metal‐ion transporter 1 (DMT1) perturbs copper homeostasis in mice
Authors: Wang Xiaoyu , Flores Shireen , Ha Jung‐Heun , Doguer Caglar , Collins James F. 
Published: November 2023

Introduction

Recent studies demonstrated that iron and copper homeostasis are intimately intertwined. This is perhaps not surprising given the similar physiochemical properties of the two redox‐active metals. Our recent studies provided evidence that copper influences intestinal iron absorption. In particular, we demonstrated that the main intestinal iron importer, DMT1, can transport copper during iron deprivation in rats and in DMT1 expressing HEK293 cells. This could be an important part of the compensatory response of the intestinal epithelium to iron deficiency given that at least one copper‐dependent enzyme is necessary for optimal iron absorption (i.e. the ferroxidase Hephaestin). The current study was thus designed to test the hypothesis that intestinal DMT1 influences copper metabolism.

Methods

We utilized mice lacking DMT1 only in the intestine (DMT1int/int) and WT littermates (DMT1flox/flox) (kindly provided by Dr. Bryan Mackenzie, Univ. of Cincinnati). 2‐month‐old mice of both sexes and genotypes were fed a control (9 ppm Cu) or a high‐copper (183 ppm Cu) diet for 4 weeks. Subsequently, measures of iron and copper status were analyzed using standard methods. All data mentioned below reached statistical significance (n = 2–5 mice/group).

Results

DMT1int/int male and female mice were severely anemic, as reflected by reduced hemoglobin and hematocrit levels (~90% reductions). Consumption of the high‐copper diet did not change these parameters. Hepatic hepcidin mRNA expression was very low in all KO mice (>99% reduction), regardless of dietary treatments. In male and female DMT1int/int mice, the spleens were enlarged (~3X larger), but consumption of the high‐copper diet normalized spleen size. Also, in male and female KO mice, hepatic copper concentrations increased (3–4X) with consumption of the high‐copper diet. In males, lack of intestinal DMT1 led to decreased serum ceruloplasmin (CP) expression (~50%); however, no change was noted in females. Moreover, expression of iron/copper homeostasis‐related genes was upregulated in duodenal enterocytes and liver tissue of male KO mice consuming the high‐copper diet, including ATP7A (2‐fold), DCYTB (>130‐fold), TFR1 (>30‐fold), and FPN1 (>10‐fold). Interestingly, expression of the gene encoding an intracellular copper binding protein metallothionein, was strongly induced in the KOs (>100‐fold in males on the high‐copper diet).

Conclusions

Although our original observations regarding copper and its influence on iron homeostasis were made in rats, we took advantage of genetic manipulations which are commonplace in mice to directly address whether intestinal DMT1 influences copper metabolism. It was noted that spleen enlargement in the KOs was corrected by high‐copper feeding. Since the spleen can by an erythropoetic organ during severe anemia, this finding suggests that copper deficiency may in‐part underlie the severe anemia. Furthermore, decreased serum CP activity is consistent with low systemic copper levels. Increased expression of genes in duodenal enterocytes and liver of the KO mice fed the high‐copper diet further support the hypotheses that intestinal DMT1 influences copper homeostasis and that copper, in turn, influences intestinal iron absorption.

Support or Funding Information

NIH grant 1R01 DK074867