DMT1 expression in the rat proximal colon is up-regulated by feeding iron-deficient diet

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University of Manchester (2003) J Physiol 552P, P122

Communications: DMT1 expression in the rat proximal colon is up-regulated by feeding iron-deficient diet

Kelly Johnston and Paul Sharp

Centre for Nutrition and Food Safety, School of Biomedical and Molecular Sciences, University of Surrey, Guildford GU2 7XH, UK

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Duodenal iron uptake is mediated by DMT1 at the apical membrane, whilst IREG1 at the basolateral membrane regulates efflux from the enterocyte. However only 10 % of dietary non-haem iron is absorbed in the duodenum, meaning that 90 % reaches the distal region of the small intestine and the colon. Interestingly, a recent report has suggested that, in addition to the duodenum, the proximal colon might also have iron transport capabilities (Bougle et al. 2002). To investigate this possibility, we have measured the expression of DMT1 in rat colon. Furthermore, to determine whether colonic DMT1 is regulated by dietary iron intake, we have fed one group of animals on an iron-deficient diet.

Male Wistar rats (250g) were pair-fed for seven days on either control (50 mg Fe kg-1) or Fe deficient (< 0.5 mg kg-1) diet. After this time animals were killed humanely and sections of duodenum, proximal colon and distal colon were removed and subjected to total RNA extraction using the TRIzol method. RT-PCR was performed using DMT1-specific primers and the PCR products resolved on ethidium bromide-stained 2 % agarose gels. Bands were semiquantified using Scion Image software and were normalised to β-actin expression in the same samples.

Alternative splicing of exon 16 of the DMT1 gene leads to mRNA variants with differing 3â untranslated regions (Lee et al. 1998) – one contains an iron-responsive element (IRE) whereas the other does not. Following feeding an iron-deficient diet, expression of the DMT1 (IRE) splice variant was significantly increased in duodenum and proximal colon (Table 1). DMT1 (non-IRE) was up-regulated in proximal colon only. Neither splice variant was modulated by iron deficiency in the distal colon. Regulation of DMT1 expression by dietary iron, taken together with our preliminary observations that DMT1 protein is expressed at the cell surface of proximal but not distal colon, supports the hypothesis that the proximal colon under some circumstances could contribute to dietary iron absorption.

This work was supported by BBSRC (grant 90/D17146).

Table 1. Effects of iron-deficient diet on DMT1 mRNAexpression. Data are means ± S.E.M. of n animals in eachgroup. Statistical analysis utilised Student’s unpaired t test,*P < 0.05.
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Table 1. Effects of iron-deficient diet on DMT1 mRNAexpression. Data are means ± S.E.M. of n animals in eachgroup. Statistical analysis utilised Student’s unpaired t test,*P &lt; 0.05.

Where applicable, experiments conform with Society ethical requirements.

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