Intestinal iron absorption is mediated by several proteins that have only recently been identified. However, several lines of experimental pursuit have suggested that there are other unknown genes involved in this important physiological process. Thus, we performed comparative gene chips studies designed to identify changes in the expression of known and unknown genes involved in iron transport in the duodenal mucosa of anemic rats at 8 days, 21 days, 6 weeks, 12 and 26-weeks-of-age. Our results demonstrate changes in gene expression that are unique at the different ages, but we also found that certain genes change across all age groups studied. We found that among iron transport genes, only the genes encoding the brush-border membrane proteins dcytb and DMT1 were consistently induced in anemia, while other genes involved in iron export from enterocytes such as ferroportin and hephaestin did not show changes in the iron deficient state. Interestingly however, we found consistent upregulation of genes that have not been described to be involved in iron transport in the mammalian duodenum. These changes include 4-12-fold upregulation of the basolateral membrane-specific copper ATPase (Atp7a), and 2-5-fold increases in a membrane bound form of ceruloplasmin, a multi-copper ferroxidase, which was seen in adult rats. As the brush-border membrane copper transporter Ctrl did not change expression levels, we suggest that copper may enter enterocytes via DMT1. There is a well-known link between copper and iron homeostasis as copper deficiency causes anemia and iron deficiency anemia leads to increased body copper levels. From these findings, we hypothesize that chronic iron deficiency leads to compensatory increases in the expression of brush-border iron transport proteins dcytb and DMT1 (which may also transport copper), increased basolateral export of copper via the copper ATPase, and increased expression of GPI-anchored ceruloplasmin, all of which may work in concert to enhance body iron delivery. In order to explore this possibility, we plan to pursue the following Specific AIMS: 1) decipher transcriptional regulation of dcytb and DMT1 by iron, and 2) characterize basolateral copper ATPase activity and protein expression in iron deficiency and characterize expression of membrane-associated ceruloplasmin in the duodenum of iron deficient rats. Overall, these studies will likely lead to increased understanding of the interplay between intestinal iron absorption and body copper homeostasis and will explore the role of GPI-anchored ceruloplasmin in intestinal iron transport.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Exploratory/Developmental Grants (R21)
Project #
1R21DK068349-01
Application #
6814889
Study Section
Gastrointestinal Cell and Molecular Biology Study Section (GCMB)
Program Officer
May, Michael K
Project Start
2004-07-01
Project End
2006-06-30
Budget Start
2004-07-01
Budget End
2005-06-30
Support Year
1
Fiscal Year
2004
Total Cost
$188,125
Indirect Cost
Name
University of Arizona
Department
Pediatrics
Type
Schools of Medicine
DUNS #
806345617
City
Tucson
State
AZ
Country
United States
Zip Code
85721
Hu, Zihua; Gulec, Sukru; Collins, James F (2010) Cross-species comparison of genomewide gene expression profiles reveals induction of hypoxia-inducible factor-responsive genes in iron-deprived intestinal epithelial cells. Am J Physiol Cell Physiol 299:C930-8
Collins, James F; Hua, Ping; Lu, Yan et al. (2009) Alternative splicing of the Menkes copper Atpase (Atp7a) transcript in the rat intestinal epithelium. Am J Physiol Gastrointest Liver Physiol 297:G695-707
Collins, James F; Hu, Zihua; Ranganathan, P N et al. (2008) Induction of arachidonate 12-lipoxygenase (Alox15) in intestine of iron-deficient rats correlates with the production of biologically active lipid mediators. Am J Physiol Gastrointest Liver Physiol 294:G948-62
Hu, Zihua; Hu, Boyu; Collins, James F (2007) Prediction of synergistic transcription factors by function conservation. Genome Biol 8:R257
Collins, James F; Hu, Zihua (2007) Promoter analysis of intestinal genes induced during iron-deprivation reveals enrichment of conserved SP1-like binding sites. BMC Genomics 8:420
Kim, Kyung-Ah; Kim, Jung-Hyun; Wang, Yuhui et al. (2007) Pref-1 (preadipocyte factor 1) activates the MEK/extracellular signal-regulated kinase pathway to inhibit adipocyte differentiation. Mol Cell Biol 27:2294-308
Collins, James F (2006) Gene chip analyses reveal differential genetic responses to iron deficiency in rat duodenum and jejunum. Biol Res 39:25-37
Ravia, Jennifer J; Stephen, Renu M; Ghishan, Fayez K et al. (2005) Menkes Copper ATPase (Atp7a) is a novel metal-responsive gene in rat duodenum, and immunoreactive protein is present on brush-border and basolateral membrane domains. J Biol Chem 280:36221-7