Intestinal Iron Transport in Iron Deficiency/Anemia

描述（由申请人提供）：肠道铁吸收是由几种最近才被发现的蛋白质介导的。然而，几条实验路线表明，还有其他未知的基因参与了这一重要的生理过程。因此，我们进行了比较基因芯片研究，旨在确定贫血大鼠在8天、21天、6周、12周和26周龄时十二指肠黏膜中参与铁运输的已知和未知基因的表达变化。我们的研究结果表明，基因表达的变化在不同的年龄是独特的，但我们也发现，某些基因在所有研究的年龄组中都发生了变化。我们发现，在铁转运基因中，只有编码刷边膜蛋白dcytb和DMT1的基因在贫血中持续被诱导，而其他参与肠细胞铁输出的基因，如铁转运蛋白（ferroportin）和hephaestin，在缺铁状态下没有表现出变化。然而，有趣的是，我们发现了在哺乳动物十二指肠中未被描述参与铁运输的基因的一致上调。这些变化包括基底外侧膜特异性铜atp酶（Atp7a）上调4-12倍，铜蓝蛋白（一种多铜氧化铁酶）膜结合形式增加2-5倍，在成年大鼠中可见。由于刷边膜铜转运蛋白Ctrl没有改变表达水平，我们认为铜可能通过DMT1进入肠细胞。众所周知，铜和铁体内平衡之间存在联系，因为缺铜会导致贫血，而缺铁性贫血会导致体内铜水平升高。根据这些发现，我们假设慢性缺铁导致刷边铁转运蛋白dcytb和DMT1（也可能运输铜）的代偿性表达增加，通过铜atp酶增加铜的基底外侧出口，以及gpi锚定铜蓝蛋白的表达增加，所有这些可能协同作用以增强体内铁的输送。为了探索这种可能性，我们计划追求以下具体目标：1)解码铁对dcytb和DMT1的转录调节，2)表征铁缺乏时基底外侧铜atp酶活性和蛋白表达，以及表征铁缺乏大鼠十二指肠膜相关铜蓝蛋白的表达。总的来说，这些研究可能会增加对肠道铁吸收与体内铜稳态之间相互作用的理解，并将探索gpi锚定的铜蓝蛋白在肠道铁运输中的作用。

DESCRIPTION (provided by applicant): 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.