Molecular Mechanisms of Intestinal Metal Ion Transport During Iron-Deficiency

描述(由申请人提供)：铁的动态平衡的总体控制发生在近端小肠上皮的运输步骤，在那里吸收被精确地调节以匹配身体铁损失。重要的是，肠道铁转运的紊乱与人类的几种重要疾病状态有关，包括慢性病贫血和血色素沉着症。缺铁时大鼠肠道铜转运增强，这可能是一种生理反应，与膳食铜在体内铁平衡的各个方面所起的作用有关。有趣的是，门克斯铜ATPase(Atpya)与二价金属转运蛋白I(DMTI)一起，在出生后不同年龄缺铁大鼠的十二指肠粘膜中被强烈诱导，DMTI可以运输铁和铜。因此，这项建议的总体目标是：1)确定DMTI和ATPTA在缺铁诱导铜运输中的作用；2)破译缺铁诱导DMTI和ATPTA的分子机制；3)确定铜对肠道跨上皮铁运输的分子机制的影响。这将通过利用细胞培养和啮齿动物模型的肠道铁运输来实现。具体目的I将验证DMTI和ATPTA的诱导是缺铁时跨上皮铜转运增加的原因的假设。铁和铜的运输研究和siRNA敲除将在我们的肠上皮细胞IEC-6细胞的体外模型中进行。一旦确定了在缺铁期间诱导铜运输的转运体(S)，我们将在体内缺铁模型中进行补充研究，包括野生型缺铁大鼠、贝尔格莱德(即DMTI缺乏)大鼠和Atpya基因敲除小鼠。特异性AIM 2，将检验DMTI和ATPTA在缺铁期间受不同分子机制调控的假说。将研究DMTI铁依赖的转录后调控(由3‘IRE介导)，并研究ATPTA在IEC-6细胞中的转录调控。最后，特定的AIM 3将检验这一假说，即在缺铁期间增加铜的运输功能，以增强肠道铁吸收的铜依赖方面。为了实现这一目标，将对缺铁缺铜大鼠分离的膜微囊中铁的转运进行研究，并测定肠细胞中的Hephestn活性和血清中的铜蓝蛋白活性。总体而言，这些研究将进一步定义在缺铁状态下促进肠道铁吸收的铜依赖过程。对这些关系的详细了解是至关重要的，因为肠道铁运输控制着全身铁的动态平衡。此外，这项拟议的研究是新颖的，因为到目前为止还没有关于缺铁期间肠细胞和肝脏铜水平增加的影响的研究报告。

DESCRIPTION (provided by applicant): The overall control of iron homeostasis occurs at the transport step in the epithelium of the proximal small bowel, where absorption is precisely regulated to match body iron losses. Importantly, perturbations in intestinal iron transport are associated with several important disease states in humans, including anemia of chronic disease and hemochromatosis. Intestinal copper transport is enhanced in rats during iron-deficiency, and this is likely a physiological response related to the role of dietary copper in various aspects of overall body iron homeostasis. Interestingly, the Menkes copper ATPase (Atpya) is strongly induced in the duodenal mucosa of iron-deprived rats at different postnatal ages along with Divalent Metal Transporter i (Dmti), which can transport iron and copper. Thus, the overall goals of this proposal are i) to determine the roles that Dmti and Atpya play in the induction of copper transport during iron-deprivation, 2) to decipher the molecular mechanisms of induction of Dmti and Atpya during iron-deprivation and 3) to determine the effect that copper has on molecular mechanisms of trans-epithelial iron transport in the intestine. This will be accomplished by utilizing cell culture and rodent models of intestinal iron transport. Specific AIM i will test the hypothesis that induction of Dmti and Atpya is responsible for increased transepithelial copper transport seen during iron-deprivation. Iron and copper transport studies and siRNA knockdowns will be performed in our in vitro model of the intestinal epithelium, the IEC-6 cells. Once the transporter(s) involved in the induction of copper transport during iron-deficiency have been identified, we will perform complementary studies in in vivo models of iron-deficiency, including wild-type, iron-deficient rats, Belgrade (i.e. Dmti-deficient) rats and Atpya knockout mice. Specific AIM 2, will test the hypothesis that Dmti and Atpya are regulated by distinct molecular mechanisms during iron-deficiency. Iron-dependent, post- transcriptional regulation of Dmti will be examined (mediated by the 3' IRE) and transcriptional regulation of Atpya in IEC-6 cells will be studied. Finally, specific AIM 3 will test the hypothesis that increased copper transport during iron deficiency functions to enhance copper-dependent aspects of intestinal iron absorption. To accomplish this goal, iron transport studies will be performed in membrane vesicles isolated from iron-deficient rats deprived of dietary copper, and hephaestin activity in enterocytes and ceruloplasmin activity in serum will be determined. Overall, these studies will allow further definition of the copper- dependent processes that are involved in enhancing intestinal iron absorption during states of iron- deficiency. A detailed understanding of these relationships is critical, as intestinal iron transport controls overall body iron homeostasis. Moreover, this proposed investigation is novel, as studies addressing the impact of increased enterocyte and liver copper levels during iron-deficiency have not been reported to date.