Molecular Mechanisms of Intestinal Metal Ion Transport During Iron-Deficiency

描述（由申请人提供）：铁稳态的总体控制发生在近端小肠上皮的转运步骤，其中吸收被精确调节以匹配身体铁损失。重要的是，肠道铁转运的扰动与人类的几种重要疾病状态相关，包括慢性疾病贫血和血色病。在缺铁的大鼠中，肠道铜转运增强，这可能是与膳食铜在全身铁稳态的各个方面的作用相关的生理反应。有趣的是，Menkes铜ATP酶（Atpya）在不同出生后年龄的铁剥夺大鼠的十二指肠粘膜中强烈诱导，沿着二价金属转运体i（Dmti），其可以转运铁和铜。因此，该提议的总体目标是i）确定Dmti和Atpya在铁剥夺期间诱导铜转运中发挥的作用，2）破译铁剥夺期间诱导Dmti和Atpya的分子机制，以及3）确定铜对肠中跨上皮铁转运的分子机制的影响。这将通过利用细胞培养和肠道铁转运的啮齿动物模型来实现。特异性AIM i将检验Dmti和Atpya的诱导是铁剥夺期间观察到的增加的跨上皮铜转运的原因的假设。铁和铜转运研究和siRNA敲除将在我们的肠上皮细胞的体外模型IEC-6细胞中进行。一旦铁缺乏期间参与诱导铜转运的转运蛋白被确定，我们将在体内铁缺乏模型中进行补充研究，包括野生型铁缺乏大鼠、Belgrade（即Dmti缺乏）大鼠和Atpya敲除小鼠。具体的目的2，将测试的假设，Dmti和Atpya由不同的分子机制，在缺铁调节。将检查Dmti的铁依赖性转录后调节（由3' IRE介导），并将研究IEC-6细胞中Atpya的转录调节。最后，特定的AIM 3将测试这一假设，即在缺铁期间增加铜转运的功能，以增强肠道铁吸收的铜依赖方面。为了实现这一目标，铁转运研究将在膜囊泡中进行，膜囊泡分离自缺乏膳食铜的缺铁大鼠，并测定肠上皮细胞中的肝啡肽活性和血清中的铜蓝蛋白活性。总的来说，这些研究将允许进一步定义在缺铁状态期间参与增强肠铁吸收的铜依赖性过程。对这些关系的详细了解是至关重要的，因为肠道铁转运控制着整个身体的铁稳态。此外，这项拟议的研究是新颖的，因为迄今为止还没有关于缺铁期间肠上皮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.