Mechanisms and Regulation of Brain Iron Uptake

描述(由申请者提供)：通常，但错误的是，我们认为我们了解铁是如何进入大脑的。现有模式的问题在于，它认为形成血脑屏障的内皮细胞仅仅是铁与转铁蛋白结合的管道。这一模式在多个方面存在重大缺陷，但最值得注意的是，它没有考虑到内皮细胞的铁需求，也没有考虑到调节大脑铁摄取的机制。这一建议的概念框架是，血脑屏障的内皮细胞远不是一个简单的管道，而是调节大脑铁代谢的焦点。我们提出了体内和细胞培养两种方法来研究脑铁摄取的动力学。我们推测，血脑屏障内皮细胞储存的铁可以在细胞外液中发现的外部因素的反应下释放到大脑中；因此，第一次展示了铁进入大脑的调节系统。因此，在完成拟议的研究后，我们将建立一个重要的和范式转变的概念，即内皮细胞控制铁进入大脑的途径，以响应他们的细胞外环境。此外，这一建议将对现有的脑铁转运范式做出以下具体的新贡献：(I)增加铁转运的新机制(Ii)展示通过铁蛋白从内皮细胞释放非转铁蛋白结合的铁，膜结合铁输出蛋白(Iii)揭示内皮细胞铁释放的调节(Iv)揭示内皮细胞储存铁，根据脑脊液或细胞外液中蛋白质水平(V)的变化，提示内皮细胞内转铁蛋白受体的调节是对细胞内铁池的响应，表明形成血脑屏障的内皮细胞的铁含量是转铁蛋白介导的脑铁摄取的调节部位。此外，拟议的研究将扩大我们对微血管中铁管理蛋白质谱动态的了解，这将为人类微血管研究提供信息，例如我们最近在不宁腿综合征患者微血管系统中的发现，或者尽管血液学参数得到解决，但与缺铁相关的脑脊液蛋白质谱的长期变化。因此，本文提出的研究对于我们了解神经疾病中微血管和脑脊液中改变的轮廓状态的功能意义是必不可少的。最重要的是，这些研究旨在了解大脑铁摄取的调节以及这些系统对释放和运输的适应性。内皮细胞对脑源性信号做出反应的适应性系统的存在是脑铁运输的一个全新概念，将影响发育性铁缺乏症和涉及脑铁稳态受损的成人神经疾病的治疗理念。

DESCRIPTION (provided by applicant): It is commonly, but wrongly, assumed that we understand how iron gets into the brain. The problem with the existing paradigm is that it holds that the endothelial cells forming the blood-brain barrier serve simply as a conduit through which iron bound to transferrin passes. This paradigm is significantly flawed in multiple points but most notably it fails to account for the iron requirements of the endothelial cells or for a mechanism for regulating brain iron uptake. The conceptual framework for this proposal is that the endothelial cells of the BBB, far from serving as a simple conduit, are the focal point for the regulation for cerebral iron metabolism. We propose both in vivo and cell culture approaches to investigate the dynamics of brain iron uptake. We postulate that BBB endothelial cells store iron that can be released into the brain in response to external factors that are found in the extracellular fluid; thus for the first time demonstrating a regulatory system for movement of iron into the brain. Thus, upon completion of the proposed studies we will establish the significant and paradigm shifting concept that the endothelial cells control access of iron to the brain in response to their extracellular environment. In addition, this proposal will make the following specific new contributions to the existing paradigm for brain iron transport (i) add a novel mechanism for iron transport (ii) demonstrate non-transferrin-bound iron release from endothelial cells via ferroportin, a membrane-bound iron export protein (iii) reveal regulation of iron release from endothelial cells (iv) reveal endothelial cells store iron, which can be released in response to levels of proteins in the CSF or extracellular fluid (v) reveal that regulation of transferrin receptors in endothelial cells are responsive to the intracellular iron pool indicating that the iron content of the endothelial cells forming the BBB is the site at which transferrin mediated brain iron uptake is regulated. Moreover, the proposed studies will expand our knowledge of the dynamics of the iron management protein profiles in the microvasculature which will inform studies on human microvasculature such as our recent findings in the microvasculature of individuals with Restless Legs syndrome or the long-term changes in CSF protein profiles associated with iron deficiency despite the resolution of hematologic parameters. Thus, the studies proposed herein are essential to inform us about the functional significance of the altered profile status in the microvasculature and CSF in neurological disease. Most importantly, the studies are designed to understand the regulation of brain iron uptake and the adaptability of the systems for release and transport. The existence of an adaptive system in endothelial cells that responds to brain-derived signals is a completely novel concept for brain iron transport and will impact treatment concepts for developmental iron deficiency and adult neurological disorders involving impaired brain iron homeostasis.