Interaction of Transferrin-Endosomes with Mitochondria is Required for Iron Transport to Ferrochelatase in Erythroid Cells

未成熟红细胞的正常血红蛋白化需要铁（Fe）由血浆转铁蛋白（Tf）传递，由Tf受体（TfR）介导。在diferic -Tf与细胞表面的同源受体结合后，Tf- tfr复合物通过内吞作用被内化，铁通过内体酸化和Steap3还原从Tf中释放出来。Fe2+通过DMT1转运穿过内体膜。铁在细胞内的内体后路径是有争议的。普遍的观点认为，低分子量的中间物伴随铁从核内体转移到线粒体。然而，我们已经建立了一个概念，即在产生血红蛋白的细胞中，铁从内体机制直接传递到线粒体机制；我们已经为这种“吻了就跑”的模式提供了强有力的证据(1)。我们提出红系前体具有特殊的适应性，促进铁从内体到线粒体的高速率运输，以满足对血红素合成的极高需求。***本研究项目的最终目的是提高我们对红细胞铁和血红素代谢的认识。在三个具体目标中，我们提出：******1)确定在红细胞发育过程中参与内核-线粒体相互作用的分子伙伴；***2)检查TfR的胞质结构域是否也与线粒体相互作用；***3)识别决定tf -核内体与线粒体的附着/分离的信号。******我们将使用一系列分子和生化方法结合尖端技术来分析核内体和线粒体之间的相互作用，并确定参与这些相互作用的分子伙伴。******我们相信，我们的建议将为细胞内铁运输机制的“亲跑”假说提供强有力的支持，即含tf的核内体将其铁原子直接交给线粒体。这项研究不仅将增强我们对这一途径的理解，而且还将加强我们对细胞器细胞内运输的认识，这代表了细胞生物学中的“范式转变”。因此，这项研究将对加拿大的学术研究产生强烈的影响。******1。Hamdi等人。工商管理学报（英文版），2016

Normal hemoglobinization of immature red blood cells requires iron (Fe) delivered by plasma transferrin (Tf), mediated by Tf receptors (TfR). Following the binding of diferric-Tf to its cognate receptor on the cell surface, the Tf-TfR complexes are internalized via endocytosis, and Fe is released from Tf by endosomal acidification and reduction by Steap3. Fe2+ is transported across the endosomal membrane by DMT1. The post-endosomal path of Fe within cells is controversial. The prevailing opinion is that a low molecular weight intermediate chaperones Fe transfer from endosomes to mitochondria. However, we have built a concept that, in hemoglobin-producing cells, there is a direct relaying of Fe from the endosomal machinery to that of the mitochondria; we have provided strong evidence for this “kiss and run” model (1). We propose that erythroid precursors have special adaptations that facilitate the high rate of iron transport from endosomes to mitochondria to meet the exceptionally high demand for heme synthesis.***The ultimate goal of this research project is to enhance our knowledge regarding iron and heme metabolism in erythroid cells. In three Specific Aims, we propose to:******1) Identify of the molecular partners involved in the endosme-mitochondria interaction in developing RBC;***2) Examine whether the cytoplasmic domain of TfR also interact with mitochondria;***3) Indentify the signal(s) that determine the attachment/detachment of Tf-endosome with/from mitochondria.******We will use a series of molecular and biochemical approaches in combination with cutting edge technology to analyze the interaction between endosomes and mitochondria and identify the molecular partners involved in these interactions.******We are confident that our proposal will provide strong support for the “kiss-and-run” hypothesis of the intracellular iron trafficking mechanism whereby Tf-containing endosomes cede their iron atoms directly to mitochondria. This investigation will not only enhance our understanding of this pathway, but will also strengthen our knowledge about intracellular trafficking of organelles that represents a “paradigm shift” in cell biology. Therefore, this study will have a strong impact on the academic research in Canada.******1. Hamdi et al. BBA 1863:2859, 2016