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

正常的未成熟红细胞的血红素化需要铁(Fe)由血浆转铁蛋白(Tf)传递，由TfR(Tfr)介导。二铁-转铁蛋白与细胞表面的同源受体结合后，转铁蛋白-转铁蛋白受体复合体通过内吞作用内化，铁通过内体酸化和Steap3还原从转铁蛋白中释放出来。Fe2+通过DMT1跨膜转运。铁在细胞内的内吞后途径是有争议的。流行的观点认为，低分子量的中间伴侣铁从内体转移到线粒体。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，铁从内体机械直接传递到线粒体；我们为这种“接吻就跑”模式提供了强有力的证据(1)。我们认为，红系前体具有特殊的适应性，促进了铁从内体到线粒体的高速率运输，以满足对血红素合成的异常高的需求。*本研究项目的最终目标是加强我们对红系细胞中铁和血红素代谢的了解。在三个具体目标中，我们建议：*1)确定参与红细胞发育过程中内切酶-线粒体相互作用的分子伙伴；*2)检测TFR的细胞质结构域是否也与线粒体相互作用；*3)确定决定TF-内小体与线粒体附着/脱离的信号(S)。*我们将结合尖端技术，使用一系列分子和生化方法来分析内小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“接吻即跑”假说提供强有力的支持，即含有TF的内体将其铁原子直接让给线粒体。这项研究不仅将加强我们对这一途径的理解，还将加强我们对细胞器在细胞内的运输的了解，这代表着细胞生物学中的一种“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。BBA 1863：2859,2016

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