与系统性红斑狼疮疾病关联的基因TMEM187在线粒体铁代谢中的功能研究

TMEM187 is a gene known to be linked with systemic lupus erythematosus (SLE) and its biological function is currently unknown. This application proposes to investigate the role of TMEM187 we recently discovered in mitochondrial iron homeostasis. Disturbance of iron homeostasis could result in increase of free radicals and insufficient biogenesis of iron-sulfur clusters and heme, thereby leading to mitochondrial dysfunction. Thus, the intra-mitochondrial iron levels must be tightly regulated. At present, mitoferrin (MFRN1/2) is the only known protein that directly imports iron into mitochondria. ABCB10 is the other known factor that interacts with and therefore stabilizes MFRN1 to satisfy iron demand for red blood cell maturation. Very little is known about how non-red blood cells uptake iron. Our preliminary studies have shown that TMEM187 functions in mitochondrial iron uptake. We found that TMEM187 expression was drastically enhanced under iron deprived condition. Furthermore, overexpression of TMEM187 resulted in mitochondrial iron overload, suggesting that TMEM187 might function as a mitochondrial iron importer. This application aims to elucidate the molecular mechanism by which TMEM187 functions in mitochondrial iron uptake and to determine how the expression of TMEM187 is regulated by iron. We also propose to explore the in vivo role of TMEM187 in red blood cell maturation and/or other physiological processes. The outcomes of this application will expand current understanding of mitochondrial iron homeostasis. More importantly, it will also help to understand the etiology of SLE and provide invaluable treatment guidance.

TMEM187是一个与系统性红斑狼疮连锁的基因，其生理功能尚未明确。本项目拟研究该基因在线粒体铁稳态中的作用。铁稳态的失衡易导致氧自由基的增加或铁硫簇和血红素合成的不足，最终导致线粒体功能受损，因此线粒体内的铁含量必须被严格地调控。Mitoferrin（MFRN1/2）是唯一已知直接参与线粒体铁吸收的蛋白，ABCB10通过与MFRN1相互作用提高MFRN1的稳定性，由此满足红细胞发育时对铁的高需求。而对非红细胞的线粒体铁吸收还知之甚少。我们的前期研究发现TMEM187是一个线粒体膜蛋白，过表达导致线粒体铁过度积累，铁匮乏时表达量急剧提高。现有数据表明该分子很可能是线粒体的一个铁转运蛋白。本项目开展的TMEM187参与线粒体铁吸收的分子机理和调控机制，及其在体生理功能的研究成果将拓宽目前对线粒体铁稳态的认识，更重要的是对揭示系统性红斑狼疮的发病机理和临床治疗具有重要的指导意义和价值。

该项目拟对一个未知功能基因TMEM187对线粒体铁代谢和线粒体的功能影响展开研究。根据前期研究结果，申请者首次提出TMEM187可能是人源细胞线粒体铁代谢的一个关键因子，在线粒体铁吸收过程中起重要作用。过表达TMEM187增加了胞质和线粒体中铁的含量，但是激活了细胞铁饥饿信号，促进了TfR1的表达，增加了铁的摄取和储存，促进ferritin的表达和线粒体铁的摄入，破坏了铁的动态平衡；而敲减TMEM187同样促进了线粒体铁的吸收；令人惊奇的是TMEM187高表达量提高线粒体的铁含量是通过诱导线粒体内膜蛋白铁转运体MFRN1实现的，低表达提高线粒体的铁含量是通过诱导MFRN1的同源物MFRN2的表达实现的。另外我们还有三点结果是超出课题申请时的预测，值得展示：.1.TMEM187参与铁死亡的进程；.为了检测过表达TMEM187是否会促进肿瘤细胞的死亡，瞬时过表达TMEM187和转染对照质粒的N2a细胞悬液接种裸鼠，两周后观察肿瘤的形成，比较肿瘤形成的大小。结果表明，接种了过表达TMEM187的细胞形成的肿瘤明显小于对照组（见结果图6F），这一实验支持过表达TMEM187的细胞会诱导细胞死亡的结果，从而降低了细胞的成瘤性，延缓了肿瘤的形成。过表达TMEM187后可以显著性增加细胞内铁的含量，提高细胞氧化应激水平，铁死亡通路相关蛋白GPX4蛋白减少，从而引起脂氧合酶介导的脂质过氧化，在铁死亡中发挥关键作用。.2.TMEM187影响高尔基的功能；.研究结果表明，人源TMEM187是定位于高尔基体上的膜蛋白，TMEM187过表达能够破坏高尔基形态，蛋白组学结果显示TMEM187参与囊泡运输。.3.TMEM187参与红系细胞的分化。.K562细胞系是人的红白血病细胞系，可体外用于研究红系细胞的分化，敲除TMEM187后血红素的合成增加，血红蛋白的表达水平增高。.本课题的研究还在进一步的深入和扩展中。