锌转运蛋白ZIP在铁再循环中的作用及分子机制

Iron is an essential trace element required for human health. Imbalance of iron homeostasis is linked to diverse diseases. Iron metabolism related disorders are major health issues in the world. Our research group conducted studies in the field of iron recycling in macrophages, and discovered the membrane protein FPN1 as an iron exporter in macrophages (Blood, 2011; Hepatology, 2012). We further identified Mon1a as a novel gene in iron homeostasis via its regulation on FPN1 localization (Nature Genetics, 2007), and TRPML1 as an endolysosomal iron release channel (Nature, 2008). Nevertheless, these findings indicated the existence of unknown iron transport systems in macrophages. The zinc transporter ZIP has been suggested in the regulation of iron homeostasis. In order to investigate the function of ZIP, we established conditional knockout mice of the gene. Our preliminary studies of Zip macrophage knockout mice discovered significant disturbances of iron metabolism, together with defects in macrophage phagocytosis, suggesting an essential role of ZIP in iron homeostasis. Herein, we propose to systematically study the functional mechanisms of ZIP in iron recycling, with ZIP knockout mice and zebrafish model systems. We plan to conduct integrated research of ZIP’s function in iron recycling at multiple levels from cell, tissue to the whole system. The research findings from our project will be important for uncovering the mechanisms of iron homeostasis, as well as improving the therapeutic approaches of iron imbalance related disorders.

铁是人体必需微量元素，其稳态失衡引发多种疾病，倍受社会关注。我们课题组前期围绕巨噬细胞铁再循环开展了系统研究，发现膜蛋白FPN1是巨噬细胞铁外排蛋白（Blood,2011; Hepatology,2012），揭示新基因Mon1a通过影响FPN1调控铁稳态（Nature Genetics,2007），还发现溶酶体铁离子通道蛋白TRPML1（Nature, 2008）。但这些研究基础显示巨噬细胞还存在未知的铁离子进出系统。有研究提示锌转运体ZIP蛋白可参与铁稳态代谢。为深入研究ZIP功能，我们制备了其条件性基因敲除小鼠。发现Zip巨噬细胞基因敲除后，小鼠显现铁代谢紊乱及巨噬细胞功能障碍，提示ZIP参与机体铁代谢。本项目拟利用Zip基因敲除小鼠及多种实验体系，在细胞、组织及整体水平展开多层次整合研究，探讨ZIP在铁再循环中的功能机制，丰富铁稳态理论，为阐明铁失衡相关疾病的防治提供理论依据。

巨噬细胞是机体先天性免疫的重要组成细胞，有细胞吞噬、抗原提呈及细胞因子分泌等多种功能，并能通过吞噬衰老红细胞参与铁再循环，是研究机体免疫及铁代谢的重要对象。本项目前期数据提示锌转运蛋白Zip10的巨噬细胞条件性基因敲除小鼠出现了血清及组织低铁表型，因此初期目标为检测锌转运蛋白Zip10在巨噬细胞铁再循环中的作用机制。在深入研究过程中，发现Zip10巨噬细胞基因敲除小鼠的铁缺乏表型是基于机体巨噬细胞数目减少后铁重吸收受阻的继发现象。基于这一关键发现，深入研究Zip10调控巨噬细胞发育的分子机制，做出以下重要发现：1）Zip10条件性基因敲除小鼠在LPS炎症刺激下存活率较野生型升高，体内炎性细胞因子水平下降；2）Zip10条件性基因敲除小鼠巨噬细胞能正常分泌细胞因子，但该细胞数目显著减少；3）Zip10条件性基因敲除小鼠巨噬细胞内锌离子水平下降，同时细胞凋亡关键因子p53的蛋白稳定性升高；4）在巨噬细胞中同时敲除p53和Zip10后，小鼠巨噬细胞数目及LPS刺激后炎症反应均较Zip10巨噬细胞单敲小鼠显著回升；5）低锌条件下，野生型小鼠在炎症刺激后出现Zip10巨噬细胞基因敲除小鼠相似表型，且该表型能通过补锌挽救。基于这些发现，得出结论：Zip10通过改变巨噬细胞中锌水平并影响p53蛋白稳定性，从而调控炎症反应中巨噬细胞凋亡水平。本项目研究成果确认Zip10为首个巨噬细胞锌转运蛋白，并为炎症及败血病等疾病的防治提供了新靶点。该研究成果发表在国际期刊Proc Natl Acad Sci U S A (2017)。此外，在该基金的支持下，还研究了铁稳态与人群肥胖及妊娠期糖尿病的发病风险关联，膳食镁摄取与心血管疾病的发病风险关联，以及ZNT10调控机体锰离子稳态的分子机制等，研究结果分别发表在Obes Rev (2015), Asia Pac J Clin Nutr (2017), BMC Med (2016) 及PLoS Genet (2017) 上。