Mobilization of iron from ferritin: new steps and details
Mobilization of iron from ferritin: new steps and details
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DOI：
10.1039/c7mt00284j
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发表时间：
2018-01-01
期刊：
影响因子：
3.4
通讯作者：
Linder, M. C.
中科院分区：
文献类型：
--
作者：
La, A.;Nguyen, T.;Linder, M. C.
许多证据表明，储存在铁蛋白中的铁是通过溶酶体中的蛋白质降解而动员起来的，但对这一过程的关注一直存在，并且缺乏其各方面的机制细节。在这里提出的研究中，铁-59标记的铁蛋白是通过放射性标记的铁预加载肝细胞（HepG2）诱导的。将这些细胞置于含有去铁胺的培养基中导致铁蛋白- fe -59的损失，但添加高浓度的还原剂或调节内部GSH浓度未能改变铁蛋白- fe -59的释放速率。共聚焦显微镜显示，缺铁增加了铁蛋白进入溶酶体的运动，当溶酶体蛋白水解被抑制时，观察到铁蛋白的过度积累。它还导致DMT1快速移动到溶酶体，这被巴菲霉素抑制。从纯化的大鼠肝/脾铁蛋白中分离得到的水合铁晶体在pH 5和7下被GSH、抗坏血酸盐、柠檬酸盐和从肝脏和J774a中获得的溶酶体液溶解。1巨噬细胞。DMT1/Nramp2的抑制和Nramp1的siRNA敲低均减少了Fe-59从溶酶体向胞浆的转移；小鼠肝细胞特异性敲除DMT1可阻止肝脏对EPO治疗的铁释放，但不抑制溶酶体铁蛋白降解。我们得出结论，铁蛋白-铁的动员不是通过细胞中还原剂/螯合剂浓度的变化发生的，而是通过铁蛋白和DMT1向溶酶体的协调运动发生的。在溶酶体中，铁蛋白降解暴露的水合铁晶体溶解在溶酶体液中，还原的铁通过肝细胞中的DMT1和巨噬细胞中的DMT1和Nramp1运输回细胞质，然后释放到血液中或储存在铁蛋白中。
Much evidence indicates that iron stored in ferritin is mobilized through protein degradation in lysosomes, but concerns about this process have lingered, and the mechanistic details of its aspects are lacking. In the studies presented here, Fe-59-labeled ferritin was induced by preloading hepatic (HepG2) cells with radiolabeled Fe. Placing these cells in a medium containing desferrioxamine resulted in the loss of ferritin-Fe-59, but adding high concentrations of reducing agents or modulating the internal GSH concentration failed to alter the rates of ferritin-Fe-59 release. Confocal microscopy showed that Fe deprivation increased the movement of ferritin into lysosomes and hyperaccumulation was observed when lysosomal proteolysis was inhibited. It also resulted in the rapid movement of DMT1 to lysosomes, which was inhibited by bafilomycin. Ferrihydrite crystals isolated from purified rat liver/spleen ferritin were solubilized at pH 5 and 7 by GSH, ascorbate, citrate and lysosomal fluids obtained from livers and J774a. 1 macrophages. The inhibition of DMT1/Nramp2 and siRNA knockdown of Nramp1 each reduced the transfer of Fe-59 from lysosomes to the cytosol; and hepatocyte-specific knockout of DMT1 in mice prevented the release of Fe from the liver responding to EPO treatment, but did not inhibit lysosomal ferritin degradation. We conclude that ferritin-Fe mobilization does not occur through changes in cellular concentrations of reducing/chelating agents but by the coordinated movement of ferritin and DMT1 to lysosomes, where the ferrihydrite crystals exposed by ferritin degradation dissolve in the lysosomal fluid, and the reduced iron is transported back to the cytosol via DMT1 in hepatocytes, and by both DMT1 and Nramp1 in macrophages, prior to release into the blood or storage in ferritin.