Kakhlon Or, Cabantchik Z Ioav
Department of Biological Chemistry, Institute of Life Sciences, Hebrew University, Jerusalem, Israel.
Free Radic Biol Med. 2002 Oct 15;33(8):1037-46. doi: 10.1016/s0891-5849(02)01006-7.
The cellular labile iron pool (LIP) is a pool of chelatable and redox-active iron, which is transitory and serves as a crossroad of cell iron metabolism. Various attempts have been made to analyze the levels of LIP following cell disruption. The chemical identity of this pool has remained poorly characterized due to the multiplicity of iron ligands present in cells. However, the levels of LIP recently have been assessed with novel nondisruptive techniques that rely on the application of fluorescent metalosensors. Methodologically, a fluorescent chelator loaded into living cells binds to components of the LIP and undergoes stoichiometric fluorescence quenching. The latter is revealed and quantified in situ by addition of strong permeating iron chelators. Depending on the intracellular distribution of the sensing and chelating probes, LIP can be differentially traced in subcellular structures, allowing the dynamic assessment of its levels and roles in specific cell compartments. The labile nature of LIP was also revealed by its capacity to promote formation of reactive oxygen species (ROS), whether from endogenous or exogenous redox-active sources. LIP and ROS levels were shown to follow similar "rise and fall" patterns as a result of changes in iron import vs. iron chelation or ferritin (FT) degradation vs. ferritin synthesis. Those patterns conform with the accepted role of LIP as a self-regulatory pool that is sensed by cytosolic iron regulatory proteins (IRPs) and feedback regulated by IRP-dependent expression of iron import and storage machineries. However, LIP can also be modulated by biochemical mechanisms that override the IRP regulatory loops and, thereby, contribute to basic cellular functions. This review deals with novel methodologies for assessing cellular LIP and with recent studies in which changes in LIP and ROS levels played a determining role in cellular processes.
细胞内不稳定铁池（LIP）是一组可螯合且具有氧化还原活性的铁，它具有短暂性，是细胞铁代谢的一个交叉点。人们已进行了各种尝试来分析细胞破坏后LIP的水平。由于细胞中存在多种铁配体，这个铁池的化学特性仍未得到很好的表征。然而，最近已使用依赖荧光金属传感器应用的新型非破坏性技术来评估LIP的水平。从方法学上讲，加载到活细胞中的荧光螯合剂与LIP的成分结合并发生化学计量的荧光猝灭。通过添加强渗透性铁螯合剂可原位揭示并定量后者。根据传感和螯合探针的细胞内分布，可以在亚细胞结构中对LIP进行差异追踪，从而动态评估其在特定细胞区室中的水平和作用。LIP促进活性氧（ROS）形成的能力也揭示了其不稳定的性质，无论ROS是来自内源性还是外源性氧化还原活性源。由于铁输入与铁螯合的变化或铁蛋白（FT）降解与铁蛋白合成的变化，LIP和ROS水平呈现出相似的“上升和下降”模式。这些模式符合LIP作为自我调节池的公认作用，即由胞质铁调节蛋白（IRP）感知，并通过IRP依赖的铁输入和储存机制的表达进行反馈调节。然而，LIP也可以通过超越IRP调节环的生化机制进行调节，从而有助于基本的细胞功能。本综述涉及评估细胞LIP的新方法以及最近的研究，其中LIP和ROS水平的变化在细胞过程中起决定性作用。
