Heterogeneity of ferrous iron-containing endolysosomes and effects of endolysosome iron on endolysosome numbers, sizes, and localization patterns.

Endolysosomes are key regulators of iron metabolism and are central to iron trafficking and redox signaling. Iron homeostasis is linked to endolysosome acidity and inhibition of endolysosome acidity triggers iron dysregulation. Because of the physiological importance and pathological relevance of ferrous iron (Fe2+), we determined levels of Fe2+ specifically and quantitatively in endolysosomes as well as the effects of Fe2+ on endolysosome morphology, distribution patterns, and function. The fluorescence dye FeRhoNox-1 was specific for Fe2+ and localized to endolysosomes in U87MG astrocytoma cells and primary rat cortical neurons; in U87MG cells the endolysosome concentration of Fe2+ ([Fe2+]el) was 50.4 μM in control cells, 73.6 μM in ferric ammonium citrate (FAC) treated cells, and 12.4 μM in cells treated with the iron chelator deferoxamine (DFO). Under control conditions, in primary rat cortical neurons, [Fe2+]el was 32.7 μM. Endolysosomes containing the highest levels of Fe2+ were located perinuclearly. Treatment of cells with FAC resulted in endolysosomes that were less acidic, increased in numbers and sizes, and located further from the nucleus; opposite effects were observed for treatments with DFO. Thus, FeRhoNox-1 is a useful probe for the study of endolysosome Fe2+, and much more work is needed to understand better the physiological significance and pathological relevance of endolysosomes classified according to their heterogeneous iron content.

内溶酶体是铁代谢的关键调节因子，对铁运输和氧化还原信号传导至关重要。铁稳态与内溶酶体的酸性相关，内溶酶体酸性的抑制会引发铁失调。由于亚铁离子（Fe²⁺）的生理重要性和病理相关性，我们专门定量测定了内溶酶体中的Fe²⁺水平，以及Fe²⁺对内溶酶体形态、分布模式和功能的影响。荧光染料FeRhoNox - 1对Fe²⁺具有特异性，定位于U87MG星形细胞瘤细胞和原代大鼠皮质神经元的内溶酶体中；在U87MG细胞中，对照细胞内溶酶体的Fe²⁺浓度（[Fe²⁺]el）为50.4 μM，柠檬酸铁铵（FAC）处理的细胞中为73.6 μM，铁螯合剂去铁胺（DFO）处理的细胞中为12.4 μM。在对照条件下，原代大鼠皮质神经元中的[Fe²⁺]el为32.7 μM。含有最高水平Fe²⁺的内溶酶体位于核周。用FAC处理细胞导致内溶酶体酸性降低、数量和大小增加，且离细胞核更远；用DFO处理则观察到相反的效果。因此，FeRhoNox - 1是研究内溶酶体Fe²⁺的有用探针，需要更多的工作来更好地理解根据其不同铁含量分类的内溶酶体的生理意义和病理相关性。