BackgroundBrain iron is an essential as well as a toxic redox active element. Physiological levels are not uniform among the different cell types. Besides the availability of quantitative methods, the knowledge about the brain iron lags behind. Thereby, disclosing the mechanisms of brain iron homeostasis helps to understand pathological iron-accumulations in diseased and aged brains. With our study we want to contribute closing the gap by providing quantitative data on the concentration and distribution of iron in neurons and glial cells in situ. Using a nuclear microprobe and scanning proton induced X-ray emission spectrometry we performed quantitative elemental imaging on rat brain sections to analyze the iron concentrations of neurons and glial cells.ResultsNeurons were analyzed in the neocortex, subiculum, substantia nigra and deep cerebellar nuclei revealing an iron level between $$(0.53\pm 2)$$(0.53±2) and $$(0.68\pm 2)\,\upmu \hbox {M}$$(0.68±2)μM. The iron concentration of neocortical oligodendrocytes is fivefold higher, of microglia threefold higher and of astrocytes twofold higher compared to neurons. We also analyzed the distribution of subcellular iron concentrations in the cytoplasm, nucleus and nucleolus of neurons. The cytoplasm contains on average 73% of the total iron, the nucleolus—although a hot spot for iron—due to its small volume only 6% of total iron. Additionally, the iron level in subcellular fractions were measured revealing that the microsome fraction, which usually contains holo-ferritin, has the highest iron content. We also present an estimate of the cellular ferritin concentration calculating $$133\pm 25$$133±25 ferritin molecules per $$\upmu \hbox {m}$$μm in rat neurons.ConclusionGlial cells are the most iron-rich cells in the brain. Imbalances in iron homeostasis that lead to neurodegeneration may not only be originate from neurons but also from glial cells. It is feasible to estimate the ferritin concentration based on measured iron concentrations and a reasonable assumptions on iron load in the brain.

中文翻译：

---

神经元和神经胶质细胞中的铁浓度以及对铁蛋白浓度的估计

背景脑铁是一种必需的，也是一种有毒的氧化还原活性元素。不同细胞类型的生理水平并不一致。除了定量方法的可用性外，关于脑铁的知识也落后了。因此，揭示脑铁稳态的机制有助于了解患病和衰老大脑中的病理性铁积累。通过我们的研究，我们希望通过提供原位神经元和神经胶质细胞中铁的浓度和分布的定量数据来缩小差距。我们使用核微探针和扫描质子诱导 X 射线发射光谱法对大鼠脑切片进行定量元素成像，以分析神经元和神经胶质细胞的铁浓度。黑质和小脑深部核显示铁水平介于 $$(0.53\pm 2)$$(0.53±2) 和 $$(0.68\pm 2)\,\upmu \hbox {M}$$(0.68±2) )μM。与神经元相比，新皮质少突胶质细胞的铁浓度高出五倍，小胶质细胞的铁浓度高出三倍，星形胶质细胞的铁浓度高出两倍。我们还分析了神经元细胞质、细胞核和核仁中亚细胞铁浓度的分布。细胞质平均含有总铁的 73%，核仁——虽然是铁的热点——因为其体积小，仅占总铁的 6%。此外，测量了亚细胞组分中的铁水平，表明通常含有全铁蛋白的微粒体组分具有最高的铁含量。我们还提供了细胞铁蛋白浓度的估计值，计算出大鼠神经元中每 $$\upmu\hbox {m}$$μm 25$$133±25 个铁蛋白分子。结论神经胶质细胞是最富含铁的细胞脑。导致神经变性的铁稳态失衡可能不仅来自神经元，也可能来自神经胶质细胞。根据测量的铁浓度和对大脑中铁负荷的合理假设来估计铁蛋白浓度是可行的。