Background

Neuromelanin-pigmented neurons, which are highly susceptible to neurodegeneration in the Parkinson’s disease substantia nigra, harbour elevated iron levels in the diseased state. Whilst it is widely believed that neuronal iron is stored in an inert, ferric form, perturbations to normal metal homeostasis could potentially generate more reactive forms of iron capable of stimulating toxicity and cell death. However, non-disruptive analysis of brain metals is inherently challenging, since use of stains or chemical fixatives, for example, can significantly influence metal ion distributions and/or concentrations in tissues.

Aims

The aim of this study was to apply synchrotron soft x-ray spectromicroscopy to the characterisation of iron deposits and their local environment within neuromelanin-containing neurons of Parkinson’s disease substantia nigra.

Methods

Soft x-ray spectromicroscopy was applied in the form of Scanning Transmission X-ray Microscopy (STXM) to analyse resin-embedded tissue, without requirement for chemically disruptive processing or staining. Measurements were performed at the oxygen and iron K-edges in order to characterise both organic and inorganic components of anatomical tissue using a single label-free method.

Results

STXM revealed evidence for mixed oxidation states of neuronal iron deposits associated with neuromelanin clusters in Parkinson’s disease substantia nigra. The excellent sensitivity, specificity and spatial resolution of these STXM measurements showed that the iron oxidation state varies across sub-micron length scales.

Conclusions

The label-free STXM approach is highly suited to characterising the distributions of both inorganic and organic components of anatomical tissue, and provides a proof-of-concept for investigating trace metal speciation within Parkinson’s disease neuromelanin-containing neurons.

中文翻译：

---

通过同步加速器 X 射线光谱显微镜分析帕金森病脑组织中的神经元铁沉积。

背景

神经黑色素色素神经元对帕金森氏病黑质中的神经变性非常敏感，在患病状态下铁水平升高。虽然人们普遍认为神经元铁以惰性的三价铁形式储存，但对正常金属稳态的扰动可能会产生更多反应形式的铁，能够刺激毒性和细胞死亡。然而，脑金属的非破坏性分析本质上具有挑战性，因为例如使用染色剂或化学固定剂会显着影响金属离子在组织中的分布和/或浓度。

宗旨

本研究的目的是将同步加速器软 X 射线光谱显微镜应用于表征帕金森病黑质含神经黑色素神经元内的铁沉积物及其局部环境。

方法

以扫描透射 X 射线显微镜 (STXM) 的形式应用软 X 射线光谱显微镜来分析树脂包埋的组织，无需进行化学破坏性处理或染色。在氧和铁K边缘进行测量，以使用单一无标记方法表征解剖组织的有机和无机成分。

结果

STXM 揭示了与帕金森病黑质中神经黑色素簇相关的神经元铁沉积的混合氧化状态的证据。这些 STXM 测量的出色灵敏度、特异性和空间分辨率表明，铁氧化态在亚微米长度范围内变化。

结论

无标签 STXM 方法非常适合表征解剖组织的无机和有机成分的分布，并为研究帕金森氏病神经黑色素神经元内的痕量金属形态提供了概念验证。