Division of Neuropathology, Department of Pathology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205,
Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and.
J Neurosci. 2018 Apr 18;38(16):4031-4047. doi: 10.1523/JNEUROSCI.2343-17.2018. Epub 2018 Mar 22.
Traumatic axonal injury (TAI) is a common neuropathology in traumatic brain injury and is featured by primary injury to axons. Here, we generated TAI with impact acceleration of the head in male transgenic mice in which specific populations of neurons and their axons are labeled with yellow fluorescent protein. This model results in axonal lesions in multiple axonal tracts along with blood-brain barrier disruption and neuroinflammation. The corticospinal tract, a prototypical long tract, is severely affected and is the focus of this study. Using optimized CLARITY at single-axon resolution, we visualized the entire corticospinal tract volume from the pons to the cervical spinal cord in 3D and counted the total number of axonal lesions and their progression over time. Our results divulged the presence of progressive traumatic axonopathy that was maximal at the pyramidal decussation. The perikarya of injured corticospinal neurons atrophied, but there was no evidence of neuronal cell death. We also used CLARITY at single-axon resolution to explore the role of the NMNAT2-SARM1 axonal self-destruction pathway in traumatic axonopathy. When we interfered with this pathway by genetically ablating SARM1 or by pharmacological strategies designed to increase levels of Nicotinamide (Nam), a feedback inhibitor of SARM1, we found a significant reduction in the number of axonal lesions early after injury. Our findings show that high-resolution neuroanatomical strategies reveal important features of TAI with biological implications, especially the progressive axonopathic nature of TAI and the role of the NMNAT2-SARM1 pathway in the early stages of axonopathy. In the first systematic application of novel high-resolution neuroanatomical tools in neuropathology, we combined CLARITY with 2-photon microscopy, optimized for detection of single axonal lesions, to reconstruct the injured mouse brainstem in a model of traumatic axonal injury (TAI) that is a common pathology associated with traumatic brain injury. The 3D reconstruction of the corticospinal tract at single-axon resolution allowed for a more advanced level of qualitative and quantitative understanding of TAI. Using this model, we showed that TAI is an axonopathy with a prominent role of the NMNAT2-SARM1 molecular pathway, that is also implicated in peripheral neuropathy. Our results indicate that high-resolution anatomical models of TAI afford a level of detail and sensitivity that is ideal for testing novel molecular and biomechanical hypotheses.
创伤性轴索损伤（TAI）是创伤性脑损伤中的一种常见神经病理学，其特征是轴索的原发性损伤。在这里，我们使用头部撞击产生的加速度在雄性转基因小鼠中产生 TAI，其中特定神经元及其轴突群体用黄色荧光蛋白标记。该模型导致多个轴突束中的轴突损伤，同时伴有血脑屏障破坏和神经炎症。皮质脊髓束是一种典型的长束，是本研究的重点。使用优化的 CLARITY 进行单轴突分辨率，我们在 3D 中可视化了从脑桥到颈脊髓的整个皮质脊髓束体积，并计算了轴突损伤的总数及其随时间的进展。我们的结果揭示了渐进性创伤性轴突病的存在，在锥体交叉处达到最大值。受伤的皮质脊髓神经元的胞体萎缩，但没有神经元细胞死亡的证据。我们还使用单轴突分辨率的 CLARITY 来探索 NMNAT2-SARM1 轴突自毁途径在创伤性轴突病中的作用。当我们通过基因敲除 SARM1 或通过旨在增加烟酰胺（Nam）水平的药理学策略干扰这条途径时，Nam 是 SARM1 的反馈抑制剂，我们发现受伤后早期轴突损伤的数量明显减少。我们的发现表明，高分辨率神经解剖学策略揭示了 TAI 的重要特征，具有生物学意义，特别是 TAI 的渐进性轴突病性质以及 NMNAT2-SARM1 途径在轴突病早期的作用。在神经病理学中首次系统应用新型高分辨率神经解剖学工具，我们将 CLARITY 与 2 光子显微镜相结合，优化用于检测单轴突损伤，以重建创伤性轴索损伤（TAI）模型中的损伤小鼠脑干，TAI 是一种与创伤性脑损伤相关的常见病理学。在单轴突分辨率下对皮质脊髓束进行 3D 重建，使我们能够更深入地了解 TAI 的定性和定量。使用该模型，我们表明 TAI 是一种轴突病，NMNAT2-SARM1 分子途径起重要作用，该途径也与周围神经病有关。我们的结果表明，TAI 的高分辨率解剖模型提供了一种细节和敏感性水平，非常适合测试新的分子和生物力学假设。
