Department of Anatomy and Neurobiology, Medical College of Virginia Campus of Virginia Commonwealth University, Post Office Box 980709, Richmond, VA, 23298-0709, USA.
Acta Neuropathol. 2015 Feb;129(2):317-32. doi: 10.1007/s00401-014-1376-x. Epub 2014 Dec 21.
Injured axons with distinct morphologies have been found following mild traumatic brain injury (mTBI), although it is currently unclear whether they reflect varied responses to the injury or represent different stages of progressing pathology. This complicates evaluation of therapeutic interventions targeting axonal injury. To address this issue, we assessed axonal injury over time within a well-defined axonal population, while also evaluating mitochondrial permeability transition as a therapeutic target. We utilized mice expressing yellow fluorescent protein (YFP) in cortical neurons which were crossed with mice which lacked Cyclophilin D (CypD), a positive regulator of mitochondrial permeability transition pore opening. Their offspring were subjected to mTBI and the ensuing axonal injury was assessed using YFP expression and amyloid precursor protein (APP) immunohistochemistry, visualized by confocal and electron microscopy. YFP(+) axons initially developed a single, APP(+), focal swelling (proximal bulb) which progressed to axotomy. Disconnected axonal segments developed either a single bulb (distal bulb) or multiple bulbs (varicosities), which were APP(-) and whose ultrastructure was consistent with ongoing Wallerian degeneration. CypD knock-out failed to reduce proximal bulb formation but decreased the number of distal bulbs and varicosities, as well as a population of small, APP(+), callosal bulbs not associated with YFP(+) axons. The observation that YFP(+) axons contain several pathological morphologies points to the complexity of traumatic axonal injury. The fact that CypD knock-out reduced some, but not all, subtypes highlights the need to appropriately characterize injured axons when evaluating potential neuroprotective strategies.
在轻度创伤性脑损伤（mTBI）后，已经发现了具有明显形态的损伤轴突，尽管目前尚不清楚它们是否反映了对损伤的不同反应，或者代表了进行性病理的不同阶段。这使得评估针对轴突损伤的治疗干预措施变得复杂。为了解决这个问题，我们在一个明确的轴突群体中随时间评估轴突损伤，同时评估线粒体通透性转换作为治疗靶点。我们利用在皮质神经元中表达黄色荧光蛋白（YFP）的小鼠与缺乏细胞色素 P450 D（CypD）的小鼠杂交，CypD 是线粒体通透性转换孔开放的正调节剂。它们的后代接受 mTBI，并使用 YFP 表达和淀粉样前体蛋白（APP）免疫组织化学评估随后的轴突损伤，通过共聚焦和电子显微镜进行可视化。YFP(+)轴突最初发展为单个 APP(+)局灶性肿胀（近端球），随后发展为轴突切断。分离的轴突段形成单个球（远端球）或多个球（血管球），其为 APP(-)，其超微结构与进行性沃勒变性一致。CypD 敲除未能减少近端球的形成，但减少了远端球和血管球的数量，以及与 YFP(+)轴突无关的一小群 APP(+)胼胝体球。观察到 YFP(+)轴突包含几种病理形态，这表明创伤性轴突损伤的复杂性。CypD 敲除减少了一些，但不是所有，亚型突出了在评估潜在的神经保护策略时，适当表征损伤轴突的必要性。
