Pantazopoulos Harry, Hossain Nayeem Mubarak, Chelini Gabriele, Durning Peter, Barbas Helen, Zikopoulos Basilis, Berretta Sabina
Department of Psychiatry and Program in Neuroscience, University of Mississippi Medical Center, Jackson, MS, United States.
Department of Health Sciences, Boston University, Boston, MA, United States.
Front Integr Neurosci. 2022 Jul 6;16:934764. doi: 10.3389/fnint.2022.934764. eCollection 2022.
Mounting evidence supports a key involvement of the chondroitin sulfate proteoglycans (CSPGs) NG2 and brevican (BCAN) in the regulation of axonal functions, including axon guidance, fasciculation, conductance, and myelination. Prior work suggested the possibility that these functions may, at least in part, be carried out by specialized CSPG structures surrounding axons, termed axonal coats. However, their existence remains controversial. We tested the hypothesis that NG2 and BCAN, known to be associated with oligodendrocyte precursor cells, form axonal coats enveloping myelinated axons in the human brain. In tissue blocks containing the mediodorsal thalamic nucleus (MD) from healthy donors ( = 5), we used dual immunofluorescence, confocal microscopy, and unbiased stereology to characterize BCAN and NG2 immunoreactive (IR) axonal coats and measure the percentage of myelinated axons associated with them. In a subset of donors ( = 3), we used electron microscopy to analyze the spatial relationship between axons and NG2- and BCAN-IR axonal coats within the human MD. Our results show that a substantial percentage (∼64%) of large and medium myelinated axons in the human MD are surrounded by NG2- and BCAN-IR axonal coats. Electron microscopy studies show NG2- and BCAN-IR axonal coats are interleaved with myelin sheets, with larger axons displaying greater association with axonal coats. These findings represent the first characterization of NG2 and BCAN axonal coats in the human brain. The large percentage of axons surrounded by CSPG coats, and the role of CSPGs in axonal guidance, fasciculation, conductance, and myelination suggest that these structures may contribute to several key axonal properties.
越来越多的证据支持硫酸软骨素蛋白聚糖(CSPG)NG2和短蛋白聚糖(BCAN)在轴突功能调节中起关键作用,包括轴突导向、成束、传导和髓鞘形成。先前的研究表明,这些功能可能至少部分由轴突周围的特殊CSPG结构(称为轴突被膜)来执行。然而,它们的存在仍存在争议。我们检验了这样一个假设,即已知与少突胶质前体细胞相关的NG2和BCAN在人脑中形成包裹有髓鞘轴突的轴突被膜。在来自健康供体(n = 5)的包含丘脑背内侧核(MD)的组织块中,我们使用双重免疫荧光、共聚焦显微镜和无偏立体学来表征BCAN和NG2免疫反应性(IR)轴突被膜,并测量与之相关的有髓鞘轴突的百分比。在一部分供体(n = 3)中,我们使用电子显微镜来分析人MD内轴突与NG2和BCAN-IR轴突被膜之间的空间关系。我们的结果表明,人MD中相当比例(约64%)的大中型有髓鞘轴突被NG2和BCAN-IR轴突被膜所包围。电子显微镜研究表明,NG2和BCAN-IR轴突被膜与髓鞘板交错,较大的轴突与轴突被膜的关联更大。这些发现首次对人脑中的NG2和BCAN轴突被膜进行了表征。被CSPG被膜包围的轴突比例很高,以及CSPG在轴突导向、成束、传导和髓鞘形成中的作用表明,这些结构可能对几种关键的轴突特性有贡献。