Hu Youli, Butts Thomas, Poopalasundaram Subathra, Graham Anthony, Bouloux Pierre-Marc
Department of Anesthesiology, The First Affiliated Hospital of Nanjing Medical University/Jiangsu Province Hospital, Nanjing, China.
Centre for Neuroendocrinology, UCL Medical School, London, UK.
Eur J Neurosci. 2019 Nov;50(9):3472-3486. doi: 10.1111/ejn.14483. Epub 2019 Jul 4.
Olfactory ensheathing cells (OECs) are a specialized class of glia, wrapping around olfactory sensory axons that target the olfactory bulb (OB) and cross the peripheral nervous system/central nervous system boundary during development and continue to do so post-natally. OEC subpopulations perform distinct subtype-specific functions dependent on their maturity status. Disrupted OEC development is thought to be associated with abnormal OB morphogenesis, leading to anosmia, a defining characteristic of Kallmann syndrome. Hence, anosmin-1 encoded by Kallmann syndrome gene (KAL-1) might modulate OEC differentiation/maturation in the OB. We performed in ovo electroporation of shRNA in the olfactory placode to knock-down kal in chick embryos, resulting in abnormal OB morphogenesis and loss of olfactory sensory axonal innervation into OB. BLBP-expressing OECs appeared to form a thinner and poorly organized outmost OB layer where SOX10 expressing OECs were completely absent with emergence of GFAP-expressing OECs. Furthermore, in embryonic day 10 chick OB explant cultures, GFAP expression in OECs accumulating along the OB nerve layers was dramatically reduced by recombinant anosmin-1. We then purified immature OECs from embryonic day 10 chick OB. These cells express GFAP after 7 days in vitro, exhibiting a multipolar morphology. Overexpression of chick anosmin, exogenous anosmin-1 or FGF2 could inhibit GFAP expression with cells presenting elongated morphology, which was blocked by the FGF receptor inhibitor Su5402. These data demonstrate that anosmin-1 functions via FGF signalling in regulating OEC maturation, thereby providing a permissive glial environment for axonal innervation into the OB during development.
嗅鞘细胞（OECs）是一类特殊的神经胶质细胞，包裹着靶向嗅球（OB）的嗅觉感觉轴突，在发育过程中穿过外周神经系统/中枢神经系统边界，并且在出生后仍持续如此。OEC亚群根据其成熟状态执行不同的亚型特异性功能。OEC发育中断被认为与OB形态异常有关，导致嗅觉丧失，这是卡尔曼综合征的一个典型特征。因此，由卡尔曼综合征基因（KAL-1）编码的anosmin-1可能调节OB中OEC的分化/成熟。我们在鸡胚的嗅基板中进行了shRNA的卵内电穿孔，以敲低kal，导致OB形态异常以及进入OB的嗅觉感觉轴突神经支配丧失。表达BLBP的OEC似乎形成了一层更薄且组织不良的OB最外层，其中表达SOX10的OEC完全缺失，同时出现了表达GFAP的OEC。此外，在胚胎第10天的鸡OB外植体培养物中，重组anosmin-1显著降低了沿OB神经层聚集的OEC中GFAP的表达。然后我们从胚胎第10天的鸡OB中纯化了未成熟的OEC。这些细胞在体外培养7天后表达GFAP，呈现多极形态。鸡anosmin、外源性anosmin-1或FGF2的过表达可抑制GFAP表达，细胞呈现伸长形态，这被FGF受体抑制剂Su5402阻断。这些数据表明，anosmin-1通过FGF信号传导调节OEC成熟，从而在发育过程中为轴突向OB的神经支配提供许可性的神经胶质环境。
