Neuroinflammation results in dysfunctional mitral cells and olfactory impairment

Olfactory dysfunction is an underestimated symptom in multiple sclerosis (MS). Here, we examined the pathogenic mechanisms underlying inflammation-induced dysfunction of the olfactory bulb using the animal model of MS, experimental autoimmune encephalomyelitis (EAE). Reduced olfactory function in EAE was associated with the degeneration of short-axon neurons, immature neurons, and mitral cells, together with their synaptic interactions and axonal repertoire. To dissect the mechanisms underlying the susceptibility of mitral cells, the main projection neurons of the olfactory bulb, we profiled their responses to neuroinflammation by single-nucleus RNA sequencing. Neuroinflammation resulted in the induction of potassium channel transcripts in mitral cells, which was reflected in reduced halothane-induced outward currents of these cells, likely contributing to the impaired olfaction in EAE animals. HuC/D+ nuclei were isolated by fluorescence activated cell sorting (FACS) representing mainly neuronal nuclei of olfactory bulb of 10-week old female C57Bl/6J mice at the acute phase of the MS model experimental autoimmune encephalomyelitis (EAE) together with their healthy control littermates.嗅觉功能障碍是多发性硬化（multiple sclerosis, MS）中被严重低估的临床症状。本研究以多发性硬化的经典动物模型——实验性自身免疫性脑脊髓炎（experimental autoimmune encephalomyelitis, EAE）为研究体系，探究炎症诱导的嗅球功能障碍的潜在致病机制。研究发现，EAE模型小鼠的嗅觉功能减退，与短轴突神经元、未成熟神经元及僧帽细胞的变性，及其突触相互作用和轴突特征谱的改变密切相关。为解析嗅球主要投射神经元——僧帽细胞的易损机制，我们通过单细胞核RNA测序（single-nucleus RNA sequencing）技术，分析了其对神经炎症的应答特征。结果显示，神经炎症可诱导僧帽细胞内钾通道转录本的表达上调，这一变化与氟烷诱导的该类细胞外向电流减弱相一致，或为EAE模型小鼠嗅觉损伤的潜在分子机制。本研究通过荧光激活细胞分选（fluorescence activated cell sorting, FACS）分离得到HuC/D阳性细胞核，样本取自10周龄雌性C57BL/6J小鼠的嗅球神经元细胞核，分别采集自EAE急性期小鼠及其健康同窝对照个体。