Stekic Andjela, Dragic Milorad, Stevanovic Ivana, Zaric Kontic Marina, Adzic Bukvic Marija, Dacic Sanja, Ninkovic Milica, Nedeljkovic Nadezda
Center for Translational Neuroscience, Department of General Physiology and Biophysics, Faculty of Biology, University of Belgrade, Belgrade, Serbia.
Department of Molecular Biology and Endocrinology, Vinča Institute of Nuclear Sciences-National Institute of the Republic of Serbia, University of Belgrade, Belgrade, Serbia.
Front Cell Neurosci. 2025 Sep 3;19:1656777. doi: 10.3389/fncel.2025.1656777. eCollection 2025.
Olfactory dysfunction is increasingly recognized as an early, non-motor manifestation of multiple sclerosis (MS), but the mechanisms underlying its occurrence remain unclear. Using the rat model of experimental autoimmune encephalomyelitis (EAE), we investigated the temporal relationship between olfactory impairment, neuroinflammation, barrier integrity, and adenosine signaling in the olfactory bulb (OB) in the early stage of EAE. The study showed that more than two-thirds of EAE animals exhibited significant deficits in the buried food test as early as 3 days post-immunization (dpi), which preceded the first motor symptoms by several days. Open field test confirmed that these olfactory deficits were not due to impaired locomotion. Transient breach to the OB tissue barrier was demonstrated at 3-5 dpi by increased FITC-dextran penetration and peripheral monocyte/macrophage infiltration into the lateral aspect of the OB. The breach coincided with activation of microglia in the outer nerve layer on the lateral aspect of the OB. Oxidative stress, including elevated malondialdehyde, nitric oxide, and superoxide ion levels along with a depleted antioxidant defense system, indicated a redox imbalance, while a transient increase in neurofilament light chain serum levels at 3 dpi indicated acute neuroaxonal injury and barrier disruption at early stage EAE. At the molecular level, the simultaneous upregulation of CD73 and adenosine A/A receptors along the pial surface and in the olfactory nerve layer suggested enhanced adenosine signaling in early barrier modulation. Spatial mapping of FITC-dextran penetration, peripheral infiltrates, and microglia activation indicated access of immune cells from the subarachnoid space into the OB parenchyma. Overall, these results demonstrate that the OB is a permissive entry zone for autoreactive immune cells in the OB in early stages of EAE, highlighting olfactory and behavioral testing as promising tools for early detection and monitoring of MS.
嗅觉功能障碍日益被认为是多发性硬化症（MS）的一种早期非运动性表现，但其发生的潜在机制仍不清楚。我们使用实验性自身免疫性脑脊髓炎（EAE）大鼠模型，研究了EAE早期嗅球（OB）中嗅觉损伤、神经炎症、屏障完整性和腺苷信号之间的时间关系。研究表明，早在免疫后3天（dpi），超过三分之二的EAE动物在埋食试验中就表现出明显缺陷，这比首次出现运动症状提前了几天。旷场试验证实这些嗅觉缺陷并非由于运动障碍所致。在3 - 5 dpi时，通过FITC - 葡聚糖渗透增加以及外周单核细胞/巨噬细胞浸润到OB外侧，证实了OB组织屏障的短暂破坏。这种破坏与OB外侧外神经层中微胶质细胞的激活同时发生。氧化应激，包括丙二醛、一氧化氮和超氧离子水平升高以及抗氧化防御系统耗竭，表明存在氧化还原失衡，而在3 dpi时神经丝轻链血清水平的短暂升高表明EAE早期存在急性神经轴突损伤和屏障破坏。在分子水平上，沿软脑膜表面和嗅神经层同时上调的CD73和腺苷A/A受体表明在早期屏障调节中腺苷信号增强。FITC - 葡聚糖渗透、外周浸润和微胶质细胞激活的空间映射表明免疫细胞从蛛网膜下腔进入OB实质。总体而言，这些结果表明在EAE早期，OB是自身反应性免疫细胞进入OB的允许区域，突出了嗅觉和行为测试作为早期检测和监测MS的有前景的工具。
