Peter Duncan Neurosciences Research Unit, St Vincent's Centre for Applied Medical Research, Sydney, NSW, 2010, Australia.
St Vincent's Clinical School, Faculty of Medicine, University of New South Wales, Sydney, NSW, 2052, Australia.
J Neuroinflammation. 2020 Jun 6;17(1):176. doi: 10.1186/s12974-020-01844-y.
Multiple sclerosis (MS) is a chronic immune-mediated disorder of the central nervous system characterized by demyelination, neuroinflammation, and neurodegeneration. Activation of the kynurenine pathway (KP) results from acute and chronic neuroinflammation leading to both immune suppression and neurotoxicity. However, the exact effects of KP metabolites and changes in neurodegenerative diseases over time are not fully understood. Studies, including those in MS models, have reported that short-term KP activation is beneficial through immune tolerance. However, the effects of long-term KP activation are poorly understood. We hypothesized that such chronic activation is responsible for the neurodegeneration in MS, and further, modulating the KP in EAE-induced mice could significantly decrease the EAE disease severity.
We biochemically altered the KP at different stages of the disease in experimental allergic encephalomyelitis (EAE) mouse model of MS and at two different enzymatic levels of the KP (IDO-1 (indoleamine 2,3 dioxygenase)) and KMO (kynurenine monooxygenase). CNS tissue and blood samples were analyzed longitudinally using GCMS, HPLC, IHC, and RT-PCR.
We showed that the KP was steadily upregulated correlating with disease severity and associated with a shift towards increasing concentrations of the KP metabolite quinolinic acid, a neuro- and gliotoxin. KP modulation by inhibition of IDO-1 with 1-methyl tryptophan (1-MT) was dependent on the timing of treatment at various stages of EAE. IDO-1 inhibition at EAE score 2 led to significantly higher numbers of FoxP3 cells (p < 0.001) in the spleen than earlier IDO-1 inhibition (prophylactic 1-MT treatment group (p < 0.001)), 1-MT treatment after EAE induction (EAE score 0; p < 0.001), and 1-MT treatment at EAE score of 1 (p < 0.05). Significant improvement of disease severity was observed in EAE mice treated with 1-MT at EAE score 2 compared to the untreated group (p < 0.05). KP modulation by KMO inhibition with Ro 61-8048 led to significantly greater numbers of Foxp3 cells (p < 0.05) in Ro 61-8048 treated mice and even more significant amelioration of EAE disease compared to the 1-MT treatment groups.
These results provide a new mechanistic link between neuroinflammation and neurodegeneration and point to KP modulation at the KMO level to preserve immune tolerance and limit neurodegeneration in EAE. They provide the foundation for new clinical trials for MS.
多发性硬化症（MS）是一种中枢神经系统的慢性免疫介导性疾病，其特征为脱髓鞘、神经炎症和神经退行性变。色氨酸分解代谢途径（KP）的激活是由急性和慢性神经炎症引起的，导致免疫抑制和神经毒性。然而，KP 代谢物的具体作用以及随着时间的推移在神经退行性疾病中的变化还没有完全被理解。包括 MS 模型在内的研究报告称，短期 KP 激活通过免疫耐受具有有益作用。但是，长期 KP 激活的作用尚不清楚。我们假设这种慢性激活是 MS 中神经退行性变的原因，并且进一步调节 EAE 诱导的小鼠中的 KP 可以显著降低 EAE 疾病的严重程度。
我们在 MS 的实验性变态反应性脑脊髓炎（EAE）小鼠模型中，在 KP 的两个不同酶水平（IDO-1（吲哚胺 2,3 双加氧酶）和 KMO（犬尿氨酸单加氧酶））改变了 KP 在疾病的不同阶段。使用 GCMS、HPLC、IHC 和 RT-PCR 对 CNS 组织和血液样本进行了纵向分析。
我们表明，KP 随着疾病的严重程度而稳步上调，并与 KP 代谢产物犬尿氨酸单加氧酶的浓度升高相关，犬尿氨酸单加氧酶是一种神经和神经胶质毒素。IDO-1 抑制用 1-甲基色氨酸（1-MT）的 KP 调节取决于 EAE 的不同阶段治疗的时间。EAE 评分 2 时的 IDO-1 抑制导致脾中 FoxP3 细胞的数量显著增加（p <0.001），高于早期 IDO-1 抑制（预防 1-MT 治疗组（p <0.001）），EAE 诱导后的 1-MT 治疗（EAE 评分 0；p <0.001）和 EAE 评分 1 时的 1-MT 治疗（p <0.05）。与未治疗组相比，在 EAE 评分 2 时用 1-MT 治疗的 EAE 小鼠的疾病严重程度明显改善（p <0.05）。用 Ro 61-8048 抑制 KMO 导致 Ro 61-8048 治疗的小鼠中 Foxp3 细胞数量显著增加（p <0.05），并且与 1-MT 治疗组相比，EAE 疾病的改善更为明显。
这些结果为神经炎症和神经退行性变之间提供了新的机制联系，并指出 KP 在 KMO 水平的调节可以维持免疫耐受并限制 EAE 中的神经退行性变。它们为多发性硬化症的新临床试验奠定了基础。
