Department of Pharmacology, School of Medicine, The University of Texas Health Science Center at San Antonio, TX, United States.
Department of Pharmacology, School of Medicine, The University of Texas Health Science Center at San Antonio, TX, United States; The Center for Biomedical Neuroscience, School of Medicine, The University of Texas Health Science Center at San Antonio, United States; Audie L. Murphy VA Hospital, South Texas Veterans Health System, San Antonio, TX, United States.
Psychoneuroendocrinology. 2018 Aug;94:1-10. doi: 10.1016/j.psyneuen.2018.04.019. Epub 2018 Apr 22.
Chronic stress or inflammation increases tryptophan metabolism along the kynurenine pathway (KP), and the generation of neuroactive kynurenine metabolites contributes to subsequent depressive-like behaviors. Microglia regulate KP balance by preferentially producing oxidative metabolites, including quinolinic acid. Research has focused on the interplay between cytokines and HPA axis-derived corticosteroids in regulating microglial activity and effects of KP metabolites directly on neurons; however, the potential role that KP metabolites have directly on microglial activity is unknown. Here, murine microglia were stimulated with lipopolysaccharide(LPS). After 6 h, mRNA expression of interleukin(IL)-1β, IL-6, tumor necrosis factor(TNF)-α and inducible nitric oxide synthase(iNOS) was dose-dependently increased along with the rate-limiting enzymes for oxidative KP metabolism, indoleamine-2,3-dioxygenase(IDO)-1 and kynurenine 3-monooxygenase(KMO). By 24 h post-LPS, kynurenine and quinolinic acid in the media was elevated. Inhibiting KMO with Ro 61-8048 during LPS challenge attenuated extracellular nitrite accumulation and expression of KMO and TNF-α in response to LPS. Similarly, primary microglia isolated from KMO mice exhibited a significantly reduced pro-inflammatory response to LPS compared to WT controls. To determine whether the substrate (kynurenine) or end product (quinolinic acid) of KMO-dependent metabolism modulates the LPS response, microglia were treated with increasing concentrations of L-kynurenine or quinolinic acid in combination with LPS or saline. Interestingly, quinolinic acid did not impact the microglial LPS response. However, L-kynurenine had dose-dependent inhibitory effect on the LPS response. These data are the first to show an anti-inflammatory effect of KMO inhibition on microglia during immune challenge and suggest that KP metabolic balance may play a direct role in regulating microglia activity.
慢性应激或炎症会增加色氨酸沿犬尿氨酸途径（KP）的代谢，而神经活性犬尿氨酸代谢物的产生会导致随后出现抑郁样行为。小胶质细胞通过优先产生氧化代谢物，包括喹啉酸，来调节 KP 平衡。研究主要集中在细胞因子和 HPA 轴衍生的皮质类固醇在调节小胶质细胞活性以及 KP 代谢物对神经元的直接影响上；然而，KP 代谢物对小胶质细胞活性的直接潜在作用尚不清楚。在这里，用脂多糖（LPS）刺激小鼠小胶质细胞。6 小时后，白细胞介素（IL）-1β、IL-6、肿瘤坏死因子（TNF）-α 和诱导型一氧化氮合酶（iNOS）的 mRNA 表达与氧化 KP 代谢的限速酶吲哚胺 2,3-双加氧酶（IDO）-1 和犬尿氨酸 3-单加氧酶（KMO）呈剂量依赖性增加。LPS 后 24 小时，培养基中的犬尿氨酸和喹啉酸升高。在 LPS 挑战期间用 Ro 61-8048 抑制 KMO 可减轻细胞外亚硝酸盐的积累以及 LPS 对 KMO 和 TNF-α 的表达。同样，与 WT 对照相比，从 KMO 小鼠中分离的原代小胶质细胞对 LPS 的促炎反应明显降低。为了确定 KMO 依赖性代谢的底物（犬尿氨酸）或终产物（喹啉酸）是否调节 LPS 反应，用不同浓度的 L-犬尿氨酸或喹啉酸处理小胶质细胞，然后与 LPS 或盐水一起孵育。有趣的是，喹啉酸对小胶质细胞 LPS 反应没有影响。然而，L-犬尿氨酸对 LPS 反应有剂量依赖性的抑制作用。这些数据首次表明，在免疫挑战中小胶质细胞中 KMO 抑制具有抗炎作用，并表明 KP 代谢平衡可能在调节小胶质细胞活性方面发挥直接作用。
