Department of Anesthesiology, Tokyo Medical University, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan.
Department of Molecular Preventive Medicine, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo 160-8402, Japan.
Int J Mol Sci. 2022 Aug 10;23(16):8924. doi: 10.3390/ijms23168924.
Microglia are key cells of the immune system in the central nervous system and are suggested to be deeply involved in the development of neurodegenerative diseases. It is well known that microglia have functional plasticity, with an inflammatory M1 phenotype and an anti-inflammatory M2 phenotype. Inhibition of choline transport in macrophages has been reported to suppress the secretion of inflammatory cytokines. However, the role of the choline transport system in regulating microglial M1/M2 polarization has not been fully elucidated to date. In this study, we investigated the mechanism of choline uptake in microglia, and its association with microglial M1/M2 polarization.
The immortalized mouse microglial cell line SIM-A9 was used for [H]choline uptake and expression analysis of choline transporters. The association between the choline uptake system and the M1/M2 polarization of microglia was also analyzed.
Choline transporter-like protein (CTL) 1 and CTL2 were highly expressed in SIM-A9 cells, and CTL1 and CTL2 were localized in the plasma membrane and mitochondria, respectively. Functional analysis of choline uptake demonstrated the existence of Na-independent, pH-dependent, and intermediate-affinity choline transport systems. Choline uptake was concentration-dependently inhibited by hemicholinium-3 (HC-3), an inhibitor of choline uptake, and increased by lipopolysaccharide (LPS) and interleukin-4 (IL-4). Expression of the mRNA of M1 microglia markers IL-1β and IL-6 was increased by LPS, and their effects were suppressed by choline deprivation and HC-3. In contrast, mRNA expression of the M2 microglial marker arginase-1 (Arg-1) was increased by IL-4, and the effect was enhanced by choline deprivation and HC-3.
Our results suggest that inhibition of CTL1-mediated choline uptake in microglia preferentially induces M2 microglia polarization, which is a potential therapeutic approach for inflammatory brain diseases.
小胶质细胞是中枢神经系统中免疫系统的关键细胞，被认为深度参与神经退行性疾病的发生。众所周知，小胶质细胞具有功能可塑性，表现为炎症型 M1 表型和抗炎型 M2 表型。已有报道称，抑制巨噬细胞中的胆碱转运可抑制炎症细胞因子的分泌。然而，迄今为止，胆碱转运系统在调节小胶质细胞 M1/M2 极化中的作用尚未完全阐明。在这项研究中，我们研究了小胶质细胞中胆碱摄取的机制及其与小胶质细胞 M1/M2 极化的关系。
使用永生化的小鼠小胶质细胞系 SIM-A9 进行 [H]胆碱摄取和胆碱转运体表达分析。还分析了胆碱摄取系统与小胶质细胞 M1/M2 极化的关系。
胆碱转运蛋白样蛋白 1（CTL1）和 CTL2 在 SIM-A9 细胞中高表达，CTL1 和 CTL2 分别定位于质膜和线粒体。胆碱摄取的功能分析表明存在非 Na 依赖性、pH 依赖性和中亲和力的胆碱转运系统。胆碱摄取被胆碱摄取抑制剂 hemicholinium-3（HC-3）浓度依赖性抑制，并被脂多糖（LPS）和白细胞介素-4（IL-4）增加。LPS 增加了 M1 小胶质细胞标志物白细胞介素-1β（IL-1β）和白细胞介素-6（IL-6）的 mRNA 表达，这种作用被胆碱剥夺和 HC-3 抑制。相反，IL-4 增加了 M2 小胶质细胞标志物精氨酸酶-1（Arg-1）的 mRNA 表达，这种作用被胆碱剥夺和 HC-3 增强。
我们的结果表明，抑制小胶质细胞中 CTL1 介导的胆碱摄取优先诱导 M2 小胶质细胞极化，这是治疗炎症性脑疾病的一种潜在治疗方法。
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