The Department of Neurology, University of California Davis, School of Medicine, Sacramento, California, USA.
J Neuroinflammation. 2011 Jan 24;8:8. doi: 10.1186/1742-2094-8-8.
Administration of exogenous interferon-γ (IFNγ) aggravates the symptoms of multiple sclerosis (MS), whereas interferon-β (IFNβ) is used for treatment of MS patients. We previously demonstrated that IFNγ induces apoptosis of oligodendroglial progenitor cells (OPCs), suggesting that IFNγ is more toxic to OPCs than IFNβ. Thus we hypothesized that a difference in expression profiles between IFNγ-inducible and IFNβ-inducible genes in OPCs would predict the genes responsible for IFNγ-mediated cytotoxic effects on OPCs. We have tested this hypothesis particularly focusing on the interferon regulatory factors (IRFs) well-known transcription factors up-regulated by IFNs.
Highly pure primary rat OPC cultures were treated with IFNγ and IFNβ. Cell death and proliferation were assessed by MTT reduction, caspase-3-like proteinase activity, Annexin-V binding, mitochondrial membrane potential, and BrdU-incorporation. Induction of all nine IRFs was comprehensively compared by quantitative PCR between IFNγ-treated and IFNβ-treated OPCs. IRFs more strongly induced by IFNγ than by IFNβ were selected, and tested for their ability to induce OPC apoptosis by overexpression and by inhibition by dominant-negative proteins or small interference RNA either in the presence or absence of IFNγ.
Unlike IFNγ, IFNβ did not induce apoptosis of OPCs. Among nine IRFs, IRF1 and IRF8 were preferentially up-regulated by IFNγ. In contrast, IRF7 was more robustly induced by IFNβ than by IFNγ. Overexpressed IRF1 elicited apoptosis of OPCs, and a dominant negative IRF1 protein partially protected OPCs from IFNγ-induced apoptosis, indicating a substantial contribution of IRF1 to IFNγ-induced OPC apoptosis. On the other hand, overexpression of IRF8 itself had only marginal proapoptotic effects. However, overexpressed IRF8 enhanced the IFNγ-induced cytotoxicity and the proapoptotic effect of overexpressed IRF1, and down-regulation of IRF8 by siRNA partially but significantly reduced preapoptotic cells after treatment with IFNγ, suggesting that IRF8 cooperatively enhances IFNγ-induced OPC apoptosis.
This study has identified that IRF1 and IRF8 mediate IFNγ-signaling leading to OPC apoptosis. Therapies targeting at these transcription factors and their target genes could reduce IFNγ-induced OPC loss and thereby enhance remyelination in MS patients.
外源性干扰素-γ（IFNγ）可加重多发性硬化症（MS）的症状，而干扰素-β（IFNβ）则用于治疗 MS 患者。我们之前的研究表明，IFNγ可诱导少突胶质前体细胞（OPC）凋亡，这表明 IFNγ对 OPC 的毒性大于 IFNβ。因此，我们假设 OPC 中 IFNγ诱导和 IFNβ诱导基因表达谱的差异将预测负责 IFNγ介导的 OPC 细胞毒性作用的基因。我们特别关注干扰素调节因子（IRFs），这些转录因子是 IFNs 上调的众所周知的转录因子，对这一假说进行了验证。
用 IFNγ和 IFNβ处理高度纯化的原代大鼠 OPC 培养物。通过 MTT 还原、半胱天冬酶-3 样蛋白水解酶活性、Annexin-V 结合、线粒体膜电位和 BrdU 掺入来评估细胞死亡和增殖。通过定量 PCR 全面比较 IFNγ处理和 IFNβ处理的 OPC 之间的所有 9 种 IRFs 的诱导。选择 IFNγ诱导强度大于 IFNβ的 IRFs，并通过过表达以及通过显性负性蛋白或小干扰 RNA 抑制来检测它们在存在或不存在 IFNγ的情况下诱导 OPC 凋亡的能力。
与 IFNγ不同，IFNβ不会诱导 OPC 凋亡。在 9 种 IRFs 中，IRF1 和 IRF8 被 IFNγ优先上调。相比之下，IRF7 被 IFNβ比 IFNγ更强烈地诱导。过表达的 IRF1 可诱导 OPC 凋亡，而显性负性 IRF1 蛋白部分保护 OPC 免受 IFNγ诱导的凋亡，表明 IRF1 对 IFNγ诱导的 OPC 凋亡有很大的贡献。另一方面，过表达的 IRF8 本身只有轻微的促凋亡作用。然而，过表达的 IRF8 增强了 IFNγ诱导的细胞毒性和过表达的 IRF1 的促凋亡作用，用 siRNA 下调 IRF8 部分但显著减少 IFNγ处理后的凋亡前细胞，表明 IRF8 协同增强 IFNγ诱导的 OPC 凋亡。
本研究确定了 IRF1 和 IRF8 介导 IFNγ 信号传导导致 OPC 凋亡。针对这些转录因子及其靶基因的治疗方法可能会减少 IFNγ 诱导的 OPC 丢失，从而增强 MS 患者的髓鞘再生。
