Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125.
Department of Pathology, University of California, San Diego, La Jolla, CA 92093.
Proc Natl Acad Sci U S A. 2019 Jun 18;116(25):12416-12421. doi: 10.1073/pnas.1811040116. Epub 2019 Jun 3.
Tet methylcytosine dioxygenase 2 (Tet2) is an epigenetic regulator that removes methyl groups from deoxycytosine residues in DNA. Tet2-deficient murine macrophages show increased lipopolysaccharide (LPS)-induced and spontaneous inflammation at least partially because Tet2 acts to restrain interleukin (IL)-1β and IL-6 expression in induced cells. MicroRNAs have emerged as critical regulatory noncoding RNAs that tune immune cell responses to physiological perturbations and play roles in pathological conditions in macrophages. To determine if a microRNA played any role in Tet2 activity, we examined the interrelationship of Tet2 action and the let-7 microRNA family, utilizing several let-7 microRNA engineered murine models. We first showed that Tet2, but not Tet3, is a direct target of the let-7a-1/let-7d/let-7f-1 (let-7adf) microRNAs in macrophages. We found that overexpression or deletion of the let-7adf gene cluster causes altered IL-6 induction both in tissue culture cells induced by LPS treatment in vitro as well as in a infection mouse model in vivo. Mechanistically, let-7adf promotes IL-6 by directly repressing Tet2 levels and indirectly by enhancing a Tet2 suppressor, the key TCA cycle metabolite, succinate. We found that Let-7adf promotes succinate accumulation by regulating the Lin28a/Sdha axis. We thereby identify two pathways of let-7 control of Tet2 and, in turn, of the key inflammatory cytokine, IL-6, thus characterizing a regulatory pathway in which a microRNA acts as a feedback inhibitor of inflammatory processes.
Tet 甲基胞嘧啶双加氧酶 2（Tet2）是一种表观遗传调节剂，可去除 DNA 中脱氧胞嘧啶残基上的甲基。Tet2 缺陷型小鼠巨噬细胞显示出增加的脂多糖（LPS）诱导和自发性炎症，至少部分原因是 Tet2 作用于抑制诱导细胞中的白细胞介素（IL）-1β和 IL-6 表达。microRNAs 已成为关键的调节性非编码 RNA，可调节免疫细胞对生理扰动的反应，并在巨噬细胞中的病理条件下发挥作用。为了确定 microRNA 是否在 Tet2 活性中发挥作用，我们利用几种 let-7 微 RNA 工程小鼠模型，研究了 Tet2 作用与 let-7 微 RNA 家族之间的相互关系。我们首先表明，Tet2，但不是 Tet3，是巨噬细胞中 let-7a-1/let-7d/let-7f-1（let-7adf）microRNAs 的直接靶标。我们发现，let-7adf 基因簇的过表达或缺失会导致体外 LPS 处理诱导的组织培养细胞以及体内 感染小鼠模型中 IL-6 的诱导改变。在机制上，let-7adf 通过直接抑制 Tet2 水平和间接增强 Tet2 抑制剂（关键三羧酸循环代谢物琥珀酸）来促进 IL-6 的诱导。我们发现 let-7adf 通过调节 Lin28a/Sdha 轴来促进琥珀酸的积累。我们因此确定了 let-7 控制 Tet2 的两种途径，进而控制关键的炎症细胞因子 IL-6，从而表征了一种调节途径，其中 microRNA 作为炎症过程的反馈抑制剂发挥作用。
