The Circadian Protein Nocturnin Regulates Metabolic Adaptation in Brown Adipose Tissue

Fine-tuning of transcriptional responses can be critical for long-term outcomes in response to an environmental challenge. The circadian protein Nocturnin belongs to a family of proteins that include exonucleases, endonucleases and phosphatases and is most closely related to the CCR4 family of deadenylases that regulate the cellular transcriptome via control of polyA tail length of RNA transcripts. In this study, we investigate the role of Nocturnin in regulating the transcriptional response and downstream metabolic adaptations during cold exposure in brown adipose tissue. We find that Nocturnin exhibits dual localization within the cytosol and mitochondria, and loss of Nocturnin causes changes in expression of networks of mRNAs involved in mitochondrial function. Furthermore, Nocturnin-/- animals display significantly elevated levels of TCA cycle intermediates indicating that they have distinct metabolic adaptations during a prolonged cold exposure. We conclude that cold-induced stimulation of Nocturnin levels can regulate long-term metabolic adaptations to environmental challenges. We performed mRNA-seq analysis on brown fat (BAT) isolated from wild-type and Nocturnin-/- littermates at room temperature or after a 4-hour cold exposure. For cold exposure experiments, age-matched 10-20 week old young adult WT and Nocturnin-/- mice were randomly assigned to cold (6C) or room temperature (22C) groups. Mice were single housed for the duration (4 hrs) of the experiment and food was removed in order to minimize individual variation. N=4-5 mice per condition.转录应答的精细调控对于机体应对环境挑战后的长期结局至关重要。节律蛋白Nocturnin隶属于包含核酸外切酶、核酸内切酶与磷酸酶的蛋白家族，与通过调控RNA转录本的polyA尾长度以调节细胞转录组的CCR4家族脱腺苷酶（deadenylase）亲缘关系最为密切。本研究旨在探究Nocturnin在棕色脂肪组织（brown adipose tissue, BAT）冷暴露过程中对转录应答及下游代谢适应的调控作用。研究发现，Nocturnin在细胞质与线粒体中均存在双重定位；敲除Nocturnin会导致参与线粒体功能的mRNA网络的表达发生改变。此外，Nocturnin基因敲除（Nocturnin-/-）动物的三羧酸循环（tricarboxylic acid cycle, TCA）中间产物水平显著升高，表明其在长期冷暴露过程中存在独特的代谢适应模式。综上，冷暴露诱导的Nocturnin水平升高可调节机体对环境挑战的长期代谢适应。本研究对室温条件下或经4小时冷暴露后，从野生型（wild-type）与Nocturnin-/-同窝仔鼠中分离得到的棕色脂肪组织（BAT）开展了mRNA测序（mRNA-seq）分析。冷暴露实验中，选取年龄匹配的10~20周龄年轻成年野生型（wild-type, WT）与Nocturnin-/-小鼠，随机分配至冷暴露组（6℃）与室温对照组（22℃）。实验全程（4小时）小鼠单笼饲养，且撤除食物以最小化个体间差异，每组设置4~5只小鼠作为生物学重复。