Contrasting effects of whole-body and hepatocyte-specific deletion of the RNA polymerase III repressor Maf1 in the mouse [RNA-Seq]

MAF1 is a nutrient-sensitive, TORC1-regulated repressor of RNA polymerase III (Pol III). MAF1 downregulation leads to increased lipogenesis in Drosophila melanogaster, Caenorhabditis elegans, and mice. However, Maf1-/- mice are lean as increased lipogenesis is counterbalanced by futile pre-tRNA synthesis and degradation, resulting in increased energy expenditure. We compared Chow-fed Maf1-/- mice with Chow- or High Fat (HF)-fed Maf1hep-/- mice that lack MAF1 specifically in hepatocytes. Unlike Maf1-/- mice, Maf1hep-/- mice become heavier and fattier than control mice with old age and much earlier under a HF diet. Liver ChIPseq, RNAseq and proteomics analyses indicate increased Pol III occupancy at Pol III genes, very few differences in mRNA accumulation, and protein accumulation changes consistent with increased lipogenesis. Futile pretRNA synthesis and degradation in the liver, as likely occurs in Maf1hep-/- mice, thus seems insufficient to counteract increased lipogenesis. Indeed, RNAseq and metabolite profiling indicate that liver phenotypes of Maf1-/- mice are strongly influenced by systemic inter-organ communication. Among common changes in the three phenotypically distinct cohorts, Angiogenin downregulation is likely linked to increased Pol III occupancy of tRNA genes in the Angiogenin promoter. Three mouse cohorts, with KO and CTRL samples : Maf1-/- on CHOW diet (5 KO, 7 CTRL), Maf1Hep-/- on CHOW diet (4 KO, 4 CTRL) and Maf1Hep-/- on High Fat diet (4 KO 5 CTRL).MAF1是一种营养敏感型、受TORC1调控的RNA聚合酶III（Pol III）阻遏蛋白。在黑腹果蝇、秀丽隐杆线虫与小鼠中，MAF1的下调可促进脂肪生成。然而，Maf1基因全敲除（Maf1-/-）小鼠却表现为体型消瘦，这是因为增强的脂肪生成会被无效的前tRNA合成与降解过程所抵消，最终导致能量消耗增加。本研究将普通饲料喂养的Maf1-/-小鼠，与分别以普通饲料或高脂（HF）饲料喂养的、肝细胞特异性敲除MAF1的Maf1hep-/-小鼠进行了对比。与Maf1-/-小鼠不同，Maf1hep-/-小鼠随年龄增长会较同月龄对照小鼠更肥胖，且在高脂饲料喂养条件下该表型会更早出现。肝脏染色质免疫沉淀测序（ChIPseq）、转录组测序（RNAseq）与蛋白质组学分析结果显示，Pol III在其靶基因上的结合占有率显著升高，mRNA积累量仅有极细微差异，蛋白质积累变化与脂肪生成增强的表型相符。肝细胞中发生的无效前tRNA合成与降解过程（正如Maf1hep-/-小鼠中可能存在的情况），似乎不足以抵消增强的脂肪生成。确实，转录组测序与代谢谱分析结果显示，Maf1-/-小鼠的肝脏表型受系统性器官间通讯的强烈影响。在三个表型特征各异的小鼠队列的共有变化中，血管生成素（Angiogenin）的下调可能与Angiogenin启动子区域内tRNA基因的Pol III结合占有率升高相关。本研究共设置三个小鼠队列，包含敲除（KO）与对照（CTRL）样本：普通饲料喂养的Maf1-/-小鼠组（5例KO样本、7例CTRL样本）、普通饲料喂养的Maf1hep-/-小鼠组（4例KO样本、4例CTRL样本），以及高脂饲料喂养的Maf1hep-/-小鼠组（4例KO样本、5例CTRL样本）。