Contrasting effects of whole-body and hepatocyte-specific deletion of the RNA polymerase III repressor Maf1 in the mouse [ChIP-Seq]. Contrasting effects of whole-body and hepatocyte-specific deletion of the RNA polymerase III repressor Maf1 in the mouse [ChIP-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. Overall design: Three mouse cohorts, with KO and CTRL samples : Maf1-/- on CHOW diet (3 KO, 2 CTRL), Maf1Hep-/- on CHOW diet (3 KO, 2 CTRL) and Maf1Hep-/- on High Fat diet (2 KO 3 CTRL). Each ChIP seq sample has its corresponding Input.

MAF1是一种营养敏感型、受TORC1调控的RNA聚合酶III（RNA polymerase III，Pol III）阻遏蛋白。MAF1表达下调可导致黑腹果蝇、秀丽隐杆线虫及小鼠体内的脂肪生成增加。然而，Maf1全基因敲除小鼠（Maf1−/−）却表现为体瘦，这是因为增加的脂肪生成被无效的前tRNA合成与降解过程所抵消，最终导致能量消耗升高。本研究将普通饲料喂养的Maf1−/−小鼠，与普通饲料或高脂（High Fat，HF）饲料喂养的、肝细胞特异性敲除MAF1的Maf1hep−/−小鼠进行对照比较。与Maf1−/−小鼠不同，Maf1hep−/−小鼠在衰老后体重及体脂均高于同期对照组小鼠，且在高脂饲料喂养下该表型出现得更早。对肝脏组织进行的染色质免疫沉淀测序（Chromatin Immunoprecipitation sequencing，ChIPseq）、转录组测序（RNA sequencing，RNAseq）及蛋白质组学（proteomics）分析显示，Pol III在其靶基因上的结合富集度升高，mRNA积累量仅存在极细微差异，而蛋白质积累变化与脂肪生成增加的情况一致。肝细胞中发生的无效前tRNA合成与降解过程（正如Maf1hep−/−小鼠中的情况），似乎不足以抵消脂肪生成的增加。确实，RNAseq及代谢谱分析（metabolite profiling）结果显示，Maf1−/−小鼠的肝脏表型受系统性器官间通讯的强烈调控。在三个表型不同的队列的共同差异变化中，血管生成素（Angiogenin）的下调可能与tRNA基因在其启动子区域的Pol III结合富集度升高相关。实验整体设计：共设置三个小鼠队列，每组均包含敲除（knockout，KO）与对照（control，CTRL）样本：1. 普通饲料喂养的Maf1−/−小鼠（3例KO样本，2例CTRL样本）；2. 普通饲料喂养的Maf1hep−/−小鼠（3例KO样本，2例CTRL样本）；3. 高脂饲料喂养的Maf1hep−/−小鼠（2例KO样本，3例CTRL样本）。每个ChIP测序样本均配有对应的Input对照样本。