Centre de recherche de l'Institut universitaire de cardiologie et de pneumologie de Québec (CRIUCPQ), Faculté de Médecine, Université Laval, 2725 Chemin Ste-Foy, Québec, Qc, G1V 4G5, Canada.
Whitehead Institute for Biomedical Research, Nine Cambridge Center, Cambridge, MA, 02142, USA; Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA; Koch Center for Integrative Cancer Research at MIT, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA.
Mol Metab. 2017 Feb 17;6(5):447-458. doi: 10.1016/j.molmet.2017.02.005. eCollection 2017 May.
The mechanistic target of rapamycin (mTOR) is a serine/threonine kinase that functions into distinct protein complexes (mTORC1 and mTORC2) that regulates growth and metabolism. DEP-domain containing mTOR-interacting protein (DEPTOR) is part of these complexes and is known to reduce their activity. Whether DEPTOR loss affects metabolism and organismal growth has never been tested.
We have generated a conditional transgenic mouse allowing the tissue-specific deletion of DEPTOR. This model was crossed with CMV-cre mice or Albumin-cre mice to generate either whole-body or liver-specific DEPTOR knockout (KO) mice.
Whole-body DEPTOR KO mice are viable, fertile, normal in size, and do not display any gross physical and metabolic abnormalities. To circumvent possible compensatory mechanisms linked to the early and systemic loss of DEPTOR, we have deleted DEPTOR specifically in the liver, a tissue in which DEPTOR protein is expressed and affected in response to mTOR activation. Liver-specific DEPTOR null mice showed a reduction in circulating glucose upon fasting versus control mice. This effect was not associated with change in hepatic gluconeogenesis potential but was linked to a sustained reduction in circulating glucose during insulin tolerance tests. In addition to the reduction in glycemia, liver-specific DEPTOR KO mice had reduced hepatic glycogen content when fasted. We showed that loss of DEPTOR cell-autonomously increased oxidative metabolism in hepatocytes, an effect associated with increased cytochrome c expression but independent of changes in mitochondrial content or in the expression of genes controlling oxidative metabolism. We found that liver-specific DEPTOR KO mice showed sustained mTORC1 activation upon fasting, and that acute treatment with rapamycin was sufficient to normalize glycemia in these mice.
We propose a model in which hepatic DEPTOR accelerates the inhibition of mTORC1 during the transition to fasting to adjust metabolism to the nutritional status.
雷帕霉素靶蛋白（mTOR）是一种丝氨酸/苏氨酸激酶，它在不同的蛋白复合物（mTORC1 和 mTORC2）中发挥作用，调节生长和代谢。DEP 结构域包含的 mTOR 相互作用蛋白（DEPTOR）是这些复合物的一部分，已知其活性降低。DEPTOR 的缺失是否会影响代谢和机体生长尚未得到验证。
我们生成了一种条件性转基因小鼠，允许 DEPTOR 在组织中特异性缺失。该模型与 CMV-cre 小鼠或 Albumin-cre 小鼠杂交，生成全身性或肝脏特异性 DEPTOR 敲除（KO）小鼠。
全身性 DEPTOR KO 小鼠具有活力、繁殖力、正常大小，并且没有表现出任何明显的身体和代谢异常。为了避免与 DEPTOR 的早期和全身性缺失相关的可能补偿机制，我们特异性地在肝脏中缺失了 DEPTOR，肝脏是一个表达 DEPTOR 蛋白并对 mTOR 激活有反应的组织。与对照小鼠相比，肝脏特异性 DEPTOR 缺失小鼠在禁食时循环葡萄糖减少。这种效应与肝糖异生潜力的变化无关，但与胰岛素耐量试验期间循环葡萄糖的持续减少有关。除了血糖降低外，禁食时肝脏特异性 DEPTOR KO 小鼠的肝糖原含量也减少。我们表明，DEPTOR 的缺失会使肝细胞中的氧化代谢自主增加，这种效应与细胞色素 c 表达增加有关，但与线粒体含量或控制氧化代谢的基因表达变化无关。我们发现，禁食时肝脏特异性 DEPTOR KO 小鼠的 mTORC1 持续激活，而雷帕霉素的急性处理足以使这些小鼠的血糖正常化。
我们提出了一个模型，即肝脏中的 DEPTOR 在向禁食过渡时加速 mTORC1 的抑制，以调整代谢以适应营养状态。
