Transcriptional control of skeletal muscle insulin resistance

描述（由申请人提供）：了解驱动 2 型糖尿病发生的最早的分子变化可能会导致新的诊断、预后和治疗干预的潜在新目标的开发。我们发现了转录因子基本螺旋环螺旋拉链家族的一个新成员，称为 MondoA，我们认为它在骨骼肌葡萄糖稳态和胰岛素抵抗中发挥着关键作用。 MondoA 主要作为转录激活剂发挥作用，与其专性异二聚体伴侣 Mlx 结合 CACGTG 基因组靶标。多项证据表明 MondoA:Mlx 复合物是细胞生物能的关键调节剂。首先，MondoA:Mlx 复合物不是组成型核蛋白，而是在线粒体外膜和细胞核之间穿梭，表明它们促进这两个重要细胞器之间的通讯。其次，MondoA:Mlx 复合物在细胞核中积累，结合其目标启动子，通过感测 6-磷酸葡萄糖水平在高血糖条件下激活其表达。第三，至少 75% 的葡萄糖诱导靶标的转录激活需要 MondoA:Mlx 复合物，这表明它们是葡萄糖依赖性转录组的主要调节因子。最后，MondoA 在骨骼肌中高度表达，骨骼肌是葡萄糖处理的主要部位，并且在许多肌肉细胞系中具有转录活性。总之，我们认为骨骼肌是 MondoA 的主要作用部位之一。我们假设 MondoA 在骨骼肌如何感知和响应葡萄糖水平的变化方面发挥着关键作用。 MondoA 的一个关键靶标是硫氧还蛋白相互作用蛋白 (TXNIP)。 TXNIP 在葡萄糖稳态和胰岛素抵抗中具有多效性作用，这部分是由其作为外周葡萄糖处理的负调节剂的功能介导的。与 TXNIP 是重要的 MondoA 效应子一致，MondoA 也是葡萄糖摄取的有效负调节剂。因此，我们假设核活性 MondoA 及其转录靶点也可能通过负向调节葡萄糖摄取来驱动骨骼肌胰岛素抵抗。 TXNIP 并不是减弱葡萄糖摄取的唯一 MondoA 效应子，这表明其他 MondoA 转录靶点也必须发挥作用。我们建议采用小鼠 MondoA 的条件删除等位基因来特异性灭活骨骼肌中的 MondoA。在目标 1 中，我们将使用该小鼠模型来确定 MondoA 在骨骼肌葡萄糖稳态中的体内功能，以及骨骼肌胰岛素抵抗是否需要 MondoA 活性，正如我们的初步数据所表明的那样。此外，我们在目标 2 中提出了全面的基因组方法，以发现骨骼肌中直接且依赖 MondoA 的转录组。最后，我们的初步数据表明 MondoA 转录活性是由线粒体超载控制的。我们将在目标 3 中测试该模型，并确定 MondoA 和 TXNIP 如何作为葡萄糖摄取的有效负调节剂发挥作用。 公共卫生相关性：转录调节因子 MondoA 在骨骼肌中高表达，是葡萄糖诱导转录的主要调节因子。 MondoA 通过对硫氧还蛋白相互作用蛋白 (TXNIP) 的正转录调节，在许多不同的细胞谱系中成为葡萄糖摄取的有效负调节剂。然而，TXNIP 并不是这方面唯一的 MondoA 效应器。在此应用中，我们提出了一种小鼠模型来确定 MondoA 在骨骼肌中的功能，并确定 MondoA 是否是胰岛素抵抗或糖尿病发展所必需的。此外，我们提出了全面的基因组学方法来确定骨骼肌中直接和葡萄糖诱导的 MondoA 转录组，这将有助于深入了解驱动胰岛素抵抗的转录程序。最后，我们提出了线粒体功能障碍如何控制 MondoA 转录活性的方法

DESCRIPTION (provided by applicant): Understanding the earliest molecular changes that drive the genesis of type 2 diabetes may lead to the development of new diagnostics, prognostics, and potentially new targets for therapeutic intervention. We have discovered a new member of the basic-helix-loop-helix-zipper family of transcription factors called MondoA that we propose plays a critical role in skeletal muscle glucose homeostasis and insulin resistance. MondoA functions primarily as a transcriptional activator, binding to CACGTG genomic targets with its obligate heterodimeric partner Mlx. Several lines of evidence indicate that MondoA:Mlx complexes are key regulators of cellular bioenergetics. First, MondoA:Mlx complexes are not constitutively nuclear proteins, rather they shuttle between the outer mitochondrial membrane and the nucleus, suggesting that they facilitate communication between these two essential organelles. Second, MondoA:Mlx complexes accumulate in the nucleus, binding their target promoters to activate their expression under hyperglycemic conditions by sensing glucose-6-phosphate levels. Third, MondoA:Mlx complexes are required for transcriptional activation of at least 75 percent of glucose-induced targets, indicating that they are major regulators of the glucose-dependent transcriptome. Finally, MondoA is very highly expressed in skeletal muscle, which is a major site of glucose disposal and is transcriptionally active in a number of muscle cell lines. Together, we suggest that skeletal muscle is one of MondoA's primary sites of action. We hypothesize a critical function for MondoA in how skeletal muscle senses and responds to changes in glucose levels. One critical MondoA target is thioredoxin interacting protein (TXNIP). TXNIP has pleiotropic roles in glucose homeostasis and insulin resistance, which are mediated in part by its function as a negative regulator of peripheral glucose disposal. Consistent with TXNIP being a critical MondoA effector, MondoA is also a potent negative regulator of glucose uptake. As such, we hypothesize that the nuclear activity MondoA and its transcriptional targets may also drive skeletal muscle insulin resistance by negatively regulating glucose uptake. TXNIP is not the sole MondoA effector in attenuating glucose uptake, indicating that other MondoA transcriptional targets must also contribute. We propose to employ a conditional deletion allele of murine MondoA to specifically inactivate MondoA in skeletal muscle. In Aims 1, we will use this mouse model to determine MondoA's in vivo function in skeletal muscle glucose homeostasis and whether MondoA activity is required for skeletal muscle insulin resistance as our preliminary data suggest. Further, we propose comprehensive genomic approaches in Aim 2 to discover the direct and MondoA-dependent transcriptome in skeletal muscle. Finally, our preliminary data indicate that MondoA transcriptional activity is controlled by mitochondrial overload. We will test this model in Aim 3 and determine how MondoA and TXNIP function as potent negative regulators of glucose uptake. PUBLIC HEALTH RELEVANCE: The transcriptional regulator MondoA is highly expressed in skeletal muscle and is a master regulator of glucose-induced transcription. MondoA is a potent negative regulator of glucose uptake in a number of different cell lineages via its positive transcriptional regulation of thioredoxin interacting protein (TXNIP). However, TXNIP is not the sole MondoA effector in this regard. In this application, we propose a mouse model to determine the function of MondoA in skeletal muscle and determine whether MondoA is necessary for the development of insulin resistance or diabetes. Furthermore, we propose comprehensive genomics approaches to determine the direct and glucose-induced MondoA transcriptome in skeletal muscle, which will provide insight into the transcriptional programs that drive insulin resistance. Finally, we propose approaches to how mitochondrial dysfunction controls MondoA transcriptional activity