Transcriptional control of skeletal muscle insulin resistance

描述(由申请人提供)：了解推动2型糖尿病发生的最早的分子变化可能导致新的诊断、预后和潜在的治疗干预的新靶点的发展。我们发现了一个名为MondoA的基本-螺旋-环-螺旋拉链转录因子家族的新成员，我们认为它在骨骼肌葡萄糖稳态和胰岛素抵抗中起着关键作用。Mondoa主要作为转录激活剂，与其专有的异二聚体伙伴MLX结合到CACGTG基因组靶标上。多条证据表明，Mondoa：MLX复合体是细胞生物能量学的关键调节因子。首先，Mondoa：MLX复合体本质上不是核蛋白，而是在线粒体膜和细胞核之间穿梭，这表明它们促进了这两个基本细胞器之间的沟通。第二，Mondoa：MLX复合体聚集在细胞核中，通过检测葡萄糖-6-磷酸水平，与其目标启动子结合，在高血糖条件下激活它们的表达。第三，Mondoa：MLX复合体是至少75%的葡萄糖诱导靶标转录激活所必需的，这表明它们是葡萄糖依赖转录组的主要调节因子。最后，MondoA在骨骼肌中高度表达，它是葡萄糖处理的主要部位，在许多肌肉细胞系中转录活性很高。总之，我们认为骨骼肌是蒙多亚的主要作用部位之一。我们假设Mondoa的一个关键功能是骨骼肌如何感知和响应血糖水平的变化。Mondoa的一个关键靶点是硫氧还蛋白相互作用蛋白(TXNIP)。TXNIP在血糖稳态和胰岛素抵抗中具有多效性作用，这部分是通过其作为外周葡萄糖处置的负调节因子的功能来调节的。与TXNIP是Mondoa的关键效应器一致，Mondoa也是葡萄糖摄取的强有力的负调节因子。因此，我们假设核活动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Mondoa抑制葡萄糖摄取的唯一效应物，这表明Mondoa的其他转录靶点也必须起作用。我们建议使用小鼠MondoA的条件性缺失等位基因来特异性地灭活骨骼肌中的MondoA。在目标1中，我们将使用这个小鼠模型来确定Mondoa在体内骨骼肌葡萄糖稳态中的功能，以及Mondoa活性是否像我们的初步数据所表明的那样，是骨骼肌胰岛素抵抗所必需的。此外，我们在目标2中提出了全面的基因组方法来发现骨骼肌中直接的和Mondoa依赖的转录组。最后，我们的初步数据表明，Mondoa的转录活性受线粒体超载的控制。我们将在Aim 3中测试这一模型，并确定Mondoa和TXNIP如何作为葡萄糖摄取的有效负调节因子发挥作用。 与公共健康相关：转录调节因子Mondoa在骨骼肌中高度表达，是葡萄糖诱导转录的主要调节因子。Mondoa通过其对硫氧还蛋白相互作用蛋白(TXNIP)的正转录调节，在许多不同的细胞系中是一种强有力的葡萄糖摄取的负调节因子。然而，在这方面，TXNIP并不是唯一的Mondoa效应者。在这个应用中，我们提出了一个小鼠模型来确定Mondoa在骨骼肌中的功能，并确定Mondoa是否在胰岛素抵抗或糖尿病的发生中是必需的。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，这将为深入了解驱动胰岛素抵抗的转录程序提供洞察力。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