Dysfunctional PGC-1alpha expression in skeletal muscle during diabetes

描述（由申请人提供）： 骨骼肌萎缩是糖尿病（DM）和其他慢性疾病的常见并发症，可导致疲劳和虚弱。肌肉质量的损失也是在这些条件下死亡的风险因素。尽管在理解引起肌肉损失的机制方面取得了重大进展，但开发药物干预以减轻萎缩的尝试一直不成功。相比之下，运动可以对慢性疾病中的肌肉产生有益的影响，尽管其效果如何实现仍不清楚。我们和其他人已经报道，过氧化物酶体增殖物激活受体γ辅激活因子1-α（PGC-1 α，一种转录辅激活因子蛋白）的水平在DM期间的骨骼肌中以及在用糖皮质激素处理的培养的肌管中降低，从而诱导胰岛素抵抗和萎缩。这是值得注意的，因为PGC-1 α在正常骨骼肌中的表达通过运动而增加，并且PGC-1 α的转基因过表达可以防止肌肉损失。PGC-1 α是整合能量和蛋白质代谢的关键“主调节器”。它通过抑制介导萎缩程序的F盒O（FOXO）转录因子的活性发挥作用。了解运动如何维持DM的肌肉功能将提高我们治疗疲劳和虚弱的能力。为了实现这一目标，我们必须首先了解萎缩过程中PGC 1 α表达失调的生化基础。本项目将检验以下假设：DM相关萎缩期间PGC-1 α表达的减少是由钙调神经磷酸酶（Cn）（一种钙激活的丝氨酸/苏氨酸磷酸酶）调节的一个或多个通路的异常信号传导引起的。我们将研究肌细胞增强因子2（MEF 2）和活化T细胞的细胞质核因子（NFATc）途径，因为这两种转录因子都是已报道在正常骨骼肌中调节PGC-1 α转录的Cn底物。第三个要研究的途径是受调节CREB 1（TORC 1）/环AMP-反应元件（CRE）-结合蛋白（CREB）通路的转导子。TORC 1是CREB的转录辅激活因子，由Cn激活，并为PGC-1 α表达所需。我们的初步数据表明，TORC 1功能在萎缩过程中受损。一旦PGC-1 α失调的机制得到表征，我们将测试运动是否能改善DM小鼠的Cn信号传导，从而导致肌肉PGC-1 α表达的增加。当这个项目的目标完成时，我们将确定Cn相关的通路，这些通路负责PGC-1 α表达的减少，从而导致萎缩。此外，我们还将确定DM肌肉中的哪些途径对运动有反应。这些信息可能有助于设计创新的蛋白质靶向治疗和退伍军人糖尿病康复疗法。拟议研究的结果也可能与免疫抑制治疗包括糖皮质激素和/或钙调磷酸酶抑制剂（即，环孢菌素A，FK 506）。许多移植受者由于慢性疾病的分解代谢影响而减少了瘦体重，而其他人则由于维持泼尼松治疗而面临维持肌肉质量的挑战。使用Cn抑制剂可能对这两种类型的患者产生负面影响。最后，我们的研究结果可以广泛适用于患有多种与萎缩相关的衰弱性疾病的退伍军人。

DESCRIPTION (provided by applicant): Skeletal muscle atrophy is a frequent co-morbidity of diabetes mellitus (DM) and other chronic diseases that causes fatigue and weakness. Loss of muscle mass also is a risk factor for mortality in these conditions. Despite significant advances in understanding the mechanisms causing muscle loss,attempts to develop pharmaceutical interventions to attenuate atrophy have been unsuccessful. In contrast, exercise can have beneficial effects on muscle in chronic conditions although how its effects are achieved remains unclear. We and others have reported that the level of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1alpha, a transcriptional coactivator protein, is decreased in skeletal muscle during DM and in cultured myotubes treated with glucocorticoids to induced insulin resistance and atrophy. This is notable because PGC-alpha expression in normal skeletal muscle is increased by exercise and transgenic overexpression of PGC-1alpha protects against muscle loss. PGC-1alpha is a critical "master regulator" that integrates energy and protein metabolism. It functions by inhibiting the activity of the F Box O (FOXO) transcription factors which mediate the atrophy program. Understanding how exercise maintains muscle function in DM will improve our ability to treat fatigue and weakness. To accomplish this goal, we must first understand the biochemical basis for dysregulation of PGC1alpha expression during atrophy. This project will test the hypothesis that the reduction in PGC-1alpha expression during DM-related atrophy results from abnormal signaling through one or more pathways that are regulated by calcineurin (Cn), a calcium-activated serine/threonine phosphatase. We will examine the myocyte enhancer factor 2 (MEF2) and cytoplasmic nuclear factor of activated T cells (NFATc) pathways because both transcription factors are Cn substrates that have been reported to regulate PGC-1alpha transcription in normal skeletal muscle. The third pathway to be studied is the Transducer of Regulated CREB 1 (TORC1)/cyclic AMP-responsive element (CRE)-binding protein (CREB) pathway. TORC1 is a transcription coactivator of CREB that is activated by Cn and required for PGC-1alpha expression. Our preliminary data suggests that TORC1 function is impaired during atrophy. Once the mechanisms of PGC-1alpha dysregulation are characterized, we will test whether exercise improves Cn signaling in DM mice, thus leading to an increase in muscle PGC-1alpha expression. When the aims of this project are complete, we will have identified the Cn-related pathways that are responsible for the reduction in PGC-1alpha expression, and thus contribute to atrophy. In addition, we will have determined which of these pathways in DM muscle respond to exercise. This information could be useful for designing innovative and protein-targeted treatments and rehabilitation therapies of Veterans with DM. Results of the proposed studies also may be relevant to Veteran transplant recipients whose immunosuppressive therapies include glucocorticoids and/or calcineurin inhibitors (i.e., cyclosporine A, FK506). Many transplant recipients have reduced lean body mass due the catabolic effects of chronic diseases while others are challenged to maintain their muscle mass due to maintenance prednisone therapy. Use of Cn inhibitors could have a negative impact on both types of patients. Lastly, our results could be broadly applicable to Veterans suffering from many types of debilitating diseases associated with atrophy.