CELLULAR ENERGETICS AS A REGULATOR OF MUSCLE MASS AND MITOCHONDRIAL CONTENT DURING MUSCLE ATROPHY

项目摘要 骨骼肌萎缩是许多慢性疾病（如癌症、糖尿病、糖尿病）致残和死亡的主要原因。 以及心力衰竭。尽管病因各异，但萎缩的肌肉有许多共同的特征，如肌肉萎缩。 线粒体含量和抑郁的能量状态。一种可能的肌肉质量和线粒体的调节器- 在萎缩过程中，代谢酶AMP脱氨酶（AMPD）是一种代谢酶，其亚型3增加至100- 200。 在萎缩期间折叠。AMPD催化AMP的代谢不可逆降解，从而也 控制腺嘌呤核苷酸（ATP ParticipADP ParticipAMP）池的大小。结合或降解AMP是特别重要的。 这一点非常重要，因为它的游离、胞质水平是由能量感应酶AMP激活的前体蛋白检测的。 蛋白激酶（AMPK），一种被充分描述的线粒体内容物诱导剂。因此，AMPD 3被独特地定位为 调节主要的细胞内能量信号，[AMP]/[ATP]比率。到目前为止， 肌肉萎缩、细胞能量学和线粒体生物发生在很大程度上是未知的。的长期目标 这个项目是为了确定新的目标，以增加肌肉质量，线粒体含量，并可能改善 萎缩肌肉的能量状态和功能。本申请的目的是确定在 肌肉萎缩AMPD 3减少线粒体产生并加速肌肉蛋白质损失。中央 一种假说是，高水平的AMPD 3，降解腺嘌呤核苷酸库，触发线粒体的丧失， 并增加蛋白质降解的速率。这部分是基于令人兴奋的初步数据， 培养的肌肉显示AMPD 3的过表达模拟萎缩的能量不足，增加蛋白质表达， 水解率，并降低蛋白质含量;而成年肌肉中AMDP 3的敲低可保护免受mus- 周期性失神经萎缩体重减轻。为了检验中心假设，我们建议击倒或删除 由于各种能量损伤而非萎缩或萎缩的骨骼肌纤维/细胞中的AMPD 3： 手术切除一条后肢的神经（减少能量需求）、食物剥夺（减少能量需求） 供应）和糖皮质激素治疗（需求增加和供应减少）。本提案的目的 目的是1）确定AMP脱氨酶作为骨骼肌线粒体丢失介质的作用 2）确定AMP脱氨酶在骨骼肌萎缩过程中作为蛋白质丢失介质的作用， rophy。目前的假设是，萎缩期间AMPD 3的丢失将增加[AMP]、线粒体生物- 起源和线粒体含量。相反，AMPD 3的过表达，由于细胞内的损伤， 能量，将引发加速蛋白质降解和肌肉纤维大小损失。预期的结果是， 这项提案展示了肌肉萎缩的能量控制，不仅将为如何控制肌肉萎缩提供新的见解， 能量学/代谢和肌肉质量是机械地联系在一起的，但也有望揭示新的 治疗目标是减缓或停止大多数（如果不是全部）萎缩状况下的肌肉质量损失。

Project Summary Skeletal muscle atrophy is a major cause of disability and death in many chronic diseases, e.g. cancer, diabe- tes, and heart failure. Despite diverse etiology, atrophying muscles share many common features, like loss of mitochondrial content and depressed energetic state. One probable regulator of muscle mass and mitochon- dria during atrophy is the metabolic enzyme AMP deaminase (AMPD), which isoform 3 is increased up to 100- fold during atrophy. AMPD catalyzes the thermodynamically irreversible degradation of AMP and thereby also controls the size of the adenine nucleotide (ATP ↔ ADP ↔ AMP) pool. Binding or degrading AMP is particu- larly important since its free, cytosolic levels are detected by the energy sensing enzyme AMP-activated pro- tein kinase (AMPK), a well-described inducer of mitochondrial content. Thus, AMPD3 is uniquely positioned to modulate a major intracellular energetic signal, [AMP]/[ATP] ratio. To date, the molecular mechanisms that link muscle atrophy, cellular energetics, and mitochondria biogenesis are largely unknown. The long-term goal of this project is to identify new targets to increase muscle mass, mitochondrial content and perhaps improve the energetic state and function of atrophic muscle. The objective of this application is to determine whether during muscle atrophy AMPD3 decreases mitochondrial production and accelerates muscle protein loss. The central hypothesis is that high levels of AMPD3, which degrades the adenine nucleotide pool, triggers loss of mito- chondria and increases the rate of protein degradation. This is based, in part, on exciting preliminary data from cultured muscle showing that overexpression of AMPD3 mimics the energy deficit of atrophy, increases prote- olysis rate, and decreases protein content; while knockdown of AMDP3 in adult muscle protects against mus- cle weight loss of denervation atrophy. To test the central hypothesis, we propose to knockdown or remove AMPD3 in skeletal muscle fibers/cells that are non-atrophying or atrophying due to various energetic insults: either surgical denervation of one hindlimb (decreased energy demand), food deprivation (decreased energy supply), and glucocorticoid treatment (increase in demand and decrease in supply). The Aims of this proposal are to 1) To determine the role of AMP deaminase as a mediator of mitochondrial loss during skeletal muscle atrophy, and 2) determine the role of AMP deaminase as a mediator of protein loss during skeletal muscle at- rophy. The working hypotheses are that loss of AMPD3 during atrophy will increase [AMP], mitochondrial bio- genesis, and mitochondrial content. Conversely, overexpression of AMPD3, because of impairment in cellular energetics, will trigger accelerated protein degradation and muscle fiber size loss. The expected results of this proposal, demonstrating the energetic control of muscle atrophy, will not only provide novel insights into how energetics/metabolism and muscle mass are linked mechanistically, but will also be expected to reveal novel therapeutic targets to slow or stop muscle mass loss in most, if not all, atrophy conditions.