Glucocorticoid control of gene expression during skeletal muscle atrophy

描述(申请人提供)：骨骼肌萎缩，或萎缩，是一个主要的人类健康问题。制动、神经损伤、恶病质、脓毒症和衰老会导致骨骼肌块显著减少，甚至危及生命，甚至损害足够的活动或呼吸功能。肾上腺糖皮质激素是骨骼肌萎缩的有力诱因。生理糖皮质激素水平支持禁食和慢性病等分解代谢条件下的肌肉萎缩。此外，合成的糖皮质激素被用作有效的抗炎药物，具有严重的副作用，如高血糖、胰岛素抵抗、骨、软骨和肌肉丧失。新的选择性糖皮质激素受体配体已被描述为抑制炎症基因的表达，但对其他类型的糖皮质激素反应基因的上调作用较弱，因此显示出良好的药物潜力。然而，这些化合物都没有被评估对骨骼肌的影响。选择性地抑制骨骼肌中糖皮质激素受体的作用将为在各种条件下缓解萎缩提供机会。在这项研究中，我们将集中于最近发现的两个E3泛素连接酶MuRF1和MAFbx在糖皮质激素诱导的骨骼肌萎缩中的作用及其转录激活。我们建议1)利用选择性基因缺失的小鼠来确定MuRF1和MAFbx基因在糖皮质激素诱导的骨骼肌萎缩中的相对作用，2)研究糖皮质激素受体在诱导肌肉萎缩中的作用，以及利用肌肉特异性的糖皮质激素受体缺失的小鼠来研究MuRF1和MAFbx的表达，3)利用染色质免疫沉淀分析来研究糖皮质激素受体和FOXO蛋白在调节MuRF1基因表达中的作用，以及4)评价选择性抗炎糖皮质激素配体对肌肉萎缩和MuRF1和MAFbx表达的影响。新开发的遗传资源、药理工具和分子技术可以在研究人员的实验室和关键合作中实现这些目标。因此，这项提议提供了一个机会，将有关糖皮质激素受体功能的新概念和尖端技术直接应用于临床相关和尚未解决的骨骼肌萎缩问题。

DESCRIPTION (provided by applicant): Skeletal muscle wasting, or atrophy, is a major human health concern. Immobilization, nerve damage, cachexia, sepsis, and aging induce significant and potentially life-threatening losses in skeletal muscle mass to the point of impairing adequate ambulatory or respiratory function. Adrenal glucocorticoid hormones are potent inducers of skeletal muscle atrophy. Physiological glucocorticoid levels support muscle atrophy in fasting and chronic illness among other catabolic conditions. In addition, synthetic glucocorticoids are used clinically as potent anti-inflammatory drugs with serious side effects such as hyperglycemia, insulin resistance, and bone, cartilage, and muscle loss. New selective glucocorticoid receptor ligands have been described that repress inflammatory gene expression but are less potent at up- regulation of other classes of glucocorticoid responsive genes, thus showing good pharmaceutical potential. However, none of these compounds have been evaluated for effects on skeletal muscle. Inhibition of glucocorticoid receptor action selectively in skeletal muscle would present an opportunity to alleviate atrophy under a variety of conditions. In this proposal, we will focus on the role of two recently identified E3 ubiquitin ligases, MuRF1 and MAFbx, in glucocorticoid induced skeletal muscle atrophy, and their transcriptional activation. We propose to 1) determine the relative contribution of MuRF1 and MAFbx genes to glucocorticoid induced skeletal muscle atrophy using mice with selective gene deletions, 2) investigate the role of the glucocorticoid receptor in the induction of muscle atrophy, as well as, MuRF1 and MAFbx expression using mice with a muscle-specific deletion of the glucocorticoid receptor, 3) investigate the role of the glucocorticoid receptor and FOXO proteins in regulating MuRF1 gene expression using chromatin immunoprecipitation assays, and 4) evaluate selective anti-inflammatory glucocorticoid ligands for effects on muscle atrophy and MuRF1 and MAFbx expression. Newly developed genetic resources, pharmacological tools, and molecular techniques are available to accomplish these aims in the investigator's laboratories and through key collaborations. Thus, this proposal represents an opportunity to apply new concepts and cutting-edge technology regarding glucocorticoid receptor function directly to the clinically relevant and unmet problem of skeletal muscle atrophy.