Glucocorticoid control of gene expression during skeletal muscle atrophy

描述（由申请人提供）：骨骼肌萎缩是一个主要的人类健康问题。固定、神经损伤、恶病质、败血症和衰老会导致骨骼肌质量的严重损失，甚至可能危及生命，从而损害足够的运动或呼吸功能。肾上腺糖皮质激素是骨骼肌萎缩的有效诱导剂。生理糖皮质激素水平支持肌肉萎缩在禁食和慢性疾病在其他分解代谢条件。此外，合成糖皮质激素在临床上被用作强效抗炎药，但有严重的副作用，如高血糖、胰岛素抵抗、骨、软骨和肌肉损失。新的选择性糖皮质激素受体配体抑制炎症基因表达，但对其他类型的糖皮质激素应答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。在骨骼肌中选择性地抑制糖皮质激素受体的作用，将有机会缓解多种条件下的萎缩。在本提案中，我们将重点关注最近发现的两种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。我们打算用选择性基因缺失的小鼠来确定MuRF1和MAFbx基因对糖皮质激素诱导的骨骼肌萎缩的相对贡献，2)研究糖皮质激素受体在诱导肌肉萎缩中的作用，以及用肌肉特异性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法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；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、药理学工具和分子技术可以在研究者的实验室和通过关键合作来实现这些目标。因此，这一建议代表了将糖皮质激素受体功能的新概念和前沿技术直接应用于骨骼肌萎缩临床相关和未解决的问题的机会。

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.