FOXO signaling and skeletal muscle atrophy

描述（由申请人提供）：骨骼肌萎缩是一种广泛的生理现象和重大的健康问题，与肌肉失用（固定、卧床、去神经支配）和各种疾病（癌症、败血症、艾滋病、糖尿病、慢性心力衰竭、慢性阻塞性肺病）有关。然而，我们对在萎缩状态下调节肌肉质量的信号分子的理解尚不明确。因此，我们研究计划的长期目标是了解在各种情况下导致肌肉萎缩的信号通路的调节。最终，了解的改善将导致确定具体干预措施的最合适目标。已知引起骨骼肌萎缩的一个蛋白质家族是FOXO家族，FOXO信号在各种萎缩情况下增加，包括石膏固定，败血症，癌症和饥饿。然而，我们对骨骼肌中FOXO信号调控的理解主要局限于通过IGF1/PI3K/Akt途径磷酸化FOXO因子。虽然这一途径在FOXO信号的调节中显然很重要，但另一种调节机制乙酰化似乎在调节FOXO信号方面同样重要，至少在培养的非肌肉细胞中是如此。然而，目前尚不清楚FOXO因子的乙酰化是否是骨骼肌中FOXO信号在任何肌肉萎缩状态下的调节机制。当前提案的总体目标是确定乙酰转移酶（HAT）蛋白和去乙酰化酶（HDAC）蛋白以及FOXO因子的乙酰化和去乙酰化在调节FOXO信号传导中与骨骼肌萎缩相关的作用。为了解决这个问题，在目的1中，我们将转染野生型（WT）或显性阴性（d.n）的C2C12骨骼肌细胞。HAT蛋白并确定其对内源性FOXO信号的调控。随后，我们将选择一种HAT蛋白在肌肉失用和癌症期间对整个骨骼肌进行进一步研究。在目标2中，我们将转染野生型（WT）或显性阴性（d.n）的C2C12骨骼肌细胞。HDAC蛋白并确定其对内源性FOXO信号的调节。随后，我们将选择一种HDAC蛋白在肌肉失用和癌症期间的整个骨骼肌中进行进一步研究。在Aim 3中，我们将用编码FOXO乙酰化突变体的质粒转染C2C12骨骼肌细胞，这些突变体模拟FOXO的乙酰化或去乙酰化形式，并确定它们对FOXO信号传导的调节。在这些目标中，我们将测量FOXO转录活性，FOXO- DNA结合，FOXO细胞定位，FOXO因子的翻译后修饰，已知FOXO靶基因子集的转录和骨骼肌纤维横截面积。这些实验的发现将导致对FOXO信号调控的更好理解，因为它与骨骼肌萎缩有关。

DESCRIPTION (provided by applicant): Skeletal muscle atrophy is a widespread physiological phenomenon and significant health problem associated with muscle disuse (immobilization, bedrest, denervation) and various diseases (cancer, sepsis, AIDS, diabetes, chronic heart failure, chronic obstructive pulmonary disease). However, our understanding of the signaling molecules that regulate muscle mass during an atrophy condition are ill defined. Therefore the long- range goal of our research program is to understand the regulation of signaling pathways that cause muscle atrophy during various conditions. Eventually improved understanding will lead to the identification of the most suitable targets for specific interventions. One family of proteins that is known to cause skeletal muscle atrophy is the FOXO family, and FOXO signaling is increased in a variety of atrophy conditions, including cast immobilization, sepsis, cancer and starvation. However, our understanding of the regulation of FOXO signaling in skeletal muscle is largely confined to the phosphorylation of FOXO factors via the IGF1/PI3K/Akt pathway. While this pathway is clearly important in the regulation of FOXO signaling, another mechanism of regulation, acetylation, appears to be equally important in regulating FOXO signaling, at least in cultured non-muscle cell. However, it is currently unknown whether acetylation of FOXO factors is a regulatory mechanism of FOXO signaling in skeletal muscle during any condition of muscle atrophy. The overall objective of the current proposal is to determine the role of acetyltransferase (HAT) proteins and deacetylase (HDAC) proteins, and acetylation and deacetylation of FOXO factors, in regulating FOXO signaling as it relates to skeletal muscle atrophy. To address this, in Aim 1 we will transfect C2C12 skeletal muscle cells with wild type (WT) or dominant negative (d.n.) HAT proteins and determine their regulation of endogenous FOXO signaling. We will subsequently select one HAT protein for further study in whole skeletal muscle during muscle disuse and cancer. In Aim 2 we will transfect C2C12 skeletal muscle cells with wild type (WT) or dominant negative (d.n.) HDAC proteins and determine their regulation of endogenous FOXO signaling. We will subsequently select one HDAC protein for further study in whole skeletal muscle during muscle disuse and cancer. In Aim 3 we will transfect C2C12 skeletal muscle cells with plasmids encoding FOXO acetylation mutants that mimic either the acetylated or deacetylated forms of FOXO and determine their regulation of FOXO signaling. In each of these Aims we will measure FOXO transcriptional activity, FOXO- DNA binding, FOXO cellular localization, post-translational modifications of FOXO factors, the transcription of a sub-set of known FOXO target genes, and skeletal muscle fiber cross sectional area. The findings from these experiments will lead to a greater understanding of the regulation of FOXO signaling as it relates to skeletal muscle atrophy.