Heat shock proteins and disuse muscle atrophy

描述（由申请人提供）： 骨骼肌废用性萎缩是一种广泛的生理现象，与固定、卧床休息、去神经支配和太空飞行或任何一般的负重活动减少有关。然而，我们对废用过程中调节肌肉质量的信号分子的理解是不明确的。因此，我们研究计划的长期目标是了解在废用过程中导致肌肉萎缩的信号通路的调节。最终，通过加深了解，将确定具体干预措施的目标。热休克蛋白（Heat shock proteins，Hsps）是一类在细胞中组成型表达的蛋白质，但其表达可被多种细胞应激进一步快速诱导。这种诱导已经显示出提供多种细胞保护功能。在肌肉废用期间，热休克家族的成员Hsp 70持续下调，并且在废用期间Hsp 70的过表达消除NF-：B和Foxo 3a反式激活的增加，并且完全防止骨骼肌萎缩。这是重要的，因为NF-：B和Foxo 3a是废用性肌肉萎缩所必需的。然而，目前尚不清楚Hsp 70过表达是否足以特异性抑制NF-κ B诱导或Foxo 3a诱导的肌肉萎缩。也不知道Hsp 70的敲低是否足以引起骨骼肌萎缩。本提案的目的是在目的1和2中确定Hsp 70表达的增加是否足以抑制NF-κ B诱导的或Foxo 3a诱导的肌纤维萎缩，以及在目的3中确定Hsp 70的敲低是否足以引起肌纤维萎缩。为了解决这些特定的目的，我们将WT IKK 2加Hsp 70表达质粒（Aim 1）、WT Foxo 3a加Hsp 70表达质粒（Aim 2）或产生Hsp 70特异性shRNA的质粒（Aim 3）注射到大鼠的骨骼肌中，并测量NF-：B或Foxo 3a活性、特定萎缩基因的mRNA表达和肌纤维横截面积。如果Hsp 70表达的增加抑制NF-：B活性和/或Foxo 3a活性，我们将通过确定Hsp 70结合的每个途径中的蛋白质来确定其机制。这些实验的发现将导致更深入地了解热休克蛋白70在骨骼肌萎缩过程中对NF-：B和Foxo 3a信号传导的调节。 公共卫生相关性： 由于废用而导致的骨骼肌萎缩与固定、卧床休息、去神经支配和太空飞行或任何承重活动的一般减少有关。在拟议的工作中，我们将在基因上过表达或敲低一种蛋白质，这种蛋白质被认为是调节肌肉大小的，并且已知在废用引起的肌肉萎缩期间被下调。这将使我们能够直接确定这种蛋白质参与骨骼肌质量的调节，并可以将这种蛋白质确定为肌肉萎缩的新治疗靶点。

DESCRIPTION (provided by applicant): Project summary/Abstract Skeletal muscle disuse atrophy is a widespread physiological phenomenon associated with immobilization, bed rest, denervation, and space flight, or any general reduction in weight bearing activity. However, our understanding of the signaling molecules that regulate muscle mass during disuse 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 disuse. Eventually improved understanding will lead to the identification of targets for specific interventions. Heat shock proteins (Hsps) are a family of proteins that are constitutively expressed in cells, but whose expression is further, and rapidly, induced by a variety of cellular stresses. This induction has been shown to provide a variety of cytoprotective functions. During muscle disuse a member of the heat shock family, Hsp70, is consistently down-regulated and overexpression of Hsp70 during disuse abolishes the increase in NF-:B and Foxo3a transactivation, and completely prevents skeletal muscle atrophy. This is important since NF-:B and Foxo3a are required for disuse muscle atrophy. However, it is currently unknown whether Hsp70 overexpression is sufficient to specifically inhibit NF-:B-induced or Foxo3a-induced muscle atrophy. It is also unknown whether knock down of Hsp70 is sufficient to cause skeletal muscle atrophy. The objective of the current proposal is to determine in Aims 1 and 2 if an increase in Hsp70 expression is sufficient to inhibit NF-:B-induced or Foxo3a-induced muscle fiber atrophy, and in Aim 3 if knock down of Hsp70 is sufficient to cause muscle fiber atrophy. To address these specific aims we will inject WT IKK2 plus Hsp70 expression plasmids (Aim 1), WT Foxo3a plus Hsp70 expression plasmids (Aim 2), or a plasmid producing shRNAs specific for Hsp70 (Aim 3) into the skeletal muscle of rats and measure NF-:B or Foxo3a activity, the mRNA expression of specific atrophy genes and muscle fiber cross sectional area. If an increase in Hsp70 expression inhibits NF-:B activity and/or Foxo3a activity we will determine the mechanisms of this by determining the proteins in each pathway that Hsp70 binds. The findings from these experiments will lead to a greater understanding of Hsp70 in the regulation of NF-:B and Foxo3a signaling during skeletal muscle atrophy. PUBLIC HEALTH RELEVANCE: Project Narrative Skeletal muscle wasting due to disuse is associated with immobilization, bed rest, denervation, and space flight, or any general reduction in weight bearing activity. In the proposed work we will genetically overexpress or knock down a protein that is believed to regulate muscle size and is known to be down-regulated during muscle wasting caused by disuse. This will allow us to directly determine the involvement of this protein in the regulation of skeletal muscle mass, and could identify the protein as a novel therapeutic target for muscle wasting.