Isoform-specific roles of the Na,K-ATPase in skeletal muscle

描述（由申请人提供）：骨骼肌无力和疲劳是心力衰竭、肌肉减少症、恶病质、肌营养不良、COPD和其他疾病中常见的使人衰弱的病症。Na，K-ATP酶活性在肌肉收缩过程中受到显著刺激，并且绝对需要保持力量和运动性能。然而，很少有研究探讨Na，K-ATP酶亚型在肌无力和疲劳中的作用。成人骨骼肌主要表达Na，K-ATP酶的α2亚型，而大多数其他组织主要表达α1亚型。α2亚型在骨骼肌中的作用及其活性刺激机制尚不清楚。本研究的中心假设是Na，K-ATP酶α2亚型提供了一种储备能力，这种储备能力在静息时基本上是无活性的，但在收缩期间迅速受到刺激，以满足对Na/K转运的增加的需求;并且其调节部分是通过Na，K-ATP酶的肌肉特异性FXYD 1亚基的磷酸化来实现的。将使用一种新的基因靶向小鼠来检验这一假设，该小鼠在成年骨骼肌中特异性缺乏Na，K-ATP酶α2（skα2-/-），并显示出明显的运动不耐受和骨骼肌无力。具体目标是：1）确定Na，K-ATP酶α2酶在维持力量和运动表现中的急性作用; 2）确定Na，K-ATP酶α2酶在横小管中的膜兴奋和抗疲劳性中的作用;和3）a，确定FXYD 1磷酸化在收缩期间通过α2-肾上腺素能受体活化对Na，K-ATP酶α2活性的急性刺激中的作用; B，确定心力衰竭中Na，K-ATP酶含量或功能改变对肌肉疲劳和运动不耐受的贡献。这些目标将采用一种综合策略来实现，该策略将小鼠中的遗传操作与从动物到细胞和亚细胞水平的功能测量相结合。总的来说，该项目将促进我们对Na，K-ATP酶α2亚型的生理作用及其在骨骼肌中调节的机制的理解，并确定用于肌无力和疲劳治疗干预的新分子靶点。

DESCRIPTION (provided by applicant): Skeletal muscle weakness and fatigue is a common, debilitating condition in heart failure, sarcopenia, cachexia, muscular dystrophies, COPD, and other disorders. Na,K-ATPase activity is dramatically stimulated during muscle contraction and is absolutely required to maintain force and exercise performance. However, few studies have examined the role the Na,K-ATPase isoforms in muscle weakness and fatigue. Adult skeletal muscles express mainly the α2 isoform of the Na,K-ATPase, in contrast to most other tissues which express mainly the α1 isoform. The role of the α2 isoform in skeletal muscle and the mechanisms by which its activity is stimulated are not known. The central hypotheses of this research is that the Na,K-ATPase α2 isoform provides a reserve capacity which is largely inactive at rest but is rapidly stimulated during contraction, to meet the increased demand for Na/K transport; and that its regulation is achieved in part by phosphorylation of the muscle-specific FXYD1 subunit of the Na,K-ATPase. This hypothesis will be tested using a novel gene targeted mouse which specifically lacks the Na,K-ATPase α2 in adult skeletal muscles (skα2-/-) and shows marked exercise intolerance and skeletal muscle weakness. The Specific Aims are to: 1) Determine the acute role of the Na,K-ATPase α2 enzyme in maintaining force and exercise performance; 2) Determine the role of the Na,K-ATPase α2 enzyme in membrane excitation in the transverse tubules and resistance to fatigue; and 3) a, Define the role of FXYD1 phosphorylation in the acute stimulation of Na,K-ATPase α2 activity by α2- adrenergic receptor activation during contraction; b, Determine the contribution of altered Na,K-ATPase content or function to muscle fatigue and exercise intolerance in heart failure. These Aims will be approached using an integrated strategy which combines genetic manipulations in the mouse with functional measurements from the animal to the cellular and subcellular level. Collectively, this project will advance our understanding of the physiological roles of the Na,K-ATPase α2 isoform and the mechanisms by which it is regulated in skeletal muscle, and identify new molecular targets for therapeutic interventions in muscle weakness and fatigue.