Mechanisms of protein-energy-wasting in chronic kidney disease

描述（由申请人提供）：肌肉萎缩是慢性肾脏疾病（CKD）的严重并发症，因为它会导致患者的发病率和死亡率。肌肉萎缩主要反映肌原纤维蛋白分解增加。令人信服的证据表明，泛素-蛋白酶体系统（UPS）是骨骼肌蛋白质损失的原因。我们已经证明，在CKD小鼠的肌肉中，IGF-1/PI3激酶/Akt信号抑制通过刺激E3泛素连接酶（Atrogin-1, MuRf-1）来增强UPS活性，从而影响UPS介导的肌肉蛋白水解。IGF-1/PI3K/p- Akt通路的缺陷刺激caspase-3激活并导致肌肉萎缩。我们还发现线粒体功能障碍和能量代谢受损会导致肌肉萎缩。在这个项目中，我计划研究ROCK1作为UPS激活和线粒体功能障碍的关键分子。初步结果表明：1)在CKD小鼠肌肉中，ROCK1活性增加，这种变化与低水平的p-Akt和线粒体裂变增加有关；2)肌肉特异性的ROCK1激活刺激肌肉蛋白水解，导致线粒体功能障碍；3)在CKD小鼠中，敲除ROCK1可改善肌肉萎缩。我们假设CKD激活ROCK1，导致PTEN激活和线粒体裂变，最终导致肌肉萎缩。我们将通过研究以下三个目标来实现这一目标：目的1：确定CKD如何激活ROCK1导致PI3K/Akt信号抑制和肌肉蛋白水解增强。目的2：确定CKD与线粒体功能障碍之间的关系，并探讨ROCK1如何介导线粒体裂变。目的3：确定药物抑制ROCK1和PTEN是否会逆转CKD引起的肌肉萎缩。我们提出了一种调节CKD肌肉蛋白和能量代谢的新途径。因为这个途径可以被药理学控制。我们的研究结果可能用于定义CKD中断的细胞生物学反应。研究结果也可能为设计治疗慢性肾病这一可怕并发症的新疗法迈出最初的一步。

DESCRIPTION (provided by applicant): Muscle wasting is a serious complication of chronic kidney disease (CKD) because it contributes to patient's morbidity and mortality. Muscle wasting mainly reflects increased breakdown of myofibrillar proteins. Compelling evidence has shown that ubiquitin-proteasome system (UPS) is responsible for skeletal muscle protein loss. We have demonstrated that in muscle of CKD mice, depressed IGF-1/PI3 kinase/Akt signaling augments UPS activity via stimulation of the E3 ubiquitin ligases (Atrogin-1, MuRf-1) that affect UPS-mediated muscle proteolysis. Defects in the IGF-1/PI3K/p- Akt pathway stimulate caspase-3 activation and contribute to muscle wasting. We also have discovered that mitochondrial dysfunction and impaired energy metabolism contribute to muscle wasting. In this proposed project, I plan to study ROCK1 as a key molecule linked both to UPS activation and mitochondrial dysfunction. The proposed project is supported by preliminary Results: 1) in muscle of CKD mice, ROCK1 activity is increased and this change is associated with low levels of p-Akt and increased mitochondrial fission; 2) muscle-specific ROCK1 activation stimulates muscle proteolysis and causes mitochondrial dysfunction; and 3) in CKD mice, knockout of ROCK1 ameliorates muscle wasting. We hypothesize that CKD activates ROCK1 leading to both PTEN activation and mitochondria fission, ultimately resulting in muscle wasting. We will accomplish this goal by studying the following three aims Aim 1: To determine how CKD activates ROCK1 leading to depressed PI3K/Akt signaling and enhanced muscle proteolysis. Aim 2: To determine an association between CKD and mitochondrial dysfunction and explore how ROCK1 mediates mitochondrial fission. Aim 3: To determine if pharmacologic inhibition of ROCK1 and PTEN will reverse the muscle wasting caused by CKD. We propose a new pathway that regulates muscle protein and energy metabolism in CKD. Since this pathway can be manipulated pharmacologically. The results of our study might be used to define cell biologic responses that are interrupted by CKD. The results also might yield the initial steps towards designing new therapies for this dreaded complication of CKD. .