Molecular mechanisms of oxidative stress in aging muscle

描述（由申请人提供）：随着年龄的增长，我们的肌肉质量在50岁以后以每年约1-2%的速度下降。这种与年龄相关的肌肉萎缩被称为肌肉减少症，人们对它的了解相对较少，它会影响身体虚弱的严重程度，并对个人健康和生活质量产生重大影响。虽然肌少症的具体机制尚不清楚，但衰老肌肉中的能量不足与肌肉萎缩和凋亡细胞死亡的前兆密切相关，这表明线粒体功能障碍可能在肌少症的进展中起重要作用。先前的研究表明，线粒体氧化功能能力随着年龄的增长而下降，这与线粒体复合体I和复合体III的氧化剂产生增加有关。然而，由于认识到存在两种不同的线粒体种群：位于肌原纤维之间平行排列的纤维间线粒体（IFM）和位于质膜下方的肌下线粒体（SSM），骨骼肌线粒体年龄相关变化的表征变得复杂。IFM可能是肌肉收缩过程中ATP的主要来源，因此我们认为，随着年龄的增长，IFM更有可能积累氧化损伤。我们的中心假设是IFM在复合物I和III中表现出更大的自由基泄漏和氧化损伤，这是导致线粒体功能障碍增加、骨骼肌萎缩和收缩功能下降的原因，与I型肌肉相比，所有这些都可能在II型肌肉中放大。在我们提出的实验中，我们将获得年轻，中年和老年大鼠，测定骨骼肌收缩功能，细胞凋亡和I型和II型肌肉的肌肉减少程度，我们将从两种纤维类型中分离IFM和SSM并测量生物能量学的关键参数。在第二个系列实验中，我们将检查相同的因素和变量，但增加了两种已被证明可以延长寿命的具有良好特征的干预措施：卡路里限制和终身轮式跑步，以确定这些干预措施显着改善与年龄相关的氧化损伤、线粒体功能障碍和肌肉损失的机制。这可能为肌少症的机制提供证据，也可能提供线粒体功能障碍对肌肉细胞功能和收缩性有负面影响的第一个直接证据。

DESCRIPTION (provided by applicant): With age we lose muscle mass at approximately 1-2% per year past the age of 50. This age-related muscle atrophy, termed sarcopenia, is relatively poorly understood, impacts the severity of frailty, and has significant effects on individual health and quality of life. While the specific mechanisms underlying sarcopenia are unknown, energy deficits in aging muscle have been strongly implicated as precursors to muscle atrophy and apoptotic cell death, suggesting that mitochondrial dysfunction may play a significant role in the progression of sarcopenia. Previous studies have shown decreased mitochondrial oxidative functional capacity with age, which was associated with increased oxidant production in mitochondrial complex I and complex III. However, characterization of age-related changes to skeletal muscle mitochondria has been complicated by the realization that two distinct populations of mitochondria exist: interfibrillar mitochondria (IFM), which are found in parallel rows between the myofibrils, and subsarcolemmal mitochondria (SSM), which are located beneath the plasma membrane. IFM are likely the primary source of ATP during muscle contraction, and we believe they are therefore more likely to accumulate oxidative damage with age. Our central hypothesis is that IFM exhibits a greater free radical leak in complex I and III and oxidative damage, and that this is responsible for increased mitochondrial dysfunction, skeletal muscle atrophy and decreased contractile function, all of which could be amplified in type II muscle compared with type I muscle. In the proposed experiments, we will obtain young, mid-aged and old rats, determine skeletal muscle contractile function, apoptosis and the extent of sarcopenia in type I and type II muscle, and we will isolate IFM and SSM from both fiber types and measure key parameters of bioenergetics. In a second series of experiments, we will examine the same factors and variables, but with addition of two well-characterized interventions that have been shown to extend life span: calorie restriction and life-long wheel running, to determine the mechanisms by which these interventions significantly ameliorate age-related oxidative damage, mitochondrial dysfunction and muscle loss. This could provide evidence for the mechanisms underlying sarcopenia, and may also provide the first direct evidence that mitochondrial dysfunction has a negative impact on muscle cell function and contractility.