Sestrin1-knockout mice as a model of facilitated muscle aging

描述（由申请人提供）：肌肉减少症是一种肌肉质量和功能的丧失，是与氧化损伤和细胞凋亡相关的衰老的常见特征。自噬是一种降解不必要的细胞成分的过程，被认为是对抗肌肉细胞损伤和死亡的机制。我们最近发现果蝇Sestrin是一种内源性的抑制衰老相关的肌肉退化。Sestrin是一类具有抗氧化、AMPK激活、TOR抑制和自噬诱导功能的应激诱导蛋白。哺乳动物有三个Sestrin（Sesn 1 -3），而果蝇只有一个Sestrin同源物（dSesn）。在果蝇中，dSesn表达在骨骼肌中高度富集。dSesn无效突变果蝇表现出加速的年龄相关的骨骼肌和心肌退化，其之前是功能障碍的线粒体、泛素化蛋白质聚集体和活性氧（ROS）的积累，所有这些都是由缺陷性自噬引起的。相反，dSesn在老年果蝇中的肌肉特异性过表达增强了肌内自噬，防止了年龄依赖性运动能力下降，并增加了疲劳耐受性。这些结果表明，Sestrin是肌肉生理学的重要稳态调节剂，其促进自噬并减弱与年龄相关的肌病。然而，为了克服昆虫和哺乳动物之间的生理差异，我们需要开发和利用哺乳动物模型来研究Sestrins在年龄相关的肌肉病理学中的作用。在哺乳动物的三种Sestrin中，Sesn 1在骨骼肌和心肌中表达最高。有趣的是，Sesn 1的表达在人类患者的退化肌肉中下调。在响应肥胖或不活动的萎缩小鼠肌肉中也观察到Sesn 1表达减少。通过腺相关病毒载体将Sesn 1重新引入到退化的小鼠肌肉中，部分恢复了功能下降。因此，在这里，我们建议产生和表征Sesn 1基因敲除小鼠，以研究更多关于内源性Sesn 1，预计具有关键的肌保护功能。通过这个模型，我们将评估Sesn 1在骨骼肌中的作用：（i）保持结构完整性和肌肉功能（运动输出）;（ii）在正常衰老过程中保持胰岛素敏感性（代谢输出）。拟议的实验将澄清哺乳动物中的Sesn 1是否确实对预防年龄相关的肌肉变性和代谢紊乱至关重要，类似于果蝇心脏和间接飞行肌肉中的dSesn。除了作为评估Sesn 1功能的相关动物模型外，Sesn 1敲除小鼠还可以用作易化肌肉衰老的有价值的模型。由于Sesn 1在人类肌肉病理学过程中通常下调，通过病毒或药理学手段补充Sesn 1活性可能为老年人群的退化肌肉提供创新的再生方法。

DESCRIPTION (provided by applicant): Sarcopenia, a loss of muscle mass and function, is a common feature of aging which is associated with oxidative damage and apoptosis. Autophagy, a process for degradation of unnecessary cellular constituents, is considered to be a mechanism to combat muscle cell damage and death. We recently found that Drosophila Sestrin is an endogenous suppressor of the age-related muscle degeneration. Sestrins form a family of stress-inducible proteins that have antioxidant, AMPK-activating, TOR-inhibiting and autophagy- inducing functions. Mammals have three Sestrins (Sesn1-3), while Drosophila has a single Sestrin homologue (dSesn). In Drosophila, dSesn expression is highly enriched in skeletal muscles. dSesn-null mutant flies exhibit accelerated age-related skeletal and cardiac muscle degeneration that is preceded by accumulation of dysfunctional mitochondria, ubiquitinated protein aggregates and reactive oxygen species (ROS), all caused by defective autophagy. Conversely, muscle-specific overexpression of dSesn in aged flies enhances intramuscular autophagy, prevents age-dependent mobility decline and increases fatigue tolerance. These results suggest that Sestrin is an important homeostatic regulator of muscle physiology that promotes autophagy and attenuates age-associated myopathies. However, in order to overcome the physiological differences between insects and mammals, we need to develop and utilize mammalian animal models to investigate the role of Sestrins in age-associated muscle pathologies. Among the three Sestrins in mammals, Sesn1 is most highly expressed in skeletal and cardiac muscles. Interestingly, the expression of Sesn1 is downregulated in degenerating muscles of human patients. Reduced Sesn1 expression is also observed in atrophying mouse muscle in response to obesity or inactivity. Reintroduction of Sesn1 through adeno-associated viral vector into the degenerating mouse muscle partially restores the functional decline. Therefore, here we propose to generate and characterize the Sesn1-knockout mice to investigate more about endogenous Sesn1, which is expected to have critical myoprotective functions. Through this model, we will evaluate the role of Sesn1 in skeletal muscles in (i) preserving structural integrity and muscle functionality (mobility output) and (ii) maintaining insulin sensitivity (metabolic output) during normal aging. The proposed experiments will clarify if Sesn1 in mammals indeed is essential for the prevention of age- associated muscle degeneration and metabolic derangements, similar to dSesn in Drosophila cardiac and indirect flight muscle. In addition to being served as a relevant animal model for assessing Sesn1 function, the Sesn1-knockout mice can be also used as a valuable model of facilitated muscle aging. As Sesn1 is generally downregulated during muscle pathology in humans, supplementing Sesn1 activity through viral or pharmacological means may offer innovative rejuvenation methods for degenerating muscle in elderly population.