Sestrin1-knockout mice as a model of facilitated muscle aging

描述(申请人提供)：骨骼减少，肌肉质量和功能的丧失，是衰老的一个共同特征，与氧化损伤和细胞凋亡有关。自噬是一种降解不必要细胞成分的过程，被认为是对抗肌肉细胞损伤和死亡的一种机制。我们最近发现果蝇Sestrin是年龄相关性肌肉退行性变的内源性抑制因子。Sestrins形成一个压力诱导蛋白家族，具有抗氧化、AMPK激活、TOR抑制和自噬诱导功能。哺乳动物有三个Sestrin(Sesn1-3)，而果蝇只有一个Sestrin同源物(DSesn)。在果蝇中，dSesn在骨骼肌中的表达高度丰富。DSesn缺失突变果蝇表现出与年龄相关的骨骼和心肌加速退化，在此之前，功能障碍的线粒体、泛素化蛋白质聚集体和活性氧物种(ROS)积累，所有这些都是由缺陷的自噬引起的。相反，在老年果蝇中，肌肉特异的dSesn过表达增强了肌肉内的自噬，防止了与年龄相关的活动能力下降，并提高了疲劳耐受性。这些结果表明，Sestrin是肌肉生理学中一种重要的动态平衡调节剂，它促进自噬并减轻与年龄相关的肌病。然而，为了克服昆虫和哺乳动物之间的生理差异，我们需要建立和利用哺乳动物动物模型来研究Sestrins在年龄相关肌肉病理中的作用。在哺乳动物的三种Sestrin中，Sesn1在骨骼肌和心肌中表达最高。有趣的是，在人类患者的退行性肌肉中，Sesn1的表达下调。在肥胖或缺乏运动的萎缩的小鼠肌肉中也观察到Sesn1表达的减少。通过腺相关病毒载体将Sesn1重新引入退化的小鼠肌肉中，部分恢复了功能的下降。因此，我们建议建立和鉴定Sesn1基因敲除小鼠，以更多地研究内源性Sesn1，它被认为具有关键的心肌保护功能。通过这个模型，我们将评估骨骼肌中Sesn1在(I)保持结构完整性和肌肉功能(运动输出)和(Ii)在正常衰老过程中维持胰岛素敏感性(代谢输出)方面的作用。拟议的实验将澄清哺乳动物中的Sesn1是否确实对防止与年龄相关的肌肉退化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。除了被用作评估Sesn1功能的相关动物模型外，Sesn1基因敲除小鼠还可以被用作促进肌肉衰老的有价值的模型。由于Sesn1在人类肌肉病理过程中普遍下调，通过病毒或药物手段补充Sesn1活性可能为老年人退化的肌肉提供创新的年轻化方法。

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.