Ca Sparks in Muscle Aging and Dystrophy

描述（由申请人提供）：Ca火花是横纹肌细胞中Ca诱导的Ca释放（CICR）的基本单位，通过共聚焦显微镜显示为肌浆网（SR）的局部Ca释放事件。虽然Ca火花在心肌中被很好地定义，但人们普遍认为这些局部Ca释放事件在完整的成年哺乳动物骨骼肌中是罕见的。由于在完整的哺乳动物肌肉中监测Ca火花活性的内在困难，CICR在肌肉功能中的调节以及CICR在肌肉老化和营养不良中的适应性变化的细胞和分子机制仍然在很大程度上未被探索。最近，我们发现，膜变形所产生的应力诱导一个强大的钙火花响应空间局限在靠近健康的年轻哺乳动物肌肉的肌膜。这些诱导的钙火花在年轻的肌纤维中是可重复的和可逆的，但在老年骨骼肌中变得短暂和静态。在具有脆弱膜完整性的营养不良肌肉中，诱导的Ca火花是不可逆的，并且从外周渗透到纤维内部。因此，不受控制的Ca火花活性可能导致SR Ca库的部分耗尽，触发增加的钙库操作的Ca进入（SOCE）并在哺乳动物骨骼肌中提供营养不良信号。我们假设，钙火花可以被用来作为衡量的CICR在肌肉健康，老化和营养不良的塑料性质。本项目中提出的实验将集中于解决以下关于骨骼肌中钙火花生理功能的基本问题：首先，什么是负责年轻健康骨骼肌中钙火花外周分布和可塑性的细胞因子？第二，钙火花和SOCE之间是否存在动态的双向耦合，这种耦合的改变是否会导致肌肉功能障碍？第三，三联体常驻蛋白如何影响健康、衰老和疾病中的钙火花功能？由于CICR的控制缺陷与许多病理状态有关，包括心力衰竭和神经退行性疾病，我们希望从我们的研究中获得的知识不仅有助于建立骨骼肌纤维中应激诱导的Ca火花的生理功能，还可能指向观察到CICR功能障碍的可兴奋细胞中的潜在治疗靶点。

DESCRIPTION (provided by applicant): Ca sparks are the elementary units of Ca-induced Ca release (CICR) in striated muscle cells revealed as localized Ca release events from sarcoplasmic reticulum (SR) by confocal microscopy. While Ca sparks are well defined in cardiac muscle, there has been a general belief that these localized Ca release events are rare in intact adult mammalian skeletal muscle. As a result of the intrinsic difficulties in monitoring Ca spark activity in intact mammalian muscle, the cellular and molecular mechanisms underlying the regulation of CICR in muscle function and the adaptive changes of CICR in muscle aging and dystrophy remain largely unexplored. Recently, we discovered that stress generated by membrane deformation induces a robust Ca spark response spatially confined in close proximity to the sarcolemmal membrane in healthy young mammalian muscles. These induced Ca sparks are repeatable and reversible in young muscle fibers, but become transient and static in aged skeletal muscle. In dystrophic muscle with fragile membrane integrity, induced Ca sparks are irreversible and penetrate from the periphery to the fiber interior. Thus, uncontrolled Ca spark activity could potentially lead to partial depletion of the SR Ca store, triggering increased store- operated Ca entry (SOCE) and providing a dystrophic signal in mammalian skeletal muscle. We hypothesize that Ca sparks can be used as a measure of the plastic nature of CICR in muscle health, aging and dystrophy. Experiments proposed in this project shall focus on addressing the following fundamental questions regarding the physiological function of Ca sparks in skeletal muscle: First, what are the cellular factors that are responsible for the peripheral distribution and the plasticity of Ca sparks in young, healthy skeletal muscle? Second, is there dynamic bi-directional coupling between Ca sparks and SOCE, and does alteration of this coupling produce muscle dysfunction? Third, how do triad-junction resident proteins influence Ca spark function in health, aging and disease? As defects in control of CICR have been linked to numerous pathologic states, including heart failure and neurodegenerative conditions, we hope knowledge gained from our studies will not only help establish the physiological function of stress-induced Ca sparks in skeletal muscle fibers, they may also point to potential therapeutic targets in excitable cells where dysfunction of CICR has been observed.