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。虽然钙火花在心肌中有明确的定义，但人们普遍认为，这些局部钙释放事件在完整的成年哺乳动物骨骼肌中很少见。由于在完整哺乳动物肌肉中监测Ca火花活性的内在困难，CICR调控肌肉功能的细胞和分子机制以及CICR在肌肉衰老和营养不良中的适应性变化在很大程度上仍未被探索。最近，我们发现由膜变形产生的应力在健康的年轻哺乳动物肌肉中引起了一个强大的Ca火花响应，该响应在空间上被限制在靠近肌上皮膜的地方。这些诱发的钙火花在年轻的肌肉纤维中是可重复的和可逆的，但在年老的骨骼肌中是短暂的和静态的。在膜完整性脆弱的营养不良肌肉中，诱发的钙火花是不可逆的，并从周围渗透到纤维内部。因此，不受控制的钙火花活动可能会导致SR钙储存的部分消耗，触发储存操作的钙输入（SOCE）增加，并在哺乳动物骨骼肌中提供营养不良信号。我们假设Ca火花可以用来衡量CICR在肌肉健康、衰老和营养不良中的可塑性。本项目拟开展的实验将重点解决骨骼肌钙火花生理功能的基本问题：第一，年轻健康骨骼肌钙火花外周分布和可塑性的细胞因子是什么？其次，Ca火花与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？三联体蛋白如何影响钙火花在健康、衰老和疾病中的功能？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力诱导的Ca火花的生理功能，而且还可能指出在可兴奋细胞中观察到CICR功能障碍的潜在治疗靶点。

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.