Loss of Numb in Muscle Dysfunction in Aging

肌肉减少和虚弱是正常衰老的必然结果，会降低功能， 福尔斯和骨折，并因此与显著的发病率和医疗保健成本相关。越来越多的 有证据表明，无力和肌肉力量的丧失是老年人福尔斯跌倒的重要原因; 提出的机制包括神经驱动力降低、快缩纤维丢失、脂肪浸润肌肉 或其他组织类型，肌原纤维装置功能障碍，或兴奋收缩（E-C）受损 偶合器.无效的E-C耦合被认为是与年龄相关的肌无力的重要原因。 EC偶联将肌膜的去极化与胞质钙浓度的升高联系起来， 导致肌动蛋白-肌球蛋白纤维缩短和肌肉收缩。此应用程序侧重于 衔接蛋白Numb在调节E-C偶联所需的胞质钙瞬变中的作用。我们建议 Numb表达的减少损害了E-C偶联并导致衰老相关的虚弱。麻木有 在细胞命运决定、不对称细胞分裂和囊泡运输中起关键作用。在骨骼肌中， Numb是卫星细胞增殖所必需的，并增强肌源性分化潜力。没有研究 已经研究了Numb在骨骼肌E-C偶联中的作用，或者研究了是否减少Numb 在衰老过程中，表达会导致虚弱。我们的初步研究表明，麻木是目前在 骨骼肌纤维，它位于DHPR附近。从20岁开始，肌肉中Numb的表达减少， 一个月的老鼠基因敲除Numb和NumbL（一种具有重叠功能的密切相关蛋白质）， 骨骼肌纤维降低肌肉强度。对小鼠成肌细胞原代培养的研究表明， Numb的敲低降低了咖啡因诱导的细胞内钙浓度的升高。这些 观察提供了令人信服的证据，麻木的肌肉力量生产的作用，本地化麻木， 三联体，并暗示Numb调节骨骼肌纤维中的钙瞬变。研究结果还表明， Numb表达减少是衰老的E-C偶联受损的决定因素。我们假设：1） 在我们的Numb/NumbL双敲出中，比力产生的减少是由于Numb/NumbL双敲出的减少。 2）Numb是EC偶联的适当调节所必需的，因为3）Numb通过以下方式调节释放： RyR 1的钙储存在SR和缺乏Numb消耗SR钙储存和4）年龄相关的 麻木表情的减少是虚弱的原因。为了验证这些假设，我们将：目标2，确定 由Numb/NumbL敲低导致的肌无力的细胞和分子基础;目的2， 确定Numb表达减少在力产生的衰老相关下降中的作用。

Sarcopenia and weakness are inevitable consequences of normal aging that reduce function, predispose to falls and fractures and are thus associated with significant morbidity and healthcare costs. A growing body of evidence implicates weakness and loss of muscle power as important contributors to falls in the elderly; proposed mechanisms include reduced neural drive, loss of fast-twitch fibers, infiltration of muscle by adipose or other tissue types, dysfunction of the myofibrillar apparatus, or impairments in excitation contraction (E-C) coupling. Ineffective E-C coupling is thought to be an important contributor to age-related muscle weakness. EC-Coupling links depolarization of the sarcolemma to a rise in cytosolic calcium concentrations which in turn causes shortening of actin-myosin fibrils and muscle contraction. This application focuses on roles of the adaptor protein Numb in regulation of cytosolic calcium transients required for E-C coupling. We propose that reductions in Numb expression impair E-C coupling and contribute to aging-associated weakness. Numb has critical roles in cell fate determination, asymmetric cell division and vesicular trafficking. In skeletal muscle, Numb is required for satellite cell proliferation and enhances myogenic differentiation potential. No studies have investigated roles of Numb in skeletal muscle E-C coupling or investigated whether reduced Numb expression contributes to weakness during aging. Our preliminary studies show that Numb is present in skeletal muscle fibers where it localizes near DHPR. Expression of Numb was reduced in muscles from 20- month old mice. A knockout of Numb and NumbL (a closely related protein with overlapping functions) in skeletal muscle fibers reduced muscle strength. Studies of primary cultures of mouse myoblasts revealed that a knockdown of Numb reduced the caffeine-induced rise in intracellular calcium concentration. These observations provide compelling evidence for a role of Numb in muscle force production, localize Numb to the triad, and implicate Numb in regulating calcium transients in skeletal muscle fibers. The findings also implicate reduced Numb expression as a causal determinant of impaired E-C coupling of aging. We hypothesize that: 1) diminished specific force generation in our Numb/NumbL double-knockouts is due to reduced Numb expression, 2) Numb is required for proper regulation of EC-coupling because 3) Numb regulates release by RyR1 of calcium stored in the SR and absence of Numb depletes SR calcium stores and 4) that age-related decreases in Numb expression are a cause of weakness. To test these hypotheses we will: Aim 2, Determine the cellular and molecular basis for muscle weakness resulting from Numb/NumbL knockdowns; Aim 2, Determine the role of reduced Numb expression in aging-related declines in force production.