RGK proteins and aging muscle

描述（由申请人提供）：随着美国预期寿命的增加，与年龄相关的肌肉无力成为日益增长的公共卫生问题。力量下降限制了老年人的活动能力，并增加了他们受伤的可能性。虚弱的增加不仅影响个人的生活质量，而且给医疗保健系统带来额外的压力。由于这些原因和其他原因，对骨骼肌衰老过程的更深刻理解对于使美国人在以后的生活中保持健康至关重要。 骨骼肌兴奋性的抑制已被确定为老年人力量下降的一个促成因素。在哺乳动物骨骼肌中，L-型Ca通道通过触发肌浆网（SR）中的Ca释放响应质膜的去极化而充当兴奋-收缩（EC）偶联的电压传感器。已经确定EC偶联受损有助于与年龄相关的肌无力。衰老肌肉中兴奋性的这种抑制（称为“EC解偶联”）的特征在于SR Ca释放的减少，这是质膜中存在的较少数量的L型通道的直接结果。单体G蛋白的RGK（Rad、Rem、Rem 2、Gem/Kir）家族的成员已被证明减少L型通道膜表达，提高了RGK蛋白介导骨骼肌中最终导致EC解偶联的塑性变化的可能性.因此，本提案的目的是研究RGK蛋白在年龄相关性肌无力中的潜在作用。具体目标#1将寻求建立一个创新的模型系统，用于研究RGK蛋白在成人骨骼肌中的功能。为此，将通过体内电穿孔将编码RGK蛋白的cDNA质粒递送至小鼠肌肉。将用膜片钳电生理学和钙离子成像来评估这个新模型系统的有效性。使用特定目标#1中开发的方法，特定目标#2将探测RGK蛋白在去神经肌肉中EC解偶联中的作用。具体目标#3将采用实时qRT-PCR和蛋白质印迹法来确定RGK蛋白质表达在老年小鼠中是否增加。这项研究的发现可能会导致药物（甚至遗传）靶向RGK蛋白的治疗应用，减缓与年龄相关的肌无力的进展。此外，在本研究过程中收集的信息也可能有助于更好地了解与恶病质、糖尿病和退行性神经肌肉疾病相关的肌无力。 公共卫生相关性：与肌肉相关的肌肉无力影响越来越多的美国人口的健康和日常活动。虽然骨骼肌兴奋性的抑制已被确定为衰老肌肉中力量不足的一个促成因素，但对肌肉兴奋性的这种丧失如何随时间发展知之甚少。因此，这项研究的总体目标是提供有关老年人肌肉无力的分子机制的信息。

DESCRIPTION (provided by applicant): As life expectancy increases in the United States, age-related muscle weakness becomes a growing public health concern. Declines in strength limit mobility and increase susceptibility to injury in older individuals. Increased frailty not only impacts the quality of life of the individual but also places additional strain on the health care system. For these reasons and others, a more profound understanding of the aging process in skeletal muscle is critical for enabling Americans to remain healthy later in life. Depression of skeletal muscle excitability has been identified as a contributing factor to reduced strength in older individuals. In mammalian skeletal muscle, the L-type Ca channel serves as the voltage sensor for excitation-contraction (EC) coupling by triggering Ca release from the sarcoplasmic reticulum (SR) in response to depolarization of the plasma membrane. It has been established that impaired EC coupling contributes to age-related muscle weakness. This depression of excitability (termed "EC uncoupling") in aging muscle is characterized by a reduction in SR Ca release which is a direct consequence of a fewer number of L-type channels present in the plasma membrane. Members of the RGK (Rad, Rem, Rem2, Gem/Kir) family of monomeric G proteins have been demonstrated to reduce L- type channel membrane expression, raising the possibility that RGK proteins mediate plastic changes in skeletal muscle that ultimately result in EC uncoupling. Thus, the purpose of this proposal is to investigate a potential role for RGK proteins in age-related muscle weakness. Specific Aim #1 will seek to establish an innovative model system for the study of RGK protein function in adult skeletal muscle. To do so, cDNA plasmids encoding RGK proteins will be delivered to mouse muscle via in vivo electroporation. The validity of this new model system will be assessed with patch-clamp electrophysiology and Ca imaging. Using the methodology developed in Specific Aim #1, Specific Aim #2 will probe a role for RGK proteins in EC uncoupling in dennervated muscle. Specific Aim #3 will employ real-time qRT-PCR and western blotting to determine whether RGK protein expression is increased in older mice. The findings of this study may lead to therapeutic applications in which pharmacological (or even genetic) targeting RGK proteins would slow the progression of age-related muscle weakness. In addition, information gathered in the course of this study may also contribute to a better understanding of muscle weakness associated with cachexia, diabetes and degenerative neuromuscular disease. PUBLIC HEALTH RELEVANCE: Age-related muscle weakness impacts the health and daily activities of a growing segment of the American population. Although depression of skeletal muscle excitability has been identified as a contributing factor to strength deficits in aging muscle, little is known about how this loss of muscle excitability develops over time. Thus, the overall goal of this research proposal is to provide information about the molecular mechanisms that underlie muscle weakness in older individuals.