Aging, AMP Kinase and Skeletal Muscle Overload

描述（由申请人提供）：严重的骨骼肌萎缩导致功能独立性和生活质量的丧失，抗阻运动训练等干预措施对恢复老年人的肌肉质量并不完全有效。与年龄相关的萎缩，以及过度负荷引起的肥大能力下降，主要发生在老化骨骼肌的快肌纤维中。静息骨骼肌蛋白质合成速率和翻译效率随着年龄的增长而下降，我们有强有力的数据表明，在静息和过载的大鼠骨骼肌中，5'- amp激活的蛋白激酶（AMPK，抑制蛋白质的翻译和合成）的磷酸化以快速抽搐特异性的方式随着年龄的增长而上调。此外，AMPK磷酸化与快速收缩肌肉过度负荷引起的肥厚程度密切负相关。这项研究的第一个目的是确定AMPK活性的升高是否与老年动物静息快速抽搐骨骼肌中蛋白质合成率的年龄相关下降有关。年轻成年（YA； 8个月）、中年（MA； 19个月）和老年（O； 30个月）雄性Fisher 344 × Brown Norway大鼠将被单次注射生理盐水或AMPK激活剂AICAR（5-氨基咪唑-4-羧酰胺-1- β - d -核呋喃苷）。在快缩跖肌（PLT）中，AMPK磷酸化/活性、混合蛋白和肌原纤维蛋白合成速率（通过3H-苯丙氨酸掺入）、影响AMPK活性的AMPK-y亚基以及控制AMPK下游蛋白翻译的潜在信号中间体将被测量。我们假设alcar刺激的AMPK-Q2活性将抑制年轻成年动物和中年动物快速收缩足底肌肉的静息混合蛋白和肌纤维蛋白合成率，使其达到老年盐处理动物的水平。本研究的第二个目的是确定AMPK活性的升高是否与老年动物的蛋白质合成率的年龄相关下降和超载的快速抽搐骨骼肌的增厚能力的年龄相关下降有关。将YA， MA和O雄性FBN大鼠进行单侧腓肠肌手术消融以慢性超载快速抽搐的PLT肌7天，在此期间将长期给予AICAR或生理盐水。7天后，将再次在PLT中测量AMPK磷酸化/活性、混合和肌原纤维蛋白合成率、肥厚、AMPK-y亚基和信号中间体。我们假设alcar刺激的AMPK-a2活性将抑制YA和MA动物的静息混合蛋白和肌纤维蛋白合成率以及过度快速抽搐PLT肌肉的肥大，使其达到O盐处理动物的水平。本研究的长期目标是阐明衰老快速收缩骨骼肌萎缩和肥厚受损的机制，为本科生和研究生提供研究机会，并为建立未来的R01基金申请提供数据。

DESCRIPTION (provided by applicant): Significant skeletal muscle atrophy results in a loss of functional independence and quality of life, and interventions such as resistance exercise training are not fully effective in restoring muscle mass in elderly individuals. Age-related atrophy, as well as the diminished capacity for overload-induced hypertrophy, occur predominantly in fast-twitch fibers in aging skeletal muscle. Resting skeletal muscle protein synthesis rate and translational efficiency decline with age, and we have strong data showing that the phosphorylation of 5'-AMP- activated protein kinase (AMPK; which suppresses protein translation and synthesis) is upregulated with age in a fast-twitch-specific manner in resting and overloaded rat skeletal muscle. Moreover, AMPK phosphorylation was tightly and negatively correlated with the degree of overload-induced hypertrophy in fast-twitch muscles. The first aim of this investigation is to determine if elevated AMPK activity is responsible for the age-related decline in protein synthesis rate in resting fast-twitch skeletal muscles of old animals. Young adult (YA; 8 mo.), middle- aged (MA; 19 mo.), and old (O; 30 mo.) male Fisher 344 x Brown Norway rats will be given a single injection of saline or the AMPK activator AICAR (5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside). In fast-twitch plantaris (PLT) muscles, AMPK phosphorylation/activity, rates of mixed and myofibrillar protein synthesis (via 3H- phenylalanine incorporation), AMPK-y subunits influencing AMPK activity, and potential signaling intermediates controlling protein translation downstream of AMPK will be measured. We hypothesize that AlCAR-stimulated AMPK-Q2 activity will suppress resting mixed and myofibrillar protein synthesis rates in fast-twitch plantaris muscles of young adult and middle-aged animals to the levels seen in old saline-treated animals. The second aim of this investigation is to determine if elevated AMPK activity is responsible for an age-related decline in protein synthesis rate and the age-related decline in hypertrophic capacity in overloaded fast-twitch skeletal muscles of old animals. YA, MA, and O male FBN rats will undergo unilateral surgical ablation of the gastrocnemius to chronically overload the fast-twitch PLT muscle for 7 days, during which AICAR or saline will be chronically administered. After 7 days, AMPK phosphorylation/activity, rates of mixed and myofibrillar protein synthesis, hypertrophy, AMPK-y subunits, and signaling intermediates will again be measured in the PLT. We hypothesize that AlCAR-stimulated AMPK-a2 activity will suppress resting mixed and myofibrillar protein synthesis rates and hypertrophy in overloaded fast-twitch PLT muscles of YA and MA animals to levels seen in O saline-treated animals. The long-term objectives of this investigation are to elucidate mechanisms underlying the atrophy and impaired hypertrophy of aging fast-twitch skeletal muscle, to provide research opportunities for undergraduate and graduate students, and to provide data on which to establish future R01 grant applications.