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，并且诸如阻力运动训练等干预措施在恢复老年人的肌肉质量方面并不完全有效。骨骼肌相关的萎缩，以及超负荷诱导的肥大能力的降低，主要发生在衰老骨骼肌的快缩纤维中。静息骨骼肌蛋白质合成率和翻译效率随年龄增长而下降，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活化蛋白激酶（AMPK;抑制蛋白质翻译和合成）的磷酸化以快收缩特异性方式随年龄增长而上调。此外，AMPK磷酸化与超负荷诱导的快缩肌肥大程度呈紧密负相关。本研究的第一个目的是确定AMPK活性升高是否是老年动物静息快缩骨骼肌蛋白质合成速率随年龄增长而下降的原因。年轻成人（YA; 8个月），中年（MA; 19个月），和老年人（O; 30个月）对雄性Fisher 344 × BrownNorway大鼠单次注射盐水或AMPK激活剂AICAR（5-氨基咪唑-4-甲酰胺-1-β-D-呋喃核糖苷）。在快速收缩跖肌（PLT）肌肉中，将测量AMPK磷酸化/活性、混合蛋白和肌原纤维蛋白合成速率（通过3 H-苯丙氨酸掺入）、影响AMPK活性的AMPK-γ亚基和控制AMPK下游蛋白翻译的潜在信号传导中间体。我们假设AlCAR刺激的AMPK-Q2活性将抑制年轻成年和中年动物快缩跖肌的静息混合和肌原纤维蛋白合成速率，使其达到老年盐水处理动物的水平。本研究的第二个目的是确定AMPK活性升高是否与老龄动物超负荷快缩骨骼肌蛋白质合成速率的年龄相关性下降和肥大能力的年龄相关性下降有关。YA、MA和O雄性FBN大鼠将经历腓肠肌的单侧手术消融以使快缩PLT肌肉长期超负荷7天，在此期间将长期施用AICAR或盐水。7天后，将在PLT中再次测量AMPK磷酸化/活性、混合蛋白和肌原纤维蛋白合成速率、肥大、AMPK-γ亚基和信号传导中间体。我们假设AlCAR刺激的AMPK-a2活性将抑制YA和MA动物的超负荷快缩PLT肌肉中的静息混合蛋白和肌原纤维蛋白合成速率和肥大至在O盐水处理的动物中观察到的水平。这项研究的长期目标是阐明衰老快缩骨骼肌萎缩和受损肥大的机制，为本科生和研究生提供研究机会，并提供数据，以建立未来的R 01资助申请。

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.