Abstract

Objective：The purposes of this study were to investigate the feature of mitochondrial biogenesis of skeletal muscle and to explore its contribution in aging process.We implicate its possible molecular mechanism and the biological significance of exercise-induced mitochondrial biogenesis in aging.Thus，the present findings offered a research data and the theory hypothesis to the aging research in relation to mitochondrial physiology，sports medicine，gerontics and aging physiologhy.

Methods：Forty-eight male SD rats were divided into six groups：5 months control group（5MC），5 months trained group（5MT），15 months control group（15MC），15 months trained group（15MT），20 months control group（20MC） and 20 months trained group（20MT）.The moderate endurance training（64％ max）was imposed on rats aged 2 month，12 month and 17 month as training in a treadmill（5°，15m ／min，45 min，once per day for 5 days）for 12 wk，respectively.The control rats remained sedentary.After the 12 weeks training treatment and 24 hours after training，the rats were anesthetized，then detected the body composition，and the skeletal muscle（typeⅠ）was rapidly excised to test the parameters in mitochondrial ultra-morphology，respiration control，ROS generation and antioxidase activity，also mitochondrial protein and transcription factors expression in mitochondrial biogenesis.

Results：（1）Body mass and body fat percentage of rats increased during the aging progress.Body fat percentage of rats markedly decreased after endurance training.（2）Mitochondria biogenesis changed in aging rat skeletal muscle，endurance training might induce increase in number density of subsarcolemmal（SS） mitochondria and in volume density of intermyofibrillar（IMF）mitochondria in allgroups，respectively.（3）Mitochondrial respiratory function decreased during the aging progress，endurance training might diminish the decline of mitochondrial respiration in skeletal muscle which was irrespective of age.（4）Mitochondrial ROS generation increased during the aging.Endurance training might improve the redox state in mitochondria.（5）The expression of transcriptional factors involved in the mitochondrial biogenesis increased during the aging process.PGC-1 α mRNA and its ptrotein expression showed different feature with the aging.Endurance training did induce the significant expression of these transcriptional factors and mitochondrial protein，especially in young age.

Conclusion：（1）Mitochondrial volume density and number density were also found to be increased during rat aging.（2） PGC-1 α protein expression decreased during aging while its downstream transcription factors increased，suggesting that some other complex pathways might be involved in mitochondrial biogenesis.（3）The phosphorylation of p38MAPK probably is a key mediator in the contractile activity-induced mitochondrial biogenesis in rat skeletal muscle and H2O2 generated in mitochondrial respiration may be involved in this process.（4）Endurance training might strongerly enhance the skeletal muscle mitochondrial biogenesis through the increased expression of mtTFA，NRF-1，PGC-1 α and p38MAPK not noly at transcription level but also in protein experession，resulting in enhancement the mitochondrial respiratory function，improving mitochondrial redox state and delayling aging process of skeletal muscle.

Key words： skeletal muscle；mitochondrial biogenesis；endurance training；aging；