Effects of Age and Exercise on Collagen Type I Gene Promoter Activity

Age and exercise affect the translation of skeletal muscle collagen and the rate of collagen turnover. However, it is unclear how exercise alters the promoter activity of skeletal muscle collagen type I. Transgenic mice containing the green fluorescent protein gene downstream of a collagen type I promoter (GFP-C1 mice) were used to measure the transcription initiation of collagen type I in skeletal muscle. Young (3-5 mo, n=24), 1-Year (10-13 mo, n=20), and old (18-20 mo, n=24) mice were exposed to voluntary running wheels for 1, 3, or 7 days. The gastrocnemius and soleus were harvested and fluorescence and protein content measured. Relative tissue fluorescence (RTF) was calculated relative to the amount of sample protein and to the animal\u27s tail fluorescence. Age and exposure time showed a significant interaction and effect on determining running distance. Young mice had the highest mean running distance with a decrease associated with increased age. Soleus muscle analysis showed a direct significant correction between running distance and increased RTF values. There was no significant correction in gastrocnemius muscle. Training caused a more dramatic effect on soleus RTF values in young mice as compared to 1-year old or elderly mice. The soleus muscle also had a significantly higher RTF than the gastrocenuius for all ages and expose times as expected for a muscle composed primarily of slow-twitch muscle fibers with high concentrations of collagen type I. In summary, young mice ran the furthest and showed the greatest soleus RTF values as compared to the old animals and the gastrocenemius muscle