Effects of age and exercise on mouse skeletal muscle type I collagen gene promoter activity

Abstract

Age and exercise affect the translation of skeletal muscle collagen and the rate of collagen turnover. However, it is unclear how exercise alters the synthesis of skeletal muscle collagen. 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 (10–13 mo, n=23) and old (18–20 mo, n=15) 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’s tail fluorescence. We found two significant statistical interactions, age by muscle (p=0.033) and age by training (p=0.049). There was an increase in RTF in both muscles at 24 hr with a decline up to 7 days of exercise with a greater effect in the soleus. In addition, training caused a more dramatic increase in RTF in muscles of old relative to young GFP-C1 mice. Soleus had greater RTF than gastrocnemius in both age groups at all training times. These data support work showing greater type I collagen in slow-twitch muscle (soleus) compared to muscle of mixed fiber type. Further, this work increases knowledge of the control of collagen metabolism by showing a direct effect of exercise on type I collagen promoter activity.