Abstract
Aging affects several tissues in the body, including skeletal muscle. Multiple types of collagens are localized in the skeletal muscle and contribute to the maintenance of normal muscle structure and function. Since the effects of aging on muscle fibers vary by muscle fiber type, it is expected that the effects of aging on intramuscular collagen might be influenced by muscle fiber type. In this study, we examined the effect of aging on collagen levels in the soleus (slow-twitch muscle) and gastrocnemius (fast-twitch muscle) muscles of 3-, 10-, 24-, and 28-month-old male C57BL/6J mice using molecular and morphological analysis. It was found that aging increased collagen I, III, and VI gene expression and immunoreactivity in both slow- and fast-twitch muscles and collagen IV expression in slow-twitch muscles. However, collagen IV gene expression and immunoreactivity in fast-twitch muscle were unaffected by aging. In contrast, the expression of the collagen synthesis marker heat shock protein 47 in both slow- and fast-twitch muscles decreased with aging, while the expression of collagen degradation markers increased with aging. Overall, these results suggest that collagen gene expression and immunoreactivity are influenced by muscle fiber type and collagen type and that the balance between collagen synthesis and degradation tends to tilt toward degradation with aging.