Atmospherically relevant PM_2.5 promotes age-related muscle atrophy in an age-dependent manner

Background: Maintaining the quality and function of skeletal muscle in the older adult has become a key topic in successful aging. However, the impact of environmental factors on skeletal muscle aging is often overlooked. Methods: This study used male mice aged 1, 6, and 15 months, which were each exposed to PM_2.5 (50 μg/m3, 2 h/day) for 5 days, and the skeletal muscles of each age group were analyzed one month after the end of the treatment to verify the age-specific effects of PM_2.5 on the skeletal muscle system. Results: Total body weight and lean body weight were significantly affected by age and PM_2.5 exposure. However, fat levels were not affected by PM_2.5 exposure. PM_2.5 exposure promoted the development of age-related muscle atrophy by inducing oxidative stress and increased expression of Myostatin in skeletal muscle of older adults. On the other hand, the damaging effect of PM_2.5 exposure on skeletal muscle mitochondria was age-related. Young and older adult mice showed extensive mitochondrial damage after PM_2.5 exposure. In particular, older adults showed a marked increase in mitochondrial fission and mitophagy after PM_2.5 exposure. Conclusions: The effects of PM_2.5 exposure on the skeletal muscle system are age-specific, with distinct damaging effects during growth and aging, whereas skeletal muscles in middle-aged mice are resistant to PM_2.5-induced damage.