Chronic Exposure Of Rodents To Inhaled Ozone Causes Mitochondrial Fission In Skeletal Muscle

Ozone (O3) is an air pollutant known to induce systemic inflammation, characterized by inflammatory cell activation and the production of reactive oxygen species (ROS). ROS are known to cause mitochondrial fission, a component of the cellular stress response and apoptosis. It is activated by dynamin-related protein 1 (DRP-1/Dmn1l) and outer mitochondrial membrane adaptor proteins such as mitochondrial fission factor (Mff), mitochondrial fission protein 1 (Fis1), and mitochondrial elongation factors (Mief1/2). The initiation of mitochondrial fission and ROS can also impair satellite cell activity, which are key for muscle repair and regeneration. PURPOSE: To determine if skeletal muscle is susceptible to ROS-mediated mitochondrial damage following O3 exposure. METHODS: Female C57BL/6 mice were exposed to filtered air or 1.5 ppm O3 for 2 h, 2x/wk for 6 wk. The gastrocnemius muscle was collected 24 h following the final exposure and either snap frozen or prepared for RT-qPCR. Tissue was examined for peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a regulator of mitochondrial biogenesis, and DRP-1 protein expression by western blotting. Gene expression of superoxide dismutase (Sod), a marker of oxidative stress, Pgc-1α and Pgc-1 beta (Pgc-1β), a regulator of mitochondrial metabolism, mitochondrial fission markers Mff, Fis1, Mief, Dmn1l, and Pax7, a transcription factor for satellite cells, were quantified using RT-qPCR; the ΔΔCt fold changes were compared relative to air-exposed animals. A Student’s t-test was performed to compare densitometry means and fold changes with statistical significance set at p < 0.05. RESULTS: Following O3 exposure, expression of PGC1-α was significantly decreased (p = 0.05) compared to air-exposed animals, while expression of Sod1 (p = 0.03), Sod2 (p = 0.02), and Mff (p = 0.01) were significantly increased. O3 exposure also caused an increase in Fis1 and a decrease in Pgc-1β and Pax7 (p = 0.03) compared to air exposure. CONCLUSIONS: These findings are the first to suggest that chronic O3 exposure differentially alters mitochondrial fission-related gene and protein expression in the gastrocnemius through systemic inflammation and ROS production, potentially influencing satellite cell activity and therefore long-term skeletal muscle health. Supported by: NIH grants ES033698, ES005022, ES004738, ES020721, T32832715 and Mistletoe Research Fellowship #836950