Effects of short-term endurance exercise training on acute doxorubicin-induced FoxO transcription in cardiac and skeletal muscle.

Doxorubicin (DOX) is a potent antitumor agent used in cancer treatment. Unfortunately, DOX can induce myopathy in both cardiac and skeletal muscle, which limits its clinical use. Importantly, exercise training has been shown to protect against DOX-mediated cardiac and skeletal muscle myopathy. However, the mechanisms responsible for this exercise-induced muscle protection remain elusive. These experiments tested the hypothesis that short-term exercise training protects against acute DOX-induced muscle toxicity, in part, due to decreased forkhead-box O (FoxO) transcription of atrophy genes. Rats (n = 6 per group) were assigned to sedentary or endurance exercise-trained groups and paired with either placebo or DOX treatment. Gene expression and protein abundance were measured in both cardiac and skeletal muscles to determine the impact of DOX and exercise on FoxO gene targets. Our data demonstrate that DOX administration amplified FoxO1 and FoxO3 mRNA expression and increased transcription of FoxO target genes [i.e., atrogin-1/muscle atrophy F-box (MaFbx), muscle ring finger-1 (MuRF-1), and BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3)] in heart and soleus muscles. Importantly, exercise training protected against DOX-induced increases of FoxO1 and MuRF-1 in cardiac muscle and also prevented the rise of FoxO3, MuRF-1, and BNIP3 in soleus muscle. Furthermore, our results indicate that exercise increased peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1α) in both the heart and soleus muscles. This is important because increased PGC-1α expression is known to suppress FoxO activity resulting in reduced expression of FoxO target genes. Together, these results are consistent with the hypothesis that exercise training protects against DOX-induced myopathy in both heart (FoxO1 and MuRF-1) and skeletal muscles (FoxO3, MuRF-1, and BNIP3).