Tetrandrine induces muscle atrophy involving ROS-mediated inhibition of Akt and FoxO3

Tetrandrine (Tet), a well-known drug of calcium channel blocker, has been broadly applied for anti-inflammatory and anti-fibrogenetic therapy. However, due to the functional diversity of ubiquitous calcium channels, potential side-effects may be expected. Our previous report revealed an inhibitory effect of Tet on myogenesis of skeletal muscle. Here, we found that Tet induced protein degradation resulting in the myofibril atrophy. Upon administration with a relative high dose (40 mg/kg) of Tet for 28 days, the mice displayed significantly reduced muscle mass, strength force, and myosin heavy chain (MyHC) protein levels. The MyHC reduction was further detected in C2C12 myotubes after treating with Tet. Interestingly, the expression of Atrogin-1 and Murf-1, the skeletal muscle specific E3 ligases of protein ubiquitin-proteasome system (UPS), was accordingly up-regulated, and the reduced MyHC was significantly mitigated by MG132, a 26S proteasome inhibitor, indicating a key role of UPS in the protein degradation of muscle cells. Further study showed that Tet induced autophagy also participated in the protein degradation. Mechanistically, Tet treatment caused ROS production in myotubes that in turn targeted on FoxO3/AKT signaling, resulting in the activation of UPS and autophagy processes that were involved in the protein degradation. Our study reveals a potential side-effect of Tet on skeletal muscle atrophy, particularly when the drug dose is relatively high.