Triptolide prevents LPS‐induced skeletal muscle atrophy via inhibiting NF‐κB/TNF‐α and regulating protein synthesis/degradation pathway

Background and Purpose Increasing evidence suggests systemic inflammation‐caused skeletal muscle atrophy as a major clinical feature of cachexia. Triptolide obtained from Tripterygium wilfordii Hook F possesses potent anti‐inflammatory and immunosuppressive effects. The present study aims to evaluate the protective effects and molecular mechanisms of triptolide on inflammation‐induced skeletal muscle atrophy. Experimental Approach The effects of triptolide on skeletal muscle atrophy were investigated in LPS‐treated C2C12 myotubes and C57BL/6 mice. Protein expressions and mRNA levels were analysed by western blot and qPCR, respectively. Skeletal muscle mass, volume and strength were measured by histological analysis, micro‐CT and grip strength, respectively. Locomotor activity was measured using the open field test. KEY RESULTS Triptolide (10–100 fM) up‐regulated protein synthesis signals (IGF‐1/p‐IGF‐1R/IRS‐1/p‐Akt/p‐mTOR) and down‐regulated protein degradation signal atrogin‐1 in C2C12 myotubes. In LPS (100 ng·ml−1)‐treated C2C12 myotubes, triptolide up‐regulated MyHC, IGF‐1, p‐IGF‐1R, IRS‐1 and p‐Akt. Triptolide also down‐regulated ubiquitin‐proteasome molecules (n‐FoxO3a/atrogin‐1/MuRF1), proteasome activity, autophagy‐lysosomal molecules (LC3‐II/LC3‐I and Bnip3) and inflammatory mediators (NF‐κB, Cox‐2, NLRP3, IL‐1β and TNF‐α). However, AG1024, an IGF‐1R inhibitor, suppressed triptolide‐mediated effects on MyHC, myotube diameter, MuRF1 and p62 in LPS‐treated C2C12 myotubes. In LPS (1 mg·kg−1, i.p.)‐challenged mice, triptolide (5 and 20 μg·kg−1·day−1, i.p.) decreased plasma TNF‐α levels and it increased skeletal muscle volume, cross‐sectional area of myofibers, weights of the gastrocnemius and tibialis anterior muscles, forelimb grip strength and locomotion. Conclusions and Implications These findings reveal that triptolide prevented LPS‐induced inflammation and skeletal muscle atrophy and have implications for the discovery of novel agents for preventing muscle wasting.