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

Abstract

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.