Glycogen Synthase Kinase 3-Beta (GSK3-β) inhibitors decrease protein degradation in L6 myotubes

Abstract

Introduction. Previous reports suggest that inhibition of GSK3-β results in muscle hypertrophy. Muscle hypertrophy may result from increased protein synthesis, decreased protein degradation, or a combination of both processes. The effect of GSK3-β inhibition on protein degradation in skeletal muscle has not been reported. We tested the hypothesis that the GSK3-β inhibitors lithium chloride (LiCl), SB216763, and SB415286 decrease protein degradation in cultured L6 myotubes. Methods. Fully-differentiated, cultured L6 myotubes, a rat skeletal muscle cell line, were treated with LiCl, SB216763, or SB415286 for 24 h. Protein degradation was assessed by measuring the release of TCA-soluble 3H-tyrosine from proteins that had been pre-labeled with the amino acid. Results. Treatment of cultured myotubes with the GSK3-β inhibitors resulted in a dose-dependent decrease in protein degradation. Results in the Table show the maximal inhibition (24–30%) caused by the GSK3-β inhibitors. Conclusions. This study provides evidence that inhibition of GSK3-β reduces protein degradation in skeletal muscle cells. The hypertrophy reported previously following inhibition of GSK3-β may, at least in part, be due to a decrease in protein breakdown. TABLE—ABSTRACT P26 − Inhibitor + Inhibitor LiCl 25 mM 13.7 ± 0.2 10.0 ± 0.1 ∗ SB216763 25 μM 11.5 ± 0.3 8.8 ± 0.5 ∗ SB415286 100 μM 12.8 ± 0.3 8.9 ± 0.8 ∗ Note. Protein degradation (%/24 hours) in myotubes treated with GSK3-β inhibitors. Results are means ± SEM with n = 6 per group. ∗ P < 0.001 versus no inhibitor by ANOVA.