β-Hydroxy-β-methylbutyrate (HMB) prevents dexamethasone-induced myotube atrophy

Abstract

High levels of glucocorticoids result in muscle wasting and weakness. β-hydroxy-β-methylbutyrate (HMB) attenuates the loss of muscle mass in various catabolic conditions but the influence of HMB on glucocorticoid-induced muscle atrophy is not known. We tested the hypothesis that HMB prevents dexamethasone-induced atrophy in cultured myotubes. Treatment of cultured L6 myotubes with dexamethasone resulted in increased protein degradation and expression of atrogin-1 and MuRF1, decreased protein synthesis and reduced myotube size. All of these effects of dexamethasone were attenuated by HMB. Additional experiments provided evidence that the inhibitory effects of HMB on dexamethasone-induced increase in protein degradation and decrease in protein synthesis were regulated by p38/MAPK- and PI3K/Akt-dependent cell signaling, respectively. The present results suggest that glucocorticoid-induced muscle wasting can be prevented by HMB.

Copyright © 2012 Elsevier Inc. All rights reserved.

Figures

Figure 1

HMB attenuates dexamethasone-induced atrophy of cultured myotubes. L6 myotubes were treated for 24 h with 1 μM dexamethasone in the absence or presence of 50 μM HMB. (A) Myotube morphology and (B) diameter were determined as described in Section 2. Results in (B) are means ± SEM with n=6 per group. * p

Figure 2

HMB prevents dexamethasone-induced increase in protein degradation and decrease in protein synthesis in cultured myotubes. L6 myotubes were treated with dexamethasone in the absence or presence of HMB as described in Figure 1. (A) Protein degradation and (B) protein synthesis rates were measured as described in Section 2. Results are means ± SEM with n=6 per group. * p

Figure 3

HMB attenuates dexamethasone-induced expression of atrogin-1 and MuRF1 in cultured myotubes. L6 myotubes were treated with dexamethasone in the absence or presence of HMB as described in Figure 1. mRNA levels for (A) atrogin-1 and (B) MuRF1 and protein levels for (C) atrogin-1 and (D) MuRF1 were determined as described in Section 2. Representative Western blots are shown in the upper panels and quantifications of the Western blots are shown in the lower panels of C and D. α-tubulin levels were determined for loading control. Results are means ± SEM with n=6 per group. * p

Figure 4

HMB prevents dexamethasone-induced increase in protein degradation and dexamethasone-induced decrease in protein synthesis through p38/MAPK- and PI3K/Akt-dependent mechanisms, respectively. Cultured L6 myotubes were treated with dexamethasone in the absence or presence of HMB as described in Figure 1. In some of the experiments, myotubes were exposed to PD98059 (PD98), SB202190 (SB20), LY294002, or rapamycin as described in Section 2. (A) Protein degradation and (B) synthesis rates were determined as described in Section 2. Results are means ± SEM with n=6 per group. * p