Glucocorticoids counteract hypertrophic effects of myostatin inhibition in dystrophic muscle
David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney
David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney
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Research Article Muscle biology Therapeutics

Glucocorticoids counteract hypertrophic effects of myostatin inhibition in dystrophic muscle

Abstract

Duchenne muscular dystrophy (DMD) is a devastating genetic muscle disease resulting in progressive muscle degeneration and wasting. Glucocorticoids, specifically prednisone/prednisolone and deflazacort, are commonly used by DMD patients. Emerging DMD therapeutics include those targeting the muscle-wasting factor, myostatin (Mstn). The aim of this study was to investigate how chronic glucocorticoid treatment impacts the efficacy of Mstn inhibition in the D2.mdx mouse model of DMD. We report that chronic treatment of dystrophic mice with prednisolone (Pred) causes significant muscle wasting, entailing both activation of the ubiquitin-proteasome degradation pathway and inhibition of muscle protein synthesis. Combining Pred with Mstn inhibition, using a modified Mstn propeptide (dnMstn), completely abrogates the muscle hypertrophic effects of Mstn inhibition independently of Mstn expression or SMAD3 activation. Transcriptomic analysis identified that combining Pred with dnMstn treatment affects gene expression profiles associated with inflammation, metabolism, and fibrosis. Additionally, we demonstrate that Pred-induced muscle atrophy is not prevented by Mstn ablation. Therefore, glucocorticoids interfere with potential muscle mass benefits associated with targeting Mstn, and the ramifications of glucocorticoid use should be a consideration during clinical trial design for DMD therapeutics. These results have significant implications for past and future Mstn inhibition trials in DMD.

Authors

David W. Hammers, Cora C. Hart, Andreas Patsalos, Michael K. Matheny, Lillian A. Wright, Laszlo Nagy, H. Lee Sweeney

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Figure 9

Myostatin ablation does not prevent Pred-induced muscle atrophy.

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Myostatin ablation does not prevent Pred-induced muscle atrophy. Adult m...
Adult myostatin KO mice received daily oral treatments of vehicle or 5 mg/kg prednisolone (Pred) for 28 days (n = 4–5). (A) Mouse body weight change was evaluated during the course of the experiment. Data were analyzed using Welch’s t test (α = 0.05) and are displayed as mean ± SEM. (B–D) Body weight (B), absolute muscle masses (C), and tibia length–normalized muscle masses (D) were measured at terminal endpoint. WT and heterozygous (Het) littermate values are included for mass difference perspective. Data were analyzed using 1-way ANOVA (effect size reported as η2), followed by Tukey’s post hoc tests (α = 0.05). Data are presented as box-and-whisker plots, with minimum and maximum values indicated by error bars; data are shown as mean ± SEM. Groups that are significantly different from each other are indicated by nonoverlapping letter designations (P ≤ 0.05). (E–G) Immunofluorescent staining of vehicle- and Pred-treated KO gastrocnemius muscles for αActinin-3, a marker of fast-glycolytic muscle fibers, and laminin (E) allowed fiber size distribution analysis of αActinin-3+ (positive) fibers (F) and αActinin-3– (negative) fibers (G) of vehicle and Pred groups. Data were analyzed using Welch’s t test (α = 0.05) and are depicted as histograms of the entire data set. Scale bars: 100 μm.