Testosterone protects against dexamethasone-induced muscle atrophy, protein degradation and MAFbx upregulation☆

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Abstract

Administration of glucocorticoids in pharmacological amounts results in muscle atrophy due, in part, to accelerated degradation of muscle proteins by the ubiquitin–proteasome pathway. The ubiquitin ligase MAFbx is upregulated during muscle loss including that caused by glucocorticoids and has been implicated in accelerated muscle protein catabolism during such loss. Testosterone has been found to reverse glucocorticoid-induced muscle loss due to prolonged glucocorticoid administration. Here, we tested the possibility that testosterone would block muscle loss, upregulation of MAFbx, and protein catabolism when begun at the time of glucocorticoid administration. Coadministration of testosterone to male rats blocked dexamethasone-induced reduction in gastrocnemius muscle mass and upregulation of MAFbx mRNA levels. Administration of testosterone together with dexamethasone also prevented glucocorticoid-induced upregulation of MAFbx mRNA levels and protein catabolism in C2C12 myotube expressing the androgen receptor. Half-life of MAFbx was not altered by testosterone, dexamethasone or the combination. Testosterone blocked dexamethasone-induced increases in activity of the human MAFbx promotor. The findings indicate that administration testosterone prevents glucocorticoid-induced muscle atrophy and suggest that this results, in part at least, from reductions in muscle protein catabolism and expression of MAFbx.

Introduction

Glucocorticoids reduce skeletal muscle mass through mechanisms that include accelerated protein degradation [1], [2], [3] which largely reflects activation of the ubiquitin–proteasome system [2], [4]. In this system, proteins to be destroyed are modified by the covalent attachment of ubiquitin by ubiquitin ligases then degraded by the proteasome [5]. The muscle-specific ubiquitin ligase muscle atrophy F-box (MAFbx, also referred to atrogin-1) has been found to be upregulated universally in muscle loss including that caused by glucocorticoids [6], [7], and to increase rates of denervation atrophy [7].

Glucocorticoid-induced muscle atrophy can be reversed by testosterone [8], [9] or nandrolone, an anabolic steroid [8], [10]. Although it would be predicted that these beneficial effects of testosterone and nandrolone would be associated with reduced protein degradation, this possibility has not been tested. Consistent with this proposal, indirect methods that employ nonradioactive isotopes of amino acids indicate that testosterone increases net protein synthesis in elderly men or burn victims and suggest that testosterone does so by reducing protein degradation [11], [12]. The effects of testosterone on dexamethasone-induced expression of MAFbx also remain unknown. We hypothesized that testosterone would protect against glucocorticoid-induced muscle atrophy when begun at the time of administration of the glucocorticoid, and that such protection would be associated with reduced protein degradation and normalization of MAFbx mRNA levels. These hypotheses were tested in a rat model of dexamethasone-induced muscle atrophy and in cultured muscle cell lines.

Section snippets

Materials

Testosterone and dexamethasone were obtained from Spectrum Chemical (New Brunswick, NJ). Propylene glycol was from Sigma (St. Louis, MO). Tritiated tyrosine was from MP Biomedicals (Solon, OH). The reporter gene pMAF3.1 expressed firefly luciferase under the control of 3.1 kb of the proximal promotor of the human MAFbx gene [13]. pRL-CMV (Promega, Madison, WI) expresses renilla luciferase.

Animals

Animal studies were approved by the Institutional Animal Care and Use Committee at the James J. Peters VA

Results

Dexamethasone significantly reduced gastrocnemius weights (Fig. 1) with a greater effect at 7 as compared with 1 day. Testosterone completely protected against such loss at both 1 and 7 days. MAFbx mRNA levels were significantly increased by dexamethasone at 1 and 7 days (Fig. 2A and B). Coadministration of testosterone significantly reduced MAFbx mRNA levels.

To determine whether the effects of testosterone extended to muscle cell lines, C2C12.AR myotubes expressing human AR were incubated with

Discussion

Our data demonstrate that testosterone prevents the initial period of dexamethasone-induced muscle atrophy. The findings complement and extend prior studies that have assessed the effect of testosterone after a period of chronic administration of glucocorticoids. Studies in men who were chronically administered glucocorticoids have shown significant increases in lean tissue mass after beginning testosterone [8], [19]. Similarly, administration of the anabolic steroid, nandrolone, to rats

References (31)

  • B.A. Crawford et al.

    Randomized placebo-controlled trial of androgen effects on muscle and bone in men requiring long-term systemic glucocorticoid treatment

    J. Clin. Endocrinol. Metab.

    (2003)
  • I.R. Reid et al.

    Testosterone therapy in glucocorticoid-treated men

    Arch. Intern. Med.

    (1996)
  • R.H. Van Balkom et al.

    Anabolic steroids in part reverse glucocorticoid-induced alterations in rat diaphragm

    J. Appl. Physiol.

    (1998)
  • R.J. Urban et al.

    Testosterone administration to elderly men increases skeletal muscle strength and protein synthesis

    Am. J. Physiol.

    (1995)
  • A.A. Ferrando et al.

    Testosterone administration in severe burns ameliorates muscle catabolism

    Crit. Care Med.

    (2001)

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    ☆

    The research reported here was supported by the Veterans Health Administration, Rehabilitation Research and Development Service (B4162C, B3347K, B3242R).

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