Characterization of the neuromuscular junction in castrated male mice

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 355-388-Sex Hormone Receptor Action & Reaction
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-372
Carlo Serra*1, Daniel Lee2, Nicolae Lucian Sandor2, Gianluca Toraldo2, Hyeran Jang1, Ravi Jasuja1 and Shalender Bhasin1
1Brigham & Women's Hospital, Boston, MA, 2Boston University School of Medicine, Boston, MA
Background: Motor neurons play an important role in maintaining skeletal muscle mass and function. Disruption of the nerve supply to muscle leads to profound loss of muscle mass and function. Class IIa histone deacetylases (HDACs) have been implicated in the induction of the muscle atrophy program in a myogenin-mediated manner upon denervation. Several lines of evidence indicate that androgens induce sex-specific differentiation of the motor neurons of the spinal neural bulbocavernosus at both soma and dendritic level, by regulating the release of neurotrophic factors from target musculature. We hypothesized that the anabolic effect of testosterone on the skeletal muscle is mediated by the signaling downstream the neuromuscular junction, and by the distribution of the HDACs inside the fibers. Here we investigated the regulation of the expression of genes associated with the neuromuscular junction by testosterone.

Methods: We used the Hershberger castration assay in rodents. 2-month old male mice were castrated and treated with testosterone propionate in corn oil (vehicle) for 7, 14 and 43 days, or with vehicle alone. Sham-operated, vehicle-treated mice, served as control.

Results: Castrated mice showed loss of the mass of both the high androgen-responder levator ani muscle and the low androgen-responder triceps muscle. Loss of the mass of the levator ani muscle was associated with increased expression of Hdac4 and Hdac5, as well as of the nuclear co-repressor NCoR1. This pattern of gene expression in castrated mice was coupled with upregulation of myogenin and Mef2C, as well as of the two main muscle E3 ubiquitin ligases MuRF1 and MAFbx. Interestingly, the levator ani muscle of castrated mice showed strongly reduced level of Hdac4 at the neuromuscular junction, and more diffused staining for Hdac4 in the sarcoplasm. A similar pattern was found for Hdac5 and for Hdca3, the physiological binding partner of Hdac4. In addition, castrated mice showed testosterone-mediated modulation of Dach2 and mir-206 gene expression. Finally, the levator animuscle of castrated mice showed reduced level of Fgf10 and Fgf binding protein 1 (FgfBP1), two positive regulators of synapse formation. Testosterone supplementation in castrated mice rescued all these changes.

Conclusion: Testosterone deprivation mimics the effect of muscle denervation on specific proteins involved in the neuromuscular structure and synapse formation. These data indicate that the anabolic effect of testosterone on the skeletal muscle might be mediated by the signaling regulated by neuromuscular activation and by the HDACs, and suggest new therapeutic approaches for neuromuscular diseases.

Nothing to Disclose: CS, DL, NLS, GT, HJ, RJ, SB

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Sources of Research Support: Department of Medicine and the Evans Medical Foundation of the Boston University (grants UL1RR025771 and UL1TR000157); National Institute on Aging (grant 5R01AG070534-07); Boston Claude D. Pepper Older Americans Independence Center (grant 5P30AG031679).