Effects of testosterone treatment on markers of skeletal muscle ribosome biogenesis

The effects of testosterone (TEST) treatment on markers of skeletal muscle ribosome biogenesis in vitro and in vivo were examined. C₂ C₁₂ myotubes were treated with 100 nm TEST for short-term (24-h) and longer-term (96-h) treatments. Moreover, male 10-month-old Fischer 344 rats were housed for 4 weeks, and the following groups were included in this study: (i) Sham-operated (Sham) rats, (ii) orchiectomised rats (ORX) and (iii) ORX+TEST-treated rats (7.0 mg week^-1 ). For in vitro data, TEST treatment increased c-Myc mRNA expression by 38% (P = 0.004) after 96 h, but did not affect total RNA, 47S pre-rRNA, Raptor mRNA, Nop56 mRNA, Bop1 mRNA, Ncl mRNA at 24 h or 96 h following the treatment. For in vivo data, ORX decreased levator ani/bulbocavernosus (LABC) myofibril protein versus Sham (P = 0.006), whereas ORX+TEST (P = 0.015) rescued this atrophic effect. ORX also decreased muscle ribosome content (total RNA) compared to Sham (P = 0.046), whereas ORX+TEST tended to rescue this effect (P = 0.057). However, other markers of ribosome biogenesis including c-Myc mRNA, Nop56 mRNA, Bop1 mRNA, Ncl mRNA decreased with ORX independently of TEST treatments (P < 0.05). Finally, lower phospho-(Ser235/236)-to-total rps6 protein and lower rpl5 protein levels existed in ORX+TEST rats versus other treatments, suggesting that chronic TEST treatment may lower translational capacity.