RhoA induction by functional overload and nandrolone decanoate administration in rat skeletal muscle.

The regulation of skeletal muscle regeneration and growth in response to functional overload is a coordinated interaction of mechanical and endocrine signaling pathways. This study's purpose was to determine if RhoA expression and activity in rat plantaris muscle was induced by functional overload with or without anabolic steroid administration. Male Sprague Dawley (125 g) rats were subjected to bilateral ablation of the gastrocnemius muscle for 3 and 21 days and treated with nandrolone decanoate (ND, 6 mg/kg b.w.) or sesame seed oil injections. Western blot analysis revealed that RhoA protein expression was induced 2.1-fold by overload and 1.9-fold by ND at 3 days. RhoA protein remained elevated by overload after 21 days (3.8-fold). In addition, RhoA protein expression in C2C12 myotubes was induced after 18 h of 1% (1.8-fold) or 2% (2.2-fold) chronic radial stretch. Competitive RT PCR revealed that RhoA mRNA concentration increased 1.9-fold with ND, 2.9-fold with overload, and 11.8-fold with overload and ND administration when compared to sham at 3 days, indicating pre-translational control of RhoA by ND and a synergism between ND and overload to up-regulate RhoA mRNA. The ratio of RhoA protein associated with the muscle membrane fraction, an indicator of RhoA activity, increased 3.7-fold after 3 days of overload compared to controls. Although ND with overload (3.8-fold) produced a larger induction of RhoA protein than overload alone, the ratio of RhoA protein associated with the membrane fraction was not altered by ND treatment at 3 days. In conclusion, RhoA is an integrator of both mechanical and growth factor signaling whose expression and activity are increased by the combination of anabolic steroid and functional overload treatments in rat plantaris muscle.