A myostatin inhibitor (propeptide-Fc) increases muscle mass and muscle fiber size in aged mice but does not increase bone density or bone strength
Phonepasong Arounleut et al. Exp Gerontol. 2013 Sep.
Abstract
Loss of muscle and bone mass with age are significant contributors to falls and fractures among the elderly. Myostatin deficiency is associated with increased muscle mass in mice, dogs, cows, sheep and humans, and mice lacking myostatin have been observed to show increased bone density in the limb, spine, and jaw. Transgenic overexpression of myostatin propeptide, which binds to and inhibits the active myostatin ligand, also increases muscle mass and bone density in mice. We therefore sought to test the hypothesis that in vivo inhibition of myostatin using an injectable myostatin propeptide (GDF8 propeptide-Fc) would increase both muscle mass and bone density in aged (24 mo) mice. Male mice were injected weekly (20 mg/kg body weight) with recombinant myostatin propeptide-Fc (PRO) or vehicle (VEH; saline) for four weeks. There was no difference in body weight between the two groups at the end of the treatment period, but PRO treatment significantly increased mass of the tibialis anterior muscle (+ 7%) and increased muscle fiber diameter of the extensor digitorum longus (+ 16%) and soleus (+ 6%) muscles compared to VEH treatment. Bone volume relative to total volume (BV/TV) of the femur calculated by microCT did not differ significantly between PRO- and VEH-treated mice, and ultimate force (Fu), stiffness (S), toughness (U) measured from three-point bending tests also did not differ significantly between groups. Histomorphometric assays also revealed no differences in bone formation or resorption in response to PRO treatment. These data suggest that while developmental perturbation of myostatin signaling through either gene knockout or transgenic inhibition may alter both muscle and bone mass in mice, pharmacological inhibition of myostatin in aged mice has a more pronounced effect on skeletal muscle than on bone.
Keywords: Anabolic therapy; Fractures; GDF-8; Osteoporosis; Sarcopenia.
© 2013. Published by Elsevier Inc. All rights reserved.
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Figures Figure 1
Myostatin-induced luciferase activity declines significantly with increasing concentration of myostatin propeptide. The pGL3(CAGA)12 – neo reporter vector contains 12 CAGA boxes previously reported to be TGF-β-responsive elements (Dennler et al. (1998) EMBO J. 17:3091–3100), a neo resistance gene, and the basic luciferase reporter plasmid pGL3 (Promega Corporation). Figure 2
Body mass (A) and change in body weight (B) for animals treated with either saline (VEH) or myostatin propeptide (PRO) weekly for over four weeks. Figure 3
Muscle parameters for mice treated with saline (VEH) or myostatin propeptide (PRO) weekly for a period of four weeks. (A) Tibialis anterior mass, (B) tibialis anterior mass relative to body weight, (C) extensor digitorum longus fiber diameter (EDL), (D) alpha-laminin stained cryostat sections of the EDL, (E) soleus muscle fiber diameter. Figure 3
Muscle parameters for mice treated with saline (VEH) or myostatin propeptide (PRO) weekly for a period of four weeks. (A) Tibialis anterior mass, (B) tibialis anterior mass relative to body weight, (C) extensor digitorum longus fiber diameter (EDL), (D) alpha-laminin stained cryostat sections of the EDL, (E) soleus muscle fiber diameter. Figure 3
Muscle parameters for mice treated with saline (VEH) or myostatin propeptide (PRO) weekly for a period of four weeks. (A) Tibialis anterior mass, (B) tibialis anterior mass relative to body weight, (C) extensor digitorum longus fiber diameter (EDL), (D) alpha-laminin stained cryostat sections of the EDL, (E) soleus muscle fiber diameter. Figure 4
Real-time PCR data for mice treated with saline (VEH) or myostatin propeptide (PRO) weekly for a period of four weeks showing increased expression of Murf1 and Mafbx in PRO-treated mice (A), Western blot showing similar increases in Murf1 and Mafbx with PRO-treatmend (B), and increased expression of BMP-2 in mice treated with propeptide (C). *P<.05. Figure 4
Real-time PCR data for mice treated with saline (VEH) or myostatin propeptide (PRO) weekly for a period of four weeks showing increased expression of Murf1 and Mafbx in PRO-treated mice (A), Western blot showing similar increases in Murf1 and Mafbx with PRO-treatmend (B), and increased expression of BMP-2 in mice treated with propeptide (C). *P<.05.
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