The Effect of Neonatal Administration of Recombinant Myostatin Propeptide on Skeletal Muscle Growth in Mice.

Abstract

Myostatin (MSTN) negatively regulates skeletal muscle growth by suppressing myoblast proliferation and muscle fiber hypertrophy. Effective suppression of MSTN leads to dramatic improvement of animal muscle growth. MSTN propeptide (MSTNpro) is a potent inhibitor of MSTN activity. Studies suggest that in some species like mice and rabbits, muscle fiber number is increasing during the early neonatal period. We postulated that enhancing muscle fiber hyperplasia of these animal species during early neonatal period might increase postnatal skeletal muscle growth of these animals. Therefore, the objective of this study was to examine the effect of neonatal administration of MSTNpro on skeletal muscle growth in mice. Recombinant truncated flatfish MSTNpro fused to mouse IgG Fc domain (fMSTNpro45-100mFc) was produced in Escherichia coli (E. coli) using pMAL-c5x expression vector and purified by the amylose and protein A affinity chromatography. About 7.52 mg of purified recombinant MBP-fMSTNpro45-100mFc was obtained from 1 L culture. The MSTN-inhibitory capacity of the purified recombinant MSTNpro was similar to that of a commercial MSTNpro produced from eukaryotic cells in a pGL3-(CAGA)12-Luciferase repeater gene assay. In an oral administration study, eight female mice (4-month-old) were mated to two males (4-month-old), and the female mice were randomly divided into two groups: control and treatment. New-born pups in the treatment and control groups were fed with MBP-fMSTNpro45-100mFc (10 μg/g pup) and PBS, respectively, twice one day apart. The pups were weaned at 4 weeks, and their body weight were measured weekly for 7 weeks after weaning. At 11 weeks after weaning, animals were sacrificed, and gastrocnemius complex (gastrocnemius, plantaris and soleus) muscle and organ (heart, liver, spleen, kidney) samples were collected and weighed. Following the oral administration experiment, the same male and female mice were used for an intraperitoneal administration study with the same experimental design. Newborn pups in the treatment and control groups were intraperitoneally injected MBP-fMSTNpro45-100mFc (10 μg/g pup) and PBS, respectively, on the first and second day after birth. At 10 weeks after weaning, mice were sacrificed for the muscle and organ weight. Either neonatal oral administration or intraperitoneal injection of MBP-fMSTNpro45-100mFc did not significantly affect body weight growth and gastrocnemius muscle and organ weights of mice. This result implies that the administration of MBP-fMSTNpro45-100mFc under early neonatal period did not enhance muscle hyperplasia in mice. However, this study did not examine either the transfer of recombinant MSTNpro into circulation or the muscle fiber number after the administration. Furthermore, dose-response was not examined. Further studies are needed to validate the potential of neonatal suppression of MSTN as a strategy to improve skeletal muscle growth of animals.