ABSTRACT
A human therapeutic that specifically modulates skeletal muscle growth would potentially provide a benefit for a variety of conditions including sarcopenia, cachexia, and muscular dystrophy. Myostatin, a member of the TGF-beta family of growth factors, is a known negative regulator of muscle mass, as mice lacking the myostatin gene have increased muscle mass. Thus, an inhibitor of myostatin may be useful therapeutically as an anabolic agent for muscle. However, since myostatin is expressed in both developing and adult muscles, it is not clear whether it regulates muscle mass during development or in adults. In order to test the hypothesis that myostatin regulates muscle mass in adults, we generated an inhibitory antibody to myostatin and administered it to adult mice. Here we show that mice treated pharmacologically with an antibody to myostatin have increased skeletal muscle mass and increased grip strength. These data show for the first time that myostatin acts postnatally as a negative regulator of skeletal muscle growth and suggest that myostatin inhibitors could provide a therapeutic benefit in diseases for which muscle mass is limiting.
Subject(s)
Muscle, Skeletal/growth & development , Transforming Growth Factor beta/antagonists & inhibitors , Transforming Growth Factor beta/metabolism , Amino Acid Sequence , Animals , Antibodies, Monoclonal/administration & dosage , Antibodies, Monoclonal/immunology , Body Weight , CHO Cells , Cricetinae , Culture Media, Conditioned , Female , Hand Strength , Humans , Male , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Knockout , Muscle Fibers, Skeletal/cytology , Muscle, Skeletal/anatomy & histology , Muscle, Skeletal/physiology , Myostatin , Protein Binding , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/immunologyABSTRACT
Myostatin, also known as growth and differentiation factor 8, is a member of the transforming growth factor beta superfamily that negatively regulates skeletal muscle mass (1). Recent experiments have shown that myostatin activity is detected in serum by a reporter gene assay only after activation by acid, suggesting that native myostatin circulates as a latent complex (2). We have used a monoclonal myostatin antibody, JA16, to isolate the native myostatin complex from normal mouse and human serum. Analysis by mass spectrometry and Western blot shows that circulating myostatin is bound to at least two major proteins, the myostatin propeptide and the follistatin-related gene (FLRG). The myostatin propeptide is known to bind and inhibit myostatin in vitro (3). Here we show that this interaction is relevant in vivo, with a majority (>70%) of myostatin in serum bound to its propeptide. Studies with recombinant V5-His-tagged FLRG protein confirm a direct interaction between mature myostatin and FLRG. Functional studies show that FLRG inhibits myostatin activity in a reporter gene assay. These experiments suggest that the myostatin propeptide and FLRG are major negative regulators of myostatin in vivo.
