Myostatin, an endogenous negative regulator of skeletal muscle mass, is a therapeutic target for muscle atrophic disorders. Here, we identified minimum peptides 2 and 7 to effectively inhibit myostatin activity, which consist of 24 and 23 amino acids, respectively, derived from mouse myostatin prodomain. These peptides, which had the propensity to form α-helix structure, interacted to myostatin with KD values of 30-36 nM. Moreover, peptide 2 significantly increased muscle mass in Duchenne muscular dystrophy model mice.

Myostatin inhibition is one of the promising strategies for treating muscle atrophic disorders, including muscular dystrophy. It is well-known that the myostatin prodomain derived from the myostatin precursor acts as an inhibitor of mature myostatin. In our previous study, myostatin inhibitory minimum peptide (WRQNTRYSRIEAIKIQILSKLRL-amide) was discovered from the mouse myostatin prodomain. In the present study, alanine scanning of demonstrated that the key amino acid residues for the effective inhibitory activity are rodent-specific Tyr and C-terminal aliphatic residues, in addition to N-terminal Trp residue. Subsequently, we designed five Pro-substituted peptides and examined the relationship between secondary structure and inhibitory activity. As a result, we found that Pro-substitutions of Ala or Gln residues around the center of significantly decreased both α-helicity and inhibitory activity. These results suggested that an α-helical structure possessing hydrophobic faces formed around the C-terminus is important for inhibitory activity.

Myostatin, a negative regulator of skeletal muscle growth, is a promising target for treating muscle atrophic disorders. Recently, we discovered a minimal myostatin inhibitor (WRQNTRYSRIEAIKIQILSKLRL-amide) derived from positions 21-43 of the mouse myostatin prodomain. We previously identified key residues (N-terminal Trp, rodent-specific Tyr, and all aliphatic amino acids) required for effective inhibition through structure-activity relationship (SAR) studies based on and characterized a 3-fold more potent inhibitor bearing a 2-naphthyloxyacetyl group at position 21. Herein, we performed -based SAR studies focused on all aliphatic residues and Ala, discovering that the incorporations of Trp and Ile at positions 32 and 38, respectively, enhanced the inhibitory activity. Combining these findings with , a novel peptide displayed an IC value of 0.32 μM, which is 11 times more potent than . The peptide would have the potential to be a promising drug lead to develop better peptidomimetics.

Inhibition of myostatin is a promising strategy for treatment of muscle atrophic disorders. We had already identified a 23mer peptide (1) as a synthetic myostatin inhibitor, and structure− activity relationship studies with 1 afforded a potent 22-mer peptide derivative (3). Herein, we report the shortest myostatin inhibitory peptide so far. Among chain-shortened 16-mer peptidic inhibitors derived from the C-terminal region of 3, peptide inhibitor 8a with βsheet propensity was twice as potent as 22-mer inhibitor 3 and significantly increased not only muscle mass but also hind limb grip strength in Duchenne muscular dystrophic model mice. These results suggest that 8a is a promising platform for drug development treating muscle atrophic disorders.