Acts specifically as a negative regulator of skeletal muscle growth. Homodimer; disulfide-linked. Interacts with WFIKKN2, leading to inhibit its activity. Interacts with FSTL3. Synthesized as large precursor molecule that undergoes proteolytic cleavage to generate an N-terminal propeptide and a disulfide linked C-terminal dimer, which is the biologically active molecule. The circulating form consists of a latent complex of the C-terminal dimer and other proteins, including its propeptide, which maintain the C-terminal dimer in a latent, inactive state. Ligand activation requires additional cleavage of the prodomain by a tolloid-like metalloproteinase. Belongs to the TGF-beta family.