(A) Following proteolytic processing of the myostatin precursor protein by furin proteases, the N-terminal propeptide and the C-terminal dimer, which is the actual signaling molecule, remain non-covalently bound in an inactive, latent complex. Latent myostatin (MSTN) is activated by proteolytic cleavage of the propeptide by members of the BMP-1/TLD family of metalloproteases. (B) MSTN and activin A suppress muscle growth by binding initially to the activin type 2 receptors, ACVR2 and ACVR2B. Boxes show biologics capable of blocking MSTN and/or activin A signaling. All of these have been tested in clinical trials in patients with muscle and/or metabolic diseases, except for garetosmab, which is a monoclonal antibody directed against activin A.