Activin receptor type-2B (ActRIIB) (ActRIIB)

Activin receptor type-2B (ActRIIB) is a high-affinity transmembrane serine/threonine kinase receptor that mediates signaling for several ligands within the TGF-β superfamily, including myostatin (GDF8), activins A and B, and GDF11 (UniProt: P27037). When these ligands bind to the endogenous ActRIIB receptor, they trigger the recruitment of type I receptors and the subsequent phosphorylation of SMAD2/3 transcription factors, which act as potent negative regulators of skeletal muscle growth and influence erythroid differentiation (PubMed: 28235118). Pathological overactivity of this signaling axis is implicated in muscle-wasting conditions like sarcopenia and cachexia, as well as in the ineffective erythropoiesis seen in myelodysplastic syndromes and beta-thalassemia (PubMed: 32051554). Pharmacological strategies to modulate this target include the use of soluble decoy receptors, such as luspatercept (a modified ActRIIB-Fc fusion protein), which sequester circulating ligands to prevent them from activating the endogenous receptor (FDA: Reblozyl). Other approaches involve monoclonal antibodies like bimagrumab that directly bind to ActRIIB to block ligand interaction, thereby promoting muscle hypertrophy and improving metabolic health (PubMed: 25143305). These therapies are being actively explored for their potential to treat a wide range of degenerative and hematological disorders.

Other names

ACVR2BActivin receptor type IIBACTR-IIBMGC116908

Ligand sequestration (ligand trap) and competitive receptor antagonism.