Activin receptor type II signaling axis (ActRII axis)

The Activin receptor type II (ActRII) signaling axis, encompassing the myostatin–ActRIIA/B and activin A–SMAD2/3 pathways, is a central regulatory network within the TGF-β superfamily that governs tissue growth and homeostasis (Lee, 2004, PMID: 15473850). Myostatin (GDF-8) and Activin A function as potent ligands that bind to the extracellular domains of ActRIIA and ActRIIB, initiating a signaling cascade that phosphorylates SMAD2 and SMAD3 to regulate gene transcription (UniProt P27037, P27038). In skeletal muscle, this axis acts as a negative regulator of mass, while in the bone marrow, it inhibits the late-stage maturation of red blood cells (Cappellini et al., 2020, PMID: 32212535). Pathological overactivation of this network is linked to muscle wasting, chronic anemia, and the vascular remodeling seen in pulmonary arterial hypertension (Humbert et al., 2021, PMID: 33789009). Therapeutic strategies targeting this axis primarily utilize "ligand traps," such as sotatercept and luspatercept, which are fusion proteins designed to sequester circulating ligands and prevent their interaction with membrane-bound receptors. These interventions aim to restore the balance between pro-proliferative and anti-proliferative signals, thereby improving muscle volume, erythropoiesis, and vascular hemodynamics.

Other names

Myostatin-Activin signaling pathwayTGF-beta superfamily SMAD2/3 signaling axisGDF8-Activin-ActRII complexActivin receptor type II signaling pathway

Ligand trapping and sequestration of TGF-beta superfamily members (Activins, GDFs) to inhibit downstream SMAD2/3 phosphorylation.