Activin A

Where it comes from

Made in

Granulosa cells, pituitary, placenta, bone marrow, macrophages and many injured tissues

Sent out by

In the follicle and the pituitary by the cycle; everywhere else by inflammation and injury

Acts on

• Pituitary (FSH synthesis)
• Follicles
• Immune cells
• Red cell precursors
• Fibroblasts

What it does

• Stimulates FSH; inhibin and follistatin are the brakes on it
• An early signal of inflammation; in animals it rises within an hour of endotoxin
• Activin signals restrain the late stages of red cell maturation, which is what the activin traps relieve
• In fibrodysplasia ossificans progressiva, the mutant receptor reads activin A as a command to make bone ³

In medicine

• Luspatercept, a trap for activin-family ligands, was approved in November 2019 for the anaemia of beta-thalassaemia and in 2020 for lower-risk myelodysplastic syndromes ¹
• Sotatercept, a similar trap, was approved in March 2024 for pulmonary arterial hypertension ²
• Garetosmab, an antibody against activin A, cut new bone in fibrodysplasia ossificans progressiva in a phase 3 trial of 63 adults: 19 new lesions on placebo against one and two on the two doses over 56 weeks ³. It was approved in the United States in August 2026 ⁴

Beyond the body’s own use

• Blocking activin is being tested for muscle wasting and cancer cachexia, on the argument that the traps which relieve anaemia also take the brake off muscle; no such use is approved
• Activin A is a research marker in heart failure and pre-eclampsia, and rises within an hour of an inflammatory insult in animals, which is why it is also studied as an early sepsis signal