Activin A is a
dimeric glycoprotein of the TGF-ß superfamily, with roles including embryonic
differentiation, trophoblast invasion of the uterine wall in early pregnancy,
and fetal/neonatal brain protection under hypoxic conditions. Activin A also
regulates bone formation and regeneration, enhances joint inflammation in
rheumatoid arthritis, and triggers pathogenic mechanisms in the respiratory
system. Activin-A signals through two type I and two type Il receptors, which,
upon ligand binding, activate their kinase activity, phosphorylate SMAD2 and 3
intracellular signaling mediators that form a complex with SMAD4, translocate
to the nucleus, and activate or silence gene expression .
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