Bone morphogenetic protein (BMP) signaling induces hepatic expression of the
peptide hormone hepcidin.
Hepcidin reduces serum
iron levels by promoting degradation of the
iron exporter
ferroportin. A relative deficiency of
hepcidin underlies the pathophysiology of many of the genetically distinct
iron overload disorders, collectively termed hereditary
hemochromatosis. Conversely, chronic inflammatory conditions and neoplastic diseases can induce high
hepcidin levels, leading to impaired mobilization of
iron stores and the
anemia of
chronic disease. Two BMP type I receptors, Alk2 (Acvr1) and Alk3 (Bmpr1a), are expressed in murine hepatocytes. We report that liver-specific deletion of either Alk2 or Alk3 causes
iron overload in mice. The
iron overload phenotype was more marked in Alk3- than in Alk2-deficient mice, and Alk3 deficiency was associated with a nearly complete ablation of basal BMP signaling and
hepcidin expression. Both Alk2 and Alk3 were required for induction of
hepcidin gene expression by BMP2 in cultured hepatocytes or by
iron challenge in vivo. These observations demonstrate that one type I
BMP receptor, Alk3, is critically responsible for basal
hepcidin expression, whereas 2 type I
BMP receptors, Alk2 and Alk3, are required for regulation of
hepcidin gene expression in response to
iron and BMP signaling.