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The immunophilin FKBP12 inhibits hepcidin expression by binding the BMP type I receptor ALK2 in hepatocytes

Silvia Colucci, Alessia Pagani, Mariateresa Pettinato, Irene Artuso, Antonella Nai, Clara Camaschella and Laura Silvestri

Key points

  • FKBP12 suppresses hepcidin by interaction with the BMP receptor ALK2.

  • Disruption of FKBP12-ALK2 interaction increases hepcidin and renders the receptor responsive to the inflammatory ligand Activin A.

Abstract

The expression of the key regulator of iron homeostasis hepcidin is activated by the BMP-SMAD pathway in response to iron and inflammation and among drugs, by rapamycin, which inhibits mTOR in complex with the immunophilin FKBP12. FKBP12 interacts with BMP type I receptors to avoid uncontrolled signaling. By pharmacologic and genetic studies we identify FKBP12 as a novel hepcidin regulator. Sequestration of FKBP12 by rapamycin or tacrolimus activates hepcidin both in vitro and in murine hepatocytes. Acute tacrolimus treatment transiently increases hepcidin in wild type mice. FKBP12 preferentially targets the BMP receptor ALK2. ALK2 mutants defective in binding FKBP12 increase hepcidin expression in a ligand-independent manner, through BMP-SMAD signaling. ALK2 free of FKBP12 becomes responsive to the non-canonical inflammatory ligand Activin A. Our results identify a novel hepcidin regulator and a potential therapeutic target to increase defective BMP signaling in disorders of low hepcidin.

  • Submitted April 20, 2017.
  • Accepted August 31, 2017.