Deletion of BMP6 worsens the phenotype of HJV-deficient mice and attenuates hepcidin levels reached after LPS challenge

Lack of either bone morphogenetic protein 6 (BMP6) or the BMP coreceptor hemojuvelin (HJV) inmice leads to a similar phenotype with hepcidin insufficiency, hepatic iron loading, and extrahepatic iron accumulation in males. This is consistent with the current views that HJV is a coreceptor for BMP6in hepatocytes. To determine whether BMP6 and HJV may also signal to hepcidin independently of each other, we intercrossed Hjv(-/-) and Bmp6(-/-) mice and compared the phenotype of animals of the F2 progeny. Loss of Bmp6 further repressed Smad signaling and hepcidin expression in the liver of Hjv(-/-) mice of both sexes, and led to iron accumulation in the pancreas and the heart of females. These data suggest that, in Hjv(-/-) females, Bmp6 can provide a signal adequate tomaintain hepcidin to a level sufficient to avoid extrahepatic iron loading. We also examined the impact of Bmp6 and/or Hjv deletion onthe regulation of hepcidinby inflammation. Our data showthat lack of 1 or bothmolecules does not prevent induction of hepcidin by lipopolysaccharide (LPS). However, BMP/Smad signaling in unchallenged animals is determinant for the level of hepcidin reached after stimulation, which is consistentwitha synergy between interleukin 6/STAT3 and BMP/SMAD signaling in regulating hepcidin during inflammation.