STAT3 is required for IL-6-gp130-dependent activation of hepcidin in vivo.
OBJECTIVE
Hepcidin is a peptide hormone that is central to the regulation of iron homeostasis. In response to interleukin 6 (IL-6), hepatocytes produce hepcidin that decreases iron release/transfer from enterocytes and macrophages and causes hypoferremia. To clarify the molecular pathways involved in hepcidin activation by IL-6, we used different mice strains in which the main IL-6/gp130 signaling pathways have been genetically disrupted.


METHODS
We generated mice with hepatocyte-specific deletion of the IL-6 signal-transducing gp130 receptor (alfpgp130 (LoxP/LoxP)), with a gp130 receptor lacking the essential region for STAT1 and -3 activation (alfpCre gp130(DeltaSTAT/LoxP)) or mice expressing a gp130 allele lacking the essential tyrosine for RAS-MAPK activation (alfpCregp130(Y757F/LoxP)). We studied gp130-dependent pathways and hepcidin mRNA expression by Western blot, reverse-transcription polymerase chain reaction, and Northern blot in vivo and ex vivo.


RESULTS
IL-6 stimulated phospho STAT3, serum amyloid A (SAA), and suppressor of cytokine signaling 3 (SOCS3) expression in livers of wild-type and alfpCregp130(Y757F/LoxP) mice, whereas this response was blocked in alfpCre gp130(LoxP/LoxP) and alfpCre gp130(DeltaSTAT/LoxP) mice. In wild-type and alfpCregp130(Y757F/LoxP) animals, significantly higher hepcidin mRNA expression was found 3 to 6 hours after IL-6 stimulation. In contrast, no IL-6-dependent regulation of hepcidin mRNA expression was found in alfpgp130 (DeltaSTAT/LoxP) and AlfpCre gp130 (LoxP/LoxP) animals. In primary hepatocytes, higher hepcidin mRNA expression after IL-6 stimulation was only observed when gp130-STAT3-dependent signaling was intact.


CONCLUSIONS
We have demonstrated that both in vivo and in vitro STAT3 is the key transcription factor responsible for IL-6 activation of hepcidin gene expression in the liver.
Pietrangelo
Antonello
A
Center for Hemochromatosis, Department of Internal Medicine, University of Modena and Reggio Emilia, Policlinico Via del Pozzo 71, 41100 Modena, Italy.
Dierssen
Uta
U
Valli
Linda
L
Garuti
Cinzia
C
Rump
Agrani
A
Corradini
Elena
E
Ernst
Matthias
M
Klein
Christian
C
Trautwein
Christian
C
D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics*; D050822:Cytokine Receptor gp130 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000502:physiology*; D064451:Hepcidins; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D051379:Mice; D008817:Mice, Mutant Strains; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology
D023181:Antimicrobial Cationic Peptides; C579599:Hamp protein, mouse; D064451:Hepcidins; D015850:Interleukin-6; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; C491411:Socs3 protein, mouse; C494087:Stat3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D050822:Cytokine Receptor gp130; D007501:Iron