Interleukin-6 induces hepcidin expression through STAT3 Original paper

What was studied?

This original research study investigated the IL-6 STAT3 hepcidin pathway as a molecular mechanism linking inflammation to hepcidin transcription in human hepatocyte-derived cells. Hepcidin is a liver-produced hormone that limits systemic iron availability by blocking intestinal iron absorption and iron release from macrophages, making it central to the anemia of inflammation. The authors mapped the human hepcidin transcriptional start site and analyzed conserved regions in the 5′ upstream promoter across multiple mammals to identify regulatory elements. Using promoter–luciferase reporter constructs, targeted mutagenesis of conserved promoter elements, chromatin immunoprecipitation (ChIP), and STAT3 gain- and loss-of-function approaches, they tested whether IL-6 directly induces hepcidin, whether STAT3 physically binds the hepcidin promoter, and whether STAT3 activity is necessary and sufficient for promoter activation.

Who was studied?

No human participants were enrolled. The experimental system was the human hepatoma-derived HepG2/2.2.1 cell line, used as a hepatocyte-like model for inflammatory signaling and acute-phase transcriptional regulation. Cells were exposed to recombinant IL-6 (20 ng/mL), sometimes with cycloheximide to block new protein synthesis, and were transiently transfected with hepcidin promoter constructs or STAT3-modulating plasmids (constitutively active STAT3-C, dominant-negative STAT3 Y705F, and STAT3-targeting shRNA). The work, therefore, represents mechanistic bench research focused on hepatocyte transcriptional control, rather than a clinical cohort study.

Most important findings

IL-6 induced hepcidin mRNA in HepG2/2.2.1 cells even when protein translation was blocked by cycloheximide, supporting a direct transcriptional effect rather than an indirect cytokine cascade. Promoter mapping showed that a 0.6 kb upstream fragment retained IL-6 responsiveness comparable to a longer 1.3 kb construct, localizing the critical response element to the proximal promoter. Systematic mutagenesis of conserved elements identified conserved element 9 (CE9) as essential: mutation of CE9 reduced IL-6–driven promoter induction to roughly one-quarter of wild type. Bioinformatic prediction suggested a STAT-binding site within CE9, and ChIP demonstrated STAT3 (not STAT1) binding to the hepcidin promoter region containing CE9 after IL-6 exposure. Functional tests confirmed causality: constitutively active STAT3 stimulated the hepcidin promoter without IL-6, while dominant-negative STAT3 or STAT3 knockdown blunted IL-6 responsiveness to levels similar to the CE9 mutant. Although this paper is not microbiome-focused and reports no microbial taxa or community signatures, it is highly relevant to microbiome–host interaction biology because IL-6/STAT3 signaling is a common downstream pathway in inflammation-driven dysbiosis and can mediate systemic iron restriction that feeds back on microbial ecology.

Key implications

This work provides a clean mechanistic explanation for the anemia of inflammation: IL-6 activates STAT3, STAT3 binds a defined response element (CE9) in the hepcidin promoter, and this interaction is both necessary and sufficient for inflammatory hepcidin induction. Clinically, it strengthens the rationale for targeting IL-6/JAK/STAT3 signaling or hepcidin itself to treat inflammatory hypoferremia, while also highlighting that STAT3-activating stimuli beyond IL-6 may drive inappropriate hepcidin elevation. For microbiome-informed practice, the key translational insight is that inflammatory cytokine milieus can lock patients into an iron-restricted state that may alter gut microbial competition for iron and confound microbiome signatures—so interpreting microbiome profiles alongside IL-6/STAT3/hepcidin status may improve diagnostic and therapeutic precision.

Citation

Wrighting DM, Andrews NC. Interleukin-6 induces hepcidin expression through STAT3. Blood. 2006;108(9):3204-3209. doi:10.1182/blood-2006-06-027631