Hepcidin regulates cellular iron efflux by binding to ferroportin and inducing its internalization Original paper

What was studied?

This study investigated hepcidin ferroportin internalization as the core molecular mechanism by which the liver peptide hormone hepcidin controls systemic iron availability. Using cell-culture models engineered to express ferroportin (Fpn) fused to green fluorescent protein (Fpn-GFP), the authors tested whether hepcidin directly interacts with ferroportin and, if so, whether that interaction changes ferroportin localization, stability, and iron-export function. The experiments focused on real-time visualization of ferroportin trafficking, biochemical confirmation of binding, and functional readouts of intracellular iron retention (ferritin accumulation and radiolabeled iron export).

Who was studied?

No human participants were enrolled. The work was performed in in vitro tissue-culture systems, primarily HEK293 cells stably expressing inducible mouse Fpn-GFP and HeLa cells transiently transfected with Fpn-GFP constructs. Hepcidin used in experiments included purified human hepcidin and chemically synthesized hepcidin, alongside comparators such as protegrin (a structurally similar cationic antimicrobial peptide) and a truncated hepcidin variant (hep20) lacking the N-terminal residues required for biologic activity. These design choices allowed the investigators to distinguish specific receptor–ligand signaling from nonspecific cationic peptide–induced endocytosis.

Most important findings

Hepcidin caused a rapid redistribution of ferroportin from the plasma membrane into punctate intracellular vesicles, and once internalized, ferroportin did not recycle back to the surface without new synthesis—supporting a “remove-and-destroy” regulatory model rather than transient receptor trafficking. Low micromolar to submicromolar hepcidin concentrations produced internalization within hours, aligning with estimated physiologic ranges discussed by the authors. Critically, internalized ferroportin colocalized with lysosomal markers and was degraded; chloroquine blocked this loss, implicating lysosomal proteolysis. Functionally, hepcidin reversed ferroportin’s iron-export effect: cells expressing Fpn-GFP normally showed reduced ferritin and reduced radiolabeled iron retention, but hepcidin restored ferritin accumulation and increased intracellular radiolabel, demonstrating inhibited iron efflux. Binding was shown directly using radioiodinated hepcidin variants: induced Fpn-GFP cells bound substantially more labeled hepcidin than uninduced cells; unlabeled hepcidin competed for binding, while protegrin and hep20 did not. Cross-linking further identified a complex consistent with hepcidin bound to ferroportin, supporting the conclusion that ferroportin is the hepcidin receptor. Although this paper is not a microbiome study and contains no microbial taxa or microbiome signatures, its central insight is highly relevant to host–microbe interactions because inflammatory hepcidin induction is a major mechanism of “nutritional immunity,” restricting iron that many microbes require.

Key implications

This work defined a post-translational “gatekeeper” mechanism for systemic iron control: rising hepcidin removes ferroportin from iron-exporting cells (enterocytes, macrophages, hepatocytes), trapping iron intracellularly and lowering plasma iron. Clinically, this provides a unifying mechanistic basis for two extremes: hepcidin deficiency (or ferroportin resistance) driving iron overload syndromes, and hepcidin excess driving hypoferremia and anemia of inflammation. From a translational microbiome perspective, the study clarifies a key host lever that shapes microbial ecology indirectly—iron restriction—suggesting that microbiome-associated inflammation could alter iron availability through hepcidin, even though microbial signatures were not measured here.

Citation

Nemeth E, Tuttle MS, Powelson J, et al. Hepcidin regulates cellular iron efflux by binding to ferroportin and inducing its internalization. Science. 2004;306(5704):2090-2093. doi:10.1126/science.1104742