Does hepcidin inhibit intestinal iron absorption and release from storage by causing ferroportin internalization and degradation?

Hepcidin acts as the master regulator of systemic iron homeostasis, functioning as a hormone that controls the entry of iron into the blood plasma. Substantial scientific evidence confirms its role in restricting iron availability by targeting the only known cellular iron exporter, ferroportin.

Mechanistic explanations

The interaction between hepcidin and ferroportin is a well-characterized molecular "lock and key" mechanism.

• Binding and Occlusion: Hepcidin binds directly to the central cavity of ferroportin when the transporter is in its "outward-open" conformation. This binding physically blocks the channel, immediately stopping iron efflux.
• Internalization: Following binding, hepcidin triggers the phosphorylation and ubiquitination of specific lysine residues on the intracellular loops of ferroportin. This ubiquitination acts as a molecular signal for clathrin-mediated endocytosis, where the cell membrane folds inward to pull the transporter inside the cell.
• Degradation: Once internalized, the hepcidin-ferroportin complex is trafficked to lysosomes. Within these acidic organelles, the proteins are enzymatically degraded, permanently removing the transporter's ability to export iron.

Clinical and physiological effectiveness

This molecular degradation has direct, systemic effects on iron levels:

• Intestinal Absorption: In the duodenum, ferroportin is located on the basolateral membrane of enterocytes (lining of the gut). When hepcidin levels are high, ferroportin is degraded, trapping dietary iron inside the enterocytes. Because these cells are naturally shed into the digestive tract every few days, the trapped iron is lost from the body rather than absorbed into the bloodstream.
• Iron Recycling and Storage: Approximately 80% of daily iron needs are met by recycling iron from old red blood cells, a process handled by macrophages. Hepcidin degrades ferroportin on these macrophages and on hepatocytes (liver storage cells). This sequesters iron within these cells as ferritin, preventing its mobilization for new red blood cell production.

Bottom line

Hepcidin inhibits both the absorption of dietary iron and the release of stored iron by triggering the internalization and lysosomal degradation of ferroportin. This mechanism is the primary cause of low serum iron in inflammatory states and is a critical target for managing iron disorders.