Ferroportin (FPN) is the sole
iron export
membrane protein identified in mammals that is abundantly expressed on absorptive enterocytes and macrophages, and is essential for physiological regulation of cellular
iron. The expression of FPN is positively induced by cellular
iron and is suppressed by liver
hepcidin in response to either increased systemic
iron or inflammatory stimuli.
Hepcidin binds to cell surface FPN inducing FPN internalization followed by lysosomal degradation of the
protein and consequently
iron efflux from macrophages is blocked and there is suboptimal
iron absorption by duodenal enterocytes. Dozens of FPN gene mutations have been identified in different ethnic populations and some of the mutations are associated with
autosomal dominant iron overload disorder described as FPN disease or
hemochromatosis type 4 that is distinct from hereditary
hemochromatosis due to HFE mutations. Clinical manifestations of
iron overload FPN disease can be classified into two groups according to whether there is selective macrophage
iron loading or parenchymal and reticuloendothelial
iron accumulation. There is evidence suggesting that altered
hepcidin-FPN interaction can modulate host's response to
infection. Resistance to
hepcidin promotes
iron egress from cells and this inhibits growth of intracellular pathogens. Conversely,
iron retention due to loss of
iron export activity by mutated FPN results in intracellular
iron accumulation and a permissive environment for intracellular pathogens.