Restoration of labile iron pool in ΔPCBP1 enteroids upon treatment with hepcidin. (A-B) Labile Fe(II) in WT and ΔPCBP1 differentiated enteroids was detected with fluorescent indicator (FerroOrange) without (A) or with (B) hepcidin pretreatment for 1 hour. Central sections of representative enteroids are shown. Images are in pairs with inset at higher magnification on the right. Quantification at right. Enteroids were grown 3 times from individual mice and iron signal from 3 to 7 enteroids in each condition was imaged and measured. Bar = 50 μm. (C) Model of PCBP1-mediated management of cytosolic iron retention and efflux. In WT enterocytes (left), dietary iron imported through DMT1 is rapidly coordinated by PCBP1, which directs excess iron to ferritin for storage and maintains free iron pool at low levels. Lysosomal turnover of ferritin, mediated by NCOA4, occurs when intracellular iron levels are low. Rates of iron efflux through FPN are low and steady. In PCBP1-deleted enterocytes (right), imported iron is not coordinated by PCBP1 and intracellular free iron rapidly rises to high levels. Rates of iron efflux through FPN are high and rapid efflux continues until intracellular free iron falls to low levels. The pool of cytosolic iron buffered by PCBP1 is absent and ferritin storage is low. Iron is initially delivered to portal circulation at a high rate (bolus effect).