FIGURE 1.

Iron homeostasis in the brain. The iron was uptake from blood through brain capillary epithelial cells. Neurons express TfR, DMT1 and Fpn; absorb iron from brain interstitium and export excess iron. Astrocytes form intimate contact with brain capillary epithelial cells through end-feet and may influence iron transport between blood and brain. Astrocytes express TfR1, DMT1 and ZIP-14; and efflux iron via Fpn partnered with ceruloplasmin (Cp). Astrocytes may also efflux iron via endothelial cells into blood. Microglia can acquire iron via TfR1, DMT1 from brain intermedium. Microglia are unable to efflux iron as Fpn is internalized from the cell surface. In aged or neurodegenerative brain, microbleeds may occur. Hemoglobin is released after haemolysis. Haptoglobin binds with hemoglobin form a tight complex. The Hb:Hp complex is bound with the receptor CD163 and undergo endocytosis. The complex are degraded after endocytosis and the iron is absorbed into intracellular iron pool and stored in ferritin. The iron flow direction is indicated by black arrows.