Researchers from the International Institute of Molecular and Cell Biology in Warsaw have identified a previously unknown role of specialized blood vessel cells in the liver, challenging existing assumptions about how the body handles free hemoglobin after red blood cells break down.
Hemoglobin is the oxygen-carrying protein inside red blood cells. Under normal conditions, small numbers of aging red blood cells rupture and release hemoglobin, which is typically cleared by macrophages – immune cells known for “cleaning up” cellular debris. However, in certain diseases where red blood cells are more fragile, large amounts of free hemoglobin accumulate in the bloodstream, where it can become toxic. Until now, this cleanup was thought to be handled almost exclusively by macrophages.
In a new study published in EMBO Reports, scientists show that liver sinusoidal endothelial cells (LSECs) – highly specialized cells lining the capillary-like vessels of the liver – are also capable of seeking out and internalizing free hemoglobin from circulation. Once inside the cells, this hemoglobin is directed into cellular pathways that safely break it down and help maintain iron balance in the body.
LSECs have long been recognized as efficient “filters” of the blood, removing potentially harmful molecules and indirectly influencing iron homeostasis by sensing iron levels and regulating its release into the bloodstream. The new findings reveal that these cells can directly take up free hemoglobin and participate in iron recycling, adding a crucial piece to our understanding of liver physiology and systemic iron regulation.
The discovery raises important questions about how this mechanism might function in liver diseases and haemolytic conditions, where excessive free hemoglobin contributes to tissue damage. Future research may explore whether targeting LSEC functions could lead to new therapeutic strategies for managing iron overload and protecting liver health.
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