How is iron transported to the bone marrow to produce hemoglobin in new red blood cells?

Sourav PanNovember 9, 2024

Answered

Iron transport to the bone marrow for the production of hemoglobin in new red blood cells is a critical process that relies on several key mechanisms and proteins. Here’s a detailed overview of how this occurs:

Iron Recycling and Transport Mechanism

1. Source of Iron: The majority of iron required for erythropoiesis (the production of red blood cells) comes from the recycling of iron from senescent red blood cells (RBCs). This recycling is primarily carried out by macrophages, particularly Kupffer cells in the liver and macrophages in the spleen, which phagocytose aged RBCs and break down hemoglobin to release iron.
2. Phagocytosis by Kupffer Cells: Kupffer cells engulf aged or damaged RBCs through a process called phagocytosis. Inside these macrophages, hemoglobin is broken down into its components: globin and heme. The heme is further degraded into iron and bilirubin. The released iron is then stored in the liver as ferritin or transported back into circulation.
3. Transport via Transferrin: Once iron is released from heme, it binds to transferrin, a glycoprotein synthesized by the liver. Transferrin serves as the primary transport protein for iron in the bloodstream. It carries iron to various tissues, including the bone marrow, where erythropoiesis occurs.
4. Uptake by Erythroid Precursors: In the bone marrow, erythroid precursor cells express transferrin receptors (TfR1) on their surface. Transferrin binds to these receptors, facilitating the endocytosis of the transferrin-iron complex into the erythroid progenitor cells. Once inside, iron is released from transferrin and transported into mitochondria, where it is utilized for heme synthesis.
5. Heme Synthesis: Iron is incorporated into protoporphyrin IX (PPIX) to form heme, a crucial component of hemoglobin. This process is catalyzed by ferrochelatase, an enzyme located in the mitochondria of erythroid cells. The newly synthesized heme then combines with globin chains to form functional hemoglobin.

Summary of Key Points

• Recycling: Most iron for new RBC production comes from recycled iron rather than dietary intake.
• Transferrin Role: Transferrin transports iron from macrophages to erythroid precursors in the bone marrow.
• Erythropoiesis: Erythroid progenitor cells utilize transferrin-bound iron for hemoglobin synthesis, essential for forming new red blood cells.