Jurnal Internasional Eritrosit dan eritroblas melepaskan zat besi
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“When a dog bites a man, it is not news, because that often happens. But if a man bites a dog, that is news ”(attributed to Alfred Harmsworth [1865–1922] a king of English newspapers). The release of iron by erythroid cells during their normal life span is of course the story of “a dog bite”. Why do erythroblasts and erythrocytes release the iron they have collected at such a large metabolic cost?
Humans evolve under conditions of endemic iron deficiency, and this remains the most common nutritional deficiency and the main cause of anemia worldwide. In adult humans, erythrocyte hemoglobin contains a large portion of iron in the body (2-2.5 g in total 3-4 g) and erythroblasts in the marrow are consumers of greedy iron (about 90% of ∼25 mg / d of iron moves). through the circulating plasma transferrin compartment). However, all metabolically active cells need iron, and the central nervous system, skeletal muscle, and heart are known to be very sensitive to iron deprivation. 2 19 – 4 Misallocation of rare iron to erythroid cells at the expense of other tissues will have serious consequences for organismal function. Thus, erythrocyte production is tightly regulated by plasma transferrin-bound iron concentrations and by iron concentrations in erythroblasts, causing erythropoiesis to slow down during the iron deficiency period, and thus leaving more iron for other tissues. At other extremes of iron availability, some cells and tissues can be damaged by excessive cellular accumulation from the form of chemically reactive iron, causing injury, fibrosis, and carcinogenesis. 5
The main source of iron plasma includes absorbed iron diets from the duodenum, iron is recycled by macrophages from senescent erythrocytes, and iron is taken from storage in hepatocytes (see figure). Iron flows from these cells into plasma through the only known exporter of cellular iron, ferroportin, 6 under the control of the hepcidin ligand, a peptide hormone secreted by hepatocytes. 7 8 1945-1955 Building a previous publication on the protective role of iron-erythoxin mediators mediated by ferroportin in malaria, 9 Zhang et al. Now present evidence that during their normal life span, erythroblasts and erythrocytes important iron release contributes to the systemic iron economy (see figure).
The earliest clue to the potential ability of erythroid cells to release iron to plasma is their abundant expression of an iron regulating element (IRE) – ferroportin isoform deficiency messenger RNA (mRNA), also found in duodenal enterocytes. 10 In both tissues, the lack of 5′IRE in ferroportin mRNA implies that the translation of these isoforms into ferroportin proteins will not be depressed by deficiency, potentially allowing duodenum and erythroblast to release iron during systemic iron deficiency, despite iron deficiency status themselves. Because most of the iron in the body is in erythrocytes and erythrocytes, the release of a small portion of this iron can provide enough of this important nutrient for iron-deficient organs, 2 19 – 4 without excessive iron depletion of the erythroid compartment. The contribution of this iron source to the systemic iron economy is now demonstrated by Zhang et al. In mice genetically engineered to lack of erythroid ferroportin. Surprisingly, the loss of iron exports from erythroblasts and erythrocytes caused a decrease in 20% of iron serum concentration and transferrin saturation. This is an underestimate of the contribution of iron efflux from live erythroid cells because, as discussed below, ferroportin-deficient erythrocytes have a shorter life span, thus returning all iron to the organism at a higher level.
development in the marrow, erythroblasts take almost all of the iron available to rapidly synthesize large amounts of heme and hemoglobin. Here ferroportin can function to prevent iron-mediated damage to the erythroblast by releasing excess iron which is not used for hemoglobin synthesis. Adult human erythrocytes, one quarter of all cells in the body, then spend 120 days in the blood circulation, with unusually high concentrations of iron-rich hemoglobin up to nearly 200,000 redox stress cycles, whereas in mice, erythrocytes experience> 500,000 cycles for 40 days in blood circulation. Here ferroportin is thought to eliminate iron leakage from damage to hemoglobin from circulating erythrocytes. Consistent with the proposed mechanism, mice lacking erythroid ferroportin have mild chronic haemolytic anemia and increased sensitivity to hemolytic stress. How iron is released from the heme hemoglobin and how to achieve ferroportin remains to be determined. Interestingly, under different conditions (i.e., iron deficiency), iron overload in ferroportin-deficient erythroid cells increases hemoglobin synthesis even during iron deficiency, producing greater erythrocytes than iron deficiency wild rats.
Erythroid cells represent the extremes of cell biology that appear to require counterintuitive adaptation, where their ability to release iron during their life span is just the latest example.
- © 2018 by The American Society of Hematology