Erythrocyte: Programmed cell death

VITTORI DANIELA; VOTA DAIANA; NESSE ALCIRA

Anemia

INTECH

Año: 2012; p. 21 - 38

Erythrocytes are produced by a complex and finely regulated process of erythropoiesis. It starts with a pluripotential stem cell that, in addition of its self replication capacity, can give rise to separate cell lineages. Erythropoiesis passes from the stem cell through the multipotent progenitor CFU-GEMM (colony-forming unit granulocyte erythroid monocyte and megakaryocyte), and then BFU-E (burst-forming unit erythroid) and CFU-E (colony-forming unit eryhtroid), to the first recognizable erythrocyte precursor in the bone marrow, the pronormoblast. This cell gives rise to a series of progressively smaller normoblasts with increasing content of hemoglobin. The nucleus is finally extruded from the late normoblast within the marrow resulting reticulocyte stage which still contains some ribosomal RNA. Erythropoiesis ends with the mature circulating red cell, which is a non-nucleated biconcave disc, performing its function of oxygen delivery. In this process, the glycoprotein hormone erythropoietin has been known as the major humoral regulator of red cell production. It is now well established that erythropoietin stimulates erythropoiesis, at least in part, by protecting erythroblasts from apoptosis. Human mature erythrocytes are terminally differentiated cells that are devoid of mitochondria, as well as of nucleus and other organelles. In circulation, the red cell is constantly tested for its capacity to undergo marked cellular deformation. This ability to change its shape is essential for optimal cell function, since the resting diameter of the human red cell far exceeds that of the capillaries and splenic endothelial slits through which it must pass (Mohandas & Groner, 1989). A two dimensional network of proteins interacting between transmembrane location and cytoplasmic surface of the plasma membrane gives the red blood cells its properties of elasticity and flexibility that allows the success of this journey.  The term anemia is derived from ancient Greek for "bloodlessness". It is a condition involving abnormal reduction of hemoglobin content. In healthy adults, there is steady-state equilibrium between the rate of release of new red cells from the bone marrow into the circulation and the rate of removal of senescent red cells from the circulation by reticuloendothelial system. Balance disruption appears by decreased cell production, increased destruction or both, leading then to anemia. Different mechanisms which may lead to anemia are blood loss, decreased red cell lifespan, acquired or congenital defects, ineffective erythropoiesis, and impairment of red cell formation.