bcl-x Prevents Apoptotic Cell Death of Both Primitive and Definitive Erythrocytes at the End of Maturation

Abstract

bcl-x is a member of the bcl-2 gene family, which regulates apoptotic cell death in various cell lineages. There is circumstantial evidence suggesting that bcl-x might play a role in the apoptosis of erythroid lineage cells, although there is no direct evidence. In this study, we used Bcl-X null mouse embryonic stem (ES) cells, and showed that Bcl-X is indispensable for the production of both embryonic primitive erythrocytes (EryP) and adult definitive erythrocytes (EryD) at the end of their maturation. In vivo, bcl-x −/− ES cells did not contribute to circulating EryD in adult chimeric mice that were produced by blastocyst microinjection of the bcl-x −/− ES cells. bcl-x −/− EryP and EryD were produced by in vitro differentiation induction of ES cells on macrophage colony-stimulating factor–deficient stromal cell line OP9, and further analysis was carried out. The emergence of immature EryP and EryD from bcl-x −/− ES cells was similar to that from bcl-x +/+ ES cells. However, prominent cell death of bcl-x −/− EryP and EryD occurred when the cells matured. The data show that the antiapoptotic function of bcl-x acts at the very end of erythroid maturation.

Mitochondria in hematopoiesis and hematological diseases

“…In this context, caspases appear to be activated through a mitochondria-dependent pathway similar to that identified in various forms of apoptosis (Zermati et al, 2001;Kolbus et al, 2002). This activation of caspases is in apparent contrast with Epo-mediated upregulation of the antiapoptotic protein Bcl-X L through activation of the transcription factor GATA-1 during terminal erythroid differentiation (Gregory et al, 1999;Motoyama et al, 1999). The main function of Bcl-X L in this differentiation pathway is supposed to be the prevention of apoptosis during erythroid development (Wang et al, 2000), for example by limiting differentiation-related caspase activation.…”

The notch pathway positively regulates programmed cell death during erythroid differentiation

“…34 Studies using bcl-x-null mice demonstrated a critical role for this gene at the end of erythroid maturation when maximal hemoglobin synthesis occurs. 35 RBPjk À/À erythroid cells show a clear upregulation of genes involved in this antiapoptotic pathway, such as EPO, EPO-R, bcl-x and bcl-2, suggesting that Notch may induce apoptosis by impinging on this pathway. Previous reports have attempted to link Notch induction of apoptosis through the p53 pathway in other systems.…”

New Insights Into Erythropoietin and Epoetin Alfa: Mechanisms of Action, Target Tissues, and Clinical Applications

“…Finally, full Bcl-x knockout mice died in embryogenesis with extensive apoptosis of immature hematopoietic cells [17], and conditional hematopoietic-specific Bcl-x knockout mice had severe anemia [18]. In both models, Bcl-x was required for the survival of erythroid cells during terminal maturation [18,19]. A recent study also demonstrated that enforced Bcl-x expression can rescue maturation of EPO-deprived erythroid progenitors in vitro, suggesting that the major erythropoietic function of EPO is to prevent apoptosis and that Bcl-x is a critical effector gene [20].…”

“…EPO is essential for life: mice with deletions of the EPO gene or the EPO-R die of anemia in utero [3,4]. Recombinant human Weiss 19 EPO (epoetin alfa) is used in clinical practice to reduce transfusion requirements during surgery [5] and to treat anemia of various etiologies, including anemia of chronic kidney disease [6], cancer-related or cancer treatment-related anemia [7], anemia related to zidovudine therapy in HIVinfected patients [8], and anemia related to ribavirin therapy for hepatitis C virus infection [9].…”