cytochrome-c-t and Anemia--Sideroblastic

Early erythroblasts from patients with refractory anemia (RA) and RA with ringed sideroblasts (RARS) show constitutive mitochondrial release of cytochrome c. Moreover, mature erythroblasts in RARS, but not in RA, display aberrant accumulation of mitochondrial ferritin (MtF). We analyzed cytochrome c release, MtF expression, and gene expression during erythroid differentiation in bone marrow cells from myelodysplastic syndrome (MDS) patients and healthy controls. Whereas none or few cultured erythroid cells from healthy individuals and RA patients expressed MtF, those from RARS patients showed MtF expression at an early stage, when cells were CD34+ and without morphologic signs of erythroid differentiation. The proportion of RARS erythroblasts that were MtF+ increased further upon in vitro maturation. Moreover, a significant overexpression of mRNA encoding cytochrome c, and proapoptotic Bid and Bax, was seen in freshly isolated cells from MDS patients. Genes involved in erythroid differentiation were also dysregulated in MDS cells. Importantly, GATA-1 expression increased during normal erythroid maturation, but remained low in MDS cultures, indicating a block of erythroid maturation at the transcriptional level. In conclusion, aberrant MtF expression in RARS erythroblasts occurs at a very early stage of erythroid differentiation and is paralleled by an up-regulation of genes involved in this process.

Topics: Adenosine Triphosphate; Anemia, Sideroblastic; Apoptosis; bcl-2-Associated X Protein; BH3 Interacting Domain Death Agonist Protein; Carrier Proteins; Cytochromes c; DNA-Binding Proteins; Erythroblasts; Erythroid-Specific DNA-Binding Factors; Ferritins; GATA1 Transcription Factor; Gene Expression; Glycoproteins; Granulocyte Colony-Stimulating Factor; Hematopoietic Stem Cells; Hemoglobins; Humans; Iron; Mitochondria; Myelodysplastic Syndromes; Proto-Oncogene Proteins c-bcl-2; Risk Factors; RNA, Messenger; Transcription Factors

Erythroid apoptosis in low-risk myelodysplastic syndrome (MDS) maybe mediated via mitochondrial release of cytochrome c and subsequent caspase activation. In the present study, we compared the in vitro and in vivo effects of proerythroid treatment with erythropoietin + granulocyte colony-stimulating factor (G-CSF) on myelodysplastic erythropoiesis regarding apoptosis and preferential growth of clones with cytogenetic abnormalities.. We enrolled 15 refractory anemia (RA) and 11 refractory anemia with ringed sideroblasts (RARS), including 5q- aberration, monosomy 7, and trisomy 8, before initiation of treatment and followed nine patients after successful treatment. The effects of G-CSF and erythropoietin were assessed. The expression of G-CSF receptor (G-CSFR) was explored during erythroid maturation. The relative growth of erythroid progenitors with cytogenetic aberrations in presence of erythropoietin was investigated.. Significant redistribution of cytochrome c was seen before treatment at all stages of erythroid differentiation. This release was blocked by G-CSF during the whole culture period and by erythropoietin during the latter phase. Both freshly isolated glycophorin A+ bone marrow cells and intermediate erythroblasts during cultivation retained their expression of G-CSFR. Cytochrome c release and caspase activation were significantly less pronounced in progenitors obtained from successfully treated nonanemic patients and showed no further response to G-CSF in vitro. Moreover, erythropoietin significantly promoted growth of cytogenetically normal cells from 5q- patients, whereas no such effect was observed on erythroblasts from monosomy 7 or trisomy 8 patients.. We conclude that growth factors such as erythropoietin and G-CSF can act both via inhibition of apoptosis of myelodysplastic erythroid precursors and via selection of cytogenetically normal progenitors.

Topics: Adult; Aged; Aged, 80 and over; Anemia, Refractory; Anemia, Sideroblastic; Apoptosis; Bone Marrow Cells; Caspases; Cytochromes c; Enzyme Activation; Erythroid Precursor Cells; Erythropoietin; Glycophorins; Granulocyte Colony-Stimulating Factor; Humans; In Vitro Techniques; Middle Aged; Monosomy; Receptors, Granulocyte Colony-Stimulating Factor; Recombinant Proteins; Trisomy