Impaired clonogenic growth of myelodysplastic bone marrow progenitors in vitro is irrelevant to their apoptotic state

Abstract 

Excessive intramedullary apoptosis has been considered to account for the paradox of hypercellular marrow and refractory cytopenias in myelodysplastic syndrome (MDS). However, a causative relationship of apoptosis to the progenitor’s defective clonogenic growth has not been sufficiently demonstrated. We investigated the degree of apoptosis and its contribution to ineffective hematopoiesis in MDS, by assessing the differential clonogenic capacity of purified “apoptotic” and “non-apoptotic” bone marrow progenitors in a short-term semisolid culture system. Although increased apoptosis was indeed detected in MDS bone marrow progenitors, there was no correlation between the existence of apoptosis and culture performance. Non-apoptotic as well as apoptotic CD34⁺ cells gave similar patterns of growth, both defective compared to normal. The ability of “apoptotic” CD34⁺ cells to proceed in colony formation as well as the abnormal growth of “non-apoptotic” progenitors are probably pointing towards the need to reconsider the role of apoptosis in the defective clonogenicity of MDS.

Abbreviations:  AML, acute myeloid leukemia, BFU-E, burst forming unit-erythroid, BMMC, bone marrow mononuclear cells, BSA, bovine serum albumin, CFU-E, colony forming unit-erythroid, CFU-GM, colony forming unit granulocyte-macrophage, CMML, chronic myelomonocytic leukemia, DiOC₆(3), 3,3′-dihexyloxacarbocyanine iodide, DMSO, dimethylsulfoxide, ΔΨ_m, mitochondrial transmembrane potential, FAB, French–American–British, FACS, fluorescence activated cell sorting, FBS, fetal bovine serum, G-CSF, granulocyte-colony stimulating factor, GM-CSF, granulocyte-macrophage colony stimulating factor, IL-3, interleukine-3, IL-6, interleukine-6, IMDM, Iscove’s modified Dulbecco’s medium, Mab, monoclonal antibody, MACS, magnetic activated cell sorting, mClCCP, carbonyl-cyanide m-chlorophenylhydrazone, MDS, myelodysplastic syndromes, PBS, phosphate buffered saline, PCD, programmed cell death, PE, phycoerythrin, PI, propidium iodide, RA, refractory anemia, RARS, refractory anemia with ringed sideroblasts, RAEB, refractory anemia with excess of blasts, RAEB-t, refractory anemia with excess of blasts in transformation, rh, recombinant human, SCF, stem cell factor, TUNEL, Terminal d-UTP nick-end-labeling

Keywords:  Myelodysplastic syndrome, Bone marrow progenitors, Apoptosis, Annexin-V, Clonogenic assay, Colony formation