Enhanced growth of myelodysplastic colonies in hypoxic conditions

Abstract

Objective-To determine the response of bone marrow progenitor cells from patients with myelodysplastic syndromes (MDS) to culture in physiologic oxygen tension.Methods-Methylcellulose progenitor assays using both unfractionated bone marrow mononuclear cells (MNCs) and purified CD34 + progenitors were performed in atmospheric oxygen (18.6% O 2 ) or one of two levels of hypoxia (1% and 3% O 2 ). Assays were performed using normal donor marrow, MDS patient marrow, acute myelogenous leukemia marrow or peripheral blood blasts, chronic phase chronic myelogenous leukemia (CML) marrow MNCs, and blast crisis CML peripheral blood.Results-The majority of MDS samples showed decreased colony-forming units (CFU) in 18.6% O 2 compared to normal controls, as expected. However, in either 1% or 3% O 2 , 9 of 13 MDS samples demonstrated augmentation of CFUs beyond that observed in normal controls, with 6 of 13 demonstrating a greater than ninefold augmentation. This effect is cell autonomous, as it persisted after purification of CD34 + progenitor cells. Additionally, the augmented response to physiologic oxygen tension is specific to MDS, as it was not observed in either acute or chronic myelogenous leukemia samples.Conclusion-These results suggest that the reported decrease in MDS CFUs reflects greater sensitivity of MDS progenitors or their progeny to the nonphysiologic oxygen tensions routinely used in vitro, rather than a true decrease in progenitor frequency. Importantly, these experiments for the first time describe an experimental system that can be used to study the growth of primary cells from patients with MDS.Myelodysplastic syndromes (MDS) are a diverse group of hematopoietic disorders characterized by persistent cytopenias and a variable rate of progression to acute myelogenous leukemia (AML) [1,2]. Historically, these disorders were recognized as anemias that were "refractory" to treatment [3][4][5][6] or as "preleukemia" in patients who subsequently developed AML [7][8][9][10][11][12][13]. While the French-American-British classification system for MDS recognized a distinction between AML and MDS as early as 1982 [14], the concept of preleukemia remains [15][16][17][18][19]. Recent work has detailed the biologic distinctions between MDS and de novo AML [20], but the historical focus on leukemic biology continues to influence studies of these poorly understood disorders [21][22][23]. Although a number of hypotheses based upon the preleukemia paradigm have been explored [24][25][26][27] The absence of a coherent mechanistic explanation for these disorders has prompted us to reexamine the assumptions behind current models of MDS [21][22][23]. The marrow of MDS patients consistently demonstrates decreased hematopoietic progenitor colonies [29][30][31][32][33][34] as well as enhanced levels of apoptosis [35][36][37][38][39][40][41][42][43][44][45][46][47]. These two findings are felt to explain the paradox of a hypercellular bone marrow with profound peripheral cytopenias observed in MDS patients [48] and sugges...

Loss of SHIP-1 protein expression in high-risk myelodysplastic syndromes is associated with miR-210 and miR-155

“…Upregulation of miR-210 regulates the hypoxic response of tumor cells and tumor growth (Huang et al, 2009). In a cellautonomous effect, MDS cells were found to grow more robustly under hypoxia conditions (Thompson et al, 2007). The low oxygen tension found in the bone marrow microenvironment may provide a selection pressure on MDS cells to survive, stimulating miR-210 expression.…”

Mitophagy in hematopoietic stem cells

“…First, hematopoietic progenitor cells from MDS patients show mitochondrial respiratory chain dysfunction, which contributes to the characteristic sensitivity of MDS bone marrow progenitors to the standard high-oxygen conditions used for culturing cells. 137 Second, bone marrow progenitors from patients with MDS or AML with myelodysplasia-related changes have mitochondrial gene expression that is dysregulated compared with that of controls. 138 Finally, subsets of patients with MDS have pathogenic mutations in IDH1 and IDH2, which encode isocitrate dehydrogenases and alter metabolism, 139 or somatic mitochondrial mutations that affect oxidative phosphorylation.…”

Iron overload in myelodysplastic syndromes (MDS)

“…MDS patients show increased levels of oxidative stress, which is further aggravated by iron overload [14][15][16][17][18][19][20][21]. The resulting oxidative DNA damage, worsened by iron overload [22], may contribute to mutagenesis in the bone marrow.…”