Hematopoietic miRNAs Expression in Myelodysplastic Syndromes.

Myelodysplastic syndromes (MDS) are clonal hematopoietic stem-cell disorders that include a broad spectrum of entities characterized by ineffective hematopoiesis and risk of transformation into acute myeloid leukemia (AML). MicroRNAs (miRNA) act as negative expression regulators of important genes as those participating in cellular proliferation, apoptosis and carcinogenesis. In this study we analyzed the expression patterns of 26 miRNA hematopoietic-related genes in patients with MDS. Total RNA was extracted from 20 MDS patients (BM and PB) and 5 normal controls. Median age of patients was 70 (range, 55–82) years. Seven patients had refractory anemia with excess of blasts (RAEB-I, n=5; RAEB-II, n=2), 7 refractory cytopenia with multilineage dysplasia (RCMD), 3 RCMD with ringed sideroblasts (RCMD-RS), 1 chronic myelomonocytic leukemia (CMML), 1 refractory anemia with ring sideroblasts (RARS) and 1 MDS associated with isolated del(5q). 15 patients presented low risk IPSS (LR) (low or intermediate-1) and 5 patients had high risk IPSS (HR) (intermediate-2 and high risk). Twenty-six mature miRNAs were assessed by Stem-loop RT-PCR and Real time PCR in ABI PRISM 7500. MiRNA expression data was normalized to overall median and relative quantification was calculated with the 2^−ΔΔCt method. The data were presented as log₁₀ of relative quantity of target miRNA. Median of normal controls was used as calibrator for all samples. Data were analyzed by class comparison methods using BRB Array Tools version 3.4.0 and TIGR multiexperiment viewer. Hierarchical clustering analysis of BM categorized two clusters corresponding to BM-MDS and BM-controls. Then, miR-142-5p (p<0.001) and miR-18a (p<0.001) were differentially expressed between BM-MDS and BM-controls while miR-103 (p=0.003) was overexpressed and miR-18a (p=0.02) was underexpressed in PB-controls with respect to PB-MDS. The analysis of miR-10a and miR-103 in PB (p=0.035 and p=0.031) and miR-181a and miR-10a in BM (p=0.044 and p=0.02) allowed us to discriminate between LR and HR groups. We also found that miR-222 was overexpressed in AML regarding MDS samples (p<0.001). It has been previously described that high activity of miR-222 is necessary to maintain low p27^KIP1 levels and continuous proliferation in certain cancer cell lines. In conclusion, this study confirms that miRNAs have a role in the pathogenesis of MDS and their transformation into AML.