Mesenchymal Stromal Cells From Myelodysplastic Syndrome Patients Show Lower DICER1 and DROSHA Expression, as Well as Decreased Mir-155 and Mir-181a MicroRNA Expression, When Compared with Healthy Controls

Abstract 397

Mesenchymal stromal cells (MSC) are closely related to the regulation of hematopoietic stem cell niche. Recently, Raaijmakers et al (Nature, 2010), published that deletion of Dicer1, a RNase III enzyme involved in microRNA biogenesis, in murine MSC-derived osteoprogenitors triggered peripherical blood cytopenias, myelodysplasia and subsequent AML, showing that molecular alterations in bone marrow microenvironment could result in clonal impaired haematopoiesis. Here, we have investigated whether MSC from myelodysplastic syndrome (MDS) patients show differences in DICER1 and DROSHA, another RNA III endonuclease, in comparison to healthy MSC. In addition, we have analyzed several hematopoietic-related microRNAs in these same samples.

Bone marrow MSC from MDS patients (n=35; 10 5q- syndrome, 4 RA, 5 RARS, 10 RCMD, 3 RAEB, 2 MDS-U and 1 hypocellular MDS) and healthy donors (HD, n=20) were isolated and in vitro expanded following standard procedures until the third passage. Additionally, paired mononuclear cells (MNC) from 13 MDS and 8 HD were obtained. Total RNA was isolated using TRIzol reagent (Invitrogen). DICER1 and DROSHA relative gene expressions were assessed by quantitative PCR (Q-PCR) using commercial TaqMan® assay (Applied Biosystems®) with GAPDH as control gene. DICER1 and DROSHA (Abcam) protein expression were evaluated in whole cell lysates by western blot, using calnexin (Stressgen) as control. Several microRNAs with known role in hematopoiesis and immune system regulation were analyzed in 25 MDS and 12 HD by Q-PCR using commercial TaqMan® MicroRNA assay (Applied Biosystems®) with RNU43 as control microRNA.

MSC from MDS showed significant lower DICER1 (0.0035±0.0020 vs. 0.0076±0.0092; p=0.044) and DROSHA (0.0070±0.0028 vs. 0.0135±0.0176; p=0.019) gene expression levels than healthy controls. Moreover, MSC from MDS showed lower protein expression of both DICER1 and DROSHA by western blot analysis, confirming Q-PCR findings. By contrast, no difference in either DICER1 (0.0197±0.0151 vs. 0.0173±0.0112; p=0.9) or DROSHA (0.0089±0.0023 vs. 0.0067±0.0037; p=0.09) gene expression were observed between MNC from MDS and HD. As far as microRNA expression, we observed a lower expression of mir-155 (0.63±0.92 vs. 0.94±0.49; p=0.007) and mir-181a (1.30±0.95 vs. 2.02±1.05; p=0.041) in MSC from MDS in comparison to healthy controls. Mir-155 and mir-181a are involved in T-cell and B-cell differentiation, while mir-155 are also related to erythroid and megakarycytic differentiation.

We conclude that MSC from MDS patients show lower expression of DICER and DROSHA, two relevant RNA-III endonucleases involved in the microRNA biogenesis, confirming recent findings in murine models. Moreover, the expression of some microRNA is impaired in these cells, raising the possibility that these microenvironmental alterations could be involved in the MDS pathophysiology.