Promoter Methylation and Decreased Expression of Mir-124 In Myelodysplastic Syndromes

Abstract 4014

The myelodysplastic syndromes (MDS) are a heterogeneous group of clonal disorders of hematopoietic stem/progenitor cells. Although demethylating agents such azacytidine and decitabine have been widely used to treat MDS, the underlying molecular mechanisms remain obscure. Abnormalities of microRNAs (miRNA) have been recently associated with hematological malignancies including MDS. The miR-124 was initially demonstrated to modulate neurogenesis. It was recently shown that EVI1-induced methylation and silencing of miR-124 were present in murine MDS cells. In the retrospective study we evaluated methylation status and expression levels of miR-124 in fifteen MDS patients (subtypes included RCUD, RCMD, RAEB-1, RAEB-2 and CMML). Genomic DNA samples were modified with bisulfite and methylation at three promoter regions of miR-124 was examined with methylation-specific real time quantitative polymerase chain reaction analysis (MQPCR). In general, we observed an increased methylation levels of miR-124 in MDS patients than that in normal bone marrow (NBM, P<0.01). In accordance with this, marked depression of miR-124 was seen in six patients when compared with NBM (more than 2 times lower), as determined with quantitative reverse-transcriptive PCR assay. Moreover, there were higher degrees of promoter methylation in cases with depressed miR-124 than that in remaining cases. A negative correlation between the expression and methylation levels was statistically significant (R= -0.498, P<0.01). The change of miR-124 was not directly related to short-term clinical response or prognosis, possibly due to limited size of the sample. However, the miR-124 amount returned to basal levels in two cases (RCMD and CMML subtypes respectively) after low-dose decitabine therapy and DNA methylation of all three loci disappeared. Continued work is underway to accumulate more cases and make long-term clinical follow-up. In conclusion, this primary work suggested a possible role of the methylation-mediated silencing of miR-124 in the pathogenesis or disease progression of MDS.