Recovery of MicroRNA from Stored Bone Marrow Aspirate Slides

Archived bone marrow aspirate slides are almost infinite, readily available resource of biospecimens that enable retrospective molecular investigations of diseases. RNAs obtained from slides has limitations in utility because of their low quality and highly fragmented nature. MicroRNAs are small (<22 nt) noncoding RNAs with various cellular regulatory roles. Due to their small size, microRNAs are less prone to degradation and modification, therefore, can be preserved well in archived tissues. The current study investigated the efficacy of archived bone marrow aspirate slides for miRNA expression analysis in pediatric leukemia. Total RNA was isolated from air-dried unstained archived slides using High pure miRNA isolation Kit with some modifications and from fresh samples using TRizol. After cDNA synthesis, RT-qPCR was then carried out using specific hsa-miR-326 LNA primers. Finally, statistical analyses were conducted using GraphPad Prism 6 software. The difference observed in miRNA expression due to disease state was far greater than the differences between archived slides and their matching fresh bone marrow specimens. In fact, the expression of archival slide smears for the miR-326 closely mimicked that of fresh-frozen tissues (0.035±0.04 vs. 0.03±0.04) (Mean±SD, p>0.05). Differential expression of hsa-miR-326 was detected between leukemic and non-leukemic samples from archived slides or fresh frozen bone marrows. The demonstration that archived bone marrow aspirate slides can be utilized for miRNA expression studies offers tremendous potential for future investigations into the role that miRNAs play in the development and long term outcome of hematologic, as well as non-hematologic diseases.