Abstracts

Rationale: MicroRNAs are a new class of small RNA molecules (21-24 nucleotide-long) that negatively regulate gene expression either by translational repression or target mRNA degradation. It is believed that about 30% of all human genes are regulated by these molecules. MiRNAs are involved in many important biological processes including cell differentiation, embryonic development and central nervous system development. The main purpose of this study was to investigate the existence of differences in microRNA expression in mesial temporal sclerosis (MTS) and to identify the regulated target-genes. Methods: Total RNA was isolated from hippocampal tissue of 4 patients who underwent selective resection of the mesial temporal structures for the treatment of clinically refractory seizures. In addition, we used control samples from autopsy (n=4) for comparison. RNA samples were used in real-time PCR reactions with TaqMan™ microRNA assays (Applied Biosystems) to quantify 157 different miRNAs. Results: Bioinformatic analyzes identified three miRNAs, which were differently expressed in patients as compared to controls: let-7d and miR-29b were over expressed in patients; whereas, miR-30d was down-regulated in patients. A possible target gene for let-7d is Nme6 which we also found to be down-regulated in patients. In addition, Mcl-1, the putative target gene of miR-29b was also down-regulated in patients. Mcl-1 is an anti-apoptotic protein of the Bcl-2 family and its tight regulation of protein levels is necessary, because insufficient Mcl-1 can result in inappropriate cell death. Nme6 belongs to NME (nm23 /nucleoside diphosphate kinase) gene family in humans and act as inhibitor of p53-induced apoptosis. Conclusions: We have identified three different miRNA species differently expressed in MTS and its target genes: let-7d - NME6, miR-30d - SON and miR29b - Mcl-1. Biologic functions related to the possible miRNA gene-targets are mainly neurogenesis, and apoptosis. Our results point to interesting potential molecular targets which should be explored further in additional studies of MTS.