Myelination: Tripathi et al.

miR-27a inhibits maturation of oligodendrocyte precursor cells to mature oligodendrocytes

Ajai Tripathi, Christina Volsko and Ranjan Dutta

Department of Neuroscience, Lerner Research Institute, Cleveland Clinic, Cleveland- 44195

Background: Micro RNAs (miRNAs) are short non-coding RNAs that regulate gene expression at posttranscriptional level by complementary binding to 3’UTR regions of target genes. Modulation of gene expression by miRNAs plays central role in neurodegenerative diseases. Recently, miRNA expression within cerebrospinal fluid (CSF)/serum/plasma has been reported to be correlated with neurological disability or disease progression in multiple sclerosis (MS) patients. However, functional validation of individual miRNA is missing which may hold a therapeutic potential.
Aim: In this study, we aimed to investigate miR-27a expression in progressive MS brain and analyze its functional role in myelination. 
Methods: miRNAs expression validation and target gene regulation was confirmed by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), immuno-in situ hybridization and miRNA-3’UTR binging assay, respectively.  Role of miR-27a in myelination was evaluated using in vitro primary rodent oligodendrocyte precursor cells (OPCs) culture. 
Results: miR-27a expression was significantly downregulated in chronic demyelinated MS lesions validated by RT-qPCR and immuno-in situ hybridization. In vitro functional assay shows that transient transfection of chemically synthesized miR-27a-3p (mimic) in OPCs/ oligodendrocytes (OLs) inhibits differentiation and maturation of OPCs into mature OLs. Intriguingly, miR-27a overexpression stalled OPCs in precursor stage and caused significant increase in levels of Chondroitin sulfate proteoglycan 4 (Cspg4/Ng2) protein without increase in OPCs proliferation. Transcriptome profiling of miR-27a overexpressing OPCs identified several genes critical for myelination and Wnt- β-catenin signaling pathway. 
Conclusions: Taken together, our results indicate that miR-27a may play a major role in arresting OPCs in the immature state leading to failure in remyelination in chronic demyelinated lesion progressive MS brain. 

Keywords: Micro RNAs, multiple sclerosis, oligodendrocyte, remyelination.

Grant Support: NIH, NINDS (NS096148) and the National Multiple Sclerosis Society, USA (RG 5298) to RD.