miR-155-3p Drives the Development of Autoimmune Demyelination by Regulation of Heat Shock Protein 40

microRNA-155 (miR-155) plays an important role in posttranscriptional gene regulation of the immune system. We and others have described miR-155 upregulation inThelper cells (Th) during the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. We have shown that mice in which the miR-155 host gene (MIR155HG) has been deactivated are resistant to EAE. MIR155HG produces two different miRNA strands, miR-155-5p and miR-155-3p, and miR-155-5p has been considered the only functional miR-155 form. Surprisingly, we found that miR-155-3p is also strongly upregulated in Th cells infiltrating the brain in EAE. Functional manipulation of miR-155-3p expression revealed its particular role in regulation of Th17 development. The search for miRNA-155-3p target genes highlighted transcripts of two heat shock protein 40 genes, Dnaja2 and Dnajb1. These two genes negatively regulated Th17 differentiation, leading to decreased EAE. Therefore, our findings provide new insights into a previously unknown mechanism by which miR-155-3p controls Th17 cell differentiation and autoimmune demyelination.