Sulfasalazine alters microglia phenotype by competing endogenous RNA effect of miR-136-5p and long non-coding RNA HOTAIR in cuprizone-induced demyelination

Sulfasalazine (SF) promotes remyelination and improves the outcome of multiple sclerosis (MS) patients. However, the underlining mechanism remains elusive. Here, we examined whether SF blocks microglia switching to a pro-inflammatory M1-like phenotype through a competing endogenous RNA (ceRNA) effects in cuprizone-induced demyelination. The microglia reprogramming effects of SF in the mice model of cuprizone-induced demyelination was measured by histological, immunohistochemical and molecular biological methods. We also measured the effects of the condition media from SF-treated microglia on the differentiation of OLN-93 cells. Insights of the mechanism of ceRNAs of miR-136-5p and long non-coding RNA (lncRNA) HOTAIR were gained from bioinformatic analysis, luciferase assays and RNA binding protein immunoprecipitation. Microglia switched to a pro-inflammatory M1-like phenotype in cuprizone induced-demyelination. Conversely, SF inhibited the M1-like polarization with the increased remyelination which was attenuated by microglia depletion. SF inhibited production of M1-like factors TNF-α and INF-γ in microglia, and thereby promoted the differentiation of OLN-93 oligodendrocytes. SF down-regulated lncRNA HOTAIR but up-regulated miR-136-5p, and thus inactivated AKT2-NF-κB in cuprizone-treated microglia. Importantly, lncRNA HOTAIR overexpression reversed the increased miR-136-5p expression by SF and thereby attenuated the inhibition of AKT2-mediated NF-κB activation. Mimic of miR-136-5p inhibited cuprizone-induced activation of AKT2-NF-κB in the microglia. In summary, SF blocks microglia switching to a pro-inflammatory M1-like phenotype by ceRNA effect of miR-136-5p and lncRNA HOTAIR in cuprizone-induced demyelination. Our findings show the therapeutic potential of SF for human MS probably by targeting epigenetic regulation in microglia.