MiRNA‐145‐5p prevents differentiation of oligodendrocyte progenitor cells by regulating expression of myelin gene regulatory factor

Abstract The roles of specific microRNAs (miRNA) in oligodendrocyte (OL) differentiation have been studied in depth. However, miRNAs in OL precursors and oligodendrocyte progenitor cells (OPCs) have been less extensively investigated. MiR‐145‐5p is highly expressed in OPCs relative to differentiating OLs, suggesting this miRNA may serve a function specifically in OPCs. Knockdown of miR‐145‐5p in primary OPCs led to spontaneous differentiation, as evidenced by an increased proportion of MAG + cells, increased cell ramification, and upregulation of multiple myelin genes including MYRF, TPPP , and MAG , and OL cell cycle exit marker Cdkn1c . Supporting this transition to a differentiating state, proliferation was reduced in miR‐145‐5p knockdown OPCs. Further, knockdown of miR‐145‐5p in differentiating OLs showed enhanced differentiation, with increased branching, myelin membrane production, and myelin gene expression. We identified several OL‐specific genes targeted by miR‐145‐5p that exhibited upregulation with miR‐145‐5p knockdown, including myelin gene regulatory factor (MYRF), that could be regulating the prodifferentiation phenotype in both miR‐145 knockdown OPCs and OLs. Indeed, spontaneous differentiation with knockdown of miR‐145‐5p was fully rescued by concurrent knockdown of MYRF . However, proliferation rate was only partially rescued with MYRF knockdown, and overexpression of miR‐145‐5p in OPCs increased proliferation rate without affecting expression of already lowly expressed differentiation genes. Taken together, these data suggest that in OPCs miR‐145‐5p both prevents differentiation at least in part by preventing expression of MYRF and promotes proliferation via as‐yet‐unidentified mechanisms. These findings clarify the need for differential regulation of miR‐145‐5p between OPCs and OLs and may have further implications in demyelinating diseases such as multiple sclerosis where miR‐145‐5p is dysregulated.