miR-20a suppresses Treg differentiation by targeting Map3k9 in experimental autoimmune encephalomyelitis

BACKGROUND: Experimental autoimmune encephalomyelitis (EAE) is a model for inflammatory demyelinating diseases of the central nervous system (CNS), a group of autoimmune diseases characterized by inflammatory infiltration, demyelination, and axonal damage. miR-20a is dysregulated in patients with CNS inflammatory demyelinating diseases; however, the function of miR-20a remains unclear. In this study, we intended to explore the role of miR-20a in EAE. METHODS: The expression of miR-20a was detected by quantitative real-time PCR (qRT-PCR) in EAE mice and patients with MOG antibody-associated demyelinating diseases. CD4(+) T cells of EAE mice were sorted, stimulated, and polarized with miR-20a knockdown. Activation and differentiation of CD4(+) T cells were analyzed by flow cytometry. The expression of target gene Map3k9 was detected by qRT-PCR and western blot experiments. The binding of miR-20a to the 3’ UTR of Map3k9 was tested by luciferase assays. The feasibility of miR-20a as a therapeutic target to alleviate the severity of EAE was explored by intravenous administration of miR-20a antagomirs to EAE mice. RESULTS: miR-20a was upregulated in splenocytes and lymph node cells, CD4(+) T cells, and spinal cords of EAE mice. Moreover, miR-20a knockdown did not influence the activation of antigen-specific CD4(+) T cells but promoted their differentiation into Treg cells. Map3k9 was predicted to be a target gene of miR-20a. The expressions of Map3k9 and miR-20a were negatively correlated, and miR-20a knockdown increased the expression of Map3k9. In addition, miR-20a binded to the 3’ UTR of Map3k9, and simultaneous knockdown of miR-20a and Map3k9 counteracted the enhanced differentiation of Tregs observed when miR-20a was knocked down alone. Furthermore, injection of miR-20a antagomirs to EAE mice reduced the severity of the disease and increased the proportion of Treg cells in peripheral immune organs. CONCLUSIONS: miR-20a suppresses the differentiation of antigen-specific CD4(+) T cells into Tregs in EAE by decreasing the expression of Map3k9. miR-20a antagomirs alleviate EAE, suggesting a new therapy for EAE and CNS inflammatory demyelinating diseases. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12967-021-02893-4.