Background: Micro-RNAs (miRs) are small non-coding RNAs that regulate gene expression by binding to mRNA transcripts and preventing translation. They can act both locally and upon distal targets via exosome release. MiRs regulate a large contingent of the mammalian genome (1) and have been shown to be important for MAIT differentiation (2), but miRs in overall MAIT function are not well-described.
Methods: We analyzed publicly available data from bulk-RNA-sequencing studies of sorted human MAIT cells. We assessed the impact of miRs on MAIT function in vitro by stimulating human and murine MAIT cells in the presence of anti-miR155 and measuring cytokine expression by qPCR and flow cytometry. We then performed single-cell RNA-sequencing (scRNAseq) on sorted murine MAIT cells pooled from global miR155 knockout mice.
Results: Our in silico meta-analysis revealed a strong and consistent pattern of miR155 upregulation in activated MAIT cells, as well as a network of other miRNAs that were consistently differentially expressed upon activation. In vitro stimulation of human MAIT cells resulted in upregulation of miR155. Treatment with anti-miR155 resulted in decreased MAIT cell function, including decreased interferon-gamma (IFNg) and interleukin-17 (IL-17) production. MAIT cells isolated from global miR-155 knockout mice had abrogated expression of proliferation-associated genes, JAK1, and significant downregulation of key leukocyte marker, CD45. Differential expression of other gene targets of conserved activation-associated miRs also suggest a role for miR155 in regulating a broader miRNA network to control MAIT function upon activation.
Conclusions: Our results suggest that miR155 and other miRs are a central component of MAIT cell activation and function. It remains unclear to what extent MAIT cell derived miR155 is released to act on distal targets via exosomes instead of acting locally, which could expand the scope of MAIT cell miRNA regulation.