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Microglia express Toll-like receptors (TLRs) that sense pathogen- and host-derived factors, including single-stranded RNA. In the brain, let-7 microRNA (miRNA) family members are abundantly expressed, and some have recently been shown to serve as TLR7 ligands. We investigated whether let-7 miRNA family members differentially control microglia biology in health and disease. We found that a subset of let-7 miRNA family members function as signaling molecules to induce microglial release of inflammatory cytokines, modulate antigen presentation, and attenuate cell migration in a TLR7-dependent manner. The capability of the let-7 miRNAs to control microglial function is sequence specific, mapping to a let-7 UUGU motif. In human and murine glioblastoma/glioma, let-7 miRNAs are differentially expressed and reduce murine GL261 glioma growth in the same sequence-specific fashion through microglial TLR7. Taken together, these data establish let-7 miRNAs as key TLR7 signaling activators that serve to regulate the diverse functions of microglia in health and glioma.
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•let-7 miRNAs act as Toll-like receptor (TLR) 7 signaling molecules in glioma•Extracellular let-7 miRNAs differentially modulate microglial biology•The sequence motif UUGU is responsible for let-7-induced microglial activation•Select let-7 miRNAs attenuate glioma growth by directly activating microglial TLR7
Buonfiglioli et al. elucidate the role of let-7 miRNAs acting as Toll-like receptor (TLR) ligands in the brain. Select let-7 miRNAs function as signaling molecules to modulate diverse microglial functions and glioma growth through TLR7. These data establish let-7 miRNAs as TLR7 signaling activators of microglia in health and glioma.