Exosome-delivered microRNAs promote IFN-α secretion by human plasmacytoid DCs via TLR7
Valentina Salvi, … , Silvano Sozzani, Daniela Bosisio
Valentina Salvi, … , Silvano Sozzani, Daniela Bosisio
Published May 17, 2018
Citation Information: JCI Insight. 2018;3(10):e98204. https://doi.org/10.1172/jci.insight.98204.
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Research Article Immunology

Exosome-delivered microRNAs promote IFN-α secretion by human plasmacytoid DCs via TLR7

Abstract

The excessive production of type I IFNs is a hallmark and a main pathogenic mechanism of many autoimmune diseases, including systemic lupus erythematosus (SLE). In these pathologies, the sustained secretion of type I IFNs is dependent on the improper activation of plasmacytoid DCs (pDCs) by self–nucleic acids. However, the nature and origin of pDC-activating self–nucleic acids is still incompletely characterized. Here, we report that exosomes isolated from the plasma of SLE patients can activate the secretion of IFN-α by human blood pDCs in vitro. This activation requires endosomal acidification and is recapitulated by microRNAs isolated from exosomes, suggesting that exosome-delivered microRNAs act as self-ligands of innate single-stranded endosomal RNA sensors. By using synthetic microRNAs, we identified an IFN induction motif that is responsible for the TLR7-dependent activation, maturation, and survival of human pDCs. These findings identify exosome-delivered microRNAs as potentially novel TLR7 endogenous ligands able to induce pDC activation in SLE patients. Therefore, microRNAs may represent novel pathogenic mediators in the onset of autoimmune reactions and potential therapeutic targets in the treatment of type I IFN–mediated diseases.

Authors

Valentina Salvi, Veronica Gianello, Sara Busatto, Paolo Bergese, Laura Andreoli, Ugo D’Oro, Alessandra Zingoni, Angela Tincani, Silvano Sozzani, Daniela Bosisio

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Figure 3

Synthetic IIM microRNAs activate human pDCs to secrete IFN-α and proinflammatory cytokines.

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Synthetic IIM microRNAs activate human pDCs to secrete IFN-α and proinfl...
(A) Sequence of synthetic microRNAs. The IFN induction motif (IIM) is boxed, while a similar motif is dashed. The relative content of GU and U are also indicated. (B) pDCs were stimulated with viral RNA40 or with the indicated microRNAs (10 μg/ml) or with vehicle alone (–) for 24 hours. The production of IFN-α was evaluated by ELISA in cell-free supernatants. Data are expressed as mean ± SEM (n = 4–6); *P < 0.05 versus (–) by 1-way ANOVA with Dunnett’s post-hoc test. (C) pDCs were stimulated with a suboptimal concentration of active microRNAs (2.5 μg/ml) alone or in combination. IFN-α production was evaluated by ELISA. Data are expressed as mean ± SEM (n = 3); *P < 0.05 versus (–) by 1-way ANOVA with Dunnett’s post-hoc test or #P < 0.05 by Tukey’s multiple comparison test. (D) pDCs were stimulated with 10 μg/ml microRNAs for 4 hours. Cell membrane was identified by an anti–MHC class II–Alexa 488 (green) mAb and the nucleus by DAPI staining (blue). IRF-7 nuclear translocation was visualized by a specific anti–IRF-7 Ab (red). The figure shows 1 representative donor out of 3; scale bars: 5 μm. (E) pDCs were stimulated as in B, and the production of TNF-α and IL-6 was evaluated by ELISA in cell-free supernatants. Data are expressed as mean ± SEM (n = 4–6); *P < 0.05 versus (–) by 1-way ANOVA by Dunnett’s post-hoc test. (F) pDCs were stimulated with miR574 for 90 minutes, lysed, and analyzed by Western blot using an anti–phosphorylated NF-κB p65 mAb. Image depicts 1 representative fluorogram out of 3 performed.