Irisin hampers β-amyloid-induced microglial inflammation via the miR-451a/TLR4/NLRP3 axis

Neuroinflammation, which is driven by microglial activation, contributes to neurodegeneration. The myokine irisin exerts anti-inflammatory effects, potentially through microRNA-mediated regulation of inflammasome components. However, the underlying molecular mechanisms remain incompletely defined. In this in vitro study we investigated whether irisin attenuates the β-amyloid (Aβ)-induced activation of human microglia via miR-451a-, miR-223-3p-, and miR-7-5p-dependent modulation of NLRP3-related genes.

For this aim, human immortalized microglia (hTERT) were LPS primed and Aβ_1-42, stimulated in the presence or absence of irisin. The expression of NLRP3, TLR4, caspase-1, IL-1β, IL-18, PYCARD, and selected microRNAs (miR-451a, miR-223-3p, and miR-7-5p) was quantified by digital droplet PCR. TLR4 expression in hTERT cells was analyzed by flow cytometry and intracellular ASC speck formation with NLRP3 colocalization and NF-κB nuclear translocation was measured by imaging flow cytometry. Cytokine release was measured in the supernatants using ELISA. Loss of function assays were performed in hTERT cells transfected with either the miR-451a inhibitor or scrambled molecules.

Irisin treatment was associated with reduced Aβ_1-42-induced microglial activation, as showed by decreased TLR4 expression, reduced markers of NLRP3 inflammasome activation (including ASC-speck formation, gene and protein expression), and NF-kB nuclear translocation. This effect was accompanied by the upregulation of miR-451a and miR-7-5p and the downregulation of miR-223-3p expression. miR-451a inhibition attenuated the irisin-associated anti-inflammatory effects, suggesting a contributory role for miR-451a in the modulation of TLR4/NLRP3 pathway in this in vitro model. To summarize, this work showed that, in an in vitro model of Aβ_1-42-activated human microglia, irisin is associated with modulation of microRNA expression and NLRP3 inflammasome-related pathways. These results provide mechanistic insight into potential interaction between exercise-related factors and microglial inflammatory responses; their possible relevance to in vivo conditions and disease contexts will nevertheless clearly requires further investigation.