MiR-124 Prevents the Microglial Proinflammatory Response by Inhibiting the Activities of TLR4 and Downstream NLRP3 in Palmitic Acid-Treated BV2 Cells

Neuroinflammation is a mechanism by which obesity or a high-fat diet leads to cognitive impairment. MiR-124, a highly expressed microRNA in the brain, can alleviate neuroinflammation by regulating microglial activation, but its mechanism is unclear. The aim of the study was to explore whether miR-124 exerted this effect through TLR4/MyD88/NF-κB p65/NLRP3 signaling in palmitic acid-treated BV2 cells. Prepared BV2 cells were treated with palmitic acid to establish an in vitro model of a high-fat diet. An miR-124 mimic and inhibitor were adopted to upregulate and downregulate the expression of miR-124, respectively. TAK-242 and NLRP3 siRNA were used to downregulate the expression of TLR4 and NLRP3. The expression levels of miR-124, signaling proteins (TLR4, MyD88, and NF-κB p65), inflammasome markers (NLRP3 and IL-1β), and microglial activated markers (CD206, Arg-1, CD86, and iNOS) were measured by qPCR and western blotting. The pyroptosis rate was assessed using flow cytometry. First, palmitic acid upregulated TLR4/MyD88/NF-κB p65 signaling, increased NLRP3 expression, elevated the pyroptosis rate, and promoted the microglial proinflammatory response in BV2 cells. Second, the miR-124 mimic and inhibitor separately alleviated and aggravated the effect of palmitic acid on microglial activation and NLRP3 expression. The miR-124 mimic also downregulated TLR4/MyD88/NF-κB p65 signaling. Third, TAK-242 did not affect the expression of miR-124 but simulated the protective effect of the miR-124 mimic on microglial activation and NLRP3 expression. Fourth, NLRP3 siRNA also inhibited the microglial proinflammatory response in BV2 cells. MiR-124 prevented the microglial proinflammatory response through TLR4/MyD88/NF-κB p65/NLRP3 signaling in palmitic acid-treated BV2 cells.