Engineered mesenchymal stem cell-derived extracellular vesicles overexpressing miR-146a alleviate neuroinflammation in Alzheimer's disease.

Alzheimer's disease is an inflammatory neurodegenerative disease for which no effective clinical treatment currently exists. We have previously reported that mesenchymal stem cell.derived extracellular vesicles delay retinal degeneration by exerting anti-inflammatory effects though the miR-146a.nuclear receptor subfamily 4 group A member 3 axis; however, it remains unclear how NR4A3 drives inflammation. Herein, we engineered mesenchymal stem cell. derived extracellular vesicles overexpressing miR-146a to explore their possible neuroprotective effects and the underlying mechanisms in both cell and animal models of Alzheimer's disease. In HT22 cells co-cultured with lipopolysaccharide-induced RAW264.7/BV2 cells, extracellular vesicles overexpressing miR- 146a significantly reduced the number of apoptotic cells and inhibited proinflammatory cytokine expression, nuclear factor (NF)-κB activation, and caspase-3/ apoptosis regulator BAX signaling. These effects of extracellular vesicles overexpressing miR-146a were replicated in 5×FAD mice. In addition, extracellular vesicles overexpressing miR-146a inhibited the activation of microglia and astrocytes, reduced amyloid-β and phosphorylated tau expression, lowered the number of apoptotic cells in the hippocampus, and improved the cognitive function of these Alzheimer's disease model mice. Mechanistically, miR-146a negatively regulated the expression of nuclear receptor subfamily 4 group A member 3 and suppressed the expression of proinflammatory cytokines and nuclear factor-κB signaling. Furthermore, NR4A3 overexpression promoted nuclear factor-κB and proinflammatory cytokine expression as well as nuclear factor-κB signaling. The upregulation of NR4A3 and the inflammatory response was reversed by miR-146a overexpression. Finally, NR4A3 was identified as a transcriptional activator of nuclear factor-κB using chromatin immunoprecipitation polymerase chain reaction. Collectively, these findings indicate that extracellular vesicles overexpressing miR-146a may alleviate the progression of Alzheimer's disease by exerting anti-inflammatory effects via the NR4A3. nuclear factor-κB axis. They are thus a potential therapeutic candidate for the clinical treatment of neurodegenerative diseases.