Silibinin restricts mitochondria-associated inflammatory pathways in LPS-stimulated murine microglia BV2 through TREM2.

Microglia are resident immune cells in the central nervous system mediating brain inflammatory responses. The flavonoid silibinin has been found to restrict the neuronal inflammatory conditions in vivo. To fully reveal the underlying mechanisms, effects of silibinin on neuroinflammation was evaluated in lipopolysaccharides (LPS)-stimulated murine microglia BV2. The increased NO level, and the up-regulated pro-inflammatory proteins including iNOS and COX-2 in LPS-treated cells were all restricted by the treatment with silibinin. Further investigation showed that, mitochondrial disorders caused by LPS, including the excessive fission, loss of mitochondrial membrane potentials and intracellular ATP levels, augmented ROS and oxidative damages of mitochondrial DNA (mtDNA), were all attenuated by the treatment with silibinin. The protective effect of silibinin against the STING and NLRP3 inflammasome pathways is attributed to its ability to restore mitochondrial quality control. Of note, triggering receptors expressed on myeloid cells 2 (TREM2), a transmembrane receptor important for modulating microglia-associated inflammation, was low in LPS-treated cells but largely preserved in cells co-treated with silibinin. Molecular docking results show that silibinin has a binding potential with TREM2, which has also been confirmed in CETSA assay. TREM2 knockdown in microglia promotes a proinflammatory phenotype and mitochondrial damage which was reversed with silibinin treatment by increasing the stability of TREM2. Our data show that silibinin reduces mitochondrial damage and proinflammatory activation in microglia through the stabilization of TREM2. These results highlight the potential of silibinin as a treatment in neuroinflammatory diseases.