Circ_0000518 Promotes Macrophage/Microglia M1 Polarization via the FUS/CaMKKβ/AMPK Pathway to Aggravate Multiple Sclerosis.

Evidence has shown that circ_0000518 is upregulated in peripheral of multiple sclerosis (MS) patients, suggesting that it may play an important role in the progression of MS. However, its specific mechanism in MS progression is unclear. In this study, the human microglial clone 3 (HMC3) cells were treated with 100 ng/mL of LPS for 24 h, then the short hairpin RNA against hsa_circ_0000518 (sh-hsa_circ_0000518) was transfected into cells and incubated for 48 h. We found increased circ_0000518 expressions, increased apoptosis and oxidative stress, increased M1 phenotype marker expression, and decreased M2 phenotype marker expression in cells, and that interfering with circ_0000518 expression reversed the effect of LPS on HMC3 cells. Online bioinformatics database analysis indicated that FUS is an RNA binding protein of circ_0000518. Next, we observed increased FUS expression in LPS treated HMC3 cells, and interfering with FUS expression reduced LPS triggered apoptosis and oxidative stress, decreased M1 phenotype marker expression, and promoted M2 phenotype marker expression. Mechanistic studies revealed that interfering with FUS promoted the polarization of HMC3 cells from the M1 phenotype to the M2 phenotype via activation of CaMKKβ/AMPK-PGC-1α pathway, whereas this promoting effect was counteracted by STO-609. In an experimental autoimmune encephalomyelitis (EAE) mouse model, we observed that circ_0000518 knockdown reduced circ_0000518 and FUS expression in brain and spinal cord tissues, reduced neurological scores in mice, and alleviated inflammatory cell infiltration in the CNS. Summarily, our study identified that circ_0000518 promotes macrophage/microglial M1 polarization through the FUS/CaMKKβ/AMPK pathway and aggravates MS.