Ultrasound reduces inflammation by modulating M1/M2 polarization of microglia through STAT1/STAT6/PPARγ signaling pathways

INTRODUCTION: Activated microglia can be polarized to the pro‐inflammatory M1 phenotype and the anti‐inflammatory M2 phenotype. Low‐intensity pulsed ultrasound (LIPUS) can attenuate pro‐inflammatory responses in activated microglia. OBJECTIVE: This study aimed to investigate the effects of LIPUS on M1/M2 polarization of microglial cells and the regulatory mechanisms associated with signaling pathways. METHODS: BV‐2 microglial cells were stimulated by lipopolysaccharide (LPS) to an M1 phenotype or by interleukin‐4 (IL‐4) to an M2 phenotype. Some microglial cells were exposed to LIPUS, while others were not. M1/M2 marker mRNA and protein expression were measured using real‐time polymerase chain reaction and western blot, respectively. Immunofluorescence staining was performed to determine inducible nitric oxide synthase (iNOS)‐/arginase‐1 (Arg‐1)‐ and CD68‐/CD206‐positive cells. RESULTS: LIPUS treatment significantly attenuated LPS‐induced increases in inflammatory markers (iNOS, tumor necrosis factor‐α, interleukin‐1β, and interleukin‐6) as well as the expression of cell surface markers (CD86 and CD68) of M1‐polarized microglia. In contrast, LIPUS treatment significantly enhanced the expression of M2‐related markers (Arg‐1, IL‐10, and Ym1) and membrane protein (CD206). LIPUS treatment prevented M1 polarization of microglia and enhanced or sustained M2 polarization by regulating M1/M2 polarization through the signal transducer and activator of transcription 1/STAT6/peroxisome proliferator‐activated receptor gamma pathways. CONCLUSIONS: Our findings suggest that LIPUS inhibits microglial polarization and switches microglia from the M1 to the M2 phenotype.