Low-intensity pulsed ultrasound suppresses synovitis by modulating polarization of synovial macrophages in mice with osteoarthritis

Abstract

Objective To investigate the therapeutic effect of low-intensity pulsed ultrasound (LIPUS) on synovitis in a mouse model of osteoarthritis and explore the possible mechanism. Methods We assessed the therapeutic effect of LIPUS on synovitis in a mouse model of destabilization of medial meniscus (DMM). The histopathology of the synovium of the knee joint was examined in 7 mice with DMM (model group), 7 normal mice (control group) and 7 mice with DMM treated with LIPUS. The proportion of iNOS- and CD206-positive cells in F4/80-positive macrophages in the synovium was detected. Cultured THP-1 macrophages were divided into control group, LIPUS group, lipopolysaccharide (LPS) group and LPS+LIPUS group, and Raw 264.7 cells were divided into LPS group and LPS+LIPUS group with corresponding treatments. The mRNA levels of polarization-related indexes (IL-1β, TNF-α, IL-10 and Arg1) were detected using real-time quantitative PCR after the treatments, and the protein levels of p-JNK and p-NF-κB p65 were detected using Western blotting. Confocal laser scanning microscopy was used to observe the nuclear translocation of nuclear factor-κB (NF-κB) in THP-1 cells after LPS or LPS+LIPUS treatment. Results In the mouse models of DMM, treatment with LIPUS significantly reduced the thicknesses of the synovium (P < 0.05), decreased the proportion of M1 macrophages and upregulated the proportion of M2 macrophages in the synovium (P < 0.05). In THP-1 and Raw 264.7 macrophages stimulated with LPS, LIPUS treatment significantly lowered IL-1β and TNF-α levels but increased IL-10 and Arg1 levels (P < 0.05). LIPUS also decreased the protein levels of p-JNK and p-NF-κB p65 in LPS-stimulated macrophages (P < 0.05) and suppressed LPS-induced nuclear translocation of NF-κB (P < 0.05). Conclusion LIPUS produces anti-inflammatory effects on the synovium in the mouse model of osteoarthritis possibly by modulating the polarization of synovial macrophages through the JNK and NF-κB signaling pathways.

Keywords

• low-intensity pulsed ultrasound
• osteoarthritis
• macrophages
• polarization