Abstract
Background: Spinal fusion is regarded as the gold standard procedure for treating spinal degeneration, tumors, and trauma. Inflammatory response is an important part in bone repair. We want to investigate the role of inflammatory macrophage (M1) and resident macrophage (M2) during spinal fusion. Methods: Thirty male Sprague Dawley rats (age: 12 weeks; weight: 300 g) were involved in the study. Spinal fusion model of SD rats was established by surgical procedures. LIPUS treatment (20 min/d, 5 d/wk) was performed three days after surgery. The rats were randomly divided into control group and LIPUS group and sacrificed on day 3 (n=6), day 5 (n=6), day 7 (n=6), day 10 (n=6) and day 14 (n=6) after spinal fusion surgery. Bone volume was measured by Micro-CT, fusion region was examined by Histological analyses, types of macrophages in the fusion area were examined by Immunohistochemical staining. Raw264.7 and BMDM cells were used in cell experiments. The cells were divided into control group and LIPUS group, control group were treated control and LIPUS group. Flow Cytometer was used to examine the rate of resident macrophages, real-time PCR was used to examine the mRNA level of anti-inflammation genes. The data was analyzed by SPSS version 22.0. Findings: Analyzing the presence of two different types of macrophages in a rat spinal fusion model, we found that LIPUS could promote spinal fusion and stimulate transition of the expression from F4-80+/Mac-2+ (M1) to F4-80+/Mac-2- (M2), leading to early appearance of resident macrophage. And cell experiments showed that the rate of CD206+ macrophages (M2) were significantly increased after LIPUS treatment. The anti-inflamation factors were increaed after LIPUS treatment. Interpretation: The earlier transition from inflammatory to resident macrophage might be one reason for the positive effect of LIPUS on spinal fusion. Funding: Young talents cultivating plan of Shanghai municipal medical and health system (2018YQ26). Changhai Hospital Youth Startup Fund (2018QNA013). Declaration of Interest: None. Ethical Approval: All procedures in this study were in accordance with the guidelines and were approved by the Laboratory Animal Ethics Center of the Second Military Medical University.
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