Positive feedback loop of HMGB1 and tumor-associated macrophages plays a key role in osteosarcoma metastasis
Abstract Background Numerous studies have demonstrated the important roles of tumor-associated macrophages (TAMs) in osteosarcoma metastasis. In osteosarcoma, higher levels of HMGB1 correlate with osteosarcoma progression. However, whether HMGB1 is involved in the polarization of M2 macrophages into M1 macrophages in osteosarcoma still remains largely unknown. Methods HMGB1 and CD206 mRNA expression was measured by qRT-PCR in osteosarcoma tissues and cells. HMGB1 and RAGE protein expression was measured by western blotting. Osteosarcoma migration was measured using a Transwell and wound-healing assay. Osteosarcoma invasion was measured using a Transwell assay. Macrophage subtypes were detected using flow cytometry. Results HMGB1 is aberrantly overexpressed in osteosarcoma, and positively correlates with the TNM III & IV stages, lymph node metastasis, and distant metastasis. Silencing HMGB1 inhibits migration, invasion, and metastasis-related proteins in osteosarcoma cells. Furthermore, the reduced HMGB1 expression in the conditioned media derived from osteosarcoma cells also induces the polarization of M2 TAMs to M1 TAMs. In addition, silencing HMGB1 inhibits the liver and lung metastases of osteosarcoma and reduces the expression of HMGB1, CD163, and CD206 in vivo experiments. HMGB1 regulates macrophage polarization through RAGE. Interestingly, the polarized M2 macrophages could induce osteosarcoma migration and invasion, which in turn results in activation of HMGB1 expression in osteosarcoma cells to form a positive feedback loop. Conclusions HMGB1 and M2 macrophages enhance osteosarcoma migration, invasion, and metastasis capability through positive feedback regulation. These findings reveal the significance of tumor cell and TAM interaction in the metastatic microenvironment.