Background: Enhanced infiltration of M2-polarized tumor-associated macrophages (TAMs) is linked to osteosarcoma (OS) metastasis and growth. Here, we aim to explore a novel miR-221-3p shuttled by M2-TAM exosomes in the growth and metastasis of OS cells.

Methods: THP-1 monocytes-derived M2-TAMs were induced by PMA/interleukin (IL)-4/IL-13 and then co-cultured with OS 143B and Saos2 cells. Overexpression or downregulation models of miR-221-3p were conducted to probe the impacts of exosome-derived M2-TAMs in OS cells. OS cell proliferative ability, colony formation, invasion, migration and apoptotic level were measured by the cell counting kit-8 (CCK-8) assay, colony formation, Transwell assay, and flow cytometry. Moreover, the SOCS3/JAK2/STAT3 axis in OS cells was testified by western blot, and a dual-luciferase reporter assay was conducted to confirm the link between miR-221-3p and SOCS3.

Results: OS cells enhanced M2 polarization of TAMs, which significantly promoted OS cells’ viability, colony formation, migration, invasion, and reduced apoptosis. Moreover, the exosomes enriched by miR-221-3p from M2-polarized TAMs (M2-TAMs) also aggravated the malignant behaviors of OS cells. However, down-regulation of miR-221-3p brought about contrary results. Further, in-vivo tests uncovered that overexpressing miR-221-3p enhanced OS cells’ growth. Mechanistically, SOCS3 was a downstream target of miR-221-3p, and up-regulation of miR-221-3p choked SOCS3 and activated JAK2/STAT3. However, the pharmacological intervention of the JAK2/STAT3 pathway obviously inhibited the malignant behaviors of OS cells, which were significantly reversed by miR-221-3p up-regulation.

Conclusion: The exosomal miR-221-3p derived from M2-TAMs aggravates OS progression via modulating the SOCS3/JAK2/STAT3 axis.