<p>Osteosarcoma (OS) is a highly aggressive primary bone malignancy with a strong predilection for lung metastasis, and the formation of a lung pre-metastatic niche represents a key early event driving OS distant dissemination. Elucidating the molecular mechanisms of pre-metastatic niche establishment is therefore critical for developing novel anti-metastatic therapies for OS. However, the mechanisms by which OS cells initiate the formation of a lung pre-metastatic niche remain poorly understood. Exosomes, as key mediators of intercellular communication, play a pivotal role in promoting tumor metastasis by shuttling functional biomolecules to remodel the microenvironment of distant target organs. In this study, we found that MG63 OS cells secreted exosomal miR-27a-3p, which targeted TNFAIP3 in lung fibroblasts, resulting in decreased TNFAIP3 protein expression. This downregulation enhanced the metastatic potential of OS cells toward lung fibroblasts. TNFAIP3 was identified as a direct target of miR-27a-3p, and TNFAIP3-Mut abrogated the regulatory effect of miR-27a-3p on TNFAIP3 expression, confirming the specific targeting relationship. Mechanistically, miR-27a-3p-mediated suppression of TNFAIP3 abrogated its negative regulation of the NF-κB pathway, leading to increased transcription of downstream inflammatory cytokines IL-1β, IL-6, and IL-8. The resulting pro-inflammatory microenvironment contributed to the establishment of a lung pre-metastatic niche, thereby promoting OS lung metastasis. These findings underscore the critical role of OS-derived exosomes in lung metastasis and suggest that exosomal miR-27a-3p may serve as a promising therapeutic target in OS lung metastasis.</p> Graphical abstract <p></p>