From bone to beyond: osteoclasts dictate metastatic fate in lung adenocarcinoma via the OLFML3-DPPA2 stemness switch.

The unfavorable prognosis of patients with bone metastasis of lung adenocarcinoma (LUAD) is largely due to both osteolytic destruction and tumor stem cell-mediated secondary metastasis. However, the mechanisms by which the bone microenvironment augments the stemness of LUAD cells remain inadequately understood. In this study, we developed a LUAD cell model with enhanced stemness, termed BM3, by subjecting the cells to three rounds of conditioning within the bone microenvironment. Our findings identified osteoclasts, rather than osteoblasts, as the principal stromal cells that facilitate the enhancement of stemness in BM3 cells. This facilitation was inhibited by the application of either a tumor necrosis factor-alpha (TNF-α) neutralizing antibody or an NF-κB inhibitor. Additionally, we established that the expression level of the secretory protein olfactomedin-like protein 3 (OLFML3) is positively associated with the stemness of BM3 cells and exerts a self-reinforcing effect on tumor cell stemness. Mechanistic analyses revealed that OLFML3 upregulates the pluripotency-associated factor developmental pluripotency-associated protein 2 (DPPA2), which subsequently promotes the expression of core stemness factors, including CD44, OCT4, and SOX2, thereby augmenting the stemness and metastatic potential of tumor cells. Clinical data suggest that serum OLFML3 may serve as a candidate biomarker for identifying LUAD patients with bone metastasis who are at increased risk of subsequent metastatic spread. Our study uncovers a novel mechanism in which osteoclasts within the bone microenvironment augment the stemness of LUAD cells via the TNF-α-NF-κB-OLFML3-DPPA2 signaling axis. This finding provides an essential theoretical foundation for developing strategies aimed at suppressing secondary dissemination following bone metastasis in LUAD.