Cholesterol-metabolic tumor-associated macrophages regulate tumor budding-like cell subpopulation to promote chordoma stemness via BACH1/ANGPTL4/SDC4 axis

BACKGROUND: Tumor budding (TB) is a well-established prognostic indicator in various epithelial malignancies. Chordoma, although a rare mesenchymal tumor, paradoxically exhibits prominent epithelial-like characteristics, as demonstrated in previous studies. In particular, it remains unclear whether TB-like (TBL) structures are present in chordoma, as well as the molecular mechanisms driving their formation and their functional impact on tumor progression, representing a critical gap in current knowledge. METHODS: Tumor budding-like grades were defined and evaluated in tumor specimens from 481 chordoma patients across 4 large cohorts using hematoxylin-eosin and immunohistochemical staining. Multi-omics profiling, encompassing GeoMx digital spatial profiling, spatial transcriptomics, bulk RNA sequencing, single-cell RNA sequencing, single-cell ATAC sequencing, and multiplex quantitative immunofluorescence, was integrated to delineate TBL cell subpopulations (TBLCs) and their interactions with cholesterol-metabolic tumor-associated macrophages (CM-TAMs). Organoid models and in vitro/in vivo functional assays were employed for mechanistic investigation and validation. RESULTS: Tumor budding-like structures were prevalent in chordoma, and higher TBL grades were associated with unfavorable clinical outcomes and aggressive phenotypes. Mechanistically, BACH1 in CM-TAMs drove ANGPTL4 secretion, which targeted the SDC4 receptor on TBLCs, thereby enhancing stem-like properties, promoting cholesterol accumulation, and accelerating malignant progression. Pharmacological inhibition of cholesterol metabolism or disruption of the BACH1-ANGPTL4-SDC4 signaling axis markedly reduced tumor invasiveness in both preclinical models and chordoma organoids. CONCLUSIONS: BACH1-driven CM-TAMs activate TBLCs via the ANGPTL4-SDC4 signaling axis, promoting stemness and cholesterol accumulation, ultimately driving malignant progression in chordoma. These findings uncover a previously unrecognized tumor-immune-metabolic interaction and suggest potential therapeutic targets for this disease.