M2 macrophage exosome‐derived Apoc1 promotes ferroptosis resistance in osteosarcoma by inhibiting ACSF2 deubiquitination

Abstract Osteosarcoma (OS) is the most common primary malignant tumor of bone. The aim of this study was to investigate the regulatory mechanisms of M2 macrophage exosomes (M2‐Exos) in ferroptosis in OS. A mouse model was established to investigate the in vivo role of M2‐Exos. We investigated their effects on ferroptosis in OS using erastin, a ferroptosis activator, and deferoxamine mesylate, an iron chelator. In vitro, we investigated whether the Apoc1/Acyl‐CoA Synthetase Family Member 2 (ACSF2) axis mediates these effects, using shApoc1 and shACSF2. The mechanisms whereby Apoc1 regulates ACSF2 were examined using cyclohexanone, a protein synthesis inhibitor, and MG132, a proteasomal inhibitor. M2‐Exos reversed the inhibitory effects of erastin on OS cells, thus enhancing their viability, migration, invasion, proliferation, and reducing ferroptosis. Apoc1 was highly expressed in M2‐Exos, and interfering with this expression reversed the effects of M2‐Exos on OS cells. ACSF2 mediated the effects of M2‐Exos‐derived Apoc1. Apoc1 interacted with ACSF2, which, in turn, interacted with USP40. Apoc1 overexpression increased ACSF2 ubiquitination, promoting its degradation, whereas USP40 overexpression inhibited ACSF2 ubiquitination and promoted its expression. Apoc1 overexpression inhibited ACSF2 binding to USP40. M2‐Exos‐derived Apoc1 promoted ferroptosis resistance by inhibiting USP40 binding to ACSF2 and promoting ACSF2 ubiquitination and degradation, thus enhancing OS development.