Nayan Yi, Muyun Wu, Xiaojie Ma, Yuhan Xie, Heng Sun, Yuxi Zhang, Xing Cui
Background Myeloma bone disease (MBD) is driven by excessive osteoclast activation and progressive bone destruction, but the role of exosomal circular RNAs (circRNAs) from myeloma cells remains unclear. Methods Exosomes from U266 and MM1S cells were isolated and used to treat THP-1 cells. Osteoclast differentiation was assessed by TRAP staining and bone resorption assay. circRNA sequencing of U266 exosomes and MBD patient blood was performed to identify overlapping circRNAs. A ceRNA network was constructed using circBank and miRTarBase, combined with single-cell RNA-seq (GSE271107) to prioritize candidate target genes. Functional experiments included circ_0002724 knockdown/overexpression in U266 cells, exosomal transfer, TRAP, bone resorption, qRT-PCR, RNA-FISH/IF, dual-luciferase reporter assay, and immunohistochemistry of patient bone marrow biopsies. Results U266-derived exosomes exhibited stronger osteoclast-inducing activity than MM1S-derived exosomes. Intersection analysis identified 14 common circRNAs, among which circ_0002724 showed the highest predicted miRNA-binding capacity and was significantly upregulated in THP-1 cells after exosome treatment. A circ_0002724-associated regulatory network identified miR-4753-3p, IFIT1, and RANK as potential downstream components. Single-cell analysis revealed that IFIT1 was highly expressed in MM osteoclast precursor cells and increased during osteoclast differentiation. Exosomal circ_0002724 was internalized by THP-1 cells; circ_0002724 knockdown reduced, whereas overexpression enhanced, TRAP-positive osteoclast formation and bone resorption activity, accompanied by altered RANK and IFIT1 expression. Dual-luciferase reporter assays supported the interactions between circ_0002724, miR-4753-3p, RANK, and IFIT1. Immunohistochemical analysis of patient biopsies demonstrated positive associations of circ_0002724, RANK, and IFIT1 with MBD severity. Conclusions Myeloma-derived exosomal circ_0002724 promotes osteoclast activation and bone resorption and is associated with regulation of the miR-4753-3p/IFIT1/RANK network. These findings provide new insights into exosome-mediated tumor–bone microenvironment communication and suggest circ_0002724 as a potential biomarker and candidate therapeutic target for MBD.