M2 Macrophage-Derived Small Extracellular Vesicles Alleviate IVDD by Inhibiting Nucleus Pulposus Cell Fibrosis through the Akt/FOXO1/PAI-1 Axis

Cell-free therapy is an emerging approach for treating intervertebral disc (IVD) degeneration (IDD). Recently, small extracellular vesicles (sEVs) from M2 macrophages have shown considerable promise in mitigating disc degeneration. The primary aim of our study was to assess whether sEVs isolated from M2 are beneficial in protecting against IDD and to further explore the underlying mechanisms. Cellular models simulating intradiscal fibrosis were developed in vitro, and an animal model of intervertebral disc fibrosis was created by needling the caudal spines of rats. The results indicate that sEVs alleviate IDD by reducing abnormal expression of fibrosis and restore the normal extracellular matrix (ECM) composition within the intervertebral disc, both in vivo and in vitro. Transcriptome sequencing revealed that PAI-1 was the gene most significantly downregulated following treatment with M2-sEVs, while the PI3K/AKT signaling pathway was activated. Based on the prediction that FOXO1 targets and inhibits PAI-1, we found that M2-sEVs suppressed PAI-1 expression by enhancing FOXO1 phosphorylation, thereby reducing fibrosis progression within the IVD and delaying IDD. M2-sEVs alleviate IDD via inhibiting nucleus pulposus cell fibrosis through the Akt/FOXO1/PAI-1 axis, providing promising therapeutic targets for IDD.