Oxidative stress-preconditioned exosomes target BMF to restore mitophagy for alleviating intervertebral disc degeneration

Exosomes derived from bone marrow mesenchymal stem cells (BMSCs) represent a promising cell-free strategy for intervertebral disc degeneration (IDD). Here, we obtained oxidative stress-preconditioned exosomes (O-Exos) from BMSCs exposed to low-concentration hydrogen peroxide. Compared with exosomes from untreated cells (N-Exos), O-Exos more effectively delayed nucleus pulposus (NP) cell senescence and attenuated IDD in vitro and in vivo. The superior effects of O-Exos were associated with restoration of Mitophagy and improved mitochondrial homeostasis in TNF/TNF-α-treated NP cells. BMF (Bcl2 modifying factor) was identified as a functionally relevant downstream target suppressed by O-Exos, and Bmf deficiency promoted Mitophagy and alleviated IDD. Further analyses showed that O-Exos relieved the inhibitory effect of BMF on BCL2L13-LC3B coupling, thereby restoring Mitophagy. In addition, exosomal Mir29a-3p was required for BMF suppression and the superior activity of O-Exos. Together, these findings identify oxidative stress preconditioning as an effective strategy to enhance exosome potency against IDD.Abbreviations: ACAN: aggrecan; BCL2L13: BCL2 like 13; BMF: Bcl2 modifying factor; BMSCs: bone marrow mesenchymal stem cells; BNIP3: BCL2 interacting protein 3; CDKN1A: cyclin dependent kinase inhibitor 1A; CDKN2A: cyclin dependent kinase inhibitor 2A; COL2A1: Collagen type II alpha 1 chain; DHI: disc height index; FUNDC1: FUN14 domain containing 1; H₂O₂: hydrogen peroxide; IDD: intervertebral disc degeneration; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MMP3: matrix metallopeptidase 3; MRI: nuclear magnetic resonance imaging; N-Exos: exosomes derived from untreated BMSCs; NP: nucleus pulposus; O-Exos: exosomes derived from H₂O₂-preconditioned BMSCs; OCR: oxygen consumption rate; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; RT-qPCR: reverse transcription quantitative polymerase chain reaction; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; TEM: transmission electron microscopy; TNF/TNF-alpha: tumor necrosis factor; TOMM20: translocase of outer mitochondrial membrane 20; TP53: tumor protein p53; WT: wild type.