Exosome-Loaded Engineered circBDNF Promotes Spinal Cord Injury Repair Through the PI3K/AKT/mTOR Signaling Axis

The brain-derived neurotrophic factor (BDNF) is a potent neuroprotective factor; however, its large molecular size limits its ability to cross structural barriers such as the blood-spinal cord barrier. This study explores the therapeutic potential of exosome-mediated delivery of engineered circular BDNF (circBDNF) to promote spinal cord injury (SCI) repair through activation of the PI3K/AKT/mTOR signaling pathway.

A synthetic circBDNF sequence encoding BDNF was used to construct a circBDNF overexpression plasmid, which was transfected into HEK293T cells to generate circBDNF-loaded exosomes (circBDNF-EXO). These exosomes were characterized via transmission electron microscopy, nanoparticle tracking analysis, and Western blotting. In vitro, the protective effects of circBDNF-EXO were evaluated in an oxygen-glucose deprivation/reperfusion (OGD) injury model in HT22 cells, focusing on cell viability, reactive oxygen species (ROS) levels, apoptosis, inflammation, and signaling pathways. In vivo, a T10 SCI mouse model was employed to assess therapeutic efficacy, using behavioral, electrophysiological, histological, and molecular analyses.

In vitro, circBDNF-EXO treatment significantly increased BDNF expression, enhanced cell viability, reduced ROS levels, mitigated inflammation, and inhibited apoptosis in HT22 cells following OGD injury. In vivo, administration of circBDNF-EXO resulted in improved motor function recovery, evidenced by increased Basso Mouse Scale scores, enhanced gait coordination, and better motor-evoked potentials. Histological analyses demonstrated elevated BDNF expression, decreased apoptosis, reduced oxidative stress, and enhanced axonal regeneration in the injured spinal cord. Mechanistically, circBDNF-EXO activated TrkB receptors and upregulated the PI3K/AKT/mTOR signaling pathway, as confirmed by Western blot analysis.

Exosome-mediated delivery of circBDNF promotes SCI repair by activating the PI3K/AKT/mTOR pathway, suppressing apoptosis, oxidative stress, and inflammation, and enhancing axonal regeneration. This innovative approach holds substantial promise for SCI treatment and deserves further exploration in preclinical and clinical studies.