Exosome-derived CDNF Inhibits Astrocyte and T Cell Activation by Regulating HSPA5 and Promotes Repair and Regeneration after Peripheral Nerve Injury

Objective
Peripheral nerve injury (PNI) often triggers a detrimental neuroinflammatory response involving astrocytes and T-cells, hindering functional recovery. This study aimed to investigate the mechanism by which Cerebral Dopamine Neurotrophic Factor (CDNF) modulates astrocyte and T-cell activation and to evaluate its therapeutic potential for promoting nerve regeneration.

Methods
Exosomes (Exo) were engineered to carry CDNF by isolating them from bone marrow mesenchymal stem cells (BMSCs) overexpressing CDNF. The effects of CDNF on the activation of cultured astrocytes and CD8+ T-cells were assessed in vitro by measuring cytokine release, cell proliferation, and activation markers using ELISA, EdU assays, flow cytometry, and Western blotting. Co-immunoprecipitation was employed to investigate the interaction between CDNF and Heat Shock Protein A5 (HSPA5). The therapeutic efficacy of exosome-delivered CDNF (Exo-CDNF) was evaluated in vivo using a rat model of chronic constriction injury (CCI), a model for PNI-induced neuropathic pain.

Results
CDNF suppressed the activation of astrocytes and CD8+ T-cells, as evidenced by reduced production of pro-inflammatory cytokines (TNF-α, IL-1β), decreased cell proliferation, and attenuated NF-κB pathway activation. Exo-CDNF was effectively internalized by astrocytes and T-cells, exerting similar inhibitory effects. Mechanistically, we discovered a direct interaction between CDNF and HSPA5. Overexpression of HSPA5 counteracted the immunosuppressive effects of CDNF. In vivo, systemic administration of Exo-CDNF alleviated neuropathic pain behaviors, reduced spinal cord apoptosis and neuroinflammation, and improved histological outcomes in CCI rats.

Conclusion
Our findings demonstrate that Exo-mediated delivery of CDNF effectively suppresses astrocyte and T-cell activation by regulating HSPA5. This study reveals a novel immunomodulatory role for the CDNF-HSPA5 axis and highlights Exo-CDNF as a promising therapeutic strategy for promoting repair and regeneration following peripheral nerve injury.