Electrical regulation of olfactory ensheathing cells using conductive polypyrrole/chitosan polymers

Electrical stimulation (ES) applied to a conductive nerve graft holds the great potential to improve nerve regeneration and functional recovery in the treatment of lengthy nerve defects. A conductive nerve graft can be obtained by a combination of conductive nerve scaffold and olfactory ensheathing cells (OECs), which are known to enhance axonal regeneration and to produce myelin after transplantation. However, when ES is applied through the conductive graft, the impact of ES on OECs has never been investigated. In this study, a biodegradable conductive composite made of conductive polypyrrole (PPy, 2.5%) and biodegradable chitosan (97.5%) was prepared in order to electrically stimulate OECs. The tolerance of OECs to ES was examined by a cell apoptosis assay. The growth of the cells was characterized using DAPI staining and a CCK-8 assay. The mRNA and protein levels of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neural cell adhesion molecule (N-CAM), vascular endothelial growth factor (VEGF) and neurite outgrowth inhibitor-A (NOGO-A) in OECs were assayed by RT-PCR and Western blotting, and the amount of BDNF, NGF, N-CAM, VEGF and NOGO-A secreted was determined by an ELISA assay. The results showed that the PPy/chitosan membranes supported cell adhesion, spreading, and proliferation with or without ES. Interestingly, ES applied through the PPy/chitosan composite dramatically enhanced the expression and secretion of BDNF, NGF, N-CAM and VEGF, but decreased the expression and secretion of NOGO-A when compared with control cells without ES. These findings highlight the possibility of enhancing nerve regeneration in conductive scaffolds through ES increased neurotrophin secretion in OECs.