Neurite outgrowth is significantly increased by the simultaneous presentation of Schwann cells and moderate exogenous electric fields

Abstract

Axonal extension is influenced by a variety of external guidance cues; therefore, the development and optimization of a multi-faceted approach is probably necessary to address the intricacy of functional regeneration following nerve injury. In this study, primary dissociated neonatal rat dorsal root ganglia neurons and Schwann cells were examined in response to an 8 h dc electrical stimulation (0-100 mV mm(-1)). Stimulated samples were then fixed immediately, immunostained, imaged and analyzed to determine Schwann cell orientation and characterize neurite outgrowth relative to electric field strength and direction. Results indicate that Schwann cells are viable following electrical stimulation with 10-100 mV mm(-1), and retain a normal morphology relative to unstimulated cells; however, no directional bias is observed. Neurite outgrowth was significantly enhanced by twofold following exposure to either a 50 mV mm(-1) electric field (EF) or co-culture with unstimulated Schwann cells by comparison to neurons cultured alone. Neurite outgrowth was further increased in the presence of simultaneously applied cues (Schwann cells + 50 mV mm(-1) dc EF), exhibiting a 3.2-fold increase over unstimulated control neurons, and a 1.2-fold increase over either neurons cultured with unstimulated Schwann cells or the electrical stimulus alone. These results indicate that dc electric stimulation in combination with Schwann cells may provide synergistic guidance cues for improved axonal growth relevant to nerve injuries in the peripheral nervous system.

Promoting Axon Regeneration and Neurological Recovery Following Traumatic Peripheral Nerve Injuries

“…This is because of the development of senescent by long-time denervated host Schwann cells, which is indicated by the appearance of senescence associated beta-galactosidase, p16INK4A, and IL6 [125]. Since Schwann cells proliferation and migration decreases with increasing time of denervation, Schwann cell senescence plays a role in the limited axonal regeneration across nerve grafts of increasing gap lengths [289]. Finally, seeding ANAs with Schwann cells promotes a similar extent of axon regeneration across sciatic nerve gaps to that induced by allografts [290].…”

“…Poly epsilon-caprolactone (PCL) conduits for rat sciatic nerve gaps induce axons to regenerate across gaps up to 1 cm in length [125,289].…”

“…Although ANAs have similar influences to autografts in supporting axonal regeneration across short gaps, they are not effective for larger nerve defects [289,296,297]. ANAs depend on the addition of Schwann cells and their extensive proliferation to support axonal regeneration.…”

“…ANAs depend on the addition of Schwann cells and their extensive proliferation to support axonal regeneration. However, the longer the ANA the greater Schwann cell proliferative that is required, which can create stress in those Schwann cells and their subsequent senescence [289]. Thus, ANAs plus Schwann cells are less effective in inducing axon regeneration across bridged nerve gap as the gap increase in length from 2 to 4 to 6 cm [289].…”

“…However, the longer the ANA the greater Schwann cell proliferative that is required, which can create stress in those Schwann cells and their subsequent senescence [289]. Thus, ANAs plus Schwann cells are less effective in inducing axon regeneration across bridged nerve gap as the gap increase in length from 2 to 4 to 6 cm [289]. However, the extent of axon regeneration can be enhanced if the Schwann cells are transfected with the ciliary neurotrophic factor (CNTF) gene to increase their neurotrophic influence on the axons [298].…”