<p>Schwann cells (SCs) are
PNS glia with numerous neuron-supporting functions, including myelination of
axons. Although lesser discussed, SCs also fulfill many important roles after
peripheral nerve injury (PNI) contributing significantly to the PNS regeneration
process. Clusters of congregated SCs (Bands of Bungner) precede axon
regeneration and facilitate the growth of extending axons to their distal
targets which is particularly important in the lesion area of severed nerves.
While this phenomenon occurs naturally, recovery from PNI can still be
inadequate, especially in nerve transection or large gap injuries. Current
treatments for nerve transection injuries are limited to coaptation of the
nerve via sutures or nerve grafts. However, poor functional outcomes or donor
site morbidity remain unaddressed problems. At the cellular level, axon
pathfinding and extension relies heavily on the interaction between SCs and
axonal growth cones. Depletion or removal of SCs at the lesion has been
implicated to poor functional outcomes. With their pivotal role throughout nerve
regeneration, we theorize axon regeneration can be improved by augmenting the
SC population at the site of injury by encouraging migration to the lesion and
via expression of morphological phenotypes that imitate the Bands of Bungner. </p>
<p>DC electric fields (EFs)
have been well studied in the past as a method to modulate cell orientation and
migration and within the context of the nervous system, have been used to
promote regeneration in lesioned spinal cords. However, very little work has
investigated the effects of electrical stimulation on glia, such as SCs. Existing
literature is lacking with regards to various aspects of SC responses, including
direction of alignment. We hypothesize electrical stimulation can modulate SC behavior
to reinforce/replicate behaviors observed within Bands of Bungner, which may be
developed into a treatment for victims suffering peripheral nerve injury. </p>
<p>We begin the current
study with a thorough investigation into electric field modulated SC behavior.
Using conventional 2D cell culture we demonstrate SC sensitivity to EFs by
analyzing alignment, morphology and migration data. We employed EFs within the
physiologic range. Waveforms used were constant DC as well as a 50% duty cycle
DC and an oscillating DC. The latter two may prove more appropriate <i>in vivo</i>
due to reduced accumulation of cytotoxic byproducts generated at the electrode
interfaces. </p>
<p>Our results highlight the
sensitivity of SCs to DC electric fields of varying waveforms. SCs showed a
strong propensity to align perpendicular to the field and display some cathodal
migration in 2D cultures. Additional studies with variable cell density
revealed cell-cell interaction further enhanced the alignment response. To more
closely replicate the nerve microenvironment, a 3D cell culture model of PNI
was created. Embedded in matrices, we found SCs displayed weaker migratory and
alignment responses compared to 2D results. The direction of galvanotaxis was
reversed, with SCs migrating toward the anode. Both alignment and migratory
responses have potential applications for PNI. The galvanotactic behavior of
SCs could be used to boost the SC population, increasing the number of Bands of
Bungner. Cell alignment would be particularly advantageous at the lesion where
axon regeneration is most difficult without the physical guidance of
endoneurial tubes.</p>
<p>This study characterizes
SC behavior in applied EFs using conventional 2D and 3D cell culture
techniques. We found SCs are sensitive to electric stimulation, supporting the
idea that applied EFs could be used to indirectly promote regeneration in
damaged peripheral nerve by modulating SC response after injury. Potential applications
include generating an EF across damaged nerves to align SCs, especially in the
lesioned area, using EFs to induce SC migration to the lesion to increase the
number of cells guiding severed axons, and pre-aligning SCs in synthetic nerve
grafts.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/9037547 |
| Date | 02 August 2019 |
| Creators | Spencer J Bunn (7038200) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Characterization_of_Schwann_cells_stimulated_by_DC_electric_fields/9037547 |
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