Date on Master's Thesis/Doctoral Dissertation

12-2007

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Committee Chair

Whittemore, Scott R.

Author's Keywords

Gene therapy; Cellular transplantation; Spinal cord injury; Schwann cells

Subject

Gene therapy; Spinal cord--Wounds and injuries; Tissue engineering

Abstract

The combination of viral mediated gene delivery, tissue engineering, and Schwann cell (SC) transplantation offer a promising strategy to enhance axonal regeneration and functional recovery following spinal cord injury (SCI). The rationale and feasibility of using such combination has been extensively reviewed in Chapter 1. The study presented in Chapter 2 showed that lentiviral vectors are most suitable in situations where stable long term transgene expression is needed, while adenovirus and retrovirus are more suited for transient gene delivery. Tissue engineering combined with Schwann cell (SC) transplantation is a promising method to enhance regeneration and remyelination of axons following a thoracic spinal cord injury (SCI). Previously, SCs in semi-permeable guidance channels made of polyacrylonitrile and polyvinylchloride (PAN/PVC) copolymers were shown to promote the growth of axons into the graft environment. In Chapter 3, we test whether different PAN/PVC mini-channel geometries affects axonal regeneration, we compared three types of channels, i.e. channels with smooth inner wall, channels with grooved inner wall, and channels filled with filaments using this model. Our results showed that grooving of the channel inner wall along the axis of the channel resulted in a significantly higher number (730.66±252.76) of myelinated axons at the channel mid-point, compared to the channels with smooth inner wall (539.4±287.63; p < 0.01), indicating an enhancement of axonal regeneration when grooves are provided within the channel. In contrast, channels filled with filaments had a significantly lower number of myelinated axons (163.54±76.04) than both the grooved and smooth inner wall channels (p < 0.001), indicating that densely-packed filaments prohibited axonal growth into the channel. This type of channels may need to be modified to incorporate growth-promoting molecules on filament surface and/or decrease the number of filaments inside the channel to provide attractiveness and/or space for more axons to grow. We conclude that the use of channels with grooved inner wall, combination with seeded SCs, is more suitable for axonal regeneration and myelination following SCI than the other two channel types. This combination can be used in further studies with the addition of regeneration enhancing factors such as neurotrophins. In Chapter 4, we examined axonal regeneration following transplantation of PAN/PVC mini-channel seeded with SCs that were infected with 3 viral vectors, i.e. retroviral, adenoviral, and lentiviral vectors. Although, animals in LZRS-DI5A SCs group had a significantly lower number of myelinated axons compared to lentiD15A group they showed significant improvement in grid walking test. We conclude that different patterns of transgene expression may enhance regeneration and myelination of different populations of regenerating axons following thoracic SCI. In conclusion, combination strategies for SCI using different transgene expression patterns and different channel inner wall geometry enhance axonal regeneration and myelination. Functional recovery however, may be the result of reorganization of spinal cord circuitry rather than successful axonal regeneration.

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