Abstract:
Spinal cord injury (SCI) leads to permanent functional disruption of the central nervous system; for which there is no current pathology-modifying or regenerative treatment. The Chondroitinase ABC (ChABC) enzyme is a promising preclinical therapy as it promotes functional neuroplasticity following CNS injury by degrading CSPGs that inhibit axon regeneration within the extracellular matrix. Due to the instability of the enzyme, effective and continuous administration of ChABC to the injured mammalian spinal cord can only be achieved through viral vector gene therapy. This approach has previously been developed using lentiviral (LV) vectors and was shown to dramatically modulate injury pathology and restore sensorimotor functions. Despite the success of the vector, clinical development of LV is likely to be antagonistic with the non-resolving adaptive immune response known to transpire following spinal cord injury. Therefore, here we apply the use of immune-evasive adenoassociated viral (AAV) vectors in conjunction with an astrocyte-specific promoter to selectively target astrocytes and thus elicit a level of transgene regulation. Using this novel vector system, the first objective of this thesis demonstrated the stable and functional expression of mammalian-modified ChABC from mammalian astrocytes in vitro. Throughout the second objective, single application of this therapy was found to enhance neuroplasticity and display modest improvements in neuroprotection in an in vivo rat model of thoracic spinal cord contusion injury. We reveal that these histological changes were correlated with significant improvement in hindlimb ladder walking performance, suggesting improvements in corticospinal tract function and recovery of descending motor control. When compared to the beneficial effects reported for LV-mChABC gene therapy, there appeared to be a delay in inducing similar effects with the AAV-mChABC construct. Despite this, the low immunogenicity of AAV compared to the LV vector conveys clinically advantage. Thus, our novel gene therapy approach provides a supportive and encouraging step towards the development of a safer ChABC gene therapy strategy for long term treatment of spinal cord injury. This preclinical study could have a significant impact for quadriplegic individuals, for whom recovery of lower limb function is an important determinant of independence.