Brain Derived Neurotrophic Factor Gene Transfer With Adeno-Associated Viral and Lentiviral Vectors Prevents Rubrospinal Neuronal Atrophy and Stimulates Regeneration Associated Gene Expression After Acute Cervical Spinal Cord Injury

Summary: Neurotrophic factors such as brain derived neurotrophic factor (BDNF) may be useful for promoting axonal regeneration and recovery after spinal cord injury. In a rodent model of cervical spinal cord injury, we injected either an adeno-associated virus or a lentivirus vector encoding the BDNF gene to transfect axotomized rubrospinal neurons. We observed successful in vivo BDNF gene transfer, the reversal of axotomy-induced rubrospinal atrophy, and the upregulation genes important for axonal regeneration.

Background: Following spinal cord injury (SCI), neurons of the central nervous system (CNS) undergo marked atrophy and fail to upregulate the genetic programs necessary to promote axonal growth. This contributes substantially to the failure of axonal regeneration and recovery after SCI. Thus, treatments such as neurotrophic factors that prevent such neuronal atrophy and stimulate the expression of such genes may have therapeutic potential for this devastating injury.

Objectives: The purpose of this study was to determine if 1) CNS neurons after acute SCI could be successfully transfected with viral vectors encoding the neurotrophic factor, brain-derived neurotrophic factor (BDNF), and 2) if the expression of this transgene could reverse neuronal atrophy and stimulate the expression of GAP-43 and Ta1 tubulin, genes important for successful axonal growth.

Materials and Methods: Male Sprague-Dawley rats underwent a partial spinal cord incision at C3/4 to transect the rubrospinal tract unilaterally. Either an adeno-associated virus (AAV) or a lenti-virus (LV) encoding the BDNF gene was then stereotactically injected into the vicinity of the rubrospinal cell bodies. Three to four weeks postinjection, rubrospinal neurons were evaluated histologically for a reversal of cell atrophy and with in situ hybridization to evaluate mRNA expression of GAP-43 and Ta1 tubulin, genes that are important for axonal regeneration.

Results: Successful transfection was observed with both the AAV and LV vectors, and the expression of the transgene was demonstrated with BDNF immunoreactivity around the area of injection. Rubrospinal atrophy was reversed with both viral vectors, although more completely and rapidly with the AAV vector. Increased GAP-43 and Ta1 tubulin expression within injured rubrospinal neurons was observed for both vectors as well.

Discussion: These results demonstrate that in vivo transfer of the BDNF gene into injured CNS neurons after spinal cord injury can be accomplished, and that the expression of this neurotrophic can augment the neuronal capacity for axonal regeneration.