654. Quantifying GDNF Levels in the Spinal Cord after Intracerebral Delivery of rAAV5 GDNF

Abstract

Top of pageAbstract Neurodegenerative diseases such as Spinal Muscular Atrophy (SMA) and Amyotrophic Lateral Sclerosis (ALS) are characterized by a loss of the lower motor neurons in the spinal cord. Gene therapy is a possible treatment for these diseases. One promising approach is the use of multiple injections of recombinant adeno-associated virus to deliver secreted trophic factors to spinal motor neurons (Kaspar, et al 2003). However the relationship between the upper and lower motor neurons can potentially be utilized to deliver trophic factors to large areas of the spinal cord via a single intracerebral injection. Previously we have demonstrated GFP and GDNF immuno-staining of cervical and thoracic spinal cord after a single red nucleus injection of rAAV5 GFP or GDNF vector. To further characterize the GDNF expression in the spinal cord, normal rats were given a unilateral injection of rAAV5 GDNF and sacrificed 6 weeks post injection. The brains and spinal cords were extracted and analyzed by GDNF ELISA. GDNF was detected in all levels of spinal cord examined. A gradient of GDNF expression was clearly observed moving from cervical through to lumbar levels of spinal cord. This follows the pattern of rubrospinal tract fibers with the number of fibers comprising the tract lessening as it moves caudally. GDNF was not detectable in GFP injected controls. These results indicate that delivery of a transgene encoding a secreted trophic factor such as IGF1 or GDNF to a large portion of the spinal cord is possible after a single injection into the red nucleus. Future directions include delivery of rAAV5 GDNF or IGF1 to the motor cortex and red nucleus of normal and diseased animals to measure protein levels along the spinal cord and investigate the therapeutic effect of this novel gene delivery route. Supported by a grant from Families of Spinal Muscular Atrophy.