534. Recombinant Adeno-Associated Virus Serotype 1 Vector-Mediated Transduction within the Murine Hippocampus

Top of pageAbstract Recent studies have shown that several of the recombinant adeno-associated virus (rAAV) serotypes have distinct biologic functions (different transduction efficiencies and cell-type tropisms) within the central nervous system. Our group reported that rAAV type 1 (rAAV1) vectors had a greater transduction efficiency than that of rAAV type 2 (rAAV2) vectors within the murine striatum. To further explore the differences between these vectors within the brain, we compared rAAV1 and rAAV2 vectors within the murine hippocampus. Methods: We engineered an rAAV type 1 hybrid vector and an rAAV type 2 vector to carry identical genomes consisting of the AAV type 2 terminal repeat elements flanking a cytomegalovirus immediate-early promoter-driven EGFP transgene. The vectors (rAAV1-GFP and rAAV2-GFP) were administrated to the brains of C3H/HeJ mice (8 weeks of age) by stereotaxic -guided injection into right hippocampus. Each mouse received 5 108 DNase resistant particles. EGFP expression was evaluated by confocal and fluorescent microscopy. Results: Mice (n = 3 for each vector type) were analyzed 5 weeks post-vector injection. In the rAAV2-GFP-injected mice, EGFP-positive cell bodies and fibers were present within the oriens layer and pyramidal cell layer surrounding the needle track (labeled by carbon black) in the CA1 area of the hippocampus. In the rAAV1-GFP-injected mice, EGFP-positive cell bodies and fibers were widely distributed in CA1, CA2, and CA3 oriens layer and pyramidal cell layer in the hippocampus ispsilateral to the injection site. Outside of the hippocampus, EGFP-positive cells were present within the septofimbrial and lateral septal nuclei (dorsal part); and EGFP-positive fibers were present within the hippocampal commissure, dorsal fornix, and dentate gyrus. Within the hemisphere contralateral to the injection site, EGFP-positive cell bodies and fibers were present within the CA1, CA2, and CA3 oriens layer and the pyramidal cell layer of the hippocampus and EGFP-positive fibers were present within the dentate gyrus. The level of EGFP expression was greater in the injected as compared to the uninjected hippocampus. EGFP (positive cell bodies and fibers) was present within the corpus callosum of both hemispheres. Serial sections through the hippocampus revealed EGFP expression extending in the rostral-caudal direction less than 0.5 mm in the rAAV2-injected mice and 2.610.34 mm in the rAAV1-injected mice. Conclusions: rAAV1 vectors have a higher transduction efficiency and more widespread distribution than rAAV2 vectors after injection into the hippocampus. Based upon the finding of EGFP-positive cell bodies within the contralateral hippocampus, rAAV1 vectors appear to undergo retrograde transportation along neuronal axons. These characteristics might prove useful in gene therapy applications targeting the hippocampus.