619. AAV9 Transduction Is Similar in Adult and Aged Mouse Brains Following Intraparenchymal Injection

We previously reported that systemic injection of AAV9 in aged mice (P550) results in significantly fewer transduced CNS cells compared to adult mice (P49). This was not due to the presence of neutralizing antibodies in the aged mice. To determine whether aging in the brain and/or the periphery is responsible for this reduction, we quantified CNS transduction following stereotaxic brain injection in aged or adult mice. Aged male Balb/c mice (n = 6, P550) and adult mice (n = 7, P50) received direct injections into the striatum and ipsilateral hippocampus with scAAV9-CB expressing green fluorescent protein or scAAV9-CB expressing glial cell line derived neurotrophic factor (GFP or GDNF). All mice were euthanized three weeks post-injection. Brains of aged and adult mice injected with scAAV9-CB-GFP were sliced and processed for near-infrared imaging to quantify vector spread and GFP intensity. GFP expression was similar in directly injected aged and adult brains. Vector spread along the rostrocaudal axis was approximately 2 mm from either the striatal or hippocampal injection site and did not vary with age. Brains of mice directly injected with scAAV9-CB-GDNF were hemisected and processed for ELISA to quantify GDNF protein levels. GDNF levels in the striatum and hippocampus reached 2x those of uninjected controls and no differences in GDNF expression were detected between aged and adult injected mice. Together, we found that AAV9 CNS transduction is similar in aged and adult mouse brains following direct injection. These results suggest that reduced CNS transduction in aged mice following AAV9 systemic injection is due to alterations in the periphery. Future studies include investigation of altered viral blood brain barrier penetration and viral retention within peripheral tissues of aged mice.