A Single Intravenous rAAV Injection as Late as P20 Achieves Efficacious and Sustained CNS Gene Therapy in Canavan Mice

Abstract

Canavan's disease (CD) is a fatal pediatric leukodystrophy caused by mutations in aspartoacylase (AspA) gene. Currently, there is no effective treatment for CD; however, gene therapy is an attractive approach to ameliorate the disease. Here, we studied progressive neuropathology and gene therapy in short-lived (≤ 1 month) AspA(-/-) mice, a bona-fide animal model for the severest form of CD. Single intravenous (IV) injections of several primate-derived recombinant adeno-associated viruses (rAAVs) as late as postnatal day 20 (P20) completely rescued their early lethality and alleviated the major disease symptoms, extending survival in P0-injected rAAV9 and rAAVrh8 groups to as long as 2 years thus far. We successfully used microRNA (miRNA)-mediated post-transcriptional detargeting for the first time to restrict therapeutic rAAV expression in the central nervous system (CNS) and minimize potentially deleterious effects of transgene overexpression in peripheral tissues. rAAV treatment globally improved CNS myelination, although some abnormalities persisted in the content and distribution of myelin-specific and -enriched lipids. We demonstrate that systemically delivered and CNS-restricted rAAVs can serve as efficacious and sustained gene therapeutics in a model of a severe neurodegenerative disorder even when administered as late as P20.

Making the White Matter Matters: Progress in Understanding Canavan’s Disease and Therapeutic Interventions Through Eight Decades

“…In both cases gene therapy methods would need to be tailored to the specific patient type since the dosage and route of administration may not be equally therapeutic in both cases. Preclinical studies using rAAV9 also showed neuronal transduction accompanied by dramatic improvement in the diseased mice (Ahmed et al 2013). Taken together, these observations suggest that de novo expression of aspartoacylase, regardless of the enzyme's physical location, can reduce NAA levels indicating that gene correction of every cell in the brain is not necessary (Matalon et al 2003).…”

“…Additionally, temporal correlations have been shown between developmental increases in aspartoacylase activity and myelination (Bhakoo et al 2001). Similar to human CD patients, brain acetate levels are reduced bỹ 80% in aspartoacylase knockout (ASPAKO) mice during peak postnatal myelination, while myelin lipids such as cerebrosides and sulfatides are reduced (Madhavarao et al 2005;Ahmed et al 2013). These data speculate that NAA-derived acetate is essential during postnatal myelination to supply substrate for some proportion of the lipids that make up myelin sheaths in the developing brain.…”

“…Pharmacological protection of oligodendrocytes against damage in demyelinating diseases could also be a promising avenue of treatment (Waksman 1999). Intravenous delivery of rAAV9 (Ahmed et al 2013) in the ASPAKO model suggests that lowering NAA levels in the brain probably led to alleviation of NAAduria as well as a decrease in edema indicating that the MWP theory could partially explain pathogenesis in CD.…”

“…However, most metabolic supplementation studies do not show any dramatic reversal of symptoms indicating that the molecular etiology might be more complicated. Thin layer chromatography (TLC) and X-ray diffraction studies conducted on ASPAKO mice indicate abnormal myelin composition in untreated animals (Ahmed et al 2013) indicating that it would be worth exploring if the diseased oligodendrocytes are unable to synthesize normal myelin or are incapable of myelination itself. It would be appropriate to indicate here that systemic delivery of AAV9 resulted in a primarily neuronal transduction.…”

“…An exciting study recently demonstrated that single intravenous injection of rAAVs that can cross the BBB achieved sustained therapeutic benefit in ASPAKO mice even when vector was administered as late as P21 (Ahmed et al 2013). This is extremely significant because untreated animals died by the age of 28 days.…”