Manipulating N-acetyl-L-aspartate transport to treat Canavan leukodystrophy

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Canavan disease is a vacuolar (“spongiform”) leukodystrophy caused by ASPA mutations that diminish brain aspartoacylase activity. Current treatments for this neurodegenerative disorder, which include dietary manipulations, administration of lithium citrate and anticonvulsants, and AAV-mediated brain parenchymal ASPA gene therapy, do not reverse or prevent progression of neurological deficits in affected infants and children. Because aspartoacylase is necessary for cleavage of the abundant brain amino acid N-acetyl-L- aspartate (NAA), brain NAA is markedly elevated in Canavan disease. We were the first to report that knocking out or knocking down Nat8l, the gene that encodes the NAA-synthesizing enzyme N-acetytransferase 8-like, prevented development of motor deficits and brain vacuolation by aspartoacylase-deficient Canavan disease (“CD”) mice. Later, we showed that intrathecal administration of an Nat8l-inhibiting antisense oligonucleotide to young adult CD mice reversed their established brain NAA elevation, motor deficits and brain vacuolation. Together, those results strongly support the hypothesis that motor deficits and brain vacuolation in Canavan disease are consequences of elevated brain NAA. Our most recent studies, presented in this grant application, indicate that constitutive deletion of Slc13a3, which encodes NaDC3, a plasma membrane sodium-coupled transporter for NAA and other dicarboxylates, normalizes brain NAA content and prevents ataxia and brain vacuolation in CD mice. Also, we have confirmed prior reports that astroglia and renal proximal tubular epithelium express Slc13a3 and NaDC3, and have localized meningeal NaDC3 expression to arachnoid mater-associated Prox1+ cells. We now plan conditional deletion studies to determine whether selective ablation of NaDC3 from astroglia (Specific Aim 1), arachnoid (Specific Aim 2), or renal proximal tubular epithelium (Specific Aim 3) is sufficient to normalize brain NAA content and reverse motor deficits and brain vacuolation in symptomatic CD mice. Results of these studies will serve to guide development of selective Slc13a3 and NaDC3 therapeutic targeting strategies for infants and children with Canavan disease.