ABSTRACT
Canavan's disease is an autosomal recessive disorder caused by aspartoacylase deficiency. The deficiency of aspartoacylase leads to increased concentration of N-acetylaspartic acid in brain and body fluids. The failure to hydrolyze N-acetylaspartic acid causes disruption of myelin, resulting in spongy degeneration of the white matter of the brain. The clinical features of the disease are hypotonia in early life, which changes to spasticity, macrocephaly, head lag, and progressive severe mental retardation. Although Canavan's disease is panethnic, it is most prevalent in the Ashkenazi Jewish population. Research at the molecular level led to the cloning of the gene for aspartoacylase and development of a knockout mouse for Canavan's disease. These developments have afforded new tools for research in the attempts to understand the pathophysiology of Canavan's disease, design new therapies, and explore methods for gene transfer to the central nervous system.
Subject(s)
Canavan Disease/metabolism , Amidohydrolases/genetics , Animals , Canavan Disease/diagnosis , Canavan Disease/enzymology , Canavan Disease/genetics , Canavan Disease/pathology , Canavan Disease/therapy , Humans , Mice , Mice, Knockout , Mutation , Prenatal DiagnosisABSTRACT
Canavan's disease is an autosomal recessive disorder caused by aspartoacylase deficiency, which leads to accumulation of N-acetylaspartic acid in the brain and blood and an elevated level of N-acetylaspartic acid in the urine. The brain of patients with Canavan's disease shows spongy degeneration. How the enzyme deficiency and elevated N-acetylaspartic acid cause the pathophysiology observed in Canavan's disease is not obvious. The creation of a knockout mouse for Canavan's disease is being used as a tool to investigate metabolic pathways in the mouse and correlate them with the patients with Canavan's disease. The level of glutamate is lower in the knockout mouse brain than in the wild-type mouse brain, similar to what we have found in children with Canavan's disease, and so are the levels of gamma-aminobutyric acid (GABA). The level of aspartate is higher in the Canavan's disease mouse brain. The activity of aspartate aminotransferase, an enzyme involved in the malate-aspartate shuttle, is lower in the Canavan's disease mouse brain. The lower weight of the Canavan's disease mouse was in direct proportion to low total-body fat and bone mineral density. These changes might be similar to what is seen in patients with Canavan's disease and could have therapeutic implications.
Subject(s)
Canavan Disease/metabolism , Animals , Aspartate Aminotransferases/metabolism , Aspartic Acid/metabolism , Body Weight , Canavan Disease/enzymology , Disease Models, Animal , Glutamic Acid/metabolism , Humans , Mice , Mice, KnockoutABSTRACT
Canavan disease (CD) is an autosomal recessive leukodystrophy caused by deficiency of aspartoacylase (ASPA). Deficiency of ASPA leads to elevation of N-acetyl-L-aspartic acid (NAA) in the brain and urine. To explore the feasibility of gene transfer to replace ASPA in CD, we generated a knockout mouse and constructed an AAV vector that encodes human ASPA cDNA (hASPA) followed by green fluorescent protein (GFP) after an intraribosomal entry site. We injected CD mice with rAAV-hASPA-GFP in the striatum and thalamus or injected rAAV-GFP identically into control animals. Three to five months after the injection, we determined the presence of ASPA in the CD mouse brain by ASPA activity assay, GFP expression, and Western blot analysis. While rAAV-GFP-injected animals displayed undetectable levels of ASPA, all detection methods revealed significant ASPA levels in rAAV-hASPA-GFP-injected CD mice. We evaluated the functional effects of rAAV-hASPA-GFP-mediated ASPA expression by standard histological methods, magnetic resonance spectroscopy (MRS) for in vivo NAA levels, and magnetic resonance imaging of CD mice. rAAV-hASPA-injected animals displayed a remarkable lack of spongiform degeneration in the thalamus. However, pathology in sites unrelated to the injected areas showed no improvement in histopathology. The improvement in thalamic neuropathology was also detectable via in vivo MRI. MRS revealed that in vivo NAA levels were also reduced. These data indicate that rAAV-mediated ASPA delivery may be an interesting avenue for the treatment of CD.
