Canavan Disease Mouse Research Articles

NAAG synthetase deficiency has only low influence on pathogenesis in a Canavan disease mouse model.

Canavan disease (CD) is a leukodystrophy caused by mutations in the N-acetylaspartate (NAA) hydrolase aspartoacylase (ASPA). Inability to degrade NAA and its accumulation in the brain results in spongiform myelin degeneration. NAA is mainly synthesized by neurons, where it is also a precursor of the neuropeptide N-acetylaspartylglutamate (NAAG). Hydrolysis of this peptide by glutamate carboxypeptidases is an additional source of extracellular NAA besides the instant neuronal release of NAA. This study examines to what extent NAA released from NAAG contributes to NAA accumulation and pathogenesis in the brain of Aspanur7/nur7 mutant mice, an established model of CD. Towards this aim, Aspanur7/nur7 mice with additional deficiencies in NAAG synthetase genes Rimklb and/or Rimkla were generated. Loss of myelin in Aspanur7/nur7 mice was not significantly affected by Rimkla and Rimklb deficiency and there was also no obvious change in the extent of brain vacuolation. Astrogliosis was slightly reduced in the forebrain of Rimkla and Rimklb double deficient Aspanur7/nur7 mice. However, only minor improvements at the behavioral level were found. The brain NAA accumulation in CD mice was, however, not significantly reduced in the absence of NAAG synthesis. In summary, there was only a weak tendency towards reduced pathogenic symptoms in Aspanur7/nur7 mice deficient in NAAG synthesis. Therefore, we conclude that NAAG metabolism has little influence on NAA accumulation in Aspanur7/nur7 mice and development of pathological symptoms in CD.

Pathological Bergmann glia alterations and disrupted calcium dynamics in ataxic Canavan disease mice.

Canavan disease (CD) is a recessively inherited pediatric leukodystrophy resulting from inactivating mutations to the oligodendroglial enzyme aspartoacylase (ASPA). ASPA is responsible for hydrolyzing the amino acid derivative N-acetyl-L-aspartate (NAA), and without it, brain NAA concentrations increase by 50% or more. Infants and children with CD present with progressive cognitive and motor delays, cytotoxic edema, astroglial vacuolation, and prominent spongiform brain degeneration. ASPA-deficient CD mice (Aspanur7/nur7 ) present similarly with elevated NAA, widespread astroglial dysfunction, ataxia, and Purkinje cell (PC) dendritic atrophy. Bergmann glia (BG), radial astrocytes essential for cerebellar development, are intimately intertwined with PCs, where they regulate synapse stability, functionality, and plasticity. BG damage is common to many neurodegenerative conditions and frequently associated with PC dysfunction and ataxia. Here, we report that, in CD mice, BG exhibit significant morphological alterations, decreased structural associations with PCs, loss of synaptic support proteins, and altered calcium dynamics. We also find that BG dysfunction predates cerebellar vacuolation and PC damage in CD mice. Previously, we developed an antisense oligonucleotide (ASO) therapy targeting Nat8l (N-acetyltransferase-8-like, "Nat8l ASO") that inhibits the production of NAA and reverses ataxia and PC atrophy in CD mice. Here, we show that Nat8l ASO administration in adult CD mice also leads to BG repair. Furthermore, blocking astroglial uptake of NAA is neuroprotective in astroglia-neuron cocultures exposed to elevated NAA. Our findings suggest that restoration of BG structural and functional integrity could be a mechanism for PC regeneration and improved motor function.

Developing Hypoimmunogenic Human iPSC-Derived Oligodendrocyte Progenitor Cells as an Off-The-Shelf Cell Therapy for Myelin Disorders.

Demyelinating disorders are among the most common and debilitating diseases in neurology. Canavan disease (CD) is a lethal demyelinating disease caused by mutation of the aspartoacylase (ASPA) gene, which leads to the accumulation of its substrate N-acetyl-l-aspartate (NAA), and consequently demyelination and vacuolation in the brain. In this study, hypoimmunogenic human induced pluripotent stem cell (iPSC)-derived oligodendrocyte progenitor cells (OPC) are developed from a healthy donor as an "off-the-shelf" cell therapy. Hypoimmunogenic iPSCs are generated through CRISPR/Cas9 editing of the human leukocyte antigen (HLA) molecules in healthy donor-derived iPSCs and differentiated into OPCs. The OPCs are engrafted into the brains of CD (nur7) mice and exhibit widespread distribution in the brain. The engrafted OPCs mature into oligodendrocytes that express the endogenous wildtype ASPA gene. Consequently, the transplanted mice exhibit elevated human ASPA expression and enzymatic activity and reduced NAA level in the brain. The transplanted OPCs are able to rescue major pathological features of CD, including defective myelination, extensive vacuolation, and motor function deficits. Moreover, the hypoimmunogenic OPCs exhibit low immunogenicity both in vitro and in vivo. The hypoimmunogenic OPCs can be used as "off-the-shelf" universal donor cells to treat various CD patients and many other demyelinating disorders, especially autoimmune demyelinating diseases, such as multiple sclerosis.

Cell-Based Therapy for Canavan Disease Using Human iPSC-Derived NPCs and OPCs.

Canavan disease (CD) is a fatal leukodystrophy caused by mutation of the aspartoacylase (ASPA) gene, which leads to deficiency in ASPA activity, accumulation of the substrate N‐acetyl‐L‐aspartate (NAA), demyelination, and spongy degeneration of the brain. There is neither a cure nor a standard treatment for this disease. In this study, human induced pluripotent stem cell (iPSC)‐based cell therapy is developed for CD. A functional ASPA gene is introduced into patient iPSC‐derived neural progenitor cells (iNPCs) or oligodendrocyte progenitor cells (iOPCs) via lentiviral transduction or TALEN‐mediated genetic engineering to generate ASPA iNPC or ASPA iOPC. After stereotactic transplantation into a CD (Nur7) mouse model, the engrafted cells are able to rescue major pathological features of CD, including deficient ASPA activity, elevated NAA levels, extensive vacuolation, defective myelination, and motor function deficits, in a robust and sustainable manner. Moreover, the transplanted mice exhibit much prolonged survival. These genetically engineered patient iPSC‐derived cellular products are promising cell therapies for CD. This study has the potential to bring effective cell therapies, for the first time, to Canavan disease children who have no treatment options. The approach established in this study can also benefit many other children who have deadly genetic diseases that have no cure.

Redirecting N-acetylaspartate metabolism in the central nervous system normalizes myelination and rescues Canavan disease.

Canavan disease (CD) is a debilitating and lethal leukodystrophy caused by mutations in the aspartoacylase (ASPA) gene and the resulting defect in N-acetylaspartate (NAA) metabolism in the CNS and peripheral tissues. Recombinant adeno-associated virus (rAAV) has the ability to cross the blood-brain barrier and widely transduce the CNS. We developed a rAAV-based and optimized gene replacement therapy, which achieves early, complete, and sustained rescue of the lethal disease phenotype in CD mice. Our treatment results in a super-mouse phenotype, increasing motor performance of treated CD mice beyond that of WT control mice. We demonstrate that this rescue is oligodendrocyte independent, and that gene correction in astrocytes is sufficient, suggesting that the establishment of an astrocyte-based alternative metabolic sink for NAA is a key mechanism for efficacious disease rescue and the super-mouse phenotype. Importantly, the use of clinically translatable high-field imaging tools enables the noninvasive monitoring and prediction of therapeutic outcomes for CD and might enable further investigation of NAA-related cognitive function.

157. High-Field In Vivo Neuroimaging to Determine CNS Gene Therapy Outcome and Probe Disease Pathomechanism

Gene therapy targeting the central nervous system (CNS) is one of the most challenging gene therapies due to the blood-brain barrier (BBB). However, recombinant adeno-associated virus (rAAV) has proved to be an excellent tool to target the CNS. Another obstacle in the setting of CNS gene therapy is the non-invasive evaluation of therapeutic outcome. While biopsies and sections of the CNS are the gold-standard to assess brain pathology and response to CNS gene therapy, the invasiveness and potentially associated complications limit its frequent use in pre-clinical as well as clinical studies. Thus, it is of no surprise that non-invasive monitoring of CNS gene therapy in vivo holds great promise for longitudinal and functional assessment of treatment response. We used high-field in vivo neuroimaging to monitor intravenously (i.v.) and intracerebroventricularly (i.c.v.) administered rAAV based CNS directed gene therapy in a mouse model of Canavan disease (CD). Characteristically, Canavan disease presents with a very high NAA peak detected by magnet resonance spectrometry (MRS) and hyper intensity on T2-weighted anatomic images using magnet resonance imaging (MRI). Consequently, we first determined the efficacy of our i.v. and i.c.v. gene therapy by those two means. In congruence with motor function and pathology data, both MRI and MRS alterations have been entirely normalized by gene therapy. Another characteristic neuropathological change on Canavan brain sections is the loss of white matter tracts, which is thought to explain neurological symptoms seen in Canavan disease patients. Thus, we hypothesized that diffusion tensor imaging (DTI) enables the assessment of white matter tract degeneration and recovery upon gene therapy without brain biopsies. Selecting thalamus and corpus callosum as regions of interest (ROI), DTI indeed shows a recovery of brain white matter integrity when utilizing 3rd generation Canavan gene therapy. Furthermore, our 3rd generation gene therapy converts this CD mouse model with the severest phenotype into “supermouse”, outperforming wild-type mouse on motor function testing. We hypothesized that functional connectivity identifies brain regions that not only show response to treatment but also indicates possible explanations for this enhanced phenotype. Using resting-state functional MRI (rs-fMRI), we show that treated CD mice have a functional connectivity pattern that is more similar to or even enhanced beyond what is seen in WT brain. This suggests facilitated inter-brain-region functional connectivity, which might provide a neural mechanism that sub-serves the observed enhanced motor function. Currently, we are investigating how the identified brain regions can promote increased motor function, and how high-field brain imaging can provide biomarkers to track the disorder and treatment response in a manner that would help facilitate the prediction of CNS directed gene therapy outcome. In summary, our data show that high-field in vivo neuroimaging is a valuable tool to monitor pre-clinical CNS gene therapy and pathology in detail, that it can provide insights into pathophysiology and that it has potential implications for the use in clinical trial outcome prediction and assessment.

349. The Cure of Canavan Disease: Is It a Scientific Fiction or Clinical Reality?

Canavan Disease (CD) is a rare and lethal inherited pediatric CNS disorder with recessive mutations in the aspartoacylase (ASPA) gene. Traditionally, its variable disease phenotypes were descripted with the congenital sub-form showing neonatal onset and the severest phenotype with early death. The two other sub-forms, infantile, and juvenile, manifest with delayed onset and milder symptoms. Some CD patients are now 20 years of age and older. To date, there is no effective treatment available. Thus, gene replacement therapy is an attractive approach for treating this devastating disease. Previously, we have shown that a single intravenous (i.v.) injection of recombinant adeno-associated virus (rAAV) expressing human ASPA (hASPA) rescues early lethality and partially restores motor function (1st generation gene therapy) in the CD knock-out (CD KO) mouse, which resembles the congenital sub-form of CD and displays the severest phenotype of all available CD mouse models, with early death at around post-natal day (p) 28. After this remarkable improvement of symptoms with our 1st generation treatment, we further optimized our gene therapy. Now, in its 2nd and 3rd generation, our gene therapy cures the disease in the CD KO mouse. Interestingly, our 3rd generation gene therapy turns CD KO mice into “supermice”, outperforming WT mice on rotarod motor function test. This rescue is persistent and currently mice at 1.5 years of age still show no signs of disease reoccurrence. CNS pathology and magnet resonance imaging (MRI) at p25 and p365 show complete normalization. To further support the efficacy of our 3rd generation gene therapy, we performed neurometabolome profiling with over 400 characterized metabolites that showed reversal of the Canavan disease related metabolic changes including myelin associated lipids. To further evaluate the potency of our 3rd generation gene therapy, we tested different doses and routes of administration. Of note, 200-fold lower doses intraventricularly (ICV) administered still rescues lethality, while mice treated ICV with 20-fold reduced dose draw even with WT mice on motor function testing. Next, we moved to the Nur7 mouse model (resembles infantile and juvenile sub-form) that displays a similar disease pattern as the CD KO mouse with respect to growth curve and neurologic symptoms but eventually re-gains weight and shows survival similar to wild-type mice. Again, we treated mice i.v. with a single dose of rAAVhASPA at p1 as our gold standard and subsequent groups at 6 and 12 weeks of age to determine the therapeutic window. Of note, mice treated at 6 weeks of age recovered within 4 weeks post-treatment. Mice treated later than 6 weeks require more time to recover but still showed significant improvement over Nur7 mutants. This recovery was also correlated by CNS pathology and MRI. Currently, we are evaluating mice that were treated at 24 weeks of age to determine if there is a time point of no return. Overall, our data show clear evidence for the cure of the disease at early and late stages of the disease in two different mouse models. In addition, this is confirmed on different levels of cellular complexity by MRI, fMRI, CNS pathology, and neurometabolic profiling.

58. Pushing the Limits for Canavan Gene Therapy into Adulthood: Is There an Age Limit for Gene Therapy in CNS Disorders?

Canavan Disease (CD) is a rare and lethal inherited leukodystrophy caused by autosomal recessive mutations in the aspartoacylase (Aspa) gene. To date, no effective treatment is available. Thus, gene therapy is an attractive approach to treat this devastating disease. Commonly associated with early death in childhood, an increasing group of patients reach teen age or even adulthood and in the process pose new challenges for families and the scientific community. The availability of a new mouse model (Nur7) with barely reduced life expectancy but full blown Canavan-like clinical manifestation prompted us to determine if there is a point-of-no-return in the gene therapeutic treatment of Canavan disease and to identify potentially limiting factors in the development of the central nervous system (CNS) and severity of the neuropathology. We previously reported that early postnatal systemic delivery of the human aspartoacylase (hASPA) gene by recombinant adeno-associated virus (rAAV) to the CNS of a CD mouse model with neonatal death rescued lethality and partially restored motor function. Now in its 3rd generation, our Canavan gene therapy completely reverses the disease phenotype in the CD KO mouse. For clinical translation to treat juvenile and adult patients, we sought to study and understand the age-limitations for Canavan disease gene therapy. We hypothesized that there is a point-of-no-return, when gene replacement therapy alone is no longer sufficient to successfully alter the disease outcome. First, Nur7 mice were treated at post-natal (p) day 1 as the gold standard. In the next step, experimental groups were dosed at 6, 12, and 24 weeks of age with a dose 10-fold higher than that for neonates. Motor function was tested for all mice 4 weeks after treatment and subsequent intervals up to one year of age for direct comparison. As expected, the earlier mice were treated, the better the therapeutic outcome. To our surprise, juvenile mice at 6 weeks of age recovered completely within 4 weeks post-injection. Although mice treated at 3 months of age and older did not respond immediately within the first 4 weeks post-treatment, they eventually showed significant improvements over Nur7 mutant control mice. Of note, cognitive function testing revealed that treated mice recover cognitively before motor function improves; this was even true for late treatment time points. Furthermore, response to rAAVhASPA gene therapy was confirmed via MRS for N-acetyaspartate, MRI, and neuropathology. Finally, our preliminary data characterizing oligodendrocytes and myelin in the Nur7 mouse model shows rapid reconstitution of myelin in mice treated at 6 weeks, underlining the potential of our therapy for later treatment. Currently, we are working on identifying molecular mechanisms limiting complete disease rescue in adult Nur7 mice to further explore options in order to successfully treat older patients. Overall, our data demonstrate that rAAV mediated hASPA expression of our 3rd generation gene therapy vector not only prevents but also rescues the clinical manifestation and pathology of the juvenile and adult model of Canavan disease at an unprecedented level, which might also have implications for other CNS disorders that require treatment in later stages of life.

RAAV Gene Therapy in a Canavan's Disease Mouse Model Reveals Immune Impairments and an Extended Pathology Beyond the Central Nervous System.

Aspartoacylase (AspA) gene mutations cause the pediatric lethal neurodegenerative Canavan disease (CD). There is emerging promise of successful gene therapy for CD using recombinant adeno-associated viruses (rAAVs). Here, we report an intracerebroventricularly delivered AspA gene therapy regime using three serotypes of rAAVs at a 20-fold reduced dose than previously described in AspA(-/-) mice, a bona-fide mouse model of CD. Interestingly, central nervous system (CNS)-restricted therapy prolonged survival over systemic therapy in CD mice but failed to sustain motor functions seen in systemically treated mice. Importantly, we reveal through histological and functional examination of untreated CD mice that AspA deficiency in peripheral tissues causes morphological and functional abnormalities in this heretofore CNS-defined disorder. We demonstrate for the first time that AspA deficiency, possibly through excessive N-acetyl aspartic acid accumulation, elicits both a peripheral and CNS immune response in CD mice. Our data establish a role for peripheral tissues in CD pathology and serve to aid the development of more efficacious and sustained gene therapy for this disease.

N-Acetylaspartate Synthase Deficiency Corrects the Myelin Phenotype in a Canavan Disease Mouse Model But Does Not Affect Survival Time.

Canavan disease (CD) is a severe, lethal leukodystrophy caused by deficiency in aspartoacylase (ASPA), which hydrolyzes N-acetylaspartate (NAA). In the brains of CD patients, NAA accumulates to high millimolar concentrations. The pathology of the disease is characterized by loss of oligodendrocytes and spongy myelin degeneration in the CNS. Whether accumulating NAA, absence of NAA-derived acetate, or absence of any unknown functions of the ASPA enzyme is responsible for the pathology of the disease is not fully understood. We generated ASPA-deficient (Aspa(nur7/nur7)) mice that are also deficient for NAA synthase Nat8L (Nat8L(-/-)/Aspa(nur7/nur7)). These mice have no detectable NAA. Nevertheless, they exhibited normal myelin content, myelin sphingolipid composition, and full reversal of spongy myelin and axonal degeneration. Surprisingly, although pathology was fully reversed, the survival time of the mice was not prolonged. In contrast, Aspa(nur7/nur7) mice with only one intact Nat8L allele accumulated less NAA, developed a less severe pathology, phenotypic improvements, and, importantly, an almost normal survival time. Therefore, inhibition of NAA synthase is a promising therapeutic option for CD. The reduced survival rate of Nat8L(-/-)/Aspa(nur7/nur7) mice, however, indicates that complete inhibition of NAA synthase may bear unforeseeable risks for the patient. Furthermore, we demonstrate that acetate derived from NAA is not essential for myelin lipid synthesis and that loss of NAA-derived acetate does not cause the myelin phenotype of Aspa(nur7/nur7) mice. Our data clearly support the hypothesis that NAA accumulation is the major factor in the development of CD.

496. From Gene Therapy to Gene Enhancement: Optimized Pre-Clinical Gene Therapy Transforms Mice with the Severest Canavan Disease Phenotype Into “Supermice”

Canavan Disease (CD) is a rare and lethal inherited CNS disorder caused by autosomal recessive mutations in the aspartoacylase gene. To date, there is no effective treatment available. Gene replacement therapy is an attractive approach for this devastating disease, although the physiologic function of AspA and its metabolite N-acetylaspartate (NAA) is still not fully understood.We previously reported that systemic delivery of the human aspartoacylase (hAspA) gene by recombinant adeno-associated virus (rAAV) to the CNS of CD mice ameliorated symptoms, partially restored motor function and increased life expectancy to the extent of wild-type (WT) mice. We further sought to investigate the mechanism behind this pre-clinical gene therapy for CD and to improve therapeutic potency. We hypothesized that Kozak sequence and codon modification of hAspA cDNA enhance therapeutic expression to transform our 1st generation AspA expression cassette into a more potent 2nd generation pre-clinical remedy and a better tool to study the physiologic role of AspA.We created expression cassettes containing codon-optimized (Opt) hAspA cDNA together with different Kozak sequences (i.e. HKz and FKz). Our in vitro and in vivo data demonstrate stronger hAspA expression and enzyme activity of the FKzhAspA-Opt vector over all other tested constructs as well as decreased NAA in the CNS below WT level by MRS analysis. Interestingly, rAAVFKzhAspA-Opt treated CD mice perform equally on inverted screen and balance beam but significantly (>50%) better than WT at p28, p90 and p180 on rotarod, suggesting that ubiquitously high expressed hAspA exerts some enhancing effect on treated mice. To confirm these findings, we moved to another mouse model of CD (Nur7 mouse). FKzhAspA-Opt treated Nur7 pups show a similar trend as seen in the CD mice on motor function tests. In addition, open-field testing to measure overall activity and anxiety demonstrates that treated Nur7 mice are more mobile with significantly longer travel distance but anxiety levels equal to WT mice. Currently, we are investigating the molecular mechanism underlying this enhanced performance of treated versus WT mice by studying the metabolome, microRNAome and the possibility of achieving therapeutic efficacy with reduced doses of the optimized vector.Overall, our data demonstrate that our 2nd generation gene therapy for CD not only completely restores the disease phenotype but also achieves motor function performance and overall activity superior to WT mice in two different CD mouse models. Using the same AAV serotype with identical tissue and cell tropism as previously published by our group, implies that excessive NAA is highly detrimental to normal physiology and the NAA re duction independent of the hAspA expressing cell type is sufficient for therapeutic success, which might also suggest a positive correlation of higher AspA activity and lower NAA levels with gene therapeutic outcome for this inborn error of NAA metabolism.

Aspartoacylase deficiency affects early postnatal development of oligodendrocytes and myelination

Canavan disease (CD) is a neurodegenerative disease, caused by a deficiency in the enzyme aspartoacylase (ASPA). This enzyme has been localized to oligodendrocytes; however, it is still undefined how ASPA deficiency affects oligodendrocyte development. In normal mice the pattern of ASPA expression coincides with oligodendrocyte maturation. Therefore, postnatal oligodendrocyte maturation was analyzed in ASPA-deficient mice (CD mice). Early in development, CD mice brains showed decreased expression of neural cell markers that was later compensated. In addition, the levels of myelin proteins were decreased along with abnormal myelination in CD mice compared to wild-type (WT). These defects were associated with increased global levels of acetylated histone H3, decreased chromatin compaction and increased GFAP protein, a marker for astrogliosis. Together, these findings strongly suggest that, early in postnatal development, ASPA deficiency affects oligodendrocyte maturation and myelination.

Mouse neural progenitor cells differentiate into oligodendrocytes in the brain of a knockout mouse model of Canavan disease

Canavan disease (CD) is an autosomal recessive disorder that leads to spongy degeneration in the white matter of the brain. Aspartoacylase (ASPA) synthesizing cells, oligodendrocytes, are lost in CD. Transplantation of neural progenitor cells (NPCs) offers an interesting therapeutic approach for treating neurodegenerative diseases by replacing the lost cells. Therefore, the NPCs transplantation to the brain of the CD mouse was studied. Injection of mouse NPCs to the striatum and cerebellum of juvenile CD mouse showed numerous BrdU positive cells at 1 month after injection. The same result was also observed in the adult CD mouse brain after 5 weeks of post-transplantation period. The implanted cells differentiated into oligodendrocytes and fibrous astrocytes, as observed using glial cell marker. This is the first report to describe the survival, distribution and differentiation of NPCs within the brain of CD mouse and a first step toward the potential clinical use of cell therapy to treat CD.

Therapeutic Options in Prevention and Treatment of Aspartoacylase Gene Mutation Resulting Abnormalities in Canavan Disease

Canavan disease (CD) is an autosomal recessive disorder, caused by mutations in the aspartoacylase gene resulting enzyme deficiency. Patients with CD have accumulation of NAAG and NAA in the brain resulting elevated urinary NAAG and NAA. Aspartoacylase gene mutation in the mouse led to multiple genomic abnormalities. Pathophysiological processes implicated in CD include spongy degeneration of the brain possibly by the abnormal genes expression / metabolic levels of NAAG, NAA, aspartate, glutamate, glutamate transporter-EAAT4, GABA receptor-GABRA6 and GABA. In addition, high expression of cell death inducing agents includes serine proteinase inhibitor 2, caspase 11 and interleukin 1- beta. Osteoporosis is also an important consequence in the CD mouse. Each of these pathways offers potential therapeutic targets and pharmacological manipulation.

Mental retardation and hypotonia seen in the knock out mouse for Canavan disease is not due to succinate semialdehyde dehydrogenase deficiency

Canavan disease (CD) is an autosomal recessive disorder caused by aspartoacylase deficiency leading to accumulation of N-acetylaspartic acid and spongy degeneration of the brain. The mouse model for CD showed low levels of glutamate and γ-aminobutyric acid (GABA) in the brain. Whether the low levels of glutamate and GABA observed in the CD mouse brain lead to abnormal production of glutamate-GABA associated enzymes and resulting succinate production is not obvious. While glutamate dehydrogenase and α-ketoglutarate dehydrogenase complex activities are lower in the cerebellum and brain stem of the CD mouse, alanine aminotransferase and succinate semialdehyde dehydrogenase (SSADH) activities and succinate level are similar to the levels observed in the wild type. Deficiency of SSADH has been suggested to be associated with mental retardation and hypotonia, similar to the clinical features of CD. The normal SSADH activity in the CD mouse brain suggests that mental retardation and hypotonia seen in the CD mouse is not due to SSADH activity and if documented also in patients with CD.

Metabolic changes in the knockout mouse for Canavan's disease: implications for patients with Canavan's disease.

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.

Expression of glutamate transporter, GABRA6, serine proteinase inhibitor 2 and low levels of glutamate and GABA in the brain of knock-out mouse for Canavan disease

Canavan disease (CD) is an autosomal recessive leukodystrophy characterized by spongy degeneration of the brain. The clinical features of CD are hypotonia, megalencephaly, and mental retardation leading to early death. While aspartoacylase (ASPA) activity increases with age in the wild type mouse brain, there is no ASPA activity in the CD mouse brain. So far ASPA deficiency and elevated NAA have been ascribed with the CD. Other factors affecting the brain that result from ASPA deficiency may lead pathophysiology of CD. The NMR spectra and amino acid analysis showed lower levels of glutamate and γ-aminobutyric acid in the CD mouse brain compared to the wild type. Microarray gene expression on CD mouse brain showed glutamate transporter-EAAT4 and γ-aminobutyric acid-A receptor, subunit α6 (GABRA6) were lower 9.7- and 119.1-fold, respectively. Serine proteinase inhibitor 2 (Spi2) was 29.9-fold higher in the CD mouse brain compared to the wild type. The decrease of GABRA6 and high expression of Spi2 in CD mouse brain were also confirmed by real-time RT-PCR. This first report showing abnormal expression of EAAT4, GABRA6, Spi2 combined with lower levels of glutamate and GABA are likely to be associated with the pathophysiology of CD.

Adeno-associated virus-mediated aspartoacylase gene transfer to the brain of knockout mouse for canavan disease

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.