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Are Astrocytes the Missing Link Between Lack of Brain Aspartoacylase Activity and the Spongiform Leukodystrophy in Canavan Disease?

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Abstract

Canavan disease (CD) is a genetic degenerative brain disorder associated with mutations of the gene encoding aspartoacylase (ASPA). In humans, the CD syndrome is marked by early onset, hydrocephalus, macroencephaly, psychomotor retardation, and spongiform myelin sheath vacuolization with progressive leukodystrophy. Metabolic hallmarks of the disease include elevated N-acetylaspartate (NAA) levels in brain, plasma and CSF, along with daily excretion of large amounts of NAA and its anabolic metabolite, N-acetylaspartylglutamate (NAAG). Of the observed neuropathies, the most important appears to be the extensive demyelination that interferes with normal neuronal signaling. However, finding the links between the lacks of ASPA activity in oligodendrocytes, the buildup of NAA in white matter (WM) and the mechanisms underlying the edematous spongiform leukodystrophy have remained elusive. In this analytical review we consider what those links might be and propose that in CD, the pathological buildup of NAA in limited WM extracellular fluid (ECF) is responsible for increased ECF osmotic–hydrostatic pressure and initiation of the demyelination process. We also hypothesize that NAA is not directly liberated by neurons in WM as it is in gray matter, and that its source in WM ECF is solely as a product of the catabolism of axon-released NAAG at nodes of Ranvier by astrocyte NAAG peptidase after it has docked with the astrocyte surface metabotropic glutamate receptor 3. This hypothesis ascribes for the first time a possible key role played by astrocytes in CD, linking the lack of ASPA activity in myelinating oligodendrocytes, the pathological buildup of NAA in WM ECF, and the spongiform demyelination process. It also offers new perspectives on the cause of the leukodystrophy in CD, and on possible treatment strategies for this inherited metabolic disease.

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Abbreviations

Ac:

Acetate

AQP4:

Aquaporin 4

Asp:

Aspartate

ASPA:

Aspartoacylase

atm:

Atmospheres

CD:

Canavan disease

CNS:

Central nervous system

CSF:

Cerebrospinal fluid

ECF:

Extracellular fluid

ECS:

Extracellular space

fMRS:

Functional magnetic resonance spectroscopy

Glc:

Glucose

Glu:

Glutamate

GM:

Gray matter

GRM3:

Metabotropic Glu receptor 3

IND’s:

Investigative new drugs

Me+ :

Monovalent metal cation

MWP:

Molecular water pump

NAA:

N-Acetylaspartate

NAAG:

N-Acetylaspartylglutamate

ODS:

Osmotic demyelination syndrome

Pn:

Paranodal

WM:

White matter

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Authors and Affiliations

  1. Center for Neurochemistry, Nathan S. Kline Institute for Psychiatric Research, 140 Old Orangeburg Road, Orangeburg, NY, 10962, USA

    Morris H. Baslow

  2. Center for Advanced Brain Imaging, Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, 10962, USA

    David N. Guilfoyle

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  1. Morris H. Baslow
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  2. David N. Guilfoyle
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Correspondence to Morris H. Baslow.

Additional information

CD, a rare genetic disorder that compromises a physiologically important tri-cellular brain metabolic system.

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Baslow, M.H., Guilfoyle, D.N. Are Astrocytes the Missing Link Between Lack of Brain Aspartoacylase Activity and the Spongiform Leukodystrophy in Canavan Disease?. Neurochem Res 34, 1523–1534 (2009). https://doi.org/10.1007/s11064-009-9958-z

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  • DOI: https://doi.org/10.1007/s11064-009-9958-z

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