Alexander Disease Mutant Glial Fibrillary Acidic Protein Compromises Glutamate Transport in Astrocytes

• Published in: Journal of neuropathology and experimental neurology Vol. 69; no. 4; pp. 335 - 345
• Main Authors: Tian, Rujin, Wu, Xiaoping, Hagemann, Tracy L, Sosunov, Alexandre A, Messing, Albee, McKhann, Guy M, Goldman, James E
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Association of Neuropathologists, Inc 01-04-2010; Lippincott Williams & Wilkins; Oxford University Press
• Subjects: 8-Bromo Cyclic Adenosine Monophosphate - pharmacology; Alexander Disease - genetics; Alexander Disease - pathology; Animals; Arginine - genetics; Astrocytes - drug effects; Astrocytes - metabolism; Biological and medical sciences; Cells, Cultured; Coculture Techniques - methods; Cysteine - genetics; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Excitatory Amino Acid Agonists - pharmacology; Excitatory Amino Acid Transporter 2 - metabolism; Flow Cytometry - methods; Gene Expression Regulation - drug effects; Gene Expression Regulation - genetics; Glial Fibrillary Acidic Protein - genetics; Green Fluorescent Proteins - genetics; Hippocampus - cytology; Kainic Acid - analogs & derivatives; Kainic Acid - pharmacology; Medical sciences; Membrane Potentials - drug effects; Membrane Potentials - genetics; Mutation - genetics; Nerve Tissue Proteins - metabolism; Neurology; Neurons - drug effects; Neurons - physiology; Patch-Clamp Techniques - methods; Rats; Transfection - methods; Nervous system diseases; Neuroglia; Glial fibrillary acidic protein; Biological transport; GFAP mutations; Astrocyte; Glutamate; Cerebral disorder; Glutamate transporter; Central nervous system disease; Excitatory aminoacid; Neurotransmitter; Alexander disease; Degenerative disease; Mutation
• ISSN: 0022-3069; 1554-6578; 0022-3069
• DOI: 10.1097/NEN.0b013e3181d3cb52

Alexander disease (AxD) is a leukodystrophy caused by heterozygous mutations in the gene for glial fibrillary acidic protein, an intermediate filament protein expressed by astrocytes. The mutation causes prominent protein aggregates inside astrocytes; there is also loss of myelin and oligodendrocytes and neuronal degeneration. We show that immunohistochemical staining for glutamate transporter 1, the major brain glutamate transporter expressed primarily in astrocytes suggests decreased levels in the hippocampi of infantile AxD patients. A knock-in mouse model of AxD also shows significant reduction of glutamate transporter 1 in the hippocampus. To explore this phenomenon at the cellular level, wild-type and R239C mutant glial fibrillary acidic proteins (the most common mutation) were overexpressed in astrocytes in culture. Western blotting and whole-cell patch clamp recordings demonstrated that the R239C astrocytes exhibited markedly reduced glutamate transporter 1 protein levels; this resulted in attenuated or abolished glutamate-induced inward transporter current. Neurons cocultured with the R239C astrocytes exhibited increased death after glutamate challenge. These results indicate that aberrant astrocytes have decreased glutamate uptake, which may play an important role in the pathogenesis of neuronal and oligodendrocyte injury and death in AxD.