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Glutamate metabolism is down-regulated in astrocytes during experimental allergic encephalomyelitis
H Hardin-Pouzet1, M Krakowski, L Bourbonnière
1Neuroimmunology Unit, Montreal Neurological Institute, Québec, Canada.
Abstract:
Experimental allergic encephalomyelitis (EAE) was induced in SJL/J mice by adoptive transfer of MBP-reactive T cells in order to investigate the role of astrocytes in pathology. GFAP protein and mRNA expression (analyzed using semiquantitative Western blot and RT-PCR techniques) were upregulated in the spinal cord of mice, which had developed a complete paralysis of hind- and fore-limbs and tail (grade 4 EAE), thus establishing that reactive gliosis occurred under these experimental conditions. Within the same samples and using similar techniques, we found that glutamine synthetase (GS) and glutamate dehydrogenase (GDH) expression were dramatically reduced. These two astrocytic enzymes are responsible for degradation of glutamate, the most abundant excitatory neurotransmitter in the brain. Since elevated levels of glutamate may be neurotoxic, we propose that the decreased capacity of astrocytes to metabolize glutamate may contribute to EAE pathology.
Insights
In experimental allergic encephalomyelitis (EAE), reactive astrocytes showed increased GFAP but decreased glutamate-metabolizing enzymes. This suggests impaired glutamate clearance by astrocytes may worsen EAE neuroinflammation and pathology.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Experimental Allergic Encephalomyelitis (EAE) is an animal model for multiple sclerosis.
- Astrocytes play crucial roles in central nervous system homeostasis and disease.
- Glutamate is a key excitatory neurotransmitter, but its excess can be neurotoxic.
Purpose of the Study:
- To investigate the role of astrocytes in the pathology of EAE.
- To examine the expression of glial fibrillary acidic protein (GFAP) and glutamate-metabolizing enzymes in EAE.
Main Methods:
- EAE was induced in SJL/J mice via adoptive transfer of MBP-reactive T cells.
- Semiquantitative Western blot and RT-PCR were used to analyze protein and mRNA expression.
- Spinal cord tissues from EAE mice exhibiting grade 4 paralysis were analyzed.
Main Results:
- GFAP expression was upregulated in the spinal cord, indicating reactive gliosis.
- Expression of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) was dramatically reduced.
- These findings suggest a decreased astrocytic capacity for glutamate metabolism.
Conclusions:
- Reactive astrocytes in EAE exhibit altered expression of key enzymes involved in glutamate homeostasis.
- Reduced expression of GS and GDH may impair glutamate degradation, potentially contributing to neurotoxicity and EAE pathogenesis.
- Targeting astrocytic glutamate metabolism could be a therapeutic strategy for EAE.