Impaired spinal cord glutamate transport capacity and reduced sensitivity to riluzole in a transgenic superoxide dismutase mutant rat model of amyotrophic lateral sclerosis.
We characterized synaptosomal glutamate transport activity in a recently developed transgenic rat model of amyotrophic lateral sclerosis (ALS) overexpressing the G93A Cu(2+)/Zn(2+) superoxide dismutase (SOD1) mutation. Using spinal cord synaptosomes, a significant reduction (43%) in the maximal velocity for high-affinity, Na(+)-dependent glutamate uptake was observed at disease end stage in G93A rats compared with age-matched controls. Similarly, a 27% reduction in maximum velocity (V(max)) was measured at disease onset, but no difference in spinal cord V(max) values were observed with presymptomatic animals compared with controls. In comparison, we observed no differences in the V(max) for glutamate clearance at disease end stage with synaptosomes from cortex, hippocampus, striatum, cerebellum, and brainstem, indicating a specific deficit in the spinal cord. The pharmacological sensitivity of spinal cord uptake to dihydrokainate suggests that the GLT-1 (glutamate transporter-1) subtype primarily mediates the transport activity. Expression analysis revealed a loss of GLT-1 as well as qualitative changes in GLAST (glutamate/aspartate transporter) but no measurable changes in EAAC1 (excitatory amino acid carrier 1) in spinal cord of end-stage G93A rats, indicating that deficits in glutamate transporters in this rat model may be glial specific. Riluzole, a neuroprotective agent used clinically to slow the progression of ALS, produced an enhancement of spinal cord synaptosomal glutamate uptake in control animals and early-stage disease G93A rats, but this effect was lost in end-stage animals. Altered expression of astroglial glutamate transporters accompanied by reduced capacity for spinal cord clearance of extracellular glutamate in the G93A SOD1 transgenic rat may account for a dampened effect of riluzole to enhance glutamate uptake at end-stage disease.
Dunlop
John
J
Neuroscience, Wyeth Research, Princeton, New Jersey 08543-8000, USA.
Beal McIlvain
H
H
She
Yijin
Y
Howland
David S
DS
D027322:Amino Acid Transport System X-AG / Q000378:metabolism; D000690:Amyotrophic Lateral Sclerosis / Q000188:drug therapy / Q000473:pathology / Q000503:physiopathology*; D000818:Animals; D030801:Animals, Genetically Modified; D004195:Disease Models, Animal; D018450:Disease Progression; D004351:Drug Resistance; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2 / Q000172:deficiency / Q000378:metabolism; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D015151:Immunoblotting; D018696:Neuroprotective Agents / Q000494:pharmacology; D009928:Organ Specificity; D051381:Rats; D011922:Rats, Mutant Strains; D017207:Rats, Sprague-Dawley; D019782:Riluzole / Q000494:pharmacology*; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism* / Q000473:pathology; D013482:Superoxide Dismutase / Q000235:genetics*; D027981:Symporters / Q000378:metabolism; D013574:Synaptosomes / Q000737:chemistry / Q000378:metabolism; D019076:Transgenes
D027322:Amino Acid Transport System X-AG; D027341:Excitatory Amino Acid Transporter 1; D027342:Excitatory Amino Acid Transporter 2; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; D018696:Neuroprotective Agents; C493400:SLC1A1 protein, human; C493394:SLC1A3 protein, human; C493398:Slc1a1 protein, rat; C493392:Slc1a3 protein, rat; D027981:Symporters; D018698:Glutamic Acid; D019782:Riluzole; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase