Increased expression of the glial glutamate transporter EAAT2 modulates excitotoxicity and delays the onset but not the outcome of ALS in mice.
The glial glutamate transporter EAAT2 is primarily responsible for clearance of glutamate from the synaptic cleft and loss of EAAT2 has been previously reported in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease. The loss of functional EAAT2 could lead to the accumulation of extracellular glutamate, resulting in cell death known as excitotoxicity. However, it is still unknown whether it is a primary cause in the cascade leading to neuron degeneration or a secondary event to cell death. The goals of this study were to generate transgenic mice overexpressing EAAT2 and then to cross these mice with the ALS-associated mutant SOD1(G93A) mice to investigate whether supplementation of the loss of EAAT2 would delay or rescue the disease progression. We show that the amount of EAAT2 protein and the associated Na+-dependent glutamate uptake was increased about 2-fold in our EAAT2 transgenic mice. The transgenic EAAT2 protein was properly localized to the cell surface on the plasma membrane. Increased EAAT2 expression protects neurons from L-glutamate induced cytotoxicity and cell death in vitro. Furthermore, our EAAT2/G93A double transgenic mice showed a statistically significant (14 days) delay in grip strength decline but not in the onset of paralysis, body weight decline or life span when compared with G93A littermates. Moreover, a delay in the loss of motor neurons and their axonal morphologies as well as other events including caspase-3 activation and SOD1 aggregation were also observed. These results suggest that the loss of EAAT2 may contribute to, but does not cause, motor neuron degeneration in ALS.
Guo
Hong
H
Department of Neuroscience, The Ohio State University, Columbus, 43210, USA.
Lai
Liching
L
Butchbach
Matthew E R
ME
Stockinger
Michael P
MP
Shan
Xiu
X
Bishop
Georgia A
GA
Lin
Chien-liang Glenn
CL
D000690:Amyotrophic Lateral Sclerosis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D016923:Cell Death / Q000235:genetics*; D002462:Cell Membrane / Q000378:metabolism; D003433:Crosses, Genetic; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects; D027342:Excitatory Amino Acid Transporter 2 / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D005904:Glial Fibrillary Acidic Protein / Q000235:genetics; D018698:Glutamic Acid / Q000378:metabolism / Q000493:pharmacokinetics; D051379:Mice; D008822:Mice, Transgenic; D009046:Motor Neurons / Q000201:enzymology / Q000473:pathology; D011401:Promoter Regions, Genetic; D013116:Spinal Cord / Q000378:metabolism / Q000473:pathology; D013482:Superoxide Dismutase / Q000378:metabolism; D000072105:Superoxide Dismutase-1; D013997:Time Factors; D019076:Transgenes
D027342:Excitatory Amino Acid Transporter 2; D005904:Glial Fibrillary Acidic Protein; D018698:Glutamic Acid; C000606291:Sod1 protein, mouse; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1; D020169:Caspases