COMPENSATORY INCREASE IN GLUTAMATE UPTAKE IS UNIQUE TO EAAC1 DEFFICIENT MICE. IS THAT ASSOCIATED WITH THE UNIQUE ROLE OF EAAC1 IN EPILEPSY AND GABA SYNTHESIS ?
Abstract number :
2.046
Submission category :
Year :
2003
Submission ID :
4048
Source :
www.aesnet.org
Presentation date :
12/6/2003 12:00:00 AM
Published date :
Dec 1, 2003, 06:00 AM
Authors :
Jehuda P. Sepkuty, Edward E. Cho, Raquelli Ganel, Jeffrey D. Rothstein Neurology, School of Medicine, Johns Hopkins University, Baltimore, MD
We have previously shown that reduced expression of EAAC1 in adult wild-type rats by antisense treatment (knockdown), led to behavioral abnormalities including staring/freezing episodes and electrographic (EEG) seizures. This effect was specific to EAAC1 (as compared to sense EAAC1, GLT-1 and GLAST antisense), and caused a 50% loss of hippocampal GABA levels. Newly synthesized GABA from extracellular glutamate was also significantly impaired by reduction of EAAC1 expression. In contrast, EAAC1 defficient mice, as reported by Peghini et-al, had no seizure activity by observation (no EEG recorded) and no compensatory change in the expression of other glutamate transporters. In a previous abstract we have shown that EAAC1 defficient mice lack seizure activity by EEG criteria and that there was a significant increase in glutamate uptake which was compensatory and we postulated that this compensation could explain the difference between the knock down rats and the knockout mice. In this study we investigated wheather the compensation reported previously was unique to EAAC1 defficient mice as compared to other transgenic glutamate transporter knockout mice (EAAT4 and GLAST).
We have compared functional glutamate uptake (total and DHK sensitive and insensitive) between glutamate transporters EAAT4 and GLAST knockout mice and wild type controls. We used also western blot analysis to check the expression of the other glutamate transporters in the EAAT4 and GLAST glutamate transporter knockout mice.
Measurements of transport activity revealed no significant change in transport activity of other glutamate transporters in EAAT4 and GLAST glutamate transporter knockout mice, suggesting that there was no compensation in these null mice. Initial western blot analysis showed some increment of GLT-1 and GLAST protein expression in the EAAT4 knockout mice. Western blot studies of other glutamate transporters in GLAST knockout mice are currently underway.
There seems to be a unique compensation in glutamate uptake in the EAAC1 defficient mice as compared to other glutamate transporter knockout mice. The mechanism underlying this observation is under investigation. The uniqueness of the EAAC1 transporter in terms of compensation may be tied to its[apos] uniqueness in terms of epilepsy and GABA synthesis. The ability to modify glutamate transporter EAAC1 activity may be an important mechanism of preventing/treating some types of epilepsy.
[Supported by: NIH (Jeff Rothstein and Jehuda Sepkuty) and EFA (Jehuda Sepkuty)]