Interindividual differences in the levels of the glutamate transporters GLAST and GLT, but no clear correlation with Alzheimer's disease

Abstract

Alzheimer's disease is a common progressive neurodegenerative disease of unknown etiology. Several different pathological processes have been identified in the brains of Alzheimer patients. To determine if reduced glutamate uptake is a contributing factor, we have measured the levels of the glutamate transporter proteins GLAST (EAAT1) and GLT (EAAT2) in human autopsy samples. The postmortem proteolysis of these proteins turned out to be fairly rapid. Brains from 10 Alzheimer and 10 control patients were therefore obtained with a relatively short postmortem delay (5 hr on average). GLT (N-terminal and central parts), GLAST (C-terminal), glial fibrillary acidic protein (GFAP) and inositol (1,4,5)-triphosphate (IP3)-receptor immunoreactivities were determined in the cingulate and inferior temporal gyri by immunoblotting. The Na+-dependent "binding" of D-[3H]aspartate and the glutamate uptake after solubilization and reconstitution in liposomes were determined for comparison. An individual variation in GLAST and GLT levels was found, but no significant correlation with Alzheimer's disease, except for a 14% lower ratio of N-terminal to central GLT immunoreactivity (P < 0.04). The levels of GLAST and GLT showed negative correlation in agreement with the idea that these proteins are differentially regulated. In conclusion, Alzheimer's disease brains can have both normal and reduced levels of GLAST and GLT.

Deletion of the γ-Aminobutyric Acid Transporter 2 (GAT2 and SLC6A13) Gene in Mice Leads to Changes in Liver and Brain Taurine Contents

“…The supernatants from this centrifugation contained the water-soluble proteins and are hereafter referred to as "supernatant." Care was taken to keep samples cold and work quickly because some other transporters have been shown to be prone to proteolysis (43,44). The pellets, containing the water-insoluble proteins, were subsequently solubilized in 1% (w/v) SDS in 10 mM sodium phosphate buffer, pH 7.4 (NaP i ), briefly sonicated, and centrifuged (39,000 ϫ g, 20 min, 15°C).…”

Postmortem Brain: An Underutilized Substrate for Studying Severe Mental Illness

“…The authors posit that the inner regions of the brain may cool more slowly than the outer, accounting for some of their results. Another study extensively examined the effects of PMI on expression of glutamate transporters in the rodent brain (Beckstr m et al, 1999). They found epitope-specific degradation of rodent glutamate transporters 1 and 2 at 24 hours PMI, compared with 0 and 12 hours PMI.…”

“…Differential degradation of different epitopes was observed after 24 hours, with selective preservation of the C termini for rodent glutamate transporters 2 and 3 at 72 hours. These effects extended to both immunoreactivity as well as glutamate transport activity (Beckstr m et al, 1999). The data in this section support the current approach in the field to match samples as closely as possible for PMI and to probe for associations between PMI and each dependent measure.…”

Strategies for immunohistochemical protein localization using antibodies: What did we learn from neurotransmitter transporters in glial cells and neurons

“…In contrast, epitopes within central parts of the EAAT2 protein, e.g. residues 107-120 and 493-508 (Beckstrøm et al, 1999;Li et al, 2012) as well as to residues 146-161 (Fig. 2) are far more resistant.…”