The Rates of Postmortem Proteolysis of Glutamate Transporters DifferDramatically between Cells and between Transporter Subtypes

摘要

Glutamate transporters limit the actions of excitatory amino acids.Because a disturbed transporter operation can cause or aggravate neurological diseases,transporters are of considerable neuropathological interest. Human samples, however, areseldom obtained fresh. Here, we used mice brains to study how fast glutamate transportersare degraded after death. Immunoblots showed that terminal GLT-1 epitopes had mostly disappeared after 24 hr. GLAST termini degraded slightly slower. In contrast, epitopes within central parts of GLT-1 and the EAAC1 C-terminus were readily detectable after 72 hr. The decline inimmunoreactivity of the GLT-1 and GLAST termini was also seen in tissue sections, butproteolysis did not happen synchronously in all cells. At 24 hr, scattered cells remainedstrongly immunopositive, while the majority of cells were completely immunonegative. GLASTand GLT-1 co-localized in neocortical tissue, but at 12 hr, many GLAST-positive cells hadlost the GLT-1 termini. The uneven disappearance of labeling was not observed with theantibodies to GLT-1 residues 493–508. The immunoreactivity to this epitope correlatedbetter with the reported glutamate uptake activity. Thus, postmortem delay may affectepitopes differently, possibly causing erroneous conclusions about relative expressionlevels.