Altered vesicular glutamate transporter expression in human temporal lobe epilepsy with hippocampal sclerosis

Vesicular glutamate transporters (VGLUTs) are responsible for loading glutamate into synaptic vesicles. Altered VGLUT protein expression has been suggested to affect quantal size and glutamate release under both physiological and pathological conditions. In this study, we investigated mRNA and protein expression levels of the three VGLUT subtypes in hippocampal tissue of patients suffering from temporal lobe epilepsy (TLE) with hippocampal sclerosis (HS), International League Against Epilepsy type 1 (ILAE type 1) compared to autopsy controls, using quantitative polymerase chain reaction and semi-quantitative western blotting. mRNA expression levels of the VGLUTs are unaffected in hippocampal epileptic tissue compared to autopsy controls. At the protein level, VGLUT1 expression remains unaltered, while VGLUT2 is significantly decreased and VGLUT3 protein is significantly increased in hippocampal biopsies from TLE patients compared to controls. Our findings at the protein level can be explained by previously described histopathological changes observed in HS. Although VGLUTs have been repeatedly investigated in distinct rodent epilepsy models, their expression levels were hitherto not fully unraveled in the most difficult-to-treat form of epilepsy: TLE with HS ILAE type 1. We here, demonstrate for the first time that VGLUT2 protein expression is significantly decreased and VGLUT3 protein is significantly increased in the hippocampus of patients suffering from TLE with HS ILAE type 1 compared to autopsy controls.