The quantitation of pre- and postsynaptic proteins in Alzheimer’s disease and effect of apolipoprotein E genotype

Abstract

In Alzheimer's disease (AD) it has been commonly thought that cell loss would be associated with the loss of terminal inputs through retrograde degradation. Brain tissue from pathologically confirmed AD cases and controls was obtained at autopsy with written informed consent and frozen at ƒ{70„aC in 0.32 M sucrose. Areas investigated included hippocampus and inferior temporal cortex, which are susceptible to AD pathology, and occipital cortex, which is relatively spared. Levels of synaptophysin, a marker of nerve terminals, were investigated by a novel sandwich ELISA and by immunohistochemistry (IHC). N-cadherin, a marker of excitatory synapses, was analysed by immunoblotting. ELISA and cortical thickness measurements by IHC confirmed that there was no significant difference in the levels of synaptophysin between controls and AD cases, but there was a difference between areas. Immunoblotting showed slight increases in the levels of N-cadherin in all areas of AD cases compared with controls, which only reached significance in occipital cortex. There was also a significant regional difference. Cases were categorized according to Apolipoprotein E genotype by RFLP. The Apo E ƒÕ4 allele occurred at a significantly higher frequency in AD cases, and was associated with a trend toward lower synaptophysin levels in affected areas. The results suggest that terminal inputs remain intact in AD and that the risk factor Apo E4 may represent a marker of severity. Preliminary studies of other protein markers, presynaptic dynamin 1, presynaptic excitatory complexin 2 and postsynaptic ƒÑCaMKII, displayed the same regional differences. Dynamin 1 and complexin 2, involved in synaptic vesicle recycling, showed lower levels in AD cases than in controls. RKT is a Judith Mason Scholar