Regional distribution of tau, beta-amyloid and beta-amyloid precursor protein in the Alzheimer's brain: a quantitative immunolabelling study.

Regional variation in the distribution of SP and NFT within the brain is well documented. Consideration of such variation is potentially of help in formulating models of disease progression. Several models propose that pathological changes in Alzheimer's disease (AD) progress in a step-wise fashion along neuronally connected regions. In this study, we measured tau, Abeta and betaAPP load in different brain regions and examined our results against models of AD progression. Blocks of brain tissue from 45 AD and 15 control cases were immunolabelled for tau, Abeta and betaAPP. Immunolabelled areas were measured as a proportion of the area of the field. Tau load was almost twice as great in the entorhinal cortex than elsewhere in the brain and was least in the cingulate gyrus. In contrast, Abeta was greatest in the cingulate gyrus and least in the entorhinal cortex. BetaAPP rankings were similar to those of tau. Thus the site with the greatest Abeta load (cingulate cortex) had the least tau and the site with the greatest tau load (entorhinal cortex) had the least Abeta. The entorhinal and cingulate cortex are neuronally interconnected. Our results might be explained on the basis that a neurone with its cell body in the entorhinal cortex and axonal terminals in the cingulate cortex shows predominately tau pathology in relation to the cell body and predominately Abeta pathology in relation to its axonal terminals. We conclude that our observations are consistent with previously described models of AD progression. It is possible that tau-rich neurones are associated through their projections to Abeta rich sites. Further work of this kind analysing differential pathological profiles in interconnected brain regions may contribute to refining this model.