βII-tubulin and phospho-tau aggregates in Alzheimer's disease and Pick's disease

Abstract

The expression of βI-, βII- and βIII-tubulin isotypes was examined by immunohistochemistry in the entorhinal and transentorhinal cortices, hippocampus and dentate gyrus in normal human brains and in cases with Alzheimer's disease (AD), Pick's disease (PiD) and in argyrophilic grain disease (AGD). The results showed that βII-tubulin predominated in the upper layers (mainly layer II) and βIII-tubulin in the inner layers of the entorhinal and transentorhinal cortices in control brains. βII-tubulin immunoreactivity was higher than βIII-tubulin immunoreactivity in granular neurons of the dentate gyrus, whereas pyramidal neurons of the hippocampus proper were stained equally with anti-βII-tubulin and βIII-tubulin antibodies. No preferential layering distribution was observed for βI-tubulin. Polymerization assays with tubulin peptides following the method of microtubule-associated protein displacement demonstrated that the βI and βIII isotypes have a higher binding capacity for tau than does the βII isotype. Interestingly, about 60% of neurons with neurofibrillary tangles in layer II of the entorhinal and transentorhinal cortices in AD were selectively stained with anti-βII-tubulin antibodies. Moderate βII-tubulin immunoreactivity was also observed in Pick bodies in PiD. Taken together, these findings support the view that high βII-tubulin content is a contributing factor in the formation of abnormal hyper-phosphorylated tau aggregates.