QUANTITATIVE IMAGE-ANALYSIS OF TEMPORAL CHANGES IN TAU-PROTEIN AND NEUROFILAMENT-PROTEIN DURING THE COURSE OF ACUTE EXPERIMENTAL NEUROFIBRILLARY DEGENERATION - NONPHOSPHORYLATED EPITOPES PRECEDE PHOSPHORYLATION

Perturbation of the neuronal cytoskeleton represents an integral featu re of neurofibrillary tangles which are characteristic neuropathologic al findings seen in Alzheimer's disease. Microtubule associated protei n tau (tau) is considered to be the major component of these lesions a lthough neurofilament proteins also are present. The present study exp lores the formation of intraneuronal tan and neurofilament protein agg regates using intracisternal administration of aluminum maltolate to r abbits. The time course of the formation of these aggregates and subse quent phosphorylation have been investigated by immunohistochemical me thods using a panel of monoclonal antibodies, with quantitation of the staining by image analysis. Neurofilament proteins begin to aggregate by day 1 following aluminum maltolate injection on day 0. Increases i n non-phosphorylated neurofilament proteins are observed first, with p hosphorylated epitopes being recognized by day 3. Tau follows a simila r pattern in that non-phosphorylated epitopes appear to precede phosph orylation. The monoclonal antibody Alz-50 which recognizes a phosphory lation-independent epitope of tau in Alzheimer's disease paired helica l filaments, demonstrates positivity in the aluminum maltolate-treated rabbits by day 3. Other tau monoclonal antibodies which recognize pho sphorylated tau in paired helical filaments (AT8 and PHF-1) show posit ive immunostaining on days 6-8. These results indicate that intraneuro nal aggregation of cytoskeletal proteins can be initiated by factors o ther than phosphorylation. However, phosphorylation occurring as a sec ondary event probably contributes to stabilization of the aggregates.