Mitotic mechanisms in Alzheimer's disease?
The mechanism(s) leading to widespread hyper-phosphorylation of proteins in Alzheimer's disease (AD) are unknown. We have characterized seven new monoclonal antibodies recognizing independent phospho-epitopes in the paired helical filament proteins (PHF) found in AD brain. These antibodies show pronounced immunoreactivity with cultured human neuroblastoma cells that are in the M phase of cell division, but have no discernible reactivity with interphase cells. Immunoreactivity with these antibodies does not localize to the microtubule spindles or chromosomes in M phase, but is confined to the surrounding cytoplasm. Similar staining in M phase is observed with cultured cells of various tissue types and species. Cells arrested in M phase with the microtubule depolymerizing agent, nocodazole, show marked increases in immunoreactivity with the antibodies by immunofluorescence staining, ELISA, and immunoblotting. In neuroblastoma cells, the appearance of the TG/MC phospho-epitopes coincides with activation of mitotic protein kinases, but not with the activity of the neuronal specific cyclin-dependent kinase, cdk5. These data suggest that the TG/MC epitopes are conserved mitotic phospho-epitopes produced as a result of increased mitotic kinase activity. To investigate this possibility in AD, we examined the staining of human brain tissue with MPM-2, a marker antibody for mitotic phospho-epitopes. It was found that MPM-2 reacts strongly with neurofibrillary tangles, neuritic processes, and neurons in AD but has no staining in normal human brain. Our data suggest that accumulation of phospho-epitopes in AD may result from activation of mitotic posttranslational mechanisms which do not normally operate in mature neurons of brain.
Vincent
I
I
Department of Pathology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Rosado
M
M
Davies
P
P
D000469:Alkaline Phosphatase; D000544:Alzheimer Disease / Q000378:metabolism / Q000473:pathology*; D000906:Antibodies; D015415:Biomarkers; D001921:Brain / Q000378:metabolism* / Q000473:pathology*; D002478:Cells, Cultured; D000939:Epitopes / Q000032:analysis; D005455:Fluorescent Antibody Technique; D006801:Humans; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D008938:Mitosis; D009447:Neuroblastoma; D016900:Neurofilament Proteins / Q000032:analysis / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism*; D010766:Phosphorylation; D014407:Tumor Cells, Cultured
D000906:Antibodies; D015415:Biomarkers; D000939:Epitopes; D016900:Neurofilament Proteins; D010750:Phosphoproteins; D000469:Alkaline Phosphatase