Amyloid deposition in APP23 mice is associated with the expression of cyclins in astrocytes but not in neurons.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the intracellular accumulation of highly phosphorylated tau protein, the extracellular formation of amyloid plaques and a significant loss of neurons. Recent evidence suggests that neuronal death in AD involves an aborted attempt of cells to re-enter the cell cycle. To study the effect of amyloid deposits on cell cycle related events in vivo, the expression of cell cycle markers was examined by immunohistochemistry in amyloid precursor protein (APP) transgenic mice (APP23 mice, Swedish double mutation). Abeta deposition in APP23 mice is associated with prominent gliosis that is characterized by an astrocytic expression of cyclins D1, E and B1 as well as the nuclear translocation of cyclin-dependent protein kinase 4. However, amyloid plaque formation is not accompanied by significant changes in the neuronal expression of cyclins or cyclin-dependent kinase inhibitors. It is concluded, therefore, that in contrast to AD, amyloid pathology in APP23 mice is not associated with changes in the expression of cell cycle markers in neurons. The results support the assumption that the neuronal re-expression of cell cycle components in AD is not a consequence of Abeta formation and deposition.