DNA Polymerase-beta Is Expressed Early in Neurons of Alzheimer's Disease Brain and Is Loaded into DNA Replication Forks in Neurons Challenged with beta-Amyloid

• Published in: The Journal of neuroscience 2006-10, Vol.26 (43), p.10949-10957
• Main Authors: Copani, Agata, Hoozemans, Jeroen J. M, Caraci, Filippo, Calafiore, Marco, Van Haastert, Elise S, Veerhuis, Robert, Rozemuller, Annemieke J. M, Aronica, Eleonora, Sortino, Maria Angela, Nicoletti, Ferdinando
• Format: Article
• Language: English
• Subjects: Adult; Aged; Aged, 80 and over; Alzheimer Disease - enzymology; Alzheimer Disease - genetics; Alzheimer Disease - pathology; Amyloid beta-Peptides - toxicity; Brain - drug effects; Brain - enzymology; Brain - pathology; Cells, Cultured; DNA Polymerase beta - biosynthesis; DNA Polymerase beta - genetics; DNA Polymerase beta - metabolism; DNA Replication - drug effects; DNA Replication - physiology; Female; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Enzymologic - physiology; Humans; Male; Middle Aged; Neurons - drug effects; Neurons - enzymology; Neurons - pathology; Retinoblastoma Protein - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.2793-06.2006

Cultured neurons exposed to synthetic beta-amyloid (Abeta) fragments reenter the cell cycle and initiate a pathway of DNA replication that involves the repair enzyme DNA polymerase-beta (DNA pol-beta) before undergoing apoptotic death. In this study, by performing coimmunoprecipitation experiments on cross-linked nucleoprotein fragments from Abeta-treated neurons, we demonstrate that DNA pol-beta coimmunoprecipitates with cell division cycle 45 (Cdc45) and with DNA primase in short nucleoprotein fragments. This indicates that DNA pol-beta is loaded into neuronal DNA replication forks after Abeta treatment. In response to Abeta the canonical DNA-synthesizing enzyme DNA pol-delta also was loaded into neuronal replication forks, but at later times than DNA pol-beta. Methoxyamine, an inhibitor of the apurinic/apyrimidinic endonuclease that allows for the recruitment of DNA pol-beta during the process of base excision repair (BER), failed to affect coimmunoprecipitation between DNA pol-beta and Cdc45, indicating that DNA pol-beta loading to the replication forks is independent of DNA breaks. However, methoxyamine reduced DNA replication and ensuing apoptosis in neurons exposed to Abeta, suggesting that an efficient BER process allows DNA replication to proceed up to the threshold for death. These data demonstrate that DNA pol-beta is an essential component of the DNA replication machinery in Abeta-treated neurons and additionally support the hypothesis of a close association of cell cycle events with neuronal death in Alzheimer's disease (AD). Accordingly, by investigating the neuronal expression of DNA pol-beta, along with phosphorylated retinoblastoma protein and neurofibrillary changes in AD brain, we show an early involvement of DNA pol-beta in the pathogenesis of AD.