The unfolded protein response affects neuronal cell cycle protein expression: implications for Alzheimer's disease pathogenesis.
Alzheimer's disease (AD) is characterized by the accumulation and aggregation of misfolded proteins. The presence of misfolded proteins in the endoplasmic reticulum (ER) triggers a cellular stress response called the unfolded protein response (UPR). Previously, we have shown that the UPR is activated in AD neurons. In actively dividing cells, activation of the UPR is accompanied by decreased cell cycle protein expression and an arrest in the G1 phase of the cell cycle. Aberrant expression of cell cycle proteins has been observed in post mitotic neurons in AD and is suggested to be involved in neurodegeneration. In this study we show that the protein levels of BiP/GRP78, an ER-stress marker, is increased in Braak stages B and C for amyloid deposits. This is in contrast to the levels of cell cycle markers cyclin D1, cyclin E and phosphorylated retinoblastoma protein (ppRb) which are decreased in Braak stage C compared to Braak stage A for amyloid deposits. In addition, we report a negative correlation between neuronal expression of ppRb and expression levels of BiP/GRP78 in control and AD cases. Activation of the UPR in neuronal cells induces changes in cell cycle protein expression similar to these observed in AD brain. ER stress inducers tunicamycin and thapsigargin down-regulate cell cycle proteins ppRb and cyclin D1 in differentiated neuroblastoma cells. In contrast, protein levels of p27, a cyclin dependent kinase inhibitor, are increased after induction of ER-stress using tunicamycin. These data suggest that activation of the UPR affects cell cycle protein expression in neurons during neurodegeneration in AD.
Department of Neuropathology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. j.j.hoozemans@amc.uva.nl
Jeroen J M
JJ
Hoozemans
Jens
J
Stieler
Elise S
ES
van Haastert
Robert
R
Veerhuis
Annemieke J M
AJ
Rozemuller
Frank
F
Baas
Piet
P
Eikelenboom
Thomas
T
Arendt
Wiep
W
Scheper
D000544:Alzheimer Disease / Q000209:etiology / Q000378:metabolism* / Q000473:pathology; D015415:Biomarkers / Q000032:analysis; D015153:Blotting, Western / Q000379:methods; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D056741:Cyclin D; D019927:Cyclin E / Q000032:analysis / Q000378:metabolism; D016213:Cyclins / Q000032:analysis / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000473:pathology; D000091342:Endoplasmic Reticulum Chaperone BiP; D005434:Flow Cytometry; D006360:Heat-Shock Proteins / Q000032:analysis; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D018832:Molecular Chaperones / Q000032:analysis; D009447:Neuroblastoma; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D017510:Protein Folding; D016160:Retinoblastoma Protein / Q000032:analysis / Q000378:metabolism; D014407:Tumor Cells, Cultured
D015415:Biomarkers; D018797:Cell Cycle Proteins; D056741:Cyclin D; D019927:Cyclin E; D016213:Cyclins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D016160:Retinoblastoma Protein