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Okadaic acid-induced apoptosis in neuronal cells: evidence for an abortive mitotic attempt
R Nuydens1, M de Jong, G Van Den Kieboom
1Department of Cell Physiology, Janssen Research Foundation, Beerse, Belgium.
Abstract:
There is increasing evidence that apoptosis in postmitotic neurons is associated with a frustrated attempt to reenter the mitotic cycle. Okadaic acid, a specific protein phosphatase inhibitor, is currently used in models of Alzheimer's research to increase the degree of phosphorylation of various proteins, such as the microtubule-associated protein tau. Okadaic acid induces programmed cell death in the human neuroblastoma cell lines TR14 and NT2-N, as evidenced by fragmentation of DNA and attenuation of this process by protein synthesis inhibitors. In differentiated TR14 cells, okadaic acid increases the fraction of cells in the S phase, induces the appearance of cyclin B1 and cyclin D1 markers of the cell cycle, and triggers a time-dependent increase in DNA fragmentation after release of a thymidine block. Fully differentiated NT2-N cells are forced to enter the mitotic cycle as shown by DNA staining. Chromatin condensation and chromosome formation are initiated, but the cells fail to complete their mitotic cycle. These data suggest that okadaic acid forces differentiated neuronal cells into the mitotic cycle. This pattern of cyclin up-regulation and cell cycle shift is compared with apoptosis induced by neurotrophic factor deprivation in differentiated rat pheochromocytoma PC12 cells.
Insights
Okadaic acid triggers cell cycle re-entry and programmed cell death in differentiated neurons. This process involves DNA fragmentation and cyclin up-regulation, suggesting a link between cell cycle attempts and neuronal apoptosis in Alzheimer
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Apoptosis in postmitotic neurons is linked to failed attempts to re-enter the cell cycle.
- Okadaic acid, a protein phosphatase inhibitor, increases tau protein phosphorylation, a hallmark in Alzheimer's disease research.
Purpose of the Study:
- To investigate the effect of okadaic acid on neuronal cell cycle re-entry and programmed cell death.
- To elucidate the molecular mechanisms underlying okadaic acid-induced apoptosis in neuronal cell lines.
Main Methods:
- Treatment of human neuroblastoma cell lines (TR14, NT2-N) and rat pheochromocytoma cells (PC12) with okadaic acid.
- Analysis of DNA fragmentation, cell cycle phase distribution (S phase), and expression of cell cycle markers (cyclin B1, cyclin D1).
- Assessment of apoptosis by protein synthesis inhibitors and DNA staining.
Main Results:
- Okadaic acid induced DNA fragmentation and programmed cell death in TR14 and NT2-N cells.
- Differentiated TR14 cells showed increased S phase fraction and cyclin B1/D1 expression after okadaic acid treatment.
- Differentiated NT2-N cells initiated but failed to complete mitosis, exhibiting chromatin condensation and chromosome formation.
Conclusions:
- Okadaic acid forces differentiated neuronal cells into the mitotic cycle, leading to apoptosis.
- The observed cyclin up-regulation and cell cycle shift in okadaic acid-treated neurons resemble apoptosis induced by neurotrophic factor deprivation.