DNA fragmentation precedes aberrant expression of cell cycle-related protein in rat brain after MCA occlusion
1Department of Neurology, Tohoku University School of Medicine, Sendai, Japan.
Abstract:
Recent experiments suggest that apoptotic mechanisms are involved in neuronal cell death after ischemic injury. Although the exact mechanism that triggers activation of apoptotic machinery remains uncertain, in vitro studies revealed that forced expression of cell cycle-related proteins induced apoptosis. Thus, aberrant expression of such proteins might be related to ischemic neuronal death. In the present experiment, we investigated expression of cell cycle-related proteins, i.e., cyclin B1, cyclin D1, cdk4, and PCNA, in rat brain after transient MCA occlusion, and compared the temporal profile of the results with that of TUNEL study, which detects double strand breaks in DNA. There were no immunoreactivities for cyclin B1, cyclin D1, and PCNA in the brain with and without ischemia. As for cdk4, however, it became present at 1 and 3 days of reperfusion after 2 h of ischemia. On the other hand, TUNEL positive cells appeared as early as 3 h of reperfusion, which peaked at 1 and 3 days. These results indicate that aberrant expression of cdk4, but not cyclin B1, cyclin D1 or PCNA, actually takes place in the brain after MCA occlusion, but this is not the causative mechanism of apoptotic cell death in the brain with ischemia.
Insights
Aberrant expression of cell cycle protein cdk4 occurs in rat brains after middle cerebral artery (MCA) occlusion, but it does not cause apoptotic neuronal death following ischemic injury.
Area of Science:
- Neuroscience
- Cell Biology
- Pathology
Background:
- Apoptotic mechanisms are implicated in neuronal cell death following ischemic injury.
- In vitro studies suggest cell cycle-related proteins may trigger apoptosis.
- Aberrant expression of these proteins could link to ischemic neuronal death.
Purpose of the Study:
- To investigate the expression of cell cycle-related proteins (cyclin B1, cyclin D1, cdk4, PCNA) in rat brains after transient middle cerebral artery (MCA) occlusion.
- To compare the temporal expression profile of these proteins with DNA double-strand breaks detected by TUNEL assay.
Main Methods:
- Transient middle cerebral artery (MCA) occlusion in rats.
- Immunohistochemical analysis for cyclin B1, cyclin D1, cdk4, and PCNA.
- Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to detect DNA strand breaks.
Main Results:
- No significant immunoreactivity for cyclin B1, cyclin D1, or PCNA was observed in ischemic or non-ischemic rat brains.
- cdk4 expression was detected at 1 and 3 days post-reperfusion following 2 hours of ischemia.
- TUNEL-positive cells, indicating DNA damage, appeared by 3 hours and peaked at 1 and 3 days of reperfusion.
Conclusions:
- Aberrant expression of cdk4 occurs in the rat brain after MCA occlusion.
- The expression of cdk4 is not the causative mechanism for apoptotic cell death in this ischemic brain injury model.
- Cyclin B1, cyclin D1, and PCNA are not implicated in the apoptotic cell death pathway following MCA occlusion in rats.
