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Nuclear-envelope nucleoside triphosphatase kinetics and mRNA transport following brain ischemia and reperfusion
B R Tiffany1, B C White, G S Krause
1Department of Emergency Medicine, Wayne State University, Detroit, Michigan, USA.
Study Hypothesis:
We attempted to determine whether the reduced egress of mRNA from brain nuclei following in vivo ischemia and reperfusion is caused by direct damage to the nuclear pore-associated NTPase that impairs the system for nuclear export of polyadenylated, or poly(A)+, mRNA.
Design:
Prospective animal study.
Interventions:
NTPase activity and poly(A)+ mRNA transport were studied in nuclear envelope vesicles (NEVs) prepared from canine parietal cortex isolated after 20 minutes of ischemia or 20 minutes of ischemia and 2 or 6 hours of reperfusion.
Results:
Brain NEV NTPase Michaelis-Menten constant (Km) and maximum uptake velocity (Vmax) and the ATP-stimulated poly(A)+ mRNA egress rates were not significantly affected by ischemia and reperfusion. In vitro exposure of the NEVs to the OH. radical-generating system completely abolished NTPase activity.
Conclusion:
We conclude that brain ischemia and reperfusion do not induce direct inhibition of nucleocytoplasmic transport of poly(A)+ mRNA. This suggests that the nuclear membrane is not exposed to significant concentrations of OH. radical during reperfusion.
Insights
Brain ischemia and reperfusion do not directly inhibit nuclear export of polyadenylated mRNA. This suggests the nuclear membrane is protected from reactive oxygen species during reperfusion events.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Ischemia and reperfusion can reduce mRNA egress from brain nuclei.
- The nuclear pore-associated NTPase is crucial for poly(A)+ mRNA export.
Purpose of the Study:
- To investigate if direct damage to the nuclear pore-associated NTPase causes reduced mRNA export after brain ischemia and reperfusion.
Main Methods:
- A prospective animal study using canine parietal cortex.
- Nuclear envelope vesicles (NEVs) were isolated after ischemia and reperfusion.
- NTPase activity and poly(A)+ mRNA transport were assessed.
Main Results:
- Ischemia and reperfusion did not significantly alter NTPase activity or mRNA egress rates in brain NEVs.
- In vitro exposure to hydroxyl radicals abolished NTPase activity, indicating enzyme sensitivity.
Conclusions:
- Brain ischemia and reperfusion do not directly inhibit nucleocytoplasmic transport of poly(A)+ mRNA.
- The nuclear membrane is likely not exposed to significant hydroxyl radical concentrations during reperfusion.