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Is the AMPA receptor subunit GluR2 mRNA an early indicator of cell fate after ischemia? A quantitative single cell
C W Alsbo1, M L Wrang, F Møller
1Laboratory of Neuropathology, Institute of Molecular Pathology, University of Copenhagen, 11, Frederik V's vej, PharmaBiotec Research Center, DK-2100, Copenhagen, Denmark. ca@nepa.ku.dk
Abstract:
After a moderate global cerebral ischemia, two hypothetical populations of pyramidal neurons are present among the hippocampal CA1 pyramidal neurons: one that will die and another one that will survive. Prior analysis of dissected hippocampal CA1 regions has shown a reduction of the GluR1-3 mRNA following ischemia. In order to identify these changes in single neurons, quantitative single cell RT-PCR was used to analyze the expression of GluR1-4 mRNA in rats 24 h after ischemia and also in rats after tolerance inducing ischemia. Control CA1 cells had a median copy-number of 290, 247, 207 and 16 GluR1-4, respectively. The tolerant cells showed small significant up-regulations of GluR1, 3 and 4 mRNA, while the GluR2 mRNA showed a more than 4-fold up-regulation compared to control cells. All the cells from ischemic animals displayed down-regulations of GluR1-3 mRNA. The GluR4 mRNA was not detectable in the ischemic animals. Our results thus show that the CA1 neurons react uniformly 24 h after a moderate ischemia independent of the fate of the neuron: thus two neuron populations with different GluR2 profiles cannot be identified in post-ischemic animals at 24 h. It seems however that an increased level of GluR2 can be used as an indicator of tolerance to ischemia.
Insights
Moderate global cerebral ischemia affects hippocampal CA1 pyramidal neurons. While all neurons show reduced GluR1-3 mRNA after ischemia, increased GluR2 mRNA indicates tolerance, suggesting it as a potential indicator.
Area of Science:
- Neuroscience
- Molecular Biology
- Ischemia Research
Background:
- Global cerebral ischemia induces neuronal death in the hippocampal CA1 region.
- Prior studies indicated reduced GluR1-3 mRNA in bulk hippocampal CA1 samples post-ischemia.
- Hypotheses suggested distinct neuronal populations (surviving vs. dying) after ischemia.
Purpose of the Study:
- To investigate single-neuron expression of glutamate receptor subunit (GluR) mRNAs (GluR1-4) in CA1 pyramidal neurons following ischemia.
- To differentiate neuronal responses based on survival or tolerance to ischemic conditions.
- To identify molecular markers indicative of ischemic tolerance.
Main Methods:
- Quantitative single-cell reverse transcription polymerase chain reaction (RT-PCR) was employed.
- Analysis focused on GluR1, GluR2, GluR3, and GluR4 mRNA expression in individual CA1 pyramidal neurons.
- Rats were subjected to moderate global cerebral ischemia or tolerance-inducing ischemia, with analysis 24 hours post-insult.
Main Results:
- Control CA1 neurons exhibited median copy-numbers: GluR1 (290), GluR2 (247), GluR3 (207), GluR4 (16).
- Tolerant cells showed modest upregulation of GluR1, GluR3, and GluR4 mRNA, with a significant >4-fold increase in GluR2 mRNA.
- Ischemic cells displayed downregulation of GluR1-3 mRNA, and undetectable GluR4 mRNA levels.
- No distinct GluR2 profiles were identified between surviving and dying neurons 24 hours post-ischemia.
Conclusions:
- CA1 neurons exhibit a uniform transcriptional response to moderate ischemia at 24 hours, irrespective of neuronal fate.
- Distinct neuronal populations with differing GluR2 expression are not identifiable at this time point post-ischemia.
- Elevated GluR2 levels may serve as a potential biomarker for ischemic tolerance in hippocampal CA1 neurons.
