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Dynamics of regional brain metabolism and gene expression after middle cerebral artery occlusion in mice
1Department of Experimental Neurology, Max-Planck-Institute for Neurological Research, Cologne, Germany.
Abstract:
The evolution of brain infarcts during permanent occlusion of the middle cerebral artery (MCA) was studied in mice using multiparametric imaging techniques. Regional protein synthesis and the regional tissue content of ATP were measured on adjacent cryostat sections at increasing intervals after vascular occlusion ranging from 1 hour to 3 days. The observed changes were correlated with the expression of the mRNA of hsp70, c-fos, c-jun, and junB, as well as the distribution of DNA double-strand breaks visualized by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL). One hour after MCA occlusion, the tissue volume with suppressed protein synthesis was distinctly larger than that in which ATP was depleted. With ongoing ischemia time, the ATP-depleted area gradually expanded and, within 1 day, merged with the region of suppressed protein synthesis. Expression of hsp70 mRNA occurred mainly in the penumbra (defined as the region of suppressed protein synthesis but preserved ATP), peaking at 3 hours after vascular occlusion. Expression of the immediate-early genes c-jun, c-fos, and junB increased both in the penumbra and the periinfarct normal tissue already at 1 hour after vascular occlusion, with slightly different regional and temporal patterns for each of these genes. DNA fragmentations were clearly confined to neurons; they appeared after 1 day in the infarct core (defined as the region of suppressed ATP) and never were detected in the penumbra. The late appearance of TUNEL after infarcts had reached their final size and the absence in the penumbra points against a major pathogenetic role of apoptosis. Permanent MCA occlusion in mice thus produces a gradually expanding infarct, the final size of which is heralded by the early inhibition of protein synthesis.
Insights
Permanent middle cerebral artery (MCA) occlusion in mice causes brain infarcts that expand over time. Early suppression of protein synthesis predicts the final infarct size, while apoptosis plays a minor role.
Area of Science:
- Neuroscience
- Ischemic Stroke Research
- Molecular Biology
Background:
- Middle cerebral artery (MCA) occlusion is a common cause of ischemic stroke.
- Understanding the spatiotemporal evolution of brain infarcts is crucial for developing effective treatments.
- Multiparametric imaging offers insights into cellular and molecular changes during ischemia.
Purpose of the Study:
- To investigate the dynamic evolution of brain infarcts following permanent MCA occlusion in a mouse model.
- To correlate biochemical changes (protein synthesis, ATP levels) with gene expression and DNA damage.
- To elucidate the role of apoptosis in infarct development.
Main Methods:
- Permanent middle cerebral artery (MCA) occlusion in mice.
- Regional protein synthesis and ATP content measurement.
- mRNA expression analysis (hsp70, c-fos, c-jun, junB).
- Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) for DNA double-strand breaks.
Main Results:
- Suppressed protein synthesis preceded ATP depletion in early stages of ischemia.
- The infarct core (ATP depleted) expanded to merge with the penumbra (suppressed protein synthesis) within 24 hours.
- hsp70 mRNA peaked in the penumbra at 3 hours; immediate-early genes (c-jun, c-fos, junB) were upregulated early in the penumbra and surrounding tissue.
- DNA fragmentation (TUNEL) was observed in neurons within the infarct core after 1 day but not in the penumbra.
Conclusions:
- Permanent MCA occlusion leads to a progressively expanding infarct in mice.
- Early inhibition of protein synthesis is a key indicator of the eventual infarct size.
- Apoptosis, as assessed by TUNEL staining, does not appear to be a major contributor to infarct progression in the penumbra.