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Reexpression of developmentally regulated MAP2c mRNA after ischemia: colocalization with hsp72 mRNA in vulnerable
1Stroke Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland.
Abstract:
Levels of mRNAs encoding the microtubule-associated proteins MAP2b and MAP2c as well as the 70-kDa stress protein [72-kDa heat shock protein (hsp72)] were evaluated in postischemic rat brain by in situ hybridization with oligonucleotide probes corresponding to the known rat sequences. Rats were subjected to 10-min cardiac arrest, produced by compression of major thoracic vessels, followed by resuscitation. The normally expressed MAP2b mRNA showed transient twofold elevations in all hippocampal neuron populations at 6-h recirculation, followed by a return to control levels by 24 h. MAP2b hybridization was progressively lost thereafter from the vulnerable CA1 and outer cortical layers, preceding both the fall in immunoreactive MAP2b and the eventual cell loss in these regions. The depletion of MAP2b mRNA coincided with an increase in the alternatively spliced MAP2c in vulnerable regions during 12-48 h of recirculation, precisely overlapping the late component of hsp72 expression that persisted in these cell populations. Previous studies have suggested that the initial induction of hsp72 provides an index of potential postischemic injury in neuron populations that may or may not be injured, while lasting hsp72 mRNA expression is associated with cell damage. In contrast, the present results demonstrate that MAP2c expression under these conditions occurs uniquely in neuron populations subject to injury. Available evidence suggests that MAP2c expression represents a plastic response in subpopulations of neurons that will survive in these regions, although it remains to be explicitly determined whether it may also be transiently expressed in dying cells. In any case, these observations demonstrate that reexpression of developmentally regulated MAP2c mRNA is a relatively late postischemic response in vulnerable cell populations, indicating that pathways regulating MAP2 splicing may be closely associated with mechanisms of neuron injury and/or recovery.
Insights
Microtubule-associated protein 2 (MAP2) mRNA changes, including increased MAP2c, indicate neuron injury and recovery pathways after cardiac arrest. This stress response occurs in vulnerable brain cells following ischemia.
Area of Science:
- Neuroscience
- Molecular Biology
- Cellular Biology
Background:
- Microtubule-associated proteins (MAPs) are crucial for neuronal structure and function.
- Heat shock proteins (hsp72) are induced by cellular stress, including ischemia.
- Differential expression of MAP2 isoforms (MAP2b and MAP2c) may play roles in neuronal response to injury.
Purpose of the Study:
- To investigate the temporal and spatial expression patterns of MAP2b and MAP2c mRNAs in the rat brain following cardiac arrest and resuscitation.
- To correlate changes in MAP2 mRNA expression with the expression of hsp72 and neuronal vulnerability.
- To elucidate the role of MAP2 splicing in postischemic neuronal injury and recovery.
Main Methods:
- In situ hybridization was used to quantify MAP2b, MAP2c, and hsp72 mRNA levels in rat brain sections.
- Rats underwent a 10-minute cardiac arrest followed by resuscitation.
- Expression levels were analyzed at various time points post-resuscitation (6, 12, 24, and 48 hours).
Main Results:
- MAP2b mRNA levels transiently increased in hippocampal neurons 6 hours post-resuscitation, then declined.
- MAP2b mRNA was progressively lost from vulnerable CA1 and cortical layers, preceding cell death.
- Depletion of MAP2b mRNA coincided with increased MAP2c mRNA in vulnerable regions, overlapping with late hsp72 expression.
- MAP2c expression was uniquely observed in neuron populations subject to injury.
Conclusions:
- Reexpression of developmentally regulated MAP2c mRNA is a late postischemic response in vulnerable neurons.
- MAP2c expression appears to be specifically associated with neuronal injury, potentially indicating a plastic response in surviving neurons.
- Pathways regulating MAP2 splicing are closely linked to mechanisms of neuronal injury and/or recovery following ischemia.