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Dominant-interfering forms of MEF2 generated by caspase cleavage contribute to NMDA-induced neuronal apoptosis
Shu-ichi Okamoto1, Zhen Li, Chung Ju
1Center for Neuroscience and Aging, Apoptosis and Cell Death Research Program, The Burnham Institute, La Jolla, CA 92037, USA.
Abstract:
Myocyte enhancer factor-2 (MEF2) transcription factors are activated by p38 mitogen-activated protein kinase during neuronal and myogenic differentiation. Recent work has shown that stimulation of this pathway is antiapoptotic during development but proapoptotic in mature neurons exposed to excitotoxic or other stress. We now report that excitotoxic (N-methyl-D-aspartate) insults to mature cerebrocortical neurons activate caspase-3, -7, in turn cleaving MEF2A, C, and D isoforms. MEF2 cleavage fragments containing a truncated transactivation domain but preserved DNA-binding domain block MEF2 transcriptional activity via dominant interference. Transfection of constitutively active MEF2 (MEF2C-CA) rescues MEF2 transcriptional activity after N-methyl-D-aspartate insult and prevents neuronal apoptosis. Conversely, dominant-interfering MEF2 abrogates neuroprotection by MEF2C-CA. These results define a pathway to excitotoxic neuronal stress/apoptosis via caspase-catalyzed cleavage of MEF2. Additionally, we show that similar MEF2 cleavage fragments are generated in vivo during focal stroke damage. Hence, this pathway appears to have pathophysiological relevance in vivo.
Insights
Excitotoxic stress cleaves Myocyte enhancer factor-2 (MEF2) transcription factors in mature neurons, leading to apoptosis. Restoring MEF2 activity prevents this neuronal death, suggesting a key role in stroke damage.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Death Research
Background:
- Myocyte enhancer factor-2 (MEF2) transcription factors regulate neuronal differentiation and survival.
- MEF2 activation by p38 MAPK is crucial for development but can be proapoptotic in stressed mature neurons.
Purpose of the Study:
- To investigate the role of MEF2 in excitotoxic neuronal apoptosis.
- To elucidate the mechanism of MEF2 cleavage and its functional consequences in neuronal stress.
Main Methods:
- Utilized N-methyl-D-aspartate (NMDA) insults on mature cerebrocortical neurons.
- Assessed caspase activation and MEF2 cleavage.
- Employed transfection of constitutively active MEF2 (MEF2C-CA) and dominant-interfering MEF2 constructs.
- Examined MEF2 cleavage fragments in vivo during focal stroke models.
Main Results:
- NMDA insults activated caspases-3 and -7, leading to cleavage of MEF2A, C, and D isoforms.
- MEF2 cleavage fragments inhibited MEF2 transcriptional activity via dominant interference.
- Constitutively active MEF2 (MEF2C-CA) rescued MEF2 activity and prevented NMDA-induced apoptosis.
- Dominant-interfering MEF2 blocked the neuroprotective effects of MEF2C-CA.
- Similar MEF2 cleavage fragments were observed in vivo during focal stroke damage.
Conclusions:
- A novel pathway involving caspase-catalyzed MEF2 cleavage mediates excitotoxic neuronal apoptosis.
- This pathway has significant pathophysiological relevance in vivo, particularly in conditions like stroke.
- Targeting MEF2 cleavage may offer therapeutic strategies for neuroprotection.