Pro-apoptotic function of GABA-related transcripts following stroke

- EGAD transcripts were up-regulated following stroke.
- EGAD expression was identified in TUNEL-positive neurons.
- Blocking of EGAD expression reduced Caspase-3 activation.
- Post-stroke re-expression of EGAD is pro-apoptotic.

Following cerebral injuries such as stroke, a structural and functional reorganization of the impaired tissue occurs, which is often accompanied by a re-expression of developmental genes. During brain development, embryonic splice variants of the GABA-synthesizing GAD67 gene (collectively termed EGAD) participate in cell proliferation, migration, and neuronal differentiation. We thus hypothesized an involvement of EGAD in post-ischemic plasticity. EGAD transcripts were up-regulated at early reperfusion times in the injured area following transient middle cerebral artery occlusion (with a peak expression of 4.5-fold at 6 h in C57BL/6 mice). Cell-specific analysis by a combination of radioactive in situ hybridization and immunolabeling revealed EGAD up-regulation in TUNEL-positive neurons. This unexpected cell death-associated expression of EGAD was confirmed in cell culture models of ischemia (combined oxygen-glucose deprivation) and apoptosis (staurosporine). Staurosporine-mediated cell death led to cleaved Caspase-3 activation, a key regulator of apoptosis following stroke. Blocking of staurosporine-associated EGAD expression via antisense RNA treatment reduced cleaved Caspase-3 activation by ~ 30%. In addition to the involvement of EGAD in proliferative processes during brain development, we found here that EGAD participates in cell death under pathophysiological conditions in the adult brain. Re-expression of EGAD in neurons following stroke may play a role in aberrant cell cycle activation, consequently being pro-apoptotic. Our observation of a new GABA related pro-apoptotic mechanism and its successful modification might be of significant clinical relevance.