Role of activating transcription factor 3 in ischemic penumbra region following transient middle cerebral artery occlusion and reperfusion injury.

The activating transcription factor 3 (ATF3) is expressed by various types of cellular insults. It has been suggested to serve diverse functions in both cellular survival and death signal cascades, but the exact role of ATF3 in brain ischemia is little known so far. Thus, the authors examined the expression pattern of ATF3 following middle cerebral artery occlusion (MCAO) and reperfusion injury. At 1-2 days after MCAO and reperfusion injury, numerous number of ATF3-immunoreacitive (-ir) nuclei was observed in the ipsilateral peri-infarct cortex, but declined rapidly at 3 days. Almost all ATF3-ir nuclei were co-localized with NeuN-ir neurons. Neither GFAP- nor OX42-ir neuroglia were co-localized with ATF3. Double labeling of Fluoro-Jade B with ATF3 showed that ATF3-ir nuclei mismatched with Fluoro-Jade B-ir neurons. To further examine the role of ATF3 in ischemic peri-infarct regions, double immunofluorescent labeling of ATF3/caspase 3, ATF3/Bcl-xl, and ATF3/HSP27 was conducted. Semiquantitive estimation showed that about 15% of ATF3-ir neurons also expressed caspase 3. However, about only 0.4% and 2.6% of ATF3-ir neurons were double-stained with Bcl-xl and Hsp27, respectively. Consequently, it would be suggested that ATF3 seem to play an important role in caspase-dependent neuronal apoptotic signal transduction pathways caused by focal cerebral ischemia and reperfusion injury.