Annexin A3 expression after stroke in the aged rat brain.

In an effort to identify new proteins involved in functional recovery after cerebral ischemia, young (3 months) and aged (18 months) male rats were subjected to middle cerebral artery (MCA) occlusion. Brains were harvested at 3- and 14-days post ischemia and proteins from the peri-infarcted and the corresponding contralateral area and total proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis followed by mass spectrometry analysis. Annexin A3 (ANXA3) was identified as one upregulated protein in the post-ischemic rat brain. Using western blotting, real-time PCR and immunohistochemistry, we confirmed that at 3-14 days post-stroke, ANXA3 expression in the peri-infarct area was consistently increased over the corresponding area of control rats. Double staining revealed that ANXA3 is produced by activated microglial cells. We found that aged rats also had more newly proliferating cells expressing ANXA3 than young rats do. Occasionally, ANXA3-immunopositive cells wraped around neurons, suggesting that annexin A3 may be involved in the removal of dying neurons after stroke.