Loss of bag-1 immunoreactivity in rat brain after transient middle cerebral artery occlusion.

Although bag-1 is a strong apoptosis repressor protein, its functions in normal or injured brains are not fully understood. In the present study, we investigated expression of bag-1 protein in rat brain after transient middle cerebral artery (MCA) occlusion, and compared the results with that of terminal deoxynucleotidyl transferase-mediated dUTP-biotin end labeling (TUNEL). Immunohistochemical analysis revealed that neuronal, choroid plexus, and ependymal cells were positively stained in the sham control brain. After 90 min of transient MCA occlusion, immunoreactivity for bag-1 progressively decreased from 3 to 48 h in the nuclei of neurons. Western blot analysis revealed that immunoreactive bag-1 was markedly decreased in the nuclear fraction. In contrast, cytosolic and mitochondrial fractions showed no or only slight change after the ischemia. TUNEL positive cells appeared at 48 h after the reperfusion, which was preceded by loss of bag-1 immunoreactivity. The present results suggest that bag-1 plays some roles in normal neuronal function, and its loss may be involved in neuronal cell death after ischemia.