UP-REGULATION OF BAX PROTEIN-LEVELS IN NEURONS FOLLOWING CEREBRAL-ISCHEMIA

The patterns of expression of the bcl-2, bar, and bcl-X genes were exa mined immunohistochemically in neurons of the adult rat brain before a nd after 10 min of global ischemia induced by transient cardiac arrest . High levels of the cell death promoting protein Bar and concomitant low levels of the apoptosis-blocking protein Bcl-2 were found in some populations of neurons that are particularly sensitive to cell death i nduced by transient global ischemia, such as the CA1 sector of the hip pocampus and the Purkinje cells of the cerebellum. Moreover, within 0. 5 to 3 hr after an ischemic episode, immunostaining for Bar was marked ly increased within neurons with morphological features of degeneratio n in many regions of the brain. Use of a two-color staining method for simultaneous analysis of Bar protein and in situ detection of DNA-str and breaks revealed high levels of Bar immunoreactivity in many neuron s undergoing apoptosis. Postischemic elevations in Bar protein levels in the hippocampus, cortex, and cerebellum were also demonstrated by i mmunoblotting. At early times after transient ischemia, regulation of Bcl-2 and Bcl-X protein levels varied among neuronal subpopulations, b ut from 3 hr on, those neurons with morphological evidence of degenera tion uniformly contained reduced levels of Bcl-2 and particularly Bcl- X immunoreactivity. The findings suggest that differential expression of some members of the bcl-2 gene family may play an important role in determining the relative sensitivity of neuronal subpopulations to is chemia and that postischemic alterations in the expression of bax, bcl -2, and bcl-X may contribute to the delayed neuronal cell death that o ccurs during the repurfusion phase after a transient ischemic episode.