Inhibition of oligodendrocyte apoptosis by sublytic C5b-9 is associated with enhanced synthesis of Bcl-2 and mediated by inhibition of caspase-3 activation

We have previously shown that generation of sublytic C5b-9, the membrane at tach complex of complement, induces oligodendrocytes to enter cell cycle an d reduces apoptotic cell death in vitro. In the present study, the cellular factors involved in apoptosis of oligodendrocyte progenitor cells and olig odendrocytes, and the inhibitory effect of C5b-9 on apoptotic process were investigated. Oligodendrocyte progenitor cells identified by mAb A2B5 that were isolated from neonatal rat brains were differentiated into oligodendro cytes in serum-free defined medium, The differentiation,, which occurs simu ltaneously with apoptotic cell death, was associated with a rapid loss of b cl-2 mRNA and increased expression of caspase-3 mRNA. Activation of caspase -3 in differentiating cells was demonstrated by the generation of 17- and 1 2-kDa fragments of caspase-3 proenzyme and by cleavage of poly(ADP-ribose) polymerase, a specific caspase-3 substrate, Cell death associated with diff erentiation was inhibited by the caspase-3 inhibitor DEVD-CHO in a dose-dep endent manner. Assembly of sublytic C5b-9 resulted in inhibition of caspase -3 activation, In addition, synthesis of BCL-2 protein in oligodendrocytes was significantly increased by C5b-9, The TNF-alpha-induced apoptosis of ol igodendrocytes was also inhibited by C5b-9. These results indicate that up- regulation of BCL-2 protein and inhibition of caspase-3 activation are pote ntial mechanisms by which C5b-9 increases survival of oligodendrocyte in vi tro and possibly in vivo during inflammation and immune-mediated demyelinat ion affecting the CNS.