Membrane vesicles shed by oligodendroglioma cells induce neuronal apoptosis

In order to investigate the mechanism by whicholigodendrogliomas cause neuronal damage, media conditionedby G26/24 oligodendroglioma cells, were fractionated intoshed vesicles and vesicle-free supernatants, and added toprimary cultures of rat fetal cortical neurons. After one nighttreatment with vesicles, a reproducible, dose-dependent,inhibitory effect on neurite outgrowth was already inducedand, after 48-72 h of incubation, neuronal apoptosis wasevident. Vesicle-free supernatants and vesicles shed byNIH-3T3 cells had no inhibitory effects on neurons. Westernblot analyses showed that treated neurons expressed a decreasedamount of neurofilament (NF), growth-associated protein(GAP-43) and microtubule-associated protein (MAP-2).Moreover procaspase-3 and -8 were activated while Bcl-2expression was reduced. Vesicles were found positive forthe proapoptotic molecule, Fas-ligand (Fas-L), and for the Bisoform of Nogo protein, a myelin component with inhibitoryeffects on neurons. Nogo B involvement in the vesicle effectswas analyzed both by testing the neutralizing capability ofanti-Nogo antibodies and by removing the Nogo receptorfrom neurons by phospholipase C digestion. These treatmentsdid not revert the vesicle effects. To test the role of Fas-L,vesicles were treated with functional anti-Fas-L monoclonals.Vesicle inhibitory and proapoptotic effects were reduced.Vesicles shed by ovarian carcinoma cells (OvCa), which areknown to vehicle biologically active Fas-L, had similar effectson neurons to those of oligodendroglioma vesicles, and theirinhibitory effects were also reduced by anti Fas-L antibodies.We therefore conclude that vesicles shed by G26/24 cellsinduce neuronal apoptosis at least partially by a Fas-L mediatedmechanism.