MATURATION-DEPENDENT VULNERABILITY OF OLIGODENDROCYTES TO OXIDATIVE STRESS-INDUCED DEATH CAUSED BY GLUTATHIONE DEPLETION

Death of oligodendrocyte (OL) precursors can be triggered in vitro by cystine deprivation, a form of oxidative stress that involves depletio n of intracellular glutathione. We report here that OLs demonstrate ma turation-dependent differences in survival when subjected to free radi cal-mediated injury induced by glutathione depletion. Using immunopann ing to isolate rat preoligodendrocytes (preOLs), we generated highly e nriched populations of preOls and mature OLs under chemically defined conditions. Cystine deprivation caused a similar decrease in glutathio ne levels in OLs at both stages. However, preOLs were completely kille d by cystine deprivation, whereas mature OLs remained viable. Although the glutathione-depleting agents buthionine sulfoximine and diethylma leate were more potent in depleting glutathione in mature OLs, both ag ents were significantly more toxic to preOLs. Glutathione depletion ma rkedly increased intracellular free radical generation in preOLs, but not in mature OLs, as indicated by oxidation of the redox-sensitive pr obe dihydrorhodamine 123. The antioxidants alpha-tocopherol, idebenone , and glutathione monoethylester prevented the oxidation of dihydrorho damine in cystine-depleted preOLs and markedly protected against cell death. When the intracellular glutathione level was not manipulated, p reOls were also more vulnerable than mature OLs to exogenous free radi cal toxicity generated by a xanthine-xanthine oxidase system. Ultrastr uctural features of free radical-mediated injury in glutathione-deplet ed preOLs included nuclear condensation, margination of chromatin, and mitochondrial swelling. These observations indicate that preOLs are s ignificantly more sensitive to the toxic effects of glutathione deplet ion and that oligodendroglial maturation is associated with decreased susceptibility to oxidative stress.